Bluetooth battery monitor

[Bewildered]

500A shunts are widely available from about £20. Firstly you'd have to ensure the voltage is correct and secondly you might have to multiply the Nasa reading by 5. Might be worth asking them 'Can I use this with a 500A shunt?"

The instructions that come with the BM2 clearly state that you cannot use the shut from the BM1

The units are only calibrated for the shunt supplied. I suspect it would work but not accurately; what use is an inaccurate meter?

[WotEver]

The instructions that come with the BM2 clearly state that you cannot use the shut from the BM1

The units are only calibrated for the shunt supplied. I suspect it would work but not accurately; what use is an inaccurate meter?

It would be totally accurate, just read 20% of actual.

 

Who wants to keep doing the maths? No-one would be my guess.

[Psycloud]

I quite like the look of this new battery monitor from Nasa. Shame it only has a 100A shunt. I don't think this is enough as I have a 2,000W inverter. 100A seems low in this day and age.

 

Has anyone tried one? I like the bluetooth feature as I can monitor my batteries when driving and from the saloon, in the evenings!

 

£90 is not bad.

 

We have the original BM1 and a 2500w inverter and they seem to play nicely. It's rare that we would use anything like 2500w though so can't say we've gone up the maximum.

[mross]

Agreed, but what would happen to the shunt if you ran 200A through it for 30 minutes? My guess it that it would overheat. In many boats this might increase the risk of a fire. Just saying.

[MtB]

Agreed, but what would happen to the shunt if you ran 200A through it for 30 minutes?

 

 

The battery bank would expire!

[Guest]

Yeah but, apart from that list, what can it do that you can't do with a slide rule? It'll never catch on.

True enough.

 

When we were kids we used to play with a block of wood, on which we would draw a keypad and a screen, and in our games these were like a smartphone that could open doors and stuff as well as communicate etc. I am still waiting for payments re. the patent. Mine had a laser cutter built into it, which my Iphone doesn't have yet.

 

If Moore's law continues to be obeyed, we aint seen nothin' yet.

[Sea Dog]

If Moore's law continues to be obeyed, we aint seen nothin' yet.

 

Anyone not familiar with Moore's Law can Google it on their smartphone. Well, maybe not everyone....

[hounddog]

It would be totally accurate, just read 20% of actual.

 

Who wants to keep doing the maths? No-one would be my guess.

it's a bit daft in this day and age that the shunt size isn't selectable in software. Computers multiply more reliably than humans.

 

As for a meter you can read on a smartphone, with a clearly lit screen and not in a pokey cupboard? wonderful.

Agreed, but what would happen to the shunt if you ran 200A through it for 30 minutes? My guess it that it would overheat. In many boats this might increase the risk of a fire. Just saying.

why on earth would a 200A shunt overheat with 200A through it ? Think man, think.

 

Clue; it has to dissipate 10W at 50mV, less than an old-fashioned light bulb.

[WotEver]

why on earth would a 200A shunt overheat with 200A through it ? Think man, think.

 

Clue; it has to dissipate 10W at 50mV, less than an old-fashioned light bulb.

It's a 100A shunt, that was his point.

[dmr]

it's a bit daft in this day and age that the shunt size isn't selectable in software. Computers multiply more reliably than humans.

 

As for a meter you can read on a smartphone, with a clearly lit screen and not in a pokey cupboard? wonderful.

 

why on earth would a 200A shunt overheat with 200A through it ? Think man, think.

 

Clue; it has to dissipate 10W at 50mV, less than an old-fashioned light bulb.

 

Many shunts, probably most, are not designed to carry their full rated current long term, something like 50% is the most they should carry continuously. I think I have also read that they loose accuracy if overheated, they are made out of funny metal.

 

...............Dave

[mross]

And some shunts have plastic components..........

[Geo]

it's a bit daft in this day and age that the shunt size isn't selectable in software. Computers multiply more reliably than humans.

 

As for a meter you can read on a smartphone, with a clearly lit screen and not in a pokey cupboard? wonderful.

 

why on earth would a 200A shunt overheat with 200A through it ? Think man, think.

