DIY Electric Car Forums banner

1 - 3 of 3 Posts

·
Registered
Joined
·
18 Posts
Discussion Starter #1 (Edited)
I have posted to this forum a few times and have gotten very valuable tips and advice. It is appreciated and my thanks goes out to all who helped.
One quick rather frivolous question, What would happen if someone took a Tesla and made a circuit to access every cell at once, like a on-off toggle switch for drag racing? Ever since I heard about the acceleration figures I always wondered about this.
I am trying not to jump around with the subject matter, but I am not always successful.
I am still struggling with the intricacies of motor controllers mostly due to not having a lot of time to study them. And never any extended continuous time to really take it all in at once.

To the situation at hand. I am almost ready to start the plunge into a road legal EV project build, just waiting on some incoming cash and then locating donor forklift(s). I originally had the idea of removing the front drive shaft of a 4x4 and using an electric motor on the front axle to be able to shut the engine down in bumper to bumper traffic. Then I realized if I could use that motor by itself, I would not need the gas engine at all. Better efficiency is always the best way to go.
Where I stand now:
I want to convert a 3/4 ton pickup or flat deck truck with gross weight average maximum under 6000 lbs. (For bigger jobs I have a big block one ton to use, but that is only about 2% of the time.) The EV truck will be used mainly at under 30 mph but some one to two mile stretches at 40 or hopefully 50 mph on level grade. Once a day several days per week at the end of the day I go on a run that is about 6 miles starting on a short 2% - 3% uphill grade with a running start, then the same on the return run. This is in the city at rush hour usually but the outbound run is usually clear for the uphill portion and the return run is empty.
Currently my plan is to find a matching pair of small sit-down forklift motors and stack them or run them inline using one for the low speed driving and kicking in the second motor when needed. Or possibly two for acceleration and one for steady state driving, or am I over-complicating it?
Can one controller operate two motors in this situation?
If I can only find a mismatched pair of motors of the same voltage, will it still work?
Can a DC EV have regenerative braking? If it can, will a small forklift have this feature?
Can a class D audio amplifier (which operates on PWM principles) be used as a motor controller?
I have already tried a manual steering truck and I prefer not to go that way, but I am capable of going without if it makes enough of a difference on range and speed. Will a small sit-down electric forklift have power steering?
I saved a bunch of controllers that I got from a customer. I initially saved two motors also, but the motors were not of any practical use for an EV, weighing around 500 lbs each. The motors were rated at 21 and 26 KW at I believe 800 rpm and used 550 volts 3 phase power. I have about a half dozen regen controllers that came with the two motors.
I am pretty sure the controllers I have won't work on this vehicle because as I understand it, forklifts are generally fitted with DC motors and the AC controllers will not work with them, which means the forklift(s) has to have a working controller. I am hoping to trade a couple of the controllers for some parts or help with the build.
I have not been able to find the answer online to these last two questions, but I think the answers are "yes";
Can a controller of any rated voltage and amperage be used with a lower value motor and battery setup? Are there any reasons not to use a controller with higher ratings than the intended system produces?
 

·
Registered
Joined
·
197 Posts
What would happen if someone took a Tesla and made a circuit to access every cell at once, like a on-off toggle switch for drag racing?
The cells are all connected anyway, but it sounds like you mean one of the old "resistor bank" controllers from the early 20th century, but with no settings below full... You can't run a brushless DC motor or AC induction motor straight from a DC battery. With a DC brushed motor, you'd probably damage the commutator at low speed due excessive arcing, or overheat the armature winding due to lack of airflow at low speed. This isn't a problem with cheap powertools because the inertia is low enough to spend minimal time at lower speeds, and because they're cheap and essentially disposable.

The above assumes the rest of your drivetrain is capable of surviving max torque at 0rpm.


I want to convert a 3/4 ton pickup or flat deck truck with gross weight average maximum under 6000 lbs.
...
Currently my plan is to find a matching pair of small sit-down forklift motors and stack them or run them inline using one for the low speed driving and kicking in the second motor when needed. Or possibly two for acceleration and one for steady state driving, or am I over-complicating it? Can one controller operate two motors in this situation? If I can only find a mismatched pair of motors of the same voltage, will it still work?
Acceleration is where you'll need most torque, and if you're going to carry the weight and mechanical drag of a second motor, you may as well use it. Doing a smooth transition from one motor to two might be difficult. If your motors don't match, you may need separate controllers or at least some extra circuitry to avoid pushing either motor beyond its limits.

