Need a small induction motor - Page 1
Forum section: electronics / beginners

author: Dmeads
author_rank: Regular Contributor
timestamp: March 15, 2019, 12:34:41 am
content: Hello!I would really like to explore electric vehicles, and I want to build my own motor controller/inverter like the ones in tesla cars (although much simpler). A youtube tutorial explained that the cars use a 3 phase induction motor and vary the frequency to control the speed.To model this, I am looking for a small 3 phase induction motor, somewhere around 20 volts or less per phase because I don't trust myself quite yet with anything higher.I have been looking around a while on ebay, but I haven't found much that looks promising.Does anyone know where I could buy one of these small motors?thanks

author: unitedatoms
author_rank: Frequent Contributor
timestamp: March 15, 2019, 02:42:56 am
content: It looks like lowest voltage 3 phase motors are avionics 48V with 400Hz ac. Very expensive. It may be possible to rewind coils on 6 pole 1 Phase 1/50 horsepower squirrel cage tiny motors for lower voltage and run them on 60HZ AC with 3 phases. There should not be an issue with different voltage as long as amper-turns match the magnetics paths of original design.

author: schmitt trigger
author_rank: Super Contributor
timestamp: March 15, 2019, 02:49:18 am
content: The smallest 3 phase motor I've seen is 1 HP, 208 volt.If you want to limit your inverter voltage to 20 or 24 volts, (for safety reasons) you can always use a 208/24 transformer in reverse, to step up the voltage.

author: Ian.M
author_rank: Super Contributor
timestamp: March 15, 2019, 04:05:52 am
content: You can get 12V alternators with output current ratings as low as 50A, so just under 1HP. Remove the diode plate and regulator assembly, short the field brushes and bring out the three stator coil connections and you can run one as an induction motor.Add a belt drive to a second one with its diode plate intact, and provision to manually vary its field current, to use as a relatively cool running variable mechanical load, regenerating back onto your DC bus.

author: Zero999
author_rank: Super Contributor
timestamp: March 15, 2019, 12:04:12 pm
content: 20V is far too low for an electric vehicle, because to get the required amount of power, you'd need thousands of Amps!It needs to run at a much higher frequency than the mains, otherwise it would be too bulky: the higher the frequency, the smaller the motor.

author: Dave
author_rank: Super Contributor
timestamp: March 15, 2019, 03:13:13 pm
content: Quote from: Zero999 on March 15, 2019, 12:04:12 pmHigher excitation frequency usually means a higher number of pole pairs inside the motor.Certain challenges arise from this: getting a good electrical angle measurement from the rotor and keeping the regulation loop fast enough inside the controller.Getting good regulation with an induction motor is hard enough as it is, especially if you're starting from scratch. Personally, I would stick with a low pole pair count motor.

author: Benta
author_rank: Super Contributor
timestamp: March 15, 2019, 06:56:06 pm
content: The choice of using 3-phase induction motors for electric cars is just a price question. PMDC are much more suitable (and available in the size you're looking for), but the rare earth magnets up the price.

author: Dmeads
author_rank: Regular Contributor
timestamp: March 15, 2019, 07:54:56 pm
content: thanks everyone!I think I will just use a PMDC motor for now.

author: Simon
author_rank: Unknown
timestamp: March 15, 2019, 08:08:42 pm
content: Brushed motors are never a favourite as the brushes have a limited life. brushless permanent magnet motors may not be a favourite either as if they loose sync it will be complicated to get things going again. An induction motor is quite tollerant and providing you know it's speed you can generate a sensible frequency drive.As this is a homebrew a brushed motor sounds ideal with or without magnets. Do you have any experience of controlling motors?

author: Gregg
author_rank: Super Contributor
timestamp: March 15, 2019, 08:17:49 pm
content: A good place to start might be a brushless PMDC battery electric drill as they have already done a lot of the packaging of mechanical components for you. Most are 3ph and have Hall effect back feed as well as nice to have things like gears, fans and reversing switches.

author: Benta
author_rank: Super Contributor
timestamp: March 15, 2019, 08:29:17 pm
content: Quote from: Simon on March 15, 2019, 08:08:42 pmI believe you are speaking about sensorless drive here. PMDC motors with Hall sensors are as uncomplicated as brushed DC motors.

author: Simon
author_rank: Unknown
timestamp: March 15, 2019, 08:31:24 pm
content: Quote from: Benta on March 15, 2019, 08:29:17 pmYes i expect a sensored motor would be less of a problem for the safety critical operation.

author: Benta
author_rank: Super Contributor
timestamp: March 15, 2019, 08:42:17 pm
content: Quote from: Simon on March 15, 2019, 08:31:24 pmSensorless PMDC drive has a very limited number of applications, Hall-sensor motors can be used everywhere in place of brushed DC motors, especially when high starting torque and speed control are important.PMDC applications without sensors include RC aircraft, automotive fuel pumps etc., where you want high power/rpm in a very limited space.They have no place in primary mover systems for cars.

author: SG-1
author_rank: Regular Contributor
timestamp: March 16, 2019, 03:00:12 am
content: I think this short video would be of interest: Electroboom (why 3-phase?)

author: james_s
author_rank: Super Contributor
timestamp: March 16, 2019, 07:01:02 am
content: If you're building a toy like a go-kart sort of thing then a BLDC motor will probably be your best bet, they are available for RC models, some quite large, up to 10HP or so. If you want to convert an actual car to electric then forget it, 20V will never cut it, there's a reason real EVs use several hundred Volts. You need several tens of kilowatts to propel a fullsized car at a reasonable speed, that's a lot of power any way you slice it and if your voltage is low that means the current has to be crazy high.

author: chris_leyson
author_rank: Super Contributor
timestamp: March 16, 2019, 08:20:05 am
content: I recently started work on a rotary "dancer arm" project for use as a wire tensioner as part of a small winding machine. I need to generate a known constant torque over a small operating angle, say 90 degrees. A rotary solenoid would be an easy solution but they are way too expensive so I've opted for a small 24V BLDC and a dsPICdem MCLV-2 controller, it will get me started and I don't have to waste time building a controller, that part will come later on. So far I've found some relatively cheap BLDC motors from ACT Motor in China, they also have distribution in Germany and for the sort of torque I need they don't cost much more than a small Chinese stepper. Also got a HURST DMA0204024B101 to try out, it's overkill for what I need but it has no detent torque unlike the ACT motors.Just a heads up on some kit I'm using to get me started with small BLDC motors. I went for a more expensive Microchip controller because I'm familiar with DSPics but there are cheaper controllers from ST, Texas and maybe Trinamic.

author: jmelson
author_rank: Super Contributor
timestamp: March 16, 2019, 04:26:40 pm
content: Quote from: Dmeads on March 15, 2019, 12:34:41 amSome nice, small motors are made by Pittman. They are quite expensive new, I got some on eBay at a good price.Mine are the 4443 series, I think. These are permanent magnet motors. You are not likely to find small 3-phase induction motors at low voltage. there are also Chinese PM brushless motors used for pumps and such things that are pretty inexpensive. These have Hall sensors so the commutation can have the correct phasing.Jon