 

Clue; it has to dissipate 10W at 50mV, less than an old-fashioned light bulb.

 

I think you will find that to maintain the accuracy specified for the monitor; the shunt and monitor will need to be calibrated as a unit. Some of the shunts on the market have an accuracy of worse than 10% from tests done on my bench.

[cuthound]

I think you will find that to maintain the accuracy specified for the monitor; the shunt and monitor will need to be calibrated as a unit. Some of the shunts on the market have an accuracy of worse than 10% from tests done on my bench.

Also as the shunt is in series with the load it will carry all of the load, so use be rated for this.

[dmr]

Speak to

 

Also as the shunt is in series with the load it will carry all of the load, so use be rated for this.

 

Well yes, a shunt would be of rather limited use if it did Not carry all of the load.

 

.............Dave

It should be possible to use a larger shunt as long as it produces a similar full scale output voltage. The next stage is to write your own app to display the results after a suitable multiplication.

The manufacturers might be willing to release details of their bluetooth data format which would help, but in my (limited) experience bluetooth communications are usually done with pretty standard serial protocols and ASCII data.

 

A little project for the winter anyone???????

 

..............Dave

[WotEver]

Bunch of shunts cheap on eBay. All with a quoted accuracy of 0.5% FS.

http://m.ebay.co.uk/itm/291412298959?_mwBanner=1

 

They're 75mV ones though.

 

It just shows that cheap doesn't mean low accuracy (necessarily).

[Geo]

Bunch of shunts cheap on eBay. All with a quoted accuracy of 0.5% FS.

http://m.ebay.co.uk/itm/291412298959?_mwBanner=1

 

They're 75mV ones though.

 

It just shows that cheap doesn't mean low accuracy (necessarily).

 

Specifications:

Voltage Drop: 75mV

Accuracy: Class 0.5

 

Can't agree it says Accuracy: Class 0.5 . 0.5 of what or what unit, and it certainly does not say FS

Edited November 27, 2016 by Geo

[WotEver]

Class 0.5 generally means FS.

 

From Wikipedia:

Class 0.5 is an ANSI C12.20 accuracy class for electric meters with absolute accuracy better than ± 0.5% of the nominal full scale reading.

https://en.m.wikipedia.org/wiki/Accuracy_class

 

Of course, they could be lying, virtually no come-back to a Chinese supplier.

Edited November 27, 2016 by WotEver

[WotEver]

It's not as bad as Victron's claimed 'Display accuracy' of 0.1% of SoC for the BMV. It's totally meaningless without an 'SoC accuracy' which they studiously avoid supplying.

 

Edited to change the ludicrous 0.5% figure to an even more ludicrous 0.1%

Edited November 27, 2016 by WotEver

[Geo]

Class 0.5 generally means FS.

 

From Wikipedia:

https://en.m.wikipedia.org/wiki/Accuracy_class

 

Of course, they could be lying, virtually no come-back to a Chinese supplier.

 

They have not specified ANSI, basically it means nothing. and no Class 0.5 does not generally means FS unless ANSI is specified. Ir was similar that on my bench gave nominal 10% of full range.

 

As for Victron

 

It's not as bad as Victron's claimed 'Display accuracy' of 0.5% of SoC for the BMV. It's totally meaningless without an 'SoC accuracy' which they studiously avoid supplying.

 

That is interesting and from where do you get that from?

 

From my copy of the spec for the BMV 602

 

Readout resolution:

Voltage (0 ... 100 V) ±0.01 V

Voltage (100 … 385 V) ±0.1 V

Current (0 ... 10 A) ±0.01 A

Current (10 ... 500 A) ±0.1 A

Current (500 ... 9999 A) ±1 A

Amp hours (0 ... 100 Ah) ±0.1 Ah

Amp hours (100 ... 9999 Ah) ±1 Ah

State-of-charge (0 ... 100 %) ±0.1 %

Time-to-go (0 ... 1 h) ±1 minute

Time-to-go (1 ... 240 h) ±1 h

Voltage measurement accuracy ±0.3 %

Current measurement accuracy ±0.5 %

Now that gives current measurement accuracy as +- 0.5%

and for

State-of-charge (0 ... 100 %) ±0.1 %

But at the head of that column is; Readout resolution:

For the BMV 700 series they have improved

Accuracy of current measurement ± 0,4%

and

State of charge (0 – 100%) ± 0,1% stays as it was, Resolution that is.

