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SmilinSam

Electrical wiring question-Relays

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SmilinSam
Got a off brand tractor here with three relays in the safety circuit. I am trying to understand what a relay does and how it does it.?. 1)Looks like from the wiring diagram that a relay is a electrically activated switch ??? 2)If so, does it take power from one direction thenanother to move the relay switch from one position to the other ?? if you follow me. I'm lost if you can't tell....

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rokon2813
yes it is an electrically operated switch. basically you put power to it and it closes (or opens depending) a circuit. Your solenoid is a relay if you understand how it works. You put power to it by turning the keyswitch and the relay connects the battery to the starter. simple explanation= simple example hope this answers your question

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BLT
Sam most relays today take milliamps to trigger them, keeping the wire size down to handle amps with short wiring runs.. The most common one is called a Bosch type relay which is a 5 pin type. Two for doing the trigger and three for what you want to do. They are dry contacts with a common and a normally closed circuit and powered to open I think. If you do a seach on them you will find a schematic. Hre is a place to go. http://www.classictruckshop.com/clubs/earlyburbs/projects/bosch/relay.htm

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JackBa
Sam, Most 12v relays are spring loaded, they only move when power is applied and return to there normal position when it's taken away. On a wiring diagram they are drawn in there unpowered position, a normally open relay looks something like _/_ and a normally closed is shown connected.

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SmilinSam
Bob, the two for the trigger would be one for ground and one for the power to energize it right? These are a 5 pin type. These things a common item available at a auto parts store, or do I need to go to the L&G manufacturer for the right piece? Anyhow thanks to you guys the lights are on upstairs now:D

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JackBa
Sam, If there is a wiring diagram on the side of the relay you can match it up at an auto parts store, if it doesnt have one it gets harder as they can be wired several ways on the inside depending on the brand and what they were trying to make that relay do.

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ReedS
Sam, to me it looks like all of the above answers are true however one fact that I did not see here is that relays are usually used in a situation where a small current is used to switch a larger one for example ,a starter solenoid. Yes there are two connections for the trigger (to energize the coil),one hot and one ground and depending on the type of relay 2 or 3 connections for the device to be switched. Relays can be switched by either applying voltage or ground (most emergency apparatus use a switched ground system to control relays which then switch the device.) Yes napa usually carries the bocsh relays so too others stores I would imagine. Be aware that there are different tpyes of relays some are diode suppressed while others are not, also make sure the amperage rating will handle the load. I hope that I am not clouding the issue any just my 2 cents.:p

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SmilinSam
These are all marked on the side with a diagram and max amperage. I think I have a good understanding of these now. This is the first time I have had to monkey with these as I never usually have a tractor here new enough to have them. Thanks Again! Sam

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BLT
Sam if you live close to an auto salvage yard, you can get a handful for a buck. That's what I do. Since cars have gone electronic, each one might contain a dozen or more. Plus they have volatge supressient diodes in them. Then your trigger terminals are term 86 for supply voltage, 85 ground. On the dry contact side it's 30 common, 87a normally closed and 87 open.

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djarvis949
second attempt, There are 'Bosch type' relays that are used for headlamps that have two # 87 terminals although 87a is still cast into the base of the relay. Be careful of the relays with the suppressor diodes built in as you WILL let the hermetically sealed smoke out of the relay if you reverse the polarity on 85 & 86. More information [url]http://www.the12volt.com/relays/relays.asp[/url]. Don PS: If I hooked the wires up on my horn backwards, Would it suck???

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