How does a generator and a fan motor 'pulser' control a dc motor?

These paragraphs are from an article about a homebuilt hybrid car in Mother Earth News.

"Any project fresh off the drawing board has its share of problems, and

the Opel hybrid was no exception. When David pressed the accelerator for the first time, he got a 300-amp surge which melted his relays. So he searched his graduate texts for the answer ... and finally found it in-of all places-an old high school physics book: A pulser was necessary to "chop" the current flow and prevent a heavy initial draw to the drive motor.

As Dave explains it, "The motor will always have full voltage and full current, but the pulser makes it 'think' the voltage and amperage are cut down to about 1/4 of what's actually available. With this gadget-which is simply a combination of a reworked car generator and an

old fan motor-I can keep the draw within limits and effectively control

the car's acceleration . . . without sacrificing the maximum current or

voltage that's necessary for high-speed driving. I could have achieved the same results with a commercially available FCR control ... but one of those units would have cut my power slightly, and cost in the neighborhood of $800! I can build my own device for about $25, and I can fix it myself if it breaks!"

Boyntonstu

Reply to
stu
Loading thread data ...

Well, since he said generator and not alternator it could mean that he uses the fan motor to drive the generator and uses the commutator in the generator to provide the switching for his pulser. When he speaks about his pulser and the motor getting full current and voltage what he means is that the power to the motor is switched on and off. The motor will average the power delivered in pulses to torque and rpm. So the lower the on time of the pulser setup the slower the motor speed. The speed drops because the torque drops. But if the above scenario is correct, using the commutator as a switch, it will wear out fast. I wonder how long it will take before he has spent 800 bucks on a bunch of 25 dollar solutions. ERS

Reply to
Eric R Snow

Also, when he says "but one of those units would have cut my power slightly", he needs to realize that the VERY slight power draw of the electronic controller (if it's designed properly) is probably far less than what it takes to drive his fan motor. Then add the issue of an extra 20 pounds of weight on an electic car, and it sounds like a loser to me.

Reply to
Larry Fishel

That's a kludge. You can buy MOSFET's capable of switching 100 amps for under 5 bux. IRF3703 is rated at 210 amps for $4.87. 210 amps would be a bit much for the package, but 100 amps is no problem with even a modest heatsink. Control cctry would be similarly inexpensive.

Reply to
Don Foreman

This is an EXTREMELY PRIMITIVE PWM motor control scheme. It uses the commutator out of a starter motor (spun by a fan motor) to interrupt the current to the traction motor. Depending on how many brushes are connected, he can get 25, 50 or 75% on-time. I built an electric VolksWagen many years ago. I used series resistance starting for the jet engine starter motor, and then controlled it with field control and the usual clutch and gears. With the field at very high strength and 48 V on the armature, it made a HUGE whine. But, it was amazingly powerful. Even though my wiring was way too light (AWG #2 or something like that) it would leap up steep hills, seeming to be a lot more responsive than the old VW engine.

Jon

Reply to
Jon Elson

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.