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

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

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

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)

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

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

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

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

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

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

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 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

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)

Physical Components Starter Battery Alternator

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

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

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

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)

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 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

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.