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Victron centaur battery charger overcharging, please help diagnose and repair

Thread starter #1
Hi there,

I have a Victron Centaur battery charger, 12v 200 amp output. It's a monster! I bought it used and am unsure of the history. The seller didn't disclose the fault (whilch I guess was why they sold it) and it took me a while to spot that it was overcharging so now I'm stuck with it and need to fix it.

On inspection it's actually two identical 100a chargers in the same case, connected in parallel. Other than a tiny 3 wire cable whose purpose I'm not sure of, there is nothing connecting the two chargers other than the battery cables and the mains cable.

It was pretty dirty inside and one fan on the front module had failed (each module has a pair of fans so there was still one running on that module). I replaced both fans on the front module with similar spec 12v computer case fans. I left the original fans on the back module and just cleaned them. They are a bit noisy but working.

The problem is, as the battery gets full, the voltage goes up, and up, and up, to 15.4v! It should max out at 14.4v. This is very damaging to my 900Ah bank of AGM batteries which are being overcharged.

So, first step was to isolate the problem by disconnecting mains power from each charger module separately. It turns out that the front module (with the new fans) charges at 15.4v when the batteries are fully charged. 1.5v more than it should!

The back module alone charges up to a relatively modest 14.9v. That's still a whole volt more than the maximum should be on the gel setting so both modules seem to have the same fault but the back one is not affected so badly.

There are DIP switches to select the charge mode (AGM, Lead Acid or Gel). I selected Gel as this has the lowest charge voltage but that doesn't help. There are no other documented settings but there is a row of jumpers and a potentiometer on each module. Victron support were very unhelpful and refused to tell me the purpose of these so I have not touched them. They said there is absolutely no calibration or adjustment facility on this charger, which i find hard to believe, surely it must be calibrated at the factory. The manual is useless. Other Victron products have detailed technical manuals so I'm very disappointed by it. They said all I can do is send it off to a Victron dealer and hope they fix it, which could be very expensive and they'll probably just try to sell me a new one.

It's possible the previous owner did find a way to calibrate it for some special purpose requiring a higher voltage and I just need to return it to normal, but the Victron guy seemed confident it was a fault, just refused to help with any more technical info.

This charger cost thousands of pounds new, has a huge capacity and accepts an unusually big range of input voltage so I'm very keen to get at least one of the modules working properly before it cooks my batteries.

I have a basic knowledge of electronics (My degree was in computer science - I'm more comfortable with things like cpu design or software development but I understand the principles of electronics and know the basics.) I can get stuck in with a multimeter and soldering iron but please use short words, I've forgotten half of what I used to know about electronics, which wasn't much!

It's currently installed in a very inaccessible place so it might be while before I can respond to any tests requiring access inside but please give me your suggestions of what to try. Also, has anyone seen a similar fault before and what was the cause? Is it economically repairable?

Thanks very much for your help.


Well-Known Member
Most Helpful Member
Welcome to ETO, syohana!

The Victron Centaur battery charger is, essentially, a switched mode power supply, per the victron manual, page 6., "Description". Two of them in parallel, as you noted.

What that means, in your case, is that it is a pretty sophisticated device (as opposed to most, simpler battery chargers). And as such, without a schematic (I also found nothing online), I'm afraid that diagnosing your problems, as well as repairing them, will be a daunting task.

That said, it is possible that some highly detailed, sharply focused pictures of the PCBs (top and underside) might reveal some damage (or some possible calobration opportunities) that could lead to some repair suggestions.
Thread starter #3
Thanks Bob, I feared that was the case. I couldn't see any obviously damaged component but there is a distinct "hot electronics" smell when it runs at full power.

I'll post photos when I have time to get the charger out as it's rather hard to access.

Meanwhile I wonder if anyone has encountered a Centaur or similar switch mode type charger/PSU with the same symptoms who could point me in the right direction for the fault?

Many thanks,

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