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Author Topic: Reading state of a 0-200VDC motor.  (Read 485 times)
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Hi,
I am hoping to use an arduino to start a turntable on a various machines when the machine starts running.
The turntable would be moved from machine to machine as required. One machine is easy as it has a spare contact that closes when the machine starts.
However, the only way to read if some of the machines are running is by reading if the motor has power or not. to make things more complicated the motor runs on 0-200VDC. (in practice its never set to run below around 30v though.)
I've been thinking about various ways for a few weeks now and the best I can think of is to use a resistor to limit the current and a zener diode to limit the voltage (4.7V perhaps) as shown in attachment.

Would this work ok?
Have I picked suitable values or should I change these and if so what to?
Or should I try something else?


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A linear signal opto isolator would be one solution.

[200V DC is as or more dangerous than mains voltages, never take
risks with it]
« Last Edit: June 17, 2014, 05:39:55 am by MarkT » Logged

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I have considered using an opto isolator , but wouldn't that require a fixed voltage to light the led consistently without blowing it at the higher voltages?
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Might I suggest a hall effect current transformer unit which monitors motor drive current.  These units are available with outputs of 5 volts DC at full range current.   This design also provides total isolation from the motor voltage.
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Might I suggest a hall effect current transformer unit which monitors motor drive current.  These units are available with outputs of 5 volts DC at full range current.   This design also provides total isolation from the motor voltage.
Thanks.  That seems like it will work well.
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I have considered using an opto isolator , but wouldn't that require a fixed voltage to light the led consistently without blowing it at the higher voltages?

The point with a linear opto isolator is the output current depends on the input current,
you choose a limiting resistor so that the maximum input voltage is full scale.

There are sophisticated linear opto isolators using two receivers and feedback to
improve linearity, but thats not what you want, a simple opto isolator with output
current roughly proportional to input current ought to be feasible.  You only need
on/off information?
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How about making it with a zener so that >=18V =18V? and 0V = 0V
One can buy zeners of particular voltage such as 11, 25 or 35.  Let me know if you want to buy one 18V Zener off me for £1 plus £1 uk p&p.
A big resistance from the (30 to 200V) to 18V must be safe so read the datasheet.
The 18V Zener goes to ground.
A second resistance from 18V goes into your potential divider to ground and could provide a reasonable 5-ish volts to an opto-isolator if you so wish.  A second zener may be used to limit that to not-more-than 4.7V as you first wrote.
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You only need
on/off information?
Thats right, i don't need to know how fast it's running, just is it running.
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You only need
on/off information?
Thats right, i don't need to know how fast it's running, just is it running.

Do you mean  "it has voltage applied" or "it is drawing current" or "it is rotating"
I know it's being picky but they really are three different variables.
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Do you mean  "it has voltage applied" or "it is drawing current" or "it is rotating"
I know it's being picky but they really are three different variables.
It is rotating.
I would just put an encoder on if there was enough room but the motor is in a tight space.
I am aware that a dc motor may have voltage applied but not draw current.
When making my voltage readings I also found that if less than 3v is applied the motor will just stall at certain points in the cycle.  Thus drawing current but not rotating.
The 0-200v is when running (it should be rotating assuming enough voltage is applied) this drops to zero when stopped. (I think both connections here are actually at +100v but that won't matter)
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If you can stick a piece of reflective tape onto a moving surface you could use an IR sensor unit to detect rotation.  No need for fancy encoder devices which are generally intended as position sensors.
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Unfortunately all moving parts are well oiled and generally quite reflective. So not only would tape be likely to come off, it may not see the difference between the tape and general surface. I'll have a look at an inductive prox could be fitted somewhere.
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Thanks for your help guys.
An inductive prox can be fitted to look at rotation of the cams on the machines. I wouldn't have thought of this without your suggestions. Plus it gets me away from reading a 0-200v input. I only have to deal with switching the power for the 110vac turntable, but that's not an issue for me.
For the code I'll have it setup to read the state change of the prox as this seems to be an easy way of reading if it is rotating or not.
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