Tracking battery drain - Chevelle Tech
Electrical & Wiring Troubleshooting electrical problems.

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post #1 of 12 (permalink) Old Jan 9th, 19, 4:29 PM Thread Starter
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Tracking battery drain

Greetings! I have a car that is draining the battery while sitting. I know I can do a load test by disconnecting the battery positive cable and testing there. Can I do the same for individual circuits at the fuse panel? In my (limited) mind it seems like the fuse pins are basically the same thing (a positive terminal and a connection to a circuit), if I test the load between the two sides will it do what I think it will?

As always, thanks in advance!

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post #2 of 12 (permalink) Old Jan 9th, 19, 4:33 PM
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Re: Tracking battery drain

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Originally Posted by Cecil View Post
Greetings! I have a car that is draining the battery while sitting. I know I can do a load test by disconnecting the battery positive cable and testing there. Can I do the same for individual circuits at the fuse panel? In my (limited) mind it seems like the fuse pins are basically the same thing (a positive terminal and a connection to a circuit), if I test the load between the two sides will it do what I think it will?

As always, thanks in advance!
Yep, remove the fuse, and put an ammeter across the contacts. Just be sure that the ammeter can handle any current that might be there.
Another way is a very low current 12v bulb. If put across the contacts, it should not glow. Just do NOT put an ammeter across a no load voltage, you will burn it out instantly, or blow its internal fuse.

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post #3 of 12 (permalink) Old Jan 9th, 19, 4:52 PM Thread Starter
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Re: Tracking battery drain

I'm not an electrician, so what does "no load voltage" mean?

Thanks!

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post #4 of 12 (permalink) Old Jan 9th, 19, 5:00 PM
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Re: Tracking battery drain

Cecil, simplify.

Get a 12V test light. Disconnect either battery cable and run the test light in series. If that test light lights up, it will show you there is a draw. Go to the fuse box and pull he interior fuse. Does the light stay lit? That circuit is not the issue. You can then pull each fuse one by one and when the light goes out, you know at least which circuit is killing the battery.

If the light stays lit with all the fuses out, it is time to unplug the alternator, and any aftermarket accesories. 90% of draws I find are either interior light or radio circuit.

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post #5 of 12 (permalink) Old Jan 9th, 19, 5:09 PM Thread Starter
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Re: Tracking battery drain

It's a 2004 Jetta, and my good friend the internet has lots of posts about people finding loads on radio, door latches, trunk lights, etc. I like this simple approach...

Thanks.
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post #6 of 12 (permalink) Old Jan 9th, 19, 5:25 PM
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Re: Tracking battery drain

Something I saw the other day but have yet to try is using a meter across the fuse and then with a chart, decipher the current amount:


I'm old school and like putting the meter inline between two points.

Jim
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post #7 of 12 (permalink) Old Jan 10th, 19, 10:18 AM
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Re: Tracking battery drain

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Originally Posted by Cecil View Post
I'm not an electrician, so what does "no load voltage" mean?

Thanks!
If you pull a fuse that for example powers something weak but constant like a newer radio or clock, then measure voltage, you will see close to battery voltage across the fuse terminals because the device is completing the circuit, but with no current flowing, voltage drop is negligible, so you will see full supply voltage.
Existing -> +----|FUSE|---|LOAD|---- -

Test like this with ammeter is OK if load is low enough -> +----| Meter |---|LOAD|---- -
But if you put ammeter across the battery like this +----| Meter|---- - Something has to blow.
Personally I would start with checking any non factory accessories, then check voltage regulator.

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post #8 of 12 (permalink) Old Jan 10th, 19, 11:13 AM
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Re: Tracking battery drain

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Originally Posted by Jim Streib View Post
Something I saw the other day but have yet to try is using a meter across the fuse and then with a chart, decipher the current amount:

The BEST Way TO Perform a Parasitic Draw Test - YouTube

I'm old school and like putting the meter inline between two points.

Jim
I just watched that, very good video, fair description, and not hard to understand, and yes, that is a great way to measure current by voltage drop over a load (the fuse). The only point he is missing in general, I assume because something with VWs, is you have to hold the door pins depressed so the door open circuit isn't grounded for dome light and other stuff.
Plus measuring voltage is a lot safer than measuring current.

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post #9 of 12 (permalink) Old Jan 10th, 19, 12:22 PM
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Re: Tracking battery drain

Unlike our old cars, putting an amp meter in series with a battery cable will always show a current draw due to electronic items that have a memory. I would disconnect and charge the battery fully (12.6 volts = full charge). Then leave it disconnected and check the voltage every 5 minutes and see if it drops and how far. If the battery is losing voltage on its own, its bad. You can also take the car and the alternator and battery load tested. This is where I usually start.
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post #10 of 12 (permalink) Old Jan 12th, 19, 10:33 AM
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Re: Tracking battery drain

A freshly charged battery will always lose voltage on its own for a while until it settles to some value. I don't know exactly how long this should take, and it may vary by battery. The value it settles to is what you want to measure to see if it's charged.
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post #11 of 12 (permalink) Old Jan 12th, 19, 9:59 PM Thread Starter
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Re: Tracking battery drain

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Originally Posted by Pioneer4x4 View Post
you have to hold the door pins depressed so the door open circuit isn't grounded for dome light and other stuff.
I'd guess that by latching the doors/hood/trunk that takes care of this...

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post #12 of 12 (permalink) Old Jan 12th, 19, 10:03 PM
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Re: Tracking battery drain

Trunk and glovebox lights that don't turn off when they should are good for fun and games when tracking this sort of stuff down.
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