HB Schunk-FC42-Stacks Eng 20

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Schunk Bahn- und Industrietechnik GmbH

Manual for Schunk

Fuel Cell Stacks

FC-42/HLC



2Manual for Schunk Fuel Cell Stacks

Table of contents

1 Preliminary remarks ......................................................................................... 6

1.1 Nomenclature ............................................................................................. 6

1.2 General ....................................................................................................... 6

2 Safety instructions ........................................................................................... 7

2.1 Installation.................................................................................................. 7

2.2 Hydrogen .................................................................................................... 7

2.3 Electrical connections ................................................................................. 8

2.4 Cooling water ............................................................................................. 8

2.5 Products created ......................................................................................... 92.6 Temperatures ............................................................................................. 9

2.7 Overpressure .............................................................................................. 9

2.8 Further information .................................................................................... 9

3 Media supplies and power connection ............................................................ 10

3.1 General points .......................................................................................... 10

3.2 Hydrogen .................................................................................................. 10

3.3 Air ............................................................................................................ 10

3.4 Water cooling ............................................................................................ 11

3.5 Media connections .................................................................................... 11

3.6 Power connection ..................................................................................... 14

4 Operating the fuel cell ................................................................................... 14

4.1 Anode supply ............................................................................................ 14

4.2 Cathode supply ......................................................................................... 15

4.3 Critical operating states ............................................................................ 15

4.4 Monitoring ................................................................................................ 16

4.5 Switching on ............................................................................................. 17

4.6 Switching off ............................................................................................. 17

5 Storage .......................................................................................................... 18

5.1 Storage of one individual fuel cell ............................................................. 18

5.2 Storage / long-term switching-off of a complete system .......................... 18

6 Transport ...................................................................................................... 19




7 Notes für system integrators .......................................................................... 20

7.1 General ..................................................................................................... 20

7.2 Electrical circuitry ..................................................................................... 20

7.3 Avoidance of open-circuit voltage mode ................................................... 22

7.4 Operating methods, mounting and installation position ............................ 22

7.5 Minimal system configuration ................................................................... 24

8 Methods for optimizing the efficiency ............................................................ 25

8.1 High-current mode ................................................................................... 25

8.2 Throttling of the cathode air ..................................................................... 25

8.3 Humidifying of the cathode air .................................................................. 25

8.4 Humidifying of the anode gas ................................................................... 26

8.5 Regulating of the quantity of air ............................................................... 26

8.6 Purging cycles........................................................................................... 27

8.7 Anode gas recirculation ............................................................................ 27

8.8 Cathode air recirculation ........................................................................... 27

8.9 Media reversal .......................................................................................... 27

8.10 External humidification ............................................................................. 27

8.11 Manual drying of the fuel cell .................................................................... 28

9 Data log and operating proof ......................................................................... 28

10 Searching for leaks ........................................................................................ 29

10.1 External leakage of the reaction gases ...................................................... 29

10.2 External leakage of the cooling medium ................................................... 29

10.3 Internal leakage of the reaction gas .......................................................... 29

11 Disposal ........................................................................................................ 30

12 Optional extras .............................................................................................. 30

13 Faultfinding and remedies .............................................................................. 31

14 Standards (selection) ...................................................................................... 33

15 Literature ....................................................................................................... 34

16 Data sheet ..................................................................................................... 35




List of figures

Fig. 1: Connection schematic for FC-42 fuel cells, example: 360 Watt module. ...... 12

Fig. 2: Connection schematic for FC-42 fuel cells, example: 1080 Watt module. .... 13

Fig. 3: Different configurations of electrical circuitry .............................................. 20

Fig. 4: Prescribed installation positions for the fuel cell ......................................... 23

Fig. 5: The most important components for the operating of a fuel cell ................. 24

Fig. 6: Ideal air stoichiometry. ............................................................................... 26

Fig. 7: Carrier for FC-42 fuel cells ......................................................................... 30

Fig. 8: U/I characteristic curve for Schunk FC-42 fuel cells .................................... 37

List of tables

Table 1: Different configurations of the output bundling ....................................... 21

Table 2: Faults and remedies ................................................................................. 31

Table 3: Standards (seletion) ................................................................................. 33

Table 4: Data sheet for Schunk fuel cells ............................................................... 35




List of ecronyms

DOE - department of energy

EMV - electromagnetic compatibility

FAQ - frequently asked questions

FC-42 - Fuel Cell with 42 single cells

HLC - Hydrogen, Liguid Cooled

OCV - open circuit voltage

PA - polyamide

PE - polyethylene

PEFC - polymer electrolyte fuel cell

PP - polypropylene

ppm - parts per million




1 Preliminary remarks

1.1 Nomenclature

The Schunk fuel cell stack is designated with the following nomenclature:

• FC-42/HLC: Fuel cell stack with 42 cells for hydrogen operation and liquid cooling.

1.2 General

In this document the term "fuel cell" stands for the Schunk fuel cell stack including

the attachment parts needed for the supplying of media and cooling water.

General statements on the water supply for and the operating characteristics of PEM

fuel cells in the relevant literature are also applicable for the Schunk fuel cell. It is

explicitly recommended that the literature listed below is read to supplement the

information in this manual.

