Paul & Sabrina's cheap DIY 144v motor controller

[MPaulHolmes]

Currently (hehe) I have a fixed throttle control, so that stepping on the accelerator really fast forces acceleration to be a little gentle. The main reason for this was to help with the current limiting, but I guess it would have the side benefit of not having the car lurch forward when you take off from a stop sign. I think it wouldn't be too hard to have the acceleration ramp-up adjustable with a little knob on the side of the controller (that secretly twists a pot inside the controller). Yes! It can be done! I just figured it out. That would be a nice feature. You can just hook up the pot to another A/D Converter channel (there are 5 or so).

You could also have an eco-knob (another glorified pot). Twisting it would adjust the current limit, from drag race to weenie mobile! (from terrible range to really good range). That wouldn't be very hard at all!

[bennelson]

On the Curtis controller in the Electro-Metro, it has analog adjustments on the side. You have to pop out a rubber plug, adjust the screw, and put the plug back in.

I have not changed the settings from whatever they were when I got the controller. The three adjustments on the controller are barely even labeled or anything.

Remotely mounting one of those adjustments on the dashboard would be slick.
Crank it to the right to smoke tires, all the way to the left when you are letting a new user drive, and somewhere in the middle for typical use.

High amps being pulled through is the single best way to wreck your range on lead-acid batteries. Turning your amperage knob down would be a great way to help maximize range. It would still be right in front of you to crank up if you have an unexpected hill, etc.

Could that adjustment be set up to work on the fly? Or would you have to reboot the controller?

On-the-fly amp adjuster know would be a neat-o feature.

[MPaulHolmes]

It could be made to work on the fly. The max current in the program is saved in the variable maxCurrent. You could just monitor those other A/D inputs maybe only 100 times a second (like the other slow changing stuff: throttle position and aluminum heat spreader temperature). You would just compute the new value for maxCurrent at that time. If you read 0v from the A/D converter, that would mean the maxCurrent should be set to the minimum value(whatever that should be), and if you read 5v, set it to whatever the largest safe maxCurrent, and something between 0v and 5v means you just set the maxCurrent to the appropriate value between the minimum maxCurrent and the maximum maxCurrent. That would be nice to have it on the dashboard too! It would be sort of worthless having the knob sitting in the engine compartment. hehe

The code for it would take about 5 minutes, and the extra circuitry would be really simple too! Identical to the throttle! But instead of reading it and setting the PWM pulse width, you would do that other stuff above.

[bennelson]

Originally Posted by MPaulHolmes

It would be sort of worthless having the knob sitting in the engine compartment. hehe

Exactly!!!

Yet that's where it is on almost all controllers! I think this would be a great feature!

[Christ]

Is the conversion factor for VDC to VAC always ~10?

I always see 12VDC to 110/120VAC, and 24VDC to 220/230/240 VAC, etc... was just wondering if you could convert 12VDC into 220VAC?

^^^^ Completely pointless question that I can't find the answer to, that might lead to some other random thought that may eventually force me to change my brake pads.. or something. Paul - you know LOL.

[MPaulHolmes]

I think you can convert any DC voltage to any AC voltage, and vice versa.

[Christ]

So it's more an issue of what's commonly done rather than what can be done? Bah - no brake changing for me.

[MPaulHolmes]

I am making another pretty major software change. Ian of Zero Emission Vehicles Australia had mentioned on the EVTech list that his 11" direct drive electric motor had sort of a hair trigger throttle at low RPM. At 10% duty, he would already be up to the full 600 amps, at which point his current limiting would kick in! He had the burnout marks in his garage to prove it. I haven't noticed this problem because I've been controlling an e-bike hub motor, which is quite different. It accelerates nice and smoothly by just controlling the PWM duty with the throttle.

So, he reprogrammed his ATMega8 micro-controller so that the throttle controlled the PWM duty AND the current limit. For example, at 10% throttle, no more than 10% of the current limit would be allowed, and no more than 10% of the PWM duty would be allowed. One of those will be less than 10% duty, but so what! Since current is proportional to torque, it makes for smooth acceleration at low RPMs.

The Torque/RPM curve of a DC motor has torque starting really high, and pwm duty starting really low, and ending with torque really low and PWM duty really high. It will be nice to have both of those under control, and not just the pwm duty.

I doubt my Curtis 72v 400amp controller uses the throttle to control current and PWM duty. It generally has a jerk when it takes off from 0 rpm. That has really annoyed me for some time. The home-made controller is going to feel WAY smoother.

[Intrigued]

I've heard this somewhere before...

but when you're up there making the big money with your controller that all the Big Boys are using...

...remember us little people!!!

[MetroMPG]

Oh, oh! Question:

When you've got the max potentiometer value input to the controller - 100% duty cycle - is it operating at higher efficiency than at some lower duty cycle?

IE is there any reason, that a physical controller bypass would be more efficient than a controller running at full boil, so to speak?