On 24 Apr 2009 at 10:35, Mike Wallace wrote:
I think you could buy a rebuilt "electronic timer" for around $50 from
Lester ... Anybody have any thoughts on this approach to upgrading the
OEM charger?
I don't think it's as simple as connecting the charger's output to the
Lestronic timer.
To see how it's used, you can check out a schematic of a typical Lester
charger. I have one for a model 9868 (120 volt / 12 volt) in the EVDL
library,
http://www.evdl.org/lib/
or direct link
http://www.evdl.org/docs/lester9868_schematic.pdf
The page is oriented at 90deg so you'll want to print it out (or twist
your
neck reading the screen ;-).
I haven't worked on a GE charger as I don't use mine, so I don't know
whether it implements the hardware that the Lester "black box" wants. For
example, at a glance, I noticed that the Lester timer controls a DC relay
on
the transformer's primary, so you'd at least have to add something like
that.
Normally you wouldn't use two charge controllers with a charger as they'd
more or less disagree over when and how to charge the battery, so I
wouldn't
recomment using both a Lester timer and one of Harry Landis's controllers,
or any other pairing for that matter.
If you want a cheap and fairly easy to build charge controller, see this
diagram :
http://www.evdl.org/docs/c_car_charger.jpg
This is a simple adjustable cycle-dropping charger design (literally right
out of an engineering handbook).
I'm not a EE by any means, but I've worked on these chargers. Most
component values don't appear to be very critical. L1 is a small 12 volt
pilot lamp. On the C-car it was one of the dash indicators. You can (and
I
did) replace it with a resistor (sorry, I don't recall the value, but it's
easy to determine empirically) and an LED plus series resistor.
CR3 is a generic SCR, chosen for the current and voltage the charger can
produce.
SCR is a small part and again almost anything that can handle 100-200
volts
should work. I think when I replaced this on mine I used something right
off the hook at the Radio Schlock around the corner from my house.
CR5 is a generic small silicon diode; IIRC a 1 amp 400v should be plenty.
CR6 is a 12.6 volt zener diode. Something close to that should work; you
might have to tinker with the values of R4 and R6.
R5 is a 5K pot which adjusts the voltage limit.
You'll probably have to tweak the values of R4 and R6 to use it for a 36
volt battery instead of a 48 volt one.
This circuit charges at a rate limited only by the charger's wiring and
transformer, until it reaches an adjustable voltage threshold. Then it
begins cycling on and off. As the battery reaches full charge, the on
cycles get shorter and the off cycles get longer. When the on cycles are
a
second or less long, and separated by a few tens of seconds, the battery
is
essentially fully charged.
This is the same simple algorithm used by probably millions of $50 NAPA
battery chargers -- and, incidentally, by Rudman Regulators, for those of
you who are road EV followers. It's essentially a faster taper charger
with
no temperature compensation or any other deluxe features, but it's cheap
and
if properly adjusted is more or less adequate for flooded batteries.
Longtime readers here know that Harry Landis and I don't agree on what
constitutes an appropriate charge algorithm for a battery used cyclically.
His is somewhat unorthodox. However, he has several advocates here, and
I'm
sure they'll be more than happy to argue in his favor. ;-)
Hope this helps.
David Roden - Akron, Ohio, USA
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
Note: mail sent to the "etpost" address will not reach me. To send
me a private message, please use the address shown at the bottom
of this page : http://www.evdl.org/help/
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
_______________________________________________
Elec-trak mailing list
Elec-trak cosmos phy tufts edu
https://cosmos.phy.tufts.edu/mailman/listinfo/elec-trak