Keep it simple: one big motor mounted where the IC engine was, with an adapter to mate the motor's (normally male) shaft to the original (ideally manual) gearbox's (normally male) input shaft. This would let you vary the gear ratio according to payload weight and terrain.
Can a DC EV have regenerative braking?
Not impossible, but people rarely bother, since DC systems are meant to be cheap and simple.
https://ieeexplore.ieee.org/document/6360991/
https://electronics.stackexchange.com/questions/56186/how-can-i-implement-regenerative-braking-of-a-dc-motor
http://www.electric-cars-are-for-girls.com/electric-motor-brushes-and-regenerative-braking.html
If it can, will a small forklift have this feature?
Electric forklifts normally operate within short distances of their base stations so maximising range isn't normally in the design brief. Easier to just add more battery, especially since adding more weight helps you balance heavier loads.

Can a class D audio amplifier (which operates on PWM principles) be used as a motor controller?
It's been done before: https://www.maximintegrated.com/en/app-notes/index.mvp/id/1951
A single-phase AC induction motor could be driven by a single-channel class D amp, but you'd probably need more than one amp and some kind of logic-controlled switching to drive 3-phase AC motors or brushless DC motors (commonly 3 connections).
Not sure where you'd find an amp capable of more than a few kW (normal household plugs here are only rated to about 3kw)
I have already tried a manual steering truck and I prefer not to go that way, but I am capable of going without if it makes enough of a difference on range and speed. Will a small sit-down electric forklift have power steering?
Either use your pickup's existing (probably hydraulic) power steering by fitting a small motor to drive a short belt, or fit an electric or electro-hydraulic steering rack from another road vehicle. I'd expect a forklift to use hydralics for the lift and any power steering probably forms part of that system.

...weighing around 500 lbs each. The motors were rated at 21 and 26 KW at I believe 800 rpm and used 550 volts 3 phase power. I have about a half dozen regen controllers that came with the two motors.
Industrial AC motors are usually conservatively rated for constant 24/7 running, often with limited airflow. Those motors may be capable of much more in a vehicle, which typically only needs max power for a minute or two unless you're climbing a mountain, and will have plenty of airflow (unless you're lugging a full load up a mountain). If you can find the brochure or datasheet for the motor, I expect there'll be another motor in the range with the windings configured differently for the same power rating at higher RPM, less torque. Both models would have the same bearings and casing, so with the right inverter/VFD/VSD you could drive your "800rpm" motor to 1800rpm by running 3x mains frequency.

I am pretty sure the controllers I have won't work on this vehicle because as I understand it, forklifts are generally fitted with DC motors and the AC controllers will not work with them, which means the forklift(s) has to have a working controller.
Yes, but it sounds like you have access to the right part sources to do your first conversion using a DC system, then drive that around while you work on an AC system!

I have not been able to find the answer online to these last two questions, but I think the answers are "yes";
Can a controller of any rated voltage and amperage be used with a lower value motor and battery setup?
Most commercially-available controllers are configurable but not all are user-configurable. People designing and building controllers will often test with low voltages and small motors. This lets them prove the design and construction are good with less risk of damaging components and do it before spending lots on batteries and mounts.
Are there any reasons not to use a controller with higher ratings than the intended system produces?
If you misconfigure the controller you could damage the motor and/or battery if you're careless or unlucky. Higher-rated controllers cost more and are usually physically bigger.
 

·
Registered
Joined
·
1,122 Posts
What would happen if someone took a Tesla and made a circuit to access every cell at once, like a on-off toggle switch for drag racing?
You only need one switch. They're already all wired together.

A Brushless motor must have it's coils pulsed in sequence by the motor controller, so it won't do anything except umm... rotate the tires to a fixed position very quickly.

A DC series motor, that's actually normal.

For example, this old 1969 York forklift I took apart has the speed controller shorted out when the accelerator pedal maxes out. It slams a contactor shut that bypasses the entire controller.

See the lower red line, and A1 that shorts out all the speed controller stuff below it.



Normally this only happens at high speed, so that you have to at least push the pedal for a half second to give it a fighting chance first.

It'd probably make the car do a backflip if it didn't weld the rotor to the brushes.
 
1 - 3 of 3 Posts
Top