Battery voltage is high and does not match controller display

Submitted: Monday, Oct 17, 2005 at 10:27
ThreadID: 122284 Views:4178 Replies:4 FollowUps:4
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Hi all,

I discovered today that our battery voltage is much higher than the readout on our controller would suggest.

We have 3 AGM batteries, new early 2005. According to our Prostar 30M controller they are running at about 13.5V. However according to my voltmeter they are running at about 20.4V. This voltage is constant (roughly) across the battery terminals, on each of the terminal sets on the Prostar (Battery, Battery Meter, and Load), in a 12V wall outlet on the wall below the Prostar, and inside a ceiling light.

The van is stored outside and had been stored for weeks with nothing but the occasional use of an internal light for a few minutes. I also gave it a topup with the mains charger for 24 hours a week or so ago. The mains was disconnected and the solar was showing 2A when I was doing this testing.

I suspect 20.4V is not good for my batteries?

Also why is the Prostar display reading so much lower voltage than is actually coming off its terminals?

I know the previous owner (Anthony) rearranged all the wiring down at the batteries. The three batteries are wired in parallel.

I'm a bit puzzled.
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Reply By: Bushtracker - Monday, Oct 17, 2005 at 17:43

Monday, Oct 17, 2005 at 17:43
Well Lucky Boggers,

There is no telling what the previous well intentioned Owner has done to that secondhand van... He did a lot of tinkering, but little travel, I think it had only done 4000 km. But I will guess at the likely priorities, blindly, but hey I have more experience with Bushtrackers than anyone else to speculate, so here goes... And mind you I am blind, and speculating, and would really have to see the van wiring and the charger and what had been tampered with and modified, and I do not even know what batteries you have.... But here is my best:

1) I would first check the battery in your voltmeter, as I learned long ago that they give wild high readings when the battery is about dead... You need to start by checking it against a know value, like the battery in your tow vehicle. At "resting state" an hour or two after not running, you would expect a reading of 13v plus or minus .2 of a volt on healthy batteries..

2) If that checks out, then you have a peculiar problem because the voltmeter on the regulator is of a much higher calibre.... And I am only guessing, but next check that the battery charger is off for at least 1 hour and check again....

3) Then push the disconnect on the solar regulator, wait an hour and check again.

4) If all else fails and you indeed have that kind of a reading, which is nearly impossible, but I have seen the phenomenon: It sounds like "surface voltage" on the batteries.... You have trouble somewhere, most likely Culprit is the batteries....

5) Fifth possibility is the Regulator going bad, but that is not likely... Most likely is damaged batteries... If they are the old AGM, those proved to be a bit fragile to being run down too far, or being left down too long... Check out everything and get back to me...

Our new batteries, out about the same time the beginning of this year, have proven near bulletproof, and so far no one has even been able to kill them... And they have gotten some real abuse unintentionally...

One more thing, be amazed, at the level of service you get from that Bloody Lone Ranger, at seven in the Monday Morning, even though you are a second hand Owner....

Happy Trails....

"The Last Stand In Open Country"

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Follow Up By: Bushtracker - Monday, Oct 17, 2005 at 17:52

Monday, Oct 17, 2005 at 17:52
One more thing, a step #6

If indeed you have a very high "Surface voltage" it is an indication of sick batteries... It will have no depth, no amperage to pull out of it, it is really not even there so to speak.... As soon as you put a large load on it, it will drop way down immediately... Since you are too far away to get to us, if this is the case.... Pull each battery out, and try and burn through this on a large charger.... But if you are at this stage for some unknown variable, it is likely the batteries are at an end stage for some reason...Not a big chance of a recovery... Again, I do not know the cause, am blind, 5000 km away, an unknown system, unknown modified wiring....

If indeed you had fully charged batteries pumped up to 20 volts, they would be "smoking hot" to the touch.... (ruined) Again I do not find that likely... You would feel the heat...

"Above and beyond the call of Duty, from the Lone Ranger...."

Semper Fidelis
"The Last Stand In Open Country"

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Reply By: TRAVLN - Monday, Oct 17, 2005 at 17:45

Monday, Oct 17, 2005 at 17:45
I strongly recommend that you check the polarity of the connections from each battery!!

If two batteries are connected in series, and the third is in parallel, this will give you a voltage readout of approx 20v.

To be in parallel, terminals must be connected +ve to +ve and -ve to -ve. I suspect that one of the batteries is +ve to -ve.

If each battery is at a charge of 13.5V, you have a total of 40.5V available. When divided by 3 batteries this still gives 13.5V, as it should. But if you have two batteries in series, you effectively only have two batteries now, so 40.5 divided by 2 becomes 20.25V.
AnswerID: 567289

Follow Up By: Bushtracker - Monday, Oct 17, 2005 at 17:54

Monday, Oct 17, 2005 at 17:54
Thanks for that try, but unlikely, like nearly impossible...
He has had the van for a while, and at series voltages, nearly all the equipment in the van would not function or burn out...
Kind Regards from da Ranger...
"The Last Stand In Open Country"

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Reply By: Bob Bushwacker - Monday, Oct 17, 2005 at 18:51

Monday, Oct 17, 2005 at 18:51
Throw your voltmeter away

Luke Electrical Pty Ltd
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Reply By: MattandLana - Tuesday, Oct 18, 2005 at 10:33

Tuesday, Oct 18, 2005 at 10:33

Thanks Steve and others. Yes it was a dying multimeter. Sorry!

My only defense is that I only recently replaced the battery in the multimeter for the first time after about a decade of (very intermittent) use and don't recall having left it switched on recently to flatten itself. Never occurred to me it might be going flat.

But dead the battery was and with a new 9V one installed - presto the van is now running at 13 volts again! Cheapest caravan fix I've ever seen!

I'm going to go and stand in the corner now ...

Clueless Matt
AnswerID: 567291

Follow Up By: TRAVLN - Tuesday, Oct 18, 2005 at 16:58

Tuesday, Oct 18, 2005 at 16:58
Sometimes the simplest of solutions is overlooked!!!!!!!!! Glad it was nothing more serious.
FollowupID: 845061

Follow Up By: Mobi Condo - Tuesday, Oct 18, 2005 at 18:08

Tuesday, Oct 18, 2005 at 18:08
Try again! Hmmph I was not logged on apparently. Any way's we have learnt heaps from this thread so only one lash as you sit in the corner Matt!
Cheers - Ian
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