I've been trying to make a simple back up charger for when the sun isn't shining and I have to crank up the generator, for 12, 24, and 48 V batteries, and anything in between.
I am sure people have done this before, but I can't find any info here.
I am using a 0-120 Vac, 10 Aac variable autotransformer/Variac, a power diode and/or a diode bridge, and a large capacitor.
I plug the Variac into the generator, connect the rectifier circuit to the Variac's output, and set the Variac's dial to the voltage that produces the charging current I need.
This Variac has a 10A fuse in its output circuit, so it limits the current to 10A regardless of the voltage setting.
It works fine using a half-wave rectifier, but I am not sure the generator likes having to deliver power on half-cycles only, may be bad for the generator long term?
Plus, I am not taking advantage of half the energy in a given amount of time, I could be putting into the batteries.
When I hook up a full-wave diode bridge to the Variac, I run into trouble. I have two bridges, one from a DC welder rated 40A 800V, the other one smaller from some electronics gear. Both bridges act the same.
With the bridge's AC terminals hooked up to the Variac's output, and the bridge's DC terminals hooked up to a scope probe or a DVM only (no load – no current flowing, except very small through the probe/DVM), the Variac's winding starts buzzing when I raise the voltage from zero to about 10 Vac-peak.
When I push it to about 15-20 Vac-peak, the buzzing gets louder and the Variac blows a 10A/250V fuze.
During this time I see a full-wave rectified voltage waveform rising on the scope, then it goes to nothing when the fuse blows.
Can't figure out why it's doing this.
Don't think it's the bridges, I've checked the diodes in forward and reverse directions, seem ok, no shorts or opens.
The bridge ratings are adequate for the charger I need.
There is no load on the bridge, so no current should be flowing, but still the Variac behaves like it was overloaded when it blows that fuse.
Has anyone messed with these universal chargers using a Variac, and run into a similar problem?
How about using a half-wave rectifier with a generator, wouldn't it damage or unbalance something inside the generator when used over an extended time period?