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Topic: 1300W Mobility Scooter Motor (Read 176 times) previous topic - next topic

jjfishboy

Hello all, this is my first post so bear with me...

I recently picked up a very large DC brushed motor from a garage sale and have been trying to figure out how to get it powered. Here are the only details i can find about this motor.

-24V DC
-57A peak
-CIM CM808-057 (the name of the motor)
-It did have a clutch which I have now taken off as i will not need it for my intended use(s)
-Equivalent of a 1.8hp engine (approx)

I know it's not much to go on but I really want to get this motor working for as cheap as possible as the motor cost me £5  ($7 or €6 for those not in the uk).

I want to use the motor for a few things just depending on what takes my fancy once i get this motor working:
-go kart
-electric outboard motor for a kayak or similar
-electric longboard
-electric bike
-huge R/C truck
...the list goes on

I have already looked into using mosfets but i can't find much information about how to safely handle really high current with mosfets. I am also looking into powering the whole system with lithium cells (either lipo or li-ion) as they can supply decent amounts of current whilst being fairly light and portable compared to lead acid. Ive also found one mosfet which isn't too expensive (NDP7060).

Oh. i also want to integrate an arduino in this project somehow as well (throttle control, battery monitoring...) because arduinos are awesome!

I would like to thank everyone who contributes to this topic.

James Johnson

cr0sh

You need a motor controller, specifically an h-bridge (for a brushed DC motor) capable of handling the current (60 amps) - you need an h-bridge so you can control the motor in both directions, as well as the speed.

An h-bridge of that size will not be inexpensive - to give you an idea:

https://www.dimensionengineering.com/products/syren50

...and I can't even recommend that because I don't know the full specs of the motor. You say it's max current draw is around 60 amps - this very well might be correct, but I don't know what its running current under load is - but likely, if everything you have said is correct, that motor controller would probably be perfect.

Another option would be to go on ebay and get one of the variable speed reversible 24 volt motor controllers for the wattage of your motor. It may or may not be cheaper, but ultimately, these controllers have a manual switch soldered on to change direction. They use a potentiometer to control speed, via what I believe to be a 555 timer. You could bypass (read as "hack") that to supply the PWM to the output mosfets via the Arduino. For the manual switch, you could get a high-current reversing relay/solenoid for an off-road winch, and control that with the Arduino as well. Caveat: Only switch the direction of the motor after at comes to a stop (otherwise, you will weld the contacts of the relay - in the best case). Of course, this option is probably beyond your current skill level right now.

You do not want to try to switch the current of this motor directly (ie - using a switch, or a relay configuration as an h-bridge) - without some kind of soft-start/stop capability, because the current level it draws is so high. Also, it is not a toy motor, so treat it like you would a go-kart engine or similar - don't wear loose closing or long hair around the spinning shaft, don't try to stop the shaft by hand, always mount (clamp) the motor securely before applying power, and when you are testing your creation (ie - playing with the Arduino code while the motor is under power) - do so with the wheels of the contraption off the ground, in case you have a "runaway" issue.

These motors can run on lower voltages, but won't have nearly the torque as it would at 24 volts. Remember, they were designed for a mobility scooter, and could likely move that scooter at 10-15 kph for many kms, before needing a recharge, all the while using SLA (lead acid) batteries and the weight of the person (plus the scooter). I can say all of this because I have more than a bit of experience playing with such chairs and scooters from helping a friend who refurbishes them for donation (and we build robots with them on the side).

Your batteries - no matter how you look at it (even if you used SLA) are going to cost more than a bit of money themselves. A LiPO pack (likely 28.8V) won't be cheap - plus you still need the charger. Personally, I would go with LiFePo drop-in replacements for SLA, unless size or shape was an issue - but they aren't cheap (they are very lightweight, tho). Whatever battery you choose, be sure to put a 50-60 amp fuse in-line with the positive pole of the pack, as close to the positive as possible (within 10 cm is ok). Such a pack, regardless of what battery chemistry you use, can easily become an impromptu welder - ask me how I know (and in the event that this occurs - that is, a direct short - with a LiPO battery, you better hope you have your insurance paid up, because fire and explosion will likely be the case - though that can happen with any battery, it is almost a surety with a shorted LiPO pack).

I know none of this is likely what you wanted to hear, but it's the truth. Large motors like these aren't cheap to control or run. That said, considering what you paid for it, you go a helluva steal - so consider that savings going toward the remainder of the project.

:D

/note - I'm a yank, so my imperial -> metric conversions are -very- approximate...!
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

MarkT

#2
Jun 15, 2016, 07:42 pm Last Edit: Jun 15, 2016, 07:43 pm by MarkT
Ive also found one mosfet which isn't too expensive (NDP7060).

That's a 20 year old device according to the datasheet - no no no!

These days you can get 1 milliohm devices at reasonable cost, for high current that's the sort
of on-resistance that makes sense.

You realize its a steep learning curve building your own high-power H-bridge?  Devices literally
explode if things go wrong (for even a fraction of a millisecond).

I'd say look at existing commercial motor drivers first (Roboteq have been recommened to me,
there will be many others.

If you want to go down the route of building an H-bridge, you need to learn several things:

1) protection circuitry is absolutely required.
2) Use MOSFET driver chips to drive MOSFETs, use one's that implement shoot-through protection
3) Expect to blow things up.  Budget for it, buy extra parts, wear eye protection.
4) Test on low voltage and current, progressively increase while checking waveforms are OK
5) a good oscilloscope is a must-have

You might want to look up the open-source motor controller project OSMC.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

TeslaIaint

What if he wants the motor to turn in just one direction? Would a 1 milliohm or similar mosfet work for speed control and on/off? Other than allowing the motor to turn in only one direction, what would be the disadvantages of the mosfet?

jjfishboy

Hi everyone and thanks for the great replies.

Yesterday I bit the bullet and though I would try and connect a 12v lipo battery straight to the motor to see what would happen. I'm still alive so i guess that counts as a success.

I may be powering the motor just off 12v maybe 15-18v later but for now the speed is good enough for my uses at 12v. The motor is very torquey (good for my intended uses) and in reply to TeslaIaint, I will probably want to reverse the motor direction but it isn't 100% nessesary at this point (although it would be advantageous).

After a bit of research i stumbled onto this: http://rover.ebay.com/rover/1/710-134428 which i found particually enticing especially at the price. it will accept both 12v and 24v so both bases are covered there. What do you all think about this. (i'm less interested in making a motor driver because of this cheap motor driver now)

Cheers, James

jjfishboy

Also one more thing i forgot to mention: I do have a few tools and equipment (oscilliscope, soldering equipment, multimeters, etc...) basically all a hobbyist needs to do some small projects.

TeslaIaint

your ebay link just goes to the ebay home page instead of your motor driver

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