/diy/ - Do It Yourself

trying to make a variable ac to dc using my variac and a diode bridge and it works with the bridge i salvaged from a circuit board but it gets quite hot when i approach the 20 amp limit. i decided to upgrade to a 50 amp heatsunk bridge however when i try to go above the forward voltage of the bridge with my multimeter attached to read the voltage the brush inside the variac sparks when changing voltage. the salvaged bridge had no issue with only a multimeters small ma load or with several amp loads. i have not tested a high amp load on the 50a bridge as i dont want to ruin my variac after it sparking under low load.