# Curtis 1231C update to 1000amps



## nimblemotors (Oct 1, 2010)

Close inspection reveals the diodes are fine, but all the fets on one side are blown. So one could just replace those 10 fets, and it would be back to a 500amp controller. Too easy, I have to do things the hard way.

The limitation here it seems to me is the diodes, that are reported to be 25amps, 18 of them = 450amps. So they must be replaced to get 1000amps.
Not easy to replace them as they are some unobtanium reverse polarity, so the T0220 mounting is on the M- backbone.


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## generatorlabs (May 31, 2014)

Hold on a sec....are you suggesting that you are going to up that controller to 1000 amps by swapping those diodes with higher rated ones?

Aren't those just freewheel diodes?

I don't see how it would be thermally possible to double the output of that controller. The way I see it that would require doubling the amount of FET's. Am I missing something? Have you done a mod like that in the past?

Just curious and trying to fill this noggin of mine with bits of useful matter


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## nimblemotors (Oct 1, 2010)

Yes they are freewheel diodes that must handle the maximum motor current.
The Curtis has only 450amps in diodes. It has 950 amps in FETs, but those are easy to change into even higher amps because they are TO247 packages which are common parts. It is the Reverse Polarity TO220 diodes that can't be upgraded with simple part swap.

What I've found and think might make them work are these 150amp diodes:
VS-150EBU02, install them upside down so the anode can be bolted to the M- rails like the old diodes with a little aluminum spacer,
and then run a lead from the circuit board and solder it to the tab. Crazy?
At 18 of them, that would be 2500 amps, maybe just use 10 for 1500 amps.

The 'thermally possible' relates to how much resistance they have, and thus how much heat they create, the existing ones are very poor at 45mohm, the part above is 4mohm,
that is 10 times less heat. In any case, might just add water cooling to it also.

Then the FETs need upgraded too, there are many that can be used, like this one at 350amps, so 10 would be 3500 amps.
http://ixdev.ixys.com/DataSheet/DS100181(IXFK-FX360N15T2).pdf



generatorlabs said:


> Hold on a sec....are you suggesting that you are going to up that controller to 1000 amps by swapping those diodes with higher rated ones?
> 
> Aren't those just freewheel diodes?
> 
> ...


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## nimblemotors (Oct 1, 2010)

Wanted to add a link to the older thread on the parts in a curtis 1231c for reference. which is where I get the 25amp diodes info, as can't find a datasheet for the parts.
http://www.diyelectriccar.com/forums/showthread.php/1231c-8601-parts-60598.html

Ian also did a teardown on another blown 1231, which has good pictures, so I don't need to take any and post them, just look here.
http://zeva.com.au/Research/Curtis/

The U-channel bus is the M-, and then you have the two top buses for B+ and B-. The fets and diodes all bolt to the M- bus, and connect to the power board with their leads, which has a B+ plane side, and the B- plane the other side, the caps all connected here in the middle.

Here is a clear picture of the fets and diodes. You can see the diodes are unusual. The mounting is the Anode, and one leg is the Cathode that is connected to the front metal tab, the left leg is just for mounting, and you can see it was melted and part of the front tab (this part from the other side). So you can see the challenge to replace these diodes with something else.


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## generatorlabs (May 31, 2014)

Those diodes are very unusual. Kinda remind me of old puck style diodes you would see in extreme voltage applications, such as steel mills etc, just a whole lot smaller. Initially when I looked at them I thought they were 2 channel diodes because of the 3 legs.

Good luck with retrofitting it. Seems like your choice of diode could work as long as it had a really fast recovery time. You kinda made me decide to dig out some old CurtisPMC SepEx controllers I had laying around my attic. One day I will open one to peek at the innards.


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## nimblemotors (Oct 1, 2010)

The new parts should arrive soon. But step 1 is to replace the Curtis control/logic board with my own microprocessor board. 
(btw, amazing that the Curtis is a fully analog device, just isn't done much anymore)

Since the power section still has 10 good fets, I will test it using those first.
Should do 250amps then. 

I'm looking for suggestions on how to bench test a motor controller with 250amp and then 1000amps and maybe even more.
I'm thinking of just coiling up some heavy gauge wire into a tub of water. 
I would want to match the inductance of the motor, not sure how to do that.
My previous motor controllers I've just used the car with an emergency brake on, but that doesn't work for any sustained tests, and I can't put the car in my garage as its full of stuff right now, so need another idea.


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## rochesterricer (Jan 5, 2011)

I remember a user on here sending off their Curtis somewhere to have it upgraded to 1,000 amps. IIRC, he ended up having reliability problems with it after that. I forget who it was, but I think it was someone who had converted a Chevy S10 truck.


