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 19:01:52 GMT
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Viewed:
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632 times
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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 3 Replies:
 | | Re: 5VDC Voltage Regulation
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| Michael Gasperi wrote: =>> =>> I would just put a 33Ohm 1/2W resistor in series with the relay coil. ^^^^^ Wes Matchett <wes@augustschell.com> wrote: =>... =>This doesn't seem to work. I am trying this first since it is the simplest =>solution so (...) (25 years ago, 27-Sep-99, to lugnet.robotics)
| | | RE: 5VDC Voltage Regulation
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| (...) Ummmm, I think Michael meant to say 33 Ohm resistor. That's what his calculation says and like soooo many others, I just looked at the answer without checking the math... Cheers, Ralph Hempel - P.Eng ---...--- Outside of a dog, a book is a (...) (25 years ago, 27-Sep-99, to lugnet.robotics)
| | | Re: 5VDC Voltage Regulation
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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 (...) (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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| Ralph Hempel <rhempel@bmts.com> wrote in message news:000001bf0901$f5...@pro150... (...) 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 (...) (25 years ago, 27-Sep-99, to lugnet.robotics)
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