Cheap DC motor control anyone?

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Cheap DC motor control anyone?

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Working on a belt sander project using a 130V PMDC motor off a treadmill. The control board got crushed so I need a simple cheap adjustable speed control. Anyone have something laying around they want to get rid of? Need 115Vac input. Thanks Dach. "Do what you can, with what you have, where you are" - Theodore Roosevelt “We reached the old wolf in time to watch a fierce green fire dying in her eyes .... I was young then, and full of trigger-itch; I thought that because fewer wolves meant more deer, that no wolves would mean hunters’ paradise. But after seeing the green fire die, I sensed that neither the wolf nor the mountain agreed with such a view.” - Aldo Leopold
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Re: Cheap DC motor control anyone?

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David Chapman via EV wrote:
> Working on a belt sander project using a 130V PMDC motor off a treadmill. The control board got crushed so I need a simple cheap adjustable speed control. Anyone have something laying around they want to get rid of? Need 115Vac input. Thanks Dach. "Do what you can, with what you have, where you are" - Theodore Roosevelt “We reached the old wolf in time to watch a fierce green fire dying in her eyes .... I was young then, and full of trigger-itch; I thought that because fewer wolves meant more deer, that no wolves would mean hunters’ paradise. But after seeing the green fire die, I sensed that neither the wolf nor the mountain agreed with such a view.” - Aldo Leopold

How about an old-fashioned phase-control light dimmer? It will give you
variable speed, though not speed "control".

Or, steal the speed control out of an unused or garage-sale 120vac
drill. The circuit is only slightly more complicated, but uses the
motor's back-EMF to sort-of regulate the speed.

I'm looking at a circuit in the GE SCR manual 5th edition on page 293.
It uses a bridge rectifier, 1 SCR, 2 resistors, 1 potentiometer (the
speed control), 1 capacitor, and two diodes.

--
It is vanity to do with more that which can be done with less.
         -- William of Ockham
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: Cheap DC motor control anyone?

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In reply to this post by Electric Vehicle Discussion List mailing list
> Date: Wed, 24 Jan 2018 00:59:48 +0000 (UTC)
>
> Working on a belt sander project using a 130V PMDC motor off a treadmill. The control board got crushed so I need a simple cheap adjustable speed control. Anyone have something laying around they want to get rid of? Need 115Vac input. Thanks Dach.

Is this permanent, or temporary/intermittent use?

I’d put a full-wave bridge rectifier as close to the motor as possible, and just call it a 120 VAC motor. Put a standard plug on it. Then you could plug it in to a wide variety of AC power control devices, as Lee suggests.

Then, it sounds like a job for a good old-fashioned variac transformer. They aren’t cheap brand new, but you can sometimes find them cheap in surplus or ham radio estate sales.

If you don’t intend this to be permanent, you could put your variac in a box with a volt meter and a couple standard AC outlets. It can be handy that way for so many things.

Lee’s ideas will still produce AC, and so would work fine for a universal (series-wound) motor, but probably not for a permanent magnet motor, which will just try to go forward and reverse at 60Hz and make a loud hum before it burns out.

But if you rectify what goes into your PMDC motor, SCR dimmers should work well. Older drills used SCR phase control, but I think newer ones use PWM, which will probably make a better speed control than an SCR phase-control will — but it will still require rectification for a PM motor.

So, rectify that puppy, and lots more options become available!

:::: Jan Steinman, EcoReality Co-op ::::

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Re: Cheap DC motor control anyone?

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Jan Steinman via EV wrote:
> Is this permanent, or temporary/intermittent use?

That's important, because while most treadmill motors have high advertised
horsepower; in fact, they rarely deliver even a small fraction of that.
>
> I’d put a full-wave bridge rectifier as close to the motor as possible,
> and just call it a 120 VAC motor. Put a standard plug on it. Then you
> could plug it in to a wide variety of AC power control devices, as Lee
> suggests.

Good point! You do have to rectify the AC before it gets to the motor.

> Then, it sounds like a job for a good old-fashioned variac transformer.

That would work great if it can handle the current. Small variacs (rated at a
few amps) are pretty common and inexpensive used. But ones big enough to handle
15 amps continuously are quite a bit heavier and more expensive (like 20 lbs and
$100).

> Lee’s ideas will still produce AC, and so would work fine for a universal
> (series-wound) motor, but probably not for a permanent magnet motor

Definitely not for a PM motor. For some reason, I was thinking he had a
universal motor, which doesn't care whether it's running on AC or DC.

