Mystery Voltage?

May 7, 2016
4,324
5,924
Poole, Dorset
Funster No
42,951
MH
Carthago Compactline
Exp
Since 2003
I have been upgrading my 12v system with a view to doing more time away from electrical hook ups. Yesterday when testing the system I got a mystery increase in voltage when I shut down the engine, having checked that the battery to battery bit was working properly. I am hoping that someone can point me towards where I should be looking. My suspicion is that there may be some incompatibility between the components I have fitted.

The components are:
Relion RB100 LiFePO4 with built in battery management system (new)
Mains charger Sterling Pro Charge Ultra 40 amp (existing)
Battery to battery charger Votronic VCC1212-45 (new)
Solar regulator Votronic MPP 350 (new)
Inverter Sterling Pro Power SB pure sine wave 300 watts (existing).

The vehicle is a Hymer with Schaudt EBL-29. Following advice from Udo Lang at Schaudt I have disconnected the mains charging by removing the 20 amp fuse from the EBL and have also diverted the primary positive engine battery connection from the EBL to the Votronic 1212-45.

At the time of my tests the solar panels were not connected to to the solar controller. The mains battery charger had performed as expected but the mains had been disconnected. Also the inverter had not been wired in. The Votronic battery to battery charger then performed as expected with 14.6 volts once the engine was running.

I then connected the 12 volt side of the inverter to the system and repeated the engine running test, so far as I recall the inverter was not switched on and nothing was plugged into it, I run it as a completely separate system from the ehu mains. I then repeated my engine running test and again the expected 14.6 volts was achieved. However when I turned the engine off this time, the voltage in the system shot up to 19 volts. I quickly disconnected the battery and let the voltage settle down. I did the test again with the same result of 19 volts after turning off the engine but this time I noticed a puff of smoke coming from the inverter.

I disconnected the inverter and in subsequent tests without it I have not seen anything higher than the expected 14.6 volts.

I brought the inverter home and it is still working normally when it is standing alone but I hesitate to reconnect it in the motorhome until I know what was happening. Anyone got any suggestions please.
 
Jan 24, 2012
1,215
810
Somerset
Funster No
19,577
MH
Hymer b694sl
Exp
Since 2012 + Caravanner for 20+ years
When inverter was on van but not switched on does this mean the 12 v supply was not connected to the inverter, or it was connected but the inverter was switched off?

When you say inverter works ok at home what supply
have you used as input?

Does inverter documents show a max and min supoly voltage? Have you exceeded it?
 
OP
Pausim
May 7, 2016
4,324
5,924
Poole, Dorset
Funster No
42,951
MH
Carthago Compactline
Exp
Since 2003
When inverter was on van but not switched on does this mean the 12 v supply was not connected to the inverter, or it was connected but the inverter was switched off?

When you say inverter works ok at home what supply
have you used as input?

Does inverter documents show a max and min supoly voltage? Have you exceeded it?

Thanks for your interest @SandraL . On the van the 12v supply was connected to the inverter but the switch on it was set to off. At home I connected it to a spare 12v battery. The high voltage trip is shown on the unit as activating at 15-16v. I have noticed that even when switched off the inverter will take a small charge to bring it's internal capacitors up to voltage, which decays fairly quickly when the battery is disconnected.

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Lenny HB

LIFE MEMBER
Oct 18, 2007
32,498
61,933
On the coast in West Sussex
Funster No
658
MH
Hymer B678 Dynamic Line
Exp
Since 2008 & many years tugging
Could be back emf from the inverter coils, i.e. voltage spikes your meter is reading. You could try seeing what happens is you read the voltage with an analogue meter, if you want to risk it again.
 
OP
Pausim
May 7, 2016
4,324
5,924
Poole, Dorset
Funster No
42,951
MH
Carthago Compactline
Exp
Since 2003
Could be back emf from the inverter coils, i.e. voltage spikes your meter is reading. You could try seeing what happens is you read the voltage with an analogue meter, if you want to risk it again.
Interesting. I haven’t got an analogue meter but I did notice that whereas the mpp display showed a fairly stable voltage my handheld one was fluctuating wildly. If it is an emf could the physical proximity of the inverter to the other equipment be inducing unexpected results? Your observations are much appreciated.
 
