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Aaron Cake
Administrator
Canada
6718 Posts |
 Posted - Nov 04 2003 : 09:37:21 AM
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Well, it appears that my abuse was too much for the little 12V motor. Last Thursday, coming back from the bar, I fireballed the motor. Literally. I was heading down my street and smelled the distinct aroma of burning varnish. Looked down, and the motor was trailing a very large flame. After putting it out and pushing it home, I found the motor was a direct short.
Sunday night I pulled it apart, and found that the comm was totally trashed. Comm bars were lifted (sign of over-current) and many connections to the coil were brittle. Most of the varnish was burnt off the coil wires, resulting in shorts everywhere.
Cause looked to be overheating. The motor does not have any real ventilation, only two slots at the front and no fan.
I bought a motor on Monday (same motor) and it is currently a the machine shop where they are making a bushing to fit the 1/2" pully onto the 8MM shaft. This bushing will thread onto the shaft (insted of being pressed on like the old one) since it has a reverse threaded section that originally was used for the nut to hold the cooling fan. That way, if I fireball this motor as well, moving to a new one should be easy.
The new motor will also receive cooling modifications. The rear of the motor will have several large vent holes drilled, and the vents at the front will be enlarged. Between the magnets, there is a lot of space on the outer casing to drill vent holes as well. At the rear, a standard PC style fan will be mounted to draw air through the front of the motor, over the hot brushes and comm, over the coil and out the back. Should make a HUGE difference, considering the motor had basically NO airflow previously.
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cirvin
Nobel Prize Winner
USA
1542 Posts |
Posted - Nov 04 2003 : 4:06:24 PM
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i would put a bunch of holes in th eback and wherevver i could and attach a fanblade to the other end of hte shaft. use the motor itself to pull air through
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n/a
DELETED (Inactive)
22 Posts |
Posted - Nov 04 2003 : 5:57:21 PM
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a computer fan will supply good airflow when the motor isn't spinning fast enough or at all, and it will take little current and easy to add
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BEatonNo1
Nobel Prize Winner
USA
1133 Posts |
Posted - Nov 04 2003 : 8:31:55 PM
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Water cooled  use aluminum pipe and wrap it around the motor, then route it throught the frame of the scooter. if you do it right you wouldnt even need a pump
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Aaron Cake
Administrator
Canada
6718 Posts |
Posted - Nov 06 2003 : 09:59:49 AM
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Nah, I think the PC fan is the best bet. That way, the fans can run while the motor is stationary, preventing heat soak (which is probably the real killer). Actually, I will have to run two fans in series since the scooter switches between 12V and 24V.
The fans will clamp directly to the rear of the motor using 3" rubber plumbing fittings. Now, I just have to wait for the machine shop to get my bushing done...
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cirvin
Nobel Prize Winner
USA
1542 Posts |
Posted - Nov 23 2003 : 12:28:39 AM
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hows the new motor?
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Aaron Cake
Administrator
Canada
6718 Posts |
Posted - Nov 24 2003 : 09:49:03 AM
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I should have posted...Took the machine shop about 2 weeks to make the new bushing because they were busy, and I wanted it to thread on instead of press on (the motor has threads on the shaft, but they are reverse threaded metric #8....yikes!). Got my bushing Wednesday of last week, and put it together that night.
I drilled tonnes of holes in the motor to venilate it. To do so, I had to disassemble it. No big deal, but it did show me how truly cheap these things are. It is underbuilt for sure. Drilled the entire rear of the housing full of holes, and then drilled around the front to blow directly on the brushes. The fans seem to draw a decent amount of air through it, and it makes a huge difference. However, I still believe there is a heat problem. The motor was never designed for this load, and is made as cheaply as possible. It is also very inefficient...by the amount of heat generated, I would guess at roughly 50% efficiency. So the fans do keep it pretty cool, and I am not seeing any of the burning on the brushes or brush wiring that I had before. There is still discolouration on the windings where the varnish has gotten hot, so I don't have a lot of faith in this motor lasting.
I have noticed that eBay constantly has 24V 300W "scooter motors" listed for around $20. They seem to be of decent quality, but I still don't see any cooling. One can only assume that they are closer to 90% efficiency, and are designed for, well, scooters. They even come with a little sprocket, but I doubt it is the proper size. This may be my ultimate solution...
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Kale
Nobel Prize Winner
Canada
795 Posts |
Posted - Nov 24 2003 : 2:54:53 PM
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That or experience the joy of liquid cooling... (Pump faster! She's gonna blow!)
Actually even that won't help much if you can't get the heat out of the coils.
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cirvin
Nobel Prize Winner
USA
1542 Posts |
Posted - Nov 24 2003 : 3:35:16 PM
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you coul try and put lik a bunch of fins on the outside for a heatsink
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Aaron Cake
Administrator
Canada
6718 Posts |
Posted - Nov 25 2003 : 09:38:59 AM
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Fins and water cooling will only cool the case, which gets only barely warm to the touch. The real heat build up is in the armature, which can only be cooled via air cooling, or conduction through the bearings. I could spend all day hacking cooling, or I could just drive this motor until it burns, then buy one designed for the load...
