# Curtis 1238, AC 50 Sluggish Performance



## Zak650 (Sep 20, 2008)

Hi,

I don't know if you are familiar with EVTV but Jack has talked in previous episodes that if the cutback voltage is set too high as the pack voltage sags it sends the controller into cutback mode and limits the power output in order to protect the battery pack.


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## Old Goat (Jun 28, 2011)

Thanks very much for the very quick response. No, sorry, I'm new to this and am unfamiliar with EVTV and don't know Jack. How can I either contact him or view his episodes on EVTV?


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## Old Goat (Jun 28, 2011)

Thanks very much for the very quick response. No, sorry, I'm new to this and am unfamiliar with EVTV and don't know Jack. How can I either contact him or view his episodes on EVTV?


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## Ziggythewiz (May 16, 2010)

Use google. EVTV

Do you know what the cutback is on the AC-50, or if it is adjustable? Check with your vendor.


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## major (Apr 4, 2008)

Old Goat said:


> .... a Curtis 1238 Controller and AC-50 motor. Very, very sluggish performance. No error messages. Cannot draw more than about 24 Amps. Can't get RPM above 1785.....


Always double check the encoder. Secure to shaft and wires correct?

Can you view parameters? If not, how can you be sure you have the motor wired for the correct direction of rotation? Either switch motor phases with parameter setting or if you don't have the programmer, swap 2 of the 3 motor leads.


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## Zak650 (Sep 20, 2008)

EVTV is at EVTV.ME watch the original episode A Conveinient Response and then progress as much a you wish. The second Speedster, duh as it is called is Jack's first car using the Curtis controller and AC-50 motor.


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## frodus (Apr 12, 2008)

Have you contacted the company you bought it from?

I bet it's going into limit mode, 36 cells is higher than the "stock" programming. You will likely need a handheld or PC programmer to change those parameters.


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## JRoque (Mar 9, 2010)

Hi. Putting out only 24A and rising speed so slowly is one odd way of handling an over voltage limit. Thirty six cells @ 3.4V each is 122V. Jack has one running with 38 cells.

I would look into the suggestions already mentioned here: 1. encoder and it's connections 2. check with a programmer or PC terminal for current limit

JR


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## frodus (Apr 12, 2008)

Actually that's exactly how it works, JRoque. Overvoltage or undervoltage both cause the car to go into limp mode. I've had direct experience with this same issue. I helped a customer with this locally and they had higher voltage pack than the normal 72V. It took us a while, but we figured out it was in limp mode. We reprogrammed the battery voltages and it immediately came out of limp mode and drove just fine. It had very slow/sluggish performance before that change and only got to about 2500RPM or so. We changed the limp mode max RPM and the motor max RPM followed. Unfortunately, one needs a programmer to change this value. I usually ask customers and change it for them before they get it, or rent the programmer to them for a couple weeks. Jack has a programmer and I'm pretty sure he needed to program a new higher voltage cutout (or he ordered it for that voltage).


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## JRoque (Mar 9, 2010)

Hey Frodus. I see, interesting - and surprising. Do they all come with a 72V limit by default and you have to program them to ~130? Or do you think this is an odd case?

JR


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## frodus (Apr 12, 2008)

The 1238-6501 is programmed for 72V and the 1238-7601/7501 are programmed for 96V. So when you use 108V, it's over the programmed parameters so it starts limiting.

The AC50 (at least as of last year) were using the 1238-7601 controller. The 1238-6501 won't go to 130V, it's limit is 108V.


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## ruckus (Apr 15, 2009)

So easy fix, drive around till the batts are low and suddenly you will have more power. It will be the only EV on the block that drives better empty. 

When it's on the edge you can turn on your lights to pass people...


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## SandRailEV (May 11, 2012)

Old Goat said:


> Just finished my project, a 95 Acura Integra with 36 LiFEPO4 cells, a Curtis 1238 Controller and AC-50 motor. Very, very sluggish performance. No error messages. Cannot draw more than about 24 Amps. Can't get RPM above 1785. I have no idea how to troubleshoot this. Curtis documentation is slim to none and I have no reference material. It almost seems as if a governor or limiter (software generated) is kicking in. When the RPM slowly (I mean REALLY slowly) increases, it almost seems like the motor speed actually starts to back off at about 1700 RPM, doesn't matter what gear the transmission is in. The throttle pot is not perfect; it is a two wire Curtis look-alike and the range of resistance is only 45 Ohms to about 3.9K ohms but I'm quite sure this is not the only problem here. I'm going to order another (3 wire) pot soon but I want to find out what else is amiss. Is there a setup code or parameter that I need to change in the Curtis controller?


The Curtis controller manual is here:

http://www.evparts.com/cms/picts/products/Curts AC Manual.pdf

It seems rather extensive to me...


