# sizing capacitors for my controller



## ww321q (Mar 28, 2008)

I hope you get some answers . Well answers that I can understand . I want to build my own controller to . But I have a very hard time with electronics being I've never had much schooling or training in that field . I also got Richard Valentine's book and every other schematic that I could find . good luck with your controller . J.W.


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## etischer (Jun 16, 2008)

I'm in the same boat you are. Are you doing a 3 phase controller too? I decided to use a smart power module, but I have 6 of the same 600a 1200v IGBT's that you have if you need spares =) 


I just fried my first IGBT pack, and learned things to make the next one blow up. I was successful in running a 3 hp motor off my IGBT for about 1/2 hour. When I hooked up my 90hp motor, thats when the IGBT fried. 

My mistake was not having flat laminated plates connect my caps to the IGBT. I used regular wire, and it was about 12" long. This wire had too much inductance which caused voltage spikes when the IGBT switches current at 3khz. 


I have a video of my "Poof" at the top of my webpage. I also have other videos of my IGBT firing circuits in action. 
http://etischer.com/awdev/

here is a pic of the original ballard drive used on the siemens ford motor, it might give you a good idea of the size of cap. I'm using 400v caps for my 230v drive. This is sized based on the caps in other 230v drives I've used.

Again, you want to keep the wires from your cap to igbt as short as possible, and flat as possible. I think the caps act as the snubber. The IGBT should have an avalanche rated diode built in if it is made to run inductive loads like motors.


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## etischer (Jun 16, 2008)

I'd also give Powerex a call, they have three documents on their webpage that are helpful. PM me and I can forward them to you.


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## Madmac (Mar 14, 2008)

Hi Etischer

I would suspect that the failure of your IGBT pack was down to gate drive issues. If both the upper and lower device turn on it will more than likely fail. If gate drive is removed and the controller shut down it might survive a single event.

The transient voltages generated by not keeping loop area small will tend to degrade the device over time. Does not need flat connections (they can produce the lowest inductance solution if done properly), twist or tape wires next to each other and keep as short as possible. If you were unlucky and the layout gave rise to very large spikes then it would kill the device. By investing in some MOV devices to clamp the voltage direct on the IGBT you may help it survive during development.

Does the Richard Valentine book have the complete design of a DC motor controller, down to mechanical drawings for heatsinks etc?
Going thru Motorola application notes that I have downloaded and looked at over the last decade (always save them on a server) came across one for 1000Amp 120Volt analogue DC motor controller (by Valentine). If it is extra information PM an email address and I will send it.

Madmac


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## popeye2008 (May 17, 2008)

Valentine's book does have full schematics of AC and DC controllers using PMW chips, but no Mechanical drawings of buss layouts or component layouts. He does give rules and considerations to follow in design. I ran across this some time ago. It's Valentines layout alright and with drawings. 
I'm trying to build a controller for a DC series wound

motor.http://vehiculeselectriques.free.fr/racingcontroller.html#top


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## Madmac (Mar 14, 2008)

popeye2008

Cool...as long as it is out there and known about.

Madmac


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## skullbearer (Jul 9, 2008)

My only experience with caps is in car audio, so I've dealt with the large .5, 1, and 1.5 farad caps.

Just one cap will usually eliminate EMI and that is primarily the reason to use caps in a high power system. A lot of people believe that caps let them run a higher spike system, and its true that with 3-6 farads (depending on the spike difference from your amp's spike rating) you can run a solid set of subs with higher spikes than your amp, but they reduce the responsiveness of your sound by just that tiny bit... and when you are playing a very very well timed fast paced song the beat won't be noticeably off, but you will notice something seems odd.


Like I said, the main application in audio for caps is purely to eliminate the EMI caused by upgraded very high amp alternators built to power (or charge in gel-battery systems) the boomin audio in a show car or some rich punk's SUV. Most of the time when caps are used they are just being sold to the customer for money, rather than for any actual purpose.


I assume though that given the need to eliminate spiking on the controller side the caps are an absolute necessity in these higher power controllers?


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## popeye2008 (May 17, 2008)

Thanks for the replies. i hope this thread doesn't end here, still hoping for some answers. Thanks


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## TheSGC (Nov 15, 2007)

Caps are used in controllers to handle the spikes, but really are only useful if you intend to have you logic boards powered by the same source of the IGBT/MOSFETs/Motor. Since the caps are only for voltage spikes, I think choosing a cap that is twice the voltage of you intended system (or close to it) and 2500 uF per IGBT used, or 200 uF for each MOSFET used would be appropriate.


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## etischer (Jun 16, 2008)

I ran my IGBT pack running a smaller motor at full speed, it wasn't till I hooked up the higher current motor that I had a problem. I don't think I'm turing on two complimentary IGBT's at the same time. 

I've talked to 3 experts on IGBT's they all agree its my DC bus wiring that caused too much input inductance. The high speed, high current switching caused high voltage spikes though that inductance.

