Matching shunt to battery monitor

[fredrussell]

I recently bought a 2nd hand Nasa BM2 battery monitor. It was cheap because its shunt was missing. You can buy these for twenty quid or so. Nasa shunt specs are 200 amp, 50 mV

My friend has just given me a 500amp 50mV shunt. Will this work with the BM2 or does the shunt amps rating have to match that of the monitor?

 

[oilybilge]

No good, sadly. 50mV/500amp means you get 50mV voltage drop at 500amps.

I recently bought this 50mV/200amp shunt from Farnell and it's very good. You can get cheaper ones but I was put off by reports of dodgy soldering and flimsy construction.

 

[fredrussell]

Thanks oilybilge - much obliged.

 

[Major_Clanger]

Out of interest, do shunts go wrong?

I ask because my BM-2 seems to be playing up. The charger and batteries are known to be good but the charge shown on the BM-2 is lower than the multimeter says, and when I waggle the shunt's wiring the display value keeps changing. It's odd because I've cleaned all the shunt's terminals and all looks okay.

 

[fredrussell]

Out of interest, do shunts go wrong?

I ask because my BM-2 seems to be playing up. The charger and batteries are known to be good but the charge shown on the BM-2 is lower than the multimeter says, and when I waggle the shunt's wiring the display value keeps changing. It's odd because I've cleaned all the shunt's terminals and all looks okay.

I’d give Nasa a ring. They’re very good with the customer support. Funnily enough I had a similar problem with my BM1. The connector pins on the display had corroded.