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mikegbr asked

Interpretating BMV712 history via app

We have recently installed a BMV712 on a syndicate owned boat and I am trying to understand what it is telling me. The boat has two 12 v Victron 220Ah batteries wired in parallel. He last discharge and average discharge have been showing 0Ah, so I have just changed the Charged Voltage setting from the default 13.2 v to 13.5 v hoping that this will give more information before resetting.

The thing that really puzzles me is that the Deepest discharge is shown as -543Ah and min battery voltage 4.17v, although the number of full discharges is showing as 0.

I don’t know what other syndicate owners have been doing with he boat but can these readings be right? I don’t understand how the deepest discharge can be -543Ah when I understand the maximum battery capacity to be 440Ah. Also, how the min battery voltage can have got to 4.17v when there is no indication of no full discharge.

Can anyone please advise if I am misinterpreting the data and, if not, whether I need to have serious words with the other syndicate members bout how they are treating the batteries?

discharge level
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9 Answers
mikegbr avatar image
mikegbr answered ·

History display

73765c4e-4004-430d-b691-4c3c1999ce18.png


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kevgermany avatar image
kevgermany answered ·

Would be good to see the battery settings.

How are you charging the batteries?

Some odd values there, why so many synchronisations?

I'd be tempted to take a note of the readings, reset the history and monitor closely. Min vtage could just be hanging around from when you installed it. Deepest discharge is rather odd. Can't explain it at all unless it's not wired correctly.

Is anything wired to the battery negatives except the shunt? Battery earth should have been moved to the load side of the shunt.

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mikegbr avatar image
mikegbr answered ·

56196c6c-6b2c-4a0a-ac16-89df3b82b612.png@kevgermany Thanks for your reply ad suggestons. The batteries are being charged via a Mastervolt Chargemaster 12/35-3 which is sometimes plugged in to shore power and at other times powered by the engine alternator.

I don’t know why there have been so many synchronizations. I am not aware that they have been done manually.

The batteries have been changed since I was last onboard. I believe that the unit was working ok when it was first installed, so will check that the wiring hasn’t been changed. In the meantime, these are the current settings:


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kevgermany avatar image
kevgermany answered ·

Guessing, but it could just be from the battery change.

What's the alternator output? You'll need something over 20A (depending on other loads) to prevent false synchronisation to 100%.

Charged voltage is possibly too low. The BMV will set 100% charged at charged voltage and chargr current of just over 17A. If you have heavy loads taking most of the alternator output you'll get a false synch to 100% after 3 minutes. Would be good to try increasing charged voltage to nearly 14.4, say 14.2V.

Suggest you reset the history and monitor.

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mikegbr avatar image
mikegbr answered ·

Battery and Victron wiring appears to be ok. However, having now run up the engine and disconnected the shore power, it appears that the alternator is not providing any charge to the batteries! I am a bit perplexed as the charge warning light goes off once the engine is running. Changing revs has no effect. The alternator drive belt appears to be a bit slack but, as far as I can tell, is not slipping. I am going to try tightening the belt but would be grateful for any other suggestions as to what might be happening.

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kevgermany avatar image kevgermany ♦♦ commented ·

Are the batteries full?

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mikegbr answered ·

Engine runningc9431962-f633-48ec-87cb-18c617d0c2e4.png


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mikegbr avatar image
mikegbr answered ·

b71bc1d0-94ae-42f8-951c-fc441dbf8a48.jpegBattery wiring:


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seb71 avatar image seb71 commented ·
Where are all those wires go?
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mikegbr avatar image
mikegbr answered ·

After further investigation, I have concluded that the split charge relay is not working, which would explain why the domestic batteries are not being charged. I am also thinking that the deepest discharge reading of -543 Ah may have been caused by the battery capacity being originally set at 220 Ah rather than 440Ah, as it should have been with 2 batteries. Can anyone confirm whether this sounds plausible?

All this is adding weight to the case that the boat should have been fitted with a battery monitor from the outset! It would have probably saved having to replace the batteries on at least one occasion.

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kevgermany avatar image kevgermany ♦♦ commented ·
To get to that discharge value is implausible, no matter what the capacity setting was, unless there's a wiring error pulling more current through the shunt than the battery. I can't imagine how this can happen unless there's a second system connected between the shunt and ground, while the bank you're monitoring's ground is at a higher voltage.

Looks like you're going to have to trace the wires as requested by @Seb71

I'd start by taking a look at the split charge relay and see what the actual failure is - and where it's wired.

There must be nothing connected between the battery side of the shunt and the battery negative. Especially an earth. This must be on the load side of the shunt.


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mikegbr answered ·

Thanks again @kevgermany . FYI, I have now discovered that the boat was left for a time over winter with the shore power disconnected but with the batteries left on. It also transpires that the battery isolator switches in the engine bay only isolate the batteries from the alternator and not the domestic circuit! I have also discovered that the boat doesn’t have a split charge relay, as outlined in the Perkins’ manual, but a Multivolt Charge Mate 2502 smart switch. This is supposed to connect the domestic and starter batteries in parallel for charging and prevent the starter battery from draining to the domestic circuit when on load. It has provision for a remote switch to be able to select off/auto/ on. The latter is to allow ganging of the batteries for starting in an emergency. Two things have emerged: a) the earth connection had come loose on the switch, so it had stuck in the off mode, so that the domestic batteries were not being charged and b) someone had hard wired the ‘on’ control terminal to the ignition switch, so that, when the earth was connected, the starter and domestic batteries were being used for starting! I am presuming that some combination of events has allowed the total discharge between the two sets of batteries to get up to -543 Ah. I thought that I had got to the bottom of it but have now found that in ‘auto’ mode, the batteries are showing as being connected in parallel for charging but the Victron unit still shows that the domestic batteries are being used for starting. I would have thought that this should have been impossible. I haven’t managed to trace all the wiring but it doesn’t appear to resemble the Mastervolt recommended installation drawing, so I am not sure what has been done. Hopefully, I can get to the bottom of it and the batteries haven’t been permanently damaged. At least, the batteries are now charging properly and I know how to prevent the domestic batteries from being used for starting.

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kevgermany avatar image kevgermany ♦♦ commented ·
Sounds like fun.

Not.

It's amazing how many bodges seem to work until someone else has a problem. Good luck sorting that out. At least there's good understanding of what going on, even if there are some more secrets to discover.


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