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Steve Conner

Tue Aug 29 2006, 12:58PM

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

It's a series circuit, so it doesn't matter if you put the current sensor "before" or "after" the tank capacitor, the current flowing through it is the same.

Reaching

Tue Aug 29 2006, 03:49PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

i dont know, its the first drsstc i spend so much effort into to make it look good and now, nothing works, dissapointing. some parts arrived today, jeah and some 400volt tvs,, i made a pcb wich is a 1:1clone of steve wards circuit he describes on his drsstc guide, maybe this will do the trick, but i dont know, i used my version of this driver with success in my drsstc6, the only thing i really changed is to use a lm393 instead of an lm311 and i changed a part of the overcurrent logic with a 7400 to get away from this funny rc combination, and it works perfect, on the first german teslathon this year i had an interrupter failure which made my interrupter go like mad with on times of about 2mS ,and i ran the coil for minutes with this settings without blowing parts, the sparks made a rattling loud noise and were brighter and longer i ever seen before, hehe okay blew some 10A fuses but no blown igbts, so really my logic works.
im not sure but i think its the high side cap charging circuit.
but i dont know, its very simple, i use an lm393 with an 1/100 voltage divider to measure the cap voltage. when power switch is on the cap charges via 190ohms resistors until i get 250volts dc on the cap, then the comparator switches a relais on via some bc238 transistors .the relais bridges the charging resistors, .i have 2 leds to show the status, charging and ready, nothing too special. okay its a high side charging circuit cause the negatives of the cap and the comparator are the same, but the circuit is an stand alone with own bridge rectifier (but same transformer)so it should have nothing to do with the driver causing the bridge to go boom.

Bennem

Tue Aug 29 2006, 05:07PM

Registered Member #154 Joined: Sun Feb 12 2006, 04:28PM
Location: Westmidlands, UK
Posts: 260

Hi Reaching,

In the picture of your lay out, you use a lot of wire (inductance)
from your buss cap to your bridge,
could induce spikes at higher buss voltage and kill your IGBT's?
Plus you said that you don't use any tvs on your bridge.

Just a thought.

Reaching

Tue Aug 29 2006, 05:46PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

but that wouldnt pop a bridge just in time when you switch on the interrupter, btw never had any problems with voltage spikes etc, and i use 12mmÂ² wire, thats a low inductance compared to my other designs.

Bennem

Tue Aug 29 2006, 06:25PM

Registered Member #154 Joined: Sun Feb 12 2006, 04:28PM
Location: Westmidlands, UK
Posts: 260

Do you use a variac to slowly increase buss voltage?
its a good idea to use one whilst de-bugging your system.
If fuses blow at lower buss voltage, problem could be GDT phasing problem,
if things work ok at lower buss voltage but start blowing fuses/IGBT's at higher voltage,
problem could be spike problem.

I had problems with my UCC driver ic's causing all weird and wonderfull problems
when i built my last small DRSSTC.

Part Scavenger

Tue Aug 29 2006, 10:59PM

Registered Member #79 Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673

Reaching, if you don't have a variac, you can make one out of an MOT. It's not "linear" it's really more of a tapped transformer, but I rewound one and made a switch bank that canceled out each lower switch (not hard if you think about it). I was going to put it on my site because it worked great, but I acidentally shorted it one day and killed it. Soon after I got a real variac so I didn't pursue it any longer. I'll see if I can dig up a picture if you want.

The advantage of this is you can have whatever-power variac you want for really cheap, however, it's not continuous. (IE. current is shut off briefly during switching.)

Reaching

Wed Aug 30 2006, 10:25AM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

i have a variac rated 2,2kW but thats not the question here. why should i put in a variac to slowly bring up the voltage until the igbts blow upt the third time,.. i know there is something wrong in my circuit or whatever and i want to find the failure until i blow more igbts. btw i have to build a new bridge cause i have only 2 40n60 miniblocks left, and the others are already build in in my other drsstcs. but i have 10 of the to 247 pack 40n60 but without diodes , i think i can use them when i can find some usable fast freewheeling diodes such as mur1560 or whatever. seems that nothing would work i build a new driver (exact 1:1 clone of steve wards drsstc guide driver) but it wont work properly, i know its not a failure in steves circuit, more a failure in my pcb but i spend 2 hours of debugging and didnt found the failure. maybe someone of you had the same problem. i tested the driver with a signal generator at the feedback input and with an interrupter on the interrupter input. the only thing the driver makes is to switch the 100khz feedback signal through the driver ics, the interrupter signal is lost on pin 7 of 74hc109,,,,

Bennem

Wed Aug 30 2006, 05:51PM

Registered Member #154 Joined: Sun Feb 12 2006, 04:28PM
Location: Westmidlands, UK
Posts: 260

Hi Reaching,

so you have no interrupter signal at pin 7?

have you chosen the correct values of R9 and C14?
this delay RC should be chosen acording to your coils running frequency.
I think Steve uses a 1nf and a 22k for his coils frequency.

Just a thought.

On second thoughts.....ignor the above, even if you had the wrong values, an interrupter signal should still be present at pin 7 of your flip flop ic.

Reaching

Wed Aug 30 2006, 06:31PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

yeah i know, i build several types of flip flop sync circuits so im somewhat confirm with them, but i cloned steves circuit 1:1 and it doesnt work, i checked everything 5 times ,looked for shorts on the pcb etc but found nothing, the circuit is exactly that in the shematic and it doesnt work, i tried out 5 different 74hc109 different 74hc14 different 555s ucc chips etc but nothing, i dont know the reason. on pin 1 of the 74hc109 is the inverted interrupter signal, pin 2 and 3 are connected to +5volt pin 4 is the feedback signal, pin 5 is the noninverted interrupter signal and on pin 6 and 7 is nothing,sometimes the right signal but only 0,5volts amplitude, seems like a pin7 short on the pcb without a short on the pcb, lol, already build the 74hc109 on a breadboard and connected pin for pin by showing the current draw of the circuit which is nearly 200ma without a load and the 74hc109 gets warm thats not normal i know. ahh i dont know

Steve Ward

Wed Aug 30 2006, 06:52PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

All ICs have proper 5V measured at the pins? I really cant imagine what the problem might be unless its simply a bad connection somewhere. Ive had bad sockets before, where some pins didnt make contact, and id spend hours trying to figure out what went wrong. Maybe use a continuity checker on each pin of the IC to the trace on the PCB. Many of the problems i encounter with my PCBs is either forgetting to supply power or ground to the chip (its the most basic thing, so i tend to overlook it of course).

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