How to use relay for GPS tracking system in vehicles

How to use relay for GPS tracking system in vehicles

12v/24v relays are widely used in automobiles. Also they are much useful in GPS tracking system. In most cases relays are connected in GPS tracking system to control the car engine on or off. Actually the relay makes engine off/on only when the engine is started by driver, if engine is not started by driver, relay is not able to make engine on, kindly note it.
relay for gps tracking and fleet management controlling engine on/off and car door on/off
Take the 12v relay as example, it has two circuits inside actually, one is 87a(or 87)—30 which is integrated into auto engine circuit; the other is 85—86 which is integrated in the GPS tracker circuit. But in a word, the engine circuit and GPS tracker device circuit belong to the 12v car circuit which is a bigger system including much more electronics like car door, etc. The two circuits are connected independently in some extent. They almost meet at the extremely small place: relay.

There are a switch and a copper wire coil inside relay. In relay not working or 87a—30 circuit on state, the switch is attached to the 87a. and no current through the copper wire coil if no current through 87a—30. There are two ways connecting GPS trackers to relay: one is GPS tracker ---87a---30, the other is GPS tracker----87---30.

For 87a—30, it’s: GPS positive + ------- 87a------30--- GPS negative - . the GPS positive is the same as positive of power cables, the GPS negative is the digital output cable. The output cable is disconnected to ground if you don’t send command to make it on. When you send command to GPS tracker by SMS or GPRS, the output cable would be connected to ground, which leads to circuit of 87a---30 is on, and current makes the copper coil generate magnetic power. The magnetic power attracts the switch to itself. Thus it breaks the 85-86 circuit which is standing for engine circuit.

For 87-30, it’s GPS positive + ------- 87------30------ GPS negative - . the GPS positive is the same as positive of power cables, the GPS negative is the digital output cable. The output cable is disconnected to ground if you don’t send command to make it on. When you send command to GPS tracker by SMS or GPRS, the output cable would be connected to ground, which leads to circuit of 87---30 is on, and current makes the copper coil generate magnetic power. The magnetic power attracts the switch to itself. The difference between the two circuits is: switch status. For the former, engine works if switch is with 87a; for the latter, engine works if switch is with 87. It means if you want to start engine with 87-30, you should make the switch attaching to 87.

This generates another good result: if somebody takes away the GSP tracker from car circuit, the car engine circuit is cut also because the switch would be back to 87a automatically if the magnetic power disappears.

If driver wants to start the engine, the 87---30 circuit should be on,  
You may check this video below for understanding how the relay function internally in gps tracking solution. Or you can check the video on Youtube .