Battery monitor counting backwards!

matt1

matt1

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Don't you just love electrickery!

Have installed a BEP DCM Battery monitor (the shunt connected by pro's as they are heavy duty cables and I wired the "sense" wires to the monitor - its was fairly straightforward). I've not had chance to really see it in action before then installing an 110 w solar panel controlled by a Victron MPPT. Again, fairly simple to install (I may regret saying that after you lot have pitched in correcting me :-) !

The MPPT has Bluetooth and is indicating I'm typically getting 3amp charge when sunny.....but the battery monitor is indicating "-0.X discharge". Even on shorepower it is indicating discharge whilst the charger is showing "float". Indeed, whilst motoring under autopilot and with the instruments and fridge on the BEP was showing -11 amps discharge. The discharge values seem to correspond with what I would expect the charge to be. Anyone know what is going on?

Some values (all taken on a sunny day within a few minutes)

No shorepower, no solar, house battery off = 13.7v , -0.5 amps discharge (there are some always on circuits)

No shorepower, solar on, house battery on = 14.3v, (3.1 amps charge on Victron MPPT app), -0.7 amps discharge at the BEP battery monitor

Shorepower on, solar on, house battery on = 14.5v , (2.9 amps on Victron MPPT), -0.7 amps discharge at the BEP battery monitor

As ever, Thanks

Matt
 
I would suspect the -ve from the MPPT is not connected to the shunt rather its directly connected to the battery terminal (Or wrong end of the shunt) so the shunt is not measuring the input current from the MPPT hence you are still seeing the -0.7 amps.

Again you need to check the battery charger is also connected properly, ie through the shunt.
 
matt1 said:
Don't you just love electrickery!
Click to expand...
Certainly do , but I am not saying why.


Have installed a BEP DCM Battery monitor (the shunt connected by pro's as they are heavy duty cables and I wired the "sense" wires to the monitor - its was fairly straightforward). I've not had chance to really see it in action before then installing an 110 w solar panel controlled by a Victron MPPT. Again, fairly simple to install (I may regret saying that after you lot have pitched in correcting me :-) !

The MPPT has Bluetooth and is indicating I'm typically getting 3amp charge when sunny.....but the battery monitor is indicating "-0.X discharge". Even on shorepower it is indicating discharge whilst the charger is showing "float". Indeed, whilst motoring under autopilot and with the instruments and fridge on the BEP was showing -11 amps discharge. The discharge values seem to correspond with what I would expect the charge to be. Anyone know what is going on?

Some values (all taken on a sunny day within a few minutes)

No shorepower, no solar, house battery off = 13.7v , -0.5 amps discharge (there are some always on circuits)

No shorepower, solar on, house battery on = 14.3v, (3.1 amps charge on Victron MPPT app), -0.7 amps discharge at the BEP battery monitor

Shorepower on, solar on, house battery on = 14.5v , (2.9 amps on Victron MPPT), -0.7 amps discharge at the BEP battery monitor

As ever, Thanks

Matt
Click to expand...

Check the that the sensing wiring ( twisted a pair and screen ) are correctly connected ( not reversed)

Check that there ate no connections to the house battery negative terminal apart from the shunt and items you dont want to monitor ( auto bilge pump for example) and no connections to the battery end of the shunt other than the battery and monitor connection

Post a diagram showing how everything is connected
 
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davidwf said:
I would suspect the -ve from the MPPT is not connected to the shunt rather its directly connected to the battery terminal (Or wrong end of the shunt) so the shunt is not measuring the input current from the MPPT hence you are still seeing the -0.7 amps.

Again you need to check the battery charger is also connected properly, ie through the shunt.
Click to expand...

Ah! So, the +ive and -ive from the panel go to the MPPT and then the +ive and -ive from the MPPT go straight to the battery terminals. It sounds like I should have wired the -ive to the shunt?
 
VicS said:
Certainly do , but I am not saying why.




Check the that the sensing wiring ( twisted a pair and screen ) are correctly connected ( not reversed)

Check that there ate no connections to the house battery negative terminal apart from the shunt and items you dont want to monitor ( auto bilge pump for example) and no connections to the battery end of the shunt other than the battery and monitor connection

So the battery end of the shunt is where the negative from the battery first connects to the shunt? Presumably the negative from the MPPT would then go to the other terminal on the shunt (eg the 2nd terminal /furthest terminal from the battery negative)?

I'll try and do a diagram if I can get to the boat during the week
Post a diagram showing how everything is connected
Click to expand...



So the battery end of the shunt is where the negative from the battery first connects to the shunt? Presumably the negative from the MPPT would then go to the other terminal on the shunt (eg the 2nd terminal /furthest terminal from the battery negative)?

I'll try and do a diagram if I can get to the boat during the week
Post a diagram showing how everything is connected
 
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matt1 said:
Ah! So, the +ive and -ive from the panel go to the MPPT and then the +ive and -ive from the MPPT go straight to the battery terminals. It sounds like I should have wired the -ive to the shunt?
Click to expand...

All loads and charging from/to the domestic bank have to go through the shunt. If they don't they don't get monitored. Don't think this will be the only thing that's wrong though. Check all other connections are in the correct places.
 
matt1 said:
So the battery end of the shunt is where the negative from the battery first connects to the shunt? Presumably the negative from the MPPT would then go to the other terminal on the shunt (eg the 2nd terminal /furthest terminal from the battery negative)?

I'll try and do a diagram if I can get to the boat during the week
Click to expand...

