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Simple Typical Relay Operational Diagram

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Since there are a few members that would like to know how a simple relay functions, I drew up this rough drawing to show just how a simple relay operates.
I hope it helps out those that are "electrically challenged".
Marty

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Actually poles #86 and #85 should NOT be reversed because the relay may have an internal flyback protection diode (which allows the coil field to collapse without the voltage spike that would otherwise be generated when switched off). The diode is properly reversed bias (when the more positive voltage is on #86) but if you reverse the poles, the diode will get burned out immediately (a direct short due to forward biasing with no current limiting, and then like a fuse becoming an open circuit) so there then may be a voltage spike whenever relay is now switched off.

You can tell if a relay has an internal protection diode by measuring the resistance between #85 and #86 - it will be less one way than the other if it has one. You must use an analog ohmmeter, however, as a digital one does not output a high enough voltage to forward bias the diode (so diode will be an open circuit and you will get same reading each way). Also note that most analog multimeters use reverse polarity on the ohmmeter scales.
 
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I do see your point Gary, but on the simple relays (and I have had them apart, both on accident and on purpose) I haven't found a diode or I would have written it up that way. I am only explaining that a relay is nothing more than a switch that is activated by 12 volts thru the coil in the relay, that then connects two points together and then releases them when the 12 volts are not present.
Thank you for pointing it out! Lets not give out bad information so I appreciate you.
You are one of the only people I know that owns a ANALOG ohm meter (well I do, but most have digital meters now) and they are a handy thing to use. I am glad you brought that up.
Marty
 
on the common relays that you find with aftermarket alarms systems, keyless entry systems and stuff like that, the diode (if there is one) will be on the plug.
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Thanks for adding that Dusty!
It is nice to have a few electrical savvy folks on here to try and explain some things that "electronically challenged" people need, so they can understand the components! I appreciate you and Gary chiming in!
I mean no disrespect in the term "electronically challenged", I am only trying to make simple explanations for the purpose of education. :thumb:
Gary, if a relay had an internal diode, would it be in series with the coil? If so, wouldn't hooking it up backwards make the relay inoperable because of the blown diode? I am wanting the thread to be educational for us all. Thanks!
 
it would be in parallel with the coil
 
Gary, if a relay had an internal diode, would it be in series with the coil? If so, wouldn't hooking it up backwards make the relay inoperable because of the blown diode?
No the diode is in parallel with the coil whether it is internal or external. Then connecting #85 and #86 backwards immediately blows (and open circuits) the diode - so the relay then performs as if there is no diode (which there now isn't) so no more voltage spike protection. The user probably wouldn't even know anything happened (unless a fast blow fuse blows) since the relay normally still operates. Without testing as I pointed out, you can't tell there is one inside. I agree most basic automotive relays don't have an internal diode although I occasionally have seen them (and nearly always see them in electronic gear). Still it's safest to just always wire #86 to the more positive voltage (than #85). Then it will always work properly (especially should someone replace the relay with one that does have a diode and blows a fuse because it's backwards).
 
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Gary, I'm so glad you mentioned this in this thread. That is why I Undeleted it so everyone that searches it gets ALL the information!
I understand the reason it might be in one (a relay) but the typical, off the shelf units, for just simple use seemed to be unprotected.
Thank you my friend!!!
Thank you to Dusty!!!
Marty
 
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