# BM1 battery monitor review and installation with pics



## andyandsue

After good advice from a few members on MHF ive bought and fitted a BM1 battery monitor and what a great bit of kit it is. Im an industrial / commercial electrician familiar with large complex installations and the BM1 was up to my high standards
The kit was well packaged with an LCD screen with night light,a protective cover,a 5m long prewired loom with quality lugs fitted,and a 100amp shunt. All connections come pre made-off to tinned ends or well fixed lugs( tug tested)

the meter shows whether the battery set is charging or discharging and by how much in amps and total time to fullcharge /discharge at that rate. other screens show amps and volts of supply at that time and % charge and total ah,s used since you reset the meter. It shows a real -time charge current for all your inputs, alternator, solar,EHU, and whatever else you've got connected .
The meter works by constantly monitoring the current flowing through a 100 amp shunt in the neutral return to the main battery terminal. Ive used shunts in the workshop and the one supplied is well made .accurate and tough. The voltage is monitored at the battery terminal for accuracy.The figures are combined in the unit then temp compensated and pushed through some good software to give an accurate estimation of AH stored( more difficult than it first seems...trust me )
The installation would be relatively easy for a competent diy-er with the only tricky bit being the tidying -up need to ensure the battery/batteries only have one neutral return cable which can be the rerouted through the shunt.I took this opportunity to install a large double pole connector block ( used in household meter cupboards some times £8) to tidy up my collection of battery leads and feeds to invertors etc. The connector block has 10 connections each able to take 35mm cable. The shunt was mounted in a double ip65 plastic box for security/safety as it has large uninsulated connections.
The monitor was fitted as part of a battery renewal /reposition project and the addition of the BM1 seem to me a perfect addition. The bm1 has a 100 amp capacity whilst the bm2 can measure 200 amp and has the facility to show starter battery voltage( but not AHs)
If you are thinking of replacing your batteries i would strongly recommend the BM1

I have no connection what so ever with the company who make the BM1

ANDREW G


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## andyandsue

*and a pic of the double pole connector*

the double ploe connector uded to tidy up wiring


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## Techno100

Very good thanks but I would not get into the habit of calling negatives neutrals. One of the main aspects of the Regs is to make sure everyone uses the correct language to avoid confusion


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## wakk44

A good clear write up with photos and very useful to anyone thinking of installing one of these monitors.

I have the compact version and concur with Andy's comments on this unit,they are an essential item for anyone that wild camps off hook up extensively.

The only negative criticism I have is that the circuit has to put into a discharge state before the % leisure battery capacity will update.Not really important though and I would not hesitate to recommend the Nasa BM1.


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## andyandsue

*cheers techno*

as a time served JIB electrician with a well used C&G 2391 and a HND in electrical and electronic engineering its always useful to be pulled up on terminology .


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## andyandsue

*yes update is tricky*

Yes wakk it must be a bit tricky for designers , i think the marine users will have a more suitable use regime for the set up for resetting the % level
Still compared to other % level meters( which just run of voltage readings) ive seen its not bad 
The really useful function is the amps function in real time i think


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## Techno100

Mine was dealer fitted by previous owner and it is no where near the tidy job yours is but it's on my to do list :wink:


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## andyandsue

*thanks*

thanks techno, i think its a great bit of kit but what might stuff a few folks is the need to ensure that the negative( never too old) is totally clean before it passes through the shunt, ive read a couple of posts complaining about inaccurate meters and it eventually transpired that a neutral had still remained on the battery terminal. the manual is very clear about it but when you poke your nose in peoples battery compartment it usually resembles a birds nest


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## Techno100

The LCD displays tend to bleed in the corners over time too but there is nothing to prevent it happening.


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## andyandsue

*lcd v led*

yes its a bit of a compromise, i looked at a couple of Chinese made meters which are LED and the" stand-by" current level was to high for me...also LEDS can make the van look like a disco sometimes

As we ski in the van ill be interested to see what happens to the LCD when the temp drops to near zero!!!


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## wakk44

*Re: yes update is tricky*



andyandsue said:


> ......................
> The really useful function is the amps function in real time i think


Definitely,this is the vital information for those of us carefully counting A/H.

To be able to calculate how much current each 12 volt appliance is consuming is very useful,my comment about the updating is relatively minor-the unit is one of the best accessories you can fit in a motorhome.


