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BMV712 with 4 6V batteries in series-parallel


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Hello,

 

I want to check the procedure for setting the Victron BMV712 batt monitor up. The manual (https://www.victronenergy.com/upload/documents/Manual-BMV-700-700H-702-712-EN-NL-FR-DE-ES-SE-PT-IT.pdf ) says that for setup, input the battery capacity in Ah (preferably using C20) and aux input.

 

I have 4 6v batteries connected in series parallel (so effectively 2 x 12v batteries).

 

Each battery (model 8GGC2) has a C20 of 180Ah.

 

I presume I only add the Ah for the batteries in parallel? (thus entering 360)

 

Cheers in advance

 

AG

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Related to my BMV712 upgrade I have discovered battery bank1 is only readying 10.2v. (bank 2 @ 12.8v)

 

The wiring looks like this:

 

batterybanks.jpg

 

I am wondering how the alternator and solar charge controllers work with a 2 bank setup. I will trace the wires for alternator and solar when next on boat. But how should this be wired such that the charging controllers are "aware" of the state charge state of both banks? (and charge both banks)

 

One of the batteries in bank 1 measured 6v the other 6.4v. 

 

Whats normal for a charged 6v batt?

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6.3-6.4v.

Find the volt drop.

 

Not familiar with the BMV712.

 

I have a similar setup but both banks (on opposite sides of boat) are permanently connected

with 50mm cable.

Not fussed about the individual current in each 12v bank.

Contrary to what I was advised. 

Works well charging evenly on shore power/alternator.

Yet to hook up solar.

 

Yep - that is the plan for tomorrow (find the voltage drop) - but the BMV712 is measuring at the terminals of bank 1 & 2 so there should be no reason for it to read different to the multimeter?

 

Are your banks connected across the positive and negative terminals?

 

I see the PO of this boat didn't connect the negative terminals until the shunt (could you join the negative side at the terminals?) and the positive terminals are separate wire runs until the battery selector switch.

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I think piece of the puzzle is going to be relevant - there is also one of these (stock photo) :

 

combiner.jpg

 

However I have not traced how it is wired. How is a "combiner" different to just joining the +ve terminals and having a isolating switch?

 

AG

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Then that stud to 1st shunt, to stud2  to 2nd  shunt to -ve bus with all the load returns.

Shunts obviously are measuring the same current as opposed yours.

It appears you have to keep yours separate, or the shunts wont differentiate.

 

 

PS: You refer to shunts (plural), I only have one shunt. If its because those two -ve wires in my diagram are actually joined to the same stud at the shunt. So there is only 1 shunt measuring the total load. But I can measure voltage for each bank separately.

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You have to calibrate the battery meter. Use a good multimeter with 2% or better rated accuracy. Ist, check for voltage drop on the cables to the meter, from the terminals they connect to. With the neg on the battery connection and the pos on the end of the sensor wire meter terminal there should be 0 volts. Do this again for the other voltage sense cable, then again for meter neg. Once you are certain there is no voltage drop there, Measure voltage at the batt terminals,with your 1/2/both switch off. Calibrate the voltage at the meter display to agree with the multimeter.

IMO I'd chuck the 1/2/both switch, put in fuses,individual bank switches, and a pos distribution bus. Neg side should be 1 cable off each bank to shunt, trying to keep them the same length if possible, then to neg distribution bus. Chargers all go to the 2 distribution busses. VSR to connect the start bank, bi directional ideally.

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Ok. A bit more investigating with multimeter revealed that in one bank one battery was at 6.3v and one at 4v giving me the 10.2v reading.

 

I have removed those batteries and charging them at home. Still not sure how they got that low given the 300w solar panels we have on board.

 

Will post a updated diagram later.

 

Will a 6v golf cart gel cell battery survive going to 4v?

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My isolating switch is manual. Its only there for safety in case a battery goes bad.

The combiner is more than just an isolation switch.

I'm not familar with that one but assume it combines the banks over a certain voltage, ie its a voltage sensitive relay.

Regarding multiple -ve on the shunt. Dunno. I guess you need two for when they are not combined. Once again

assuming is dodgy, i guessed it was two channel switchable, at monitor as not depicted as joined at shunt.

