I'm probably going to try the diode method first. There are some ultracheap 1000 V 10 amp diodes available. I might put some of them in parallel. I doubt that has the same problem. And then it can be used for any other appropriate brushed universal motor device.
I suspect that it will not achive the desired effect ! Recall that a universal motor will happily run on ac or dc, the motor brush gear simply chops up a dc supply to create an alternating field.
Never having actually placed a diode in series with a universal motor, not a lot. I belive that the motor current will increase to try and compensate for the drop in speed due to the load. The motor will try to maintain its speed.
It is however an interesting experiment and I would be interested in your findings.
Not that it matters, but the argument is lost... The original point was that the motor is spinning too fast to be an induction motor. Therefore, the 5500 RPM specification either applies to the motor or the motor is spinning faster than that. Talking about reduction gears doesn't help refute the fact that it's a brushed universal motor.
But of course you may argue about whatever pointless thing you wish to argue about...
I know. I just looked up a 20 amp DO4 case diode and current surge is
400 amps. I couldn't find any definitive start-up specs for AC/DC motors just some comments like "double" or "several times" the rated current. When they say the motor is a 14 amp motor - they do mean it might pull 14 amps when cutting.
My bench table saw has a universal motor in it and is rated at 15 amps. I've popped the 10 amp breaker on the power strip a half dozen times in 5+ years, and then cutting things like wet 4X4 wood with a dull blade. The power strip probably has a cheap thermal breaker on it, the 20 amp house circuit has never tripped.
I can rip 8 foot 2X4's without tripping a breaker.
I can't prove it, but would bet serious money it would work with a 20 amp diode.
John Doe wrote in news:m5d282$si5$1@dont- email.me:
I missed a part of the discussion due to the limitations of my news servers so I may tell no news. Nevertheless:
This type of machines usually have universal motors. They can be slowed down by ordinary dimmer like controllers. This however is not very effective as lowering the voltage will make the speed very dependend of the load. The best way to control this type of motors is using DC and PWM.
In my experience Al will not be cut very effective by an abrassive disk. The soft Al will smooth the disk by filling the spaces in it. I got the best results using a saw blade with hardened steel teeth as for hardwood,
An induction motor can be dynamically braked by connecting DC to the windings. This can be done with a capacitor and a diode. I think that if the brushes are shorted and DC is connected to the windings this would work like an induction motor. See this link:
The key is DC current... where does one get that from a device that only has an off/on switch to a series motor with no magnets for self generation? You can dynamically brake a series motor but it's not as simple as just connecting the A1 and A2 together.
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