• Fuel Cell manual (DOE Department of energy, 2004)

• Fuel Cell Systems explained (Larminie, Dicks, 2006)

• Brennstoffzellen – Entwicklung, Technologie, Anwendung (Heinzel/Mahlendorf/Roes,

2006)

With the fuel cells of the type FC-42, it is a matter of PEFCs with a proton-conducting

membrane. The fuel cells are designed for use with pure hydrogen on the anode side

and air on the cathode side. They are cooled by liquid and can be used in a

temperature range of 5 to 70 °C. The fuel cell requires no maintenance provided that

the parameters stated in the data sheet are maintained.




2 Safety instructions

2.1 Installation

The fuel cell may only be operated indoors when there is an adequate air change

rate1 and/or there is an extraction system and an approved hydrogen sensor has

been installed. In operation FC-42 fuel cells consume oxygen and accordingly may

not be used in closed rooms.

It must be ensured that the ambient temperature around the fuel cell is below the

spontaneous ignition temperature of hydrogen and that no sparks can occur at the

place of installation.

The relevant standards are to be maintained2. For permissible temperatures at the

place of installation see the data sheet in the appendix. The fuel cell should be

installed in such a way that the air and hydrogen outlets are at the lowest point so

that the process water created can flow out3.

If when it is being operated the fuel cell is not in a housing that provides protection

against contact, then all the metal parts of the fuel cell that are located externally -

with the exception of the two electric contact poles - must be carefully earthed; see

here also IEC 60529.

2.2 Hydrogen

The installation of the hydrogen supply must be carried out in accordance with the

relevant standards4.

For further information on handling hydrogen see the EU safety data sheet in

accordance with EU directive 91 / 155 EEC and 93/112 EU.

1 The air change rate stated takes account of the consumption of oxygen by the fuel cell as well as of

the maximum amount of hydrogen and of moisture release to the room.

2 For references to a selection of these standards see section 13: Standards

3 See recommended installation layout in section 7.44 For references to a selection of these standards see section 13: Standards




Hydrogen is / has:

• a colourless and odourless gas,

• easily inflammable,

• subject to igniting spontaneously if it flows out at high speeds,• lighter than air,

• asphyxiating at high concentrations,

• an explosion range (in air) of 4 - 77 %, and

• an ignition temperature of 560 °C.

It is recommended that the working area in which hydrogen is used is equipped with

safety systems, (e.g. hydrogen sensor, forced ventilation etc.)

2.3 Electrical connections

If two or more fuel cells are connected together electrically in series, then the open-

circuit voltage is greater than 50 V and there is the risk of a fatal electric shock. The

relevant standards are to be observed.

• It is essential that short circuits are avoided (to prevent risk of sparks and

explosions!).

• The electrical connections are to be executed in such a way that

o reliable electrical contact is ensured under all circumstances,

o the connections cannot become loose in an unintended manner,

o they are protected against corrosion, and

o contact with the ambient surroundings is not possible.

• The relevant EMC prescriptions are to be observed.

2.4 Cooling water

Additives5 (e.g. anti-freeze) added to the cooling water can be poisonous. Contact

with and/or drinking/swallowing of the cooling water is to be avoided. Common

cooling water additives contain as a rule corrosion protection agents and anti-fouling

additives which can be harmful to the health. Accordingly please observe the warning

instructions on the containers of the additives used.

5 See section 3.4 - water cooling




2.5 Products created

The water that is created in the course of the process (hereafter process water) may

be discharged into the sewer system without any misgivings. It does not contain anysubstances that are harmful to the environment. Nevertheless the process water

should not be drunk / swallowed. The system for leading away the process water

should be dimensioned in such a way that the quantity that is discharged (see data

sheet) can be led off in a reliable manner.

2.6 Temperatures

The surfaces of the FC-42 can reach temperatures in excess of 60 °C. The installation

must be executed in such a way that contact is prevented (risk of burns!).

The materials used are such that safe and reliable operation of the fuel cell is only

ensured within the range of temperatures stated in the data sheet. If the temperature

of the fuel cell exceeds or falls below this range of temperatures (even once), then it

is possible that the fuel cell is no longer operationally safe and accordingly should

then be checked by an expert before being used again.

2.7 Overpressure

If the values specified (see appendix) for the maximum pressure on the cathode and

also on the anode sides are exceeded (even once), then it is possible that the fuel cell

is no longer operationally safe and accordingly should be checked by an expert

before being used again.

2.8 Further information

Further information in particular on safety strategies for fuel cell systems is

published in IEC 62282-2 Fuel cell technologies, Part 2: Fuel cell modules.




3 Media supplies and power connection

3.1 General points

• The materials selected for the media supply systems should be selected carefully.

• It must be ensured that no metallic ions get on to the membrane on the anode or the

cathode sides.

• It must be ensured that no particles can get into the fuel cell.

• Pipe cross-sections and pressures (see data sheet) are to be dimensioned in such a

way that undersupplying of the fuel cell is not possible under any operating states.

• It must be ensured that no oxygen gets on to the anode side during operating of the

fuel cell since oxygen can damage the catalyst on the membrane. (This can occur in

particular if and as soon as the stock of hydrogen available for the fuel cell is used upso that at purging air instead of hydrogen is drawn in. This does not represent a

problem if the fuel cell is ventilated in a currentless state.

• The materials selected for use must be such that they are resistant to / stable at a

temperature at least 20 °C (safety margin) above the maximum intended working

temperature of the fuel cell system but in any case to a temperature of at least 80 °C.

• If plastic hoses are used, then care must be taken that these cannot kink (observe

minimum permissible bending radius).

