Hi and
to the forum.
The problem is that I get significant voltage drop on batteries number 1 and 2 when battery control module is telling me I have still 75% battery left.
Battery number one is the "main ground".
If you are referring to "Cells" 1 and 2 in the same battery pack then weak cells may be the cause. It shouldn't matter where the cells are positioned in the series string as they are should all be subjected to identical current loads.
The only exception to this would be if the
BMS (battery control module) was drawing more residual current from a small number of cells, which could eventually cause those cell to discharge more than the rest over a long period of time, but this is unlikely to have any noticeable affect with your large capacity
(200Ah) cells if they are regularly charged and fully balanced.
You say you have significant voltage drop but you don't mention either the unloaded or the loaded voltage.
If your
BMS allows you to monitor individual cell voltages, and they are all roughly the same after a full charge, but cells 1 and 2 are dropping significantly lower than the rest under load, then you obviously have a couple of weak cells that are causing the problem.
Does the
BMS show 75% just before it cuts out or does it quickly revert back to 75% after the motor has stopped?
It would be interesting to know how the remaining capacity, total battery voltage and individual cell voltages reported by the
BMS compare with these figures:
Am I drawing too much Current?
As you haven't said what the continuous current rating is for your battery or
BMS is, or how much current you are actually drawing, it's difficult to say if you are drawing too much current.
However, if the maximum battery current setting in the controller is set to the default 220A then you could be drawing too much current, as
these 200Ah LiitoKala cells have a maximum continuous discharge current rating of 202A.
And
this LiitoKala 12V 200Ah battery only has a maximum continuous discharge current rating of 100A!
Are my connections bad?
If the voltage is dropping low enough to trigger the low voltage protection in the controller you would need to carefully monitor the voltage at the battery to see how low it drops just before the controller cuts out.
If you still have the standard battery settings in the controller, it should not cut out until the voltage drops below 42V. If your battery voltage is also around this figure then your connections and cables are probably good.
However, if the voltage measured at the battery is considerably higher than the voltage at the controller just before the cutout occurs, then you may have either poor connection/s or your battery cables may be too thin for the amount of current being drawn.
You might want to see if it is possible to set the
Low voltage protection value (V) to
40V instead of 42V and also see if you can set the
Low voltage triggering current reducing (V) to
51.6V instead of 44V to hopefully extend your range when the battery drops below 20% capacity
Alan EDIT: Links to referenced LiitoKala cell and battery specifications added
