Running a 1/4 hp 90 vdc motor at 120 vdc?

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richard newman

Titanium

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Jul 28, 2006

Location

rochester, ny

• May 28, 2016

• #1

I just bought a foot pedal speed controller to use with a fractional hp dc motors. Fully depressed the pedal gives 120 vdc. Most of the motors I see out there are 90 vdc, can I run 120 thru them without doing much damage? The motor will be lightly loaded and see only occasional use. Or must I find a 120 vdc motor?

Not sure this is the right forum, but it's electrical...

 

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Ziggy2

Stainless

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Jun 22, 2013

Location

Northern Il

• May 28, 2016

• #2

If it is just a simple foot pedal switch controller, it will not output 120vdc. There is a reason that the 90VDC rating was developed and that is rectified and filtered 120VAC gives you 90VDC. Did you measure the voltage with the motor running? If not, this is a false reading.

If the foot pedal switch actually does output 120VDC with a motor connected, then it would have have an internal step up transformer or some sort of voltage increasing circuitry. Most manufactures do not go to this effort since 90VDC is the standard.

 

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richard newman

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Jul 28, 2006

Location

rochester, ny

• May 28, 2016

• #3

I measured the output voltage with no load, will have to try it connected to a motor. It's very similar to foot pedal speed controls for the Foredom flex shaft machines.

From the manufacturer:
This LUCAS #9XR speed control with Special Electronics with a proprietary design, was designed for the purpose of operating the 115 volt Foredom Heavy-Duty 1/3 hp DC current motors such as the Foredom TX series & similar permanent magnet DC motors from Foredom.

Products about halfway down the page

 

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Ziggy2

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Jun 22, 2013

Location

Northern Il

• May 28, 2016

• #4

richard newman said:

I measured the output voltage with no load, will have to try it connected to a motor. It's very similar to foot pedal speed controls for the Foredom flex shaft machines.

From the manufacturer:
This LUCAS #9XR speed control with Special Electronics with a proprietary design, was designed for the purpose of operating the 115 volt Foredom Heavy-Duty 1/3 hp DC current motors such as the Foredom TX series & similar permanent magnet DC motors from Foredom.

Products about halfway down the page

Click to expand...

I don't think this is actually a DC controller. I think it is probably a triac based controller that ouputs a variable voltage ac. it probably does not output DC. Universal motors are capable of running from AC or DC and can have their speed controlled by voltage unlike a traditional AC motor that is frequency dependent.

I would not recommend using it on your DC motor since it will probably not work and could damage the DC motor windings if left on very long.

You need an actual DC controller that outputs DC and will probably be SCR based.

 

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richard newman

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Jul 28, 2006

Location

rochester, ny

• May 28, 2016

• #5

Lucas makes the controller in both an AC and DC models, and Foredom Says they make dc powered flex shafts as well

From the Foredom FAQ:
Foredom flexible shaft power tools have either Universal motors which can operate on either AC or DC power, or Permanent Magnet (PM), which operate only on DC power.
Series TX, TXH, LX, LXH and PGX are PM type motors. The speed controls that work with these motors - C.TXR, C.EMX, and C.SXR - have a built-in rectifier that converts the AC from the outlet to the DC required by the motor.

So I'm thinking maybe these really are true DC contollers? Is there a way I can tell without damaging a motor?

I chose DC rather than universal because I need low speeds, the universals are way too fast for me

 

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Ziggy2

Stainless

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Jun 22, 2013

Location

Northern Il

• May 28, 2016

• #6

If this was a package deal that you purchased, then you will probably be all right. If the controller is SCR based then it will not output 120VDC with a motor connected.

Best to check with a DMM.

 

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richard newman

Titanium

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Jul 28, 2006

Location

rochester, ny

• May 28, 2016

• #7

Not a package deal, bought it to use with a lower speed PM motor.

Can I use a light bulb as a load on the controller to check voltage with a DMM?

 

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CalG

Diamond

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Dec 30, 2008

Location

Vt USA

• May 28, 2016

• #8

Light bulbs might be a bit weak i the reactance department.

 

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awander

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Jun 11, 2012

Location

Eastern PA

• May 28, 2016

• #9

Yes, a light bulb will show you something. Use at least a 100W bulb, and measure with your meter set to DC Volts, and again with it set to AC Volts.

An AC Controller should read basically 0 on a DC Meter. And approximately 120VAC when the bulb is at it's brightest.

If it is a DC controller, with the bulb at it's brightest, you will read around 120VDC, and maybe a small ripple voltage of AC.

 

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richard newman

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Jul 28, 2006

Location

rochester, ny

• May 29, 2016

• #10

I put a 300W load on the controller, measured 105VDC. Reversing polarity gave me -105VDC, so I'm sure it's a dc output.

Which brings me back to my original question- Is it ok to run a 1/4hp Baldor 90VDC motor at 105VDC? Once again, just intermittently, and at light load.

 

mike_kilroy

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Sep 2, 2010

Location

Farmersville, oh (Dayton/Cinti area)

• May 30, 2016

• #11

Yes 105v on 90v mtr is fine. 120 with lighter load would have been also. Fyi, max volt is determined by commutator max bar to bar voltave to prevent excessive sparking while switching (rotating). It is not a sudden death thing, just a tad more sparking if fully loaded.

 

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richard newman

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Jul 28, 2006

Location

rochester, ny

• May 30, 2016

• #12

Thank you Mike.

 

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Monarchist

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Oct 2, 2012

Location

Sol, Terra

• May 30, 2016

• #13

richard newman said:

I put a 300W load on the controller, measured 105VDC. Reversing polarity gave me -105VDC, so I'm sure it's a dc output.

Which brings me back to my original question- Is it ok to run a 1/4hp Baldor 90VDC motor at 105VDC? Once again, just intermittently, and at light load.

Click to expand...

Yes. It ain't a light-bulb, and will BE 90 VDC or near-as-dammit. Physics, not controller-foo.

The 105 VDC measurement you took almost certainly included a small AC component from SCR commutation overshoot. Any decent 'scope WILL show it to you. SOME DMM can do as well. SOME will let you measure it 'sort of' by putting them into an AC range on DC source.

The motor will be 'integrating' the current back to 'improved copy of' sine-wave anyway, EG: rectified power, not battery or rotating power.

Ampere-turns do the motating. Voltage is not a DC motor's main course meal. And then there is CEMF.

No fear unless it gets hot enough to stink... It WILL get hot anyway. Motors just do that.




Bill

 

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poobah

Plastic

Joined

Jun 5, 2017

• Jun 5, 2017

• #14

Did it work?

richard newman said:

I put a 300W load on the controller, measured 105VDC. Reversing polarity gave me -105VDC, so I'm sure it's a dc output.

Which brings me back to my original question- Is it ok to run a 1/4hp Baldor 90VDC motor at 105VDC? Once again, just intermittently, and at light load.

Click to expand...

Hi Richard,

I was just wondering if it worked?

I bought a Leeson 1/3 HP 90v DC motor and wanted to buy the LUCAS #9XR to control the speed for a pottery wheel I'm making. Like y ours, light load and intermittent use. Did you buy and use the Lucas pedal? Did you have to buy an AC to DC converter to use with it too? Or did you hook it up directly to the motor?

Thanks so much... I've been researching this so I could build this for my kids and had no idea how in depth and difficult this little project turn out to be!

THanks,

Bill

 

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richard newman

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Jul 28, 2006

Location

rochester, ny

• Jan 5, 2020

• #15

poobah, just saw your post. I never got around to this project, took a different route altogether. How did it work out for you?