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(ET) Thoughts on the ET charger.


Thoughts on the ET charger. 

 Any constant voltage charger (power supply) will charge batteries. When
you first connect any constant voltage supply (as the ET charger is) the
power supply will try to put out its maximum current into the load the
discharged batteries.

As the batteries start to charge the voltage of the pack comes up and
the amps start to go down. Amp flow from the charger to the batteries
stops when the voltage of the supply and the load are the same. 

So, why did General Electric put a Ferro-resonant power transformer on
the elec-trak when a much simpler charger would have worked?

I am sure it has to do with how the owners would charge their new
tractors. In the 70's not every one had a 20 amp 120 volt outlet in the
garage just waiting for some new electric device. In fact I am sure some
people used extension cords with lots of voltage drop. Just a small
change in input voltage to a simple transformer and rectifier would
cause the output amperage to drop a lot causing longer recharge times. 

 Constant charge voltage is desirable to quickly charge depleted
batteries and not cook them at the end of the charge by using a higher
voltage to make up for the voltage sag at first. The timer took care of
long term cooking if you forgot to unplug the charger as GE knew people
would. No attempt was made to use a three stage charge system as is now
sometimes used. Remember micro processors were not the norm back then.
Turning the charger on and off to keep a constant pack voltage is a good
idea, but must have been rejected as it required the owner to keep his
tractor plugged in. 

 So it was build a solid state linear power supply to keep voltage
constant or a low parts count easy to service Ferro-resonant transformer
with only a few extra parts.

And the winner is?

 Keep those extension cords warm. 

  Dwight 

 

Dwight L. Hazen
Indiana University, UITS
Bloomington, In. 47408-7378
812-855-5367    
Ham Radio wb9tlh arrl net http://wb9tlh.ampr.us