I studied about brushless motors, and how to use multimeter to figure out the windings from the leads, using a hard drive motor and VCR head. The hard drive and VCR head both had 4 terminals, 3 leads for the coils and 1 for the center lead between the 3 coils.
I am doing the procedure on 24v brushless lawn mower motor. There are 3 large leads. There is ALSO a 4th SMALLER wire crimped into the windings, is only 18 gauge. I removed the heat shrink tube where the 18 gauge connects, and it appears to be crimped into the copper windings with a copper band splice crimp. I thought I would find a device to help me explain what this wire does. It seems like it would be far too small for this to use as the main center lead in the 3-coil pattern, compared to the size of the other 3 leads. Is the first time I'm doing this so, my understanding is definitely not thorough.
Does anyone else have comments, help me figure out what this small 4th wire does on this motor?
May be just a ground, the center point or "neutral" wire on a wye connected motor carries little current, how does it Ohm?
EDIT: It may be brought out for phase sensing or ??
I forgot to mention. I check resistance and my meter report 0.00. I checked again, shut off meter turn back on, same 0.00. Reads same for any combo of the 3 wires.
When I check hard drive motor, i got readings and it checked out. I used same method to test lawnmower brushless.
I must be doing something wrong. Or the lawn motor is shorted, if i read 0 ohm across all 3 leads. I did not see any evidence of a short, but i did not dismantle the stator shaft from outrunner magnet housing to access and inspect rear of the coils.
The driver supplied stopped working correctly. It wouldn't start - just a few revolutions then stop. I took whole thing apart, found suspicious color dye leak from capacitors. I tried to replace and test again, but it still didn't work. I decided it will be easier for me to find a driver or make own rather than figure out this thing with the hall-effect sensors, that mounted inconvenient for testing.
If resistance is << 1 ohm, I guess I would need something more sensitive than my standard handy multi-meters since I never needed to test something that sensitive.
You can buy very cheap electric bike 3-phase motor drivers from ebay at various power levels... a lot cheaper and easier than designing and building one yourself.
This whole project is a remote-control lawnmower, I parted out an electric wheelchair scooter and used the motor wheels to drive it. It actually works impressive the neighbors are definitely curious and stops traffic people get out and watch.
I bought an "80 amp" ESC module, commonly used for R/C airplanes - with 22" props. I am skeptical of it's 80 amp rating, since that's a whole hell of alot of power for what this small device looks like and who knows how good this matchbox size heat sink does if anything. I do not believe the makes design this for long term endurance.
Tired of testing and debugging I hooked it up to the motor and everything appears to work great as clockwork on my bench. I will reassemble the mower this afternoon as the grass is so long, I am eager to actually mow the lawn, since it's now an exciting task.
Using a smaller lithium battery pack to test, and my cheap amp/watt meter inline, I was measuring only draw of up to 9 amps PEAK and 6 amps continuous with no load. As I used a glove to simulate a load on the motor, it did not seem to draw more current. I do have the heavy lead acid batteries I have yet to test with so I can study the difference in draw using a 18650 pack -vs- the lead acid.
I have attached the pictures of the original driver (for curiosity sake). It has to-220's I can't read since they face each other and eventually are mounted to aluminum angle brackets on the motor mount housing. It's 2 parts, the other controller part went up to the mower where 2 levers activated magnet / hall effect sensors (for safety). There were serial lines between the two circuit boards, that I did not have the motivation to decode the signalling. The boards are covered in thick heat resistant and water tight sealer, and are MULTI-LAYER. For me, it was a hacking nightmare - but someone else with more skills and patience may have had success. It was not worth my effort since the brushless 80-AMP esc cost $30 with delivery.
Yes, it actually is cheaper to buy ESC module, than it would be to make my own. I think I would need like 6 mosfets, 3 n-channel, 3 p-channel. Then, I guess 6 more transistors to trigger high voltage mosfets (or more expensive logic level mosfets). Then an array of capacitors, that had to be +50v or higher rated. I wanted to use this opportunity to try and learn to make one myself, but I felt the whole summer would go by and the lawn would not get mowed.
Well, it's certainly a biggish 3-phase motor controller Presumably the 5-way pcb - connector on the top right of pic 1 are for hall effect sensor inputs ( 5-way : +,-, and 3 phases )
allanhurst:
Well, it's certainly a biggish 3-phase motor controller Presumably the 5-way pcb - connector on the top right of pic 1 are for hall effect sensor inputs ( 5-way : +,-, and 3 phases )
My comments in post #5 apply.
Allan.
It was a nightmare. The waterproof coating was practically indestructible and heat resistant. After wrestling with that, soldering iron on 400 (c) held to contacts that would not fully get wet. The board was mounted upside down, inside the housing make it impossible for me to get leads on it when connected to the motor - without spending 1/2 a day re-fabricating.
So far the $30 remote-control ESC spins the motor. About the torque and RPM? I can't say yet I have to get mounted on the mower and try and cut grass to see how lame or strong the difference in the driver is. The rc-ESC has no hall effect sensors so I assume there is no force-feedback for this controller to control the rpm power on a random increased load.
There are at least 2 types of controllers for 3-phase motors with a dc supply ...........
Those on rc aircraft engines presume the motor follows the spinning field, and are controlled by frequency.
Those on electric bikes have hall-effect sensors on the motor to tell the controller when to switch phases, and the power is controlled using the throttle input to give a much higher frequency variable pwm to each phase as it's selected.
