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Old 11-26-2009, 02:09 PM   #2631 (permalink)
Mark Weisheimer
 
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Hey! I got the pwm working on the dsPIC! It's running 6 at the same time in complementary mode. In other words, 3 are running independent of each other, while the other 3 are the NOT of those 3. And dead time is built in! I can use that chip for synchronous rectification! It's perfect for it. Soon(ish) I'm going to order like 20 of those new 230amp 200v mosfets, and use them for freewheel mosfets and regular mosfets. I'm not sure about how much dead time to build in, but the default from the Application Note AN908 is 0.000002 seconds, so I'm using that right now. Derating it 1/2 allows for over 1000 amps. The voltage spikes at that current level should be around 25 volts, so it should still be fine at 144v nominal. I've also got Bob Woolery's 1000amp shunt in my hot little mits. Thanks, Bob! Another alternative is to split M- into 2, and just measure 1 of them with the LEM.
Paul,

I'll check the surplus place near here that has big a** current shunts.
They had 2000 amp shunts the last time I was there, but the stock
changes often, so I'll see if I can check next week.

Is the bare board and programmed mcu available?
I'm ready to order 2 of each!

Thanks
Mark

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Old 11-26-2009, 02:33 PM   #2632 (permalink)
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Quote:
Originally Posted by Weisheimer View Post
Paul,

I'll check the surplus place near here that has big a** current shunts.
They had 2000 amp shunts the last time I was there, but the stock
changes often, so I'll see if I can check next week.

Is the bare board and programmed mcu available?
I'm ready to order 2 of each!

Thanks
Mark
The PC boards, parts kit and micro are available from MPaulHolmes website
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Old 11-26-2009, 04:32 PM   #2633 (permalink)
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Ya, I have a few microcontrollers, with Fran's super fancy code all rip roaring and ready to go. I also have a bunch of control boards that just got here from China, so we lowered the price some since we ordered extras, so it was cheaper than before for us. That was a run-on sentence.
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Old 11-26-2009, 05:20 PM   #2634 (permalink)
Mark Weisheimer
 
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Originally Posted by MPaulHolmes View Post
Ya, I have a few microcontrollers, with Fran's super fancy code all rip roaring and ready to go. I also have a bunch of control boards that just got here from China, so we lowered the price some since we ordered extras, so it was cheaper than before for us. That was a run-on sentence.
Paul,

Thanks for the reply, I wasn't sure because I had already been to
the site and saw the note about Holidays and all. I'm cramming too, so
I do understand. I'll place my order today!

Thanks
Mark
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Old 11-27-2009, 11:49 AM   #2635 (permalink)
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Got my motor rpm sensor up and running today and began thinking of an rpm limiter circuit for the controller. What would you guys think about using an lm2917 frequency to voltage converter connected to the hardware overcurrent circuit in the revolt? It could be setup to drop out the pwm at a certain rpm with low component count. Quite important for myself with an 11" forklift motor.
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Old 11-27-2009, 12:35 PM   #2636 (permalink)
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Interesting, Jack! So, the LEM output goes to the comparator. You would just connect the LEM output to the output of the frequency to voltage converter. What is the affect of having 2 different voltages tied to the same point? (LM393 pin 2) I guess it would cause current to flow into the LEMs output if the LEM output was at a lower voltage than the LM2917 output, and vice versa. What does the LM393 pin 2 see if you give it 2 separate voltages. Is it the average of the 2, or how the heck does that work?! I've never thought of that before! But if you do that, you might need to increase the time that the hardware shuts off the mosfet driver. Right now it's for about 1/4000 of a second. Maybe increased to a whole second?

Hey! Alternatively (not recommended), you could just cut the line from the current sensor to the LM393 right near the LM393 pin 2. Then just have the lm2917 go into that input. The hardware overcurrent doesn't ever come on after the PI loop is tuned to the motor.
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Old 11-27-2009, 01:25 PM   #2637 (permalink)
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Just looking at the schematic it could be hooked up to turn on q3 which would have the same result. I'll build up the circuit and see how it works. Might be worth incorporating into the next build.
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Old 11-27-2009, 01:41 PM   #2638 (permalink)
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Holy cow, I forgot about the undervoltage circuit! ya! That sound perfect!
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Old 11-27-2009, 02:40 PM   #2639 (permalink)
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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!!!!!!!!!!!!!
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Old 11-27-2009, 02:48 PM   #2640 (permalink)
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Very interesting mr.bond! I'm using a compound wound motor so may not be as easy but a great feature none the less

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