Battery monitor shunt, Lithium.

[Neeves]

I assume your battery monitor is something like this:
Battery Monitor 50A/100A/350A VOLT Capacity Tester Voltmeter Ammeter DC 80V | eBay
As well as the wires going from the actual shunt resistance to the meter head, there seems to be an isolated terminal for a sense wire from the +ve terminal of the battery. This would go to the meter head unit via the same screened multi-way cable as the current sense lines. It probably powers the meter head as well as allowing the head unit to measure the battery volts.

That +ve wire should have a fuse in it near the battery.



The name 'shunt' for a parallel current path is long established, it's probably related to a railway shunting yard where you have lots of parallel tracks to sort goods wagons?
Rather than the colloquial term for a collision between vehicles.
As well as being a term for a current sensor, it can be an adjective for any component in parallel.

Ours is 'similar' but the shunts look identical. Our display is circular rather than rectangular. There are a number of suppliers of 'similar' products - I think they are different suppliers as their displays are different, different shape and different display colours. Oddly none of them define who actually makes them (so they could be made by the same company). Historically this was common, everything was simply defined as 'Made in China'. But they have become more brand conscious so the absence of a manufacturer is - odd.

You can buy through Aliexpress who we have found reliable - if things go wrong they honour their promises. We bought this kit through Temu as they ship from Oz and so far have been fast and reliable. In the past we have bought much direct from factories in China, we ran a business selling into China and have the linguistic skills - but Aliexpress and now Temu (who operate in the UK but certainly US) have made it easier

The meter is supplied with a short screened cable but they also supply a 1m extension, shown in the ad. The screened cable (shown in the ad) with the small rectangular plug connects to the white female socket on the shunt. We don't need the extension cable as the shunt is next to the meter. The sense wire runs from the positive pole of the battery to one of those 2 little grub screws or the the green socket on the shunt (it has two even smaller grub screws to secure the sense wire). There is no reason provided why there are effectively 4 different locations on the shunt for the sense wire. I made up the sense wire this afternoon but have not attached it yet. The connections of the sense wire to the shunt are decidedly fiddly, tiny, and I have the shunt attached to a panel, with the display above, and I'll need to take the shunt off to connect.

The main positive cable has 80 amp circuit breaker about 0.5m from the battery - I think you might be saying this is inadequate, too slow or not near enough...? I assume you refer to a 'T' fuse (not any old fuse).

Primary charging is solar with the facility to use a B2B off an alternator.

The problem is that I have no way of knowing the state of charge on the battery, hence the meter. I can read volts and amps but they don't tell me state of capacity.

Thanks for your input and for the background on the word shunt. Oddly the Chinese call it a 'Sampler' - as in 'it samples data'.

Jonathan

 

[Kelpie]

I'll bite - why then did you instal a battery mon?

I can think of other things to spend stg100 - first up, some malt whisky.

Jonathan.

I wanted to add a second battery, with its own BMS, so a monitor became necessary.
Mine cost about £50.
I'm glad I fitted it, it's much easier to glance at the screen than to switch to an app on my phone.

 

[B27]

Ours is 'similar' but the shunts look identical. Our display is circular rather than rectangular. There are a number of suppliers of 'similar' products - I think they are different suppliers as their displays are different, different shape and different display colours. Oddly none of them define who actually makes them (so they could be made by the same company). Historically this was common, everything was simply defined as 'Made in China'. But they have become more brand conscious so the absence of a manufacturer is - odd.

You can buy through Aliexpress who we have found reliable - if things go wrong they honour their promises. We bought this kit through Temu as they ship from Oz and so far have been fast and reliable. In the past we have bought much direct from factories in China, we ran a business selling into China and have the linguistic skills - but Aliexpress and now Temu (who operate in the UK but certainly US) have made it easier

The meter is supplied with a short screened cable but they also supply a 1m extension, shown in the ad. The screened cable (shown in the ad) with the small rectangular plug connects to the white female socket on the shunt. We don't need the extension cable as the shunt is next to the meter. The sense wire runs from the positive pole of the battery to one of those 2 little grub screws or the the green socket on the shunt (it has two even smaller grub screws to secure the sense wire). There is no reason provided why there are effectively 4 different locations on the shunt for the sense wire. I made up the sense wire this afternoon but have not attached it yet. The connections of the sense wire to the shunt are decidedly fiddly, tiny, and I have the shunt attached to a panel, with the display above, and I'll need to take the shunt off to connect.

