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Victron Battery monitor BMV 702 and cable


Camel
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I don't know if this needs a smiley face or a frowny face!
Victron just went nuts - screaming it's head off about a fault (Axpert blissfully unaware of a problem)... 1 battery with 2 cells dead! Wow, completely unexpected on a newish set like this (3/4 months old). Took it out of the bank and test seperately, yup it is screwed. So halved my battery capacity and monitoring the others because Vicron still seems unhappy but I think that is because I have left the balance/midpoint cable in place while testing (obviously 2 batteries on one side and 4 on the other is not a good combo - will go fix now).

Fixed - Now to monitor for another fault in the left over bank, they will need to all balance first.

Edited by KLEVA
Fixed
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29 minutes ago, KLEVA said:

Victron just went nuts - screaming it's head off about a fault (Axpert blissfully unaware of a problem)... 1 battery with 2 cells dead! Wow, completely unexpected on a newish set like this (3/4 months old).

If you did not have a Victron you would not know - I sound like an old granny but monitoring you batteries and having systems in place to give you early warning is well worth it. Your mishap convinces me that the kit (even the gimmicky voltmeters) monitoring my batteries is money well spent. Just need Carl to do some thermal imaging once the batteries are 1-2 years old.

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So far 3 taken out - 2 with faulty cells and one oddity - Seems perfect until it is under load, then drops rapidly to 9V or less. Hopefully have a working bank now - so far absolutely no (0%) deviation. Will let them get back to normal  (but only a 100Ah bank now :( ).

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I think the issues were related to the batteries, They were wrong for the system in the first place (Ca/Ca so Axpert cannot deliver a proper equalising charge (needs 63V, Axpert max is 58.4). I think the 2 dead cells created the problem and the issue I had with reading the midpoint - Didn't expect that the batteries would already be faulty when I connected the BMV, and that there was one on each side of the midpoint in each bank. I think it was only when the 3rd one hit graveyard (probably because it was compensating for the dead cell), that it became so obvious. Might still be able to recover the 3rd one with some care.

Without BMV and midpoint connection, the problem would have run on even longer. Even with the midpoint it was missed for a while because the faulty were on either side of the midpoint, and the fact that I was still getting to know/understand the unit.

 

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I have the same setup with my batteries but I see you have a wire connecting battery2 neg to battery7 pos.

I do not have that cable in. I believe it is for the victron midpoint reading.

Any other reason for that?

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According to the install instructions, which I followed (except for mistakenly having the shunt the wrong way round for a while):

Shunt is connected to battery negative, the other side goes to the invertor. B1 is then connected to +ve (48V) and B2 (the midpoint) can be connected to the mid/middle point (where 24V point would be). The middle points of each bank are then connected together. All cables to the shunt and the B1 & B2 points should be exactly the same length (so that there is limited diference in voltage drop across the battery cables (especially under load). Setting 69 on the Victron must be set to Mid. The Shunt can easily be installed the wrong way around, which won't harm anything, but the readings will be wrong and will show negative values instead of positive for the current readings and also the % values will seem to be going the wrong way. Look carefully at the drawing (it isn't mentioned anywhere else in the docs, so got me very confused until set right by some of the people on this site).

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Sorry, just a feedback to those that are curious - Supplier replaced the batteries without question, although was also surprised that 2 had dead cells. Have the 3rd one undergoing a dedicated test by a engineer friend, if it's fine it will go back in with the new ones later this week one I have made sure all are at same balance (manual balancing, not an enjoyable task). Hopefully all sorted, supplier has already said he will accept the findings if that one has to be replaced too.

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15 minutes ago, KLEVA said:

Sorry, just a feedback to those that are curious - Supplier replaced the batteries without question, although was also surprised that 2 had dead cells. Have the 3rd one undergoing a dedicated test by a engineer friend, if it's fine it will go back in with the new ones later this week one I have made sure all are at same balance (manual balancing, not an enjoyable task). Hopefully all sorted, supplier has already said he will accept the findings if that one has to be replaced too.

Invest in some battery balancers Kleva (I know you just got the BMV) 

My banks highest midpoint deviation value under charge I have seen was 0,078v and only for a few seconds most of the time it hovers at around 0.01-0.02v. Currently under load sitting at 0.015v

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@viper_za - I will as soon as I get back from picking my money tree, oh wait...

My solar has already cost me more than I spent on the house 13 years ago. We have given up medical aid and a badly needed replacement car for my wife. So exactly which kidney do you need? Or more importantly, do you have a place for me to stay when the WENCH finds out that I have to spend more money on "that <profanity redacted> system, that doesn't work, blah blah blah!"? And I still left out that there is a R16,000 bill for a tree that still has to be removed (why I only get 4 hours sun per day)... :D

 

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