Nasa Battery Monitor.

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doug748

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In the summer I thought I was going blind, all the boat lights went dim and I found the service battery with about 10 volts in it. The electrolyte was also low. Anyway I worked around it and eventually charged the battery up. It got me home ok, I don't have a great many electrical requirements.

I figured out that either:

The battery had gone duff - it is about 4/5 years old c 80Ah boat/caravan type. or

I had failed to charge the battery on a number of consecutive days, charging the start battery in error and running the service battery down with the autohelm - I don't really believe this. or

There was a short somewhere in the system.

What is the collective wisdom on this?


I have sort of decided to fit a NASA battery monitor over the winter, because I guess it would help show up any short circuits pretty sharpish and also confirm, at a glance, the charge/discharge status of the main battery. I don't want to be foxed again by a dead flat battery. Is this a sensible option?

I understand the battery capacity remaining function is a bit of guessology. I would take that with a pinch of salt.
Is there any good reason to pay the extra 30 quid for the BM2 unit?
 
Had one but wouldn't have another. A decent digital voltmeter can be read as well for a fraction of the price - plenty on ebay. A low voltage relay can also be installed to switch on an LED or even a buzzer if the voltage falls too low.

Sontay offer these at varying voltages.

PS

The other key reason for not getting another was it packed up after 2 seasons.
 
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I love my BM1.

I don't pay attention to the remaining, hours, but it's excellent for measuring the amps in and the amps out, so once you've zeroed it at a reasonable highly discharged level, then you always know more or less how many amps you have left before you ought to start the engine and put more back in.
 
doug748 said:
Is there any good reason to pay the extra 30 quid for the BM2 unit?
Click to expand...

The BM2 has a 200 amp measuring range , the BM1 only 100amps

If you have a system which allows the house battery to be used for starting you may need the BM2 for its higher rated shunt
 
Surely the original problem is gassing due to overcharging. Have a measure of the battery voltage after the motor has been running for a while (or on well charged batteries.)
shouldn't be more than 14.4v.
Granted , a good battery monitor would have alerted you to this, if in fact the battery is being fried, but better to sort the prob then spend if you still feel the need,
 
You'd be better off spending the money on extra batteries to boost the capacity. Extra batteries are the most cost-effective electrical improvement.
 
I recently fitted a BM2 and it gives me a bit more confidence as to the state of things and when I need to be charging the batteries.
Watching the current drain has now prompted me to change to LED interior lights.
Only gripe with the BM2 is that it only comes with a four core cable meaning you have to run a separate wire for the second bank.
 
The BM2 counts up to 200A whereas the BM1 counts up to 100A. I got the BM2 because I have a 2500w inverter so I often draw more than 100A. For the amount of time I might draw more than 200A, the loss of counting doesn't matter.

You only need to buy the BM2 if you are going to regularly draw more than 100a.
 
I do start the engine on the house battery now and again, but as long as the shunt etc will not be damaged by this, I will probably go for the cheaper option.

Not sure about overcharging, I have never seen more than 14+ish volts at the battery terminals. As I don't use the engine a great deal and have a swinging mooring, the batteries are probably low for a fair amount of time. I do have a small windgen but this is a relatively feeble thing coupled to a 80amp battery, I would have thought? It certainly never shoves the voltage much over 12v.

Thanks for all your thoughts
 
doug748 said:
I do start the engine on the house battery now and again, but as long as the shunt etc will not be damaged by this, I will probably go for the cheaper option.

Not sure about overcharging, I have never seen more than 14+ish volts at the battery terminals. As I don't use the engine a great deal and have a swinging mooring, the batteries are probably low for a fair amount of time. I do have a small windgen but this is a relatively feeble thing coupled to a 80amp battery, I would have thought? It certainly never shoves the voltage much over 12v.

Thanks for all your thoughts
Click to expand...
You might want to consider looking at the charging system, by the sounds of it they rarely get a full charge. Takes a loooong time for an engine to fully charge a battery, if the only other source is an ineffective windgen then sounds like your batteries live constantly at less than full charge, they really don't like that one bit :)
Even a small solar panel & cheap reg might help a lot.
Echo others, very accurate panel voltmeters can be had off eBay for next to nothing.
 
doug748 said:
I do start the engine on the house battery now and again, but as long as the shunt etc will not be damaged by this, I will probably go for the cheaper option.
Click to expand...

I have no problems occasionally starting 1800cc engine through the 100a shunt but, it starts at first turn so not a long cranking current draw.
 
doug748 said:
Thanks for that info Graham.

My engine is half your capacity and a good starter so I should be ok.
Click to expand...

I believe people have asked NASA about starter currents " overlaoding" the shunt and or the monitor.

IIRC they have indicated, while not committing themselves, that the shunt will withstand a moderate overload and that the monitor will measure the higher currents although not actually display them.
 
VicS said:
I believe people have asked NASA about starter currents " overlaoding" the shunt and or the monitor.

IIRC they have indicated, while not committing themselves, that the shunt will withstand a moderate overload and that the monitor will measure the higher currents although not actually display them.
Click to expand...

And to add, I emailed NASA about this earlier this year and the response: The cable supplied is rated in excess of 100 Amps load so as long as you do not exceed this it is perfect for intended purpose. It [black cable] and the shunt will withstand much higher loads for short duration so if engine fires quickly we cannot see it being a problem.
 
BM1's work just fine for me. I have two.

I can't make sense of the suggestion that there is a tradeoff between whether to monitor and battery capacity - though both are important. My monitors tell me voltage and current which let me know what is going on - is something switched on? is a battery dangerously low? You might want to believe their % charge - it doesn't seem miles out.

Bigger batteries give you a bigger buffer - you've still got to put as much in as you take out. The advantage of bigger capacity is to cope with bigger peaks and troughs. I have big capacity because my pathetic underway charging capability means that I'm counting the days between shorepower mooorings to see if I can keep the fridge running. Capacity is great, but it is not a substitute for monitoring what is going on. Pre-monitor days I used to faff around with multi-meters (still do actually), but I glance at the monitors several times a day in passing and have a real time sense of present loads and remaining capacity.

I've been on huge yachts with less battery capacity than my wee one. They have worked just fine because they have had charging systems that can pump serious amps in. I don't have this option.
 
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