3.2 Hydrogen

Hydrogen of a purity of at least 3.0 is to be used (without proportions of CO). If

doubt exists on the composition of the hydrogen, then the statement of purity of 3.0

is not enough. It must be ensured that the contamination present consists exclusively

of nitrogen, inert gases, fully saturated hydrocarbons and residual moisture. Typical,

known "poisons" for catalysts, e.g. compounds containing sulphur, must be at levels

of < 0.1 ppm; all other contamination < 5 ppm. The piping has to be in accordance

with the current standards.

3.3 Air

The air fed in may not contain any organic solvents, oil aerosols, smoke gases or

other contamination. The use of a dust filter (class F4) as well as a filter for organic

and inorganic compounds is advisable.




3.4 Water cooling

Normal mains water, to which an anti-freeze agent (in the ratio 3 : 1) and an anti-

fouling additive (prevents biological contaminating of the cooling water) have been

added, serves as the cooling medium. In no case may distilled or deionized water beused since this could attack the material of the fuel cell or fuel cell system

components. (For quantities, pressure and connection see the data sheet). Examples

of suitable anti-freeze agents:

• Glysantin ProtectPlus / G48

• GlycoShell

• Mobil 3+

Important:

The use of an anti-freeze agent in the cooling circuit does NOT mean that the

fuel cell stack may be used at a temperature < 0 °C. Its use serves merely to

provide protection against corrosion and decay. A measurement of temperature

in the coolant is only meaningful when the flow of coolant is at least 5 % of the

standard value.

Care is to be taken that there are no bubbles of air in the cooling circuit. Bubbles

of gas can be effectively separated off with a compensating reservoir in thecooling circuit.

3.5 Media connections

By reason of the connection facilities on the two end platens of the module, the

supplying of the stack with hydrogen, air and cooling water can be carried out in a

number of different ways. However it is explicitly recommended that the media are

fed in or, as the case may be, led off in accordance with the following diagrams. The

connection holes which are not needed for the particular case are to be closed in a

gastight manner with suitable plugs (G 1/4" and G 3/8", of plastic - PA, PP or PE). All

the screw plugs and blank plugs needed in accordance with the images below are

contained in a plug kit available as an optional extra (see section 12).



Fig. 1: Cpower lu

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Fig. 2:the po

Connectioner lug).

schematic f r FC-42 fuel cells, exam

Man

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3.6 Power connection

At each end of the fuel cell there is an M5 female screw thread for the power

connection. Suitable, low-corrosion cable lugs (e.g. nickel-plated, silver-plated,

gold-plated) are to be used for the power connection and secured to prevent themfrom coming loose. The fact that the connection cables are adequately insulated and

are of dimensions suitable for the intensity of current must be ensured at all times.

Important:

The screws may not be screwed in too far since otherwise they will contact the

collector and press this into the final graphite platen. The fuel cell can be

destroyed in this way. The length of the thread (from the upper edge of the end

adapter) may not exceed 10 mm. Tightening torque: maximum 2 Nm.

The threads of the power lugs are not suitable for carrying high mechanical loads,

e.g. for the situation that they are used for holding the fuel cell in a housing).

4 Operating the fuel cell

General information is given in this section on the operating of the FC-42 fuel cell. In

part the information has been taken from publications and is intended to represent a

starting basis for the development work carried out by the system integrator.

4.1 Anode supply

• Pressure-led (dead-end): In this mode a constant level of pressure (see data sheet) is

maintained at the anode inlet. The anode outlet is kept closed by a valve except when

it is opened periodically in pulses in order to "purge" the anode. Cycle times and

pulse duration must be laid down in accordance with the particular mode of

operation. Typically the valve is kept closed for 60 s and is opened for 1 s.• Flow-led: Hydrogen flows through the fuel cell continuously on the anode side. Here

the quantity of flow depends on the current generated and must be set so that it is

overstoichiometric at all times. If the supply is understoichiometric, the fuel cell

absorbs air via the anode side whereby this can lead to irreversible damage to the

catalyst. In certain circumstances a purging process in which the mass flow is

significantly increased can also be necessary in flow-led mode in order to drive out

condensate that has formed effectively.

• Moistening of the anode gas: In both the afore-mentioned modes moistening of the

anode gas can lead to an increase in efficiency.




4.2 Cathode supply

The cathode can be operated exclusively in flow mode since the air consists to

approx. 80 % of inert gas and contains only approx. 20 % oxygen. The quantity of air

needed for stable operating of the fuel cell depends on the current generated andmust at the same time fulfil the conditions necessary to maintain the water balance.

At low operating temperatures a higher quantity of air is necessary than at higher

operating temperatures in order to permit the process water created to be absorbed.

The air stoichiometry measured at the cathode outlet can lie between 1.2 and 1.4. In

addition it can be necessary to drive out the condensate arising during operating of

the fuel cell by periodically increasing the air flow.

If the fuel cell is operated at a cathode outlet temperature of > 55 °C, active

humidification of the cathode gas offers advantages in respect of the output andservice life of the fuel cell.

4.3 Critical operating states

These operating states lead to irreversible damaging of the fuel cell even if they act

only for a very short time and must be avoided in all circumstances:

1. Depletion of the fuel under load as caused, for example, by throttling or shutting off

of the hydrogen supply.

2. Presence of air on the anode side. This operating state can be caused by "open

anode" mode (i.e. not "dead-end mode") coupled with an inadequate supply of

hydrogen. The fuel cell then sucks in air via the anode outlet. This causes the catalyst

on the anode side to be oxidized and thereby permanently damaged.

