Subject:
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RE: 5VDC Voltage Regulation
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Newsgroups:
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lugnet.robotics
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Date:
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Mon, 27 Sep 1999 18:08:43 GMT
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Original-From:
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Tilman Sporkert <(tilman@)NoMoreSpam(activesw.com)>
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Viewed:
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624 times
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You need to limit the current through the relay. Just add a resistor in
series with the relay. You can experiment, using a voltmeter, or you can
calculate the proper value from the relay specs. Relays specs usually list
the resistance of the coil. Lets say it's 1000 Ohms. If you add a 470 Ohm
resistor, then the relay will only see 2/3s of the RCX output voltage. I
believe the formula would be:
U_Relay = (R_Relay / (R_Relay + R_Resitor)) * U_RCX_Output
I recommend that you always put the output at full speed. You don't want to
supply pulses to the relay - it will draw too much current that way (AC vs.
DC).
A voltage regulator is overkill, and much too complex. You need to add at
least one capacitor, and two diodes - one to protect the regulator from
reverse voltage, and one to absorb the back EMF pulse when you turn off the
relay. You can accomplish your goal with just a single resitor instead.
Tilman
P.S. I once bought 100 of the small 5V relays from Radio Shack. They had to
special order them because they obviously don't have that many in the store.
When I came to pick them up, they gave me these two huge plastic bags
stuffed full with little relays in large display blister packs.
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Message is in Reply To:
 | | 5VDC Voltage Regulation
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| I'm in over my head with a project and need some help. I'm trying to use an RCX output port to control a 5VDC SPDT Relay from Radio Shack (part #275-240A). I need to limit the voltage of the port to 5 volts. How can I accomplish this? Is a voltage (...) (25 years ago, 27-Sep-99, to lugnet.robotics)
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