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## vicdicdoc

I fitted one of these in my van several years ago - worth every penny as I know exactly what's going into & out of the batteries


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## peedee

I really must get round to fitting mine, I have only had it 8 months!
peedee


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## andyandsue

*get it fixed peedeee*

get it fixed. Its display is better than the TV and its got 4 channels


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## Philippft

Well not being a sparky I found this a bit confusing to say the least.
I have a new motorhome with the Sargent EC500 power supply unit with the EC300 power control system fitted, so assume my charging system is 'up to date' and requires no further improvement. 

(Someone will challenge that for sure!).

Anyhow, moving on, can someone please explain to me what a 'shunt' is, it's purpose and function.

Thanks in advance.


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## Penquin

A related question, and probably no-one can give a definitive answer.....

I am looking at fitting such a monitor and have read excellent reviews of the Victron BMV 600 as well as some very good reviews of the Nasa BM1.......

I have also read that the BM1 does not do as much and is not good at zeroing when fully charged.....

Has anyone any strong views on the two? It is VERY unlikely that anyone has ever done a direct comparison, but who knows?

There is a considerable difference in price (about £105 for the Nasa BM1 and about £130 for the Victron), so is there a sufficiently clear advantage in the Victron over the Nasa?

Not exactly on topic - the pics that have been posted of the installation are superbly clear and there are several clear pointers to successful installation - such as the essential "clean up" of the negative (point noted :lol: ) connection.

Any advice would be greatly appreciated, thanks in advance and I hope this is not too far off the original topic as it may well reinforce the installation......

Dave


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## listerdiesel

Philippft said:


> Anyhow, moving on, can someone please explain to me what a 'shunt' is, it's purpose and function.
> Thanks in advance.


It's a current-carrying device that enables the main current in a circuit to pass through its body, while the device actually showing that current is a much lower current meter which takes a proportion of that main current to read.

Typically, a 60mV / 100A shunt would be used to measure up to 100A, while the meter itself only needs 60mV to read full scale.

http://en.wikipedia.org/wiki/Shunt_(electrical)

We use them all the time in our chargers, from 10A up to 250A, but the meters are always 60mV, we just change the scales for different current ranges. The shunt output is also used by the charger to detect its output current.

Peter


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## javea

Penquin said:


> A related question, and probably no-one can give a definitive answer.....
> 
> I am looking at fitting such a monitor and have read excellent reviews of the Victron BMV 600 as well as some very good reviews of the Nasa BM1.......
> 
> I have also read that the BM1 does not do as much and is not good at zeroing when fully charged.....
> 
> Has anyone any strong views on the two? It is VERY unlikely that anyone has ever done a direct comparison, but who knows?
> 
> There is a considerable difference in price (about £105 for the Nasa BM1 and about £130 for the Victron), so is there a sufficiently clear advantage in the Victron over the Nasa?
> 
> Not exactly on topic - the pics that have been posted of the installation are superbly clear and there are several clear pointers to successful installation - such as the essential "clean up" of the negative (point noted :lol: ) connection.
> 
> Any advice would be greatly appreciated, thanks in advance and I hope this is not too far off the original topic as it may well reinforce the installation......
> 
> Dave


 

I went for the Victron because Eddie at Vanbitz said it was the better device and he knows about these things!


Mike


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## airstream

*Midland Chandlers*

Hi,
Depending if you are in a rush to buy? Midland Chandlers do a "freaky friday" where a 20% discount is offered

The price at MC is £130 so with discount its around the same price

You get a larger shunt with the Victron - which is best I have no idea I have two Victron - one in boat one in van both 6yrs old and no probs

Next "freaky friday" may not be until March but you would need to ring a branch and see if they can advise

Ray


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## Philippft

.[/quote]

It's a current-carrying device that enables the main current in a circuit to pass through its body, while the device actually showing that current is a much lower current meter which takes a proportion of that main current to read.

Peter[/quote]

Thank you Peter.

All of that is completely lost on me!