3. Overheating of the fuel cell stack. At T > 75 °C (in operation), the membranes can be

destroyed if there is inadequate humidification. The temperature of the cathode

exhaust air should always be kept below 75 °C.

4. Short circuit or, as the case may be, very low total voltage (below 75 % of the nominal

voltage). In this operating state it is very probable that a number of cells change their

polarity. Such a "pole-changing" leads to permanent damage to the fuel cell.

Operating states at < 75 % of the nominal voltage may only be set for a restricted

period. At the same time care must be taken that the fuel cell is not thermally

overloaded and that the individual cell voltage does not fall below 0.3 V.




Further disadvantageous operating modes, which can lead to a reduction in service

life / output, are:

• OCV (open circuit voltage) mode

• Frequent switching operations in which the maximum current (see data sheet) isexceeded

• Inadequate or excessive humidification

• Unfavourable installation position resulting in the flowing out of the condensate

being hindered

• All substances which damage the membranes or catalysts6

Important:

If permanently damaged, the pole-changed cell will generate not electricity buthydrogen (electrolysis). In such a case hydrogen can be detected in the cathode

exhaust gas during operating of the fuel cell even though the FC-42 continues to

be tight from the anode side to the cathode side. In this case the fuel cell is no

longer operationally safe and must be sent back to the manufacturer for disposal.

4.4 Monitoring

During operating of the fuel cell the following values should be monitored at all

times:

• Voltage of the fuel cell (in the case of bundling the total voltage of a bundle)

• Current of the fuel cell (in the case of bundling the current of each individual cell

stack)

• Difference in temperature between return flow and outward flow of the cooling liquid

• Temperature of the fuel cell measured in the cathode exhaust air, directly at the

outlet of the stack

• Consumption of hydrogen

If one of the values as measured lies outside the particular permissible range (see

data sheet), the fuel cell is to be switched off immediately and separated from the

load. Please check that all the connections with the fuel cell are in good order and

that the fuel cell is being supplied with all operating media; in addition check your

6 If a suitable filter (see section 3.3) is installed where the cathode air is drawn in, no contamination

from the environment can reach the cells.




system for malfunctions.7

The consumption of hydrogen should lie within ± 5 % of

the calculated value in one interval.

Note:

The hydrogen consumption is calculated from the number of individual cells and

the current. The following holds good: Mass H2 needed in order to generate a

current of 1 A for one hour at one cell: 0.03765 g (i.e. mH2 = 23.72 g/h with 42

cells and 15 A). Under conditions close to the ambient pressure and temperature

the consumption of hydrogen is: 7 ml/min/cell/A.

4.5 Switching on

When switching on the fuel cell the following sequence is to be followed:

1. Switch on cooling

2. Switch on air supply

3. Switch on hydrogen supply

4. Purge anode with hydrogen

5. Check the open-circuit voltage (should be > 35 V)

6. Switch on electrical load

4.6 Switching off

When switching off the fuel cell the following sequence is to be followed:

1. Disconnect electrical load

2. Shut off hydrogen feed

3. Open anode outlet (purge valve)

4. Shut off supply of air (fuel cell is now depressurized)

5. Switch off cooling (switching off the cooling in a time-delayed manner may beadvisable)

7 See FAQs and Service questionnaire at www.schunk-fuelcells.com




5 Storage

In general one has to differentiate between the storing of one individual fuel cell and

the storing of a system in which the fuel cell is installed.

5.1 Storage of one individual fuel cell

If the fuel cell is not to be operated for more than 5 days, care must be taken that no

microorganisms move in. Accordingly before storing it at room temperature the fuel

cell should be heated up briefly to 75 °C without electrical operation and then blown

through with dry (40 % R.H. at 20 °C ± 5 °C) air that is free of oil and dust (for approx.

20 minutes, approx. 50 l/min) in order to dry it. Finally the media inlets and outlets

should be closed with suitable blind plugs (e.g. from the plug kit available as anoptional extra).

5.2 Storage / long-term switching-off of a complete system

Before a complete system is stored, the cathode is to be ventilated and thus

depressurized. A filter mounted on the inlet side (see section 3.4) prevents

contamination being able to get into the fuel cell. On the outlet side it must be

ensured by means of a suitable mechanism that no coarse contamination from the

ambient surroundings (chemical compounds, dust, insects) can get carried in. In

general it is sufficient when the system is closed with a simple flap. Gastight sealing

of the cathode is not necessary.

Before the system is switched off and depressurized, anode and cathode should be

freed of condensate by means of a suitable purging process (e.g. relatively long

purging or postrunning of the cathode blower).

After this the anode is depressurized via a valve. Ideally before the system is

switched off permanently the anode should be subjected to controlled ventilation by

the cathode blower until the open-circuit voltage has fallen to zero.

If the fuel cell has not been in operation for > 5 days, it must be assumed that it will

have to be operated for approx. 5 minutes until the full output is achieved through

self-humidification. Approx. 50 - 60 % of the full output is to be reckoned on

immediately after switching on.)




6 Transport

If a fuel cell is transported in a moist state, it must be ensured that it is not subjected

to temperatures in excess of or below the permitted temperatures (see data sheet).

Ideally the fuel cell should be dried and protected against frost. A check can be made

with the aid of appropriate temperature recording devices (e.g. "FreezeWatch" from

3M) as to whether the temperature fell below 0 °C.

The instructions given in section 5 (storage) should be followed in particular with

extended transportation (> 5 days).

