Re: (ET) charger info

["David Roden (Akron, Ohio, USA)" <roden ald net>]

> Say I use my tractor 
> for 30 minutes or so, to move something, mow a small patch, etc... 
> How would I know where to set the charger at to recharge my 
> batteries, rather than just guessing at the amount of discharge and 
> setting it at "A-I"?

30 minutes is actually a significant amount of use time.  If you were 
just moving it out of the garage, around the driveway, and back in, that 
would be pretty inconsequential.

The rule of thumb I've heard for lead batteries is to charge them if you 
have withdrawn 5% or more of capacity (measured as amp-hours at the 20-
hour rate).  If the battery will be unused for some time (say 24 hours or 
more) this becomes more critical.  The reason is that, with time, the 
lead sulfate formed during discharge becomes less able to take part in 
the chemical reaction during charge; thus capacity is lost.

How do you know how many amp-hours you've used?  Some folks have added 
amp-hour or watt-hour meters to their ETs.  One such animal is made by 
Cruising Equipment and is called the E-meter.  It is a bit tricky to 
install; if you add one, follow the wiring diagrams ~exactly~ or you will 
destroy it.  They cost around $200.

The problem in this case is that the ET's crude charger control (a timer) 
may make the risk of overcharging the batteries greater than the risk of 
sulfation from leaving them sit.  But for 30 minutes of mowing, I'd say 
running the charger for an hour or so shouldn't hurt and might help.

BTW, for those whose chargers fail, here's a quick and dirty fix.  Junk 
the charger and buy three $40 automatic car battery chargers at the 
hardware store.  Reconnect your lift so it's at either 12 or 24 volts (so 
you can pair evenly discharged batteries).  Connect the chargers to pairs 
of 6v batteries.  If you have small enough chargers, they may even fit in 
the front of the tractor where the old charger was, and can be connected 
permanently to the batteries (I recommend a 15 amp fuse in each charger 
connection).

Now you have better (though still not optimal) charge regulation, and the 
chargers can put more into the batteries which run the lift (which are 
always lower than the rest of the pack) without overcharging the ones 
that don't.  I still recommend unplugging the chargers after 18-24 hours, 
however.  I use this method with a shutoff timer.

By the way, most capacity loss attributed to memory effect in nicads is 
caused by depressed voltage.  Repeated overcharge can cause the nominal 
voltage to drop.  Even though the same amount of energy is available from 
the battery, the voltage drops below the electronic device's minimum 
voltage threshold sooner.  The cure is a complete discharge to zero volts 
followed by a full equalizing charge.

As for lead batteries, I have only heard of one case of alleged memory 
effect.  It involved Hawker Genesis batteries ~only~.  It manifested  
itself as a premature rapid loss of capacity.  I haven't been able to 
learn more about this problem yet, so I may be premature in calling it 
"memory effect."

Hope this helps.


David Roden - Akron, Ohio, USA
1991 Solectria Force 144vac
1979 General Engines ElectroPed 24vdc
1974 Honda Civic 96vdc
1970 GE Elec-trak 36 vdc