NASA BM1 showing 104% SOC???

[SlowlyButSurely]

Fitted a Nasa BM1 a few days ago and since then I turned the charger off for a couple of days and SOC went down to 65% which seems about right. Then I switched the charger back on again and let the batteries recharge. Now fully charged the SOC reading is 104%. How does that work?

 

[Richard10002]

Mine has done that since new - I fairly quickly came to realise that the SOC reading on the NASA BM1, or BM2, bears little resemblance to reality.

All other features are excellent, (as long as you zero the cumulative AmpHours when full).

 

[Poecheng]

Spinal Tap version ?

 

[wiggy]

You can adjust the battery capacity on the unit to make it read zero or there abouts when fully charged.

 

[GrahamM376]

It's quite normal. The BM1 is set up when batteries are fully charged and rested for a period, ideally with no load. Voltage when just or still being charged will be higher so will the indicated capacity, which is in my experience more of a guide than fact.

 

[SlowlyButSurely]

Thanks for the replies chaps. That makes sense now.

I do like the Spinal Tap idea. I might try and tweak the capacity setting so that it shows 110% when fully charged!

 

[sailaboutvic]

I went through this some months back , it was explain that the BM1 SOC wasn't reliable , I stop taken any notice of it and just took note of the voltages now.

 

[LittleSister]

I turned the charger off for a couple of days and SOC went down to 65%

Even allowing for the reading being a rough guide, rather than definitive, that seems a big fall unless there was a significant load on the batteries while it was off charge.

 

[SlowlyButSurely]

Even allowing for the reading being a rough guide, rather than definitive, that seems a big fall unless there was a significant load on the batteries while it was off charge.

Yes, it's the fridge mainly but since using the BM1 we have found a couple of surprises eg. the hifi uses 1A which is something I hadn't thought about. We have 2 x 100Ah batteries on the domestic bank and the BM1 was showing 71Ah used so I think the SOC was about right.

 

[pcatterall]

Despite what some say I have found the SOC once set to my real battery capacity to be quite a reasonable guide