Paul & Sabrina's cheap DIY 144v motor controller

[Roger Heuckeroth]

Originally Posted by SteveU

Thanx, that's what I expected. So, assuming rewinding the field is undesirable, we do a buck conversion to produce a low voltage/ high current for the low-z field winding. Since we want a field controller anyway, it comes for ~free. Next question: how bad are the field core AC losses? ie do we need an external choke in series? Probably a good idea for EMC compliance anyway?

... Of course, there are practical limits like the field current must not be too low.

Steve

I've heard of people trying this with no success. A controller out of Italy (Zappi I believe) tried to achieve regen by separately controlling the field on a series wound motor. They had a lot of problems. I think it is possible, just not practical, but I would love to be proven wrong. In theory it sounds like a good idea.

[MPaulHolmes]

I think I'll be ready to test version 1.1 tomorrow, which is basically the control board from the old controller, with just a few different things soldered on, like the 16.000 MHz crystal, and a 3 ounce copper power section. It's mainly so I can drive to the alternative energy fair on Saturday. Also, the software went through more revisions today. I tried to look at each line as ask myself, "what if the interrupt is called here?", or "What if it hangs here?" There were quite a few gotchas that I caught. I tested the control board in the garage, and everything seems to be working well. The power section is still untested. It's pretty simple, but you never know. It's going to be another sickening moment when I hit that gas pedal.

I'm hoping that sampling the current at the same point on the PWM waveform each time will give a smoother feel to the throttle, even though the control board shares a ground with the power section. When the better control board is done, I think things will be way cleaner and smooth.

The software really is better this time, so we'll see what difference that makes. I predict an improvement, but nothing like when the control board is done. One of the guys has been busy trying to finish a project, so there's been a bit of a delay with finishing the control board layout. I think I'll order a single board after its done to try things out, rather than breadboarding it. Then if things seem to work well with Ben's controller, maybe the beta testing can start.

-Paul

[ga2500ev]

I ran across a design for a mechanical chopper that looks like an excellent choice for a starting or backup controller.

It's so simple a caveman can do it!

Fundamentally you mount an insulator and conductor rod together in a V shaped wedge configuration. Then you mount motor brushes on a sliding assembly opposite one another touching the combined rod. Finally you spin the rod with a motor. As the brush assembly slides from the insulated side towards the conductor side, the brushes spend more time touching the conductor thereby providing more power to the motor.

No mosfets, no electronics, no drivers. Completely mechanical.

I think I have my first project to work on.

I'm also already thinking that if the sliding brush assembly is controlled by a microcontroller, then the possibility of having current control becomes possible to do because the pedal and the brushes are no longer directly coupled.

Take a look. Give a comment. If this actually works then a truly inexpensive, easy to build, high powered, high voltage alternative may be available.

Battery Vehicle Society :: View topic - Mechanical Speed Controller

ga2500ev

[MPaulHolmes]

Originally Posted by ga2500ev

It's so simple a caveman can do it!

Careful, you are offending the Geico cavemen... They are pretty sensitive.

That looks like an awesome idea! If you make one, I would love to see how it turns out! There are so many talented mechanical people on here (adapter plate! Oh no! hahaha!) that they should be able to put one together.
Mounting the commutator thing would be pretty easy!
Is it bad for the motor to get PWM current that hasn't been filtered by a capacitor bank?
Here's what would be hard for me:

I've never worked with servos before. Are they tough to make work?
Is it hard to mount the brushes? How to drill right down the middle to attach the post in the center of the double V thing? Is it hard to have a micro-controller control the servo motor? A servo motor controller is sort of expensive isn't it?

Build one! If that works really reliably, that would be awesome!

[Roger Heuckeroth]

Originally Posted by ga2500ev

Take a look. Give a comment. If this actually works then a truly inexpensive, easy to build, high powered, high voltage alternative may be available.

