Monitor Page Cell Voltage Discrepancy

49 views
Skip to first unread message

SKM

unread,
Jun 7, 2021, 7:56:29 PM (5 days ago) Jun 7
to electrodacus
I am hoping to get some help with voltage discrepancy that I see on the first page of the SBMS0 monitor page.  My SBMS0 monitor page is indicating approximately +0.1v higher than the actual cell voltage (per cell).  It seems like there may be some kind of offset.  In addition, the total battery bank voltage Indicated on the monitor page is approximately +0.8v higher than the actual.  It appears that the total battery bank voltage is a result of the erroneous individual cell calculation rather than a direct measurement of the battery bank. 

Has anyone experienced anything like this and how did you address it? Is there something I am missing?

1) Is it possible there is a voltage offset?  If so, where can I modify it.
2) Is the total battery bank voltage displayed a calculation of the individual cell voltages?

Thank you,
SKM

Dacian Todea

unread,
Jun 8, 2021, 2:14:05 PM (4 days ago) Jun 8
to electrodacus
Individual cells may show higher voltage is cell balancing is performed.  
1) There is no offset that you can modify the ISL94203 is factory calibrated and should be super accurate within no more than 3mV relative or 15mV absolute. Are you sure your multimeter is accurate ? I test each SBMS0 before shipping and I will notice if there was such a problem.
2) The total battery voltage is calculated as sum of all cell voltages and not measured separately.

Do you have a photo showing this high voltage measurement ? Is this always the case or just on some occasions ? Also is this higher voltage during charging ? as if so then it may also be the voltage drop on cells connections that will add to the cell voltage you may measure at terminals.


SKM

unread,
Jun 10, 2021, 1:55:59 AM (3 days ago) Jun 10
to electrodacus

Hi Dacian,

Thank you for your response and confirming the displayed total bank voltage is calculated.  This explains why the actual and indicated bank voltage do not match.  So, the primary question is why the actual individual cell voltage and displayed cell voltage do not match. This is puzzling as the voltage displayed at the monitor is higher than the voltage measured at the cells.  Normally, I would expect a lower value at the monitor due to potential voltage drop.

I should mention that I have extended the cell monitoring ribbon wire via a Winford connector to the cell terminals.  However, the voltage measured at the cell terminal and at the Winford connector is the same, but are lower than what is displayed on the monitor.  I used two different multimeters to make the measurements with the same results.  I believe the delta difference is present at all times.  Attached are pictures of the multimeters, Winford connector, cell #1 voltage at Winford (3.27V) and Monitor page  display (cell #1’ 3.36V).  The actual bank voltage is 26.19v compared to displayed 26.89v.  At this point, I have no indication what the problem could be.  Appreciate any additional feedback.

Thank you,
Sam

.
6075D78B-3209-4C40-AB5D-7C9D5D07DA6A.jpeg
EAF7B06B-A83C-4FB1-BEF1-92239F9E26F1.jpeg

SKM

unread,
Jun 10, 2021, 1:57:11 AM (3 days ago) Jun 10
to electrodacus
39F0B957-7CB7-4EC7-967C-542183589EC3.jpeg
3AE03CFE-70AD-4932-89EB-43D8CBCDFBBD.jpeg

Dacian Todea

unread,
Jun 10, 2021, 2:49:07 PM (2 days ago) Jun 10
to electrodacus
Sam,

Not sure what to say as I have not seen this sort of problem before. The 26.89 - 26.19V = 0.7V /8 = 0.0875 seems to match what you measure as delta for each cell and if two of your meters measure the same thing even if not acurate meters seems to be to significant to blame the meters. Maybe something happened with the ISL94203.
Can you maybe connect the ADC2 or ADC3 to the battery+ and see what voltage that will measure (that is not as accurate but should be good enough to give an idea).
Will you be OK sending the SBMS0 back to me ?(I will refund you the shipping cost). What about temperature indication is that within the 3 or 4C from ambient ? seems a bit hot to be +31C
 

SKM

unread,
Jun 11, 2021, 11:24:43 AM (yesterday) Jun 11
to electrodacus
Good morning Dacian,

Yes, this is a bit puzzling.  I will go ahead and connect ADC2 or 3 to the +battery and further investigate to determine the root cause.  The temperature should be close to ambient (~15C) and I have not connected the temp wire yet.  So, I am not sure why there is a 31C temp indication.  

My unit is installed on the boat and we are currently cruising Pacific North West with the hope that Canadian border opens up to the cruisers soon.  So, I am not able to remove and return the unit at this time.  However, I had planned to order another SBMS0 as spare to keep on the boat.  I will go ahead and do that.  As soon as I receive the spare, I will install and see if the problem is resolved.  If so, then I will return the first unit at that time.  Regarding spare unit, I have couple of questions:

  -  Do I need to have a Wifi module to have EXTIO5 and EXTIO6 available?
  -  How soon will a new SBMS0 be available?  When the unit is available, will determine which address it needs to be sent to

Thank you,
Sam

Marinepower

unread,
Jun 11, 2021, 12:38:02 PM (yesterday) Jun 11
to electrodacus
Sam,

I am watching this thread with interest, as I also have a marine application, use a break-out board, and am having some voltage irregularities from time-to-time.  My voltages seem to occasionally read low however, not high. 

I seem to get a lot of ISL 94203 communication errors any time I have to re-plug in the SBMS (which has been frequent recently, as its only been installed for a few weeks and I am still working out some details).  I have to plug in the unit 3 - 5 times before the error clears (and SOC goes by default to 49%).  Are you by any chance having the same issues?

MP

SKM

unread,
Jun 11, 2021, 1:07:14 PM (yesterday) Jun 11
to electrodacus
Good morning MP,

Yes, high voltage display is not usual.  I haven’t disconnect the ribbon wire cable from the unit since I noticed the voltage discrepancy.  That is one of my next steps to see if it could resolve the issue.  I will do that today and will share findings.  BTW, how or where do you find ISL communication errors? Diagnostic page?

Thx,
Sam

Dacian Todea

unread,
Jun 11, 2021, 2:31:15 PM (yesterday) Jun 11
to electrodacus
Sam,

That 31C is the ISL94203 IC internal temperature and should be normally closer to ambient unless there was a charge cile with cell balancing just before you took that photo.
This is the new SBMS0 model that you have and so the IO5 and IO6 are available on the main unit no need for WiFi/USB addon.
I ship about once every two weeks so next shipment will be around the end of this month then how long it takes to get there from the time I send will depend on your location.

MP,

It seems in your case is a bad connection or slow insertion of the 12pin connector. If some of the pins are making contact quite a bit later than others the ISL may be powered before the microcontroller and that is when you get those ISL94203 communication errors at the start. So just check the connections maybe soldering on that adapter board and insert the cable more confidently (faster) so all pins are powered at about the same time having the connector inserted straight.

Reply all
Reply to author
Forward
0 new messages