# Input Voltage Effect on Curtis A/C Controllers



## dougingraham (Jul 26, 2011)

The lower voltage affects where the torque starts to roll off. It will affect the peak horsepower output. The torque is almost flat up to a particular RPM. Lowering the voltage lowers this RPM.

At some point it might be better to go with the 650 amp controller and simply accept the lower voltage.


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## ekwok117 (Sep 6, 2014)

dougingraham said:


> The lower voltage affects where the torque starts to roll off. It will affect the peak horsepower output. The torque is almost flat up to a particular RPM. Lowering the voltage lowers this RPM.
> 
> At some point it might be better to go with the 650 amp controller and simply accept the lower voltage.


I just saw your response on the Tesla battery thread. That is exactly what I am trying to plan for. 

Looking at the curve and considering sag, I'm starting to think running the higher voltage range (+1 more pack) may work. The curve shows that the max 4.2V (7*6*4.2=176.6) drops down pretty quickly. If I keep my cell voltage below 4.0V (168V at pack level) at all times, which would probably increase cycle life anyways, I should be able to utilize the most out of the motor/controller. For reference, I would be running over 2C. Sorry, this is becoming more of a battery topic.

What do you think?


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## dougingraham (Jul 26, 2011)

I don't have direct experience with the 1239 controller to answer this for certain. From what I have read, if you have 48 LiFe cells fully charged the controller won't arm until you lower the voltage a little. The comment was that sometimes you might have to turn on the headlights until the voltage would drop enough (load from the DC-DC converter). 48 *3.4 = 163.2 volts. I think that is lower than what you are talking about. So I suggest you talk to HPEVS before you commit.

Charging your Tesla cells to only 4.0 volts per cell is going to limit your capacity to about 75% of full capacity. They will probably last a lot longer if you do this but giving up 25% of your capacity is significant.

I have tested a couple of varieties of Lithium cells and obtained a fairly consistent reading. I have not tested the Tesla Panasonic 18650 cells so these could be off a little but I would expect it to be no more than a couple of percent variation from this chart.

4.20 volts = 100%
4.15 volts = 90%
4.10 volts = 83%
4.05 volts = 78%
4.00 volts = 75%
3.95 volts = 66%
3.90 volts = 60%


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