The position of the fuel cell during transportation is optional but it should be packed

with good padding to reduce the effect of impacts and high accelerations;

acceleration sensors on the packing or on the fuel cell itself (e.g. "Shockwatch") canbe fitted to display what acceleration the fuel cell was subjected to.

Important!

There can be residues of coolant in the fuel cell which should be removed (blown

out) before transport. In addition it is recommended that all media connections

are closed with blank plugs.




7 Notes für system integrators

7.1 General

The PEM fuel cells of type FC-42 are designed as a modular system and can be

bundled together in a variety of ways in order to achieve the outputs and operating

voltages desired. The desired constellation must be stated when ordering since the

fuel cells are supplied bundled together in a turnkey state.

7.2 Electrical circuitry

The possibility of electricity being fed back into a FC-42 fuel cell (e.g. from other fuelcells in a module or from batteries in a hybrid system) must be reliably excluded.

This can be achieved by means of, for example, a Schottky diode with a punch-

through voltage that is as low as possible (< 500 mV) and a load current that is as

low as possible in the shut-off direction. In addition it is recommended that the fuel

cell is isolated completely electrically with a suitable relay prior to extended "off"

phases. Alternatively the individual overall voltage and the individual overall current

can be monitored with a monitoring circuit and an individual load-shedding process

activated in the case of a malfunction.

Different levels of direct current and different classes of output can be achieved by

bundling the fuel cells together in series or parallel in accordance with the circuit

variants shown in the sketches.

Fig. 3: Different configurations of electrical circuitry (parallel / in series / parallel and in series)




There are 4 different operating modes:

Voltage led: The voltage of the fuel cell is led in a forced manner and the current sets

itself in accordance with the characteristic curve. In this mode overloading of the fuel

cell is easy to avoid and an undervoltage can be easily excluded. Feeding back intothe fuel cell must always be excluded.

Current led: The current that is drawn from the fuel cell is set externally. Here care

has to be taken that the voltage does not fall below the minimum working voltage of

the fuel cell (see data sheet). Here too feedback into the fuel cell must be excluded.

Output led: The desired output is set externally for the fuel cell. Here voltage and

current set themselves dynamically in accordance with the characteristic curve. It

must be ensured that current and voltage remain in the permitted working range andthat no feedback into the fuel cell takes place.

Resistance led: With a pure Ohmic load, current, voltage and the output supplied set

themselves in accordance with Ohm's law and the dynamic characteristic curve.

Current and voltage must lie in the permitted working range. Here a feedback from

the load is not possible.

Important:

Even if an electrical feedback from the load is not possible, such a feedback can

result from the coupling together of a number of fuel cell modules.

Table 1: Different configurations of the output bundling

Voltage / V

24 48 72 96

Current / A Wattage, W and in brackets the number of FC-42 basic modules

15 360 (1) 720 (2) 1080 (3) 1440 (4)

30 720 (2) 1440 (4) 2160 (6)

45 1080 (3) 2160 (6)

60 1440 (4)




7.3 Avoidance of open-circuit voltage mode

A situation in which the fuel cell remains in a state above 85 % of the open-circuit

voltage for periods of more than 10 minutes has an unfavourable effect on its service

life and efficiency. Accordingly in a hybrid system (battery / fuel cell) it isadvantageous for the fuel cell to be switched off completely if the output falls below

approx. 20 % of the nominal output. If the load is thrown off, the fuel cell should be

changed to a zero-potential state.

A cyclic operating mode with OCV mode (e.g. OCV - 0.5 V/cell - OCV) should also be

avoided (i.e. to avoid frequent switching on and off of the fuel cell).

The fuel cell can be discharged electrically with a low current (1 - 5 % of the nominal

current) by, for example, putting a resistance into circuit.

7.4 Operating methods, mounting and installation position

Different operating methods are possible and the particular ones that are

advantageous depend on the ambient conditions, system configuration and

installation position of the stack.The standard counterflow configuration is the

configuration with which good results are achieved in an unhumidified system (see

Fig. 6). Other flow directions, which are matched to the particular operating

conditions of the fuel cell, are possible.

With all configurations care must be taken that the condensate created during

operating is carried out completely and does not run back into the cell stack.

(Standing condensate generally makes its present noticeable by a gentle "gurgling"

sound). Accordingly only the following two installation positions are to be

recommended:




1. The fuel cell is stood on one of the cooling plates angled at 0 - 5° to the

horizontal.

2. The fuel cell is stood on one of the consumers (short face side) angled at

0 - 5° to the horizontal.

With both installation positions it is to be recommended that the cooling water flows

upwards, i.e. from the bottom to the top, through the fuel cell whereas the outlets for

air and hydrogen should be at a low point if possible (c.f. section 3.5 - media

connections).

Important:

In no case may the fuel cell be secured by using the M5 holes in the end adapters.The forces acting through the use of these for securing can damage the fuel cell

irreversibly. Instead a tensioning or clamping mechanism should be provided

which surrounds the fuel cell and holds it firmly in position.

The use of the M5 tapped hole on the face of the fuel cell for the mounting of

light system components (e.g. diodes for the electrical isolation of the individual

fuel cell stacks) does not represent a problem.

0°‐5°0°‐5°

Fig. 4: Prescribed installation positions for the fuel cell (1. = left, 2. = right)




7.5 Minimal system configuration

Fig. 5: The most important components for the operating of a fuel cell with and without cathode humidifier




8 Methods for optimizing the efficiency

8.1 High-current mode

While being operated, FC-42 modules may be electrically "short-circuited" at

intervals of not less than two minutes for a maximum of 200 ms. Such a high-current

operation should be realized with a semiconductor relay (e.g. CRYDOM D1D40) or a

MOSFET (e.g. MOSFET FQP85N06) since the contacts of a mechanical relay would fuse

(the fuel cell is a capacitor with a high capacitance!). The brief high-current pulse can

bring about an increase in efficiency of some 5 - 15 %.

