Soft Starter.

Thread Starter

R!f@@

Joined Apr 2, 2009
9,758
I am planning to make a soft start circuit since the Tranny I intend to use in my Big Daddy PSU is tripping my 10A CB. :mad:

The Tx is around 2000VA. It has 4 windings of 60V capable 8.3A Continues.
My PSU will have 4 outputs, all isolated so I can series them and parallel them if needed. :D

My question is simple.

What will you use for the series power resistor tht limits the inrush current.

I thought of series connecting 4 X 10Ω10W . So 40Ω 40W.

Will it do. What will u recommend for the delay time. 1 sec or more.

The smoothing caps will be 10,000μf . per winding.
 

ScottWang

Joined Aug 23, 2012
7,117
Are you affraid of the current reducing by the limiting resistor, although the capacitor 10000uf could store the energe on itself, the load need the continuing current, but that will stop by the resistor, so you have to considering the voltage drop.

Maybe you can using the Magnetic Field of Toroid to replace the resistor.
 

THE_RB

Joined Feb 11, 2008
5,438
Toroidal transformers should have a series resistor added to the primary winding circuit to reduce the extremely high inrush current.

The ratio of inrush current to operating current is so high that you don't need a fancy solution, just drop 2-3% of operating power in the resistor which has little to no noticeable effect on normal operation besides dissipating a couple watts in a 10W resistor.
 

Thread Starter

R!f@@

Joined Apr 2, 2009
9,758
Well..! u guys are off the point.

I know how to make one.
My question is what would be a feasible value series resistor for the primary in rush current limiter.
I never tried for a 2000VA one. I can make one for 500VA one.
But for the 2000VA one the resistor needs to be powerful and different value.

I wanted to try with a 40ohm 40W one. Will it be suitable or blow.

My Supply has inrush limiter with a bypass relay at the secondary side.

My problem is tht the CB trips sometimes even with the transformer alone. The damn thing is heavy. I can barely lift it.
I got it from a peavey 2000 amp.

RB got close to what I wanted to know.
2 to 3 % drop. OK lemme do some calculation

Oh and um tranny is an EI one
 
Last edited:

t06afre

Joined May 11, 2009
5,934
Try Google and <transformer soft start> or <transformer softstart> The Elliott Sound Products site give a decent explanation about this topic
Edit: Would it not be more easy to just rip the inrush protection unit from the peavey 2000 amp
 
Last edited:

THE_RB

Joined Feb 11, 2008
5,438
NTC surge limiters function better than a simple resistor, but have a much higher incidence of fail.

Like I said, when the ratio of inrush current to operating current is very large, a resistor of the right value works quite well. If that ratio is lower then a thermistor will work the best.
 
Top