Do I have a broken Clipper BM2 battery monitor, or something more serious with my batteries?

[aaronwood66]

Having finished my renovations, I have been staying on board a lot more. I don't use a great deal of power - I have a fridge but don't use it, so the only power used is charging USB devices, lights, and the general essential boat appliances, (plus Webasto in colder months).

 

Between running the engine and the last few sunny months, I have always had topped up batteries, so I had a bit of a shock when my Clipper BM2 battery monitor started to show some strange readings. It came with the boat, so I don't know how old it is, but I have been using it over the past few years without any issues.

 

I woke up yesterday to find the Amps reading seems to be stuck on 199A charge. It still says this when disconnecting all charging methods, and turning all loads on at the same time. I have double checked the connections (everything fine), and also ran through the set up procedure from scratch, No luck.

 

My batteries are reading 12.9 on my multi-meter, so nothing seems to be wrong there. I am stumped and thinking buying a replacement battery monitor might be the only way? Any suggestions before I do this would be much appreciated :)

[Tony Brooks]

My first action would be to remove all the power from the meter for several minutes so it goes blank and see if it resets itself when powered up again.

[MtB]

I agree with Tony. Reboot it and if it still claims 199A charging current (which seems highly unlikely), bin it and fit a Victron  BMV 702. 

 

Bear in mind you'll need to invest in a magnifying glass to read it though. 

 

Or in extremis, RTFM.

 

 

 

 

 

P.S. it occurs to me this could possibly be a shunt problem, not a BM-2 fault. Have you checked the shunt is all ok, and not (for example) submerged in a few inches of water?

 

 

[aaronwood66]

Thanks very much, @Tony Brooks and @MtB

 

I had tried to disconnect everything and left it half an hour before re-connecting, but it was still stuck on 199A.

The shunt seems OK - it's mounted high up an under a ledge in the engine bay, so no chance of water getting in/around. Nothing has come loose. Very strange!

 

MtB - thanks for the Victron recommendation.

[Jen-in-Wellies]

Can you take a photo of the shunt for us? These sorts of monitors work by measuring the voltage across the shunt. The shunt is a known low resistance. The higher the voltage drop measured across it (but still below around 75mV), the higher the current flowing across the shunt. If it is reckoning 199A plus, then it is finding, or hallucinating that there is a very high voltage drop across the shunt. There could be other reasons for this than the monitor box itself being on the blink that might be more easily fixed than buying a whole new monitor.

[MtB]

59 minutes ago, Jen-in-Wellies said:

Can you take a photo of the shunt for us? These sorts of monitors work by measuring the voltage across the shunt. The shunt is a known low resistance. The higher the voltage drop measured across it (but still below around 75mV), the higher the current flowing across the shunt. If it is reckoning 199A plus, then it is finding, or hallucinating that there is a very high voltage drop across the shunt. There could be other reasons for this than the monitor box itself being on the blink that might be more easily fixed than buying a whole new monitor.

 

Good point.

 

Temporarily disconnecting the cable from the shunt output terminal would guarantee no volt drop across the shunt, so if the BM-2 still reads 199A with it disconnected, a busted BM-2 is the diagnosis. Also, 199A looks to me like it could be the max value it can display - so there might actually genuinely be a very high voltage dropping across a possibly faulty shunt causing the 199A display.

[Tracy D'arth]

1 minute ago, MtB said:

 

Good point.

 

Temporarily disconnecting the cable from the shunt output terminal would guarantee no volt drop across the shunt, so if the BM-2 still reads 199A with it disconnected, a busted BM-2 is the diagnosis. Also, 199A looks to me like it could be the max value it can display - so there might actually genuinely be a very high voltage dropping across a possibly faulty shunt causing the 199A display.

But at 199 amps something would be very hot by now!

 

The other possibility is that the wires from the shunt are somehow getting shorted to a voltage from some other circuit.

[MtB]

Just now, Tracy D'arth said:

But at 199 amps something would be very hot by now!

