New Project involving old water pump motor

[gourami]

I recently came into possession of a 3/4 horsepower motor that was used for a well pump. I want to use it for a small electric vehicle, like a scooter or moped. Here is my idea, and I would really like advice to see if it would work.

The motor's specs are:
60Hz
230v
6.8 Amp
.55KW
3450 RPM

Other parts:
2 car batteries
2 UPS modules
some type of gearing and driveshaft

My Plan:
Take the two car batteries, and connect them to the UPS's Inverters. Take the 120v from each inverter and put it into each 120v wire of the motor. Motor drives two rear wheels through a differential of some type.

Suggestions or comments?

[Samstag]

You can't connect two inverters to double the output voltage.  They'll spend most of the time fighting against each other until one or the other dies a fiery death.  They also aren't very good at providing high-current output, which is what that motor is going to want.

If the invertors are good ones you can use one opf them with the batteries in parallel to power the motor.  You'll get a lot less startup torque but the top-end RPM shouldn't suffer too much.

[danny_galaga]

can you have a look to see what type of motor it is? if it has brushes, it wont need to run on AC. you'll still need to get the voltage up (for DC it will have to be about half that of the AC, so around 100-120V)

if it has brushes, instead of car batteries and inverters, you could use NiCad batteries. you could probably get something going with sub C cells as used in RC car battery packs. maybe 15 of these. thats about $400 bucks worth. compare to the prices of the other parts, and the fact that it will be a lot lighter and more compact...

that was the first pack i found on the net. you can get cheaper and/or lower amperage and spend maybe only $200. charging might be a pain. youd either need a custom made charger or unplug all the batteries and charge the individual 7.2V packs!


hmmm, im thinking now you might want to save that motor for some other project. while in general higher voltages tends to be more efficient (voltage drop is proportionally lower) a scooter or what have you would be much more easily built with a lower voltage motor. 24V is a good size. then two sealed motorcycle batteries in series.

[TOK]

Check this place out... Found it on another forum and thought it was really cool. I don't like the bike they used for the demo, but I think I'm going to get their universal kit and put in on a BMX bike. Will be fun while riding bikes with the kid. 

http://www.dpxsystems.com/

[Ken Layton]

During startup, an electric motor can easily draw double the current than what it normally operates on.

[danny_galaga]

During startup, an electric motor can easily draw double the current than what it normally operates on.

can be way more. i know that a truck starter that draws say 100A while cranking, can draw over 500A for the first .25 second anyway. and to test it you apply a dummy load. it could be drawing closer to 1000A for several seconds!

[TOK]

Kind of a hypothetical question, but something you can do with a scooter that you can't do with a regular electric motor... If you push it forward a bit manually before applying power which starts spinning the motor, does it lessen the startup draw?
As an example, think of an R/C car with an almost dead battery, it can't overcome its own mass if you apply power, but if you push it forward lightly and apply power, it can have enough to keep moving for a pretty long time.

[danny_galaga]

Kind of a hypothetical question, but something you can do with a scooter that you can't do with a regular electric motor... If you push it forward a bit manually before applying power which starts spinning the motor, does it lessen the startup draw?
As an example, think of an R/C car with an almost dead battery, it can't overcome its own mass if you apply power, but if you push it forward lightly and apply power, it can have enough to keep moving for a pretty long time.

exactly right. a series wound motor at rest draws a huge amount of current. this is why they have full torque from zero rpm. the current draw is directly proportional to the rpm, the faster its spinning, the less current it draws. i guess you could say it approximates infinity- zero rpm= infinitly high current. infinite rpm = zero current draw. its not true in real life of course.

basically it boils down to the fact that its effective resistance is higher at speed because of back EMF (the fact that as a motor spins, it is also generating a current, which somewhat offsets the current it is drawing). coincidentally, the fact that the motor generates current from spinning is the basis for regenerative braking.

so yes, giving the scooter a 'push start' means the effective rpm isnt at its lowest. if you always push started this electric scooter, you would greatly increase its range...

[Ummon]

I think the largest point here is gourami doesn't know the basest of these technical details to start this project. Ideas are fine, but often won't get ya far on their own.

[danny_galaga]

yeah, but its not a HUGE project. i say have a crack at it Gourami! that or something else fun...

[gourami]

Well, I suppose for now, Suitcase MAME will be primary. Check out the thread I started in Projects.

[Ed_McCarron]

Controlling the speed of a single phase AC motor is no fun.

If you're bound and determined to try something like this, go DC.  Much more hobbiest friendly, unless you want to jump directly to three phase stuff.

http://www.npcrobotics.com/products/viewprod.asp?prod=33&cat=20&mode=gfx

Not cheap, tho.  Scott motors similar to this one pop up on ebay every now and then.

A couple of years back, I built an electric go-kart for a competition using this motor.  It does 0-30mph in a few seconds, while pulling 200+ A thru a forklift speed controller.











Its really fun when drunk.  Has an amazing tendency to dump you on your pants.

Video of karts from the previous competition.  Only rules:  24x24 footprint, and electric powered.

[Ed_McCarron]

Found the 'completed' pic.

[danny_galaga]

man, i imagine youd have to lean way over the steering wheel to keep it from flipping!  i see you have an anderson connector. i used to sell them (",)

[Ed_McCarron]

Yes.  Powerpoles are your friend.

Thats the "Oh ---steaming pile of meadow muffin--- the main contactor has welded and theres no brakes" disconnect.

[danny_galaga]

Yes.  Powerpoles are your friend.

Thats the "Oh ---Cleveland steamer--- the main contactor has welded and theres no brakes" disconnect.

 

[DaOld Man]

We used to use those type of connectors on AGV (Automatic Guided Vehicle)'s at work.