Relays & there main purpose/function?

-
J

JoeDust451

Well-Known Member
Joined
Jul 1, 2005
Messages
1,348
Reaction score
27
I want to here from some of you what a relay really does, whats it main function, why they are so important to use with nitrous/fans/elec. fuel pumps ect., i'm no electrician, & never will be IMO, my brother on the other hand has mastered this field, but i can rebuild & engine that will leave him scratching his head lol. Sooooo, the reason i'm asking is, i was thinking of running one for my MSD streetfire box, but was told there is no need for it, i was under the impression (by what others have told me over time) that a relay helps control voltage/current from drifting or spiking, is this true??
 
1. Relays can carry more current more effectly than the common switch due to their larger endlosed contacts.
2. They eleminate the need for long runs of high amp / large r gauge wire. Very small switch contacts and wire can signal the relay to open or close.
There is even a weight savings in that if it matters.
A relay has a coil in it, therfore It can produce a spike. Most relays are diode protected inside. That means if its hooked up wrong,
it dies.
You'll need to decide what type relays is best for you, diode protected or universal.
 
What he said.

Basically control a large amperage circuit with a small amperage switch.

Also more than one source can activate the relay.
 
Here is an example of added control with a relay:

Lets say you need to power a high current load (fan). The fan current is may be greater than you can operate via the ignition switch. You however would like the fan to always go off when the ignition is off. In this case wire a circuit using the ignition switch to provide power to a relay to switch the power to the fan. The fan circuit should be supplied by the battery and properly fused. The relay coil takes about 0.1A, and a 1" square relay may switch upto 30A depending on specifications. A thermostat switch could be in the coil circuit and control could be automatic.
 
69swinger340391 said:
What he said.

Basically control a large amperage circuit with a small amperage switch.

Also more than one source can activate the relay.
Click to expand...

What he said plus the fact that when you don't run a relay and run the full amperage through a toggle switch like in the case of an electric fan or fuel pump, or even fog lights, chances are that right away or in a short time, you WILL melt your switch and hopefully pop the fuse unless the switch is a weaker link in the circuit than the fuse is which means you CAN BURN YOUR CAR TO THE GROUND!!!
Most switches are marked with the amperage they can handle BUT don't rely on that, run a relay ALWAYS!!!!

If you are running accessories like a electric fuel pump or electric fan you should get someone who knows what they are doing to install some relays for you if you are not comfy doing it yourself.

You can google several relay wiring install diagrams but a reputable auto audio/video install shop is a good alternative also.

Nothing like smoke coming from behind the dash on your dream car.
Talk about ***-pucker from hell.
 
Ok, i'm getting there purpose now, basically they take the "load" off of the wireing or switch. So, is it safe to say i won't need a relay for this MSD streetfire box sence it doesn't have a toggle switch?
 
JoeDust451 said:
Ok, i'm getting there purpose now, basically they take the "load" off of the wireing or switch. So, is it safe to say i won't need a relay for this MSD streetfire box sence it doesn't have a toggle switch?
Click to expand...

I dont know what current that part requires or draws. If it pulls like 30 amps it will be overheating the original ignition feed wiring through your ignition switch.
Some ignition systems do need high amp supply.
 
JoeDust451 said:
Ok, i'm getting there purpose now, basically they take the "load" off of the wireing or switch. So, is it safe to say i won't need a relay for this MSD streetfire box sence it doesn't have a toggle switch?
Click to expand...


Does your ignition box come with proper wiring installation instructions?

It should be pretty detailed on what you need to do for wiring it up.
 
Yeah its detailed, doesn't mention running a relay, i wouldn't think it would be hard on the ignition because its wired off the battery just like a 6AL, the only wire is the small red that goes to "key on" power to trigger the box, i do thing i'll run a fuseable link on the "batt' power large red though.
 
That small red wire on your MSD most likely draws less than the original ignition did. I know my Mallory box is triggered off a small red wire that runs to the ballast resistor and it only draws about 1 amp. The original ignition probably drew 5 amps or more. If you look at the MSD box it has real big Red and Black power wires that run directly to the battery. That is where all the load is at. Therefore there is really no need for a relay....Unless you want to have an auxiliary power cut out switch wired in that is controlled by that relay.

One last thing to mention about relays is they don't actually help with voltage drop or spikes. Their nothing more than an electronic switch and act exactly the same as any other switch except they are triggered by another B+ supply.
 
You must log in or register to reply here.
-

Back
Top