BMV-702 Main & AUX Battery Connections Transposed

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chris-ebsworth asked Apr 7, '21

BMV-702 Main & AUX Battery Connections Transposed

Hi All

Marine system with shore power and 230A alternator

Quattro 12/5000/230/2 x 75

CCGX

BMV-702

4 x 150 AGM Main Batteries

1 x 100AH Starter Battery

I have discovered that since new 2 years ago the main battery bank sense wire is connected to B2 AUX input on the shunt and the AUX (Starter) battery sense wire is connected to the B1 input.

The CCGX battery monitor is set to Automatic which means that the BMV is selected by default.

So when running on batteries the CCGX displays the main bank current but the starter battery voltage.

So does this mean as I suspect that the charging algorithm is compromised??

I.E. when the shore line is re connected the main battery bank charges but according to the voltage of the starter battery??

I would be very grateful for your thoughts.

BMV Battery Monitor

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Answer 1 · 2021-04-07T14:29:47Z

JohnC answered · Apr 07, 2021 at 02:29 PM

Hi @Chris Ebsworth

IF you've enabled DVCC, then the shore power charge may have been compromised, but probably really only with the adaptive algorithms also enabled.

Maybe there's been some overcharging, and you may be able to detect something on the VRM graphs.

Without DVCC then there shouldn't be any effect, except perhaps some inaccuracy in the SOC readings. That may pass through to the kWh history in the BMV, and if you use that, then maybe time for a history reset.

Not much you can do about it now except fix it, move on, and hope for the best. And wonder why it took 2 years to spot it.. :)

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chris-ebsworth commented · Apr 07, 2021 at 03:31 PM

Hi John

Thank you for taking the time to answer. DVCC was not enabled however unfortunately all 4 batteries are quite swollen and their capacity reduced indicating that overcharging has occurred. I have since corrected the wiring and the displayed voltage now follows the 4 stages of Bulk, absorption, float and storage.

New batteries required I fear!!

Cheers

Chris

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chris-ebsworth commented · Apr 07, 2021 at 04:27 PM

Hi John, I am getting conflicting information from the original installer which leads me to the nub of my question.

If the CCGX is set to display the Main Sense Voltage B1 on the BMV-702 is this the actual voltage that is used by the Quattro to control the battery charge??

This is the crucial question.

Cheers

Chris

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JohnC ♦ chris-ebsworth commented · Apr 08, 2021 at 05:29 AM

@Chris Ebsworth

Without DVCC enabled, the Quattro should use it's own voltage sense. You should be able to confirm this if you have VRM logging, with the Quattro widgets.

I wouldn't give up on your batts just yet. The real difficulty you face there is that you have 4x parallel 'strings', and you can't control the current through each batt. If you suspect they may be faulty, test them for temperature after a substantial charge session. Even just touching them, if you can detect differences with (say) one batt, then disconnect it. But don't discard it, as it may be the only good one.

Or separate them all (or one at a time) after a full charge and see how well each holds it's V over 24hrs with no load. You really need to get down'n'dirty with the evil things to assess them. Swearing doesn't help either! :)

Check the maker's recommendations for 'equalization' too, and if ok you could try that. I'd do that one-at-a-time for best results.

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chris-ebsworth JohnC ♦ commented · Apr 08, 2021 at 08:26 AM

Thank you very helpful.

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