The main positive cable has 80 amp circuit breaker about 0.5m from the battery - I think you might be saying this is inadequate, too slow or not near enough...? I assume you refer to a 'T' fuse (not any old fuse).

Primary charging is solar with the facility to use a B2B off an alternator.

The problem is that I have no way of knowing the state of charge on the battery, hence the meter. I can read volts and amps but they don't tell me state of capacity.

Thanks for your input and for the background on the word shunt. Oddly the Chinese call it a 'Sampler' - as in 'it samples data'.

Jonathan

The sense wire needs a fuse close to the + terminal of the battery, because that wire is thin and if shorted to ground will catch fire. It does not need to be any special fuse, probably just a 1A blade fuse or similar which will blow before that wire overheats.

IF you want to turn off your battery monitor to avoid it draining the battery when you're not using the boat, I would wire + terminal > fuse > switch > terminal on shunt.

The monitor won't draw much current so the voltage drop in that path should not matter, so long s nothing else is sharing any of the wiring. I have a small fuse box wired direct to the + terminal of the house battery, for solar charge and a bilge pump, I would wire the monitor sense lead to that.



By the way, I'm led to believe that some of these monitors are not really what we want, they only record discharge current, whereas we really want to either count charge and discharge separately, or the nett charge-discharge?

 

[rogerthebodger]

A 100Ah battery, whatever its chemistry, holds over a kWh of energy.
That's a lot of heat, enough to do a lot of damage or start a real fire.

I have 12 105 Ah Lead Acid batteries on my boat plus my engine start battery so I have a lot of stored energy.

I have 1800 liter Diesel capacity and all stored energy can be dangerous if misused.

Even compressed air/gas can be dangerous. I have seen compressed gas cylinders explode

Of cause an LPG cylinder when heated in a fire will cause major damage.

It all about taking procorousions to reduce the danger as everting in life

Batteries have fuses fuel tanks are fire proof material and LPG cylinders are in fire froof containers and have leak detection and control valves

It looks like LifePO4 batteries are the safest and as long as they are protected from fire like LPG and fused to shut off any short circuit's they should be no more dangerous than Lead Acid batteries and stored fuel/LPG or stored alcohol

On my boat I eplaces large shunts but Hall effect current detection devices to cut down on resistance , heat build up and any volt drop as my bow thruster is rated at 600 Amp consumption at 12 VDC

 

[B27]

I think lead-acid boat systems cause few problems because they are generally simple, and 'good practice' has evolved over time, based on 100 years of automobile experience.

I'm not sure I have complete confidence in amateur developments of relatively complicated stuff like BMS's, using things like alternators outside of what they were designed for, and the trend for higher levels of power and energy storage.

 

[rogerthebodger]

I'm not sure I have complete confidence in amateur developments of relatively complicated stuff like BMS's,

The difference in an amateur and professional development id the an anateur is not limited by cost and profit whereas a professional development is must take into account cost and profit

A Knowledgeable amateur and make a better job that a provisional who dose to make money.

It all about knowledge and skill and not is the person is considered an amatuer or profisional as one must make money whereas the other does not so had no time constraint

Also there is a syndrome that states someone who knows a little knowledge does not know what he does not know where as a person with a much wider range of knowledge knows what he does not know.

As the saying does a little knowledge is a dangerous thing

 

[mattonthesea]

Slightly off thread question: I have a NASA BM1 which has a 100A limit. Is this the monitor or the shunt limit? Could I replace the shunt with a higher rated one if I wanted to include the inverter current?

 

[rogerthebodger]

Slightly off thread question: I have a NASA BM1 which has a 100A limit. Is this the monitor or the shunt limit? Could I replace the shunt with a higher rated one if I wanted to include the inverter current?

