Strange Nasa BM1 problem

VicMallows said:
We'll it seems you DO have other connection(s) to the domestic bank negative, apart from the shunt.

As we have all said numerous times, the negative side of the domestic battery bank must ONLY be connected to the shunt ..... not to the starter battery negative ..... not to anything else. (as per VicS diagrams).

ALL other connections should be to the other side of the shunt (or to a something connected to the other side of the shunt, such as a busbar or the engine block).

Vic
Click to expand...
hi so your saying take the starter battery and the inverter neg to the bus bar as per first pic
if thats the case il try that cheers Mark
 
foden01 said:
hi so your saying take the starter battery and the inverter neg to the bus bar as per first pic
if thats the case il try that cheers Mark
Click to expand...

Essentially yes. However the starter battery negative needs to go as directly as possible to the starter negative (almost certainly the engine block). There should also NOT be a direct connection to the engine block from the domestic battery negative ...... only (if at all) from the busbar side of the shunt.


(VicS .... pics are there OK for me)

Vic
 
VicMallows said:
................................................................................
(VicS .... pics are there OK for me)

Vic
Click to expand...

That's odd all I see are messages that say they have been moved or deleted.
:confused:

However you have hopefully identified Foden01's problem .
 
VicMallows said:
Agree. Tried to do a screen-grab but failed miserably. Basically the pic showed the two domestic batteries paralleled, with quite a few further connections to the two negative posts.

Vic
Click to expand...

The pictures have now appeared ! Can see them in Foden01's Photobucket album too!
( really mystified by that)

As you say too many connections on the( negative) battery posts. There must be only one and that one is the shunt.

The other side of the shunt should go to a bus bar and all the other negative connections should be transferred to that bus bar

Also when two batteries are connected in parallel the positive terminal of one should be used as the combined positive terminal for the pair and the negative terminal of the other should be used as the common negative terminal.
More details about this and how to connected three or more in parallel to be found at http://www.smartgauge.co.uk/batt_con.html
 
VicS said:
No, same two messages.

I can edit the links and go to the album where they should be. http://s441.photobucket.com/albums/qq139/lockkeeper01/
but they aren't there.

They must have been deleted after you viewed them and you are now viewing cached pictures on your computer.

Or something...?
Click to expand...

Other shot appears to have a lot of power electronics in a small area, with two heatsinks the wrong way round.

Brian
 
My own BM-1 suffered from no discharge reading from new in March of this year until the last month or so when it suddenly began to show a 0.2A discharge. Even though I then reset the monitor, on returning the following weekend it was once again showing the 0.2A discharge. I now have to go to the hassle of actually removing the positive battery connections each time I leave the boat, else after a week the monitor will show a total loss of charge of 35A.

Aaaaaaarghh!
 
Babylon said:
I now have to go to the hassle of actually removing the positive battery connections each time I leave the boat, else after a week the monitor will show a total loss of charge of 35A.
Click to expand...

Mine has always exhibited this 'zero-drift' problem .... and I rather assumed it was just an inherent design problem (my batteries are totally isolated when I leave the boat apart from the BM-1 itself). It is just as likely to be a net charge as a discharge, and no amount of trying to find the exact 'zero' setting helps. I have reached the conclusion that the zero setting is dependent on the precise battery voltage, suggesting poor internal voltage regulation in the BM-1. Temperature may be a factor, but I'm sure it is predominantly voltage related.

After a week or so away I simply reset the AH counter. If I expect to leave the boat for longer I disconnect the BM-1 anyway to save the small but significant current drain.

Vic
 
foden01 said:
hi Brian it is a small area i have fitted another fan to work in line with the fan you see on top of the heatsink
Click to expand...

You can get a cheap digital thermometer with a remote sensor, on Ebay for a couple of quid, allow you to keep your eye on the temp. The heatsinks should have the fins vertical, two look horizontal, if you are looking down onto them.

Brian
 
VicMallows said:
. I have reached the conclusion that the zero setting is dependent on the precise battery voltage, suggesting poor internal voltage regulation in the BM-1. Temperature may be a factor, but I'm sure it is predominantly voltage related.
Click to expand...

It is more likely zero drift due to the very low voltages/currents you are using to monitor current, coupled to temp variation in components.

Just try working out what voltage 0.2 amp represents at the shunt, assuming a 100A 50 mV, 0.2 amp = 0.0001 volt. this you have to get to the gauge via all the cable, terminal, terminal blocks, factor in that resistance varies with temp, feed that into the electronics that are also temp dependent.

It's one of the problems with battery monitoring, current counting or trying to read voltages, to many variables, what you get is only a guide.

Brian
 
halcyon said:
You can get a cheap digital thermometer with a remote sensor, on Ebay for a couple of quid, allow you to keep your eye on the temp. The heatsinks should have the fins vertical, two look horizontal, if you are looking down onto them.

Brian
Click to expand...

hi Brian can you send us a link to one of these digital thermometer cheers Mark
 
halcyon said:
It's one of the problems with battery monitoring, current counting or trying to read voltages, to many variables, what you get is only a guide.
Click to expand...

True, and I am quite happy working around the limitations as indicated. After all this is relatively cheap mass produced equipment ..... not top-end laboratory stuff.

I think though it would save people a lot of confusion if the manufacturers were a bit more honest and acknowledged the limitations, rather than make bland comments like "the instrument MUST be left connected at all times to ensure accuracy". In the case of the BM-1 specifically this is blatantly untrue.

Vic
 
foden01 said:
hi Brian can you send us a link to one of these digital thermometer cheers Mark
Click to expand...

The item number is 260664662399, £3.25, I have one in my chiller box, trying to find time to see it my thermostat will work, and give me a useable amperage consumption.

Brian
 
VicMallows said:
True, and I am quite happy working around the limitations as indicated. After all this is relatively cheap mass produced equipment ..... not top-end laboratory stuff.

I think though it would save people a lot of confusion if the manufacturers were a bit more honest and acknowledged the limitations, rather than make bland comments like "the instrument MUST be left connected at all times to ensure accuracy". In the case of the BM-1 specifically this is blatantly untrue.

Vic
Click to expand...

Totally agree, I've spent the last 30 years playing with battery monitoring, I don't have the nerve to make some of the claims I see people make.

A lot comes down to not what you say, but what you infure, but don't say.
Maybe that's why I'm not retired, and still working.

Brian
 
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