I got something home that seems to be usefull and heavy as well. While it is unused it sits quietly in a corner, but if i use it it starts to rumble with 120Hz.
This is Variac or autotransformer. This particular unit is 3phase 10kW model. If i feed it 3phase 400Vac it will make from 90Vac to 450Vac.
Conversion is made by transformer core. To vary the voltage i can move secondary transformer core out of primary by a knob on the outside.
So i decided to make 3phase rectifier of an old army ammo can. First i got 3 phase bridge. A nicely shaped cooling fins and one 100uF film capacitor rated to 900Vdc. I added a 50A forward diode so i cant connect the whole thing wrong.
Once i connected it and tested everything it became clear alu fins will heat up. So i got one 230Vac cooling fan over the fins.
I do have to be near the thing when it charges since it doesnt have any voltage control. I simply set it to battery voltage with some overhead so the desired current flows and then over time current slowly diminishes as voltage equalises.
In the face of my car full charge i need to reset voltage at least 3 times to get to 400Vdc desired battery voltage.
I am sure i could make a simple DC voltage detector to cutoff the main AC contactor. But for now it works as excellent home charger backup.
leafdriveblog 