IT a combination of both

The sun will dro a set voltage when 100 Amps pass through the shunt

The meter will then read tha volt drop and indicate 100 Amps on the indicator and use this in any calculations

If more the 100 amps pass through the shunt it will send too high a volt drop. It may not damage the meter but it may not to the calculation correctly

I used to have a 200 Amp shunt with a meter that would display 200 when 200 Amps passed through th shunt. In my case 600 Amps could pass through the shunt when my bow thruster operated . The meter would show an overload but no dambe would occur

 

[VicS]

Slightly off thread question: I have a NASA BM1 which has a 100A limit. Is this the monitor or the shunt limit? Could I replace the shunt with a higher rated one if I wanted to include the inverter current?

Nasa have been asked about this in the past, in connection with engine starting from the monitored battery bank
100 amps is the max reading which the BM1 will display. The shunt will safely carry considerably more but the display will not show more than 100 amps. Nasa said that the electronics will however use the actual current in its calculations of state of charge. There's probably a limit but Nasa have not said what that might be. You do not say what current your inverter will draw.

The shunt rating for the BM1 is 100amps, 50mV which means that when 100 amps flow through it the potential difference (pd) across it is 50mV. ( Ohms law therefore tells us that the actual resistance of the shunt is 0.5 mIlli-ohms ) The shunt for the BM2 is rated at 200amps, 50mv ( and has a resistance of 0.25milli-ohms )

If you change the shunt to one with a different resistance the calibration of the monitor will be completely wrong. If, for example, you fitted a BM2 shunt all the current readings will be only half of their actual value.

.

 

[Neeves]

The difference in an amateur and professional development id the an anateur is not limited by cost and profit whereas a professional development is must take into account cost and profit

A Knowledgeable amateur and make a better job that a provisional who dose to make money.

It all about knowledge and skill and not is the person is considered an amatuer or profisional as one must make money whereas the other does not so had no time constraint

Also there is a syndrome that states someone who knows a little knowledge does not know what he does not know where as a person with a much wider range of knowledge knows what he does not know.

As the saying does a little knowledge is a dangerous thing

I might disagree with part of your post. In some cases the professional will use top of the range and most expensive kit. Th owner may use kit fit for the task in hand but not on a Mercedes approved product list. Equally a professional will recommend top of the range, again he is not paying.

 

[Kelpie]

I might disagree with part of your post. In some cases the professional will use top of the range and most expensive kit. Th owner may use kit fit for the task in hand but not on a Mercedes approved product list. Equally a professional will recommend top of the range, again he is not paying.

Yes it's probably quite easy for a pro to just say 'Victron everything' and demand that you turn over your best food locker to the installation, to make it easier.

 

[Neeves]

The sense wire needs a fuse close to the + terminal of the battery, because that wire is thin and if shorted to ground will catch fire. It does not need to be any special fuse, probably just a 1A blade fuse or similar which will blow before that wire overheats.

IF you want to turn off your battery monitor to avoid it draining the battery when you're not using the boat, I would wire + terminal > fuse > switch > terminal on shunt.

The monitor won't draw much current so the voltage drop in that path should not matter, so long s nothing else is sharing any of the wiring. I have a small fuse box wired direct to the + terminal of the house battery, for solar charge and a bilge pump, I would wire the monitor sense lead to that.



By the way, I'm led to believe that some of these monitors are not really what we want, they only record discharge current, whereas we really want to either count charge and discharge separately, or the nett charge-discharge?

My understanding is they record the sum of input and output (which is what I'm used to as that is how the Xantrec worked). All the power in and out, or the sum of, is measured. The Xantrec then added or subtracted from the maximum capacity to deduce battery state (the Xantrex tended to go out of sync and needed re-zeroed over time). The only way to determine amps in was to switch off any power usage, the only way to determine, say solar, was turn everything else off. You could leave everything on and disconnect solar - the difference was the solar. You could do the same switching off each input or output in turn and determine what they contributed (or not)

My understanding is these units work similarly.

