DC variable speed motors

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SteveM
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DC variable speed motors

Post by SteveM »

Just saw this on ebay.

https://www.ebay.com/itm/371603903331

3/4hp variable speed DC motor, 1480-5400 RPM.

Figure if I used that with a 2-sheave pulley setup for a high and low range to offset torque loss at low speeds, that would give me all the power and / or speed I need for my benchtop lathe and mill (both Pratt & Whitney 3C).

How would this work, particularly compared to a 3-ph with VFD? The VFD setup would cost more adding up the motor and VFD cost, I think.

How smooth running are these for machining?

Here's the description:
Description: This is a brand new 3/4 HP DC Motor with Solid State Variable Speed Control.
Please read the specs completely and carefully to make certain this will work for you:
Note: This drive starts at 1425 no-load RPM...it does NOT start at zero
3/4 HP DC brushed type motor
1425 to 2850 No-load RPM speed range (as measured by digital photo tachometer)
We sell 3-rib belts and pulleys in our tool store if you want to reduce the speed
Clockwise rotation (facing end of motor shaft)(rotation can be reversed by switch power leads inside control)
Motor can be mounted via (3) 6mm Screws on the motor face in a 2-1/2" (64mm) circle 120 degrees apart
Motor shaft is 591" (15mm) diameter
The motor shaft is 2-7/16" (62mm) long overall
Motor body is 3-1/8" (79mm) diameter x 7-1/2" (191mm) long
DC Motor control (solid state)
Input power: 120 Volts / 4.5 amps / 1 Ph / 60 Hz
Controls motor speed from approximately 1425 no-load RPM (slightly delayed soft start) to 2850 no-load RPM
Control box measures 5-1/2" tall x 2-3/4" wide x 4-1/8" deep + projections for switches and cord grips
With safety switch, variable speed control knob, & built-in resettable circuit breaker
Heavy duty 6 ft grounded cord plus 3 ft cord between motor & control
Screws included to mount control box
With motor mounting socket head cap screws
Motor produces its best torque in the top half of its speed range


Steve
Rich_Carlstedt
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Re: DC variable speed motors

Post by Rich_Carlstedt »

I would seriously look at the specifications presented.
First the specs say 2800 RPM and your post says 5400 ?
Second, there is no mention of fan cooling and a 3 inch Diameter 3/4 HP motor makes heat.. lots.
So then you have to consider duty cycle .. Can it run continuously ?
I personally do not like the minimum low RPM stated ( 1400) , that is too high for me in a DC motor where you want or use torque at low RPM.

Just my opinion
Rich
John Hasler
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Re: DC variable speed motors

Post by John Hasler »

Treadmill motor. Good for 3/4 hp for perhaps five minutes out of each hour. Ok motors when you can get them cheap or free but you have to derate them. The controller looks like junk. The package is over priced.
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Bill Shields
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Re: DC variable speed motors

Post by Bill Shields »

Pass on it for lathe. Enough said by others

Spend a few more $ and do it properly
Too many things going on to bother listing them.
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Steggy
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Re: DC variable speed motors

Post by Steggy »

This motor is an intermittent-duty unit.

Also, if you carefully read the nameplate in the one photo it says "60 Cycles". I must say I've not run into too many DC motors that run on 60 cycles. :D
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John Hasler
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Re: DC variable speed motors

Post by John Hasler »

BigDumbDinosaur wrote: Wed Sep 01, 2021 11:56 pm This motor is an intermittent-duty unit.

Also, if you carefully read the nameplate in the one photo it says "60 Cycles". I must say I've not run into too many DC motors that run on 60 cycles. :D
May be a series wound "universal" motor.
Inspector
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Re: DC variable speed motors

Post by Inspector »

I would be more tempted by one of these industrial sewing machine motors. I'll admit to only having a bare minimum of sparky knowledge.

https://www.ebay.com/itm/Eagle-EA-750-B ... 632-2357-0

Pete
SteveM
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Re: DC variable speed motors

Post by SteveM »

Inspector wrote: Thu Sep 02, 2021 9:48 am I would be more tempted by one of these industrial sewing machine motors. I'll admit to only having a bare minimum of sparky knowledge.

https://www.ebay.com/itm/Eagle-EA-750-B ... 632-2357-0

Pete
That certainly looks interesting.

Motor looks like it has a lot better cooling with all the fins.

Having the mounting and not having to fabricate anything is also a plus.

The motors for the 3C lathe and mill mounts under the bench.

Looks like it's reversable, too, which is nice for the lathe, but mandatory for the mill (the vertical head reverses the rotation).

Steve
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Steggy
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Re: DC variable speed motors

Post by Steggy »

John Hasler wrote: Thu Sep 02, 2021 9:15 am
BigDumbDinosaur wrote: Wed Sep 01, 2021 11:56 pm This motor is an intermittent-duty unit.

Also, if you carefully read the nameplate in the one photo it says "60 Cycles". I must say I've not run into too many DC motors that run on 60 cycles. :D
May be a series wound "universal" motor.
Could be, although when was the last time you heard of "cycles" being used to refer to AC frequency?
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Music isn’t at all difficult.  All you gotta do is play the right notes at the right time!  :D
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Bill Shields
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Re: DC variable speed motors

Post by Bill Shields »

Cycles? Still used...may be gauche but still understood
Too many things going on to bother listing them.
John Hasler
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Re: DC variable speed motors

Post by John Hasler »

Probably not the manufacturer's nameplate.
whateg0
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Re: DC variable speed motors

Post by whateg0 »

BigDumbDinosaur wrote: Fri Sep 03, 2021 7:55 pm
John Hasler wrote: Thu Sep 02, 2021 9:15 am
BigDumbDinosaur wrote: Wed Sep 01, 2021 11:56 pm This motor is an intermittent-duty unit.

Also, if you carefully read the nameplate in the one photo it says "60 Cycles". I must say I've not run into too many DC motors that run on 60 cycles. :D
May be a series wound "universal" motor.
Could be, although when was the last time you heard of "cycles" being used to refer to AC frequency?
We use cycles all the time in my work.
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