Hi All,
I have an issue that is really difficult for me to solve.
I have an isolation transformer on my bench. The primary is connected to 120 VAC mains. It has a fuse in series (5 amp slow blow) that I added to the primary. The transformer is a 3 kva with 1:1 isolation, that drives a variac on the secondary (0 to 140 vac). The issue is it constantly blows fuses. Today I even blew a 7 amp slow blow fuse! IT IS NOT A CURRENT INRUSH ISSUE! Here is the possible conditions:
SWITCH POWER ON:
1. Turn variac to 0 v while main power is off, then turn on isolation transformer (turn main power on), no problems! (with load or no load on secondary, still no problems!) - so not inrush.
2. Turn variac up to 120 v while main power is off, turn on isolation transformer, no problems! (with load or no load on secondary, still no problems!) - so not inrush.
SWITCH POWER OFF:
3. Turn variac to 0 v, then turn isolation transformer off, no problems! (with load or no load on secondary, still no problems!)
4. Leave variac at 120 v (or so), then turn isolation transformer off, FUSE BLOWS about 4 out 10 times! (with load or no load on secondary, SAME Problem!) - so it is outrush.
Since I tend to be absent minded while powering down, I hit #4 above quite often!
Pleas help! My patience, my fuse supplies and my wallet is suffering!
Thanks for your reply,
DM