Re: [TCML] microbrute DRSSTC

[Joe Mastroianni <joe@xxxxxxxxxxxxxx>]

Hi Alton
I get 6" to 12" arcs. I've heard of people getting 24" arcs but I don't know how they do it.

Getting longer arcs could require any number of things. I would try these in the following order:

1) adjust the tuning. This means adding or subtracting wire from the primary 1/4 a turn at a time. Keep in mind the wire that is part of the primary that is not coiled but just goes to and from tne terminals in the board also counts.  Keep messing around until you can peak the arc size. I see from your email address that you are a ham radio operator. (I am too. I am AL3A.). Tune your coil the way you would tune a linear amp or by tuning in the swr on an hf antenna. Vary the wire length in the primary till you get a peak.

2) get a scope and measure the pulse output from the interrupter. You want 200us max on the duty cycle. But if you're not getting 200us the arcs won't get very big.  Going over 200 microseconds won't make the arcs bigger, usually, it will just draw more current.

3) raise the voltage on the over current protector slightly, but only after you've done steps one and two. That protector is what's keeping those igbts from blowing up, so be careful.

73
Joe

Sent from my iPad

On Jan 9, 2013, at 3:39 PM, w5als <w5als@xxxxxxxxx> wrote:

> 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
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