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Discussion Starter · #1 ·
This is my review of the BM-1 battery monitor. I struggled if I should put this review up as I never determined if the problems I reported was user error or with the monitor. There tech support didn't have much to offer and only responded to me once. It looked to me like a limitation of the product but I could be wrong. I even exchanged my 6volts thinking it was a battery problem.

 

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A few thoughts:

#1 Your batteries are NOT yet broken in.. They WILL NOT hold voltage well until 20-30+ deep cycles.

#2 Your charger is woefully inadequate and something is not right. It peaks at 7A but the battery voltage is stuck at 12.9V and the BM is showing a 75% of charge...? A loaded voltage of 12.5 with .2A is going to be closer to 83-84% SOC but we know the voltage is not in agreement with the DVM...

#3 Your charger is probbaly not charging the batteries to full. This is a very, very, very, very common problem with many so called "Smart" chargers. Most smart chargers are VERY, VERY dumb. What charger do you have...?

#4 The NASA is one of the sloppiest battery monitors I have tested (see your own voltage comparisons)... The Victron and Xantrex Link-Pro & Link Lite are much more controllable.

#5 IMHO the BM-1 is an informational tool only. It does not calculate correctly for Peukert, and when you email the company with technical questions about why it will not remain accurate, and you have the tools as I do to KNOW THIS, they simply can't answer them.

On two occasions I have received two different answers as to how it calculates the % charge. Neither answer came from anyone whom I suspect even knows what a Peukert's constant is :confused:... It would appear they have pre-chosen a fixed Peukert for you and this may or may not be anywhere even close to what you have.

#6 You simply can't have 0 Ah consumed and be at 75% SOC....:confused:

#7 Unless you know the actual physical capacity, only testing can tell you this, reducing it will cause the SOC screen to miscalculate. 220Ah is a pretty good guess but it still may not be right...

#8 Good quality Ah counters can be great tools for folks who carefully set them up and then recalibrate with known bank capacities at least once per year. They can be extremely accurate but it is what data goes in and is programmed in that makes them less accurate. Battery temp, Peukerts constant, actual Ah capacity, charge efficiency and many other factors all need to be right for the Ah counter to be accurate.. If you have solar then you will also need to perform manual resets because NO Ah counter works well with "auto synching" and solar.....

Just yesterday I replaced a Link 2000R that was well beyond its useful life. The owner was doing exactly as he should and synching manually when his bank was accepting less than 1-1.5% of its capacity at 14.4V. The problem was his Link 2000 was doing as many of them are at this age and that is DRIFTING out of accuracy.

With 46A flowing into the house bank the Ah counter was showing him 7A net going into the house bank with no loads on the system.... I replaced the Link 2KR with with a new Link Pro & Bamlar MC-614 regulator. It is now in full agreement with the Fluke....

His bank was capacity tested this past spring so that is accurate too, as well as the Peukert because the Link Pro allows you to do this. The Link Pro also has a battery temp sensor to help keep it even more accurate. He is also adding a Balmar Smart Gauge for his SOC and will use the Link Pro as his "information" on current....

Good quality Ah counters, well calibrated, can be great tools, key there is good & well calibrated......

If you want to read more about amp hour counters and how to test for your own banks capacity, and what that entails, I have a lot in this article..

Battery Monitoring
 

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Discussion Starter · #3 ·
Thanks Maine Sail very helpful. I have had you site bookmarked for a few years and love it. Went with the BM-1 because it is sexy with it big screen. But after my testing and you analysis you have confirmed it is better that nothing but to take it with a grain of salt.
 

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Discussion Starter · #4 ·
#1 Your batteries are NOT yet broken in.. They WILL NOT hold voltage well until 20-30+ deep cycles.
>>Good to know thanks.

#2 Your charger is woefully inadequate and something is not right. It peaks at 7A but the battery voltage is stuck at 12.9V and the BM is showing a 75% of charge...? A loaded voltage of 12.5 with .2A is going to be closer to 83-84% SOC but we know the voltage is not in agreement with the DVM...
>>I also suspect my charger was a bit under powered or just not that good. I am now running on mppt solar charger on 100W same results.

#3 Your charger is probbaly not charging the batteries to full. This is a very, very, very, very common problem with many so called "Smart" chargers. Most smart chargers are VERY, VERY dumb. What charger do you have...?
>>> I am using the NOCO Genius 7200 but i suspect it isn't anything impressive. I am mon a mooring so only ever use it once or twice a year. Solar all the time.

#4 The NASA is one of the sloppiest battery monitors I have tested (see your own voltage comparisons)... The Victron and Xantrex Link-Pro & Link Lite are much more controllable.
>>>Agreed

#5 IMHO the BM-1 is an informational tool only. It does not calculate correctly for Peukert, and when you email the company with technical questions about why it will not remain accurate, and you have the tools as I do to KNOW THIS, they simply can't answer them.
>>>Agreed

On two occasions I have received two different answers as to how it calculates the % charge. Neither answer came from anyone whom I suspect even knows what a Peukert's constant is :confused:... It would appear they have pre-chosen a fixed Peukert for you and this may or may not be anywhere even close to what you have.

#6 You simply can't have 0 Ah consumed and be at 75% SOC....:confused:
>>> I had reset the AH counter as i assumed the battery was full. My understanding is when the battery is full reset it so it counts down. But cont recall where i got that from.

#7 Unless you know the actual physical capacity, only testing can tell you this, reducing it will cause the SOC screen to miscalculate. 220Ah is a pretty good guess but it still may not be right...
>>>That was the only suggestion from NASA. I have 230AH batteries they told me to try 220 or 210. Didn't help.

#8 Good quality Ah counters can be great tools for folks who carefully set them up and then recalibrate with known bank capacities at least once per year. They can be extremely accurate but it is what data goes in and is programmed in that makes them less accurate. Battery temp, Peukerts constant, actual Ah capacity, charge efficiency and many other factors all need to be right for the Ah counter to be accurate.. If you have solar then you will also need to perform manual resets because NO Ah counter works well with "auto synching" and solar....
>>>agreed

Thanks for the response. I am not expecting anyone to help me fix it as i think it is working the way it can.

If you want to read more about amp hour counters and how to test for your own banks capacity, and what that entails, I have a lot in this article..

Battery
 
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