Multi-meters and electrical troubleshooting.

Bill EnnisGreg Jurkowski

Parable of the Lakes

Poseidon

Energy

Neptune

Poseidon to Neptune

• Lakes must be different elevations• Horizontal ducts merely direct flow to a ramp.• Ramps are where energy is available as flow.• Flow is controlled by size and length of duct,

angle of the ramp, and the height difference of the lakes.

• Flow from Poseidon to Neptune is constant along all ducts.

Ramp

• No energy (elevation change) in the horizontal sections.

• There is in energy in the flow. Gallons, buckets or pounds per second.

• The ramps do work with this energy. Water wheels, turbines, pumps, etc…..

• At the bottom, the energy is used up. Poseidon will empty eventually, if not recharged by weather or pumps.

Lakes to Batteries

• Think of Poseidon as the positive side of your battery.

• Buckets are collections of charges. We measure charge in coulombs. Buckets/second = coulombs/sec=amps. 1amp is 1 coulomb per second.

• Neptune is negative. Elevation (energy) difference between positive and negative is volts (12 for us).

Resistance

• In an enclosed tube, a larger diameter allows a greater flow, while a long tube creates more resistance to flow. On a ramp, we use the flow to do work for us, which also creates resistance.

• If we don’t put resistance in the flow, the flow will be too great for the pipes, and a circuit breaker (flood gate) activates. Otherwise, we could destroy the conduit with the elevated flow.

• Flow is proportional to (potential) energy difference, and inversely proportional to resistance.

Equation time

• Bigger potential gives bigger flows, but greater resistance gives smaller flows.

• This is commonly states as V=IR€

Current =Potential

Resistance

€

or I =VR

One last equation, I promise….

• The rate of energy used in the ramp is power.• Power is proportional to potential (energy)

difference, and flow rate.• Power = Potential × Current or P=VI• Our DC potential is limited to 12 volts, so we

get 12 watts of power for every 1amp of current (60watts for 5 amps).

Crap, now I’m really going to sleep…

• So here’s a cool chart about battery potential and %charge.

• Lets look at a simple circuit.

Meters

• We can measure potential (energy) drop across a battery, across a wire, across some load (ramp).

• Meter must be set to Volts DC. This is a safe measurement under most conditions.

• This shows where energy drops exist in a circuit

• Current measurement requires thought.

Current flow

• To measure current flow, the current moves through the meter unimpeded. The current flow across a 12 volt could reach 300 amps. Your meter cannot handle that

• Figure how many amps you should have using 1 amp for every 12 watts.

• Most economical meters can not handle more than 10amps. So don’t use it on a windlass.

• Move red lead on meter to Amps, turn dial to DC Amps. • Use meter wires as a connection to the load.

Current

• Never leave the meter dial on current. If you try to measure voltage with the meter on current, you short circuit the load you put the probes across. This can destroy the resistor at the 10amp level, and blow the fuse if you are set to measure milliamps.

• The safest thing to do for your meters sake is turn it off after every measurement.

Get on with it……

• There are two other great measurements you can do with a multi-meter…

• Continuity. Usually on the dial as a loudspeaker or cone. Uses an internal battery to check that charge can flow.

• This is measured with the energy source disconnected. This is the best way to check a switch.

• Resistance Ω is also measured with battery off, and gives a quantitative estimate of resistance.

What does this look like on a sail boat

• Like this?

No, probably like this

Terminology

• Positive busses are where switches hook to the battery. Usually a long strip of connected screw.

• Negative busses are similar in appearance, but just act as a common ground for all load elements.

• There is usually a circuit breaker between the positive buss connection and the switch.

Handy table

The right wire for the job.

• http://www.bdbatteries.com/wirerules.php