Other units may differentiate between different power sources, wind, solar alternator - but I don't know how as solar amps are the same as wind amps etc. I could envisage a system where individual amps produced or used could be measured and recorded and then used for totals etc - but it seems unnecessary and complicated (expensive)

I'll have a look at the positive wiring and see if I can add the sense wire to something else - or simply add a little fuse. I'm going to wire up the monitor later today and once I've ascertained everything works I'll disconnect the sense wire until I incorporate a fuse. Thank you for the advice. I did wonder about overheating the sense wire - and then dismissed it. I'm glad you mentioned it.

My next door neighbour is an electrician - he is supervising. I am also asking here and assimilating the comments.

My views are similar to yours - there are dangers in allowing amateurs access to certain technologies and systems - yachting is the perfect example where we can modify anything and as long as nothing goes wrong - no-one knows. Modify gas, electrics, water (salt and fresh) and no-one other than the person doing it knows. These, or this, forum actually encourages this. Threads on building Lithium battery banks and all that implies are here for anyone to read and act on. We all have responsibilities in what we post, or do not post. Being an expert and seeing an error and not posting to correct the error (because of pride or dislike of an individual member) is immoral.

Jonathan

 

[Neeves]

Yes it's probably quite easy for a pro to just say 'Victron everything' and demand that you turn over your best food locker to the installation, to make it easier.

My meter costs 1/3 that of the NASA or Victron units - if it works, great - if it does not work, I've wasted a lot of time but I'll get my money back.

But if it works and I extrapolate the savings - its huge.

Coopec (what happened to him) maybe he is sailing, built his own 43' yacht. I wonder how much he saved. It would be interesting to know. He was PBO in the flesh (or at least on the internet) and in THIS forum.

Jonathan

 

[Neeves]

If you change the shunt to one with a different resistance the calibration of the monitor will be completely wrong. If, for example, you fitted a BM2 shunt all the current readings will be only half of their actual value.

.

Except that you can recalibrate the meter. The meter needs owner input of the battery capacity. The meter I am using is the same meter for no shunt upto a 350 amp shunt - and if you bought the wrong shunt then you need a new (another) shunt - but the meter is the same. Or that is my understanding from someone who made the mistake - though he might have been selective in admitting his error.

I was under the impression that the NASA Lithium unit is different to the Lead unit but the displays are the same whatever shunt you use.

But it was not important and I did not exhaustively investigate.

Jonathan

 

[VicS]

Except that you can recalibrate the meter. The meter needs owner input of the battery capacity. The meter I am using is the same meter for no shunt upto a 350 amp shunt - and if you bought the wrong shunt then you need a new (another) shunt - but the meter is the same. Or that is my understanding from someone who made the mistake - though he might have been selective in admitting his error.

I was under the impression that the NASA Lithium unit is different to the Lead unit but the displays are the same whatever shunt you use.

But it was not important and I did not exhaustively investigate.

Jonathan

You can zero the current reading but you cannot alter the calibration.
The BM1 and BM1 lithium use a 100amp 50mV shunt, The BM2 uses a 200amp 50mV shunt

The BM1 lithium version differs in the way it calculates the % SoC and time to charge or discharge but It measures the current in the same way as the lead version

 

[Neeves]

The sense wire needs a fuse close to the + terminal of the battery, because that wire is thin and if shorted to ground will catch fire. It does not need to be any special fuse, probably just a 1A blade fuse or similar which will blow before that wire overheats.

IF you want to turn off your battery monitor to avoid it draining the battery when you're not using the boat, I would wire + terminal > fuse > switch > terminal on shunt.

I'm not going to ignore your advice - I will add a fuse. Again my thanks.

For my own education: Why might the suppliers of the shunt not recommend a fuse. They have no idea how the components might be wired and cannot know that it might be possible to, accidentally, earth the Sense wire

Our sense wire has a plastic cover, as do most cables, and we have used double thickness of heat shrink at each end and there is a minimum of bare wire, enough to wire to the positive pole on the battery and more than enough for the connection to the shunt (its over long and I'll cut back when I find how much I need).

