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MPaulHolmes · 04-23-2014, 01:43 AM

Lots of debuggIng this afternoon after work. It's all almost good to go as far as the software and circuit board goes.

The soliton people have 10's of thousands of dollars of igbts (we keep buying from them on ebay. haha) that they match for turn-on point, diode voltage drop, etc... We basically had one shot, with a couple orders of 6 igbts. There's just no way to guarantee current sharing in the IGBTs with a sample size that small. So, let's say igbt1 has a voltage drop of 1v when its on. And IGBT2 has a drop of 0.9v when its on. We weren't able to do anything about this due to our gross poverty. LOL. Let's pretend that, as a result, IGBT2 is passing 600amp while IGBT1 is passing 400amp.

Well, that's a shame. Now we need to lower the current for everyone so that IGBT2 is in safe territory. Now IGBT1 is only passing like 200amp. What a waste!

PLAN B: With 3 feet of 2 gauge cable, you get a voltage drop of 0.193v at 400amp, and a drop of 0.289v at 600amp. Basically, that's a difference of 0.1v. Now, it's like we were the big boys! IGBT2 has a voltage drop (counting its cable) of 1.189v, and IGBT1 has a voltage drop (counting its cable) of 1.193v. Now, because they have the same voltage drop, they would both be sucking the same amount of current. So, it wouldn't be 600amp and 400amp anymore. They will be driven closer to each other. Being forced to share current better. But you can always just dump that idea and stick a big bus bar across it. But right now, each of the 3 igbts has its own current sensor, and its own hardware overcurrent circuit, so there's no way that one can go out of bounds.

i2 - i1 = (v1 - v2)/R. Where i2 is igbt2 current, and v2 is igbt voltage drop, and R is resistance from the cable.

04-23-2014, 01:43 AM	#6480 (permalink)
MPaulHolmes PaulH Join Date: Feb 2008 Location: Maricopa, AZ (sort of. Actually outside of town) Posts: 3,832 Michael's Electric Beetle - '71 Volkswagen Superbeetle 500000 Thanks: 1,362 Thanked 1,202 Times in 765 Posts	Lots of debuggIng this afternoon after work. It's all almost good to go as far as the software and circuit board goes. The soliton people have 10's of thousands of dollars of igbts (we keep buying from them on ebay. haha) that they match for turn-on point, diode voltage drop, etc... We basically had one shot, with a couple orders of 6 igbts. There's just no way to guarantee current sharing in the IGBTs with a sample size that small. So, let's say igbt1 has a voltage drop of 1v when its on. And IGBT2 has a drop of 0.9v when its on. We weren't able to do anything about this due to our gross poverty. LOL. Let's pretend that, as a result, IGBT2 is passing 600amp while IGBT1 is passing 400amp. Well, that's a shame. Now we need to lower the current for everyone so that IGBT2 is in safe territory. Now IGBT1 is only passing like 200amp. What a waste! PLAN B: With 3 feet of 2 gauge cable, you get a voltage drop of 0.193v at 400amp, and a drop of 0.289v at 600amp. Basically, that's a difference of 0.1v. Now, it's like we were the big boys! IGBT2 has a voltage drop (counting its cable) of 1.189v, and IGBT1 has a voltage drop (counting its cable) of 1.193v. Now, because they have the same voltage drop, they would both be sucking the same amount of current. So, it wouldn't be 600amp and 400amp anymore. They will be driven closer to each other. Being forced to share current better. But you can always just dump that idea and stick a big bus bar across it. But right now, each of the 3 igbts has its own current sensor, and its own hardware overcurrent circuit, so there's no way that one can go out of bounds. i2 - i1 = (v1 - v2)/R. Where i2 is igbt2 current, and v2 is igbt voltage drop, and R is resistance from the cable. __________________ kits and boards Last edited by MPaulHolmes; 04-23-2014 at 02:49 AM..