Coles Notes: Need to wire in some lights + horns, which relay to buy?

I'm ready to install a bunch of lighting and horns on both my truck and wrx and needed to purchase a few relays to make everything work nicely. I have used relays before and figured it was as easy and walking in and picking up a relay......... then I looked at what was availiable and realized I had no clue what I need.

First off, I know the difference between SPST and SPDT... I want SPDT.

But then you start getting relays with diodes and resistors in them, some even have diods AND resistors. From a users standpoint, is there a difference between the 2? What are the pro and cons of this setup?

Looking at the hella relays online, at both rallylights and other sites, I see the rating on the relay is 20/40 amps..... how can there be 2 ratings for the same relay? can it really handle 20 or 40 amps???? (on my wrx I might eventually have 2 sets of hella lamps running of a single relay so I would want a 40 amp relay).

Finally, contact material. Rallylights gives you a choice of contact material, either AgNi or AgSn02. Any real difference between the 2? Which one should I buy?

Finally, are there "better" and "junkier" relays? Reading the supertones thread and how their cheap relays will fuse into the on position kinda scares me.... and yet, i'm not sure if relays i'm purchasing now are any better.

usually you will want SPST relays, especially for a simple on/off from a switch.

resistors/diodes... you don't have to worry about those in a dc circuit with a contact switch and a resistive element at the other end. (light or horn) Relays can generate a massive EM pulse on the lines that some things can't absorb, the diode/resistor will filter that out.

Coles Notes: Need to wire in some lights + horns, which relay to buy?

I'm ready to install a bunch of lighting and horns on both my truck and wrx and needed to purchase a few relays to make everything work nicely. I have used relays before and figured it was as easy and walking in and picking up a relay......... then I looked at what was availiable and realized I had no clue what I need.

you need relays :D

First off, I know the difference between SPST and SPDT... I want SPDT.

a SPST is a single position single throw relay, this is the most common.
http://www.rallylights.com/hella/hella%20images/forma.gif
a SPDT is a single position double throw relay. we dont usually use these for lighting. but heres a pic.
http://www.rallylights.com/hella/hella%20images/formc.gif

But then you start getting relays with diodes and resistors in them, some even have diods AND resistors. From a users standpoint, is there a difference between the 2? What are the pro and cons of this setup?

a relay with a resistor helps eliminate voltage spikes. good for some systems, again, not really needed to lighting.
This was taken from rally lights. but, its great info.
Voltage spikes from 300V to 500V can occur momentarily when a relay is switched off. Sensitive electronic equipment can be damaged or malfunctions can occur if these spikes each the vehicle electrical network without suppression. A relay with a resistor reduces these voltage spikes to less than 100 Volts. A relay with a diode eliminates them completely. The correct polarity of the connections is marked on the diode protected relay.

Looking at the hella relays online, at both rallylights and other sites, I see the rating on the relay is 20/40 amps..... how can there be 2 ratings for the same relay? can it really handle 20 or 40 amps???? (on my wrx I might eventually have 2 sets of hella lamps running of a single relay so I would want a 40 amp relay).
not sure on the 20/40 amps. all that i can think of is that is for dual voltage systams, 12v/24v. now, these are mostly common 30amp relays, and i know lots of people use 4lights per relay, but i really like to keep things on the safe said and run one relay per set of lights. that way i know i am not taxing the relay.

Finally, contact material. Rallylights gives you a choice of contact material, either AgNi or AgSn02. Any real difference between the 2? Which one should I buy?

now, if i remember corectly, the AgNi is what almost every relay uses, from the crap china ones you buy at autozone to whats in your car now. the AgSn02 is made to work harder, and can take more of a instant burst of power. good for high amp items (i am just going of memory from my damn EE clases, so it could be wrong)

Finally, are there "better" and "junkier" relays? Reading the supertones thread and how their cheap relays will fuse into the on position kinda scares me.... and yet, i'm not sure if relays i'm purchasing now are any better.