8.2 Throttling of the cathode air

A brief (less than 500 ms) throttling down of the incoming stream of air when the

fuel cell is under load can bring about an increase in efficiency of some 10 %. This

procedure should be followed not more often than once every 2 minutes. In general

the efficiency of PEM fuel cells is superior when they are operated dynamically rather

than under constant conditions.

8.3 Humidifying of the cathode air

At temperatures in excess of approx. 50 °C more water is removed from the fuel cell

via the cathode exhaust air than is created by the reaction. As a result the membrane

dries out and its efficiency falls. By humidifying the cathode air the water equilibrium

can be kept stable over a wide temperature range. For a closed humidifying circuit it

is necessary that the process water, that is contained in the cathode exhaust air to a

large extent, is transferred to the flow of incoming air. A membrane exchanger can

be used for this purpose. In analogous fashion the condensed and purified process

water can be sprayed in via nozzles or injected in in the form of a mist with ultra-

sound. At the same time the spraying/injecting in of the water brings about a

considerable cooling effect. With active feeding back of water it must be ensured that

only pure, ionfree water is being recirculated.




8.4 Humidifying of the anode gas

At high levels of output water is transported from the anode to the cathode by

electro-osmosis. This can lead to the membrane drying out on the anode side so thatthe efficiency falls. Humidifying of the anode gas to a dew point of approx. 5 K below

the cell stack temperature can lead to an increase in efficiency.

8.5 Regulating of the quantity of air

The moisture content balance of the fuel cell can be optimized by regulating the

quantity of air as a function of the current and the temperature. In particular one can

prevent thereby the cathode being flooded with excess water. This state is very

critical at low temperatures. At high temperatures an excess of air can lead to the

membrane drying out very rapidly.

Fig. 6: Ideal air stoichiometry for different levels of moisture content of the ambientair, plotted via the stack temperature (measured in the air flow of the cathode outlet).




8.6 Purging cycles

At periodic intervals the anode must be purged in order to remove and carry out inert

gases and/or condensate. The purging of the anode can be carried out by, for

example, arranging that the outlet valve for the hydrogen is opened every 60 s forapprox. 0.5 - 2 s at a preset primary pressure (e.g. 250 mbar).

8.7 Anode gas recirculation

Here the anode gas is transported from the anode outlet to the anode inlet with the

aid of a gastight pump (e.g. a membrane pump). The ratio between the fresh gas fed

in and the recirculated gas should be approx. 1:1. If recirculation is carried out in this

way the purging intervals can be extended very considerably. It must be explicitlystated that the pump is resistant to hydrogen and water vapour.

8.8 Cathode air recirculation

A homogeneous distribution of moisture and efficient removal of condensate without

drying out of the stack is achieved if a proportion of the cathode outlet air is fed back

to the cathode inlet.

8.9 Media reversal

If the electrodes have become contaminated by, for example, contaminated reaction

gases, a "cleaning" of the fuel cell can be brought about with the aid of a media

reversal. In addition this operating mode is to be recommended in order to humidify

the fuel cell uniformly in the situation that it has previously become too moist on the

cathode side.

8.10 External humidification

If the fuel cell is being used for the first time following a relatively long period of

storage, one must reckon on a period of time elapsing before the fuel cell has

humidified itself and can produce its full output. This process can be accelerated by

means of an external humidification system. With the aid of a conventional steam

generator the fuel cell can be subjected to a throughflow of vapour from distilled

water (!!!) via the existing media connections for approx. 2 - 3 minutes. When

operating of the fuel cell is commenced thereafter, the full output will be available at

an earlier stage.




8.11 Manual drying of the fuel cell

If the electrodes of the fuel cell become too moist as a result of, for example, an

inadequate flow of air or a too low temperature, then the fuel cell must generally be

dried manually in order to restore its full efficiency again. To be recommended hereis the use of the cathode blower in combination with an external power source. A Y-

piece connection can be used in order to dry both cathode and anode at the same

time. When drying the fuel cell care must be taken that the maximum pressure never

exceeds 300 mbar.

9 Data log and operating proof

Should it be wished to advance a claim under warranty, then proof must be presented

that the fuel cell was not being operated under pathological conditions (e.g. excess

temperature, undervoltage, hydrogen deficiency, contamination etc.). The proof is to

be presented in the form of a data log without gaps of the fault scenario whereby the

log should include the period prior to the occurrence of the fault, this period to be >

15 minutes and whereby it should include the following measurement parameters:

Sampling rate 1 Hz for all measurement parameters

• Voltage at the power lugs of the fuel cell

• Current at each individual stack of the fuel cell

• Temperature of the return-flow cooling water

• Temperature at the outlet from the cathode

In view of the very considerable burden recording of the above data places on the

fault-recording memory, it should be noted that recording of merely the minimum

and maximum values of the above parameters is sufficient to prove that the fuel cell

was not operating / being operated properly.

Similarly proof must be presented that the anode was supplied exclusively with

hydrogen of the required quality (c.f. section 3.2). For the supply of air to the cathode

proof must be presented that filters were installed that were capable of absorbing to

an adequate extent all the organic and inorganic contamination.




