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March 20, 2010, 07:22:14 PM

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Author Topic: Problem with relay board  (Read 642 times)
mancinip
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« on: December 06, 2009, 02:43:37 PM »
I'm trying to run a small electric motor switched on via a relay board.  Everything works fine as far as turning the motor on and off, but sometimes when I turn it on, it causes the IO-204 to momentarily lose its network connection.  I am a total noob as far as electronics, so I may have done something wrong.  Any ideas?
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texasclodhopper
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« Reply #1 on: December 07, 2009, 06:41:10 AM »
First, describe what the "small electric motor" is. Is it AC or DC? What voltage and current?

If it's a small DC hobby motor, you may be seeing results of brush noise. You'll need to add capacitors across the motor terminals to suppress the noise.

(Brush noise is a kind of spark transmitter.)
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mancinip
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« Reply #2 on: December 07, 2009, 10:22:19 AM »
It is a DC hobby motor (3V, not sure about the current).  If it helps, you can see the motor  here.  Assuming you're right that I need a capacitor, how do I figure out what size capacitor I need?
« Last Edit: December 07, 2009, 10:26:54 AM by mancinip » Logged
jason
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« Reply #3 on: December 07, 2009, 01:29:28 PM »
I've seen this happen as well with large solenoids.  Even though the solenoid was isolated from the IO-204, it would still cause a reset.  At the time I just thought I was imagining things...  looks like others are seeing the same thing.  It could be EMI as texasclodhopper has suggested.

Are you by chance running the motor off of the IO-204's power?  I could see that being a problem since the motor will cause an huge current draw when it first kicks on and still power from the IO-204.
« Last Edit: December 07, 2009, 01:59:21 PM by jason » Logged
Jason Winters
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mancinip
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« Reply #4 on: December 07, 2009, 04:57:35 PM »
No I have a separate power supply (2 AA batteries) that is connected to the motor through the relay.
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texasclodhopper
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« Reply #5 on: December 07, 2009, 07:26:45 PM »
About the capacitors, get a bag of cheap ceramic disc caps. Start with a value of 0.1 mfd and solder a couple of them across your motor leads.

See if you notice an improvement. If not, add a couple more. If this isn't the reason for the problem, you could add 400 without helping, but a couple of them should do it.

Try a different motor. Try a small computer fan. See if that has the same problem. The motor in the fan doesn't have brushes.
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mancinip
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« Reply #6 on: December 08, 2009, 07:22:58 AM »
OK, thanks.  I'll give it a try.
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mancinip
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« Reply #7 on: December 13, 2009, 12:54:03 PM »
.2mF seems to do the trick.  Thanks for the help.
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