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Basic Electronics » How do I determine the throw characteristics of a Relay

March 07, 2011
by Twarter369
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I have a Tyco 110/120V Relay part # PCLH206S1A. After reading the Datasheet at http://datasheet.octopart.com/PCLH-206A1S-Tyco-Electronics-datasheet-15179.pdf I still can't determine what the minimum voltage to trip the relay is? I was looking at the nominal voltage of +24v but that seems high to me.

I know that the circuit goes from PB1 to a PNP transistor(9014b). Since a PNP runs current from Emitter to Collector with the Base at a lower voltage: I would hook up B to the MCU, the +24v (or whatever the trip voltage is) to E, then C goes to the contact of the coil....correct so far?

March 07, 2011
by 6ofhalfdozen
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Twarter,

According to the datasheet, you have the 110V coil powered version, which according to the datasheet needs AT Least 80% power to turn on (ie ~85V AC). I am pretty sure you will NOT be able to do anything directly from the NK. You would most likely need to run some kind of big power FET from the NK to turn your relay on/off, but it would need to run 110V at which point you why not use the powerfet or a 12VDC relay. As for your question of how you determine the power throw voltage, it is listed near the top under the "Must Operate" listings. The 206 version which you have is 110/120V AC, while you might be getting confused with some of the DC versions like the 201D,202D,203D,204D,205D . that's my take on it, though some of the electrical gurus might have be able to point you in a better direction.

March 07, 2011
by mongo
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The easy way to tall an AC relay from a DC relay is to look at the end of the post in the middle of the coil. If there is a copper band embedded in it, chances are it is an AC coil. The band is a shading coil, which generates an extra magnetic field to maintain the pull on the armature during the zero crossing and phase inversion of the supply voltage. Without it, the coil buzzes.

If the coil has a smooth and plain looking stub, it is probably DC.

Most have their voltages printed on them somewhere. Even the tiny little relays have it printed somewhere too. Some have it right on the coil, some have it embossed in the case.

The relay that is mentioned here, also, if an AC coil, should read about 34 ohms.

March 07, 2011
by Twarter369
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Now I am REALLY confused :(

Here is my setup. I have a pond pump that runs 110VAC @ ~3a. I want to switch that with my relay via my MCU.

I have pin PB1 connected to the PNP. I know a PNP can use A/C to control D/C (the basis of audio amplifiers as I understand them)but can they Use D/C to control A/C? There is no way the 2n2000 or the 9014b Transistors I have can handle switching ~85VAC even if that is the case.

I am working off of the theory behind this project. http://www.sparkfun.com/tutorials/119 I asked for an eq. relay because they didn't have the specified one.

March 07, 2011
by Twarter369
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Okay, after a little more research it boils down to this not being the right type of relay for what I want. Figures! I looked up the Datasheet for the Relay in the picture (maybe where I shoulda started) and it clearly says the coil operates with 5vdc. This confirms what I suspected that IF the coil could be switched with DC it would be easy to spot.

~85v seems like so much to switch a relay. I mean, is that a common relationship, only a 20% gain in controllable power?

March 08, 2011
by bretm
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20% difference in voltage. Power is another story. The switched contacts probably handle much more current than the coil does.

March 08, 2011
by Twarter369
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Well, as I understand it Watts = Volts x Amps So in this case 110 X 3 = 330 and 85 X 3=255 and 255+20%(60)= 315...so 20% power looks about correct. I think this would be because the amperage (the multiplicative factor) is consistent. Please let me know if I am misunderstanding any of this. My background is in Software Development, the Electronics is new to me still.

March 08, 2011
by bretm
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3 amps is the current that the switching contacts can handle. The coil handles much less current. It has a resistance of 3,400 ohms at 110VAC and the nominal power is 1.4 watts (if we're looking at the same datasheet).

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