More on battery equalising logic

[j.joyce@sri.org.au]

Lee, I am am very interested in what you have to say about battery
equalisation. I must admit I think the traditional way of intentionally
overcharging to equalise a battery pack has never appealed to me.

I like your logic and I have a thought that I would like comments on. Those
of you who design DC controllers may also want to comment ... because I
have no idea what effect my idea will have on the transient voltages and
currents that might be experienced by the batteries and controller.

What I think might work is if the battery pack was wired through the PWM
controller so that the batteries are in series during the "on" cycle of the
controller and then switched so that all the batteries are parallelled
during the "off" cycle.

I think what this would achieve is for the "good" batteries to pass a
current to the "poor" batteries during the period they are parallelled
(this would be self controlling by virtue of the voltage difference between
the good and bad batteries and thus no sophisticated electronics would be
required). My scribbles on a piece of paper suggest that all that would be
required is some 50 amp rated wiring between batteries and one solid state
device to switch between parallel and series connection. Could this
switching duty be assigned to the so called "free wheel" Diode or MOSFET
found in most controllers ?

The reason I suggest that this be done when the controller is in use rather
than overnight or during charging is that the "correct" voltage difference
between the good and bad batteries will only be seen when they are under
load. I am presuming that the voltage recovery of each battery during the
brief off period of a 15 kHz PWM controller is minimal.

At a first guess I don't think this arrangement would be compatible with
regen braking, but I don't think this concerns too many of us.

I am not an expert in the electrical field but does this sound at all
feasible ?

James Joyce
Soon to be E-Dub owner .... parts arrive soon ... ?? days to covert