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## palmer_md (Jul 22, 2011)

rochesterricer said:


> I remember a user on here sending off their Curtis somewhere to have it upgraded to 1,000 amps. IIRC, he ended up having reliability problems with it after that. I forget who it was, but I think it was someone who had converted a Chevy S10 truck.



http://www.diyelectriccar.com/forums/showthread.php/curtis-1231c-upgrade-144v-1200-ampsi-35944.html


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## Tesseract (Sep 27, 2008)

Besides the freewheeling diodes and MOSFETs you also need to increase the ripple current capacity of the input capacitor(s). Usually this means larger and/or more and/or better capacitors. 

Also note that if any of the high current pathways are through the PCB that is going to be a serious bottleneck.

Finally, as I explained in more detail in a previously referenced thread, the voltage drop across the on-resistance of the low-side MOSFETs is used as the current feedback signal. The problem here is that the latest generation MOSFETs have on-resistances that are *much* lower than the vintage used in the 1231C, and so you could increase the current limit point far more than the improved MOSFETs can actually handle. More specifically, you can't grun more than 50-55A through a TO-247 MOSFET *regardless* of what its datasheet says it can handle unless you submerge the thing in Fluorinert.

If you are doing this is an academic exercise or just to tinker, etc., then more power to you, but I, personally, wouldn't hack a Curtis and then put it in a vehicle I drove on the open road, and I'm pretty sure I could hack one but good...


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## nimblemotors (Oct 1, 2010)

About ready to test out a 100 amps in the updated setup.

I moved the B- connection from the side to the middle, and have the current sensor installed around it. 

For the diodes, I removed a section of the power board that didn't really have anything on it that was important  and then put another B+ busbar extension on top using the existing bus bar taps. Now the diodes can bolt to the M- bus and the B+ bus. Just cut away about half for now, left the rest of the N-Channel switches in the board on that side until I know how much power each component can actually handle.

So for now I have one N-Channel and one Diode, and will run it 100amps or more and see how it goes.


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## 67BGTEV (Nov 1, 2013)

nimblemotors said:


> About ready to test out a 100 amps in the updated setup.
> 
> I moved the B- connection from the side to the middle, and have the current sensor installed around it.
> 
> ...


Wish I was lil' bit more closer, so that I could have stopped by and had a look at this thing..


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## nimblemotors (Oct 1, 2010)

Finally getting back to the controller.
Thought I would post the scope trace when running it through a testload
at 26volts. I'm concerned about the -26volts it shows at initial turn-on.
At turn-off it rings up to 36 volts for about 10ns. Running at 17khz.
This is with a single diode and single mosfet installed.
I've seen it peak at 165 amps, have keep it steady at around 80amps so far don't want to blow up too many parts.


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## nimblemotors (Oct 1, 2010)

So now we are doing fine up to about 85amps, 
when going above that for very long, it is blowing up the switch.
The diode has no problem.
The first pic shows the bad ringing when turning the switch off, getting 2x the voltage. That has been fixed with a snubber, but now the turn on is getting bad ringing (second pic) and I'm thinking this is blowing up the IGBT.
Anyone with a clue give me your thoughts.


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## nimblemotors (Oct 1, 2010)

Y'all knew I would solve the problem without any help right? 
Now good with 120amps continuous, as far as I need to go 1x


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## nimblemotors (Oct 1, 2010)

Have tested the controller up to 600 amps before the test battery pack ran out.
So now I have to move on to the battery charger project..

I have also taken my Curtis 1204 controller, and updating that to 100 volts and 600 amps.
A very cheap and easy way to build a DC motor controller.
Start another thread on that?


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## nimblemotors (Oct 1, 2010)

Here is the little 1204 running at 512 amps. All the 70v pack could muster.
Every part from Curtis has been modified/replaced.
Isn't that Radio Shack prototype logic board nice with all the wire jumpers.


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## epyon (Mar 20, 2008)

I wish I could just pay you to do my controller for me . Or just send you parts . Are you gonna water cool it or put a big fan in the box , like 14 "inches or two 10" inch radiator fans ?


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## nimblemotors (Oct 1, 2010)

The 1231 or the 1204? The 1204 is a pretty small setup, and will need water cooling at this level of power. heck even stock 36v it is inadequate.



epyon said:


> I wish I could just pay you to do my controller for me . Or just send you parts . Are you gonna water cool it or put a big fan in the box , like 14 "inches or two 10" inch radiator fans ?


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## epyon (Mar 20, 2008)

Liquid cooling a DC Curtis controller ? Custom case , chill plate , everybody say's it , but never seen it done . But , a Curtis that can do 450 amps all day would be the wet dream every one wants .


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