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Re: [TCML] microbrute DRSSTC



HI Joe
I have a question for you still about my coil, I finally got it to fire off, it does about 6 in arc's but the over current led come on all the time and pull the arc down. I have it set at 3 volt I try tuning it but did not make a difference. I finally had to change ever IC to get it working again, got little to no help from there tech. support he is gone out of the country till next month. Any ideas on what would cause the problem. Also how big of arc's do you get on your coil.
thanks
alton



On 1/1/2013 11:34 PM, Joe Mastroianni wrote:
HI Alton
Primary wires backwards?  Ok, well, that's a start and I think achieves the same thing as reversing the wires through the CT.   Also, I don't remember what voltage corresponds to what but maybe 3.2V allows 500A or something?   I run mine with the overcurrent set pretty low.  (I forget where it is set...but I set it so that my wife's students can't blow it up)   Probably you should start even lower than 3.2V.  If you're blowing up IGBTs you've got too much current one way or another, and first thing you should do is run at lower tank voltage and fiddle with the tuning.  We can presume you don't have dead time problems as all that's preset with the parts Dan has on the board.    I never run mine above 70VAC input to the tank, and I get nice 12" arcs that are just ok with me.  My wife uses the microBrute in the physics class she teaches about electricity, so it sees a lot of action and is pretty reliable.

Those IGBTs can be pricey.  I bought a full tube of them through digikey way back when I built the microBrute and have pretty much blown through all of them for one reason or another over the past 2 years.  Dan buys them in bulk so you may be able to get them cheaper through him.

Anyway, you're on the road.  From here on out it's all about tuning, getting the right interrupter freq and pulse width, and choosing the right breakout, etc.  That's all trial and error and you can have a lot of fun fiddling with it.

Best
Joe


On Jan 1, 2013, at 7:11 PM, W5als wrote:

Hi Joe
     I found my first problem, the primary wires were backwards. I switch them it
Fire off, I brought it up twice and the over current did what should have since
R25 is set at .70 volts. I turn it up to 3.2 volts it came on for 3-4 seconds and
Went off would not work any more. I than check the IGBT's and one had shorted
have no idea why that happen.
Thanks
Alton

Sent from my iPad

On Jan 1, 2013, at 6:24 PM, Joe Mastroianni <joe@xxxxxxxxxxxxxx> wrote:


Hi Alton,
Well, if everything was working correctly and you just weren't triggering the IGBTs, you'd at least get a little current draw that would be charging up the DC caps in the DC supply, but then that would probably tail off as well.  So, the whole thing may stem as a problem that you're not triggering the IGBTs, even though the circuit is buzzing away with the gate triggering signal.

OR - it could be that for some reason you're not actually charging up the DC supply.  Your HV diodes could be blown up (but probably not).   (Very carefully) Check the voltage across C41 (you could also do this at any other number of places)  to make sure you're actually getting a tank supply. If not, and you have no current draw at all from your variac, then something is just plain not connected (or a trace is broken on the PCB, or your 5A fuse is blown, or CR43 and CR44 are blown up...but I doubt it).

If you do have a good DC supply on the tank circuit, then you're just not triggering the IGBTs.  That could be lots of things...like your VRxx protection diodes are screwy but also unlikely, or more likely, your GDT is wound wrong.  That would be very easy to get wrong.  Look at the output on a scope and make sure you've got good pulses coming off there to the gate of each IGBT and make sure they're correctly phased.  If they're not phased right, you're going to know right away because things would smoke.  Both IGBTS on at the same time can become a cause to run in bigger coils..;)

Or -the pulses from your interrupter may just be too short...  Gotta check that with a scope.  I think the maximum pulse width he suggests is 200ns, but my memory is very bad, and it is possible to have such a short pulse width that nothing happens.

Good luck with your debugging,

Joe


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HI Joe
     I have reverse the wire through the current transformer did not help. the one strange thing
is on the 5amp fuse side it pull no current at all through my variac with a current  meter on it.
I have also tried tuning it too never pull current or get a arc. I still think something in or around
the IGBT's is just not right.
alton
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