SMC Relay/Cap

[SeattleSy#1255]

Question regarding the relay I am going to use for the SMC alki....

There are 4 terminals on this relay...12v in, 12v out, ground, and "on/off switch".........

12v in is for power in from battery
12v out is for power out to alki
ground is ground

what is the on/off terminal for...do i not use this and is this terminal used for the option of turning the relay on and off? I figure i don't use this because the alki can be turned on and off from the cab...is this correct?

Lastly, the capacitor---where is that put in line? I am figuring in the power out line between the relay and the alki control box correct?

I am just flat out stupid with electornics so spare me on this one...

TIA

 

[Loeryder]

Jeff,

12V in would be your supply line, preferrably a fused line right off the alt. or batt.
12V out will be the + power TO the smc control box.
On/off would be an ignition ON + wire, so that the relay only gets powered on when the key is ON.
Ground, you got that one, right? lol

The capacitor is used as a filter, it goes between the supply line to the smc box and ground.
Make sure you have the polarity correct. Ceramic disk capacitors usually dont matter but an electrolytic will.
It acutally grounds out any high frequencies so there is no "noise" being introduced to the trucks electrical system when the pump kicks on.

Hope this helps,

 

[SeattleSy#1255]

Jason thanks for the reply...a few more questions related to your response:

With the 12V in ........what fuse would work best?

With the on/off ..........what wire (probably off the firewall right?) is best to use? I don't understand how this only allows for the relay to get power when the key is on, when you have the 12v power wire directly from the battery or alt. connected to it as well? Isn't that supplying it with power? So are you saying there are basically two power wires to this thing, one from the battert/alt. the other from a wire that is only hot on ingition?

Ok, glad i got the ground correct!

I am confused about the cap.? For the lack of better terms, its a little ball shaped thing with two wire outlets on it, can you explain this better for me?

Thanks for for the tollerance!

 

[InvisiBill]

Think of the relay like a faucet. There's 12V-in, 12V-out, and a "signal" wire to tell it when to let power go from the in to the out. The in will always be hot, like you said. But power will only go through the relay when the signal wire is hot.

The capacitor is an electrical noise filter. By what Jas said, you just hook it up parallel to the control box. Hook the positive lead of the cap to the + on the box, and the negative lead to the - on the box (or on the wires, it's the same thing). It allows some of the noise on the power line to bypass the box and go directly to ground, basically.

 

[Loeryder]

Think of the relay as a remote switch.

You are using your ign ON to send the full voltage through the relay to the smc kit. You do not want power to the box when the key is off. Technically you could but you'd have to remember to manually turn off the alky every time you drove.

Here is a diagram of how to use a relay for fog lights.

Replace the lights with your SMC alky, run the + off the alt instead of the battery and the switch is really jsut a tapped wire that is on with ign.
In my case I ran a tap off my fuse box to triger the ign ON relay, better than tapping the box for the whole load.
there may be an easily accessible wire underhood to tap, but I prefer underhood to stay uncluttered where possible.

The capacitor, hmmm.where to start.
A Capacitor can be viewed as 2 devices.
One a small battery that will charge up to a DC voltage and try to maintain that voltage, whether it be by releasing stored current or by drawing a lot of current quickly to recharge. Its reistance varies with voltage.
Thats where it becomes a filter. The capacitor will ground out frequency bands based on its capacitance.
So we are doing 2 things, we are reinforcing the voltage at the pump supply and we are filtering out high frequencies that cause noise.
The capacitor is installed ACROSS the power feed, (+ to +) (- to -).

I will search for the correct capacitance for our application and I do recall it being a ceramic disk type.

 

[SeattleSy#1255]

Great that helps a ton...thanks again..

only i don't know is what fuse to use between the battery/alt and the relay?

Thanks again for the help Bill and Jason..big help!

 

[Loeryder]

20A blade fuse should be plenty.

No prob.

 

[SeattleSy#1255]

one last question here....

installing the capacitor across the power feed---not sure what that means...

using the fog light diagram as an example, would that mean between the power wire off relay #87 the ground to that fog light?

I guess i dont know what the power feed is...is it the above mentioned or is it the battery?

hope that isn't to confusing!

 

[Loeryder]

The cap will go from pin 30 to ground.

 

[SeattleSy#1255]

got it...thanks!

 

[SeattleSy#1255]

The cap will go from pin 30 to ground.

to bring back an old post real quick...when you say the above do you mean to splice into the wires on pin 30 and the ground wire or is it actually suppose to be connected (saudered or something???) to the terminals on the relay?

 

[SeattleSy#1255]

bump...still looking for his answer...

TIA