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Old 08-14-2021, 04:27 PM   #1
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Bus Gage Voltage high and alarms

I recently installed a battery isolator into my Skoolie to charge the house batteries while driving. It worked well right out of the box. I then ran into an issue where the Voltage gage on the dash would spin to the max, beep once, and then the warning light goes on.

I plugged into shore power, got some charge on the house batteries and the voltage went back to normal. The weird thing is, if I disconnect the house batteries the voltage indicator goes to max and throws the light on. I uninstalled the isolator thinking maybe it was part of the issue, and it was still at max voltage with the warning light. I disconnected the bus batteries hoping to reset the computer, and that didn't work. I'm not an expert with DC and I'm not sure what else I should try. My only solution at this point is to not let the house batteries die. It just seems odd that the bus needs the house batteries connected or else the voltage indicator will go crazy.

Any ideas out there. My volt meter shows just over 14 volts at the house and bus batteries regardless of the two being connected or not.

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Old 08-14-2021, 05:28 PM   #2
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I think you have to see if the voltage reading is real with a meter. It sounds like you could have a wacky ground problem but itís tough to say. If you can consistently create the problem it may be a good idea to see if you can measure the voltage at the bus fuse panel to see if itís really high or if the dash is losing its mind.

Assuming 12v systems the only way I can see to get high voltage like that is if thereís a connection from the bus battery ground to the positive of the house batteries, which could happen if you have a hot wire shorting to the bus chassis somewhere. If you can disconnect the positive side of the house batteries when the problem is occurring and it goes away you may have to track down that problem, and perhaps ground the house system to the bus chassis too (which will cause a short to blow a fuse or melt the wire if thereís a problem). Kinda just ranting but I hope that helps!
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Old 08-16-2021, 09:10 PM   #3
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Thanks for the input. I disconnected the house battery from the bus entirely. It threw the alarm. I checked the voltage on the bus battery and its at 12.7. When I turn the bus on it goes to 14.25. I'll probably bring it in to have it troubleshot.
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Old 08-16-2021, 09:18 PM   #4
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Originally Posted by knightrunner10 View Post
Thanks for the input. I disconnected the house battery from the bus entirely. It threw the alarm. I checked the voltage on the bus battery and its at 12.7. When I turn the bus on it goes to 14.25. I'll probably bring it in to have it troubleshot.

Sounds like you have an issue with the dash or gauge, which at least rules out something youíve done for the most part, but will be harder to fix potentially. You could check all the connections and wires there which might help but itís not the easiest stuff to get to.
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Old 08-16-2021, 09:45 PM   #5
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14.25 volts

Do you mean 14.25 volts with engine running?

14.25 is too high in my opinion. With the engine running, 13.8v at the battery is the highest I would like to see. Object is 1 volt higher than a fully charged battery. A fully charged lead acid battery is 12.75, roughly.

I think at that level. 14.25, you may get into, electronics issues. 14.25 volts will boil batteries. Recheck fluid levels in all cells.

Verify gage reading of 14.25 at the batteries.

785. 207. 7600.

Telephone if ya wanna talk about it.
William
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Old 08-16-2021, 09:47 PM   #6
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Looking on truck forums its possible that the alternator has a voltage regulator in it and when I tied the two batteries together, the alternator adjusted to the larger battery bank, so when the batteries are disconnected, it thinks the voltage is high. I'm pretty amateur at this, so I could be wrong. Either way, I think its out of my wheel house. For now, I'm just going to leave it alone, and take it in at the end of the season for a PM, and have them look at it.
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Old 08-16-2021, 09:54 PM   #7
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Originally Posted by magnakansas View Post
Do you mean 14.25 volts with engine running?

14.25 is too high in my opinion. With the engine running, 13.8v at the battery is the highest I would like to see. Object is 1 volt higher than a fully charged battery. A fully charged lead acid battery is 12.75, roughly.

I think at that level. 14.25, you may get into, electronics issues. 14.25 volts will boil batteries. Recheck fluid levels in all cells.

Verify gage reading of 14.25 at the batteries.

785. 207. 7600.

Telephone if ya wanna talk about it.
William

In my experience 14.25 isnít too high, itís fairly typical. Could be wrong but Iím fairly sure dumb alternators do that.. agreed that itís not the best for batteries but thatís how alternators were forever.
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Old 08-16-2021, 10:15 PM   #8
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Quote:
Originally Posted by knightrunner10 View Post
Thanks for the input. I disconnected the house battery from the bus entirely. It threw the alarm. I checked the voltage on the bus battery and its at 12.7. When I turn the bus on it goes to 14.25. I'll probably bring it in to have it troubleshot.
Alternator problem? Seems strange that it started with the isolator but perhaps, maybe, the additional load damaged the alternator.

What is your configuration? One Chassis Battery, two? Then how many house batteries, and what is the configuration?

Is there any chance you connected the batteries in series instead of parallel, thus potentially frying the alternator?
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Old 12-02-2021, 12:22 PM   #9
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Just an update, I brought it into a shop, and they found a fuse that blew that was throwing the error. I'm still not sure why it worked fine when connected to Shore power, but just a reminder to check fuses first. I'm having the shop connect the isolator directly to the alternator which will take the fuse out of the equation.
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Old 12-02-2021, 01:51 PM   #10
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Taking out a fuse.

Please keep us informed for the next couple of years about the condition of the isolator, alternator, batteries, and associated wiring. I would like to see how this works out long term.

William
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Old 12-03-2021, 12:31 AM   #11
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Charging your "house" batteries through an isolator is a good solution. I went one step further and added a second alternator. If your bus has room for a second alternator and the pulleys to drive it I think it is the Cadillac solution. Some alternators have "remote sensing" that sets up the alternator to maintain a set voltage at the battery terminals even when there is voltage loss through the battery cables. Having a battery switch is also a good option to cross connect RV and bus electrics in an emergency.
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