Question about E-motors

[Christ]

I was at my local TSC (Tractor Supply Co, Inc.) browsing around while speaking with one of the cashiers about fixing her horse trailer for her, when I noticed the incredibly low price tag on electric compressor motors.

My question is this:

Would a 110VAC motor rated at 5HP "Continuous Duty" be sufficient to drive a car small car at speeds around 30MPH around town? I know it doesn't take much to drive a Metro... just wondered how little I could honestly get away with.

I think, since it's rated at 5 HP continuous, I could get away with running it for short times much higher than that, which would make acceleration more bearable, not that it's that big a deal, really.

If not a Metro, what about one of those little dune-buggy things?

[MetroMPG]

You could probably - barely - get away with a motor that small in a light car.

How would you control it? (AC) And with what kind of pack voltage?

[Ryland]

The motor on my 1,400 pound electric car is a 6hp continues duty and looks like it can peek out at around 40hp... 40,000 watts! an inverter that can handle that is going to be hard to find and expensive I would think.

[jamesqf]

I think you're going to need more than 5 hp. Some rough calculations (coasting down a long hill) gave me roughly 15 hp required to move my Insight at 60 mph on the level. And of course you're going to need more power for hill climbing.

But maybe one of those 5 hp motors on each wheel?

[Daox]

I thought something like this would be a good idea too. However, two weekends ago I talked to a knowledgeable motor guy at the EV build day about single phase 110V AC. He said that single phase 110V AC isn't even as efficient as DC. You have to go to three phase to get the extra efficiency. So, unless you go to three phase, DC is really the way to go.

[Christ]

Well, the thought was that it would be for around town only, so controller isn't really necessary, I'd probably use a contactor, which I can explain below. At the same time, I'm not worried about going more than 30 MPH, and it only takes ~5 HP (according to Darin's calculator thingy) to move 35 ish, IIRC.


Back to the contactor -
Instead of using a controller, because it's a low-power, low speed application, and because I don't really care about smooth acceleration, I just figured I could get away with a contactor.

I thought about whether or not I could just run it on a 120VDC battery pack, as well, but couldn't find any info on it. Anyone?

If I were to try this, and the contactor idea doesn't pan out, I'd probably be more likely to find a controller and go with dual motors on a single speed control, making it capable of doing the 10 mile trip to my father's house, as well.


Ryland - If I went with the dune-buggy thing, they don't even weigh in at 1400 lbs, although it would after the battery pack. I think the curb weight less engine and transmission and related accessories is still under 300 lbs, actually. They use ATV tires, but can be exchanged for highway capable trailer tires.

[bennelson]

120V with a contactor!

Ouch! Whiplash!

Maybe you could slip it with a belt tensioner like on a riding lawn mower!

[extragoode]

There's a lot of information I've gotten off of Drag Racing 1964 Electric Chevelle. He uses two or three contactors to build a multi speed "controller" that switched the circuit from parallel to series the same way the killacycle does for a cheap drag racing EV. If you want to go cheap, but hopefully avoid the whiplash Ben's talking about, it'd be worth a look. I'd be surprised that a 5hp motor would do much whipping but I have zero experience. He was also only using 72V, but had a much larger engine.

What kind of AC electric motor is it? I remember there being a general purpose cheap motor type, used for fans usually, that doesn't care whether you feed if AC or DC, but are horribly inefficient. Then there is also the brushless inductive motors that obviously will do nothing if you give them DC. Does any of that make sense at all?

[Christ]

That's my biggest concern. I know that a 5 HP motor is only rated for 5 HP, but I can't see it really producing more than that without a controller feeding it more. Just being hooked up on it's own, with a contactor or a series of contactors, I just can't imagine it really being all that bad... if it were to get bad enough, I'd just hook a torque damper between the motor and transmission, I guess. I'm not really interested in building a complete EV, I just wanted to maybe build something to get around town and such.

You can compare the two options I was looking at here:
Regal-Beloit Electric Air Compressor Motor, 5 HP 15 amp - 3241192 | Tractor Supply Company
and here: Regal-Beloit Electric Air Compressor Motor, 5 HP 21 amp - 3241281 | Tractor Supply Company
They're both rated for "Comp" duty, which is continuous. I do believe they both have overheat protection, as well.

[Bicycle Bob]

Find out what kind of motor you are looking at before guessing about what to feed it and how much it can take for short bursts. There is a wide variation, even within inductive AC types.