help - Strange NASA BM1 battery monitor behaviour

[GHA]

http://www.ebay.co.uk/itm/DC-0-99V-...urement_Equipment_ET&var=&hash=item27eec7d1a5

going down to tens of millivolts rather than hundreds may seem a little bit overkill but it's nice to have. And agree, it's great having an accurate reading of volts at the battery, readings further down the chain or after the shunt can be surprising out when a load of current is going in or out.

Still doesn't help the OP though, that's a wierd one.

 

[VicS]

http://www.ebay.co.uk/itm/DC-0-99V-...urement_Equipment_ET&var=&hash=item27eec7d1a5

Why 3 wire ?

 

[GHA]

Why 3 wire ?

Measuring range is different from the power supply range.

 

[sunquest]

Why 3 wire ?

You made me think then Vic as I fitted 3 to keep an eye on the battery banks for domestic, starting and genny.
Extract from another supplier.

Pinout
•Red: Positive Power supply
•Black: Negative Power supply (0V) - also used as the negative measurement voltage
•White: Positive measurement voltage

Remember this is the 3 wire Version module, which means with the supply voltage maintained, and with the measuring voltage at 0v the display will still be on, so you can see the full swing of the measuring voltage from 0v to 32v. Unlike 2 wire versions where the display will start to dim and turn off when the measuring voltage starts to drop below 5v, since the 2 wire version uses the measuring supply to also power the unit.

 

[VicS]

You made me think then Vic as I fitted 3 to keep an eye on the battery banks for domestic, starting and genny.
Extract from another supplier.

Pinout
•Red: Positive Power supply
•Black: Negative Power supply (0V) - also used as the negative measurement voltage
•White: Positive measurement voltage

Remember this is the 3 wire Version module, which means with the supply voltage maintained, and with the measuring voltage at 0v the display will still be on, so you can see the full swing of the measuring voltage from 0v to 32v. Unlike 2 wire versions where the display will start to dim and turn off when the measuring voltage starts to drop below 5v, since the 2 wire version uses the measuring supply to also power the unit.

So this needs a separate battery or an isolating power supply module.

 

[GHA]

So this needs a separate battery or an isolating power supply module.

Only if you want to measure below 4.5v or above 30v, according to the specs. At least that's how it works with a similar amp/volt meter. Just double up the reds onto the battery positive.