Paul & Sabrina's cheap DIY 144v motor controller

[sawickm]

Things that would be nice to see on the next AVR micro “Rev.E” Controller:

1. Different ATMEGA with more memory and I/O (but compatible with ATMEGA168).
2. Plug-in External Gate Driver/Power Supply (MOSFET or IGBT).
3. On-board CanBUS interface via SPI. - CAN-SPI Adapter
4. Throttle interface – Plug-in 5k Pot or TPS

The CanBUS interface would be nice on the “Rev.E” Controller because a lot of effort was done by Paul for a CanBUS BMS and Charger and could be used with the new ATMEGA controller. It would be added to RS-232 and Ethernet (adamj12b) communication ports.

The dsPIC is still a slick controller having up to 6 or 8 PWM independent or synchronized outputs. Depending on the firmware (1) universal controller could be configured for DC, SR, or AC systems. The DIY’er would just plug in an external MOSFET or IGBT driver / power module.

No reason that both controllers could be developed – ATMEGA for low cost DIY systems, and dsPIC for higher end DIY systems.

- Mark

[sawickm]

Originally Posted by Greg Fordyce

You could add a general disclaimer like the one on the bms project I have been involved with below. Adapt and use any of it you like.

A disclaimer was added to the Open ReVolt Wiki
Open ReVolt - EcoModder

- Mark

[jyanof]

Originally Posted by sawickm

A Wiki "Open ReVolt Problems/Failures" section was added to the Wiki.

Open ReVolt - EcoModder

-Mark

Mark - could you add a link in the failures section to this post?

Joe's controller failure, repair, and fix

I think that'd be the easiest way of adding that to the wiki. I'd add it myself, but it seems I have to relearn how to edit wiki's every time, and since you volunteered...

[DJBecker]

If I could suggest a few features:

An 8 channel ADC to measure these traction-side voltages:

Traction voltage referenced --isolated from house voltage

Battery-side voltages:
0: Traction battery voltage (battery voltage before contactor, up to 250V)
1: Capacitor rail voltage (Voltage at middle capacitor, up to 250V)
2: Capacitor rail ripple -- Capacitor-diode coupled, filtered (1KHz 3db, simple C+RC filter) ripple voltage sample. Zener clamped

Motor-side voltages:

3: Output rail waveform (fast sample)
4: Output rail drive level (filtered negative excursion)
5: Output rail freewheel level (filtered positive excursion)

Internal voltages
6: Gate driver voltage+
7: Gate driver voltage-

8:
Frame voltage offset/impedance -- a safety check for leakage current, high impedance balanced bridge. Perhaps better done in the BMS.

The point of most of these should be obvious. Some are to verify correct operation, and others are to understand heat and efficiency problems as well as to know how close to the edge the devices are operating at.

The capacitor rail and motor output channels should be fast samples, without a low-pass filter. A smart controller could build a waveform report by slightly shifting the sample offset every cycle. That gives an instrument cluster display controller the opportunity to show an oscilliscope-like display, or can be stored in a data logger for later analysis.

The gate driver voltage monitoring is because I'm planning on trying a software controlled combined pre-charge / gate drive approach. It uses a small relay, a MOSFET with sleazy isolated gate drive, and a few resistors and capacitors.

At initial power-on a PWM channel drives the MOSFET (through an isolator) to build the gate power supply voltage up to a safe level. When the ADC reports that the gate supply is a bit above the minimum operation voltage (about 9V, thus we have positive gate control) the controller switches to pre-charge mode.

In precharge state the controller uses the same MOSFET to precharge the main capacitor bank. It stops the PWM output momentarily, closes the pre-charge relay contact, and waits 100msec for the relay contact to settle. It resumes the PWM going from narrow to wide pulses to keep the current approximately constant, always under 1 amp. When the voltage monitor reports that the capacitor bank is within a few volts of battery voltage, it switches the PWM off, opens the relay contact, waits for 10 msec, and enables the main contactor. It then switches to operating voltage mode.

In operating voltage mode it runs the PWM output to generate the target gate voltage. That's usually about 18V, but may be closer to 30V for some devices.

There are several advantages to this design.

First, we can eliminate or shrink some bulky components such as the gate DC-DC converter and the precharge resistor. The gate driver might take a few amps peak, but for well under 0.1% of the time. A DC-DC converter module provides great isolation, but way more average power than we need.

By using smart control we can eliminate the precharge power resistor and use a much smaller relay. The traditional approach is using a relay and power resistor. Both have to be hefty because of the initial power surge, not because they handle much total energy. Increasing the resistance drops that surge, but a slow RC charge tail means that precharge time gets to be annoying. With this design the relay never sees current while switching and the max current is limited, so it can be small. The pulse width is actively controlled, so even with a small initial current the precharge can be finished quickly because we linearly ramp instead of having a tail.

(I don't think that we shouldn't completely eliminate the precharge relay. It's a good idea for safety and isolation, although a small fuse might be good enough to protect against a failed-shorted MOSFET.)

This is software controlled, so the gate voltage can be reduced as the threshold and breakdown voltages drop with temperature. Or just to find the most effective operating point for different conditions, as we are essentially changing the turn-on time by using a higher voltage.

The MOSFET and gate drive can be really sleazy. In fact we want both to be crappy to minimize switching transients. And most of the power the MOSFET switches is going to be wasted anyway. The gate drive really only needs to be strong enough to keep the battery rail ripple from switching the MOSFET on.

A final advantage is one I consider to be the most important. We can run self-checks and diagnostics.

Before starting we can verify traction voltage, establish a baseline, and can check that the capacitor bank and gate voltage are both negligible.

Initial gate supply startup lets us check that the MOSFET is switching and that no gate driver is shorted.

If the main capacitor voltage increases we can report a stuck-on precharge relay.

The relay contact stabilization period lets us check that the gate supply capacitor is still good (less than 1V drop).

After the first timer period of precharge we can verify that the rail voltage is rising. If not we have a shorted MOSFET or other device.

If the rail voltage stops rising approximately linearly, we have a questionable semiconductor. (Note that the incandescent pilot light used for discharging the bank will draw less current as the voltage rises.)

When we stop precharge we sample the motor output to check for leakage or disconnect (very unlikely).

After the relay open period we sample the rail voltage to verify that the incandescent pilot lamp has been drawing power and we have lost a few voltage.

After the contactor has closed we verify that we have fully battery voltage and thus the contactor works.


The disadvantage of this approach vs. Paul's is that we now actually need a traction power supply. You can't "dry test" without traction power. Perhaps there is a sleazy way (9V battery clipped onto gate power?) to mitigate this.

Wow, that was way more than I planned on writing. Especially since I'm not certain that anyone here has an interest.

[sawickm]

Originally Posted by jyanof

Mark - could you add a link in the failures section to this post?

Hi Joe,

I added your links to the Wiki's "Open ReVolt Problems/Failures" and "Open ReVolt Testing" Open ReVolt - EcoModder

- Mark

[DJBecker]

I added a bit about the case design. Most of it is guess from what I read in this thread.

Paul, if you would please correct the most glaring errors...

Open ReVolt/Case - EcoModder

[jpirkola]

Hi everyone,

i just ordered my Open ReVolt KIT a week ago (I was at about page 200 in this thread) and have been making my way through all of the posts (I'm up to about 375).

I'm a mechanical guy not an electronics guy so of course a few things have me confused.

The kit I'm going to get is revision 2C. I've been looking all over and really cannot find a difinitive list of the hardware features and software features that will come with this controller.

I see functions to automate precharge and power up mentioned sometimes and sometimes not. I see RPM limiting mentioned amd sometimes not.

Is there a complete list of the functions that will come with the 2C package. Are there "Extra" features that can be added?

A little background on the proposed controllers use.

I have converted a Cub Cadet Garden tractor to EV. I use it for quarter scale tractor pullingas well as a ride around and light chore duty on the farm. I am going to be using it to pull a converted mower deck next year. Right now it is running at 48 volts with a 6.7 inch Prestolite 24 volt motor and an Alltrax 7245 controller. The tractor weighs in at 1150 lbs. ready to pull I plan on a 120 volt pack of 20 16 ah hawkers for now so getting up to 500 motor amps is possible.

For pulling I want/need more voltage to get the wheel speed up. So on any weekend I might expose the controller to a gentle tour around the farm or I might hook it to a 10,000 lb. weight transfer sled. When I pull I will be most likely getting all the kW available in the battery pack for 15 or 20 seconds.

Are there any suggestions on modifications from the people out there using the controller. I will be placing the controller on top of a 12 x 8 inch finned/fan cooled heat sink. The controller will be up under the hood of the tractor so it will not be exposed to too much weather.

What about tinning the Buss Bars?
Fan cooling inside the case?
Water cooling the heat spreader?
Can the controller be programmed to only work with a specified voltage even though the pack my be much higher.
Motor stall is a concern when pulling. If I'm reading correctly the controller will protect itself the motor and pack from this.
Rpm limiting has been mentioned is this part of the 2C package

Any suggestions or help is accepted.

Jim

[Grimm]

Originally Posted by LouMan

everybody get together and put idea's on the table for a new and exciting ver. E one that is newbie friendly, full of new features, maybe a new pic or arm controller with a grafixs output screen with controller data would be neat, the explorer program shows raw data about the controllers workings but how about a advance screen that shows human data form in degrees and graphs that is understandable without mental recalculations about what the raw data means?

I would hate to see this project die (I've been holding off my conversion for months now in hopes of seeing a SM version)

In regards to displays, I came up with an idea for a cheap solution a little while ago using a spinning POV display.

Here's the thread: http://ecomodder.com/forum/showthrea...ons-14601.html

[duncan]

Hi Everybody
After all of the fuss over the Toyota throttle problems the problem appears to have been in the driver's software - with the driver believing his foot is on the brake where it was actually on the throttle

I would like a panic button that tells the controller to cut current,
(my software could fail at some point!)

Should I do this by putting a switch in the throttle pot line?
Or is this a feature that should be added to the new board?

[jyanof]

Originally Posted by jpirkola

Hi everyone,

i just ordered my Open ReVolt KIT a week ago (I was at about page 200 in this thread) and have been making my way through all of the posts (I'm up to about 375).
...

What about tinning the Buss Bars?
Fan cooling inside the case?
Water cooling the heat spreader?
Can the controller be programmed to only work with a specified voltage even though the pack my be much higher.
Motor stall is a concern when pulling. If I'm reading correctly the controller will protect itself the motor and pack from this.
Rpm limiting has been mentioned is this part of the 2C package

Any suggestions or help is accepted.

Jim

Cool!

Yes, tinning the buss bars is a good idea - not sure if paul does this for you or not, but there's that cheap tinning solution out there that works well.

Fan cooling the insides shouldn't be necessary - testing showed that most heat was generated by the mosfets/diodes and the heatspreader/heatsink is their primary thermal path to the air.

water cooling would be good, but I've had success with my air cooled heatsink. I cruise at 200A though, but do push 500A continuously while accelerating. this was in 110F summer weather, btw.

Not sure what you mean by programming the controller to work with other voltages. It'll take up to 144V nominal. The input voltage affects the throttle response and that can be programmed. It also affects the overspeed cutout settings, which are disabled by default and user defined. Otherwise, it should all be good...

The controller monitors motor amps (limits to 500A) and internal temperature (decreases output at 65C, no output at 75C (I think, maybe paul can verify). So, it protects itself, but not the motor. If you're worried about the motor, you'll need some other sort of temperature monitoring device for that. well, i guess the controller does have an overspeed cutout, so that does protect the motor. it just doesn't know the motor's temperature and it can't really tell with it's stalled.

As for overspeed cutout, there are a couple settings that go into that, and I think it only works for a series-wound motor. (not sure what your prestolite is...) I have my notes somewhere...

A couple of suggestions:
-use a single 12v battery as your traction pack with your motor in neutral when you first get it together and test it out. if something is wrong, there's less chance of things going poof. You could also use a lightbulb instead of the motor. you won't really be able to control the brightness (since the software is expecting much higher amps), but it should at least turn on and off.
-use adam's RTD explorer to to help trouble shoot any problems in the beginning, changing controller settings, and monitoring the controller temperature for the first few runs. keep in mind it'll probably run a little hotter with higher input voltage when you upgrade the pack.