I like to use Bosch relays. i have had real good luck with them. stay away from the rat shack ones. Tyco ones arnt too bad either.

oh, and i am thinking of buying a bunch of wiring items, good relays, good bases, all the stuff us lighting people like, so we could have one place to buy good stuff and be from a nice vendor on here :D

Shane

The standard Hella/Bosch "cube" relays are usually SPDT, terminal #30 is the common, 87 is NO, and 87a is NC. Since most applications only require SPST and the NO contact, the 87a/NC rarely gets used.
If a diode is needed it can always be added to a relay that does not have one to begin with, any generic IN400x series diode can be used.
And I agree that you shouldn't use Radio Shack relays for automotive purposes, they are best left for light-duty indoor applications.

Ok, let me add a bit more detail to this and maybe you guys can help point me in the right direction (or a part number.. lol)...

I am very likely going to be ordering the relays from rallylights just because I have a bunch of things i'm going to be ordering from them anyhow.. (haha.. 3rd order in 3 weeks..).

I was thinking of using SPDT relays because they cost the same as SPST relays and will give me a bit more flexability IF I need it.

I need relays for a few on going projects for both the WRX and my pickup truck.

WRX -
1) Building relay harness for high beams. I have already purchased the connectors to build a relay harness for the high beams ('06 wrx, so seperate high beam bulb). Now I still have to figure out the wiring for this as I understand it is a switched ground system. Reason for the harness is two fold. A) I want brighter high beams and the relay will help me maximize my soon to be installed HIR bulbs. B). I want to be able to tap the high beams for a signal without having to cut the factory wire, this is for a set of hella FF75's driving lights. I figure I would need at least one relay for this setup. Would a Standard SPST relay do?

2) Powering the FF75 on the WRX..... light kit comes with a relay already, I assume this relay is of high enough quality that I don't have to throw it out yet..... i'm hoping...may replace this relay with one that has dual output pins as I *might* add another pair of FF50's up front if I feel I need more light.

3) Hella Horns, A single SPST relay is good here. One concern I have is the number of threads showing how the kit relay has broken and fused to the ON position. Is it necessary to replace this with a larger / better relay?? do I need a diode or resistor for this relay?

Truck - '07 f-150

1) Hella Supertones - Slightly different setup here. The truck is a work truck and often when opening or closing the tailgate, driving machines by the truck etc the alarm will "chirp" at you. This could get very painful with supertones setup. SO... The idea here was to have one relay be triggered with a ignition source, powering a second relay. The first relay (SPDT) would be used to switch between the regular stock horn (when key is out) and hella's (when the key is in).. A second relay (SPST) would be used to power the supertones, taking the load off the stock circuit. Do I need a relay or diode for either of these relays?

2) Fog lights - Hella Micro DE's.... Will be tagged to factory circuit... I'm assuming the kit relay is good enough.

3) Driving lights - Hella FF1000 with 100w bulbs.... Have to check rating on kit relay, may have to upgrade here.

Finally, does anybody know what they mean when they say the amperage rating on the relay is 20/40... does that mean 20 or 40 amps at 12v?

...the HIR bulbs don't draw any more current than stock...and just upgrading the factory grounds is the place to start with this one, I think

....the best way to 'do' this kind of 'thinking' is to draw it all out on a large sheet of paper and visualize the whole thing...one circuit at a time


...and adding a power distribution block may be a good idea if ya gonna do multiple hi-current installs

100w bulbs in the ff1000's will BE ****ING REALLY BRIGHT AND HOT!!!!!!!!!!!!!!! and you should be aware that you should NOT leave them 'ON' if the vehicle will be stopped for any length of time....melting is possible

grounds already upgraded in the wrx...... going to upgrade the alt wire to complete the big 3 later (stereo being installed in trunk).

harness for highbeam is to ensure max voltage to the highbeams.... want to make the most out of the HIR bulbs.

As for distribution block, i'm looking into the blue sea one for use under the hood :)

oh, don't forget, to ask for the NASIOC discount :D i think they give you like 10-15% off :D

Shane

OH!!.. I didn't know about the discount... DOH...

oh well..... another excuse to put another order down :)... do we need to call them to get the discount?