Light dimmers typically use triacs, which are AC devices. But speed controls for
electric drills more often use SCRs, which do have a DC output. The circuits I
mentioned from the GE SCR manual are all suitable for PM DC motors as well as
shunt and series motors, because they use SCRs for control. SCRs are better
suited to inductive loads.

> So, rectify that puppy, and lots more options become available!

Yes. :-)

--
It is vanity to do with more that which can be done with less.
         -- William of Ockham
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: Cheap DC motor control anyone?

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In reply to this post by Electric Vehicle Discussion List mailing list
Jan, thanks for the input on this. Lee I really appreciate the lead on the GE handbook, I downloaded it and indeed that circuit on pg 293 looks perfect for this project;  I am kind of helping / mentoring a friend of one of my sons with his project and he doesn't have anything for money so its a fantastic find. Looks like we can build it for under 10 bucks and it is simple and will do everything he needs it to do so its an "Occamatic" solution. One question tho, you said something about it needing a capacitor and looking at the schematic I don't see one, in the notes below the drawing (fig. 10.5) it says "A capacitor on the arm of R2 is not a cure because there will be no phase shift on the reference due  to full wave rectified charging." I wonder if an R/C drain to ground between the SCR and C1 might accomplish turning off the SCR quickly? Since this is a pm motor I will just leave out the field connection and diode piece. BTW, would you just put the 15 amp fuse in the "hot" AC lead before the bridge rectifier? Or is there a better place in the circuit? Thanks again, I really appreciate you you taking the time to offer advice. Dach.
 
 

    On Wednesday, January 24, 2018 8:17 PM, Lee Hart via EV <[hidden email]> wrote:
 

 Jan Steinman via EV wrote:
> Is this permanent, or temporary/intermittent use?

That's important, because while most treadmill motors have high advertised
horsepower; in fact, they rarely deliver even a small fraction of that.
>
> I’d put a full-wave bridge rectifier as close to the motor as possible,
> and just call it a 120 VAC motor. Put a standard plug on it. Then you
> could plug it in to a wide variety of AC power control devices, as Lee
> suggests.

Good point! You do have to rectify the AC before it gets to the motor.

> Then, it sounds like a job for a good old-fashioned variac transformer.

That would work great if it can handle the current. Small variacs (rated at a
few amps) are pretty common and inexpensive used. But ones big enough to handle
15 amps continuously are quite a bit heavier and more expensive (like 20 lbs and
$100).

> Lee’s ideas will still produce AC, and so would work fine for a universal
> (series-wound) motor, but probably not for a permanent magnet motor

Definitely not for a PM motor. For some reason, I was thinking he had a
universal motor, which doesn't care whether it's running on AC or DC.

Light dimmers typically use triacs, which are AC devices. But speed controls for
electric drills more often use SCRs, which do have a DC output. The circuits I
mentioned from the GE SCR manual are all suitable for PM DC motors as well as
shunt and series motors, because they use SCRs for control. SCRs are better
suited to inductive loads.

> So, rectify that puppy, and lots more options become available!

Yes. :-)

--
It is vanity to do with more that which can be done with less.
        -- William of Ockham
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: Cheap DC motor control anyone?

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David Chapman via EV wrote:
> Jan, thanks for the input on this. Lee I really appreciate the lead
> on the GE handbook, I downloaded it and indeed that circuit on pg 293
> looks perfect for this project...

> One question tho, you said something about it needing a capacitor and looking at the
> schematic I don't see one...

Fig 10.5 is a "quick-n-dirty" circuit that works, but has issues at the
low-speed end. Have you used a cheap light dimmer, and noticed that the
brightness is unstable at the dim end of the range? Same thing with that
circuit; the motor speed will be unstable at the low end.

Look a little farther in the book, at fig. 10.6 and 10.7. These are
improved circuits that add a 0.2uF capacitor and 2N4987 trigger device.

The 2N4987 is an oddball part from GE that is hard to get today. Newark
has them for $5.68

http://www.newark.com/nte-electronics/2n4987/t-unilateral-switch/dp/75R9697?CMP=AFC-OP

The 2N4987 is what GE called an SUS. It is really just two transistors
(one NPN, one PNP, a resistor, and a zener diode). These are all 10 cent
parts, so you can make it yourself. The GE datasheet shows the circuit.

Or, you can replace it with a modern part. Every manufacturer has a
different name for it. Common variations are SIDAC or DIAC. I'd try the
MCC DB3-TP, www.digikey.com DB3-TPMSCT-ND $0.21 each.

