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Balmar MC 612 Issue

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23 hours ago, Island Time said:

The fuse is not supposed to blow. It's there to protect the wire and prevent a fire - it's doing that. Oh, and you have done the test - replaced the fuse. Remember that the sense wire is connected directly to the battery, and could carry ANY current the battery can supply if it is connected to neg directly. To be like this would be a failure of a component in the reg, which is not serviceable. Replace it.

Hi IT,

I haven't been able to get the fuse to blow again. Would this change your recommendation on replacing the unit?

Started and ran the engine several times today, behaved normally. If I take the fuse out it will run at high voltage. Put it back in, runs fine.

Note that we did have the sense wire on the house batts, which is behind the VSR and therefore can't be 'seen' by the alternator when it is closed. I've shifted the sense wire to the start batt, which can always be seen by the alternator.

We've also determined why we don't get a high voltage alarm. The lead from the appropriate terminal on the regulator doesn't actually connect to the dash lamp. Amature hour!

I successfully got into the programming functions and documented the current set up, and changed the programme. From that I've found that the regulator is putting out about 0.3v more than the bulk set point. i.e. it was putting out 14.8/14.9v on Pro2, where the bulk set point was 14.6v. I changed to Pro1 which has a set point of 14.1v and the regulator and the batts were all saying 14.5. This appears to be the compensation limit. I'm yet to work out what that is and what is going on.

But in terms of replacing the unit, it appears to work in that all the lights come on, I can access and change the programme, it passed the diagnostic tests, and puts out current. There is this question about going to the compensation limit, and I'm yet to sit down and watch it go through and entire charge cycle and confirm everything is fine.

Noting that last week we found our isolator switches had shat themselves. the backing screws had fractured the plastic housing, so the copper rotator was not hard up against the contacts. There is a possibility this was causing voltage spikes, and how do you say "load shedding events". I suspect if anything was going to damage the regulator, that sort of stuff would have achieved it.

If I need a new regulator, I need a new regulator, (I've already sussed price, supply and model etc) but I'm keen to understand and confirm this one is not working properly / what is wrong with it.

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I believe I've worked out the compensation limit question. It is temperature compensation. Mid point is 25degC.

Ambient temp currently is about 15degC, i.e. 10 deg lower than mid point.

My new batteries have temperature compensation of 30mV/C. A random example Victron VRLA battery has 24mV/C. At 10 degrees cooler, the regulator is adding 0.3v / 0.24v to the target voltage to compensate for the cooler ambient temp. I expect that if I warmed up the temp probe to 35degC, the regulator would reduce the bulk charge voltage by 0.3v.

If this is correct, A. I can test it really easily by warming the temp probe, and B. my regulator is actually working properly and without any apparent issues. 😀

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Not answering for IT of course, but I don't fix things until I KNOW they are faulty UNLESS they are going to majorly inconvenience me.

Your tests proved device ok, so why not trust them? ~

You  swapped out several devices and we weren't privy to the results as changes were made. So

wasn't easy to fathom. As in, alt to start- sense to house. VSR wiring diag. Switching system. Why it happened, with 7V on start, sense on house, &  faulty switches??

Any one or all of them.

The voltage increase with the sense blowing in my mind is predictable as stated previously.

Your latest setup , as you have laid out  is not idea in terms of the system. ie charging start from alt and vsr to house. 

But your fix illustrates your previous problem and is even portrayed by Rod Collins  below.. So keep going, well done.

The 1,2,both, off is irrelevant. Could be replaced in diag with VSR/ACR and single switches for emergency combinations or retained if you have it.

So in this instance sense to C common terminal for all scenarios. If using VSR/ACR big imbalance is unlikely, Alt-->house, Sense -> House. Connected so sense ALWAYS see alt output in disconnect mode.

Temp compensation is either working or not working as you are finding out. 


Matt has an understanding and exposure to the variables I will never have. The industry standard is "component old & suspect- replace it".

Murphy sayes it will fail at an inopportune moment.

Relay your dilemma to Balmar support and they will tell you to replace it. 

Old and grumpy -so I have two of everything (electronic) that may fail & make me grumpier.

M2CW-open to correction for errors omissions.

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1 hour ago, Black Panther said:

Toilet hoses i would replace rather than try to clean.

I thought you old skool types just used a bucket?

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OK, so this is a progression. I thought the sense wire blew it's fuse all the time?

Turns out it doesn't.

The install manual was not followed. The sense wire MUST be connected to the battery that the alternator can see, ALL the time, as when disconnected it will go to full field to try to raise the (sense wire) voltage to the specified voltage. Do not connect a sense wire anywhere else but to the battery - that's why its's fused.

This is the issue with remote diagnostics. Without an accurate circuit diagram it can lead you down the wrong path very easily.

Yes the .3v is most likely temp compensation, and the device is working as designed,

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