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RE: [SPAM] Re: (ET) Charger repair.



Ralph wrote:

>I think the ET charger might work ok, but you may have to change the
capacitor or add a 
> resistor in >series with it to tune it to 50Hz.   A 1000va step down
transformer would 
> only give you about 8.4 amps at 120 volts.  I think you will need more
then that for 
> bulk charging.

Ralph,

oops, I think I made a miscalculation. I thought our charger puts out 25A
for the
36V system which would be 900W, if I take an efficiency of 0.9 then I get
1000W.
What I didn't think of was that the charger actually does its bulk charging
around
39-40 V and probably topps out at 43-44V. Now from what I read somewhere
else the 
transformer based chargers don't supply full current anymore at the 
top-end 
voltage. Is this correct? Does it have a "natural" tapering built in that
reduces
the charge current at higher voltages, when the batteries reach full (and
thus limits 
the total power in?). It if does put out 25A at 44V then thats 1100W which
would
be too much for the step down transformer I had in mind. What happens if
such a 
small tranformer is slightly overloaded? Could I simply add a cooling fan?

Or am I falling into the VA vs. Watt trap? I guess then a 1000VA 
transformer
may 
not be sufficient to supply a 900W load. My knowledge about AC inductance 
is
a bit rusted, but I remember something about reverse current flow/phase
shift 
that doesn't add to the real power but still heats the wire. So if they
count
this current into the VA rating on the transformer then it probably is 
quite
a bit to small. I found a larger one (15A 120V output) but its twice as
heavy
and also almost twice as expensive after shipping. Maybe I should go back 
to

using my small 12V "modular" charger array.  

Markus