I would suggest that as the accuracy of SoC relies on settings made by the user there is no way Victron can state an accuracy for SoC readout. Settings incorrect etc etc. However it does give the user the advantages of voltage and current reading to a good accuracy which if it has been set up properly and accurately should give an accurate SoC so long as the battery is fully charged each time and an eye kept open for capacity degradation and setting adjusted. Of course its current and voltage accuracy is better than the smartgauge's

Smartgauge Accuracies

STATE OF CHARGE (CHARGE) +/- 10%

STATE OF CHARGE (DISCHARGE) +/- 5%

VOLTAGE +/- 0.5%

Edited November 27, 2016 by Geo

[WotEver]

Yeah, even more useless.

 

It gives a readout of a meaninglessly inaccurate figure (so inaccurate that they don't give a figure for it) of 0.1%.

 

I can give any boater in the country a reading that's within 0.1% of what I want it to be from the comfort of my own armchair. It won't mean anything though, just like Victron's won't.

 

Would be good if you read the specs right.

Edited November 27, 2016 by WotEver

[WotEver]

 

I've corrected the daft 0.5% to the even more daft 0.1%.

[WotEver]

I note that rather than reply to me you went back and edited your post 20 minutes after I replied. No need to be so shy.

 

As you correctly point out, there are so many settings that the Victron gives the user the opportunity to muck up it's impossible for them to give an SoC accuracy. I wasn't going to mention it but thank you for demonstrating that with zero user intervention the SmartGauge will always be within 5% accurate for SoC on discharge. No ifs, no buts, no messing, it just works. Unlike the Victron.

[Geo]

Yeah, even more useless.

 

It gives a readout of a meaninglessly inaccurate figure (so inaccurate that they don't give a figure for it) of 0.1%.

 

I can give any boater in the country a reading that's within 0.1% of what I want it to be from the comfort of my own armchair. It won't mean anything though, just like Victron's won't.

 

Would be good if you read the specs right.

 

 

I've corrected the daft 0.5% to the even more daft 0.1%.

 

 

I note that rather than reply to me you went back and edited your post 20 minutes after I replied. No need to be so shy.

 

As you correctly point out, there are so many settings that the Victron gives the user the opportunity to muck up it's impossible for them to give an SoC accuracy. I wasn't going to mention it but thank you for demonstrating that with zero user intervention the SmartGauge will always be within 5% accurate for SoC on discharge. No ifs, no buts, no messing, it just works. Unlike the Victron.

 

Ah so how have I read the specs wrong?

 

You see it does tell me you are not a qualified engineer when you cannot distinguish between a resolution and an accuracy for an instrument.

 

As for editing my post you are much mistaken, the edit was to add the the smartgauge accuracies, it took a few minutes to find the Merlin spec for it. I felt it was only fair to put the information for the two together rather than just post grumbling about one monitor as you did without putting up the information correctly.

 

BTW none of the spec information was typed it was all cut n pasted from the relevant pdf pages, so did not need editing and was not edited or altered by me.

 

So for the second time of asking where did you get the information "Victron's claimed 'Display accuracy' of 0.5% of SoC for the BMV." from because it was totally wrong.

 

ETA and still is totally wrong

Edited November 27, 2016 by Geo

[WotEver]

I'm no engineer. I'm just a guy that knows a bit about some subjects and a master of only a very few (and still learning about those).

 

And I know when someone is squirming and obfuscating too

[Geo]

I'm no engineer. I'm just a guy that knows a bit about some subjects and a master of only a very few (and still learning about those).

 

And I know when someone is squirming and obfuscating too

 

lol and you claim I am read a spec wrong lmao

 

Maybe you should not make statements that are not correct, then they would not need correcting