48 Volt Carger conversion ?

Thread Starter


Joined Apr 30, 2009
I have a Lester 48 volt 17 amp battery charger. it has an electronic controller/timer encapsulated in epoxy and has obviously gone bad. It also has 2 SCR's that are shorted. I called to price the controller and it's $200 so it's not worth that to me.

So, I plan to convert it to just a straight charger eliminating the SCR's and the controller/timer module similar to another model they have (schematic shown below) and just use a plug in timer to control the charge time.

My question is, what is the separate transformer coil and capacitor for ?





Joined Nov 7, 2013
As the scrs may have been used to taper the charge, it's possible that they use a higher voltage in the scr chargers.

I would watch for over charging.

A lower capacitor value lowers the charge voltage and current.

A 6μf cap that measured about half cut finishing voltage output about 15%.


Joined May 19, 2014
Feroresonant transformers are a lost art in the US. The transformer in this charger will perform as a constant current output over a wide voltage range. Perfect to charge a battery.
The separate coil connected to the capacitor is the control portion of the feroresonant transformer. The transformer controls the output by controlling the saturation of the core. The greater the saturation the less output.
To state it simply, that winding and capacitor makes the transformer act like a battery charger and not a power supply. I hope you get the difference.


Edit: I forgot to say that a feroresonant battery charger came with a used electric golf cart I bought.
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Thread Starter


Joined Apr 30, 2009
Thank you all ! The SCR use makes sense. And that's very interesting regarding the separate coil/capacitor, I never heard of this before.

However, I've realized the transformer on this model (Lester 25930) has only 2 separate secondary coils. Each producing about 51 V AC. No 3rd coil.

So I've decided it's best to just replace the electronic module and the SCR's and have it like new again. Still about 1/2 the cost of a new one.

Mark, this is for a 3 seat golf cart "limo".

Thanks again, I appreciate the info and help,