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Re: (ET) Ooops, timer died
Here is a simple but effective charger controller. It was used in the old
CVI Comuta-Car. I found an almost identical reference design in an
engineering manual.
http://www.evdl.org/docs/c_car_charger.jpg
This one is designed for a 48 volt battery, but it shouldn't be difficult
to
modify for 36 volts. You could try swapping CR6 for a 9.4 volt zener, or
adjusting the values of R4 and R6, which with R5 act as a voltage divider
into CR6. R5 provides fine trimming of the finishing voltage.
L1 is a small 12 volt indicator lamp. In the C-car, it was one of the
instrument panel indicators. If anyone wants to try building this, I'll
see
if I can find one in my old parts box to check its current. However, you
should be able to determine and appropriate value experimentally. I'm not
sure it's all that criical anyway. I actually used a resistor and LED in
my
C-car, but I don't recall the value of resistor I used.
SCR is a small low-current SCR. When mine failed, I used a generic one
from
Radio Shack (2 amp?) and it worked fine. CR3 is an SCR with ratings
appropriate for the charging voltage and current you're regulating.
When the battery reaches the preset target voltage, 2.4 to 2.5 volts per
cell, the charger begins to cycle on and off. The closer the battery gets
to full, the shorter the on periods and the longer the off periods (lower
duty cycle). This is a coarse PWM which reduces the average charging
current. When the "ready" light is blinking off briefly every 10-20
seconds,
the battery may be considered full. Pull the plug. This charger should
not
be left connected indefinitely.
If you want a faster charge with a higher average finishing voltage and
current, turn up R5, and turn off the charger when the ready light is
blinking off every 5-10 seconds.
This controller has no temperature compensation, so a bit of voltage
trimming summer and winter isn't a bad idea. You'll also want to adjust
it
down a bit as the batteries age.
This circuit shouldn't be used as a battery maintainer. But then, I've
found that battery maintainers generally do more harm than good.
David Roden - Akron, Ohio, USA
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