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Old 11-29-2009, 09:25 AM   #2655 (permalink)
Greg Fordyce
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Motor rpm and battery current protection.

I have just managed to go through the 267 pages of this thread.

Well done to Paul and Sabrina for starting this project and a round of thanks to everyone who has contributed to the project.

I have just started work on a conversion of a 99 Daewoo Matiz. I have a 1231C controller from my first conversion, but have decided to sell it and get one of these kits, so Paul you should be getting an order from me soon. One thing I noticed is that all the bolts, screws etc. are inch sizes. In europe metric are the only readily availble sizes. So my question is, are all the screws, bolts included in the kit?

One thing that has made me decide to give this controller a go was the way you have implemented torque control with the throttle. The Curtis uses speed control and the main problem I had with that was in reverse gear it was extremely sensitive.

The other thing that conviced me was this;
Originally Posted by MPaulHolmes View Post
Here's a message from Fran:

If you simply want to protect the motor from overspeed, I think you can do that pretty well simply in software using the control board as is.

The RPM of a series field motor is pretty simple.

RPM = K * Volts / Current

K is simply some constant for the motor in question. Volts is simply PWM duty cycle. So for a first attempt, we can do this:

if ((PWM / Current_Feedback) > User_Adjustable_Constant) then cut PWM to zero for some time. It should be good enough to save motors from self destruction by high RPM.

He's going to add over-revving protection to the software. No need for ANY ADDITIONAL HARDWARE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ALLL SOFTWARE!!!!!!!!!!!!!
A very neat idea, even the Zilla can't do this without a seperate rpm sensor. My motor is a NetGain Impulse 9. Once I get the car going I can help find the correct value for K for this motor.

I have thought of something else that would be nice to have and I think it has been mentioned before. How about also incorporating a battery current limit as an option. It could probably be done with a couple of lines of code that could be commented out if not required. In my case I am going to be using a 144v 120ah lithium battery pack. I want to limit it to 300 amps battery current to protect the cells. At slow speeds the motor amps will still be able to reach the 500 amp limit even with a battery current limit of 300 amps. With this sort of current protection in the software it could even be possible to add some more freewheeling diodes to increase the motor current capability limits of the controller at slow speeds without having to add more mosfets.

This idea has come from looking at Lee Hart's Sunrise EV project. For this car, which uses a Warp 9 motor directly coupled to the differential, he has specified a Zilla Z2K so that he can safely handle the large motor amps at slow speed. It seems to me that he is paying for a lot more controller than he needs, and if the Open Revolt can be adapted for higher motor current and low battery current by building it with the required mosfets and diodes for a particular use then you don't waste money buying components you don't need. The only thing I am not sure about is the capacitors. Is there a general rule for mow many capacitors you need? Is this based on the amount of motor current or battery current that the controller can handle?


Last edited by Greg Fordyce; 11-29-2009 at 10:51 AM..
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