[swoozle]

Originally Posted by evimarn

Hi any links please as doing a search seems leading to nowhere.
Thanks for the expert help .

http://www.evbmw.com/

[evimarn]

Originally Posted by swoozle

http://www.evbmw.com/

Hi thanks just what I was looking for.);

[JRoque]

Hi. Someone already mentioned but I would add your bulk capacitance bank even when just testing. Good luck!

JR

[z_power]

There's a lot of useful information about driver circuits in Semikron's application notes AN7002 and AN7003, easy to find in internet.

[swoozle]

Originally Posted by z_power

There's a lot of useful information about driver circuits in Semikron's application notes AN7002 and AN7003, easy to find in internet.

Yes, those look very useful, thanks.

[swoozle]

OK, new IGBTs and some experiments. Please take a look and help us understand what's going on.
These are all one IGBT with a 12V battery source running a starter motor.
All have the same time scale and V scale except the last trace (V scale increased to show the driver signal, time scale the same).

C-E trace, no snubbers, increasing but low PWM, amps probably around 20
IMG_7333.JPG

One snubber added.
IMG_7335.JPG

Two snubbers added (though one had long leads)
IMG_7337.JPG

same with stable PWM somewhere around 50%, current at ~35amps
IMG_7340.JPG

The drive signal with 12V source and starter motor load.
IMG_7341.JPG

The snubber. They came with the used IGBTs and we can't find any info on it.
IMG_7343.JPG

[cpate]

So we don't really understand why our voltage traces don't look like those shown in other people's pictures of their oscilloscopes when testing their controllers. But we're pretty confident that the snubbers are helping. The first snubber that we added, with extra short leads, helped a lot. The second one, which had the standard leads that were about .75" longer, helped less. I looked around for better snubbers and I found these:

http://www.digikey.com/product-detai...240-ND/2783740


2.9 mOhm ESR, 29 amp ripple current rating, 5 microfarads. These have about 5x the capacitance of the ASC snubbers that we have, but I don't know if their ripple current rating/inductance/resistance is any better. Do you guys think that these will quell the voltage spikes to acceptable levels?

[subcooledheatpump]

Am I reading that scope correctly? It seems you are jumping up to 60 volts during turn off

Have you added any bulk capacitance?

What gate resistor this time? It looks like it's not fully saturating the IGBT

[cpate]

Originally Posted by subcooledheatpump

Am I reading that scope correctly? It seems you are jumping up to 60 volts during turn off

Have you added any bulk capacitance?

What gate resistor this time? It looks like it's not fully saturating the IGBT

Yup 60 volts or higher seems to be the spike level when the motor is starting. We haven't added any bulk capacitance, just stuck with the round 400v 380uf cap and added the snubbers. The gate resistor is up to 11.2 ohms + .56 ohms on the emitter. Hmm what does a non-saturated IGBT look like? The curve downwards after the spike?

[subcooledheatpump]

The C-E should look roughly like the gate drive signal

The IGBT Should be on for the duration of the pulse, that should look like a flat line. Then it should almost instantly fall to zero, another flat line. Just like the gate signal.

Personally, I would add some big capacitors to that, keep the snubber, but add some 6000 microfarad capacitors, rated at 400 volts. change the gate resistor to a slightly lower value, 10 ohms, then try again with the same setup. You really shouldn't be spiking that high with only 12 volts. It should really not spike above 15 volts.