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 19:52:45 GMT
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Viewed:
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648 times
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This indeed does work fine, with he proper resistor. :)
Voltage across the coil is now 4.74VDC.
Thanks to all for the input - when I get a working model I'll put it on my web
site.
-Wes
Wes Matchett wrote:
>
> Michael Gasperi wrote:
> >
> > Ralph Hempel <rhempel@bmts.com> wrote in message
> > news:000001bf0901$f58c67a0$0500000a@pro150...
> > > > 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 would just put a 33Ohm 1/2W resistor in series with the relay coil.
> > According to the spec for the relay, the coil wants 5V at 90ma. The RCX
> > outputs about 8V with full power so that is 3V too much. The resistor must
> > eat up the 3V at 90ma. V/I=R so 3/.09=33 ohms. I^2 R=Power so (.09)^2
> > 33=.27W so use a 1/2W. = RS#271-1104.
>
> This doesn't seem to work. I am trying this first since it is the simplest
> solution so far and I have a 330hm resistor at hand. Without the resistor the
> voltage across the coil with he port set to level 7 is 7.17. When I add the
> resistor in series the coil no longer functions and the voltage is 7.74.
>
> The coil specs listed by Micheal are correct and I believe I have the proper
> resistor (I'm a little rusty at reading them, but Orange/Orange/Brown is
> correct, yes? And I read a value of 229 on my meter) Is something else wrong?
>
> -Wes
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Message has 2 Replies:
 | | Re: 5VDC Voltage Regulation
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| Don't forget to apply a reverse biased diode across the relay. If you forget this the coil will generate large voltage spikes when the power is removed. This may hurt your RCX. (25 years ago, 27-Sep-99, to lugnet.robotics)
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Message is in Reply To:
| | Re: 5VDC Voltage Regulation
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| (...) This doesn't seem to work. I am trying this first since it is the simplest solution so far and I have a 330hm resistor at hand. Without the resistor the voltage across the coil with he port set to level 7 is 7.17. When I add the resistor in (...) (25 years ago, 27-Sep-99, to lugnet.robotics)
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