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## eddievanbitz

Penquin said:


> A related question, and probably no-one can give a definitive answer.....
> 
> I am looking at fitting such a monitor and have read excellent reviews of the Victron BMV 600 as well as some very good reviews of the Nasa BM1.......
> 
> I have also read that the BM1 does not do as much and is not good at zeroing when fully charged.....
> 
> Has anyone any strong views on the two? It is VERY unlikely that anyone has ever done a direct comparison, but who knows?
> 
> There is a considerable difference in price (about £105 for the Nasa BM1 and about £130 for the Victron), so is there a sufficiently clear advantage in the Victron over the Nasa?
> 
> Not exactly on topic - the pics that have been posted of the installation are superbly clear and there are several clear pointers to successful installation - such as the essential "clean up" of the negative (point noted :lol: ) connection.
> 
> Any advice would be greatly appreciated, thanks in advance and I hope this is not too far off the original topic as it may well reinforce the installation......
> 
> Dave


Hi Dave the Victron will work accurately with Solar panels the Nasa doesn't.

We made Nasa aware of this about three years ago and they didn't seem to care as it is, primarily marine product where panels are used a lot less.

Other than that you can read it without your glasses

Eddie


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## andyandsue

*problem*

whats the prob with panel eddie


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## Penquin

eddievanbitz said:


> Hi Dave the Victron will work accurately with Solar panels the Nasa doesn't.
> 
> We made Nasa aware of this about three years ago and they didn't seem to care as it is, primarily marine product where panels are used a lot less.
> 
> Other than that you can read it without your glasses
> 
> Eddie


Thanks Eddie, that is EXACTLY the sort of information that I wanted and gives me the answer I needed - the Victron it will be for me.....

I am just about to install solar panels - once the weather gets to the sort of value where thermals won't be needed for the Sikaflex to cure.....

So the ability to work with solar panels is an essential pre-requisite for my choice.

I am VERY grateful for that prompt and very helpful answer.

Dave


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## wakk44

I had my Nasa BM1 working in conjunction with 2 solar panels for several years and it worked fine,indicating the current they were generating in real time accurately,you could even tell when a cloud obscured the sun.

A bit more info from Eddie is required methinks.


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## eddievanbitz

*Re: problem*



andyandsue said:


> whats the prob with panel eddie


When the Nasa registers a small charge, it will not show the quiescent discharge over the same period.

In effect, you sit watch a sort of status quo and assume that everything is OK and then the sun goes in and the Nasa recalculates and updates.

The display then goes from 100% to 82% (example) in a few minutes causing panic and mayhem (and lots of phone calls to Van Bitz LOL)

Also as already stated the 500Ah shunt is far more practicable

We have a Nasa BM1 on the Van Bitz exhibition unit and I fitted a Victron to my new motorhome back in the Spring.

I am running 2 x 130W panels and I use a 2000 W pure sine wave inverter/100Ah Charger so the Victron was the clear choice for the extra £50 - £60 pounds.

Also I get a lot more information out of the Victron unit, but to be fair I tend to only read the SOC (State of Charge) readout

Eddie


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## eddievanbitz

wakk44 said:


> I had my Nasa BM1 working in conjunction with 2 solar panels for several years and it worked fine,indicating the current they were generating in real time accurately,you could even tell when a cloud obscured the sun.
> 
> A bit more info from Eddie is required methinks.


Hi In actual fact there were several posts on MHF regarding this two or three years ago.

All the while a small charge is being registered the unit will not show a discharge, unless a decent load is drawn across the shunt. This then means when the unit either receives a discharge or the sun goes in the unit has to update. This causes concern.

Nasa told us that yes they knew about it, but as it is, and they are, primarily a marine company, where it is not a problem, they had no intention of looking to resolve the issue.

We stopped selling them

Eddie


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## Techno100

Part I





Part II


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## wakk44

Thanks for that Eddie,I personally use the Nasa unit mainly for the volts and amps display and for that it will accurately tell me what the solar panels(also on board charger and alternator) are kicking out.

The SOC display is a bit of a pain as it has to go into an overall discharge state to update the % charge left in the batteries and time to charge/discharge.

I found that it would eventually update during darkness when no solar charge was being generated and the 12 volt system went into a discharge state. 

For monitoring the 12 volt system including the output from the solar panels I find it to be accurate and very useful particularly when off hook up.The SOC did work but I just had to wait until darkness for it to update.


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## andyandsue

*good points well made everyone*

Yes . many people actually believe what state of charge meters say!! and its understandable if you dont have a tech background.I would say that both types are suitable and perhaps most problems arise with peoples understanding of the nature o f electricity . Simply explaining watts,amps and volts is often a painfull uphill task.


