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Re: Skip's DRSSTC



Original poster: Skip Greiner <sgreiner@xxxxxxxxx>



Tesla list wrote:

Original poster: Steve Ward <steve.ward@xxxxxxxxx>

Hi Skip



Question: These IGBTs do not have internal diodes. Presently I have
400v bidirectional surge suppressors external to the IGBTs. Is this
considered sufficient?



NO WAY! You *must* have a diode across each IGBT. Its some sort of miracle that they havent failed yet. I do note that you are running 7AAC input for only 18" sparks... how hot are those IGBTs getting??
The IGBTs are mounted on a fan cooled heat sink. They are just getting warm to the touch with 120vdc on the big filter capacitor. Don't forget, the secondary winding is only 18" tall.


I am going to raise the AC input voltage up to 240, a little at a
time. Can I increase  the suppressor voltage to, say, 500v ?


You should use around 440V for the clamping (2x 220V TVS is what i use on my coils). This allows for 420VDC max which is usually plenty for some big sparks.
This is exactly what I have now and the suppressors are right across the IGBT leads.

If you are using these IGBTs in an H-bridge at present and are using
them on DC, can you let me know the maximum DC that you have used successfully?
They are in an H-bridge and the maximum DC so far is 120v. That is what is getting me 18" sparks. I will be taking them up tomorrow now that I have your comments. Will let you know tomorrow.


They should be fine to 400V... assuming you 1)put those diodes in there! and 2) have sufficient decoupling capacitors and TVS on each IGBT, also be sure to minimize (and i really mean *minimum*) the inductance between IGBTs, and their TVS and decoupling caps.
I do have the TVSs and decoupling caps on each IGBT. I guess that is why they are still alive.

Steve

Skip