I am creating a temporary setup for a lead acid charger, using a rewound Microwave transformer, a bridge rectifier, and a giant filter capacitor (30,000µF).
Wound turns until I got 14 volts filtered on the output of the capacitor.
I tried to charge the battery, but it seemed to get "stuck" at 11.8-12 volts, and not charge up to the 13.5 volt charge.
I know this might not be the best charger setup, but I fried my charger, and need a temporary set up. I AM watching the voltage constantly, and making sure it does not reach above 13.5.
The battery is a 17 amp hour 12 volt lead acid
And the reason I am using the Giant capacitor is I am using it for equipment in parallel with the battery and charger that is very sensitive to hum.
Best Answer
When you measured the 14 volts I bet that was with the load and battery disconnected. Under load conditions, the transformer and bridge rectifier would drop a volt or two.
Transformers are never perfect and the coils have series resistance that cause imperfect "regulation". Series leakage inductance also contributes to the problem.
For the rectifier, the volts lost across a single silicon diode might be about 0.5 volts on very light loads but when charging, each diode voltage will be more like 0.7 volts and, for a bridge rectifier lose an extra 0.4 volts in total.
You know the answer by now, add 5% (ish) more turns to the secondary.