[blueblizzard816]

I'm looking for a way to make a cheap and easy to build (by theory) controller.

I've poked around on the forums and really liked the idea of the mechanical PWM controller (

http://www.diyelectriccar.com/forums/showthread.php/mechanical-pwm-46258.html

) but it looks like there are too many limitations for an EV application.

This sounds like a dumb question to me, but what the heck. Is there any reason why I can't just put a large potentiometer in series with the batteries and the motor and use that as my throttle to control the power output?

Have there been any other feasible attempts to build a simple (DC motor only) controller for EV applications?

My specialty is ME, not EE so try to explain it in a way that will make sense to me!

[peggus]

With the right motor you can control it with just a potentiometer and a contactor. Using a sepex motor you can control the field with a potentiometer and just connect the armature to the pack, via contactor.

The field power is just a few percent of the propulsion power so the losses in the pot are acceptable, you still need a sizable pot though, (rheostat).

With full field power (low pot resistance) the motor will spin very slowly, to speed it up- reduce the field power.

With a series motor, the power losses in the pot would be too great to deal with.

[major]

Originally Posted by blueblizzard816

This sounds like a dumb question to me, but what the heck. Is there any reason why I can't just put a large potentiometer in series with the batteries and the motor and use that as my throttle to control the power output?

Not a dumb question. Sure, you could do it. The potentiometer would need to be about ten times the size of your motor. And it would waste half of the battery energy needed for every acceleration. And at any speed less than full speed, it would waste considerable amounts of power.

Good news, it could double as a cabin heater If there was any room left for a cabin on the vehicle after finding a place to mount such a large pot. See if you can even find a 25 kW pot.




This is a 7 kW pot. You'd need like 3 or 4 of these. It weighs something like 150 pounds.

Other than that, good idea

major

[DavidDymaxion]

This is how my car operates (for now, anyway). It is quite drivable this way for city speeds at 48V. Something I would add is keep the clutch and transmission -- you'll need to slip the clutch to get going to prevent a huge jerk. With sepex it is great fun to get regen on the downshifts.

I read some old golf cart controllers would have 24V + starting resistor, 24V, and 48 V as three steps. The starting resistor was meant to be used for just a moment.

Originally Posted by peggus

With the right motor you can control it with just a potentiometer and a contactor. Using a sepex motor you can control the field with a potentiometer and just connect the armature to the pack, via contactor.

The field power is just a few percent of the propulsion power so the losses in the pot are acceptable, you still need a sizable pot though, (rheostat).

With full field power (low pot resistance) the motor will spin very slowly, to speed it up- reduce the field power.

With a series motor, the power losses in the pot would be too great to deal with.

[peggus]

As bad of an idea as the giant pot is, you can take comfort in the fact that someone came up with a worse idea and actually tried it.

Scroll to the bottom of the page for the salt water immersion controller.
http://www.poormansev.com/id24.html

[DIYguy]

I've got a $100 controller for you. It's a range switch out of an industrial DC weld power supply. I used this to move my truck around the garage..in and out etc. before I had controller stuff done.

It's like the home made stick shift...thingy...only a little more "refined" lol..

Want it?

[rillip3]

Also, there is an open-source controller for what you are seeking, made by DIY'ers. It's called the Open ReVolt controller. The easiest way to make one would probably be to start with a kit unless you've done something similar.

http://www.paulandsabrinasevstuff.com/store/page3.html

Note that I haven't and do not plan on doing this myself, but it's my understanding this is fairly cheap, i.e. < $300. Your mileage may vary.

[blueblizzard816]

I saw that on the budgetev link (http://www.poormansev.com/id24.html) the controller looks like it connects a varying series of batteries directly up to the motor through that "stick shift" to control the power output to the motor in the form of a finite number of power levels.

The first thing that popped into my head after look at it was if the batteries will drain un-evenly.

Should I even bother looking into this?

Thanks for all your guys'/girls' help! I am learning A LOT and your is very much appreciated!

[rillip3]

ignoring the sheer genius/idiocy of that setup for a moment, yes, unless you rotate your batteries, you will draw them unevenly.

[peggus]

A contactor controller may be an option for you, the better way to do them is to series/parallel the batteries so you get even discharge across the pack at all speeds. Some googling should get you started.