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## Old Goat (Jun 28, 2011)

Thanks ever so much for the suggestions. Turns out the problem was in the initial setup. Several things were wrong, but most noticeable was the throttle pot range was only 0.3 _to 1.85V and the darned controller was expecting 0 to 5 V. There were a couple of other settings that were fairly easy to correct once I got the laptop talking to the controller effectively. All is sweet now. Again, thanks for your suggestions.

Dave_


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## dragonsgate (May 19, 2012)

Now that you have it going give us some reports on performance and the like. I have been considering swapping out my dc motor for an ac50. I made a phone call and found out HPEV has some upgrades for the ac50 coming in the near future. So enjoy your ride and keep us informed.


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## ricklearned (Mar 3, 2012)

I am picking up my AC35 motor and controller package on Friday. 

I haven't ordered my batteries yet so I probably will only be able to run some tests with the car on jackstands while using some small gel cell alarm batteries I have lying around. I can't wait to see the wheels turn.


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## Supergrover (Jul 23, 2009)

dragonsgate said:


> ...I made a phone call and found out HPEV has some upgrades for the ac50 coming in the near future...


Did they provide any details as to what upgrades are in the works?

Thanks!


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## dragonsgate (May 19, 2012)

Yes they did. Even though Bryan at HPEV told me some of what was coming I am not sure if he wanted me to start blabbing about it. One thing he told me and the distributer I buy from confirmed is they are working on a new converter/controller to bump the ac50 up to 144 volts. I think he said it was a Curtis. Also they are getting their own in shop dino so they can test on site. Now you got me going and I can’t stop. He might have mumbled something about an ac51 with heavier windings. If I go any further I am sure I will get the details muddled. It has been two days ago that I was told and I didn’t write any of it down.


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## ricklearned (Mar 3, 2012)

dragonsgate said:


> Yes they did. Even though Bryan at HPEV told me some of what was coming I am not sure if he wanted me to start blabbing about it. One thing he told me and the distributer I buy from confirmed is they are working on a new converter/controller to bump the ac50 up to 144 volts. I think he said it was a Curtis. Also they are getting their own in shop dino so they can test on site. Now you got me going and I can’t stop. He might have mumbled something about an ac51 with heavier windings. If I go any further I am sure I will get the details muddled. It has been two days ago that I was told and I didn’t write any of it down.


I was at an EV show in LA a couple of weeks ago and heard a similar thing from the people at Curtiss. They told me that HPEV had a couple of 144v controller prototypes for evaluation. They did not tell me to keep it to myself. On this Friday I am going to Ontario to pick up my AC35 package that I ordered from Thunderstruck. While there I will ask how the evaluation is going. I'm a noobie so I am sure I won't pick up on the technical stuff like our more experienced posters.


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## JRP3 (Mar 7, 2008)

The 144V Curtis is no secret, there is still some question as to what the max current will be, I think it's limited to 500 amps, instead of the 550 or 650 of the 120V 1238-7501 and 7601.


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## dragonsgate (May 19, 2012)

Dragonsgate said "Even though Bryan at HPEV told me some of what was coming I am not sure if he wanted me to start blabbing about it."
JRP3 said "The 144V Curtis is no secret, there is still some question as to what the max current will be, I think it's limited to 500 amps, instead of the 550 or 650 of the 120V 1238-7501 and 7601." Dragons gate says "Boy! that is a load off my mind."


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## ev-converter (May 24, 2012)

ricklearned said:


> I was at an EV show in LA a couple of weeks ago and heard a similar thing from the people at Curtiss. They told me that HPEV had a couple of 144v controller prototypes for evaluation. They did not tell me to keep it to myself. On this Friday I am going to Ontario to pick up my AC35 package that I ordered from Thunderstruck. While there I will ask how the evaluation is going. I'm a noobie so I am sure I won't pick up on the technical stuff like our more experienced posters.


500amp @ 144/160vdc 12v contactor makes AC-50 really sing


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## JRP3 (Mar 7, 2008)

1238-7601 at 650 amps x 120V = 78KW
The new controller at 500 amps x 160V? = 80KW, not that impressive even if it can actually run at 160V.


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## Supergrover (Jul 23, 2009)

JRP3 said:


> 1238-7601 at 650 amps x 120V = 78KW
> The new controller at 500 amps x 160V? = 80KW, not that impressive even if it can actually run at 160V.


Well, 80kW isn't great, but it isn't that terrible either. To put those figures into perspective, the Nissan LEAF is also 80kW with a single fixed gear ratio. I would think an 80kW motor mated to a manual transmission should yield pretty respectable performance as long as the vehicle isn't too heavy. The LEAF isn't particularly light and it still has some punch off the line. 

I just wish there were some more competition and choices in the AC realm.


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## JRP3 (Mar 7, 2008)

I'm not saying the 80KW isn't good, I'm saying that claiming the new Curtis controller, (which might only add 2KW or so), makes a big difference with the AC50 is dubious at best.