> Thanks again, I really appreciate you you taking the time to offer
> advice. Dach.

You're welcome! Best success with your project. :-)
--
It is vanity to do with more that which can be done with less.
         -- William of Ockham
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: Cheap DC motor control anyone?

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In reply to this post by Electric Vehicle Discussion List mailing list
> From: Lee Hart <[hidden email]>
>
> David Chapman via EV wrote:
>> Lee I really appreciate the lead
>> on the GE handbook, I downloaded it and indeed that circuit on pg 293
>> looks perfect for this project…

So, it sounds like one of the goals of the project is to put something together from components?

Because I thought Lee’s idea of finding a variable-speed electric drill at a thrift store or yard sale was really an excellent idea.

You can probably do so for less than the costs of buying components, especially if you’re going to pay “single piece” shipping on them.

And the drill speed control has the advantage of having been designed for motor speed control. Newer ones even use pulse-width-modulation, which you can tell if it makes a squealing or whistling sound at low speed. That sort of controller is going to give you the best low-speed control, with lots more torque.

:::: The more the work is left to nature, the greater the net yield but the longer the time required... Thus sometimes the most apparently productive and high-yielding sources of energy involve a lot of activity for little return, while long-term investments, especially in naturally grown forests, provide the greatest value for future generations. -- David Holmgren <http://www.lmgtfy.com/?q=David+Holmgren>
:::: Jan Steinman, EcoReality Co-op <http://www.ecoreality.org/> ::::

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Re: Cheap DC motor control anyone?

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I would go the variable speed drill direction.  Lee, from my experience SCRs have a tendency to false trigger on noise.  I was burn a few times.  I remember using a GE SCR for an alarm circuit.  I could not get it from false triggering.  I talked to the SCR designer at GE and he never could come up with an answer.  I redesigned using transistors and NAND gate chip and everything was OK.   Another possible choose is to look on the web for a motor speed controller kit.  I think Jameco makes a kit.  One time, I purchased a motor controller from a local surplus store.  I suggest looking for a controller that works .... forget a one off design.


________________________________
From: EV <[hidden email]> on behalf of Jan Steinman via EV <[hidden email]>
Sent: Friday, January 26, 2018 4:58 PM
To: [hidden email]
Cc: Jan Steinman
Subject: Re: [EVDL] Cheap DC motor control anyone?

> From: Lee Hart <[hidden email]>
>
> David Chapman via EV wrote:
>> Lee I really appreciate the lead
>> on the GE handbook, I downloaded it and indeed that circuit on pg 293
>> looks perfect for this project…

So, it sounds like one of the goals of the project is to put something together from components?

Because I thought Lee’s idea of finding a variable-speed electric drill at a thrift store or yard sale was really an excellent idea.

You can probably do so for less than the costs of buying components, especially if you’re going to pay “single piece” shipping on them.

And the drill speed control has the advantage of having been designed for motor speed control. Newer ones even use pulse-width-modulation, which you can tell if it makes a squealing or whistling sound at low speed. That sort of controller is going to give you the best low-speed control, with lots more torque.

:::: The more the work is left to nature, the greater the net yield but the longer the time required... Thus sometimes the most apparently productive and high-yielding sources of energy involve a lot of activity for little return, while long-term investments, especially in naturally grown forests, provide the greatest value for future generations. -- David Holmgren <http://www.lmgtfy.com/?q=David+Holmgren>
[http://lmgtfy.com/assets/sticker-b222a421fb6cf257985abfab188be7d6746866850efe2a800a3e57052e1a2411.png]<http://www.lmgtfy.com/?q=David+Holmgren>

LMGTFY<http://www.lmgtfy.com/?q=David+Holmgren>
www.lmgtfy.com
LMGTFY


:::: Jan Steinman, EcoReality Co-op <http://www.ecoreality.org/> ::::
Welcome to EcoReality!<http://www.ecoreality.org/>
www.ecoreality.org
EcoReality is a nascent ecovillage on Salt Spring Island, British Columbia, Canada, dedicated to the ethics and principles of Permaculture, and to providing our own shelter, food, and energy in a sustainable and renewable manner. We do this by growing our own food, including raw goat milk and other protien sources, producing our own energy, including biomass, biodiesel and other sources, and by distributing our excess to the surrounding community, via direct farm gate sales, farmers markets, local grocers, and other channels. We are currently seeking one or more additional capital partners to take us to the next step of building thirteen unit of zero-carbon, zero-mile housing, using natural building techniques and materials.



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