SLR secondary overheats!!! Need an expert advice! / High Voltage / Forums

Forums

4hv.org :: Forums :: High Voltage

« Previous topic | Next topic »

SLR secondary overheats!!! Need an expert advice!

1 2 3 4 next

Move Thread

LAN_403

baleworker

Mon Nov 03 2008, 02:13AM

Registered Member #1596 Joined: Fri Jul 18 2008, 08:43PM
Location: USA
Posts: 65

I think litz wire did help with my primary, it stays cool, but the secondary now heats up like crazy, goes to 80C-90C!!!
I am using awg 26 wire and the current is only 200mA rms. The load is fullwave rectifier followed by an arc between 2 copper electrodes.
Is any reason why secondary would overheat? I guess skin effect is not an issue at 100kHz and 26awg. Cant think of anything...
Anyone experienced something similar?
Any input is highly appreciated!!!

P.S. I use a small inductor in series with the primary. I tried making it with 6x18awg wires and they got super hot, replaced with litz and it stays as cool as ambient.

Steve Conner

Mon Nov 03 2008, 11:40AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Maybe it arced over internally and now has some shorted turns.

baleworker

Mon Nov 03 2008, 01:48PM

Registered Member #1596 Joined: Fri Jul 18 2008, 08:43PM
Location: USA
Posts: 65

Steve McConner wrote ...

Maybe it arced over internally and now has some shorted turns.

I have tried 4 different transformers, including 3 which were vacuum potted. Same result!!!
Will try it under oil next, and see what happens.
Anybody ever experienced any issues with heat? So frustrating, I am about to give up...

Dr. Dark Current

Mon Nov 03 2008, 10:11PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Well, only 3 things can heat the winding- resistive losses, heat conduction from core, and corona losses.
If you measure the secondary resistance, you can calculate resistive loss (take skin effect in mind) and compare it with the actual loss.

If the calculation matches, well, then you need more copper on your secondary...
If it does not, there can be additional losses from corona or shorted turn(s) in the secondary.

baleworker

Tue Nov 04 2008, 03:09AM

Registered Member #1596 Joined: Fri Jul 18 2008, 08:43PM
Location: USA
Posts: 65

1. Resistive loses: Secondary resistans is about 20 ohms, so at 200 mA: Pr=0.2^2*20=0.8W I dont believe that kind of power is capable of heating up all that copper to 80 degrees in 10 minutes. I am running 100kHz with awg 26. its good till 107 kHz as far as skin effect goes. Proximity effect may be?

2. I put it all under oil and sucked the air out, still got pretty warm after a few minutes.

3. Core lose? Well, the core stays kinda cool, i tried removing the windings fast and its considerably cooler than secondary. I thought core was the reason, but its not, secondary is the main heat source.

Will try to dewound it to see if there are any signs of shorts or internal arcing.

Anything else I can try?

Electroholic

Tue Nov 04 2008, 03:31AM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

is it a multilayered coil? can it be dielectric losses?

baleworker

Tue Nov 04 2008, 02:02PM

Registered Member #1596 Joined: Fri Jul 18 2008, 08:43PM
Location: USA
Posts: 65

Electroholic wrote ...

is it a multilayered coil? can it be dielectric losses?

I've tried multiple coils, all multilayered. One of them had multiples layers separated by mylar film, another one had multiple sections, whithin each section there were no insulation between the layers except for potting epoxy.
I am kinda excluding corona now becasue the arc runs at about 1kV and it give a really tiny voltage to cause any internal discharge.
Also since the voltage drops to 1kV, primary voltage also drops, and it reduces V-sec dramatically, so core lose is out of picture as well.
Could it be proximity effect?

baleworker

Wed Nov 05 2008, 05:08AM

Registered Member #1596 Joined: Fri Jul 18 2008, 08:43PM
Location: USA
Posts: 65

Alright, now I really need some help!!!
After moving the primary from under the secondary to the other leg of the core, transformer runs barely warm!!!
The thing is I cant have a primary on the other leg since leakage inductance is too big and no way to get a desired frequency/current combination!
Why would the primary under the secondary cause so much loss and is there are any way to reduce leakage inductance?
I am sure there are a lot of professional people on here who really understand electromagnetics and how things work. Please advice a novice!!!

M3mristor

Wed Nov 05 2008, 06:31PM

Registered Member #1738 Joined: Fri Oct 03 2008, 08:48AM
Location:
Posts: 5

do you have this problem if you run at a other frequency(90-110kHz)?
perhaps there some bad resonance. can you measure capacity between primary and secondary?

and what is slr?

baleworker

Wed Nov 05 2008, 08:16PM

Registered Member #1596 Joined: Fri Jul 18 2008, 08:43PM
Location: USA
Posts: 65

M3mristor wrote ...

do you have this problem if you run at a other frequency(90-110kHz)?
perhaps there some bad resonance. can you measure capacity between primary and secondary?

and what is slr?

SLR is a series load resonant, there is a capacitor in series with the primary, so it forms a resonator along with the primary leakage inductance. Here is how primary current looks like at 50% duty cycle:

and 25% duty cycle:

Once upper igbt opens, current follows a sin wave, goes all the way back to zero, and thats when transistors turns off and current swings in the opposite direction. Then lower igbt opens.
So there is aconstant on time=1/2 of a period. And there is also a dead time of at least 1/2 of a period.

I will try measuring inter-winding capacitance. What effect can it have on operation?

1 2 3 4 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob