Paul & Sabrina's cheap DIY 144v motor controller

[mcudogs]

I have been looking into extra functions that could be included on the control board. We have 6 spare I/O pins on the Atmega, 3 of these are A/D capable.

Possible functions are
Start Input - wired to the cars start switch - operates main contactor
Reverse Input - from gear box reverse switch - restrict power in reverse
Fault indicator - drive dashboard light
Brake Light In - reset pwm to zero when brakes are applied
AC Plug In - wired to switch operated when charger is plugged in
Speed Sensor In - wired to hall effect sensor on motor shaft
Battery volts measurement - connected via a linear optocoupler circuit

[KcElectricMan]

First post after spending a couple of days reading all the posts. I am excited to build my controller and have had e few ideas for features that would really make this a full feature unit.

Since the idea of using a Atmega16 is being kicked around how about lets think about putting an H-Bridge into this so we can go in reverse without a transmission. Not everyone would need to build that part of the circuit if they only wanted forward rotation.

The following old diagram that I have found many times over the years uses N and P channel Mosfets for simplicity.

The Using MOSFETS Website: H-bridge using P and N channel FETs

Here is an excellent simple explanation of how an H-bridge works.

http://www.barello.net/Papers/H-Bridge.pdf


Even on a light weight Metro that would allow us to remove the transmission and just keep the differential and re-case it. That would shave about 30 pounds off the package. For heavier Units this could be a very significant gain.

An added benefit to this setup is the possibility to regen during breaking. Want to slow down? throw on the P- channel at a low rate. Kinda like a a Jake brake on a semi-tractor. Not full braking just a couple of hundred amps at the most.

Just some thoughts on some features I would like to see. I think all the work that had been done on here is fantastic and I can see how this could be a really great controller when completely finished.

[MPaulHolmes]

There's a wire that operates the main contactor right now.

[dlaing]

If we add an 8-1 multiplexer, we can check up to 8 inputs with only 4 pins.
Start Input
Reverse Input
Brake Light In
AC Plug In
Speed Sensor In
We can check most of these every second, for the rest of the time we could have the speed sensor (hall effect?) connected to an interrupt.

[jyanof]

Originally Posted by MPaulHolmes

The EVTech people told me that too fast of a change in voltage or too large a voltage into an A/D channel can cause latchup.

Joe, one experiment you could do, (although I don't recommend it) is to turn up the hardware overcurrent shutdown point some (also change the software to allow for higher current) then slam on the gas. I predict at 16 MHz that you would get latchup with the LEM 300. It's actually a very noisy signal. I looked at it on the oscilloscope. It seems to me to be the most obvious cause of the latchup

.

Eek! sounds dangerous! Everything seems rosy at 16 Mhz, so I may not risk it at this point.

Originally Posted by MPaulHolmes

Anyway! Temperature is what we're talking about! Sounds like good savings for the mosfets. Cutting the resistance from 20 Ohms to 10 Ohms could only be done safely if we used 2 mosfet drivers. Voltage spikes would increase. Any idea what they are like right now? 144v isn't too close to 200v, but it isn't really far away either.

wait - are the gate resistors 20 ohm or 30 ohm? They're 30 ohm on the wiki schematic...

Originally Posted by MPaulHolmes

One thing to consider: The capacitors are rated for 3000 hours at 105 degC. Right now they are only getting into the 60's so that doesn't sound that bad. Even if they did get to 100 degC, if you drove for 1 hour per day at 100 degC, you could drive for around 10 years.

Nice! I vaguely remember some talk about 85C, but if it's 105C that's even better! I agree then - temps in the 60s is probably better than fine. In fact, we may not even need active cooling - just seal up the case and let it heat up.

[MPaulHolmes]

Hey Joe! Yes, the gate resistors were 30, but I changed them to 20 in the last 3 (yours, Bens, Adrians).

Here's the capacitor datasheet:
http://www.panasonic.com/industrial/..._ed_ts_dne.pdf

These are some pretty robust caps.

I don't have any info on the number of hours for the mosfets/diodes at a given temp.

[jyanof]

Originally Posted by MPaulHolmes

Hey Joe! Yes, the gate resistors were 30, but I changed them to 20 in the last 3 (yours, Bens, Adrians).

oh, that changes things slightly!

Heat generation at full frequency: 334W
Heat generation at half frequency: 217W
change: 35% reduction

Predicted temps should now be:
mosfet: 58
heatsink: 51

So, I guess the prediction is still too low, but it's a hair closer.

The numbers at the bottom of my post for reduction in heat generation were assuming 30 ohm gate resistors. They've dropped a little:

15 Ohm Rgate - 16% less heat generation
10 Ohm Rgate - 33% less heat generation
5 Ohm Rgate - 51% less heat generation

I'd like to put my scope on there and check out the voltage spikes...

Originally Posted by MPaulHolmes

I don't have any info on the number of hours for the mosfets/diodes at a given temp.

I asked about that - apparently, thermal cycles play a bigger role than actual temperature. I guess actual life is hard to estimate.

[bones007]

I have been reading this thread for a couple months now and what attracted me here in the first place was a search for a power steering / accessory motor controller. There are a couple gasoline powered vehicles that have an electric-hydraulic power steering pump that can be scavenged, or new commercial solutions exist, but I see a couple problems with these solutions:

-If you are choosing a used electric power steering pump from an old vehicle (ex MR-2: Installing the Electro-Hydraulic Power Steering System) there is a limited supply and their availability at a good price is hit or miss

-New commercial versions are expensive. I had a quote for almost 800 buck from Power Steering Kit.

-Both solutions require sizing your 12V system to be able to handle the large peak current draws that can occur with those systems (~60A). Running off pack voltage would be better for efficiency sake.

I don't currently have an EV but I am planning a conversion next summer and I was thinking that why not take advantage of the power steering pump that came with my "glider" in the first place. All I need is a motor to turn the pump.

Perhaps a motor like one from an electric lawn mower or some other motor.

Then I thought that it would be nice to reduce the power steering boost when running above a certain speed to avoid wasting energy....I need a controller.

I was thinking that a single mosfet/diode/cap stage would probably be enough for the power steering pump motor. The canev.com 12V systems have a peak 60A = 720W. At 120V that current is only 6A for the same power. That should nicely fit into a single mosfet/diode/cap stage.

If the microcontroller was fitted with a main motor RPM sensor, and could output a second PWM signal to a separate mosfet driver circuit, there you have it - a power steering motor controller inside the main motor controller.

Those of you with an EV, what are you doing for power steering? Simply looping the lines is not an option for me as I would like my wife to be able to drive this thing, and I don't know if she could handle it without power steering.

Can the current micro-controller handle two PWM channels. Is there enough computational cycles leftover to handle the adjustment of the PWM of the power steering pump motor according to the motor RPM?

I have enjoyed reading these posts, all 2147 of them. Great work everyone. I can't wait until I can place an order for a kit.

[MPaulHolmes]

It's a simple(ish) thing to use a different micro. The One of the Atmel chips that I have looked at for Sync-Rect. has 6 pwm channels. I don't think the coding is that different.

[mcudogs]

I just noticed in the controller schematic that the throttle pot input doesn't have any clamp diodes to stop the input voltage going over +5 or under gnd. On the Zilla site throttle pot wiring interference is specifically mentioned as a problem. Maybe that's what is causing Joe's controller to lock up.