Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old October 20th 15, 01:07 AM posted to sci.electronics.repair
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Default Motor speed controller

I need to control the speed of a 1/3HP 120V AC motor. This motor/speed control would go onto a wood lathe and replace the pulley system which is now in place. Does anyone know of a solid state speed controller that I could perhaps build to to this? Thanks, Lenny

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Old October 20th 15, 07:10 PM posted to sci.electronics.repair
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Default Motor speed controller

On Monday, October 19, 2015 at 7:07:47 PM UTC-4, wrote:
I need to control the speed of a 1/3HP 120V AC motor. This motor/speed control would go onto a wood lathe and replace the pulley system which is now in place. Does anyone know of a solid state speed controller that I could perhaps build to to this? Thanks, Lenny


I think that this motor came out of a sump pump of the type that stands on the top of a sort of 3 foot pedestal. The pedestal would then go down into a hole such as the basement floor. Float switches would turn it on to keep the cellar from filling up with water.

This motor has no brushes and I'm fairly certain that it has a start winding because you can hear the centrifugal switch engage and disengage during start up and slow down. I do not have the exact speed information at hand however I do know that this motor runs at around 3000RPM. There is also very large capacitor on it as well.

So from what I'm reading here is there no real practical way to control the speed of this type of motor other than (as Mr. Cook mentioned) using a stepped pulley arrangement? Lenny


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Old October 20th 15, 08:05 PM posted to sci.electronics.repair
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Default Motor speed controller

On Tue, 20 Oct 2015 08:40:49 +0100, N_Cook wrote:


Pulley system increases torque at low speed of cutting Electronic
gubbins can only decrease torque at low speed


You would hardly notice any difference with a well-designed, modern
controller. I bought one for a 415V 3ph industrial lathe I bought, which
enables me to run it from 240V 1ph. The low speed torque is astounding -
and the soft-start setting removes the lethality of hitting the start
button when you've left the key in the chuck! Well worth the money - and
you can still use gearing and pulleys with it for total versatility.

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Old October 20th 15, 08:52 PM posted to sci.electronics.repair
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Default Motor speed controller

On Tuesday, October 20, 2015 at 1:10:15 PM UTC-4, wrote:
On Monday, October 19, 2015 at 7:07:47 PM UTC-4, wrote:



I think that this motor came out of a sump pump of the type that stands on the top of a sort of 3 foot pedestal. The pedestal would then go down into a hole such as the basement floor. Float switches would turn it on to keep the cellar from filling up with water.


Is a sump pump motor intended for continuous operation? Or is it a duty cycle type motor? Wondering whether it will stand up to lathe operation.
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Old October 21st 15, 03:33 AM posted to sci.electronics.repair
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Default Motor speed controller

Cursitor Doom wrote:

N_Cook wrote:

Pulley system increases torque at low speed of cutting Electronic
gubbins can only decrease torque at low speed


You would hardly notice any difference with a well-designed, modern
controller. I bought one for a 415V 3ph industrial lathe I bought, which
enables me to run it from 240V 1ph. The low speed torque is astounding -



** Torque from an electric motor depends mainly on current flow in the windings, so if a controller can supply the rated full load current at low rpms there is no loss of torque.

Controllers for induction motors ( aka Variable Frequency Drives) reduce the AC frequency and voltage fed to the motor to reduce rpms. Current flow is monitored so the windings do not overheat when the motor is heavily loaded or stalled.

But if increased torque is what is needed at low speeds, stick with the pulley system.


.... Phil
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Old November 1st 15, 03:15 AM posted to sci.electronics.repair
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Default Motor speed controller

My sump pumps run for as little as 30 seconds per hour to almost continuous operation. The temperature will depend on the load.

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Old December 1st 15, 10:10 AM posted to sci.electronics.repair
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Default Motor speed controller

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