Vectron Battery Monitor BM1

[1simon]

Hi  All,

I have noted that iwith no shore power, my Vectron Battery Monitor BM1, will show a hioghet battery voltage reading when I redcue load.
E.g. Monitor is showing battery voltage to be 12.4V. As soon as I reduce the load by switching off equipment, e.g. the fridge, the Battery Monitor will show the voltage reading to  be higher e.g. 12.6V

Why is this?

Regards
Simon

[1simon]

Dear All,

Apologies, the Battery Monitor is a Clipper BM-1 not Vectron.

Simon

[Kibo]

Battery voltages will "recover" slightly when not under load. Hence the slightly higher reading.

I actually have a Victron BM1 monitor and will check without load for interest but in realistic usage you will always have some load (especially fridge) so using the monitor to follow discharge and charging needed at max 50% discharge it is better to use the "normal" load conditions for the battery bank since the amp draw is what the monitor uses to calculate the time to 50% discharge.

[Escapade]

Hi, i have recently installed the NASA Clipper BM-1 and find same behavior as you describe.
It is normal that voltage slightly increases when significant loads are disconnected.
That is one of the reasons why I have installed the battery monitor, as looking at the battery voltage to guess the state of charge was at times misleading and making me believe that battery was more discharged than it actually was.
Atb

[Symphony]

Battery voltage readings when in use are misleading as an indicator of state of charge. They only have meaning when the battery has been rested. Same with the state of charge bar on the instrument. This is because of the algorithm used to measure charge and discharge.

The useful information is the amps going in and out which is an accurate measure of your consumption and allows you to do a quick check on how much of your capacity you have used. Example. I have 280ah of house capacity. When sailing with instruments on, autopilot engaged and fridge running the readout shows 4 amps consumption. The total hours capacity 280/4 = 70, and if I want to keep to only 50% discharge I have 35 hours usable capacity. The monitor gives similar information of hours left to total discharge based on its measure of current capacity. However it is not super accurate because of the inaccuracy of measuring capacity in use.

Note also that it is rare to get the battery up to full charge unless charging from shorepower. Getting the last bit of charge in is very slow as you will see when using the engine the current going in is very low when you get to near full charge.

[1simon]

Noted your comments Symphony.
How long should battteries be rested prior to checking voltage for a meaningful voltage reading. And I assume that by rested you mean reducing load to zero?

[Symphony]

Turn the isolator switch off. If you have just run the engine the monitor will show typically 13.6v or so if the battery is well charged then slowly drop - could take 12 hours to resting voltage. Just checked mine and it is reading 12.9v which is virtually fully charged and the capacity bar is at 100%. The engine was last used on Sunday and had run about 8 hours over the long weekend. The battery was fully charged before that as I had it on shorepower.

[1simon]

Thanks Symphony.
What about resting the battery to  take a reading when not on shorepower, and after it was under load? Do  you need resting time of 12 hrs as well?

[Symphony]

Resting means not having any load or charging. So, disconnect from shorepower. Normal Bavaria wiring switches on the battery charger as soon as you connect to shorepower, although some people rewire with a switch to control the charger so you can use the 240v circuits with the battery unconnected.