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Old 03-18-2010, 11:31 PM   #3231 (permalink)
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A few days ago Paul was asking about schematic drawing tools.

Has anyone taking Kicad for a spin?

Main Page - KiCad

Looks like it may be a bit easier than the GDA toolset.

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Old 03-18-2010, 11:34 PM   #3232 (permalink)
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Quote:
Originally Posted by bigh View Post
Question on the Caps - is there any reason that we're using 16x 820uF instead of less higher capacity ones?
Two reasons: heat dissipation and lowering the effective series resistance (ESR). Caps present a resistance in the path they are installed in. Having more caps lowers that resistance, which means you can move more current in and out of cap bank.

Also caps heat up. The more caps you have, the less they heat up because it spreads the load.

So it's better to have more smaller valued caps than a few larger ones.

That's my understanding of the issue.

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Old 03-18-2010, 11:44 PM   #3233 (permalink)
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Quote:
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Question on the Caps - is there any reason that we're using 16x 820uF instead of less higher capacity ones?
yes.more amps
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Old 03-19-2010, 12:20 AM   #3234 (permalink)
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I think Fran is too busy (that's why he doesn't post). He's all out there making crazy PMSM motor controllers, BMS's, 20-30kW 3 phase chargers. The man is insane, in a good way.

I haven't really messed with KiCad much. I just got used to that free software, and haven't bothered to learn anything else. Maybe I should.

Hey Lou! It would be cheaper for you to order the bag of parts from the wiki I think, if you don't mind a tiny bit extra work of placing the order for all the dang stuff. That sounds like a pretty interesting idea! I can't wait to hear how it works out!

The new control board will be ordered probably in the next week or 2. I think I'm getting 4 of them. I have a really really good feeling about it this time. Something tells me it's going to work. I already milled my fancy heat spreader so the top and sides are perfectly smooth.

Flatmann! Pretend you are sick! I used to do it all the time! If you go for sick day number 10, you will have to barf up a lung, so you better make this one count. (ferris beuler's day off) How do you spell bueler? oh well.
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Old 03-19-2010, 05:33 PM   #3235 (permalink)
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Quote:
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..... (ferris beuler's day off) ....
Hey Paul that was one of mine favorite movies when i was on school

I wish you luck with that new project
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Old 03-19-2010, 08:27 PM   #3236 (permalink)
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Quote:
Originally Posted by LouMan View Post
I got the phase shift idea from my motherboard it has 16phase power to the cpu each mosfet has a 16 clock rest before it has to switch again, I got a pic program to take the pwm in and split it into 4 outputs each igbt will have a 3 clock rest before it has to switch again 4khz from 16khz/4 witch gives the igbt plenty of time before the next cycle,
I will still have 16khz at the motor but each igbt will only be at 4khz,
well give me a email when you get a spare baord & chip
I have not seen the start of this discussion but it looks to me as though each of your IGBT will have to be rated for full motor current.....unless they are overlapping then the first that come on has to handle full current.
I am not seeing what the advantage would be?
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Old 03-19-2010, 09:11 PM   #3237 (permalink)
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i think the igbt's have issues with turning off at 16khz, so the problem is the whine at lower freqs.
this system(when it works) would eliminate the low hz whine while still being able to use the slower igbt's.

implementation would be tough tho. like how do you handle overlap of on times from one to the next. etc.
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Old 03-19-2010, 09:14 PM   #3238 (permalink)
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I am pretty sure modern IGBTs will handle 16kHz happily.
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Old 03-19-2010, 09:21 PM   #3239 (permalink)
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depends on the pull down strength you have setup.
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Old 03-19-2010, 09:24 PM   #3240 (permalink)
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Quote:
Originally Posted by squiggles View Post
I have not seen the start of this discussion but it looks to me as though each of your IGBT will have to be rated for full motor current.....unless they are overlapping then the first that come on has to handle full current.
I am not seeing what the advantage would be?
I agree. Better would be to have all the IGBT's share the load. However, to do that you have to derate the max current each can carry because they will share unequally based on structure, temp, and gate characteristics. In short 4 400A IGBTs cannot carry 1600A.

A good paper on the subject is the Dynex application note AN5505. You can find it here:

Application Notes - Power - IGBT

Rules of thumb:

1) Derate the max current.
2) Use individual gate resistors for each module.
3) Put all the modules on the same heat sink.
4) If you cannot match the modules, then put a load sharing resistance on the emitters of each module.


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