Yes all the power going into or out of the house battery must pass through the shunt if it is to be monitored. I would not even make an exception for items like auto bilge pumps, but I noticed it in the BEP literature and edited my post accordingly

Normal rule is no connections to the battery negative except the shunt and no connections to the battery end of the shunt except the battery and the monitor All other negatives go to the other end of the shunt. or a common negative bus bar connected to it
 
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I'm sure you followed the MPPT instructions to the letter and installed the new equipment “directly to the battery”, but not via the shunt bus bar.

Often extra equipment is added at a later date and the installer may well follow the installations instruction. Make sure you tell an electrician fitting new kit that you have a Battery Monitor installed.

The installation manuals are usually not very clear, especially the BEP. The shunt must be as close to the battery as possibly – for most brands on the negative post – and a new bus bar must be installed immediately after the shunt to take all the negative cables, and any new one that might be fitted later. The instructions are usually that all battery negative cables MUST go via this bus bar. This is in itself confusing as a stand alone house bank will always have a cable on each negative and positive stud to tie several batteries into one big capacity bank. With multiple batteries in parallel, and not all in the same location, it is often difficult to know what wires are going where. If not all of the devices drawing current or charging the service bank are going through the shunt then the Ah count will be wrong.

With a battery monitor installed that has the shunt in the negative cable the bus bar becomes the new negative post for the service bank. So the starter battery common negative - that connects the starter negative to the house bank negatives - must also be connected to the bus bar. This error is probably one of the major causes of battery monitors not reading the alternator charging amps going through the service battery.

This will happen when split charging VSRs or diodes join the banks together. This supplies positive volts to the starter bank and the service bank. Now try and follow the return path of the electrons to the alternator from the service battery. This will be via the service battery negative stud and then, via common earth, to the starter battery negative stud, which is usually wired to the engine block and hence to the negative of the alternator. This will bypass the shunt and not show any current into the service battery when the service battery is charging.

Moving the starter battery common negative to the other side of the shunt always confuses people because they think the shunt will then also be monitoring the charge current going into the starter battery!!!!

A very well respected marine engineer in Maine, USA, found that “perhaps 7 out of 10 battery monitors he sees installed by both pro's and DIY's are wired incorrectly (shunt wiring) and 9.5 out of 10 are programmed incorrectly.”

That is why the 13 year old Smartgauge that doesn't use a shunt has been so successful.
 
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Shunt/battery connection confuses many. Easiest way to get one's mind around it is just to think of the shunt as an extended battery terminal. One end of the shunt goes to the battery and then everything which would have gone to that battery pole goes to the other end of the shunt.
 
sailinglegend420 said:
With a battery monitor installed that has the shunt in the negative cable the bus bar becomes the new negative post for the service bank. So the starter battery common negative - that connects the starter negative to the house bank negatives - must also be connected to the bus bar. This error is probably one of the major causes of battery monitors not reading the alternator charging amps going through the service battery.

This will happen when split charging VSRs or diodes join the banks together. This supplies positive volts to the starter bank and the service bank. Now try and follow the return path of the electrons to the alternator from the service battery. This will be via the service battery negative stud and then, via common earth, to the starter battery negative stud, which is usually wired to the engine block and hence to the negative of the alternator. This will bypass the shunt and not show any current into the service battery when the service battery is charging.
Click to expand...

So you're saying that the starter negative has to go to the load side of the shunt, or the monitor won't see the current from the alternator to the domestic bank ?
 
I'm hoping to go to the boat this evening so will try and sketch out the current configuration and post it on here. I can at least confirm the -ive from the MPPT is connected direct to the battery not the shunt (as I did that!) and by all accounts that is part of the problem!
 
sailinglegend420 said:
With a battery monitor installed that has the shunt in the negative cable the bus bar becomes the new negative post for the service bank. So the starter battery common negative - that connects the starter negative to the house bank negatives - must also be connected to the bus bar. This error is probably one of the major causes of battery monitors not reading the alternator charging amps going through the service battery.
Click to expand...

Perhaps you need to think that through again...
 
Quote Originally Posted by PaulRainbow
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So you're saying that the starter negative has to go to the load side of the shunt, or the monitor won't see the current from the alternator to the domestic bank ?
Click to expand...

Thats right. If the engine negative goes direct to the domestic battery the charging current will bypass the shunt.

Moreover the monitor will record the starter battery charge current as a discharge from the domestic battery and the starter motor current as a domestic battery charge current
 
VicS said:
Thats right. If the engine negative goes direct to the domestic battery the charging current will bypass the shunt.

Moreover the monitor will record the starter battery charge current as a discharge from the domestic battery and the starter motor current as a domestic battery charge current
Click to expand...

question to you then ;

So you're saying that the starter negative has to go to the load side of the shunt ?
 
PaulRainbow said:
So you're saying that the starter negative has to go to the load side of the shunt, or the monitor won't see the current from the alternator to the domestic bank ?
Click to expand...
I thought you'd be the first one along to question my post. After 40 years in the business I still don't understand how you could call yourself a marine electrical engineer, or why the moderators keep allowing you to post here. I would have thought you would have seen this wiring error hundreds of times by now.

I really am sorry for this continual criticism of your posts but from what I can see on the threads I've posted on almost every time you open your mouth you put your foot in it - big time!

pvb said:
Perhaps you need to think that through again...
Click to expand...
Sorry pvb you need to read my post through again!

VicS said:
....Moreover the monitor will record the starter battery charge current as a discharge from the domestic battery and the starter motor current as a domestic battery charge current
Click to expand...

What you all need to do is look at the diagram from Graham376's link below and trace the path of the electrons and you will see why my posting is correct.

Graham376 said:
The starter battery negative goes to the load side of the shunt (not the battery side) ..... NASA diagram here, page 3. https://www.nasamarine.com/wp-content/uploads/2015/12/Clipper-BM1BM2.pdf
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He's the only guy who understands!
 
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