Battery Vehicle Society :: View topic - Mechanical Speed Controller

ga2500ev

I actually had a very similar idea, but I was thinking along the lines of drag racing where you want the ability to handle thousands of amps. For a street vehicle I think electronic PWM is still a better way to go.

[Roger Heuckeroth]

Originally Posted by MPaulHolmes

Is it bad for the motor to get PWM current that hasn't been filtered by a capacitor bank?

Good catch Paul! Not too bad for the motor, but really bad for the batteries. Definitely put some filter caps into this design to prevent murdering the batteries. Batteries don't like AC at all.

[bennelson]

Has regenerative braking ever entered into our open source controller discussion yet?

My motorcycle uses a Permanent Magnet motor coupled directly (by chain) to the rear sprocket. It seems like a perfect setup for regenerative braking.

I never designed the cycle for regen originally because a controller that would handle it costs more, and I have heard poor comments about the most popular brand that supports it.

Also, I have no idea how one controls the regen braking - sensitivity, how to turn it on and off, etc.

Since we have so many smart electronics guys on here, would anyone care to address what it would take to add support for regeneration as a feature?

"It's too complicated, and adds a lot of expense" and "Dude, you are the only one using a Permanent Magnet Motor" are both acceptable responses.

[Wherewolf]

Here's another poormans controller - Driving a powerglide....

budget ev controllers

Wherewolf

[MPaulHolmes]

I spoke to the EV Tech list about the mechanical chopper, and I guess it's been around for quite a long time. Here's Lee Hart's comments:

This idea is the original PWM "chopper" of Tom Edison's time. Before
transistors, before SCRs, even before vacuum tubes there were still
switches.

Yes, you can build a PWM controller with mechanical switches. But this
crude version implies that the builder has no idea how a PWM works, and
never studied the old ones that really *did* work every day in the 1900s.

The fundamental problem is arcing. You can't just switch an inductive
load on and off; the inductance insists that the current *must* flow
somewhere, so you get hideous amounts of arcing that will rapidly
destroy the switch.

Nowdays, we put a freewheel diode across the motor to carry the current
while the switch is off. This at least keeps the switch voltage from
rising past the battery pack voltage. This circuit was widely used well
into the 1990's for things like tape players to control the motor speed.
The switch was operated by a flywheel governor to adjust PWM based on
RPM and thus to efficiently regulate motor speed with no electronics.

In the old days before diodes, they developed other techniques. They
used a second switch in place of the freewheel diode. To deal with the
crossover time when both switches might be on or off, they added
inductors and capacitors to form a resonant circuit.

A typical circuit would have an inductor and two switches in series with
the battery. The motor had another inductor in series (or its field
winding if a series motor), and was connected across the lower switch.
Capacitors were connected to resonate with the inductors at the desired
PWM frequency.

The two switches were operated by various mechanical contraptions (lots
of mechanical ingenuity went into them). The switches were arranged so
you could control the percent on-time of each. Sometimes it looked like
a commutator being spun by a motor; and sometimes it was more like a big
relay wired like a buzzer (called a vibrator).

Today, we call these circuits resonant or quasi-resonant mode ZVS or ZCS
converters.

[adamj12b]

I came across this thread earlier today, and I have to say Good Job! It is awesome that someone is trying to make it more affordable to build EV's.

I have been reading through the thread, but it is going to take me awhile to get through all 101 pages. Have the schematics for the controller been posted yet?

My 2 cents on the regeneration: Based on my experience with robotics and regeneration, you need to leave the mosfets open, even a very small amount to be able to charge the batteries. You would have to have the motor spinning fast enough to cancel out the voltage of the battery pack causing it to start charging. This seems very difficult to achieve with a HV DC motor. You could try it by going down a large hill in a low gear with the peddle pressed very slightly. If you have an inline current gauge, it should actually go down, and eventually negative. When it goes negative, you are charging your batteries. I would love to hear from somebody who could try this. You might want to check with the creator of the controller first though, having not seen the schematics for the controller yet, I am unsure if damage could occur or not.

I look forward to following this thread.

-Adam