Jan 24, 2012
1,215
810
Somerset
Funster No
19,577
MH
Hymer b694sl
Exp
Since 2012 + Caravanner for 20+ years
As all works with inverter disconnected suggest that is the problem. A puff of smoke is always bad news . Looking at adverts for your inverter suggests input voltage max of 15 v. I suppose its possible this was exceeded, and maybe this caused some damage.
Suggest you phone sterling and confirm their inverter is happy at 14.6 and the max input voltage.
Electrolytic capacitor have voltage ratings, a popular one is 16v and very close to your working voltage. This may be a red herring if sterling have used higher rated capacitors!!!
Inverter switch, are there any components between 12 terminals and the switch?
Have you opened inverter for a visual check and a smell check?

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OP
Pausim
May 7, 2016
4,324
5,924
Poole, Dorset
Funster No
42,951
MH
Carthago Compactline
Exp
Since 2003
Suggest you phone sterling and confirm their inverter is happy at 14.6 and the max input voltage.
I spoke to Sterling earlier. I didn’t specifically ask about the max input voltage but gave them the details of what I had been doing. They immediately asked about the solar panels because they have had capacitors burn out from over voltage from this source but I explained the panels had been unplugged. They said I could send it back to them for checking but I am starting to think about spending out on a new inverter instead, hopefully a more robust one.
I did have a look inside the inverter, no particular smells but did notice the plastic sleeve on one component was not intact. Difficult to see properly without dismantling more than I felt comfortable with.
 

pappajohn

LIFE MEMBER
Aug 26, 2007
40,366
38,123
Dark side of the moon
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172
Exp
Since 2005
You can't get a quart in a pint pot so there's no possible way to get 19v from a 12v system.....even at 14.6v.
Whatever was showing 19v is reading wrong.

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OP
Pausim
May 7, 2016
4,324
5,924
Poole, Dorset
Funster No
42,951
MH
Carthago Compactline
Exp
Since 2003
Decided to buy a new Victron 12/500 inverter with ve bluetooth dongle. I don't think I was ever going to be comfortable sleeping with an unsolved mystery running and we need the supply all night for medical equipment. Also decided a slightly bigger one would allow for recharging ebikes when on the move. Thanks for the helpful posts.
 
OP
Pausim
May 7, 2016
4,324
5,924
Poole, Dorset
Funster No
42,951
MH
Carthago Compactline
Exp
Since 2003
I have now installed the Victron inverter and no more mystery voltages. I think the problem must have been with the Sterling inverter, though it appears to behave well enough when bench tested. Perhaps an incompatability issue with the Votronic b to b, or perhaps the 14.6v charge was too close to the Sterlings 15v high voltage cut off. I think the emf suggested by @Lenny HB is the likeliest explanation.
 

magicsurfbus

Free Member
Oct 11, 2010
4,685
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NW England
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14,057
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Bessacarr Coachbuilt
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Since 1997
A bit of a long shot but has your solar controller been by-passed? The direct voltage from a solar panel can easily exceed 14.6v.

I speak as one who had to take his MH back to the dealership after one of their fitters wired my solar panel direct to my inverter without even troubling the leisure battery.

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OP
Pausim
May 7, 2016
4,324
5,924
Poole, Dorset
Funster No
42,951
MH
Carthago Compactline
Exp
Since 2003
A bit of a long shot but has your solar controller been by-passed? The direct voltage from a solar panel can easily exceed 14.6v.
The solar controller was connected to the system and appears to function properly but at the time of the problem the panels were unplugged. The problem only occured after I turned the engine off, at which time I was expecting the voltage to decay, instead it shot up. My suspicion fell on my older Sterling inverter because the problem only occured after I wired it in. My new Victron inverter is now connected and the problem has not reappeared, which is a relief..
 
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