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## andyandsue

*whats a shunt .last explanation*

whats a shunt? its the bright metal bar in the grey box in my photo. its a piece of metal with a highly accurate reading of its resistance (ohms) its impossible to push the high levels current(amps) through a normal multimeter so its common practise to let it all flow through a shunt and measure the effect it has on the shunt instead. only any use on DC (direct current)


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## tude

*Bm1*

I have the bm1 with a 130 watt solar panel and 2 x 110 elecsol battery's
All I can tell you is every time I turn something on ie lights water pump tv etc etc this bm1 tells me what is coming out of the battery's.it also tells me wat the solar is putting in aswel. It's simple I have a switch on my solar regulater so I can transfer the charge to my cab battery .that way I can see on my display wat the solar is putting in.


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## peedee

Well I have got as far as installing the shunt in the battery compartment on one of the dryer milder days we have recently had and now have the task which I didn't particularly want to tackle of getting the cable through the ducting to the control panel and making a hole for the meter. I hope I don't have to take too much apart to achieve this goal.

The Victron looks a better product but it is a bit OTT in my case. I just like to see what amps are being taking out of the battery and it's voltage. I also use a generator to top up, not solar panels.

peedee


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## listerdiesel

Philippft said:


> Thank you Peter.
> All of that is completely lost on me!


OK, let's try something a little easier then:

I f you have a panel meter, the movement that swings the needle round takes very little current or voltage to move, in the case of our ammeters it is 60mV or 0.06Volts.

Now, to read your 100A current going through your wire, we obviously couldn't pass that through the tiny wires in the meter, they couldn't possibly carry any serious current, so we use the shunt.

The shunt will develop a voltage across its length proportional to the current flowing through it, so at 100A there will be 60mV across its terminals, at 50A there will be 30mV and so on. The voltage developed is directly proportional to the current passing through the shunt.










Note that the shunt has two heavy connections and two smaller connections for the meter. This one is 250A / 60mV.

So you now have a shunt in the wire, and the meter connected to it.

The meter will have a Full Scale Deflection (FSD) of 60mV, that is the needle will go to full scale (100A) when the meter has 60mV across its terminals. The shunt will develop 60mV when it has 100A passing through it.



















Such meters are classed as 'Indirect Reading' types and will have a symbol of a shunt on the scale with the FSD figure in mV alongside it.










You can use the shunt for analog and digital meters, as long as the input FSD figure for the display device matches the shunt output.

Peter


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## Philippft

listerdiesel said:


> Philippft said:
> 
> 
> 
> Thank you Peter.
> All of that is completely lost on me!
> 
> 
> 
> OK, let's try something a little easier then:
> 
> I f you have a panel meter, the movement that swings the needle round takes very little current or voltage to move, in the case of our ammeters it is 60mV or 0.06Volts.
> 
> Now, to read your 100A current going through your wire, we obviously couldn't pass that through the tiny wires in the meter, they couldn't possibly carry any serious current, so we use the shunt.
> 
> Peter
Click to expand...

Thank you for taking the time to put that together for me, I really appreciate that. However, I'm still confused! I have a modern motorhome (2011) and all my circuts are protected by fuses with the biggest fuse at 30 Amps. Where is the 100 Amps coming from on your system ?


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## listerdiesel

Philippft said:


> Thank you for taking the time to put that together for me, I really appreciate that. However, I'm still confused! I have a modern motorhome (2011) and all my circuts are protected by fuses with the biggest fuse at 30 Amps. Where is the 100 Amps coming from on your system ?


The shunt and meter can be any range of amps that you want, it hasn't got to be 100A.

Bear in mind that the main circuits are fused for lighting etc., but the alternator/charging circuits aren't normally fused, they will have a fusible link instead, which is a high-current carrying capacity fuse.










That is the engine compartment fusebox for the Discovery, the three fusible links in the foreground are 100A and 50A, and there is the big strip of metal on the right which is the safety strip to protect against dead shorts across the battery.

Most charging circuits would normally carry up to 100A quite easily, the Discovery has a 130A alternator.

Peter


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## eddievanbitz

Philippft said:


> listerdiesel said:
> 
> 
> 
> 
> 
> Philippft said:
> 
> 
> 
> Thank you Peter.
> All of that is completely lost on me!
> 
> 
> 
> OK, let's try something a little easier then:
> 
> I f you have a panel meter, the movement that swings the needle round takes very little current or voltage to move, in the case of our ammeters it is 60mV or 0.06Volts.
> 
> Now, to read your 100A current going through your wire, we obviously couldn't pass that through the tiny wires in the meter, they couldn't possibly carry any serious current, so we use the shunt.
> 
> Peter
> 
> Click to expand...
> 
> Thank you for taking the time to put that together for me, I really appreciate that. However, I'm still confused! I have a modern motorhome (2011) and all my circuts are protected by fuses with the biggest fuse at 30 Amps. Where is the 100 Amps coming from on your system ?
Click to expand...

