[FlyingElectron]

I'm thinking about upgrading the tiny 1/5HP motor on my Micro Mill with something a little heftier, and was researching the stock motor that came with my Micro Mill. It looks like the company also made fan motors for box fans and automotive radiator fan motors. This got me thinking if I could use any DC permanent magnet motor as a replacement (with new speed control of course)? Car radiator fans look like they are pretty hefty drawing about 12 - 14 amps @ 12V with the benefit that the 12V could be supplied by an old computer power supply.

So I'm curious if a DC permanent magnet motor is just a DC permanent magnet motor, or if there are different types? And are there any obvious reasons why a radiator fan motor would be unsuitable?

Thanks!

[escott76]

I'm thinking about upgrading the tiny 1/5HP motor on my Micro Mill with something a little heftier, and was researching the stock motor that came with my Micro Mill. It looks like the company also made fan motors for box fans and automotive radiator fan motors. This got me thinking if I could use any DC permanent magnet motor as a replacement (with new speed control of course)? Car radiator fans look like they are pretty hefty drawing about 12 - 14 amps @ 12V with the benefit that the 12V could be supplied by an old computer power supply.

So I'm curious if a DC permanent magnet motor is just a DC permanent magnet motor, or if there are different types? And are there any obvious reasons why a radiator fan motor would be unsuitable?

Thanks!

One of the most popular combat robot motors of all time was the venerable "EV" which was a Bosch motor, almost identical to car fan motors. Countless teams have used this motor as drive or weapon motor in many sized robots. Personally I've used it to spin a pair of 14" lawnmower blades, drawing upwards of 70A during spinup, and 40-50A cruise. Motor never failed, but I blew tons of cells with that arrangement.
I'd say something similar would do great with a few caveats. Pay attention to your cooling. Fan motors are meant for intermittent duty, and usually have the air of the fan to cool them. In robots the length of the match usually puts you into intermittent territory. You'll want to be operating decently below the motors rated current for continuous use. You also want to be careful what gets blown though there. These are generally not enclosed motors, so if you aren't careful damaging swarf could get in there.
One other thing. Although 12A at 12V would appear to be 144W which is around 1/5HP, understand that what you are talking about there is INPUT power. Without knowing the efficiency of the motor (and gearing too, but that's another story) you won't know your output HP, which is what really matters at the cutter. I can tell you that PMDC motors seldom exceed 50% efficiency. That would give you 1/10th or less at the cutter. Just something to keep in mind.

[HawkJET]

I can tell you that PMDC motors seldom exceed 50% efficiency.

This is complete bull****! If you are getting less than 50% efficiency, You really messed up big time in your design. In a properly designed system, PMDC motors can achieve efficiencies near 90%. It takes A LOT of screwing up to drop BELOW 50%.

You don't just find a motor in the junk yard and use it for whatever. Electric motors have a specific operating range. You need to take that into account with any kind of motor (be it an internal combustion engine or electric motor).

I do contract work for a company that designs and builds brushless DC motors. In some instances, efficiencies in the low 90% are possible with efficiencies of 80% being routine.

[escott76]

This is complete bull****! If you are getting less than 50% efficiency, You really messed up big time in your design. In a properly designed system, PMDC motors can achieve efficiencies near 90%. It takes A LOT of screwing up to drop BELOW 50%.

You don't just find a motor in the junk yard and use it for whatever. Electric motors have a specific operating range. You need to take that into account with any kind of motor (be it an internal combustion engine or electric motor).

I do contract work for a company that designs and builds brushless DC motors. In some instances, efficiencies in the low 90% are possible with efficiencies of 80% being routine.

Easy there chief. Brushless DC and brushed DC (sorry I didn't clarify brushed DC earlier) are different and have different efficiencies. Yes, a BRUSHLESS motor can get near 90%, but I'd wager you aren't going to find a BRUSHLESS automobile fan motor, but perhaps you are just special.
After many years of working with this specific kind of motor, measuring it's input and output power I can say specifically that it approaches 50% best case. What is your specific experience with brushed automobile fan motors?
Maybe YOU don't find a motor in a junkyard and use it for whatever, but the OP could well be on to something with the concept here (although his power supply is a little on the anemic side for the app).

[HawkJET]

Brushless DC and brushed DC (sorry I didn't clarify brushed DC earlier) are different and have different efficiencies. Yes, a BRUSHLESS motor can get near 90%

And so can BRUSHED motors. There are thousands of R/C model airplanes and helicopters that are powered by brushed motors. If the efficiency of those motors was only 50%, they would NOT work!

If you are getting less than 50% efficiency, you are using the wrong motor or it is the wrong application, PERIOD. And that is my point.

If you have been using radiator fan motors, and measuring less than 50% efficiency, the problem is NOT the motor as you imply. Again, this is my point. If you measure such poor efficiencies, that should be a big red flag telling you that you need to do your homework and get an appropriate motor. Unless of course you don't care about efficiency in that application - but don't then make a blanket assumption that all motors are inefficient, the system is.

