Is that motor really only 2.5A? If so, then the motor driver I'm looking at should be able to handle way more than enough than 2 of my wheelchair motors, right? I was just always under the impression that wheelchair motors use a lot more current than just a measly 2 1/2 amps.
I'm going to buy a cheap ammeter from Amazon then, and I'll try and check the current while the motor is running.
I don't really know how to load it though because I can't mount it back to the wheelchair as I have made semi-permanent modifications to the motor's mounting hardware.
Oh yeah, the wires should be no problem. I'm hooking up my own wires from the wheelchair motor to (2) 12V wheelchair batteries in series, so I have full access to the wires.
Sounds like I should play around with the way I use the ammeter, so I will do that. The meter is arriving today, so I'll do my little tests this weekend.
(I still don't know how I'm going to 'load' the motor, or how I'm going to 'stall it' unfortunately)
You never physically stall a powerful motor at full supply voltage, that's far too risky. Just measure the winding
resistance using a more modest current (clamping the shaft if it actually moves).
A 4-terminal measurement is needed (Kelvin connection), so 2 multimeters are needed, one to measure
current and the other voltage.
If you have a bench supply try putting 1A through the motor, then the voltage is directly convertible to ohms.
Expect a sub-ohm value BTW.
Full stall current = supply voltage / winding resistance.
So I was finally able to do my test yesterday, and now I'm worried I messed up my motor.
First, I hooked up the motor to 1 wheelchair battery, with the ammeter around the positive wire, this went fine and the ammeter read about 4.5A if I remember right.
Then, next is when things got ugly - I hooked up both of my wheelchair batteries in series. I tested the voltage output and it was at about 25.5V. Then I hooked up the wheelchair motor...
Things happened kind of fast so I'm not 100% sure on the numbers, but...for the first couple of seconds things seemed ok - the wheel spun a lot faster than when I had 1 battery connected to it, and I think the ammeter read about 8.5A for a couple seconds. But then for some reason the wheel started getting slower and slower and I started smelling a burning smell, and a little smoke came from the motor and the number on the ammeter starting going lower and lower, like down to 5 (or something like that). Naturally I disconnected it freaking out thinking I may have burned out my motor.
Why did this happen? Is it because the 2 batteries in series produced 25.5V instead of 24V? Is my motor permanently damaged now?
I let the motor set for a little while then hooked up just 1 battery to it, and it seemed to have ran ok. It could just be my imagination from the incident messing with my mind, but it may have ran a little slower than usual when I've hooked it up to the battery in the past...I don't know. I'm just hoping that I didn't permanently damage it.
I noticed your motor has CCW rotation on the name plate. Some DC motors are made to rotate in only one direction. If you go in the wrong direction the brushes will arc really bad. Have you been rotating the motor in the same direction for all of your tests?
Take a look at the commutator and see if it looks black and burnt. Ask me how I know.
Did you apply power to the brake to release it? Perhaps you got the brake shoe very hot?
Wheelchair motors have a brake solenoid on the end that needs 24V across it before the motor
shaft can turn freely. If you forget this it will place a lot of mechnical load on the shaft and turn most
of your input power (24V x 8A) into friction heating.
detown:
I noticed your motor has CCW rotation on the name plate. Some DC motors are made to rotate in only one direction. If you go in the wrong direction the brushes will arc really bad. Have you been rotating the motor in the same direction for all of your tests?
Take a look at the commutator and see if it looks black and burnt. Ask me how I know.
Wheelchair motors go equally in both directions.
[ The left and right motors have to go in opposite directions normally I think ]
I was just going by the CCW on the name plate. Usually bi direction motors will not have rotation specified on the data plate.
It kind of surprised me when I saw the CCW on the motor and realized these were wheelchair motors that rotate in both directions.
Hmm, maybe with worm drive they go the same way for forwards, so they might be assymetrical, but its not a large assymetry and the motor has to go backwards to spin on the spot.
