NASA battery monitor.

[Boat&Bikes]

I have been given a Nasa monitor BM1 model which has a 100amp shunt.Our boat has 4x110 leiure plus 1 x110 amp batteries.We also have a victron charger/inverter 1600 watts with i think from memory chargers at 70amp max.Engine is a Beta 38 twin alts i think 40 amp to starter and 75 amp to leisure batteries.My question is will the NASA monitor be ok to fit? Im not sure that the shunt is of sufficent capacity?

 

Cheers.

[by'eck]

You really need a higher current shunt. The Victron Combi with its inverter running at max power will draw 150 amps or more.

[Chalky]

I've got a nasa BM-1, 400Ah battery, 70A alternators, 800W inverter. The main problem you'll have is with the inverter. 1600W is well over 100A if running flat out. For short periods (seconds) the shunt would be ok, however it won't necessarily stand running full power continuously. Where the problem will come is in the BM-1 itself. It uses an integrator that feeds into an analogue input and this can get seriously out of sync for loads above its max design input. I've never had an issue but Gibbo suggested there is at least one unit on the market where exceeding the max threshold causes the calculation to become inverted (arithmetic overflow). The one we've got has issues with battery SoC and I mainly use it as a volt meter and ammeter, the battery SoC display being largely ignored.

[Boat&Bikes]

You really need a higher current shunt. The Victron Combi with its inverter running at max power will draw 150 amps or more.

 

We dont run the inverter at anywhere near max but i take your point.Do you know if its acceptable to use say a 200 amp shunt with a Nasa BM1? Also what would happen if we overloaded the shunt?

 

Cheers.

[by'eck]

The NASA BM2 has a 200 amp shunt but the manufacturers claim the shunts and wiring are not interchangeable with the BM1, although they are both standard 50mV (the voltage across the shunt at max rated current).

[Gibbo]

I've never had an issue but Gibbo suggested there is at least one unit on the market where exceeding the max threshold causes the calculation to become inverted (arithmetic overflow).

 

It wasn't me. I do remember someone else saying that.

Edited October 22, 2012 by Gibbo

[Proper Job]

The NASA BM2 has a 200 amp shunt but the manufacturers claim the shunts and wiring are not interchangeable with the BM1, although they are both standard 50mV (the voltage across the shunt at max rated current).

Isn't that why they're incompatable?

 

The BM1 equates 50mV as 100Amps

The BM2 equates 50mV as 200Amps

 

I bet there's something fairly simple inside them that makes the difference though

[Gibbo]

I bet there's something fairly simple inside them that makes the difference though

 

I bet there isn't

[Proper Job]

I bet there isn't

Just when I'm thinking life might be simple

[Bobbybass]

I bet there isn't

Smart gauge..that's what they need.

 

It will measure batteries...make the tea...and keep you warm on cold nights...

[Tony Brooks]

I bet there isn't

 

 

I suspect its firmware. If it is in some form of programmable ROM and you could get the image then maybe you could update it. However I expect it is all soldered and it is simply not practical.

[Proper Job]

Smart gauge..that's what they need.

 

...and keep you warm on cold nights...

Only if you omit to put the inline fuse in place and wire it up wrong

[Gibbo]

There will be gain setting resistors on the sense amplifier that would have to be changed. They will be the size of ant shit.

 

Then the firmware in the micro processor would have to be changed. The firmware will be copy protected so you won't be able to read it out anyway, and even if you could, it would take 6 months to work out what needed changing.

[Richard10002]

There is an opinion in the yachting world that the BM-1 will count in excess if 100Ah, but merely won't display over 100Ah. Similarly, the BM-2 will count in excess of 200Ah, but won't display.

 

A search of the forums on www.ybw.com would reveal the sources - I believe them to be well respected in engineering and electrical fields.

[Boat&Bikes]

So....safe to fit and if i exceed the 100amps it wont explode etc?

[smileypete]

Isn't that why they're incompatable?

 

The BM1 equates 50mV as 100Amps

The BM2 equates 50mV as 200Amps

 

I bet there's something fairly simple inside them that makes the difference though

OP could put a 75mV 150A shunt in, start about £6ish on Ebay. That will give 50mV at 100A but handle 150A no problem. Depends whether the BM is a working one and what it does when it sees >50mV on it's shunt input.

 

It might just read overload and not count it towards it's charge calculations, an email to their tech support might get the answer (and confirm it can't be converted to read 200A like a BM2)

 

Edit: Just read Richard10002's message above, sounds good.

 

cheers, Pete.

~smpt~

Edited October 22, 2012 by smileypete

[alan_fincher]

I don't know what margin of error is built in, but surely the greater possibility is that a 100 Amp shunt might not like having 150 Amps passed through it, rather than the monitor itself will get damaged if (say) 75 mV appears at the input.

 

Of course if you actually managed to completely burn the shunt out, then the monitor would end up seeing a lot more than 50 (or even 75) milliVolts, though.

Edited October 22, 2012 by alan_fincher

[bowten]

The Victron 1600/70 combi if fitted with the battery monitor BMV 600 supplied by Victron comes with a 500A/50mV shunt,so does this indicate that a 100 amp shunt is advisable?

Edited October 22, 2012 by bowten

[Gibbo]

I just checked a NASA BM1

 

It's a 50mV/100A shunt

 

Exceeding 50mV works for a small margin. It displays up to 104 amps then doesn't go any higher. It doesn't wrap around or do anything silly as someone else said they did.

 

The amp hour counter does not deal with anything higher than 104 amps. Despite what ybw say.

[Grace and Favour]

Smart gauge..that's what they need.

 

It will measure batteries...make the tea...and keep you warm on cold nights...

 

Are you sure that you don't mean a "Smart Girl"?

[Boat&Bikes]

I just checked a NASA BM1

 

It's a 50mV/100A shunt

 

Exceeding 50mV works for a small margin. It displays up to 104 amps then doesn't go any higher. It doesn't wrap around or do anything silly as someone else said they did.

 

The amp hour counter does not deal with anything higher than 104 amps. Despite what ybw say.

 

 

So would you think it ok to fit?

[Gibbo]

So would you think it ok to fit?

 

Your inverter will overload it.

 

Good engineering practice dictates that nothing is ever run at maximum rated capacity. Only a fool does that. Yet for some reaosn people run 100 amp shunts at 100 amps. A proper engineer would never run one past about 65 to 70 amps. Your inverter will be way higher than even 100 amps.

[Boat&Bikes]

Your inverter will overload it.

 

Good engineering practice dictates that nothing is ever run at maximum rated capacity. Only a fool does that. Yet for some reaosn people run 100 amp shunts at 100 amps. A proper engineer would never run one past about 65 to 70 amps. Your inverter will be way higher than even 100 amps.

 

 

Thanks for your help,guess i shall have to buy one with a bigger shunt.I am suprised that NASA make these as they would appear to be to small to be of much use.

 

Cheers,

 

Ian.

[Chalky]

Thanks for your help,guess i shall have to buy one with a bigger shunt.I am suprised that NASA make these as they would appear to be to small to be of much use.

 

Cheers,

 

Ian.

 

Looking at the rest of the kit they sell I suspect it's geared towards the yachting fraternity where there's less reliance on the engine and consequently lower power consumption.

[bowten]

The Victron 1600/70 combi if fitted with the battery monitor BMV 600 supplied by Victron comes with a 500A/50mV shunt,so does this indicate that a 100 amp shunt is advisable?

Obviously it doesn't.