1. 12 Volt Marine Electrics
Mike Litzkow

2. 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

3. 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?

4. Basics of Electricity Voltage, Current, and Resistance Ohm’s law
Watt’s law
Wire size

5. Basic Electrical Circuit
Resistance
Starter motor
Nav lights
Radio
Battery
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

6. Parallel Circuits Parallel circuits on your boat can (usually) be
Thought of as simpler individual circuits

7. Basic Electrical Faults
Open Circuit
Short
Circuit
Battery
Resistance
(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)

8. Volts, Ohms, and Amps Resistance Battery (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

9. Ohm’s Law Current is directly proportionial to voltage and
inversely proportional to resistance
I - current (Amperes)
V - electromotive force (Volts)
R - resistance (Ohms)

10. Alternative Forms of Ohm’s Law
Voltage, current, and resistance in a circuit are fundamentally related
If we know any two of them, we can easily calculate the other

11. Watt’s Law Power is directly proportionial to voltage and
directly 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

12. Alternative Forms of Watt’s Law
Voltage, current, and power in a circuit are fundamentally related
If we know any two of them, we can easily calculate the other
These come from combining Watt’s law with Ohm’s law

13. Choosing a Light Bulb
Take old bulb to hardware store and match physical form
New bulb must be 12 Volts
How many Watts should new bulb be? Why is this important?
Perko 170 Series Navigation Lights
12 V
0.83 A
Alternative method: measure current
in bulb that’s still working
Remember Watt’s Law
The Power is 12 X 0.83 or approximately 10 Watts

14. 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

15. Coffee Pot - Continued Seafit Marinco 15 Amp rated 15 Amp rated
10 Amp fused
Seafit
15 Amp rated
Watt’s law deals with power, but these devices are rated by the current
they can safely handle.
Using alternative form of Watt’s law
I = 130 Watts / 12 Volts
I = 11 Amps

16. Measuring Equipment Built-in analog meter Lighter plug volt meter
(not very accurate)
Built-in digital meters
(probably accurate)
Lighter plug volt meter
( $18)
Hand-held digitla multi-meter
with current clamp ($154)
Hand-held digital
multi-meter ($40)

17. Physical Components
Starter
Battery
Alternator

18. Battery, Starter, and Alternator
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

19. Battery Testing Rest Voltage 12.6 – Full charge 12.4 – ¾ charge
If your 12V battery is really at 12V, you’re in trouble!
Capacity
Load to ½ cold cranking amps
Hold for 15 seconds
Voltage should remain above 9.6

20. Alternator Testing Automotive Type Alternator Marine Alternator
13.8 to 14.2 volts with engine running above idle
Marine Alternator
Voltage may be higher or lower, but should always be above battery’s rest voltage

21. Quick System Test Attach digital volt meter
Check rest voltage – should be 12.6
Disable engine from starting
Crank 15 seconds
Voltage should remain at 9.6 or above
Switch batteries and repeat steps 2 & 3
Start engine and check charging voltage
Should be 13.8 to 14.2 (auto type alternator)

22. 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.

23. 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
Wind Instruments
Nav Lights
1.5
3 lights 1A each on 1/2 time
VHF Radio
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

24. Try again… Alternative 1 Buy 200 AH batteries at $250 each
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
Wind Instruments
Nav Lights
1.3
3 lights 1A each on 10 hrs/day
VHF Radio
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 2 Buy LED tri-color light using 1/2 A - $300.
Reduces 1.3A avg draw to 0.2A.