Nasa Battery BM1 Monitor Issue

[scw]

Hi There,

I recently bought a sail boat that has all the electrics setup with a 12v marine leisure battery, two solar panels, it can also be connected to shore power. There is a Nasa BM1 battery monitor and everything for the last month or so has been working as it should, the battery monitor has been showing the correct inputs and outputs, battery charge etc.

We did our first sail (4 hours in fairly choppy seas) got to our location, I looked at the battery monitor and saw a flashing alarm / bell symbol and all the volts/amps that were reading correctly went to what is shown in the screenshot. The readings are with the shore power connected....

All the electronics on the boat are functioning fine, the battery is showing the correct voltage when I connect another tester tool, I even replaced the battery with a fully charged leisure battery to rule out battery issues and that made no difference to the battery monitor input/outputs. As you can see the battery percentage indicator is also reading as near empty and that since it went faulty would have always been between 80/100%.

I have looked at the cables and i can't see anything loose.

Has anyone got any recommendations to help troubleshoot the issue? I am not skilled in electronics but would like to learn how to isolate the issues so i know what needs replacing. Any advice would be much appreciated.

 

[Binnacle]

Do you have a copy of the BM1 manual ? If not Nasa have one here

BM1-BM2+ Booklet (nasamarine.com)


If you have changed the battery you will need to re-set the system so that the monitor can 'learn' the new battery characteristics.

What voltage does the battery read with another meter ? What are the rates of the two solar panels ? Are they connected in series/parallel, and through a controller ? If a controller, what readings ?


Before that, I'd go through the wiring inch by inch and waggle the connections, and check the fuse (what rating ?).

 

[lumphammer]

The red wire with the in line fuse is both the source of power to the BM1 and the measurement point for the battery voltage. As you are not reading battery voltage on the display I would check that wire first, including the fuse. As far as I am aware thee is nothing in the setup that should stop the battery voltage from being displayed, it is more about setting battery capacity so that the BM-1 can work out an estimate of the State of Charge.

 

[Rappey]

Disconnect the power to the bm1 as they seem to become more and more inaccurate over time. The percentage and bar graph should be taken with a pinch of salt.
The amps and voltage always seem to be OK.

 

[scw]

Do you have a copy of the BM1 manual ? If not Nasa have one here

BM1-BM2+ Booklet (nasamarine.com)


If you have changed the battery you will need to re-set the system so that the monitor can 'learn' the new battery characteristics.

What voltage does the battery read with another meter ? What are the rates of the two solar panels ? Are they connected in series/parallel, and through a controller ? If a controller, what readings ?


Before that, I'd go through the wiring inch by inch and waggle the connections, and check the fuse (what rating ?).

Thank you for the reply. I just downloaded and printed the manual out so will go through that later when I get back on the boat. I wasn't aware about the monitor needing to be reset wit the new battery, i will go through that. The other meter tester read 13v. Not sure about the solar ratings or how they are connected (I will start tracing the cables), they look fairly old, I didn't get any information from the previous owner so trying to learn as i go with it.

I think your recommendation going through the wiring inch by inch is going to be my best option at this stage.

Thanks again.

 

[scw]

Disconnect the power to the bm1 as they seem to become more and more in accurate over time. The percentage and bar graph should be taken with a pinch of salt.
The amps and voltage always seem to be OK.

Thanks for that, i will try disconnecting it.

 

[scw]

The red wire with the in line fuse is both the source of power to the BM1 and the measurement point for the battery voltage. As you are not reading battery voltage on the display I would check that wire first, including the fuse. As far as I am aware thee is nothing in the setup that should stop the battery voltage from being displayed, it is more about setting battery capacity so that the BM-1 can work out an estimate of the State of Charge.

Thanks for that information. Really appreciate it.

 

[biscuit]

There was a NASA BM1 indictator fitted to my present boat, and it had been for several years before, but the readings were ultra confusing until I realised that the 2 domestic batteries were not set up in parallel! Once corrected its been a really useful instrument.

 

[scw]

There was a NASA BM1 indictator fitted to my present boat, and it had been for several years before, but the readings were ultra confusing until I realised that the 2 domestic batteries were not set up in parallel! Once corrected its been a really useful instrument.

Thank you, that is good to know. There is one leisure battery and one for the engine. I don't think they are connected (but there are a lot of cables so need to check that out) I do want to add a second leisure battery so can look at how to setup a parallel connection correctly. Thanks.