I'll definitely find some MOV's to put on. You're talking about putting MOV's on the DC Bus input on the IGBT right? The firing circuit is turn key, I don't think I need to condition anything there. My wiring on the low power side is about 2" long. The DC bus will be alot stiffer once I get a battery and battery cables, right now my dc bus is supplied via extension cords from the wall. 





Madmac said:


> Hi Etischer
> 
> I would suspect that the failure of your IGBT pack was down to gate drive issues. If both the upper and lower device turn on it will more than likely fail. If gate drive is removed and the controller shut down it might survive a single event.
> 
> ...


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## etischer (Jun 16, 2008)

does this help























popeye2008 said:


> Valentine's book does have full schematics of AC and DC controllers using PMW chips, but no Mechanical drawings of buss layouts or component layouts. He does give rules and considerations to follow in design. I ran across this some time ago. It's Valentines layout alright and with drawings.
> I'm trying to build a controller for a DC series wound
> 
> motor.http://vehiculeselectriques.free.fr/racingcontroller.html#top


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## popeye2008 (May 17, 2008)

Valentines schematic for a DC motor does show MOV(s) but I don't see any on the AC design. Valentine uses a smart power module PM6400HA060 and mentions that it contains gate drivers and protection circuitry. But certainly verify this for yourself, as you may already have, before taking my inexperienced word for it. Valentine still employs opto-isolation between the smart IGBT and control. Also there appears to be an exterior, to the module, free wheeling diode MUR3060WT. This book is ten years old.


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## popeye2008 (May 17, 2008)

Thanks etisher, I have seen that and I'm considering a similar buss design for my two IGBTs.


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## Madmac (Mar 14, 2008)

> I've talked to 3 experts on IGBT's they all agree its my DC bus wiring that caused too much input inductance. The high speed, high current switching caused high voltage spikes though that inductance.


There are three possible causes of the failure. Before risking another IGBT pack ($330 or what ever you paid) it is sensible to try and find the reason.

The first is excessive voltage due to ringing on the DC rail. I would guess that you tried to rotate the motor at low speed so the current taken on the DC rail was probably not that great as the motor inductance would cause the current to ramp up. Add a MOV across the DC rail on the IGBT as well as keeping the loop area created by your DC rail connections small, ie run them together and keep as short as possible. The leads to the cap should also be kept short. Possibly add a film capacitor.

The second is problems with the drive circuit on the existing controller. The isolated power supply on this was designed to charge and discharge much smaller gate capacitance than the size devices you are using. If the drive voltage is not high enough the IGBT switches will end up running in linear mode. The ratings under these conditions are only a few 10s of Amps, the device will quickly overheat and fail.

Finally is a problem with connections or timing between the existing controller and the IGBT module that leads to both devices being on at the same time. The deadtime between the upper and lower devices will be designed for a faster smaller part. Using a much higher power and slower device they may both be on for a small amount of time each pulse they switch. This can be measured using the scope and checked with the switching times in the device data sheets.



> Originally Posted by *popeye2008*
> _Valentine's book does have full schematics of AC and DC controllers using PMW chips, but no Mechanical drawings of buss layouts or component layouts. He does give rules and considerations to follow in design. I ran across this some time ago. It's Valentines layout alright and with drawings.
> I'm trying to build a controller for a DC series wound
> 
> motor.http://vehiculeselectriques.free.fr/...oller.html#top_


For those people interested in building a DC motor controller I would suggest looking at the above link as the design has been fully engineered along with good details of how to build the high current section so that it will work reliably. The only thing missing is the layout for the control PCB.

Madmac


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## etischer (Jun 16, 2008)

Thanks for the input. 

I checked with Powerex and I got the impression the signal conditioning done in the smart power module I'm using is the same as the smaller module I pulled out. I'm no longer using individual IGBTs. I'll certainly throw a scope on there and make sure things look ok before running a motor again. I was a bit impatient =) I was trying to pull 20% speed on my first run =) Oops. 

I'll have to see if there is a way to programatically increase the time between when the top pulse end and bottom pulse start, I know the secret back door into the drive software. I ran a light bulb in series with the DC bus before trying to run the motor. If I had overlap in IGBTs firing, I should see some current in the bulb with a scope. I'll check the dc bus for ringing too. I think I may need more caps, I have two 400v 3,300 uF right now. 

I'm also planning on putting MOV's across the DC bus input. I also plan to have the caps and IGBTs bolted to a small plate so there is as little inductance and resistance as possible. I will make the bus plates as close as possible so induced voltage spikes will get rejected. It all makes sense to me, and I'm exicted to give it another go around!


Thanks again for all your help! I've been learning alot. 
-eric




Madmac said:


> There are three possible causes of the failure. Before risking another IGBT pack ($330 or what ever you paid) it is sensible to try and find the reason.
> 
> The first is excessive voltage due to ringing on the DC rail. I would guess that you tried to rotate the motor at low speed so the current taken on the DC rail was probably not that great as the motor inductance would cause the current to ramp up. Add a MOV across the DC rail on the IGBT as well as keeping the loop area created by your DC rail connections small, ie run them together and keep as short as possible. The leads to the cap should also be kept short. Possibly add a film capacitor.
> 
> ...


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