Paul & Sabrina's cheap DIY 144v motor controller

[MPaulHolmes]

Ya, Adam's is also a freewheel diode design. I'll make a freewheel mosfet GCode. It won't be hard at all.. I have a robot in that dang garage that etches whatever I command! Well, stepper motors. But that's sort of a robot. You wouldn't have to pay extra at all. I needed to do that. I was going to anyway for goodness sakes! haha. The control board will need some changes. 2 DC-DC converters, high and low side mosfet drivers, etc...

That sounds fun! We'll teach those MIT punks a lesson! long live S.P.S.C.C.! STick the synchronous rectification version with the new and improved 200v 230amp mosfets on a dang go-cart and melt the tires! Short bursts of maybe 2000 amps. hahaha. Well, thicker power pcb too. haha.

[regmeister]

haha... I'll get back to you later on.

I'm actually thinking of driving it with a 2qd controller, but I just recently blew the fets out of that, so I'll see if I need to restore that board.

ohh they're airlifting the skier out. he was sitting up earlier, blew his knee out.

[MPaulHolmes]

that's terrible! I hope he's ok.

[esoneson]

Originally Posted by MPaulHolmes

...... son has a HORRIBLY STINKY DIAPER, and won't let Sabrina change him......

Sabrina: You one very smart lady!

[Greg Fordyce]

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

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?

Greg.

[MPaulHolmes]

Hey Greg! I'm going to start ordering the AtMega168 instead. The Atmega8 is pin compatible with it, so there are no software or hardware changes necessary. The poor ATMega8 was just about full! hehe. Now we will have 16k flash memory instead of 8k.

Ya, all the little bolts and screws and who knows what comes with it. The only thing that I haven't included in the past is some sort of glue when you stick the little thermistor into the hole drilled in the face of the heat spreader, but I'm pretty sure metric based glue will work well there.

Battery amps are being measured in software. Just a couple lines would be needed to disable the mosfets for a particular number of pwm periods if the battery amps exceeded 300.

This controller has a ripple rating of about 180 amps. Fran was telling me that worst case ripple current is at 50% duty, which is half of the motor amps, or 250amp in this case. So, it's almost rated continuous for the worst case. You could put in some 1000uF caps instead of the 820uF ones I've been using. They would barely fit, and you would then have a ripple rating of about 190amp, with a 20% reduction in ESR.

Joe in Phoenix wasn't having trouble with them overheating in 40-45 degC weather with his driving. Not a lot of mountains though. The temp of the capacitors climbed to around 65 degC, and held there. They are rated for 3000 hours at 105 degC. I hear you double the life for every 10degC drop in temp, so they should be good for around 12,000 hours?

One thing to note: Even at 0 rpm with a locked rotor, the motor current still follows the throttle really well. I've graphed the results of it. No overshoot from a step response. So no concern about large current near 0 rpm, unless you feel like making large current near 0 rpm. In which case you just step on the pedal more! hehe.

I've made a prototype 144v 700amp controller with some Schottky 200v 120amp freewheel diodes. They seem very well matched to the 200v 130amp mosfets. I haven't tested it at 700amps though. I mailed it off to someone. I couldn't have safely tested it with my crappy motor I think. The schottky version costs an extra $50 for the price of the very expensive stinking diodes! Over $8 each! ripoff! We were going to add that as an option on the kit page I think. It just concerns me that I haven't tested it at that current level. It's definitely in the prototype phase. At least I can say for sure that the 60 amp diodes work for quite a while. Ian from Zeva has used them in a controller for about 1 year now, and nothing has exploded! Joe's controller has run since the beginning of July.

By the way:

One annoying thing about the controller is that you need to turn on the 12v power to the controller before closing the main contactor and pre-charge circuit. Well, that's just to be safe. In reality, I think it's not a problem to precharge at the same time, but I would turn the 12v power on first, and off last. It has all the logic protecting against overcurrent and undervoltage. Also, the 12v power input needs to be isolated from the pack voltage. So, use the car's 12v auxiliary battery, or a DC-DC supply or something. The input can be anything in the range of 9v to 18v.

[Greg Fordyce]

HI Paul,

Originally Posted by MPaulHolmes

Hey Greg! I'm going to start ordering the AtMega168 instead.

And when you fill that one up you can then move to the AtMega328 for a whopping 32k

... but I'm pretty sure metric based glue will work well there.

Yes, I keep the metric glue next to the left handed screwdrivers.

Battery amps are being measured in software. Just a couple lines would be needed to disable the mosfets for a particular number of pwm periods if the battery amps exceeded 300.

Cool, I will have a look at this later.

For now I will just go with the standard kit. In my Volvo the Impulse 9 motor and Curtis controller would pull away from a standstill in third gear and could go all the way to 65mph. It was sluggish till about 5 mph though, so I didn't do this often, really it only happened when I forgot to change back to 2nd after coming to a stop. Then for a brief moment I would think the batteries were dying before realizing I was in the wrong gear.

Now this same motor is going into the Matiz which should weigh in the region of 900kg. The Volvo weighed in at 1,400 kg. I've gone all metric on you again and you want to hear something really funny, I am actually from California so metric is a second language to me. So I am hoping the lighter car will have decent acceleration off the line so that I can just lock the gearbox in 4th gear and never have to worry about changing gear. If I am not happy with the acceleration, I will look into upgrading the diodes so the controller can supply more current (and torque) at slow speeds.

Just have to find the money for it. But if I put it on the plastic at the end of the week I won't have to find the money till the middle of January, may do that.

Greg

[MPaulHolmes]

One thing to mention. upgrading to the better diodes can be done, but would be a pain. You would have to have a good desoldering station, or a $6 solder sucker from Ebay, like I use. I've replaced individual mosfets like that before. It was not what I would call fun. It's what I would call, "anger time".

By the way, I just now tested the pwm outputs in complementary mode on the new dsPIC. I was able to control them with a throttle circuit that inputted into one of the A/D channels! The A/D converter was initialized correctly! hurray!!! At this point, I could actually take the piece of garbage breadboard circuit sitting on my desk and run some sort of synchronous rectification controller! It would probably blow up, but it would work at least for a little while. Really I need to add the hardware overcurrent stuff and all that other crap. REally what I'm going to do is just modify the Rev. 2c circuit for this microcontroller. Then I'll already have all the protective stuff all done! I think that it's relatively minor what needs to happen to make it work. For the high side drive, I'm just using a second 12v-12v DC to DC brick that will power a 2nd mosfet driver for the high side mosfets. The DC-DC has an isolation of 3kV for 1minute, so I think it will be fine.

The neat thing about the synchronous rectification is that it more efficient until you get to really really high currents. It's like using freewheel diodes with a 0.2 or 0.3v drop until you get to like 400 or 500amps. Then it's up into the 0.6 range, and a little higher, it gets crappier, but I'm not going to be pulling 230 amps per device. I have a family and I want to see my son grow up.

The PWM outputs have a dead time of 2 us and are the NOTs of each other. hurray!

[Greg Fordyce]

Ah, but I have a cunning plan for upgrading. Basically it involves finding someone else who wants a controller, sell them the power section and build another.

[MPaulHolmes]

oh ya, good idea! haha!