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Old 02-05-2013, 07:52 PM   #1
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Multimeter to test for Battery Drain

Our MH house battery will drain down within a few hours with "only" the refer on. Obviously we have a drain somewhere else. Lights, A/C, inverter, etc are off. i have read about using a multimeter to test for battery drain.....please tell me where the red and black cords should be plugged into the multimeter and what the "guage" or "reading" should be set to. THANKS!!!!!!
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Old 02-05-2013, 08:24 PM   #2
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checking battery drain

in my experance many multi meters are not able to measure dc current except mily amps. if you are trying to check battery draw while the rig is not being used i would put a 12v taillight bulb in series with the ground cable from the battery if the bulb light lights there is a draw
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Old 02-05-2013, 08:34 PM   #3
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Probably you do not have an "inverter".......but a "converter" Right?
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Old 02-05-2013, 08:39 PM   #4
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I have an inverter and converter
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Old 02-05-2013, 09:53 PM   #5
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If you are just testing to see if there is a a load on the battery with everything off, disconnect the positive battery lead first.

(Now let me see if i get this straight)

Using a 12v test light is easier IMHO.
Anyway, connect the ground of the test light to the disconnected positive cable, and touch the test probe of the light to the positive battery post. If you get any light, you have a short.
It should work the same way with a multimeter, if you see any voltage on the meter, same as above.
It's been a while since I've done this, so forgive any mistakes, but I'm pretty sure this is right.
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Old 02-05-2013, 10:08 PM   #6
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not quite right. The tests above using a test light will likely show that something is causing a draw. However, the described multimeter test puts a voltmeter in series, and that won't work. It needs to be set on the ampere setting and it will show how many amps are drawn.

However, if it's a lot, you might blow the fuse in the multimeter.

Another way is to go to Digi-key and buy a very high current say, 10-20 amps (that's 100-200W or so @ 12V) resistor in .1 ohm. Put this in series with the positive battery cable and the battery. Put a voltmeter across the resistor and the voltage will be 10x the current draw in amps.
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Old 02-05-2013, 10:19 PM   #7
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Quote:
Originally Posted by larrydp View Post
Our MH house battery will drain down within a few hours with "only" the refer on. Obviously we have a drain somewhere else. Lights, A/C, inverter, etc are off. i have read about using a multimeter to test for battery drain.....please tell me where the red and black cords should be plugged into the multimeter and what the "guage" or "reading" should be set to. THANKS!!!!!!
larrydp, I know you said that the inverter is off but ARE YOU SURE its off. I left my inverter on one time while boondocking and forgot to switch the refrigerator from auto to LP gas only. I was amazed how quickly my batteries drained down with the fridge using 120 volts from the inverter instead of LP.

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Old 02-05-2013, 10:31 PM   #8
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1. Always disconnect the NEGATIVE cable. That way, if you accidently short to ground with the wrench, nothing happens. On the positive side you could have hundreds of amps current.

2. Cheap an dirty test: Get fuses in 1, 3, 5, 7.5 and 10 amp sizes. You can borrow them from a fuse box in another vehicle rather than buying them.

3. Starting with the 10 amp, jump from the cable end to the battery post. If it does not blow in 10 seconds, you are drawing less than 10 amps. Repeat, using progressively smaller fuses. When one does blow, you know about what the current draw is.
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Old 02-05-2013, 10:34 PM   #9
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Your battery is bad.

Plug in to shoreline and measure the voltage across the positive and negative leads of the battery. Put the voltmeter in the DC voltage range.. If you get 13.5 or more and can charge it over night then see if it holds a charge. If just the refer or a couple of lights kills it in a couple of hours the battery is shot.

How old is the battery? Have you removed the terminals and other wires for a good cleaning?
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Old 02-05-2013, 10:41 PM   #10
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Originally Posted by bluepill View Post
1. Always disconnect the NEGATIVE cable. That way, if you accidently short to ground with the wrench, nothing happens. On the positive side you could have hundreds of amps current.

2. Cheap an dirty test: Get fuses in 1, 3, 5, 7.5 and 10 amp sizes. You can borrow them from a fuse box rather than buying them.

3. Starting with the 10 amp, jump from the cable end to the battery post. If it does not blow in 10 seconds, you are drawing less than 10 amps. Repeat, using progressively smaller fuses. When one does blow, you know about what the current draw is.
bluepill, Thats the neatest trick I've ever heard of. I'm no electrical wizard, but I can do alot of my own wiring and this sounds like an idea I will have to keep in mind for future testing purposes.

Thanks,
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Old 02-05-2013, 11:29 PM   #11
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Sammie that is a clever idea.

Could even get fuses in the 1-5 amp ranges. Not the plastic ones but the old style glass fuses.
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Old 02-06-2013, 06:57 AM   #12
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One of the best things I bought is this dc amp clamp meter

Craftsman Digital Clamp-On Ammeter - Tools - Electricians Tools - Multi-Meters & Meters

It will measure dc amps and is a great price - I have found so many items that have a current drawer when I think everything is off.

Stephen
1999 Tradition
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Old 02-06-2013, 07:26 AM   #13
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Multimeter

THANKS for all of the responses! I will try to respond here.
Am I sure the inverter is off? I assume it is since i have no power to my tv, microwave, etc.
How old is the battery? less than one year. a dealer put a load test on it and said it was ok. I have taken the cables off and terminals are clean and tight.
I had Googled " how to test for battery drain". that is where they talked about hooking a multimeter between the Negative cable and the Negative terminal. then it discussed pulling one circuit breaker at a time until the meter "changes". that seems to make sense to my tiny brain but i don't know where the red and black probes of the multimeter should plug into the multimeter and what the "dial" should be set to....???
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Old 02-06-2013, 07:35 AM   #14
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I think that your battery is not holding a charge, when you replace your battery I would check on or get a solar panel to maintain batteries if you have available sun at least 7.2 hours a day.

Good luck, James
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