Hi Peter, the average motorhome is built for the average use by the average user. No offence meant at all, but for mainstream manufacture you have to cater for the biggest (average) available market.

No everyone wants to use their vans in the same way. Your charging system for example will probably charge at a rate of say 20 amps per hour (Ah) So over a 24 hour period that would be fine whilst on hook up.

My charge was changed from a standard 50Amp charger to a 100amp charger as I have added additional batteries. I have six 135Ah batteries.

Equally I have a 2000w pure sine wave inverter this will peak at 3600w for thirty minutes. Roughly that would be drawing about 360Amps per hour frm my battery bank!

These modifications to my van mean that if I do start the built in generator and the 100Ah charger can put a significant amount of power into my battery bank in a short time, but, with a big bank of batteries and a large pure sine wave inverter and couple of big solar panels, I can run most things without the need for the generator or mains hook up.

So it is when you have slightly different needs from the norm, that these types of figures come into play

Eddie


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## listerdiesel

eddievanbitz said:


> So it is when you have slightly different needs from the norm, that these types of figures come into play
> Eddie


Agreed, the figures I quoted were purely for example, you can have almost any size shunt and associated circuitry to suit what your own needs are.

Peter


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## Philippft

listerdiesel said:


> Philippft said:
> 
> 
> 
> Thank you for taking the
> 
> Bear in mind that the main circuits are fused for lighting etc., but the alternator/charging circuits aren't normally fused, they will have a fusible link instead, which is a high-current carrying capacity fuse.
> 
> Peter
> 
> 
> 
> Thanks again Peter, I'm enjoying this education. So, going back to your original post, if I have got this correct, the shunt you put in was to protect the voltage coming directly from the alternator to the leisure batteries ?
Click to expand...


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## listerdiesel

Philippft said:


> Thanks again Peter, I'm enjoying this education. So, going back to your original post, if I have got this correct, the shunt you put in was to protect the voltage coming directly from the alternator to the leisure batteries ?


No, the shunt is purely a device to enable you to take off a tapping to attach an ammeter to, that's all it does.

Fuses, Fusible Links, MCB's are all protection devices.

Peter


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## andyandsue

*thanks fellas*

thanks fellas

anyone fancy tackling an explanation of power in AC next?

No!!!!!!!!!!!!!!!!! only joking


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## Philippft

listerdiesel said:


> No, the shunt is purely a device to enable you to take off a tapping to attach an ammeter to, that's all it does.
> 
> Fuses, Fusible Links, MCB's are all protection devices.
> 
> Peter


Right! I think I've got it! (had it, lost it, now found it again LOL).

On my control panel, when not on hook up, there is a reading of how many amps are being taken out of the leisure batteries, so my assumption is this is more or less the same ?????

(I'm loving this, it's better than school).

Thanks again,
Philip aged 6.1/2.


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## JohnWebb

I actually have the big version on my boat and the compact version in the motorhome. The motorhome has a solar cel and an Efoy. In both cases they work fine for me. I know the current being taken or given and the volts. It gives an opinion on the state of charge. The big one also gives the Amp Hrs total which is very useful, tells me whether I am up or down when mid channel and want to ensure the power will last out to drive the nav computer, instruments and auto pilot, not a problem in a motorhome!

Incidentally, a shunt is just a bit of metal with a known but very small resistance. When current passes through it there will be a small voltage drop. This is measured and allows the current to be calculated. Make sure everything passes through it.


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## Penquin

*Quote;* "*You are never too old to learn*" from an old English Proverb....

'Nuff said methinks....... :lol: :lol:

Dave


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## Landyman

What an excellent and informative thread and what a fount of knowledge there is on this forum.
I have also just increased my learning.

Thanks to all those who have spent time contributing.

Landyman.


