Nasa BM1 at end of life?

[Pasarell]

I have a Nasa BM1 battery monitor fitted new about 4 years ago to monitor the state of my batteries. It's wired correctly through the shunt and has always worked pretty well. Charging is from mains 40A charger that is rarely used except in winter, from 2 x 100W solar panels working through a Victron 100/30 MPPT regulator, a Marlec HRDi regulator connected to a Rutland 913 wind generator and a Balmar 100A alternator when the engine is running
The BM1 under reads current in and battery voltage compared to the solar and wind regulators by a small and consistent amount. Checks with a good digital multimeter have always confirmed the 2 regulators as being accurate.
The SoC reading on the BM1 has always fluctuated wildly but I never take serious note of that as they are known to be inaccurate anyway.

This all changed a few days ago when the BM1 reading for battery voltage is, typically 0.5 - 0.8V below the other readings until the batteries have been on float charge for some time when it will suddenly jump to the correct figure.
As a liveaboard I keep a close eye on battery voltage and total A consumption / replenishment. Does this change in V reading indicate my BM1 is reaching the end of its life?

I have a domestic battery bank of 600A and the BM1 is only connected to this bank. Solar only charges the domestic bank. I also have a 100A windlass / thruster battery in the bow charged by a Balmar DC - DC charger from the domestic bank. This battery is a few weeks old but the domestic bank is 5 years old.

Any thoughts appreciated.

 

[[70521]]

Give NASA a call they will give you lots of advice.

 

[Pasarell]

Thanks. I will do that but collective wisdom here is usually more impartial that manufacturers

 

[Richard10002]

I have a BM2, which has been fine since I fitted it almost a decade ago, although I rarely check its' voltage reading against the actual batteries.

I think poor connections can lead to voltage drop so, first thing* I would do would be to disconnect and wires related to the NASA, make sure all is clean and shiny, and reconnect. I cant recall if there is a factory reset facility, but I would do that as well. I would also get my meter out and check voltage in a variety of relevant places.

After the above, I'm stuck for now

* actually, first thing I would do is check the voltage at the batteries, to make sure that it is the BM1 that is reading low, and not your other things reading high

 

[[70521]]

Thanks. I will do that but collective wisdom here is usually more impartial that manufacturers

That's not my experience, within 10 posts the esteemed members of the forum go well off topic.

 

[Rappey]

Ive found that over time the BM1 gets more inaccurate.. Disconnect it and start again and its back on track.

 

[Pasarell]

Thanks Rappey, I will do that today.

Thanks for the other thoughts. All connections are good and the battery readings are the same as the other monitors suggest.

Kind of agree with you Sandy but since I'm only at 2 suggestions of remedy so far I'm well within the safety limit!

 

[Stemar]

That's not my experience, within 10 posts the esteemed members of the forum go well off topic.

I beg to differ. The esteemed members stay on track. It's the others (the members?) who wander off topic, at least here.

Hmm, so what does that make Sandy and me? ?

 

[Alfie168]

Thanks. I will do that but collective wisdom here is usually more impartial that manufacturers

NASA are very good at doing their best to help. They gave me every assistance when I damaged my LED nav light and supplied me with parts very economically to repair it. If you want equivocation try Raymarine.

 

[pvb]

The BM1 under reads current in and battery voltage compared to the solar and wind regulators by a small and consistent amount. Checks with a good digital multimeter have always confirmed the 2 regulators as being accurate.
The SoC reading on the BM1 has always fluctuated wildly but I never take serious note of that as they are known to be inaccurate anyway.

This all changed a few days ago when the BM1 reading for battery voltage is, typically 0.5 - 0.8V below the other readings until the batteries have been on float charge for some time when it will suddenly jump to the correct figure.

If you've double-checked all the connections, and this is still happening, it sounds like the Nasa monitor is faulty. Perhaps Nasa will agree to look at it and fix it, although as it's 4 years old they might not.

If you decide to replace it, consider a Victron BMV-700 monitor instead. It's much more accurate, has many more features and, at £121, isn't much more expensive than the Nasa BM1. Plus, it has a 5-year warranty!

Victron Energy Battery Monitor BMV-700

 

[Pasarell]

Just shows what the threat of redundancy can do. It had been misbehaving for a week but yesterday suddenly went back to normal. Not accurate but consistent as before.
Shame really pvb because I was already planning the Victron version as my Christmas present to me