HELP!!! Coach batteries not recognized by inverter

[MtLaw]

We have an 85 Prevost which has had fairly substantial updates. Several years ago we had a new Magnum inverter/battery charger installed. The unit has a substantial set of house batteries which are all new. The coach also has a set of batteries (not new but good). The coach also has a generator which has its own battery for charging, which is also new. The coach has a 24 volt system and the house batteries are wired so as to deliver both 24 and 12 volts depending on the need. None of these thing have been modified recently.

The coach has 2 merge switches which 1. join the house batteries with the coach batteries and 2. join the house batteries with the generator start battery.

The house batteries were replaced this year. The guy who did it for me is very bright and handy and believes the coach worked properly after he was done w/ the new coach battery installation.

We took the bus out for a test weekend and found that the house batteries are not being recognized by the inverter. When we hit the merge switches the inverter kicks on, drawing from the starter batteries for the coach and the generator. However when the merge switches are flipped off, the remote controller for the Magnum says "low battery" and the inverter does not recognize the house batteries. The house batteries are fully charged.


We have spent 3 days trying to figure this out

Any ideas or suggestions would be greatly appreciated!!!!!!!!

[MEXICOWANDERER]

Diagram?

Ask OEM

Prevost

But, are your wires MARKED? A diagram is useless unless your wires are color coded or marked.

[CA_Traveler]

MtLaw wrote:
Actually, he did take a picture, that is finally how he caught the mistake.

I would love to have a schematic on my coach or a similar one. If you have any suggestions where to get one I would appreciate it.

I always recommend that YOU take pictures before any work is done.

[MtLaw]

Actually, he did take a picture, that is finally how he caught the mistake.

I would love to have a schematic on my coach or a similar one. If you have any suggestions where to get one I would appreciate it.

[YC_1]

Great. May I suggest taking several pictures for future reference. No reason for an expert to make an honest mistake. I would be finding a schematic from somewhere for future reference as well.

[MtLaw]

For all you kind enough to reply, you were all correct!!!! My expert did not wire any of the cable in the wrong place, but there was one cable that had fallen down behind the large battery bank and he missed it.
Hence the obvious problem.
However, we did find a number of other problems so all was not a waste.

Thank you all again for your input.

MtLaw a/k/a Lee Henning

[MEXICOWANDERER]

This thing may be a hell of a lot more complicated than some of you realize. I have seen a BUNCH of 24-12 100 amp converters on big buses, the 12 tracks the 24 at exactly 50% of the 24's voltage.

Therefore there would be ONE alternator one the rig and it would be 24 volt.

If the inverter fed off of the 24-12 converter (they have a low voltage cutoff) the inverter would operate off the 24 volt battery bank for awhile then cut out. If the rig were running the alternator would supply enough converted power to keep the inverter happy.

This means the 12 volt system is isolated. What on the bus is 12 volt? Something charges 12 volts like the rig's converter when it is plugged in and the generator's alternator unless it has a dedicated battery.

This needs to be examined piecemeal. One stupid wire left disconnected or connected to the incorrect terminal causes this.

The BRADY BMP21 wire marking tool in the right hands eliminates or drastically reduces the incidence or error.

Series parallel switches took at hike thirty years ago. The rig has to have some form of conversion to allow the 24 volt charging system to charge the 12 volt system. Find out from Prevost what they used and then troubleshoot that device first. Not necessarily for failure, but for a misconnected error.

[GBaxter]

Definately sounds like the 24v inverter is connected to 12v when the merge switch is off. Your battery guy needs to look at his connections again.

Prevost used to always use a 24v alternator. They also used a Vanner equalizer that is a 24v dc to 12v dc converter to run the 12v systems for the chassis and interior lighting etc.

Gary

[MtLaw]

Thank you all for your thoughts. (I am an idiot about these things so please bear with me.) The bus has a 24 volt alternator which charges the 12 volt bus batteries via the parallel connections. The bus batteries also have two of them which deliver 12 volts to the 12 volt system.

The magnum inverter is also a 24 volt system. With the merge switch on, the magnum inverter reads the 24 volts off the bus batteries and would invert.

The large deep cell coach batteries are all steady at just over 13 volts. The input to the inverter shows approx. 12 volts when the merger switch is off.

HUM??????

[YC_1]

If the merge switch allows the inverter to run and the engine batteries are 12 volts then the inverter is 12 volts. So measuring the voltage across the engine batteries is a way to work backwards towards the house batteries. I would run the model number of the inverter past the factory and find out if it is a 12 or 24 volt setup. Pictures of the battery banks would be helpful.

I would love to see a diagram of this setup if someone has one.

[mena661]

Take a voltage reading of your house batteries and see if they're wired for 12V or 24V. Check your inverter to make sure it's either 12V or 24V. The make and model number of the inverter should be sufficient to figure that part out (12V or 24V). If you're batteries are wired for 12V and your inverter is 24V, there's your problem.

[Chris_Bryant]

I agree with Fred- quite often these coaches use 24 volt inverters. I disagree with Fred about the alternators costing $450 though- I believe 270 amp oil cooled alternators are the smallest Prevost used, with builders either adding a second, or installing larger.

[dougrainer]

They make 24 and 12 volt Inverter/chargers. WHICH do you have??? I will bet a 24 volt Inverter/charger. Your problem and solution depends on which you have. Doug

[Golden_HVAC]

My guess is the starter and inverter are on the 24 volt system.

My next guess is the inverter is only connected to 12 volts at the coach batteries. Also lets hope there is a 100 amp fuse (give or take) for the merge switch, so that if I am right, and the coach battery for the inverter where wired wrong, then it will trip the fuse, not put 24 volts to a battery bank incorrectly wired for 12 volts.

My guess is the inverter and it's 4 batteries are in one bank, and anoter bank is for the 12 volt system that only runs the house lights, pump, aqua hot and inside fans.

I am also guessing that the engine has two alternators, one for the 24 volt starter batteries, and now it also runs the inverter battery bank, and also a 12 volt system for the headlights, some controls, running lights, and small loads. IT should also be charging the 12 volt battery bank.

There might be a 24 volt to 12 volt converter, but it would have been easier to install a second alternator back in 85, so they did it that way back then.

If your inverter has a remote control system, check the input voltage in the system. If it reads low voltage when not merged, see if it says 12.8 input. Then switch it on with the merge switch, if it reads 24 volts input, then you are applying 24 volts to a 12 volt battery bank, don't do it for very long, the battery will overheat and might explode. (30 seconds should be OK).

If this is what you found (inverter needs 24 volts input, but only has 12 volts input) you can change the inverter battery from 2 or 4 in parrelle to in series so that you get 24 volts output. Not all 4 in series *unless they are 6 volt with only 3 cell caps on each battery) if you have 12 volt battery, then two in series makes 24 volts. If 6 volt for each battery, then 4 in series makes 24 volts.

Sounds like you need to have the guy who installed the batteries look at it again. Probably just need to change around a couple of wires to get it back to normal. He might not have guessed the inverter has a 24 volt input to it, and wired all the batteries to 12 volts instead of some to 12 and some to 24 volts.

But I might have all this wrong, so it will take a mechanic putting hands on it, looking at the inverter input volt rating, and everything else to make sure it is right. It really sounds like you will need a electrician on the site.

I would also causion you about driving it or running the engine to much. IF the 24 volt alternator is connected to a battery wired for 12 volts, those batteries can overheat, and possibly explode. Or you might melt down a $450 130 amp 24 volt alternator. And it is possible that Leese Nivell is no longer in business, so getting a new alternator might be difficult, rebuilding is possible though.

Fred.

[MrWizard]

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