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## peedee

peedee said:


> Well I have got as far as installing the shunt in the battery compartment on one of the dryer milder days we have recently had and now have the task which I didn't particularly want to tackle of getting the cable through the ducting to the control panel and making a hole for the meter. I hope I don't have to take too much apart to achieve this goal.
> 
> peedee


It took most of yesterday to route the cable and make the hole, job is at last done and only have to connect up and put all the panels I had to remove back. 5 meters of wire was only just long enough for the run from the battery compartment to the control panel. If I can get some decent pics I will post later.

peedee


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## listerdiesel

*Re: thanks fellas*



andyandsue said:


> thanks fellas
> 
> anyone fancy tackling an explanation of power in AC next?
> 
> No!!!!!!!!!!!!!!!!! only joking


What do you want to know? :twisted:

Peter


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## listerdiesel

Philippft said:


> Right! I think I've got it! (had it, lost it, now found it again LOL).
> 
> On my control panel, when not on hook up, there is a reading of how many amps are being taken out of the leisure batteries, so my assumption is this is more or less the same ?????
> 
> (I'm loving this, it's better than school).
> 
> Thanks again,
> Philip aged 6.1/2.


There is probably a shunt being used in the existing system, yes.

Peter


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## andyandsue

*no no not meee*

Not me peter im quite ok with 3 phase AC. In fact if ever you drive into Sheffield on the Parkway cop a glance to your right as you arrive and that lovely combined incinerator / steam turbine/DHW plant is one of mine (partially that is)


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## peedee

Job done except for tidying the cables up in the battery compartment. Got too cold to continue to work outside. will wait for a warmer spell.

peedee


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## listerdiesel

Looks good, well done!

Peter


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## Philippft

I have another question! 
Is it possible using my multi-meter to measure how many amps are being fed into my leisure batteries from the alternator, when the engine is running.

Is it as simple as setting the correct setting on my multi-meter and sticking the probes on the battery terminals.

Thanks in advance.


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## wakk44

Philippft said:


> I have another question!
> Is it possible using my multi-meter to measure how many amps are being fed into my leisure batteries from the alternator, when the engine is running.
> 
> Is it as simple as setting the correct setting on my multi-meter and sticking the probes on the battery terminals.
> 
> Thanks in advance.


Yes it is possible but no it is not as simple as that.

To measure amps you have to connect the multimeter in series with the the +ve lead of the battery.In practice this means removing the battery terminal and connecting a lead from the multi-meter to it and the other lead to the battery terminal.A word of caution here,select a high amps scale on the multimeter otherwise it could be damaged.

If you put the probes across the battery terminals is will simply indicate volts.


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## listerdiesel

Don't go there!

You 'can' do it, but you're playing around with high-current-capable circuits, get it wrong and your wiring and possibly your m/h will be toast.

Best thing to do is get a DC Clamp Meter, then clamp it round one of the charging leads to the battery and make sure the jaws are fully closed.

The clamp meter measures current by induction and you do not need to undo any connections.

We've got a couple at the factory which I think I know the location of, if you want to pop over one of the days, we can check for you. We are in Rushden.

Peter


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## andyandsue

*good job PeeDee/clip-on dc amp meter?*

good job of the meter PeeDeee...what does your van take with everything turned off..mine got a "residual current of around 0.2a

listerdiesel(peter)... didn't think you could get "clip- on "dc amp meters as they rely on induction driven by an AC current..pls enlighten!


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## Techno100

http://www.electrotechnik.net/2009/09/how-does-dc-clampmeter-work.html

http://www.maplin.co.uk/dc-ac-current-clamp-multimeter-629713


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## peedee

*Re: good job PeeDee/clip-on dc amp meter?*



andyandsue said:


> good job of the meter PeeDeee...what does your van take with everything turned off..mine got a "residual current of around 0.2a


It shows a 0.1A discharge and a 0.2A charge.

peedee


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## andyandsue

*yes yes yes*

Hall effect transistors ...of course
Ive spent far too long working on cables the size of tree trunks
must get up to speed

cheers sue and andrew


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## Philippft

listerdiesel said:


> Don't go there!
> 
> You 'can' do it, but you're playing around with high-current-capable circuits, get it wrong and your wiring and possibly your m/h will be toast.
> 
> Best thing to do is get a DC Clamp Meter, then clamp it round one of the charging leads to the battery and make sure the jaws are fully closed.
> 
> The clamp meter measures current by induction and you do not need to undo any connections.
> 
> We've got a couple at the factory which I think I know the location of, if you want to pop over one of the days, we can check for you. We are in Rushden.
> 
> Peter


Thank you for your generous offer Peter. However, now not necessary, I put a load on my leisure batteries and ran them down by 10% or so, then measured voltage of batteries, then started engine and measured again, voltage increased from 12.6 - 13.4 ish. So, this tells me that my alternator charges both my cab and leisure batteries and this all I wanted to confirm.


