BM showing 6v!

[Clodi]

Strange one

My set-up is as follows, 6 Trojan (3 12v bank) SmartSolar MPPT 150/35, NASA BM-2, Phoenix 12/250, Centaur 12v100amp mains charger, Victron Battery Protect. I use a gennie to charge as required. No shore power.

At 3am this morning all was normal the BM showed 13.9v.

At 7am the domestic bank was off, the BM showed 6v!

I immediately checked the individual battery voltages, each bank of 2 showed 13.1. I checked all fuses, all ok, I checked the master switch. Turned on the engine expecting to see a largish charge, but nothing to write home about the 80amp alternator was putting in the usual small amount one expects when the batteries are in 'float'.

I climbed back out of the engine bay only to find all is back to normal.

Any ideas what the fault would be that would cause the BM to read 6v? The battery protection is set to cut out at 12.5v.

Obviously, I'll check all the 'joins' etc, but I'm getting too old for this kind of excitement.

[Tony Brooks]

Dirty/loose battery terminals?

[MtB]

23 minutes ago, Clodi said:

Any ideas what the fault would be that would cause the BM to read 6v? The battery protection is set to cut out at 12.5v.

 

Well the first thing I'd do is pull the BMV712 (is that what you mean by "BM"?) out and measure the voltage on the terminals on the back with a digital voltmeter. If the terminals are at 6v while the batts are at 12.5 then you'll know you have a wiring problem. If the terminals are at 12.5 them your BM is goosed.

 

(Oh hang on, you said a Nasa BM2. Same comment applies though.)

[Clodi]

I think it's solved. The Victron Battery Protect has developed a fault. The symptoms started to repeat but this time showing 8.7volts I bridged across the 2 pos terminals on the Battery Protect with a spanner &, hey presto back to normal, So having a cuppa then back to double checking all connections and removing the BP.

Why the Battery protect seems to restrict the volts I have no idea but it was getting pretty warm.

[Clodi]

I've now found out via the Victron community the this 'fault' is not uncommon with the battery protect. It is sometimes caused by a faulty installation where a reverse charge can occur by, for instance, incorrect solar installation. However, I was aware of this having followed the Victron installation instructions to the letter. I have been told how to try reprogramming the unit but also advised to return to them under warranty. I'm going to return to them but only once I have fully charged the batteries using the Gennie and checking their voltages after resting, for peace of mind as I have heard some frightening tales of battery banks being severely damaged after this fault.

I know this has not happened to me as I personally checked each individual Trojan battery within hours of the fault occurring and there was nowhere for the  volts/amps to escape to, but imagine if we had been away from the boat for an extended period !