Consider this: the motor is a 12V cooling can motor from a car. In stock form, it draws about 10A and is about 50% efficient. That means that 50W is being burnt up as heat in regular operation. No big deal...I'm running it at 24V, where it pulls 35-40A under load. Half of that is being burnt up as heat in the (undersized) coils of the armature. These motors are pretty much a lost cause. Besides, a "proper" motor will be MUCH more efficient, thus trippling my range...if not more...Commercial scooters with crappy friction drives, 300W motors and only 7AH of battery get 10 miles....I have 20AH of battery, and an efficient chain drive...Should be good for 20 miles easily...
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Kale
Nobel Prize Winner
Canada
795 Posts |
Posted - Nov 25 2003 : 1:56:54 PM
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Too bad you couldn't get your hands on a surplus military chaingun or minigun driver motor... I bet they'd be really high quality.
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n/a
DELETED (Inactive)
2 Posts |
Posted - Nov 27 2003 : 12:48:54 AM
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You should be aware that the motor you describe is made to work 5 minutes or less and rest for about 10 mins., the way a car's cooling fan normally works, however, rewinding the coils with a 2 or 3 numbers down the original wire gauge you could make it last longer.
I have recently made an attiny15 based motor control for a chinese scooter (the original control was a piece-o-crap, the motor was also burnt, so i had to rewind it as well) and it was really easy, you know, you just use the pwm at about 20khz with a 2 quad circuit (aka regenerative braking), an adc channel to read the speed control, another to read the motor voltage, and yet another to sense the current, the sensor being some 18awg turns coiled forward and then backwards (to kinda reduce the inductance) to make an improvised .01r, so when the motor draws x current it reduces the output voltage to prevent the motor from burning. |
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Aaron Cake
Administrator
Canada
6718 Posts |
Posted - Nov 27 2003 : 09:19:10 AM
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I'm not sure the duty cycle you describe for these fan motors is accurate. In city driving, the fan will be on nearly constantly after the thermostat opens up on a warm day. 10 minutes of creeping in the city without a fan means an overheated engine...While not in a stock application, the same fan used in my RX-7 would be on from the time the engine got to operating temperature, until the car was either shut off or there was enough natural airflow through the rad (highway). However, there is obviously a big difference between turning a fan at 10A and running a scooter at 30A+.
Yes, the motor could be rewound, and I have thought of that...Is it worth my time? Probably not.  At that point, the brushes become a problem, and the fact is that the motor still doesn't have real bearings and will probably still be inefficient...A real "scooter" or wheel chair motor is probably the best bet. However, that said, I still might try to rewind it since I've never done that before. Can't be too hard...
As for a PWM controller, I made my controller box easily replacable. So when I get some time I can get a real PWM going (probably just based off the simple one on the site...regen seems pointless) and easily switch...I found these cool twist-grip pots that I am just itching to use...
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n/a
DELETED (Inactive)
2 Posts |
Posted - Nov 27 2003 : 4:18:32 PM
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Well, what I propose is increasing the number of turns in each coil with a thinner wire than the original, in such manner that the volume of wire remains the same, that will draw less current, but the scooter will accelerate slower. To get the right number of turns just calculate the section of the wire, multiply it by the original number of turns and then divide it by the section of the new wire. I use double amidanel copper wire wich tolerates up to 200ºC. No need to say that the conections and winding direction of the coil shouldn't be changed at all.
You should consider the regen (if you plan to build the control), it will make your battery run longer, the mosfets wont heat up heavily because of the EMF and CEMF of the motor (believe this, I made a control for a wheel chair and it was all tears 'til the regen) and is not really hard to implement, in fact the pwm on your page can be modified with another gate out of the same ic, two transistors, a diode, a cap and a zener to drive the clamping mosfet, but I should say that I prefer the uC because of its stability, or an op amp based pwm wich would be larger but also very good.
If you are interested in help with a uC or op amp based pwm, just say the word.
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gokartmaniac
Apprentice
Germany
105 Posts |
Posted - Nov 28 2003 : 11:48:20 AM
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i found one of those power wheel electric car toys at the dump and it has two six volt 112 amp hour batteries and they work i was thinking of turning it into a electric scooter it also has two motors however i dont know anything about them or was thinking of taking the 9.6 volt battery from my laptop and another six volt 12 amp hoour battery and hooking them up to it and go ten miles an hour on a toy designed for four miles an hour hows that sound
Seth A. Meredith |
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cirvin
Nobel Prize Winner
USA
1542 Posts |
Posted - Nov 28 2003 : 12:55:05 PM
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th motors on a hot weels tingy ar geard. you can remove th motor itslf and it will go fastr. that is one hell of a battery!
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Electric Scooter Sadness