10 Searching for leaks

10.1 External leakage of the reaction gases

In order to prove whether the fuel cell is leaking into the ambient surroundings

(external leak) from the anode or the cathode, the following quantitative method can

be used:

• Close both the anode and cathode outlets (e.g. with suitable blank plugs) in a

gastight manner

• Subject anode and cathode via a common pressure line (e.g. with a T-piece) to a test

pressure of 100 mbar, using air as the testing medium.

• Close the common pressure line in a gastight manner (by clamping or with the aid of a suitable shut-off valve).

• Measure with a pressure gauge and a stopwatch the time that elapses for the

pressure in the closed space to fall from 100 mbar to 50 mbar. This time should be

longer than that stated in the data sheet.

10.2 External leakage of the cooling medium

In order to prove whether the cooling circuit is leaking into the ambient surroundings

(external leak), the following quantitative method can be used:

• Close the coolant outlet (e.g. with a suitable blank plug) in a gastight manner.

• Subject the cooling system to a test pressure of 100 mbar, using air as the testing

medium.

• Close the pressure line in a gastight manner (by clamping or with the aid of a suitable

shut-off valve).

• Measure with a pressure gauge and a stopwatch the time that elapses for the

pressure in the closed space to fall from 100 mbar to 50 mbar. This time should be

longer than that stated in the data sheet.

10.3 Internal leakage of the reaction gas

In order to prove whether the reaction gas can leak from the anode side to the

cathode side, the following quantitative method can be used:

• Close the anode outlet (e.g. with a suitable blank plug) in a gastight manner. The

cathode should be left open to the ambient surroundings.



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13 Faultfinding and remediesTable 2: Faults and remedies

NoFault

descriptionNo

potentialcause

No Measures / checksNotes /

further measures

1The output of the fuel cell

is too low

1Supply of air inadequate

1

Check that the cathode blower is generating anadequate volumetric flow taking into account allpressure losses (pipe system, filter, fuel celletc.)

For production of asuitable air supply seesections 3.3 and 4.2and the data sheet

2Check that the cathode supply system is free of condensate

3Check that the regulating of the quantity of air istaking place properly.

2Supply of hydrogen

inadequate

1Check that the hydrogen supply is generatingan adequate volumetric flow taking into accountall pressure losses For production of a

suitable hydrogensupply see sections 3.2

and 4.1 and the datasheet

2Check that the pressure level of the hydrogen

supply lies in the given working range.

3Check that the anode is being adequatelypurged, i.e. to ensure removal of condensateand inert gas

3The electrodesare too moist

1Check that the air supply is sufficient to preventcondensate forming

2Check that the fuel cell is mounted in theoptimum installation position.

For installation positionsee section 7.4

3Check that the fuel cell is reaching an adequateworking temperature

4Dry the fuel cell, e.g. with the aid of the cathodeblower

See section 8.11

4The electrodesare too dry

1 Is the supply of air to the fuel cell so high that itis drying out?

2Is the working temperature of the fuel cell toohigh?

3Humidify the fuel cell before commissioning itafter an extended period of storage with the aidof a steam generator

See section 8.10

5The electricalworking point isunsuitable

1Check that the current being drawn from thefuel cell is not too high

2Check that the fuel cell is not being operated ata working voltage that is too low

6The electricalconnection isinadequate

1Check the mechanical connecting of theelectrical contacts.

For further informationon the electricalconnecting see section7.2

2 Check that the electrical connection is notgenerating heat during operating.

3Check that the electrical connection is notshowing a voltage drop.

4Check that no corrosion is visible on theelectrical contacts.

7The electrodesare contaminated

1Check that the hydrogen being supplied is of adequate purity.

See section 3.2

2Check that there is no contamination in thecathode air.

See section 3.3

3Carry out a media reversal in order to clean theelectrodes

See section 8.9




NoFault

descriptionNo

potentialcause


further measures

2

The fuel celldoes notreach thespecified

open-circuitvoltage

1

There is aparasitic electricalload on the fuelcell

1Check that the fuel cell is completely separatedfrom all consumers.

2Check the electrical connections for creepage

and short circuits

2Supply of air isinadequate

1 See above (measures under 1.1)See sections 3.3 and4.2

3Supply of hydrogen isinadequate

1 See above (measures under 1.2)See sections 3.2 and4.1

4The electricalconnection isinadequate

1 See above (measures under 1.6) See section 7.2

5The electrodesare contaminated

1 See above (measures under 1.7) See section 8.9

6The fuel cell hasan internal shortcircuit

1 Check whether the fuel cell generates heatwithout being under load

If an internal shortcircuit is established,then the fuel cell mustbe replaced

2Check the time for the voltage to decreaseunder separated load compared with the figurein the data sheet

3Check the electrical connections for creepageand short circuits

7The fuel cell hasan internal leak

1Check whether the fuel cell generates heatwithout being under load If an internal leak is

established, then thefuel cell must bereturned to themanufacturer for repair or to be exchanged.

