reading relay diagram

[stilivn]

I bought a dual battery isolator and crossed the negative and positive terminals on installation and it has never worked. I pulled it apart today to try and sort it out. Now it seams the relays in it arent switching, can someone please explain this diagram to me and how it should work , cheers.

[bushy555]

I typed out a page of info this morning and lost it before hitting submit.

The numbers 30, 85, 86 and 87 are international standard numbering for pins for the standard 30 and 40 amp relay that you buy from relay shop. Such as kmart, super cheap and your local petrol shop.
Various other manufactured relays will have a different pin layout and can be numbered differently.

Pins 30 and 87 are the switching load, that is, in between these two pins is where the heavy duty switch lies which actually turns your lights (LED bar) on and off.
This switch is activated, usually, by an electromagnetic force from a coil that is close by (the middle box thing in the picture) which the two pins 85 and 86 are connected to. These two pins go to battery and to a switch on your dash. The coil is a very low current draw, usually around 15 to 30 milliamps (Thousanths of an amp), in comparison to the heavy duty switch which can be upwards of 40 amps in these standard type of relays.

The left hand box is a typical icon/photo/drawing of a diode hanging off the side of the coil. After the coil has been turned on, and you go to turn it off, when the large switch flings back to its normal OPEN resting position, it being metal causes a reaction or phenominon with the coil, and thus the coil produces a voltage. This voltage can sometimes be higher enough to be called a spike and the movement of the switching piece of metal moving past the or away from the coil is the basis of what is known as electro magnetic force (EMF). Or in this case back emf. The diode is there to stop this back emf high voltage spike from going any further down the wires and killing any sensitive computerised equipment.

The diode in place can also stop the coil side of the relay from working in one direction. Ie, Depending on the direction of the diode, it may be possible that if positive +12v is placed on to 85 and negative/ground placed on to 86, then the realy works fine. Change polarity around (Negative on to 85 and positive on to 86) and the relay may now not work due to the diode.
This is not always the case, again, it is dependant on the type of diode and its actual placement in line or in parallel to the coil. (If I am wrong, am happy to be told by a more guru person).
A lot of cheaper or older relays will not even have this diode in place, and the relay will work whichever way you wire it up.

The dashed line indicates the movement of the heavy current switching bit of metal, or I guess, the theoretical link that is the magnetic force of the coil between the coil itself and the actual switch bit.

So, relay not working?
put +12v on to 85 and negative/ground on to 86. Does the relay turn on/off?
No? Change the polarity over on pins 85 and 86.
Work? If not, then the coil is most likely stoooofed.

[-Scott-]

bushy has pretty much nailed it.

The box with the line through it represents the relay coil, although most people these days leave out the diagonal line.

The other box hanging off the side is some form of spike/surge suppression - multiple different types available, and some will prevent the coil from energising if it's connected wrong.

(Technicality: the coil is an inductor, that prefers to have constant current flowing through it. When a coil is turned off, the current wants to keep flowing, and can generate high voltages in an effort to keep the current flowing - see a petrol engine spark plug for an example. Surge suppressors on a relay coil give the current somewhere to go, or the allow the energy to dissipate harmlessly. The suppressor is required on the coil regardless of the load on the relay contacts.)

Bottom line: connect the relay properly. If it still doesn't work, chances are that it's stuffed. Buy a new one.

[stilivn]

thanks guys may be the earth isnt getting contact on the relay will test in next few days.

[80's_delirious]

Nice explanations boys

[dillza_69]

A bit of "for your information"

Ive had this issue several times on friends cars where they have been in mud and/or water where lights (or whatever load you are running) wont work. Multimeter shows 12vdc at the lights (with lights disconnected for fault finding) but when they are reconnected they wont work. Dirty contacts in the relay can still give a 12vdc no load voltage. As soon as load is applied the voltage drops and lights no work due to high resistance contact in relay. Hope this makes sense but it could be a trap for people with limited electrical knowledge.

In short change the relay if you are having electrical issues after playing in mud