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Old July 16th, 2009, 10:19 AM   #1
ascot01
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Need 0-10 vdc from 48 vdc

I need to benchtest a dc motor drive and the motor and need to fabricate a variable switch or rheostat to give the 0 - 10 vdc input for speed control.

My source voltage is 48 vdc.

I can use resistors to make voltage dividers and pushbuttons to step the voltage incrementally from 1 to 10 volts but I need a smooth sliding type switch like a pot or rheostat but cant figure out how to make it. I know there's something fundamental I'm missing here, it can't be that difficult.
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Old July 16th, 2009, 11:32 AM   #2
eebads2391
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Step down transformer ? ?

It's output would be proportional to the input
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Old July 16th, 2009, 11:50 AM   #3
Steve Bailey
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Connect a 38K fixed resistor in series with a 10K pot. Total current will be 1 mA. Power is 0.048 watt.

You could do the same with 19K fixed resistance and a 5K pot. In that case the current is 2 mA and the power is 0.096 watt.

This is basic Ohm's law stuff.

Quote:
Step down transformer ? ?

It's output would be proportional to the input
eebads2391, if you have a transformer that can step down a DC voltage, I suggest you apply for a patent.
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Old July 16th, 2009, 11:50 AM   #4
leitmotif
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I would use a reostat (potentiometer) off the 48 VDC.

Dan Bentler
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Old July 16th, 2009, 11:54 AM   #5
CowDung
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Quote:
Originally Posted by eebads2391 View Post
Step down transformer ? ?

It's output would be proportional to the input
Transformers are only good for AC...
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Old July 16th, 2009, 12:12 PM   #6
ascot01
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Thanks very much, I'll order those parts.
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Old July 16th, 2009, 12:57 PM   #7
bernie_carlton
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These answers are neglecting the input impedence of the drive. Thoough if it is pretty high then the affect on the voltage divider would be negligible.
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Controlling outputs is the PLC's way of getting its inputs to change.

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Old July 16th, 2009, 01:06 PM   #8
Steve Bailey
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I just realized that I should have asked whether or not the drive has terminals defined to connect a speed pot. It's such a common method of establishing a speed preset that it would be somewhat of a surprise if the drive isn't already set up for it.

If you can post a link to the user's manual for the drive, perhaps we can point out how to accomplish what you need to do.
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Old July 16th, 2009, 03:13 PM   #9
leitmotif
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Forgot about that too. Some I have seen include the pot.

Dan Bentler
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Old July 16th, 2009, 03:23 PM   #10
eebads2391
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I know , sorry, getting confused with something ive seen from the CB radio days that were sold to truck drivers

24 v dc in 12 dc out

Sorry for misleading comment
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Old July 16th, 2009, 04:32 PM   #11
ascot01
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Thanks for your help

Advanced Motion Controls
www.a-m-c.com
Brush Type PWM Servo Amplifier
model 120A10


i don't see a pot for manually adjusting the 0-10 input unless it's under the cover.
I uploaded spec sheets and 2 pictures.
Attached Images
File Type: jpg MC1.jpg (78.9 KB, 12 views)
File Type: jpg MC2.jpg (90.8 KB, 10 views)
Attached Files
File Type: pdf 120a.pdf (189.7 KB, 18 views)
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Old July 16th, 2009, 05:27 PM   #12
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I've done this in the past with just a battery, no need for the 48v supply.

A 1.5 volt battery will give you roughly 15% of your top speed. Two will give you 30%, and so on.

Here's a down-and-dirty 0 - 10 volt adjustable supply that uses only four parts.

http://media.photobucket.com/image/0...pson/0-10V.jpg

Or you can go for the voltage divider circuit - just two parts.
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Old July 16th, 2009, 05:32 PM   #13
Steve Bailey
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Take a look at page G-18, the paragraph headed "Reference Potentiometer Wiring".

http://www.a-m-c.com/download/docume.../instnotes.pdf

This is a drive for a motion control system. It needs a +/- 10 vdc speed command to make full use of its capabilites. Positive speed command makes the motor turn in one direction. Reverse polarity to reverse direction.
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Old July 16th, 2009, 07:25 PM   #14
leitmotif
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Quote:
Originally Posted by Steve Bailey View Post
Take a look at page G-18, the paragraph headed "Reference Potentiometer Wiring".

http://www.a-m-c.com/download/docume.../instnotes.pdf

This is a drive for a motion control system. It needs a +/- 10 vdc speed command to make full use of its capabilites. Positive speed command makes the motor turn in one direction. Reverse polarity to reverse direction.
I think a little attention should go to what he wants the motor to drive ie conveyer or some servo type application.

SO what does the motor drive? What are your expectations?
What is HP of motor?

If he does not need servo performance why go with servo drive?

Have run (short bench test) small 1/4 HP 90 VDC permanent magnet motors off just a 9 V electronincs. Worked well.
Dan Bentler
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Old July 16th, 2009, 07:35 PM   #15
ascot01
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Thanks so much

Rootboy I'm not quite up to speed on the symbols..what is that triangle? A diode or gate maybe? Thanks for the drawing.

Steve thanks for the article I would've never recognized paragraph 3.7 as the answer. That looks like the easiest solution.

Last edited by ascot01; July 16th, 2009 at 07:52 PM.
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