2Check the time for the voltage to decreaseunder separated load compared with the figurein the data sheet

3Check the time for the pressure at the anode todecrease in comparison with the figure in thedata sheet

3The fuel cellbecomes toohot

1

The electricalworking pointselected is notsuitable

1 Operate the fuel cell in the given voltage range

2 Operate the fuel cell in the given current range

3 Check the load profile in respect of time

2

The supply of coolant is too low/ the temperatureof the coolant istoo high

1

Check that the coolant pump supplies anadequate volumetric flow that takes account of the given pressure losses of the complete pipesystem, of the fuel cell and of the cooler

2Check that there is no contamination in thecooling system

3 Check that the coolant being used is suitable See section 3.4

4Check that the coolant pump is not sucking inair

3There areinclusions of air inthe cooling circuit

1 Vent the cooling circuit

2Check that the coolant pump is not sucking inair

4Hydrogen isgetting to thecathode

1 Check the piping system for leaks

2 Check the fuel cell for internal leaks See section 10.3

5 Air is getting tothe anode

1 Check the piping system for leaks.

2 Check the fuel cell for internal leaks See section 10.3




NoFault

descriptionNo

potentialcause


further measures

4The fuel cellremains toocold

1

Only a lowelectrical outputis being taken

from the fuel cell

1 Increase the electrical output being drawn

2 Improve the insulation of the system

3Reduce the cooling output; in certaincircumstances it may be necessary to put abypass to the heat exchanger into circuit

2

Themeasurement of temperature isfaulty

1Check that the media is flowing around thesensors

2Measure the temperatures at the cathode outletand in the coolant circuit

3The coolingoutput is too high

1Reduce the cooling output; in certaincircumstances it may be necessary to put abypass to the heat exchanger into circuit

14 Standards (selection)

Table 3: Standards (seletion)

An overview on all the standards to be applied is given in IEC 62282-2.

IEC 62282-2 Fuel cell technologies, Part 2: Fuel cell modules

IEC 60079 (alle) Electrical apparatus for explosive gas atmospheres

IEC 60352 (alle) Solderless connections

IEC 60529 Degrees of protection provided by enclosures




15 Literature

James Larminie; Andrew Dicks, Fuel Cell Systems explained, second edition,

März 2006

Heinzel, Angelika; Mahlendorf, Falko; Roes, Juergen, Brennstoffzellen –

Entwicklung, Technologie, Anwendung, 3. Aufl., Heidelberg 2006

U.S. Department of Energy, Fuel Cell Handbook – Seventh Edition by EG&G

Technical Services, Inc., 2004




16 Data sheet

Table 4: Data sheet for Schunk fuel cells

Ambient conditions

Storage temperature (dry unit) -10 bis +50 °C

Ambient temperature during operating 5 - 70 °C

Relative humidity of ambient air (operating and

storage)

40 - 95, not condensing %

Operating conditions

Operating temperature (not humidified) 5 - 50 °C

Operating temperature (humidified, dew pointapprox. 5 - 10 K below stack temperature)

< 70 °C

Max. temperature of the surfaces 75 °C

Electrical properties

Nominal current * 15 A

Nominal voltage * 24 V

Nominal output * 360 W

Minimum voltage (briefly, 5 s) 15 V

Open-circuit voltage 36 - 42 V

Service life ***** > 1500 h

Mechanical properties

Mass 2100 g

Dimensions LxWxH 188 x 130 x 53 mm

Interfaces

Electrical connection M5-female screw thread

Max. tightening moment 2 Nm

Media

Purity of hydrogen 99.99 %, noCo

Hydrogen consumption 0 - 4 l/min

Max. pressure drop, anode * 15 mbar

Max. pressure drop, cathode * 30 mbar

Process water generated at full load * 180 g/h

Max. inlet pressure, anode 300 mbar

Oxygen content of feed air 20 - 30 Vol.-%

Air consumption 0 - 40 l/min




Media (continuation)

Max. inlet pressure, cathode 300 mbar

Max. pressure difference, anode/cathode 300 mbar

Max. gas temperature at inlet **** 65 °C

Minimum gas temperature at inlet **** 5 °C

Max. gas temperature at outlet **** 75 °C

Gas leakage, anode to cathode ** > 300 s

Gas leakage to outside *** > 900 s

Leakage, coolant system to outside ***

Cooling medium

> 600

water/ glycol

s

Coolant throughput >0,5 l/min

Max. pressure drop, coolant 300 mbar

Max. temperature difference, return flow -

outward flow in the coolant

5 K

Max. coolant pressure 1 bar

* Can vary by ± 15 %

** Time for the cathode-anode pressure difference to change from 100 mbar to 50 mbar with air as

testing medium; see also leak rate measurement further below.

*** Time for the cathode and anode pressure difference vis à vis ambient surroundings to change

from 100 mbar to 50 mbar with air as testing medium.

**** Holds good for anode and cathode.

***** After the specified time the output is at least 90 % of the nominal output. The precondition forthe validity of this statement is that the fuel cell has not been operated under pathological

conditions (e.g. excess temperature, undervoltage, hydrogen depletion, contamination etc.). The

proof of this is to be kept up with a complete data log (see section 12 - data log).

****** The voltage drop is measured on the basis of the current OCV.

Important:

All statements in the data sheet are typical average values and are based on

measurements made under ideal conditions. The values stated are guide-linevalues and are not guaranteed.




Fig. 8: U/I characteristic curve for Schunk FC-42 fuel cells




The manual is protected by copyright. The rights justified thereby and in particular the rights in

connection with the manual of translating, printing, removing figures therefrom, transmitting by

radio, reproducing by photo-mechanical or similar means and storing in data processing systems

remain reserved.

If a new version of this manual is published, then all earlier versions lose their validity.

Each and every liability of the supplier is excluded for damage or loss that results from improper

operation or unprofessional installation.




Rev 2.0 [eng]

(04/2008)

Schunk Bahn- und Industrietechnik GmbH

Hauptstraße 97

35435 Wettenberg

www.schunk-sbiw.com

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