Another Motor question

[Hank Merkle]

I have purchased a 1 HP 90V DC motor(Ebay is great!) I plan to use for my lathe. I want varible speed and forward and reverse. I plan to use 110 v 60 hz. What is the best way to sccomplish this?
I assume a diode bridge and some kind of potentiometer. What I am really hopeing is that someone can tell me the size of diodes and pot.

Thanks in advance for the support!

Hank Merkle

[Kenneth George]

Hank I did just about what you are talking about to my old Grizzly lathe I use to have. I think you will find out that you need quite a bit more electronics to get the job done. I ended up purchasing a variable speed DC motor controller for mine. I also found that in the end the DC motor lost much torque on the lower end speeds so I had to change out the Pulley’s and sacrifice high end speed for low end torque. I think I ended up with a maximum speed of about 1300 RPM but that was fine with me I never really exceeded that anyway.

Do a search over on ebay for “dc variable speed” and a bunch of controllers will show up.

Ken.

[Hank Merkle]

Thanks Ken,
Unfortunately that is what I kind of thoughtthe answer was, but I was hopeing I was wrong!

Hank

[Don Baer]

What Ken said about the DC controller is true. The Physiscist in me requires that I correct the miss-conception that the motor loses torque. The torque is constant with a DC motor it's just that HP is lower at lower speeds. HP = TorquexRPM/63025 (assuming the torque is measured in in.lb.) A 1 HP motor will deliver 36 in.lb. of torque. at 1/2 speed it will only deliver 1/2 HP. I don't mean to go on about this but I see this miss statement all the time and feel a need to correct it.

[tod evans]

don, while i`ve got your ear how about putting together a list of parts that folks could assemble to convert their lathes to variable speed? say a 1hp package and a 2-3hp package, something that would prove servicable but not break the bank. seems as though lotsa folks are doing the hit-n-miss trying to e-bay a conversion that actually ends up costing more time and money than they`re really worth. thanks, tod

[Frank Chaffee]

What Ken said about the DC controller is true. The Physiscist in me requires that I correct the miss-conception that the motor loses torque. The torque is constant with a DC motor it's just that HP is lower at lower speeds. HP = TorquexRPM/63025 (assuming the torque is measured in in.lb.) A 1 HP motor will deliver 36 in.lb. of torque. at 1/2 speed it will only deliver 1/2 HP. I don't mean to go on about this but I see this miss statement all the time and feel a need to correct it. Thanks Don.
…And to think that all these years I’ve been dividing by 63,000! Guess it’s no wonder why none of my machines worked.:o

Frank

[Don Baer]

Tod,
Sure I'd be glad to. Let me take some time to put it together.

[tod evans]

thanks in advance don!
when you get a list together how `bout starting a new thread and titling it so the info can be accessed through the smc search engine?
tod

[Henry C. Gernhardt, III]

If you're stuck on DC, Hank, I'd go with a commercial controller, definitely. Although a diode bridge will give you DC, it is pulsing DC, and then there are issues with the transformer(s), diode ratings, etc.

I could go into a short dissertation about power supplies, the differences between linear and switching, and all manner of other things, however I don't believe it would be an effective use of threadspace. If you are interested in the nitty gritty, however, just give me a PM.

[lou sansone]

I have built a lot of machines with dc motors, brushless dc, servo and ac VFD,s ... For the money your best bet will be the AC VFD in the 2 to 3 hp range for most lathes
lou