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## navigator

*BM1 Battery Monitor*

This the second van where we have installed a BM1 batter monitor and find the information very useful when motorhoming 'off grid'. I fitted this one over a year ago and decided to do some additional wiring today to take advantage of the option to display the starter battery as well as the leisure battery voltages.

I have run a cable between the orange wire on the connector block and the +ve connection on the starter battery (as figure 2 here) but the display still reads zero volts. The BM1 works perfectly on all other display options.

Can anyone point me in the direction of a cause or cure for this please?

Cheers


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## Techno100

Have you wired the starter battery negative to the shunt also?


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## navigator

Techno100 said:


> Have you wired the starter battery negative to the shunt also?


Hi Andy,

I wasn't sure whether the negatives at the shunt were common, so I ran a fly wire between the shunt negative and the starter battery negative, but to no avail.

Cheers,

Ian


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## Techno100

I'm not sure what the problem is then. I'd fit a battery master instead, at least you'll know the starter won't be any lower than half volt less than the leisure.

Edit
I'd put a voltmeter across orange and the shunt, if there is still no reading then there isn't a circuit.


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## mike800966

*BM1*

A very interesting topic. I fitted a BM1 about 4 years ago and it worked perfectly once we got the negative cabling sorted out.

Everything was fine until the starter battery died on us in Portugal, thats another story.

Since then the BM1 displays a continuous discharge of about 0.7Amp wait for it,,,,,,, until I press the panel illuminate button in which case it then changes to a more realistic level which then happens to agree with the small ammeter showing the solar output. When everything is off, it shows about -0.7A, pressing the illum it settles at -0.0/-0.1.

Thinking the flat starter battery incident may have damaged the shunt, I changed it, without effect. I have emailed Nasa but as said earlier, motorhomes are not really their scene.

Anyone got any suggestions apart from replacing the head end unit which I cant afford to do?

Mike


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## Techno100

Engineers menu, re calibrate
Page 7 of Navigators link


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## mike800966

*BM1*

Thanks for the thought, yes, the eng mode. Thats how I set it up . With a decent meter in the neg lead, so I'm happy that when it settles to zero that it means just that. 
I just cant get my brain why turning on the panel led alters the current display. I just wonder if vibration perhaps has introduced a little resistance up at the back of the unit? or even perhaps its a cable fault in that pre prepared cable?

Seems odd but was all fine until the starter batt died

Mike


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## Techno100

I inherited mine pre installed and it had been fitted wrong, the black & white wires that must NOT be joined together before reaching the shunt. Owner paid good money and still badly fitted.

Mine says I have 185hrs to discharge just now :lol:


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## andyandsue

*bench test it1*

mike800..id plan to spend a few hours bench testing it. use a totally isolated battery and reconnect all the wiring loom as per the diagram,with a bit of luck you could do it without removing the meter from it site. then re calibrate it and see if the problem persists

andy and sue


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## Christine600

Interesting thread!

I have upgraded my van with new solar panels and a new solar controller. And I would like to see how well they charge.

Is it possible to install these battery monitors so that they only show the amps coming from the solar controller - or do they have to show the overall amount of amps going in/out of the battery?


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## mike800966

*Nasa BM1 Battery monitor system update and thanks*

Some time ago I reported that the display was unpredictable depending on whether the panel lighting led was on or off! At that time it was suggested that I take everything out and check it on the bench well 2 years later the leisure battery died ((6 months out of warranty) I got fed up with it and wanted to tidy it all up.

NASA had said dismissively that"there was resistance somewhere" 
Anyway the long and the short of it was that I found a wire in the choc strip that was partly clamped on the conductor but also on the sheath, since then it has worked perfectly.
I know its been along time coming but thanks to Andy or was it Sue? for the advice, perhaps it might help someone else.

Mike


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## mike800966

I have a small ammeter permanently in the cable coming from the panel, before the reg. 
it is helpful to be able to see what the panel produces and how it varies with sun level but it wont be the same as what is going into the battery as in my case the Solar Reg and the Calira protects the battery from being overcharged and just cuts back the current entering the battery.
Mike


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