219: Sunday 18th December 2011

Fitted 120v charger back on today. Worked fine, first charge, 80% indicator came on almost straight away. I ran a tester across each battery and found my 2 suspect batteries at 16v and the others at around 14v. About 3 hours later the charger had finished and I got 4 miles and it was flat again. Ran a tester again and found 12.5v on most, but 10.15 and 11.2v on the 2 suspect batteries. Charged again for about 3 hours and got 7 miles after running the screen heater to clear the frost off the screen, so that is better. I am hoping that I can get the batteries to cycle up and take more charge over the next few charges. I want to get the battery monitoring system up and running very soon now, so I can see exactly what is happening while I am driving. I have handed this over to my friend now who is using it as a case study for developing several modular systems. My system shall include a display board, a dual CAN board and 2 CAN 10 way measuring ports. This all connects together with serial links over CAN and a USB connection for programming. Looking forward to this now.


  1. With Your lead-acid batteries it is ok to measure the voltage, but when running on LiFePo,
    this will not give You useful results, as it is impossible to get a reliable info about the state of charge from measuring the voltage of LiFePos(except full or empty, but not in between, the curves are too flat!)
    You will have to count Ahs ! Dont forget about this when developing any BMS-System
    Voltage (of each single cell!) is only needed for defining the end of charging and discharging then.

  2. Thanks Franz, I shall have a current sensor connected to the system and as it is open source, it can be programmed for whatever is connected and displayed however I like. This is the beauty of the system. There is limited scope for monitoring the voltage of say, 40 Lithium cells, but what it will show by having lots of bar graphs is if one cell is not the same. They should all move together about the same amount. If one is bad, it will show up against the others. I can set up all sorts of warnings as well. For now I am planning 20 inputs, with 10 at the front and 10 at the rear with a CAN connection for each box, so each signal can be read seperately on the CAN links. I shall find the perfect balanace eventually.

  3. You might save some space when displaying
    only minimum, average and max for normal info.
    of course with the possibility to check every
    cell individually.ten or twelve bars are wonderful for lead acid batteries, bot dont forget the future, and there will be fourty
    or fifty lithium cells....... ;-)
    The system must tell You if there is something
    wrong! Even if You dont watch it!