From: "David Roden (Akron OH USA)" <roden ald net>
To: elec-trak cosmos5 phy tufts edu
Subject: Re: (ET) battery charger controller
Date: Mon, 14 Aug 2000 23:24:29 -0400
On 14 Aug 2000, at 20:44, harry landis wrote:
> I like 38V because that is about the voltage that a fully charged 36V
pack
> will settle to with no load. That's 2.11 V/cell.
You are charging at float voltage. That is acceptable for batteries used
in float service, such as in a UPS system, but not for cylic service. It
can take literally weeks for a battery to reach full charge at this
voltage. If you use your tractor weekly and charge to only this level,
you are probably undercharging your batteries. In time, they will become
sulfated and lose capacity.
Your charger will also not equalize the pack adequately at that voltage.
The ideal charge regimen for lead batteries in cyclic use is to charge
constant current until they reach 2.45 to 2.50v per cell (2.35 for gel
batteries), then hold at that voltage until current falls below about
0.02 times the capacity of the battery (less for sealed batteries). At
that point the charge should be terminated. Periodically an additional
equalization charge should be applied: hold the current at 0.02 times the
battery capacity for 2-6 hours with voltage unlimited. On an unmodified
ET, which discharges the batteries unequally because of the tapped
battery pack, equalization should be performed on every charge cycle.
Obviously the minimally controlled ET charger can't perform the above
regimen.
The Fair Radio charger which Christopher Meier recommended can do it if
you control it manually (which means a lot of babysitting).
There exist a number of microprocessor controlled chargers which perform
it very well. I'm familiar with the ones which are available in road-EV
voltages, but I'm sure there are others which are suited to ET (golf car)
voltages.
A Lester Lestronic type golf car charger uses a DV/DT algorithm with a
similar effect, except that I've found that their finish rates are often
set higher than the optimum for golf car batteries, typically about 8
amps. They can be and should be ordered with a lower finish rate of 5
amps. These chargers are the standard of the golf car industry for a
good reason. They are a good value.
Harry's charger sounds like a cycle dropping type. This is similar to
the inexpensive "automatic" chargers sold in auto parts stores.
David Roden - Akron, Ohio, USA
1991 Solectria Force 144vac
1991 Ford Escort Green/EV 128vdc
1979 General Engines ElectroPed 24vdc
1974 Honda Civic EV 96vdc
1970 GE Elec-trak E15 36vdc
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