Sample rate of battery monitor

[roaringgirl]

I have a shunt and a BEP battery monitor which shows voltage, net current in/out and capacity. The shunt is wired between the negative bus and the battery, so absolutely everything goes through it. There are multiple chargers on board: engine alternator, solar, wind, towed generator. It is clear from looking at the wind-gen's charge regulator panel and the BEP shunt monitor simultaneously that the windgen and tow-gen input is mostly not registering on the battery monitor (although you *can* see the windgen push up the voltage).

As the battery monitor keeps a tally of Ah in/out in order to give battery charge state, it can't do this if it doesn't register input from the windgen and towgen - to the extent that on a recent passage the batt monitor was showing 12.9V (full for AGM) while the capacity was 0Ah!

My explanation for this behaviour is that the wind and tow gen inputs fluctuate a lot and the battery monitor is a) too insensitive and b) has too low a sample rate to accurately monitor them.

Does anyone have any other explanations?

Does anyone know of any battery monitors that don't have the same shortcomings?

 

[pvb]

It is clear from looking at the wind-gen's charge regulator panel and the BEP shunt monitor simultaneously that the windgen and tow-gen input is mostly not registering on the battery monitor (although you *can* see the windgen push up the voltage).

You need to double-check the wiring first, starting with the screen on the twisted pair.

 

[roaringgirl]

You need to double-check the wiring first, starting with the screen on the twisted pair.

I'm not sure what you mean by the 'twisted pair'. Note that the batt monitor *does* register current through the shunt from the solar panels and the alternator. I'm absolutely certain that the batt monitor is wrong and the windgen and tow-gen DO charge the battery - we would have killed the batteries through running them completely flat several times over by now if not, and we would have run out of water on our Atlantic crossing!

 

[peteK]

I have a totally different one and it has to be over 100ma before it shows on display but voltage still rises.

 

[pvb]

I'm not sure what you mean by the 'twisted pair'. Note that the batt monitor *does* register current through the shunt from the solar panels and the alternator. I'm absolutely certain that the batt monitor is wrong and the windgen and tow-gen DO charge the battery - we would have killed the batteries through running them completely flat several times over by now if not, and we would have run out of water on our Atlantic crossing!

Using the shunt, the monitor measures current flowing in and out of your battery bank. If it registers some charging devices but not others, the fault is surely not with the monitor, but with the wiring.

The twisted pair is a pair of thin wires which the monitor uses to measure the voltage across the shunt, and therefore calculate the current flowing. The twisted pair should be screened, and the screen acts as the negative supply to the monitor. The handbook says that if the monitor isn't showing current, to check the screen connections. However, as you now say that it does register some charging current, it's likely that this isn't the problem.

 

[roaringgirl]

However, as you now say that it does register some charging current, it's likely that this isn't the problem.

Sorry, it only occurred to me after your post. Thanks for your help!

 

[ithet]

I have one of these BEP monitors. Have you set it up correctly and not recently done a factory reset? In particular have you set up the zero amps calibration - on factory reset mine shows -9a until I make the zero adjustment. You do not show the amps reading. I have also had contact with BEP about the amps resolution and they have confirmed that it is only to nearest 0.5a. The amp hour figure is a calculated value and relies on a number of settings. I think your first actions should be to get to a state of known full charge and then set the displays 'actual capacity' to your battery's full amp hours, then see what happens. I have a pdf manual if required.

 

[roaringgirl]

I have one of these BEP monitors. Have you set it up correctly and not recently done a factory reset? In particular have you set up the zero amps calibration - on factory reset mine shows -9a until I make the zero adjustment. You do not show the amps reading. I have also had contact with BEP about the amps resolution and they have confirmed that it is only to nearest 0.5a. The amp hour figure is a calculated value and relies on a number of settings. I think your first actions should be to get to a state of known full charge and then set the displays 'actual capacity' to your battery's full amp hours, then see what happens. I have a pdf manual if required.

I carefully calibrated the current reading per the manual a couple of months ago and reset the 100% reading too. Thanks for the offer, I have a paper copy of the manual here. It is *very* interesting that it only detects to the nearest 0.5A, this could be a major factor for us. At the point where we saw 0Ah and 12.9V we had been running the tow-gen and the wind-gen for about 100hours straight. At that wind & boat speed they each give around 2-5A, so the tenths of an amp matter a lot. We had also been running the (8A) watermaker for a few hours a day (say 16h over the 100hr period = 128Ah at 12V) - and the BEP has no trouble at all registering its current drain!