The OP asked if a radiator fan motor will work. I am saying, don't just grab anything from a junk yard and expect it to work well without further analysis.

[diecutter]

The motors used in treadmills have tons of torque and usually come with a speed controller. I have seen numerous articles where they were adapted to drill presses, lathes, and mills with good results. They can often be bought thru surplus catalogs or salvaged from junked treadmills. Another advantage is that the speed controller works off the wall outlet.

[FlyingElectron]

I think in my situation, the radiator fan motor is probably going to work and I do feel better about using it now that I know that something similar is used in battlebots. I understand it's not going to be super efficient but it's probably going to have some advantages to what I have now. I'm still researching the idea so all input for and against is always welcome.

Right now my stock motor is a 110V DC motor that draws 1.5A and the stock speed controller is a 120V AC bridge rectifier which controls speed through PWM. It says 1/5HP on the motor, but I'm not sure how that is calculated. I haven't dragged my oscilloscope out to the garage to actually measure what the voltage waveform going to the motor looks like, but since it's a bridge rectifier, I'm assuming its going to look like a bunch of chopped semicircles so the motor never really draws 1.5A continously because of the semicircles.

I'm thinking that the advantages of the 12V radiator fan are that I can supply a full 12V DC all the time to the motor since the 12V will be coming from a switched power supply (probably a dedicated 12V switched power supply not a computer power supply) and I can still control speed by doing PWM on the 12V supply. The other advantage for me is that it is easier for me to build a solid state 12V H-Bridge to do motor reversal then it is to build a 110V (155V Peak?) solid state H-Bridge.

The motors used in treadmills have tons of torque and usually come with a speed controller. I have seen numerous articles where they were adapted to drill presses, lathes, and mills with good results. They can often be bought thru surplus catalogs or salvaged from junked treadmills. Another advantage is that the speed controller works off the wall outlet.

I've been kicking myself for the last few weeks for not picking up the surplus treadmill motor and speed controller that I saw a lot of people using for the last few years, I think it was from surpluscenter?. I think they were from GE treadmills and there were thousands of them available and they were cheap, but I haven't seem them for sale for a while so I think they finally sold out.

[escott76]

And so can BRUSHED motors. There are thousands of R/C model airplanes and helicopters that are powered by brushed motors. If the efficiency of those motors was only 50%, they would NOT work!

If you are getting less than 50% efficiency, you are using the wrong motor or it is the wrong application, PERIOD. And that is my point.

If you have been using radiator fan motors, and measuring less than 50% efficiency, the problem is NOT the motor as you imply. Again, this is my point. If you measure such poor efficiencies, that should be a big red flag telling you that you need to do your homework and get an appropriate motor. Unless of course you don't care about efficiency in that application - but don't then make a blanket assumption that all motors are inefficient, the system is.

The OP asked if a radiator fan motor will work. I am saying, don't just grab anything from a junk yard and expect it to work well without further analysis.

I fly those airplane and helis. Tell me again what their efficiency is based on what, your conjecture? Or I can base my statements on years of measured and logged data. I do my homework, I record results. I optimize the system.
If you have further comments based on actual experience using these specific motors I'm sure the comments would be welcome in this thread, but if you want to keep bashing me about what you think you know about motors, do the OP a favor and send me a PM.

[HawkJET]

but if you want to keep bashing me about what you think you know about motors, do the OP a favor and send me a PM.

Who's bashing whom?

I've been working for motor manufacturers since 1979. I was the entire mechanical engineering department for Compumotor (now part of Parker-Hannifin) for it first year in existence. I have designed and built several dynomometers and tested many, many motors on them (which includes measuring their efficiency). I have designed and developed motors as well as built in excess 100 motors with my own hands.

Electric motors are routinely 70% to 80% efficient (and some as much as 90%) when used as they were intended. If you use an electric motor outside of its design envelope you can get efficiencies below 50%. I don't doubt you have data to support your horrible efficiencies. All I'm saying is that by choosing a different motor or specifying the motor to your specific application, you will easily achieve 70% to 80% efficiency. Just because you have the wrong motor, doesn't mean the right motor is less than 50% efficient too!

I understand it's not going to be super efficient but it's probably going to have some advantages to what I have now. I'm still researching the idea so all input for and against is always welcome.

WAIT a minute! Just because one person said they got horrible efficiencies in their specific application, it doesn't mean the motor will be inefficient in your application.

I would not be surprised if you got 80% efficiency. You will probably be using it in a situation more like what it was designed for. In general, the slower you turn a motor, the less efficient it is. You will probably be fine using it as a spindle motor. You just want to make sure it is geared properly.

[SScnc]

Well Hawkjet, It certainly looks like you are one of the top motor experts here on the zone so are there any motors that you would recommend as replacements for the micro and mini mills that can also provide higher RPM's ?

Thanks