 

The other possibility is that the wires from the shunt are somehow getting shorted to a voltage from some other circuit.

 

 

No the point is that 199A is a false reading, caused by an abnormally high volt drop of (say) 0.001v across the shunt, caused by a bad connection inside the shunt. 

 

(The BM-2 actually being a volt meter calibrated in Amps.)

[Tracy D'arth]

20 minutes ago, MtB said:

 

 

No the point is that 199A is a false reading, caused by an abnormally high volt drop of (say) 0.001v across the shunt, caused by a bad connection inside the shunt. 

 

(The BM-2 actually being a volt meter calibrated in Amps.)

I see your point, that if the shunt resistance increased due to a bad connection  or partial breakage in the shunt itself, then the 2 wires would have more voltage for a given current across them.

But in that case the current capacity of the shunt/wiring would be limited and the OP would be experiencing lack of power from the batteries.

As usually the starter current also flows through the shunt, he/she would not be able to start the engine.

 

What would it read if a wire was disconnected? I have never tried that.

Edited July 14, 2023 by Tracy D'arth

[Tony Brooks]

8 minutes ago, Tracy D'arth said:

As usually the starter current also flows through the shunt, he/she would not be able to start the engine.

 

I am far from sure that is universal, in fact I think it would be wrong and likely to damage the shunt in the long term.

[Tracy D'arth]

14 minutes ago, Tony Brooks said:

 

I am far from sure that is universal, in fact I think it would be wrong and likely to damage the shunt in the long term.

Agreed, I am in error there. If the battery management is only on the cabin battery then no, the starter current is not via the shunt.  But I have often seen the shunt in the combined negative cable when the starter current does pass through the shunt.

If the battery management is only on the cabin battery then the charging current reading is inaccurate as it does not read the current charging the engine battery.

[aread2]

I know for certain my shunt is not in the starter circuit.

[Tony Brooks]

1 minute ago, Tracy D'arth said:

Agreed, I am in error there. If the battery management is only on the cabin battery then no, the starter current is not via the shunt.  But I have often seen the shunt in the combined negative cable when the starter current does pass through the shunt.

If the battery management is only on the cabin battery then the charging current reading is inaccurate as it does not read the current charging the engine battery.

 

I accept it can be the case, we only have to remember the ongoing posts to the forum.

 

If it is a bog-standard twin alternator engine, then the current flowing into the domestic battery will be the domestic alternator output and accurate, with this type of monitor current into the domestic battery is all that matters because it needs that to calculate its "lies".

[Tracy D'arth]

2 minutes ago, Tony Brooks said:

 

I accept it can be the case, we only have to remember the ongoing posts to the forum.

 

If it is a bog-standard twin alternator engine, then the current flowing into the domestic battery will be the domestic alternator output and accurate, with this type of monitor current into the domestic battery is all that matters because it needs that to calculate its "lies".

Agreed again but for the old timers like me the bog standard was a single alternator engine!   😏

[Tony Brooks]

1 minute ago, Tracy D'arth said:

Agreed again but for the old timers like me the bog standard was a single alternator engine!   😏

 

Me too, and Gibbo chided me for saying that as far as I was concerned I wanted to monitor total alternator output, not just the domestic battery charge. I even had my shunt in the alternator positive, being an earth return machine.

[Tracy D'arth]

4 minutes ago, Tony Brooks said:

 

Me too, and Gibbo chided me for saying that as far as I was concerned I wanted to monitor total alternator output, not just the domestic battery charge. I even had my shunt in the alternator positive, being an earth return machine.

I would agree with you that monitoring the whole alternator output is desirable on a single alternator set up. I would prefer monitoring charge and discharge separately if it was not so complicated to do so. It is never done though.

[ditchcrawler]

3 hours ago, Tracy D'arth said:

But at 199 amps something would be very hot by now!

 

The other possibility is that the wires from the shunt are somehow getting shorted to a voltage from some other circuit.

