Power Wise 28115 G04 E-Z-GO Golf Cart Charger Schematic (Ferroresonant)

[Kugelsicher]

Traced out the circuitry for an EZ GO golf cart charger,  Power Wise model 28115 G04, while attempting a repair. I thought it was interesting and perhaps it will be of help to someone.
The charger and cart aren't mine. In spite of the charger being covered in mud, nothing is wrong with it. There is an 8-bit micro-controller that checks for a minimum voltage that the cart battery apparently isn't meeting. The charger doesn't indicate this in any way.
It's a ferroresonant transformer that is powered from the mains through a relay; however, all of the electronics are powered by the DC output side (or the golf cart battery itself when not charging).

[SeanB]

Most common fault with ferroresonant devices is that resonating capacitor going low value, which results in poor regulation, though you also will have to be aware the voltage across that capacitor is very much higher than mains, and is dependent on load current. Capacitor 10% low in value change it, and preferably with a 440VAC rated motor run capacitor over the 370VAC rated one, as it will last longer there. Have seen them burn those capacitors out, with the converter working fine just with lots of noise and smoke. Otherwise the diodes failing, though normally they are pretty reliable, as the limiting results in a very long conduction angle as the secondary coil saturates and presents a almost square wave output, so the diode conducts over a larger portion of the sine wave. that and inherent voltage limiting within limits, so the lead acid batteries get to float voltage and stay there.

[Kugelsicher]

Thank you for the advice. The unloaded output measured 44V. I don't know what's normal and I only energized it briefly as I suspect it isn't designed for no load. The cap measured right on 20uF but it was on a multimeter not an LCR meter; so I don't know what the ESR is and I know leakage looks like extra capacitance. Given your comment that they're often the point of failure; I'll go ahead and replace it before returning it. The spade connectors were so rusted on that cap terminals that I had to break them off and replace them; so that probably should've told me to just replace the cap