Electric car conversion: Project ForkenSwift

[MetroMPG]

Well, we tested the motor today in both directions. With the field connections reversed (compared to “stock”), the motor turns much more slowly: 1480 RPM @ 12 volts, vs. 2275 RPM.


I’ve just posted a question to the EV list. 800 RPM seems to me like a huge difference to be fixed with a brush timing adjustment alone. Then again, what do I know? I’ve already demonstrated I’m no expert!


Will post back when I’ve learned more.

[MetroMPG]

SW makes another important observation:

Originally Posted by SW

I read that it's actually possible to overspeed series wound motors if you run them w/o a load even though speed limits current flow. I would think the comm timing could have a huge effect on how the field and armature fluxes interact. I have no personal experience though.

You're right about overspeeding a series motor with no load. At least I've read the same thing.

Ours stabilized at 2275 RPM on 12v (no load, "stock" rotation direction). I'm sure it would have been a different story had we spun it on its rated 48v - we would have had a problem.

On the EV list: Jim Husted, a well regarded motor technician, asked me for pics of the motor. I'm happy he replied - I'm sure he'll be able to further my education.

[MetroMPG]

The EV list folks seem to be leaning towards it being a brush timing issue, but the expert requested another specific motor pic, and I'll wait to do anything until I hear from him.

If you want to see pics of the motor & its guts:

http://metrompg.com/offsite/baker-pu...or-detail.html

What I have learned:

You can eyeball whether a series motor is using advanced brush timing by comparing where the brushes contact the commutator relative to the bolts that hold the field coil shoes in place. If it all lines up (brushes inline with the field bolts, it's neutral timing.

A quick look at our motor shows that its timing is in fact advanced for stock rotation (the field pole shoe bolt heads are the painted ones on the casing with the hex heads - the black marker lines line up with the brushes when the end cap is in place):





We'd have to move the brushes the equivalent distance to the other side of the shoe bolts to have the same timing for the direction we want to use the motor.

Also learned: for "street" EV use, 10 degree advance is good. 13 degrees for racing.

Haven't tried it yet. Will wait to hear from Mr. Husted.

[MetroMPG]

The crowd reacts...

Neat photos of motor guts!

[MetroMPG]

Futzed with the brush position this afternoon: got the motor spinning at 2K RPM in the "right" direction for the ForkenSwift. I'm sure I could have gotten it up to OEM speed, but I was working by myself (kind of hard to hold the (unbolted) end cap in place AND hold the tachometer while the thing is whirring away on the workbench).

So I guess our next step is to modify the end cap and brush plate to be able to lock it down in the new position. Which just means drilling a few new bolt holes and making some jumper wires / jumper bus bars.

Prediction! ... The ForkenSwift's wheels spin under electric power this weekend (on jack stands).

[MetroMPG]

More crowd reaction:

Originally Posted by SW

Wicked cool! (as they say around here)

Originally Posted by SVOboy

Mehbe I'll start saving immediately, hmmm...

What an inspiration!

[MetroMPG]

Also been reading up on motor "red lines". The tag on "Otis" (the motor's nickname from now on, now that I know who made it ) doesn't say what it is.

I think it's safe max speed is in the neighbourhood of 3-5K RPM for typical series wound motors from a few things I've read. We need to know these things to plan what gear to be in

Here's a good account (with great pics) of someone blowing apart his Civic Wagovan's motor about a week after he got it on the road. He calculated afterwards that he spun it up to about 6K when the commutator went kablooie and blew its brains out on the pavement. (He also perservered in good humour and just had it rebuilt by the same motor guru who explained Otis' brush timing to me.)

Some of the good purpose-built EV motors are apparently good to 10k (kevlar straps on the rotor, etc).

[MetroMPG]

Reactions to blowing up an e-motor...

Originally Posted by DAX

Wow. That's amazing...I never knew you could blow a motor up like that! Like he said...good thing his friend wasn't troubleshooting under the car when it happened. Glad he got it fixed though...I bet it was $!

Originally Posted by SW

"I bet it was $"

...but not like throwing a rod in an ICE.

[MetroMPG]

Originally Posted by Metrompg almost 2 weeks ago
Prediction! ... The ForkenSwift's wheels spin under electric power this weekend (on jack stands).

So much for predictions. I suck at those.

Anyway, spending a little holiday time working on the motor. It's all back together: new holes drilled to reposition the brush plate & end cap, couple of new wires inside, a few new extended bus bars on the field coils, all of which permits the brush timing to be properly adjusted for CWCE rotation.

Tested, it happily spins up to 2250+ RPM in the good direction on 12v.

Going back now to see if I can get it back on the transmission before supper time.

NOT going to predict that I'll spin the wheels electrically today. But am kind of aiming for that...

[MetroMPG]

It's aliiiiiiiive...

http://www.youtube.com/watch?v=NebLkPulpNg