That was my thought as its probably full scale deflection, if you can have that digitally 

[aaronwood66]

4 hours ago, Jen-in-Wellies said:

Can you take a photo of the shunt for us? These sorts of monitors work by measuring the voltage across the shunt. The shunt is a known low resistance. The higher the voltage drop measured across it (but still below around 75mV), the higher the current flowing across the shunt. If it is reckoning 199A plus, then it is finding, or hallucinating that there is a very high voltage drop across the shunt. There could be other reasons for this than the monitor box itself being on the blink that might be more easily fixed than buying a whole new monitor.

 

Thanks for all these comments - a problem with the shunt is certainly something I never considered, as it just looks so solid and sturdy as components go. I know it is wired correctly (as it has been working fine for the past few years) but when I go back to the boat this weekend I will take a photo and examine it more closely. And report back. Thanks!

[Tony Brooks]

It looks, from Google images, as if the BM2 shut uses a pair of brass rods soldered into the two end terminal blocks, so I wonder if there is a solder failure. That is likely to give a high resistance and high reading. Probably worth taking a magnifying glass to it.

[MtB]

6 minutes ago, Tony Brooks said:

It looks, from Google images, as if the BM2 shut uses a pair of brass rods soldered into the two end terminal blocks, so I wonder if there is a solder failure. That is likely to give a high resistance and high reading. Probably worth taking a magnifying glass to it.

 

Or just disconnect the output lead which guarantees there is no current flowing, and see if the display stays at 199A, or drops to zero.

 

If it drops to zero, there is either a shunt fault or the current really is 199A (or higher)!! 

 

A clamp meter would come in handy here, too. 

 

 

 

 

 

 

[aaronwood66]

Finally the rain let up and I managed to have look. I undid all connections on the shunt and inspected it - I couldn’t see any obvious damage/problems. But on reconnecting everything (just before I was going to check your idea @MtB, the 199A issue went away and it appears normal again). Not sure if I wriggled something on the shunt and it might still be faulty… I’ll keep a close eye on it. Thanks to everyone for their input and help.

 

[Tony Brooks]

Thanks for the feedback.

 

If you are sure the terminal were clean and tight, it makes me even more suspicious of the shunt. If it does, it again try slightly twisting the brass blocks with a spanner and see if the fault goes away. If so, it points to the soldering on the shunt.

[Alan de Enfield]

23 minutes ago, aaronwood66 said:

Finally the rain let up and I managed to have look. I undid all connections on the shunt and inspected it - I couldn’t see any obvious damage/problems. But on reconnecting everything (just before I was going to check your idea @MtB, the 199A issue went away and it appears normal again). Not sure if I wriggled something on the shunt and it might still be faulty… I’ll keep a close eye on it. Thanks to everyone for their input and help.

 

 

 

Having 5 wires connecting to one terminal is not 'best practice' and actually contravenes the 'Small Boats Wiring' ISO Standard.

 

Consider running a single cable from the shunt to a bus-bar and then attach each wire to a terminal on the bus-bar.

 

 

 

 

 

[Puffling]

47 minutes ago, Alan de Enfield said:

 

 

Having 5 wires connecting to one terminal is not 'best practice' and actually contravenes the 'Small Boats Wiring' ISO Standard.

 

Consider running a single cable from the shunt to a bus-bar and then attach each wire to a terminal on the bus-bar.

 

 

 

 

 

It's only the BM2 which permits so many tags to be connected. I have the BM1: four connections are the absolute maximum, and I even had to ditch the compression washer to squeeze that many on.

I ran a bulky cable to a commoning post for more connections, which is something the OP might consider.

Battery post

[Tony Brooks]

43 minutes ago, Puffling said:

It's only the BM2 which permits so many tags to be connected. I have the BM1: four connections are the absolute maximum, and I even had to ditch the compression washer to squeeze that many on.

I ran a bulky cable to a commoning post for more connections, which is something the OP might consider.

Battery post

 

Please, how will that help? he will still need to put his five connections onto the post PLUS the new bulky cable. it would work if it were a suitable multi- stud bus bar