Are big wirewound resistors acceptable for snubbers

I spoke to someone a few years ago who remebers his parents making composition resistors, the guy at the radio store supplied the parts and his parents mixed up the composition packed it into the bodies attached the leads and beked them in their oven, after cooking the resistance was measured and the resistor painted,

body multiplier, tip 1st digit, spot second digit. tolerance 20%

AFAIK the ones with stripes were machine made.

that said the recipe for composition resistors must be out there somewhere... it's probably not radically different from pencil lead. kaolin and graphite.

the website doesnt work well with firefox. but they have peak pulse power/energy ratings in their datasheets. eg a CHP-2 resistor is rated at 2W, 25C and 1.33W 70C, but can eat a repetitive 800W pulse thats

Cheers Terry

When both the top and bottom IGBTs are on, basically you are shorting the input to the bridge. If there is a big capacitor at the input to the bridge, the currents in the IGBTs will be really high and will probably be destructive if you use a high supply voltage. If there is a resistor in the snubber then the majority of the capacitor voltage is dropped across the resistor during the time that the top and bottom IGBTs are both on, and Ohm's law will tell you what sort of current to expect, but at least it will be lower than without the resistor.

I think you should go to using dead time if you are using a snubber with a capacitor, and you must do so if there is no resistor in series with the capacitor.

By the way, if you put a copper pipe inside your wirewound resistor (not touching the resistor wire or terminals, but just sitting inside the ceramic former) then this will reduce the inductance a bit. It will probably still have far too much inductance though.

Chris

Yes.

While this is true, my Semikron 23 drivers sense shorting (which is high voltage between collector and emitter) and shut down promptly and softly.

What you say makes perfect sense indeed. I should try it using a proper resistor in series with the cap.

That's a great thought. I have a large (4") wirewound resistor and I could try placing a copper pipe in there. Or, maybe, I will just wait until I get my carbon resistors.

By the way, I won some 0.33 ohm 1 watt resistors on ebay, a 6 pound reel of them. I think that it's a good deal and I could sell them in smaller batches and get my money back. I would use them in something like 10x5 matrix (a series of 5 rows of 10 parallened resistors in each) to get sensible resistance and wattage rating.

I will play some more, but I am limited in what I can do without proper resistors. I will see if using inductance in series on the supply line would change anything.