 

[pvb]

It is *very* interesting that it only detects to the nearest 0.5A, this could be a major factor for us.

The 2005 manual I've seen says it has 0.1A resolution. Maybe you have an earlier version of the monitor.

 

[ithet]

The 2005 manual I've seen says it has 0.1A resolution. Maybe you have an earlier version of the monitor.

I think my manual is the same, but the display is only to nearest 0.5a. Does yours show 0.1-0.2-0.3a etc?

 

[ithet]

Here is what Mastervolt (the brand owner of BEP) told me.

My query:

I have a BEP 600-DCM V2.3 fitted to my yacht here in the UK.

The previous owner fitted it, but I have checked the wiring carefully and all seems OK. Although generally OK, I have a couple of queries.

1) When I do factory reset and no loads, the meter shows a 9A discharge. I can zero this out using the "AMPS ZERO" function, but is this amount of offset reasonable?

2) The meter only displays amps to one decimal place and in steps of 0.5A, I thought there should be more current resolution and two decimal places?

I have the meter connected to a 270Ah house battery bank.


Reply:

The BEP 600-DCM comes with a 450A - 50mV shunt.
This means that at 450 Amps current through the shunt will cause voltage-drop over that shunt of 50mV.
It is this voltage drop that is measured and interpreted by the display.
In that same ratio 45A will cause a voltage drop of 5mV, so a 1mV voltage drop will show a 9A on your display.
So when zeroing out 9A you correct in fact a 1mV voltage drop, what is very acceptable.

The resolution is indeed 0,5A and with the previously explained this means a voltage drop-resulotion of 0,056mV per 0,5A.
These are very small margins and therefor it is important to use twisted and screened wiring from the shunt in order to prevent induction
and other electro-magnetic fields influencing the measuring voltages.
I hope this gives you some perspectives on this matter.



With kind regards,

Leo van der Werf
Sr. Service & Training Engineer

 

[pvb]

I think my manual is the same, but the display is only to nearest 0.5a. Does yours show 0.1-0.2-0.3a etc?

I don't have a BEP monitor; I now have a Simarine Pico monitor.

 

[pvb]

I have a BEP 600-DCM V2.3 fitted to my yacht here in the UK.

Ah, the 2005 manual I referred to is for version 3.2 of the monitor.

 

[ithet]

Ah, the 2005 manual I referred to is for version 3.2 of the monitor.

I think mine is actually 3.2 and I made a mistake in my email, but I am sure the earlier versions (without a bilge pump monitor function) are also the same. But the manual is at best misleading which was the reason for my enquiry to the manufacturer. The 1/10 amp resolution probably refers to the display matrix, but the system as a whole only discriminates to nearest 0.5a. I see this quite clearly in use, with say, the display flicking between 0.5a and 1.0a etc.

 

[Baggywrinkle]

Stupid question, I assume you were measuring with all electrical loads turned off? ..... if not then the wind-gen and towed gen output could be simply running the boat electrical system, leaving little to charge the batteries?

 

[roaringgirl]

Stupid question, I assume you were measuring with all electrical loads turned off? ..... if not then the wind-gen and towed gen output could be simply running the boat electrical system, leaving little to charge the batteries?

Yes, measured measured with all inputs and outputs switched off.

 

[pvb]

Yes, measured measured with all inputs and outputs switched off.

If all the inputs were switched off, you wouldn't have seen any charge current...

 

[roaringgirl]

If all the inputs were switched off, you wouldn't have seen any charge current...

Yes. The '0' in the picture is 'capacity remaining'. Clearly something is wrong as the battery can't have 0 capacity remaining and yet 12.9V - the monitor is failing to count the Ah in from the wind and tow gens correctly so its tally is wrong.

 

[pvb]

Yes. The '0' in the picture is 'capacity remaining'. Clearly something is wrong as the battery can't have 0 capacity remaining and yet 12.9V - the monitor is failing to count the Ah in from the wind and tow gens correctly so its tally is wrong.

Back to post 2 then.

 

[roaringgirl]

In this discussion, have we not already discounted a wiring problem as the solar and alternator charge does register on the monitor? All charge sources are connected to the same negative bus (and therefore to the same shunt)