It is common for brushed motors to advance the brush timing slightly to improve forwards full-speed performance at the expense of slow speed or reverse, under the assumption the motor runs most of
the time at full forwards speed - sometimes this is a bit of a nuisance (typical 2-motor robots tend to
pull to one side as a result unless compensated for).
I removed/disconnected the brake several weeks ago because I couldn't even get the wheel to spin with that thing connected. Once I removed it I was able to start getting it to spin.
Not sure if this is necessary, but here's before and after:
I'm sure you guys believe me about the battery outputting more than 12V, and I'm not even sure if this is relevant, but wanted to show that the batteries are outputting more than 12V:
Do I need to use some kind of 24V regulator or something?
I think I've been having the motor spin the same direction in all of my tests, but I could be wrong.
I don't know what a commutator is or what it looks like, but I'm not sure if I want to try to disassemble the motor...but I will if you guys really think I need to.
The commutator is the brass thing on the armature where the brushes make contact. Some motors have an inspection plate that you can remove to check the brushes.
If not you have to disassemble the motor. Not really a big thing.
domiflichi:
So I was finally able to do my test yesterday, and now I'm worried I messed up my motor.
First, I hooked up the motor to 1 wheelchair battery, with the ammeter around the positive wire, this went fine and the ammeter read about 4.5A if I remember right.
Then, next is when things got ugly - I hooked up both of my wheelchair batteries in series. I tested the voltage output and it was at about 25.5V. Then I hooked up the wheelchair motor...
Things happened kind of fast so I'm not 100% sure on the numbers, but...for the first couple of seconds things seemed ok - the wheel spun a lot faster than when I had 1 battery connected to it, and I think the ammeter read about 8.5A for a couple seconds. But then for some reason the wheel started getting slower and slower and I started smelling a burning smell, and a little smoke came from the motor and the number on the ammeter starting going lower and lower, like down to 5 (or something like that). Naturally I disconnected it freaking out thinking I may have burned out my motor.
Why did this happen? Is it because the 2 batteries in series produced 25.5V instead of 24V? Is my motor permanently damaged now?
Its a bit mysterious still, given the brake isn't the issue - normally the current peaks when you connect
and drops rapidly as the motor reaches full speed to a few amps (2 or 3 would be normal for this size of motor).
The wheel should spin twice as fast with twice the applied voltage - did you measure this of just guess?
Have you run the motor without the gears and wheel attached? Is the shaft turning freely by hand?
Normally if the motor slowed down the current would be rising, not falling (unless the batteries were dead).
You are using adequate wiring and connectors aren't you?
BTW watch out for electrocution when you disconnect the battery and generate a spark - that'll be
enough to be lethally dangerous if you are in the circuit.
Well here's another video I uploaded that has my new clamp meter showing the amps.
Looking at my ammeter, it seems to stay at around 4.3A. Does this mean that if things were working right, it should be about 8.6A when I have 24V running the motor, or does it not work that way?
As far as wiring and connectors, I'm using 10 gauge wire (I think) and 8 gauge ring terminals. I have the connections on the battery side connected with the washer/nuts that came with the battery. On the wheelchair motor side, it's not as good I guess - 1 wire is shoved into the terminal of the 4-pin connector coming off of the wheelchair, and I just manually touch the 2nd wire to the 2nd terminal of the same connector coming off the wheelchair. It does create a small spark every time I touch it like this.
When I did that test that I mentioned in a previous post with both batteries, it did seem like the motor ran twice as fast (briefly), but have no idea - I didn't measure the speed (don't even know how), so it's just a guess.
I have not run the motor without the gears and/or wheel yet. Taking apart the motor makes me slightly nervous as I am slightly worried that I won't be able to put it back together right. The shaft/wheel does turn with resistance, but yeah it turns.
Looking at the video(s) I linked, am I doing this unsafely? I really don't want to be electrocuted.
Hi,
Can you do your test again, this time keeping the clamp meter off the side of the motor, where its magnetic field is?
Place it near the battery terminal.