[BC] Lead acid batteries.

[Harold Hallikainen]

> My car runs on ten 180-Amp-hour 12-Volt deep cycle batteries connected
> in series.  Keeping the charge balanced is difficult to say the least.
> I keep close records on each battery and I can attest to the fact that
> the ones that are discharged the deepest fail first.

Several years ago, I built a battery monitor for use in electric cars. The
monitors were mounted on the negative terminal of each of the series
connected 12V batteries. A lead went to the positive terminal. The monitor
would watch the battery voltage. If it went above a certain threshold, a
power resistor was switched across the battery (PWM with the duty cycle
ramping up or down as required to stay at the threshold voltage). The
power resistor was in a TO-220 case and heat sunk to the negative post of
the battery. Another wire went to the positive terminal of the battery
"below" this one in the string. This measured the voltage drop across the
cable connecting the two batteries to get an indication of charge or
discharge current. All the data (voltage, current, temperature, PWM duty
cycle) was put in a packet and drove an optical coupler. The transistor on
the output side of the opto was connected across an open collector bus
with all the other battery monitors. This bus went to a dashboard mounted
display and battery charger controller. You could see the condition of
each battery during charge or discharge. During charge, the charger would
start cycling on and off as batteries hit their threshold voltage that
turned on the PWM bypass resistor. On the open collector bus, data was
sent by each battery monitor on a random schedule every second or two.
There were occasional collisions resulting an a packet being discarded.
Most of the packets got through though.

So, there are some comments on charge balancing!

Harold

-- 
FCC Rules Updated Daily at http://www.hallikainen.com