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## Hippie Djohn (Oct 24, 2011)

JRP3 said:


> 1238-7601 at 650 amps x 120V = 78KW
> The new controller at 500 amps x 160V? = 80KW, not that impressive even if it can actually run at 160V.


That's not how you calculate power for 3-phase AC motors.

use this:
P=√3*V_RMS*A_RMS*cosφ
V_RMS = (Batt_voltage/√2)

But yes the ratio is the same.



JRP3 said:


> I'm not saying the 80KW isn't good, I'm saying that claiming the new Curtis controller, (which might only add 2KW or so), makes a big difference with the AC50 is dubious at best.


Voltage will sag less with 500A if we assume the cells are the same.
So higher voltage @ load = more power.


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## JRP3 (Mar 7, 2008)

Good point about the voltage sag, which will be more or less of an issue depending on the cells used.


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## Coulomb (Apr 22, 2009)

Hippie Djohn said:


> That's not how you calculate power for 3-phase AC motors.
> 
> use this:
> P=√3*V_RMS*A_RMS*cosφ
> V_RMS = (Batt_voltage/√2)


True. But cosφ is typically around 0.82, which is very close to √2 / √3, so the √3 / √2 * cosφ comes to close to unity anyway. So the very convenient Batt_Voltage * A_RMS is a great approximation. There are also the losses of the controller, if you want to get really pedantic; at around 130 VDC, the ~2.0 - 2.5 V drop across each IGBT (and there are two in series) becomes moderately significant. Less so at 160 V, of course, but not by much. [ Edit: as pointed out below, this is actually an argument to use phase voltage and current, not the approximation. ]


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## Hippie Djohn (Oct 24, 2011)

Coulomb said:


> True. But cosφ is typically around 0.82, which is very close to √2 / √3, so the √3 / √2 * cosφ comes to close to unity anyway. So the very convenient Batt_Voltage * A_RMS is a great approximation. There are also the losses of the controller, if you want to get really pedantic; at around 130 VDC, the ~2.0 - 2.5 V drop across each IGBT (and there are two in series) becomes moderately significant. Less so at 160 V, of course, but not by much.


True... but if we are calculating single hp's for the new Curtis it will make a differens ;-)
If the power is calculated direcly from the phase current and voltage, it includes the controller loss.


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## frodus (Apr 12, 2008)

Just got off the phone to ask a bit about things. The new Curtis is 144V 500A with an isolated 12V side (you supply 12V from DC-DC and everything is now isolated). 

They're still working on everything and there's no ETA on arrival of the new controllers or if those specs are final or final specs on the motors.


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## mizlplix (May 1, 2011)

Thx Trav.

Make me miserable.

Miz


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## 914EV (Mar 16, 2012)

Hi Travis,

I am converting a 914 and using an AC-31 motor and Curtis 1238-6501 controller. From your statements, it sounds as though I can reprogram the controller to operate at 108 VDC with the same limit for regeneration. Is that a correct assumption? 

Thanks,

Bill
914EV


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## frodus (Apr 12, 2008)

You should not OPERATE it at 108V, the controller maxes out at 108V, so you need to be below that to allow for regeneration. Tha max number of lifepo4 cells I'd do on that would be 30, but it might be possible for 32 if you make sure your batteries settle after charging before you go out (turn on DC-DC to load them).


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## mizlplix (May 1, 2011)

It is now almost a year later and Curtis has not coughed up that new controller....

The new rumor is "Any time now" and another source says "end of 2013".

Any concrete information out there about the new 144Volt controller?

TY, Miz


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## frodus (Apr 12, 2008)

A large batch is on it's way to Curtis USA to be tested. They will ship to HPEVS once tested.


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## Bowser330 (Jun 15, 2008)

frodus said:


> A large batch is on it's way to Curtis USA to be tested. They will ship to HPEVS once tested.


It will be very interesting to see the performance graphs from the AC-50 and AC-75 with the new 144V controller. If they make a 650A model it could be a 94kw system (if you had minimal battery sag)


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## tomofreno (Mar 3, 2009)

Bowser330 said:


> It will be very interesting to see the performance graphs from the AC-50 and AC-75 with the new 144V controller. If they make a 650A model it could be a 94kw system (if you had minimal battery sag)


 They rewound an AC50 to make the AC51 they have in the scion with the new controller (Edit 3/23/13: Bill says they have put the AC51 on the back burner now), and there is an AC76 for use with it as well, with similar peak torque as the AC75. Iirc, the AC51 has around 20% higher peak torque than the AC50, and about 3k base speed - rewound for higher torque with the 500A peak current controller. I think the AC50 would have base speed over 5k with the new controller, but only about 80 ft-lb peak torque. Sure wish Curtis had given the new controller higher peak current. With 500A, it has the same peak power as the 1238-7601 controller.


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