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Old 05-12-2024, 07:00 PM   #1
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How to find a power drain in my Bus

Hey folks,

We have found that the bus batteries are draining down in a few days to completely dead.
These are the batteries that start the engine, not the LIon house batteries.
I found that sometimes the headlights stay on, but that stopped happening after a while.
Now, I see that the battery charge indicator on the dashboard display stays on after the engine is shut off.
Not sure why that is happening.
It should drop to zero.

My wife was concerned that the sprayfoam we sprayed near the bus electrical panel to keep mice from getting in might have melted some of the bus wires and might be creating a short somewhere.

I saw in another post the suggestion to use a clamp style ammeter to help with our hunt for the power draining culprit.

Any troubleshooting suggestions or approach would be greatly appreciated.
I did a quick search in the forum, but didn't see anything.

Thank you.

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Old 05-12-2024, 09:53 PM   #2
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Recently ran down a drain on a tractor and this is how I did it. I pulled every fuse I could find then disconnected a battery cable, either one, and put my DMM in-between while set on amps. Installed a fuse one at a time and watched my DMM and then knew what area my drain was in. Some more detective work and found out the volt meter was on all the time so I disconnected it, problem solved.
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Old 05-13-2024, 08:10 AM   #3
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Most if not all busses have battery drain from the ECM, as it's always on. School busses are intended to be driven daily so the alternator will overcompensate for the drain and keep the batteries charged.

If you aren't driving it for days at a time, it's gonna drain to zero. This is why many of us skoolie users are adding battery disconnects so we can disconnect the battery with a quick switch preventing the drain.

Food for thought.

I recommend the 2000Amp Cole Hersey Disconnect.
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Old 05-13-2024, 10:52 AM   #4
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Thank you very much both of you.
Excellent suggestions.
I also found this video, for anyone else who finds thus post.
https://youtu.be/xBVmbYBxMyo?si=1hTxVMLDo5qWNeiQ
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Old 05-13-2024, 01:14 PM   #5
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I do it similar to that video, except I use a battery disconnect like this and then parallel my multimeter clips to. Then I can turn off the key and shut the door so that the various modules power down like they normally would. If you disconnect the terminal and then reconnecting through your meter clips, the modules can shutoff outright, which won't show which modules are staying in hibernation mode too long(or indefinitely).

An old school bus likely won't have numerous modules like I describe, but if you're chasing a parasitic draw on a car, you can chase forever if you don't follow the above steps, and most meters won't pass enough amperage to turn the key on or start the vehicle.
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Old 05-13-2024, 02:10 PM   #6
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Thank you very much.
I'm definitely going to incorporate a quick release on each of our two batteries.
And I'm looking forward to doing a little detective work.
Hopefully it's not the spray foam melted thru any wires.
That would be a mess.
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Old 05-13-2024, 02:57 PM   #7
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I have not had any issues on my shuttle bus, fortunately.

When I first bought it it would run down unless I started it each week-that was because it had old batteries. Once I replaced them all was good.

If there are vampire loads (like the ECM, as others indicate) you might consider a trickle charger.

I bought but have not installed a DCDC trickle charger to top off the chassis batteries from the LiFePo, which is maintained from the solar panels. If you have a house battery and solar, that might be a good option.
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Old 05-21-2024, 06:21 PM   #8
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A little late, but I have to agree with the sporty ricks method, except mine is slightly different. I measure the amps between the ground battery cable and the ground on the battery and then start pulling the fuses one at a time until you find the one that stops the drain, anything over about two apps is a problem AMPs not apps
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Old 05-21-2024, 08:46 PM   #9
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I don't know if the same problem exists with ECMs in school busses, but my C4 corvette losses its mind in the ECM is the battery is disconnected. When the engine is started after such occurrence, the computer has to re-learn parameters for the engine for awhile. While the ECM is in learn mode the engine run rich and doesn't run well.
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Old 05-22-2024, 08:34 AM   #10
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2 amps is way too high. You're looking at tenths of amps. Anything more then that will leave a battery dead after a week.
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Old 05-30-2024, 04:27 PM   #11
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Quote:
Originally Posted by Booyah45828 View Post
2 amps is way too high. You're looking at tenths of amps. Anything more then that will leave a battery dead after a week.

Yep. On a car we're looking for 80 milliamps or less, preferrably lower but that's grudgingly acceptable as newer cars have so many active systems. Sub 50 ma is better.
2a.... that's a battery killer!
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Old 05-30-2024, 06:50 PM   #12
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2 amps makes me think there is something left over. like a camera system box or such that is powering up when the bus is off even if theres no longer any cameras.. or maybe a radio that doesnt power down correctly..
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Old 05-30-2024, 09:27 PM   #13
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My bad. It doesn't have to be that that high (2 amps) to drain the battery. It's just what I have seen in most of the ones I have traced.
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