# Curtis 1238 Controller question?



## frodus (Apr 12, 2008)

It depends on the model of curtis you have. there are quite a few flavors of 1238's.

1238-7501 = up to 130V before it cuts out.
1238-6501 = up to 108V before it cuts out.
1238R-7501 = up to 130V before it cuts out.
1238R-7601 = up to 130V before it cuts out.

So if you have a pack that is 140V fresh off the charger, it won't allow the 1238-7501 to start, but if you put on some accessories to draw the pack down via the DC-DC, and you're at 129V, it'l start.


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## cruisin (Jun 3, 2009)

Even though you can start a 1238 at 129v, keep in mind that when you go into regeneration before using some of your storage, the controller will cut it off at 130v or close to it. Having said that, I would suggest you shoot for a pack voltage around 120v to allow room for regeneration. Depending on the weight of your ride and the terrain, regeneration can be more than you expect.


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## lactak (Jun 27, 2011)

Hi I am a beginner and I would like to ask if I can use curtis 1238-7501(every where is written 72-96V) when I have battery pack 108V?
Thanks


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## cruisin (Jun 3, 2009)

lactak said:


> Hi I am a beginner and I would like to ask if I can use curtis 1238-7501(every where is written 72-96V) when I have battery pack 108V?
> Thanks


The controller and motor will handle up to 130vdc. However, when using regen, the pack should not be more than about 124v to provide ample voltage increase during regen or braking power. I have 124v pack and never see regen run it up to 130v.


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## frodus (Apr 12, 2008)

We already answered that question here Lactak.

108V will be fine, but if your pack is 108V nominal, and you charge it and it's over 130V, you won't be able to start the controller.


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## tomofreno (Mar 3, 2009)

> Even though you can start a 1238 at 129v, keep in mind that when you go into regeneration before using some of your storage, the controller will cut it off at 130v or close to it. Having said that, I would suggest you shoot for a pack voltage around 120v to allow room for regeneration. Depending on the weight of your ride and the terrain, regeneration can be more than you expect.


 I agree, and you should also set the User_Overvoltage parameter in the controller software to a value that will prevent over charging of your pack. The controller will limit its output voltage to this value or below during regen. If you bottom balance your pack you will have to enter a pack voltage where your highest voltage/lowest capacity cell is at a voltage safely below over charging. Its straightforward for a top balanced pack. The Nominal_Voltage parameter value for a 1238-7501 controller is 96V. User_Overvoltage is set as a percentage of that. You will notice when it takes effect, the vehicle will fail to slow down as much as it normally would with regen. I've had it cut in at about 80% SOC with regen current over 100A. Edit: if for some reason you set it lower than the pack voltage after full charge, you won't be able to turn on the controller - found this out when I added an extra cell and forgot to adjust the User_Overvoltage parameter.


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## Bowser330 (Jun 15, 2008)

cruisin said:


> The controller and motor will handle up to 130vdc. However, when using regen, the pack should not be more than about 124v to provide ample voltage increase during regen or braking power. I have 124v pack and never see regen run it up to 130v.


you have 124V *nominal* pack?


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## cruisin (Jun 3, 2009)

Bowser330 said:


> you have 124V *nominal* pack?


Yes, I have 6,500 18650 cells like the Tesla which has over 8000. 235ah @ 124v. range in excess of 125 miles using the AC50. They took a real interest in my design in 2005 when they were still working on their design.


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