Jonathan

 

[Neeves]

I assume your battery monitor is something like this:
Battery Monitor 50A/100A/350A VOLT Capacity Tester Voltmeter Ammeter DC 80V | eBay
As well as the wires going from the actual shunt resistance to the meter head, there seems to be an isolated terminal for a sense wire from the +ve terminal of the battery. This would go to the meter head unit via the same screened multi-way cable as the current sense lines. It probably powers the meter head as well as allowing the head unit to measure the battery volts.

That +ve wire should have a fuse in it near the battery.

Its a steep learning curve

The two little brass threaded connectors are NOT for the sense cable, they simply short the battery when you attach the sense cable - guess how I know.

No harm done.

The sense cable connectors, the little green socket below the rectangular meter socket, are tiny (see the picture in the link provided by B27). They do not offer a robust nor secure point to attach the sense cable - as is (which can be as thin as 0.3mm). I have decided to use the largest single copper wire I can find and crimp the sense cable to the copper wire. A single copper wire can be securely inserted into the female connector and then crimp the sense cable to the wire (the single copper wire will be about 1mm).

I have seen the connector for the sense wire in computers - where they might be ideal, small wire diameter, used within a secure 'box' etc. In leisure application where the wiring needs to be both secure and robust - not the best choice.

One step forward, one step back. When I have the meter installed I'll be an expert - worthy of the high charges of marine electricians - but I only need to do it once!

Jonathan

 

[mattonthesea]

Nasa have been asked about this in the past, in connection with engine starting from the monitored battery bank
100 amps is the max reading which the BM1 will display. The shunt will safely carry considerably more but the display will not show more than 100 amps. Nasa said that the electronics will however use the actual current in its calculations of state of charge. There's probably a limit but Nasa have not said what that might be. You do not say what current your inverter will draw.

It's a 1kW inverter but the blurb says it will give twice that for a short while for the surge power off things starting up. So a short burst of 170A from time to time but mainly up to 85A

 

[Neeves]

After the few hiccups I have the meter installed and working as expected. Reads voltage, amps and total battery capacity (and more). It does not define amps in, amps out but simply calculates totals so adds input, usage and displays total and then adds, or subtracts, this to the battery capacity. It also has a memory function but I have not had time to use this.

The shunt meter display, the round meter in the green board, indicating battery capacity at 100% and Amps being used of 6.364 amps. The upper display totally independent of the shunt meter defines voltage of 13.8 volts. The new negative bus bar is in the bottom eight of the picture


This, below, a poor picture of the shunt. The sensing wire is to be joined to the green, cubic terminal block. Using wire from domestic electric cabling was the solution. As B27 suggested the power to the display is via the sense cable.

Not bad for a cheap, rejected (by most), meter.

 

[Neeves]

So far our cheap and cheerful battery monitor aka 'a coulomb meter' - with shunt costs at least half that of a mainstream supplier. Our meter does what it says on the box, see posts above. It mayn't be blue tooth enabled. Most are not waterproof - the one we bought is waterproof (one reason to choose that particular unit) but what water proof means is not part of specification.

The displays are either around 50mm circular or rectangular.

Most of these cheap units are made in China and look very similar, if not identical to each other. They are supplied with no shunt and upto a 350 amp shunt. It may be possible to source one, some, with bigger shunts - it was not of interest us. The absence of a shunt and/or its size determines price, bigger shunt slight higher price.

Our installation and usage instructions were simple, if a bit 'quaint'. Installation only needed patience and very small fingers.

If you are interested simply google "coulomb meter" ; 'battery monitor with shunt" and add Lithium if that is the application (they are offered for Lead as well).

You will get hits from eBay, Temu, Aliexpress and a number of other outlets. They all look the same....

We bought through Temu - you make your own decisions (our meter has only been in use for a day - hardly time to offer a cast iron warranty). Delivery was swift, within a week. The unit was exceptionally well packed, heat sealed poly bag outer, bubble wrap inside, then a small, robust cardboard box with a foam insert and the two items in recesses in the foam.

Good luck

Jonathan