# controller components



## jehan12413 (Feb 4, 2010)

Just recently I read a post about a controller which listed the MOSFETS used along with current rating on resistance and freewheel diode setup. Now I can't remember where the post is or the title. Can anyone help me find it?


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## rillip3 (Jun 19, 2009)

jehan12413 said:


> Just recently I read a post about a controller which listed the MOSFETS used along with current rating on resistance and freewheel diode setup. Now I can't remember where the post is or the title. Can anyone help me find it?



I think you're talking about your last reply on this thread:

http://www.diyelectriccar.com/forums/showthread.php?t=45562


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## jehan12413 (Feb 4, 2010)

I found it under "1000 amps on the loose" thanks


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## EVfun (Mar 14, 2010)

Actually, that does bring up an interesting point. I'm about to have a spare Curtis 1221B controller and I wouldn't mind using modern silicon to pull off an upgrade. I suspect I choose better capacitors, diodes, and mosfets and get a bit more than 400 amps out of one. Have their been any others treads that cover upgrading these controllers, especially with change details or inside pics?


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## Tesseract (Sep 27, 2008)

EVfun said:


> ...I'm about to have a spare Curtis 1221B controller and I wouldn't mind using modern silicon to pull off an upgrade. ...


Possible, but there are several caveats:

1. Curtis uses the voltage drop across the MOSFETs when they are on as a proxy for motor current. So, changing to MOSFETs with lower Rds[on] will automatically increase the current limit - perhaps to something a lot more than the MOSFETs can actually handle. Try to keep in mind that no matter what the datasheet says the silicon die can handle - eg, 230A! - those tiny little legs are the real limiters to how much current can be handled. 25A per TO-220 part and 50A per TO-247 is the generally accepted maximum.

2. The capacitors inside the Curtis controllers are rated for about 1/10th the motor current but the maximum RMS current seen by these capacitors is 1/2 the motor current. Underrating the caps by 5-10x is common practice - even Otmar does it in the Zillas - because until very recently you didn't have to worry about battery packs having the capacity to be able to drive an EV hard for a long enough period of time to boil their little insides out. That's no longer the case now that Lithium Iron Phosphate cells have a much lower lifetime cost than lead acid.

3. The freewheeling diodes in the Curtis' are dual diodes with the maddeningly difficult to find common anode connection. This, so far as I know, sets a hard upper limit to the increase in voltage/current that can be obtained, irrespective of the beefing up done elsewhere.

4. The gate driver in the Curtis' is woefully inadequate. It barely has enough punch to turn the stock MOSFETs on and off in reasonably short times. If the MOSFETs you choose have a higher total gate charge (Qg on the datasheet) then they will switch even slower, and probably promptly blow up.

Good luck kludging what I consider the ultimate kludge!


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