# My Cheap and Dirty DC controller



## gerd1022 (Jun 9, 2008)

decided to start a new thread instead of posting on the now slightly off topic thread about controllers...

I am progressing on my controller design, finished the power side layout, seen here:
Powerside2.JPG

The driver/controller board has been tentatively designed... im going to clean it up today and post a schematic.

if any of the EE guys here could give me some advice, that would be great!
If this works, i'm planning on making up a full bill of materials and instructions on building and everything...


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## TheSGC (Nov 15, 2007)

I am having a hard time trying to figure out what the 2nd IGBT is for as a diode. It doesn't make any sense (to me) in it's placement. 

Unless the lower IGBT is supposed to be the diode and the upper one be the IGBT. But then shouldn't the (-) be the IGBT. Every DC controller I have seen uses the (-) side to attached to the IGBT/PWM system.

Do you have schematics yet? BTW - I am in school for Electrical/Computer engineering and this controller seems backwards in almost every way.


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## gerd1022 (Jun 9, 2008)

hmm yeah youre right... somehow when going from my schematic (which is right) to my 3d model, i screwed something up...

ill go check that and fix the model...


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## gerd1022 (Jun 9, 2008)

here we go... i think this is right now


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## TelnetManta (Jun 5, 2008)

How close are you to testing?


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## gerd1022 (Jun 9, 2008)

i'll probably have a low power test next week.

i just need to order the components for the driver circuit, but i had some credit card fraud, and cant use my card for awhile...


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## gerd1022 (Jun 9, 2008)

Ok so i recently tried to recollect the EE class i took last year to design the current limiter... It is wicked simple, and i have no idea if it would work but heres a schematic.

The idea is that the current sensor will give a value from 0-2.5 volts which corresponds to 0-600 Amps... In the circuit the voltage divider pot gives an adjustable reference voltage that the op amp compares to the current sensor voltage. 

The output goes to the current limiting pin on the chip which is set to limit the current when the voltage is 100mV. Not sure how it will like getting a TTL signal? i have a very vague idea what im doing, but this makes a bit of sense right?


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## TheSGC (Nov 15, 2007)

gerd1022 said:


> Ok so i recently tried to recollect the EE class i took last year to design the current limiter... It is wicked simple, and i have no idea if it would work but heres a schematic.
> 
> The idea is that the current sensor will give a value from 0-2.5 volts which corresponds to 0-600 Amps... In the circuit the voltage divider pot gives an adjustable reference voltage that the op amp compares to the current sensor voltage.
> 
> The output goes to the current limiting pin on the chip which is set to limit the current when the voltage is 100mV. Not sure how it will like getting a TTL signal? i have a very vague idea what im doing, but this makes a bit of sense right?


I have a very similar design. All you are doing is creating an op-amp system that will bring the output pin high when the current sensor has reached the "adjusted" voltage. I actually went a little further than that with my PIC and had the shunt signal amplified (with an op-amp) and fed through the A/D converter and it will spit out the AMPS in a 0-5 volt range of 0-500 AMPs.


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## gerd1022 (Jun 9, 2008)

alright cool... at least im on the right track. i think i will upgrade to a PIC sometime or another... for right now, im gonna go with the MC33033... and save time by not programming.


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## Doc (Jul 5, 2008)

gerd1022 said:


> Ok so i recently tried to recollect the EE class i took last year to design the current limiter... It is wicked simple, and i have no idea if it would work but heres a schematic.
> 
> The idea is that the current sensor will give a value from 0-2.5 volts which corresponds to 0-600 Amps... In the circuit the voltage divider pot gives an adjustable reference voltage that the op amp compares to the current sensor voltage.
> 
> The output goes to the current limiting pin on the chip which is set to limit the current when the voltage is 100mV. Not sure how it will like getting a TTL signal? i have a very vague idea what im doing, but this makes a bit of sense right?


That 0-2.5V lead me to suspect you are using a Tamura sensor or one with a Vcc/2 as offset...?
If you are, It's output for 0-2.5V will most likely be 600-0A. You could do this if you run it backwards. 
If you want to measure 0-600A, the output is 2.5-5V (or 2.5-4V for the Tamura), so you have to set the ref to 5 (or 4V)


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## EVBug (Aug 19, 2008)

Ok, looks cool. How many amps would you say it's rated for? If you add more IGBT's will it handle more amps? Or perhaps have a longer duty cycle at a lower amperage? How will you control the switching frequency? Or do the IGBT's themselves handle that? Will they change to a different switching frequency when they get hot like a Curtis controller does?

I swear, I'm not trying to throw wrenches into your works, I'm just curious.


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## gerd1022 (Jun 9, 2008)

thanks doc... no matter how many times i see that datasheet, i never remember that. but thats the beauty of the pot, you can just adjust it to what you need

to VW: the PWM side is controlled by the MC33033 chip, datasheet here:
http://www.onsemi.com/pub_link/Collateral/MC33033-D.PDF

My circuit is based on the one down near the bottom of the datasheet for brushed motors except it isnt an h-bridge cause i dont need reverse.

the circuit is attached, except i have since changed the driver to one more suited for these IGBT's. I will probably add another IGBT eventually to have a 1000A current limit, but to get it running I am going to limit this one to 500A which should move me along no problem in a 2200 lb car...


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## Doc (Jul 5, 2008)

gerd1022 said:


> the circuit is attached, except i have since changed the driver to one more suited for these IGBT's...


Why have you changed the driver?
Have you found one better then the IXYS?

BTW I read earlier in this thread that you had problems related to the driver not being able to charge up the IGBT.
If I remember correctly :S You can calculate the required current by: VC/t or the time by: VC/A
So if you want to know how much current it takes to charge 100nF to 12V in 100nS it's: 12*0.0000001/0.0000001 = 12A


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## gerd1022 (Jun 9, 2008)

yeah i am going to use this driver:

http://www.pwrx.com/pwrx/docs/vla500_01.pdf

im in the process of designing a PCB around the application circuit on the datasheet that will mount directlyu on the IGBT. When its done i'll post the schematic and PCB files...


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## Doc (Jul 5, 2008)

gerd1022 said:


> yeah i am going to use this driver:
> 
> http://www.pwrx.com/pwrx/docs/vla500_01.pdf
> ...


What made you choose that one? Just curious, because I can't see any real advantage...


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## gerd1022 (Jun 9, 2008)

a few reasons:

1. This driver pulls a negative voltage when the pulse width is low. This is recommended for the larger IGBTs because it quickly drains the gate charge.

2. It is designed for the family of igbts that i am using

3. The datasheet for the pwrx driver has much more information, including a recommended driver circuit which is easy to use and should be more robust.

4. I burned through three ixys modules (i was doing something wrong each time, but still... it didnt inspire confidence in the hardware)

Price is not a reason... the pwrx driver is $40 compared to like $2...


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