12 Volt Marine Electrics

Mike Litzkow

Introduction

• My background

• Plan– Start with some problems– Learn stuff that will be useful in solving those

problems– Try to apply what we’ve learned to solve the

problems

Problems

• Can I replace my navigation light bulb with one from a hardware store?

• Can my lighter plug power my coffee pot?

• Are my starter, alternator, battery working?

• Why doesn’t my engine start?

• How long will my batteries last?

Basics of Electricity

• Voltage, Current, and Resistance

• Ohm’s law

• Watt’s law

• Wire size

1 Volt1 Ohm

Basic Electrical Circuit

Battery

Resistance

•Starter motor

•Nav lights

•Radio

Electrons leave the negative pole of the battery, flow through the resistance, and return to the positive pole of the battery

Electrons always have to flow in a complete circuit

Parallel Circuits

Starter motor Nav Lights Radio

Starter motor Nav Lights Radio

Parallel circuits on your boat can (usually) beThought of as simpler individual circuits

Basic Electrical Faults

BatteryResistance

(load)

Short circuit – electrons can flow through the circuit without reaching the resistance (wire overheats, danger of fire)

Open circuit – electrons don’t have complete path (nothing happens)

ShortCircuit

1 Volt1 Ohm

Open Circuit

Volts, Ohms, and Amps

BatteryResistance

(load)

A flow rate of 6.24 X 1018 electrons per second is an electrical current of 1 Ampere (Amp)

Electrical pressure is required to make the electrons flow through the resistance. This pressure is measured in Volts

The resistance is measured in Ohms

1 Volt will push 1 Amp of current through 1 Ohm of resistance

1 Volt1 Ohm

1 Ampere

I - current (Amperes)

V - electromotive force (Volts)

R - resistance (Ohms)

Ohm’s Law

R

VI

1 Volt1 Ohm

1 Amp

Current isdirectly proportionial to voltage andinversely proportional to resistance

Alternative Forms of Ohm’s Law

R

VI IRV

I

VR

Voltage, current, and resistance in a circuit are fundamentally related

If we know any two of them, we can easily calculate the other

Watt’s Law

VIP

1 Volt1 Ohm

1 Amp

Power isdirectly proportionial to voltage anddirectly proportional to current

P - power (Watts)

V - electromotive force (Volts)

I - current (Amperes)

Note: these are the same Watts as in a 100 Watt light bulb

Alternative Forms of Watt’s Law

I

PV

V

PI

Voltage, current, and power in a circuit are fundamentally related

If we know any two of them, we can easily calculate the other

VIP

RIP 2R

VP

2

These come from combining Watt’s law with Ohm’s law

Choosing a Light Bulb

Perko 170 Series Navigation Lights12 V0.83 A

1. Take old bulb to hardware store and match physical form2. New bulb must be 12 Volts3. How many Watts should new bulb be? Why is this important?

VIP Remember Watt’s Law

The Power is 12 X 0.83 or approximately 10 Watts

Alternative method: measure currentin bulb that’s still working

MarinePro Coffee Pot

• Brews Fresh Hot Coffee in Minutes • See-Through Water Gauge (Easy to Make Just the Right

Amount of Coffee).• Thermo Glass Carafe with Stay-Cool, Sure-Grip Handle.• Auto-Shutoff.• Plugs directly into your 12-Volt cigarette lighter.• Uses Standard #2 Cone Filters (Note: 2 Filters are

included, along with a coffee scoop).• 6' of Power Cord.• 130 Watts• CE Certified

Coffee Pot - Continued

Marinco15 Amp rated10 Amp fused

Seafit15 Amp rated

Watt’s law deals with power, but these devices are rated by the currentthey can safely handle.

Using alternative form of Watt’s lawI = 130 Watts / 12 VoltsI = 11 Amps

V

PI

Measuring Equipment

Built-in analog meter(not very accurate) Built-in digital meters

(probably accurate)

Hand-held digitalmulti-meter ($40)

Lighter plug volt meter( $18)

Hand-held digitla multi-meterwith current clamp ($154)

Physical Components

Battery

Starter

Alternator

Battery, Starter, and Alternator

• Battery– Stores energy and provides it to starter when

needed

• Starter– Uses energy from battery to crank the motor

• Alternator– Generates electricity to recharge the battery

afterwards

Battery Testing

Rest Voltage•12.6 – Full charge•12.4 – ¾ charge•12.2 – ½ charge•12.0 – ¼ charge

Capacity•Load to ½ cold cranking amps•Hold for 15 seconds•Voltage should remain above 9.6

If your 12V battery is really at 12V,you’re in trouble!

Alternator Testing

Automotive Type Alternator– 13.8 to 14.2 volts with engine

running above idleMarine Alternator

– Voltage may be higher or lower, but should always be above battery’s rest voltage

Quick System Test

1. Attach digital volt meter

2. Check rest voltage – should be 12.6

3. Disable engine from starting– Crank 15 seconds– Voltage should remain at 9.6 or above

4. Switch batteries and repeat steps 2 & 3

5. Start engine and check charging voltage– Should be 13.8 to 14.2 (auto type alternator)

Battery Capacity Calculations

• Add up the current draw of all devices you want to use (or measure)

• Multiply by number of hours or service you need

• Result is in Amp hours.– Should be less than 30% of Amp hour rating

of battery. Otherwise you will significantly shorten it’s life.

Race Chicago to Macinac – 4 days

Original Estimage

Device Draw Comments

Computer 4.0 8A supply operating at 1/2 capacity

Cabin light 1.0 Avg 1 light on 1/2 the time

Depth Sounder 0.5 Runs continuously

Knotmeter 0.1 Runs continuously

Wind Instruments 0.1 Runs continuously

Nav Lights 1.5 3 lights 1A each on 1/2 time

VHF Radio 1.5 Runs continuously

Subtotal 8.7 Amp hours per hour of operation

Daily Total 208.8 Amp hours per day of operation

Race Total 835.2 Assuming race completed in 4 days

Capacity Needed 2784.0 Maximum draw down 30%

Capacity Available 300.0 3 batteries of 100 AH each

Try again…Revised Estimate`

Device Draw Comments

Computer 0.4 Computer on standby except 6 min / hr

Cabin light 0.2 1 light 2 hrs/day (flashlights rest of time)

Depth Sounder 0.5 Runs continuously

Knotmeter 0.1 Runs continuously

Wind Instruments 0.1 Runs continuously

Nav Lights 1.3 3 lights 1A each on 10 hrs/day

VHF Radio 0.1 2 hrs/day - monitor with handheld rest of time

Subtotal 2.6 Amp hours per hour of operation

Daily Total 63.4 Amp hours per day of operation

Race Total 253.6 Assuming race completed in 4 days

Capacity Needed 317.0 Maximum draw down 80%

Capacity Available 400.0 4 batteries of 100 AH each

Alternative 1Buy 200 AH batteries at$250 each

Alternative 2Buy LED tri-color lightusing 1/2 A - $300.Reduces 1.3A avgdraw to 0.2A.