Paul & Sabrina's cheap DIY 144v motor controller

[Darxus]

Suggestions:

1) Asynchronous mosfet switching. Instead of switching all mosfets on and off at once for one massive pulse, hook the batteries up to the controller in 6 (number of pwm outputs on the ATMega168) isolated packs, and stagger their mosfet switching. Shouldn't that significantly reduce load on things like capacitors and diodes, reducing heat / loss?

2) Switch battery input between parallel and serial connections. Efficiency graphs from the Enertrac motor thread on endless sphere show that for every RPM, there is a most efficient voltage (related to Paul's great tests on the relationship between volts, amps, speed, and torque). So it would be nice if you could adjust the input voltage based on the motor RPMs, but doing it manually should still be useful. Battery packs could be hooked up to switch between, for example, 36v 40A, 72v 20A, and 144v 10a, by switching them from full parallel, to parallel / serial, to full serial. Implemented as a pair of banks of manual contactors? (Combining #1 and #2 should make for an interesting diagram.)

3) Why wouldn't running some capacitors across the motor terminals be useful for smoothing things out?

(Freaking long thread.)

[adamj12b]

Originally Posted by exrdega

Hey guys this is my first post.
To have more room for the conductors I reversed the long bus bar. It now sticks out the far side. The build instructions for 2c are quite good.
However it is way beyond me to operate avr studio to program my controller.
RTD explorer, PonyProg, after two weeks of reading My head is sore. You make it sound so easy. What have i missed.

Welcome Exrdega!!

What kind of trouble have you been having with RTD Explorer? When I started designing it, I wanted it to be as simple as possible.

Is there any questions about it I can answer for you??

-Adam

[exrdega]

Hi,
after my build its time to test. Green light on yellow light was flashing now on.
Cannot communicate with the Atmega chip.

[Greg Fordyce]

Originally Posted by exrdega

However it is way beyond me to operate avr studio to program my controller.

Easy solution, get one already programmed by Paul.

Other Components at Paul & Sabrina's EV Stuff!

Greg

[Greg Fordyce]

Originally Posted by exrdega

Hi,
after my build its time to test. Green light on yellow light was flashing now on.

Green light is simply a power indicator. Yellow light flashing means the controller has a fault. For bench testing the controller, connect a 0-5k pot across the throttle wires and turn down to 0. I used a 0-20k pot for my bench testing as one was close to hand, it doesn't matter to much for bench testing, just need those 2 wires connected to something. Reconnect your 12 volt supply and check the leds. You don't need to connect the traction pack at this stage, but remember the 12v supply for the controller and the traction pack must be separate and isolated.

Cannot communicate with the Atmega chip.

Are you using RTD explorer? Try the above test first and get the yellow light on solid. Then try connecting with RTD explorer.

Greg

[adamj12b]

The yellow light will blink if the throttle is high or disconnected, the current sensor is out of range or disoconected.

RTD explorer will tell you what the problem is without the throttle pot connected. As long as the serial communications are working.

-Adam

[jyanof]

You bring up some good points - I've actually thought about a couple of these and thought I'd share my conclusions.

Originally Posted by Darxus

Suggestions:

1) Asynchronous mosfet switching. Instead of switching all mosfets on and off at once for one massive pulse, hook the batteries up to the controller in 6 (number of pwm outputs on the ATMega168) isolated packs, and stagger their mosfet switching. Shouldn't that significantly reduce load on things like capacitors and diodes, reducing heat / loss?

I believe this is called interleaving. You're right in that interleaving will allow you to run at a higher switching frequency and reduce the stress on the capacitors. Or, you can run at the same frequency, but have your fets alternate switching if you have 2 legs (or switch every 6th pulse if you have 6 legs) which will mean your mosfets are on for half (or 1/6th) the time. This will reduce the stress on the mosfets.

There are two drawbacks. First, whichever leg is on has to carry the full amount of current. So, if this controller were to have 2 banks of mosfets that alternate switching, they'd both have to be sized for 500A. That means twice the number of mosfets (roughly speaking - you might be able to get away with one or two less, but at some point the instantaneous current will blow them).

The second is that the heat losses will still be roughly the same. The same amount of current will be switched at the same frequency. The same amount of heat is produced, just spread around between two (or more) legs. Or, if you up the frequency, there will be even more losses than before.

2) Switch battery input between parallel and serial connections. Efficiency graphs from the Enertrac motor thread on endless sphere show that for every RPM, there is a most efficient voltage (related to Paul's great tests on the relationship between volts, amps, speed, and torque). So it would be nice if you could adjust the input voltage based on the motor RPMs, but doing it manually should still be useful. Battery packs could be hooked up to switch between, for example, 36v 40A, 72v 20A, and 144v 10a, by switching them from full parallel, to parallel / serial, to full serial. Implemented as a pair of banks of manual contactors? (Combining #1 and #2 should make for an interesting diagram.)

Yes, switching high voltage increases the switching losses, so a lower input voltage would increase efficiency. However, as of now, the most inefficient operation of the controller is the moment the car accelerates from a stand still. Calculations show that it is operating near 90% efficiency at this point and rises as the vehicle accelerates. I guess a lower input voltage would buy you a few percent for those several seconds of acceleration. You'd have to decide if it is worth the cost and complexity of added contactors. When cruising at 50% duty cycle and 200 motor amps, it's about 97.5% efficient.

3) Why wouldn't running some capacitors across the motor terminals be useful for smoothing things out?

They may, but I don't think there would be any significant benefit if the motor saw less ripple. There aren't any controllers out there with caps on the output, afaik.

(Freaking long thread.)

I'm glad I got in when it was only 40 pages long :P

[exrdega]

Thanks Adam Greg and all involved. I found a broken wire in my serial cable. Your help is much appreciated. RTD works great.

[ChedMpls]

Back in post 3399 mcudogs talked about putting copper bus bars, solder, and PCB into an oven to solder them together. With this method would i need to tin the bars and board first? A different method he mentions requires tinning but the oven method didn't specifically mention it so i'm really hoping i could skip a step and still get a solid connection. i'll probably try this with some scrap copper pieces but i'd love some input before i stick my actual parts in the oven!

I'm ordering parts and want to know if i can save $23 by skipping silver filled epoxy.

btw.. how would i send a reply/ message to just one person in this forum? i wanted to ask mcudogs this question without ELONGATING the thread! didn't see an email in his "contact info"

about backordered parts from digikey - i went with part# P11621-ND which is a 2" tall power cap and i plan on using a 2" tall aluminum heat spreader bar to match. I also will try those 230a 200v alternate mosfets Paul mentioned.

[Darxus]

Originally Posted by jyanof

First, whichever leg is on has to carry the full amount of current. So, if this controller were to have 2 banks of mosfets that alternate switching, they'd both have to be sized for 500A.

No. That's why I said split the battery pack up into six packs connected to the controller. So each bank of mosfets only gets one sixth of the current.

Originally Posted by jyanof

Yes, switching high voltage increases the switching losses, so a lower input voltage would increase efficiency.
....
Calculations show that it is operating near 90% efficiency at this point and rises as the vehicle accelerates.

I've read a number of cases where people end up switching their balance of amps and volts to get better maximum speed, or better low speed acceleration. Being able to do this while driving would give you both.