Wish I'd bought The Victron 712. Balmar still haven't released the BT gateway and software for the SG200 to update FW.

Bit of a fiasco really.

Mine is set up similar IT described with 6 HD fuses, biffed the 1/2/both for four individual House, Emergency (combine), start, isolate.

Complements of MS (Rod)

Obviously you can split the bank up to suit. ie 2( 2x6v in series) in parallel. And connect with heavy cable to suit location. Not optimum

but convenient. for weight.

Nice diagram.

 

You do it in Microsoft paint too? ????

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Ok, so I got around to a bit more tracing of wires today. It looks like this (so far):

 

WIRING SO FAR.jpg

 

The immediate issue I have realised is that I have been using that big black 1/2/Both/Off switch as a battery on/off switch (which it is I guess) - but the way it is wired this also disconnects the batteries from the solar charging over winter, so any parasitic discharge (like bilge pump and other always on stuff) would have slowly drained the batteries.

 

Just a theory at this point - does it seem valid?

 

I am not certain where the DC panel is connected yet - will trace that next time.

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You could leave it on both and put another switch on house loads/dc panel. Or replace with four separate switches as IT said.

Motor ground should be to other side of shunt along with

-ve load returns. Nice drawing!

Must do one for ships papers docs.

Your 1/2/both/0ff isn't the idiot proof one if that pic is correct. (diode frier)

Make before break,  fixes that.

 

https://forums.sailboatowners.com/threads/1-both-2-off-switches-thoughts-musings.137615/

 

Ok - I will add to the diagram as I get time - but its worth adding there is a dedicated starter battery (which uses that combiner).

 

You said IT suggested 4 switches?

 

Switch Bank 1

Switch Bank 2

Switch ? 

Switch ? 

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Ok - I will add to the diagram as I get time - but its worth adding there is a dedicated starter battery (which uses that combiner).

 

You said IT suggested 4 switches?

 

Switch Bank 1

Switch Bank 2

Switch ? 

Switch ? 

Al, you must realize that I do this for a living, right? I'm not going to design an electrical system for you, and provide diagrams for no charge, sorry.

I'm happy to help out with the odd question etc, as it's of benefit to other site users, and is what the site is for.

 

So, all battery banks should have an isolating switch, and there should be a mains switch, which normally disconnects the switchboard from the pos bus. Some use 2 pole switches which disconnect neg as well.  House batts (at least) should be fused. Start bank fusing is optional. There is often a 24hr circuit (main switch does not turn it off) for things like auto bilge pump, stereo memory etc.

Splitting your house into two banks will consume the batteries life more quickly. Here is an example - if your daily consumption is 100ah, and you have a 200ah bank, thats 50%. Then swap to the other bank. However, if you combine the banks, then you have 400ah, and your daily load is only 25%. Shallower discharge cycles provide more batt life. It makes sense to combine house banks to one, as large as possible. IMO

Lateral, before publishing someone's design on here, it may well be a good idea to ask them first? For the reasons outlined above. We marine sparkies need to eat!

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Al, you must realize that I do this for a living, right? I'm not going to design an electrical system for you, and provide diagrams for no charge, sorry.

I'm happy to help out with the odd question etc, as it's of benefit to other site users, and is what the site is for.

 

 

 

Sure - my question about four switches only arose out of a reference to IT - which I could not find earlier in the thread.

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Back to Rod drwg.

*House 

*emergency

*start

*Isolate-always on. Bottom left.

The link I provided to Rods reasoning is worth reading.

I guess it comes down to what you are comfortable with.

 

PS: I never saw the link to Rod's drawing?

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For the benefit of anyone in this situation in future, I think the failure was down to a number of thigs:

 

1. First and foremost the Alternator regular for the house we set to FDL (Flooded Deep Cell) - changed to GEL.

2. The isolation which we turned off actually isolated the battery from he charging bus bar / solar

3. Being next to engine compartment (heat) doesnt help

4. Solar controllers (Genasu Gv10 also dont have a mode for GEL

 

Hope it helps out someone in future.

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Slightly off subject, but Gels are not the best choice for House. Gels are best suited for long term storage where they are may discharge only occasionaly, like a remote backup stations for cell towers etc. If sealed is the requirement, then AGM are the better choice for deep cycling

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