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New Coilgun Kicker project + IGBT Problems

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Wolfram

Tue Jan 29 2008, 01:44PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

Take a look at the HGTG20N60A4D IGBT, it's a much cheaper option. It can handle the same voltage, the same continous current, and almost the same pulse current. It also has a built-in reverse diode to catch reverse volrage spikes that can be very damaging to the IGBTs. The cost is just over 4 dollars from Digikey if you buy 10 or more.

Gianluca

Tue Jan 29 2008, 06:00PM

Registered Member #1261 Joined: Thu Jan 24 2008, 09:11PM
Location: Milan, ITALY
Posts: 5

Hey everyone! I am so happy about your kindness. I wasn't expecting sooo many nice people in a forum.

Thx for the Digikey option but unfortunately I live in Italy and the only options to buy electronic material are RS, Farnel and Distrelec. They are expensive and it's almost impossible to find everything that's in Digikey catalogue.

Anyway, I don't trust built-in diodes, usually their current rating is not so high and they tend to burn leaving the igbt unprotected. I put a freewheeling diode between the + of the cap and the collector of my IGBT (anti parallel to the coil). No overvoltages should occur with this configuration right? The snubber network with the C and R would have been a much better option, I know. Unfortunately the PCB is already done and since it works now, I am just too lazy to change it!

For future reference I am quite confident about the reason of my IGBT failure: gate overvoltage. They just don't like voltages over the 20V range! It was actually written in capital letters under Maximum Ratings in the datasheet :-s but I knew may people overvolt Vge up to 30V with no consequences but that is not my case!

Anyway... the kicker it's just a monster! It accelerates a 400g iron rod up to 10 m/s to kick the ball. I have almost finished a speed trap to have proper results (I was using a 25fps cam coder now for measuring speed).

Marko

Tue Jan 29 2008, 09:56PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hello gianluca, welcome!

Anders M. wrote ...

Take a look at the HGTG20N60A4D IGBT, it's a much cheaper option. It can handle the same voltage, the same continous current, and almost the same pulse current. It also has a built-in reverse diode to catch reverse volrage spikes that can be very damaging to the IGBTs. The cost is just over 4 dollars from Digikey if you buy 10 or more.

Anyway, I don't trust built-in diodes, usually their current rating is not so high and they tend to burn leaving the igbt unprotected.

Not to spread any misconceptions here, the built in diode, or any diode anti parallel to the switch will not do anything against overvoltage in this case.

Voltage created by the inductive kick will not be in reverse, but in same direction for the IGBT and will just add to supply voltage.

Spend some time looking at the circuit and you'll see what I'm talking about.

Inductive kick is reverse only for inductor voltage drop, so diode across the inductor will conduct it. This wastes power though and I think it would be better and more economical solution to use SCR and control the energy by controlling the capacitor voltage. (you have that pic-controlled boost converter anyway?)

Marko

ramses

Tue Jan 29 2008, 10:20PM

Registered Member #1208 Joined: Thu Jan 03 2008, 05:30PM
Location: Chesterland, OH
Posts: 154

holy crap!! almost 8% efficiency. wow. good job.

Backyard Skunkworks

Tue Jan 29 2008, 11:21PM

Registered Member #1262 Joined: Fri Jan 25 2008, 05:22AM
Location: Maryland, USA
Posts: 451

Gianluca wrote ...

Thx for the Digikey option but unfortunately I live in Italy and the only options to buy electronic material are RS, Farnel and Distrelec. They are expensive and it's almost impossible to find everything that's in Digikey catalogue.

I just checked and Mouser ships to Italy for $25USD flat rate, they have pretty much the same stuff as digikey, over 800,000 parts.

http://www.mouser.com

TheMerovingian

Tue Jan 29 2008, 11:39PM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

Gianluca wrote ...

For future reference I am quite confident about the reason of my IGBT failure: gate overvoltage. They just don't like voltages over the 20V range! It was actually written in capital letters under Maximum Ratings in the datasheet :-s but I knew may people overvolt Vge up to 30V with no consequences but that is not my case!

I drive my IGBTs with 23V on the gate provided by a dc-dc converter in my coilgun and no problems, did you protected the IGBT with a snubber network?

Gianluca

Tue Jan 29 2008, 11:59PM

Registered Member #1261 Joined: Thu Jan 24 2008, 09:11PM
Location: Milan, ITALY
Posts: 5

For Marko. I know about the inductive kick-back mechanism. In fact, as I said in my previews posts, I adopted a diode across the coil that conducts as soon as the igbt closes (ideally). The diode is a stth15r06 from ST Microelectronics. Quite a nice model by the way

For the 8% efficiency.... it's quite a good achievement! Anyway, the speed is on the 10m/s range, I haven't done (yet!) accurate measurement, it could be 9 m/s at least!
The solenoid is quite well made using low resistance wire and two foils of high permeability material to cover everything. The barrel is ceramic, only 1.5 mm thick and no eddy currents at all (obviously). The core inside is made with pure iron; plus low speed helps a lot with timings and switching problems

Thanx for the tip about Mouser.com

For the Merovingian... no! There is nothing in my layout apart the gate driver (tc4432), the igbt, the coil and the coil freewheeling diode. At 12V everything goes smoothly. At 24v the igbt tends to die

I must say that it's quite stressed....it works in 15min cycles with 1-2 shots per minute...

Steve Conner

Wed Jan 30 2008, 10:10AM

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

Digikey also ship to Italy:

Fabio

Mon Oct 06 2008, 09:47AM

Registered Member #122 Joined: Fri Feb 10 2006, 12:55PM
Location: Milano Italy
Posts: 148

Hi Gianluca!

We have many free sources of high power surplus in Italy (mainly from UPSs and power conditioning).

Simply join to ALTATENSIONE mailing list and ask for free surplus (

)

Ciao!
Fabio.

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