Electrical Leakage ?

[Charlie]

Originally Posted by osirissail

Okay, everybody has told you one way or the other how to find your problem. Simply put do the following:
1. With the Battery switch in the off position take any and all wires off the battery switch common terminal.
2. Measure with a voltmeter from the battery common terminal to the ship's battery negative/ground buss.
- - If you are reading any voltage the Battery switch is leaking.
3. Install a new battery switch.
4. Repeat #1 & 2 with the new battery switch.
- - If you are reading "0" volts with the voltmeter in the 0-12VDC or 0-20VDC (depends upon the voltmeter scales) - fine. Reconnect all the wires to the common terminal.
** Part 2 - Assuming your boat has a DC ammeter on the panel . . .
5. Turn on the new battery switch which will connect a battery to the common terminal.
6. Turn off all the circuit breakers and disconnect any wires that are "hot wired" to the battery by opening its/their fuse(s). Leave all the wires that are connected to the common terminal of the battery switch alone.
- - Check each "load side" of each circuit breaker with the voltmeter measuring from the load side of the circuit breaker to the ship's DC ground buss. With the circuit breaker in the "off" position there should be no voltage showing on the meter. If a voltage is present you have a bad circuit breaker. Replace any bad circuit breakers.
7. With all c/b's off and fuses removed, you should see zero draw indicated on the power panel ammeter. If not, there is a stray wire or something touching a feed wire in your circuit panel or your alternator diodes or battery splitter diode (if you have one) is leaking.
8. Find the stray wire and reposition it or replace it. If there are none then take your alternator into the shop and have it checked.

Simple straight forward answer. Gotta love it.

[Lady A]

Many times a faulty ground cable can be the culprit. Make sure your battery connections are clean and tight. Try to pull the batter cables out of the lead connector hard. They should hold, if they pull out even an 1/8th inch that may be your problem

[nial]

Orisissail, your simple, straightforward advice has me baffled. What is a battery common terminal? My battery has just the usual two, positive and negative. I know the battery selector switch is leaking because I am getting voltage from the common lug when switch is in off position. I do not have an ammeter on my electrical panel, just a volt meter that shows battery voltage when it's switch is depressed. A very basic system. What I seem to have trouble explaining is the following; even though the battery selector switch is faulty that shouldn't drain the battery when everything else is turned off unless one, or more, of those things is also faulty.
nial

[osirissail]

It sounds like your battery switch is only an "On/Off" type switch with one terminal (that's the correct name for the place where the electrical cables attach. A "lug" is a type of terminal) for the battery and one terminal for the ship's loads (goes to circuit breakers, alternator, etc.). The terminal where the ship's loads are attached is the "common" terminal. Most larger boats have more than one battery and use a battery switch that is label with a version of "Off", "1", "Both", "2". Each battery is connected to either the "1" or the "2" terminal and the ship's loads (c/b panel, etc.) are attached to the "common" terminal. To be able to discuss marine electricity you need to keep the names of things standard.
- - Any switch should not show a voltage on the "load" side when it is turned "off". If it does and there is nothing else in the boat that is generating/supplying DC power, then the switch is bad and should be replaced. The purpose of the battery switch is to first allow you to disconnect the battery from the ship's load in case of an electrical fire. It is also used to be able to disconnect the battery(s) from the ship's loads to keep the battery from being drained during boat storage.
- - So you may have two separate but related problems. One the battery switch is bad - so replace it.
- - Second there may be a short or "leak/drain" on the battery that should not be there.
- - As I suggested in step 5 the next thing to do is to turn on the battery switch which will allow full voltage to be measured on both sides of the battery switch. Then turn off every circuit breaker and disconnect all "hot wired" loads (if any) to the battery by removing their fuse(s). Then test each circuit breaker for a bad circuit breaker.
- - Now you have eliminated all possible drains except two. One is a stray wire that is touching a positive terminal/lug/whatever somewhere and draining off power. The other possibility is that there is a leak in your alternator diodes.
- - To determine which is the problem, disconnect the alternator feed wire that runs from the alternator (+) terminal to the battery switch.
- - This is where you need an ammeter in the circuit between the "common" terminal of the battery switch and the cable/wire running to the ship's DC panel. With all the c/b's OFF there should be no current shown. If there is there is a short somewhere - find it (see step 6).
- - Reverse the procedure now by removing the ship's loads(DC panel) wire/cable, from the ammeter and push it aside. Then hook the alternator feed cable to the ammeter. If there is a current showing then the alternator is leaking. Get it tested and fixed.