dc relay

It don't, you are just creating a magnet to pull the contacts in.

These are rated 40Amps. $3 per at Princess Auto...I finally found the one near me and had a chub the whole time I was there!! haha

I realized the points won't matter....there ARE numbers on the contacts (5contacts...2-coils, 3-switch {n/o & n/c})....but these numbers don't lead you to think ones pos or neg!

The DC polarity of conventional electromechanical relay windings usually isn't an issue; if they won't work one way, switch the wires to hook 'em up the other. There are very sensitive relays that have magnetized cotact armatures and thus the polarity of the winding current is important. But because you say you got these relays "cheap," I doubt that you'll have trouble with polarity.

Rather than winding polarity, what's important about relays are the voltage and current ratings of both the winding and the contacts. These ratings are usually stamped or embossed on the base. Be sure that you don't apply too much voltage to the winding or you'll burn it out, and make sure that your power source can supply enough current for it to operate. With a car battery, the winding current draw won't be an issue as long as the winding voltage is rated for at least 12-16 volts.

As far as the contacts are concerned, don't exceed their voltage rating or they'll arc. And (probably most important) make sure that the load doesn't draw more current than the contacts can handle. If your load current draw exceeds the contact current capacity, you'll weld the contacts shut, melt them, start a fire, or all of the above. Automotive applications are by nature low-voltage/high-current devices, so automotive relays are designed accordingly; really fat, beefy contacts with a short-throw armature.

Scotty '99 TJ 4.0L '99 XJ 4.0L '03 BMW Z4

*** No animals were harmed during the production of this reply ***

SB,

If there are 2 coils, these may be latching relays. Latching relays lock in the "ON" position when one coil (the "SET" coil) is energized. The voltage needed to set it can then be removed and the relay will stay "ON" until the other coil is energized (the "RESET" coil). If so, then polarity might be an issue. Maybe, maybe not.

The "n/o" and "n/c" markings mean "normally open" and "normally closed." That is, when the relay is in its de-energized state, the contacts marked "n/o" are open, like a switch that's shut off. Vice-versa for the "n/c" contacts, which are closed when the relay is de-energized. Of course, energizing the relay reverses these states for each set of contacts.

HTH

Scotty '99 TJ 4.0L '99 XJ 4.0L '03 BMW Z4

*** This reply requires 4 size "AA" batteries (not > These are rated 40Amps. $3 per at Princess Auto...I finally found the one

Thanks Scotty/Bill....

I understand how a relay works....I'm an electronics tech and don't like to 'test' polarities if I can help it! :D

These aren't "cheap" relays relative to manufacturing (ok, it probably was a philipian sweat-shop -- they do great work!) but were "cheap" in relation to being surplus and were on sale!

I know they put on 'fold-back' (or feedback) diodes to help prevent the coils from discharging back in to the line (ok, I said I'm an EL-tech and now can't remember if it only applied to AC designs!).

I'm working off the flu and have been OD'ing on cold medicine. I'm useless lol too much!

Anyhow, here's a link I found that has the perscribed numbering on the bottom of the relay. (look at 2nd image down)

tells me at least that there are certain pins used for definedpolarities....not that it isn't swappable....but....I dunno. Where's my buckleys!

I'm such a doped up spaz!! lol I just read the link I put in there and it don't make a difference which gets what....

I swear guys...I haven't been eating paint chips!!

SB,

Yep, I was just about to ask you if you'd been eating paint chips.

I'm a retired EE myself, worked for the phone company since Alexander wore a tool belt.

You're right. For a lighting app like this you won't care about polarities. The only thing that might get tricky is the dual-coil business you mentioned in your previous post. If these are latching relays, replace the toggle switch in your circuit with a couple of n/o push-button switches -- one for "ON" and one for "OFF." Each P/B switch would then activate its corresponding coil.

Good luck!

Scotty '99 TJ 4.0L '99 XJ 4.0L '03 BMW Z4

*** CAUTION: Reading this reply may make you drowsy ***

SB,

I just re-read your previous post about the contact ratings. I believe I mis-read it the first time and that you were saying that there are TWO CONTACTS for the coil, not TWO COILS. If so, I apologize for wasting yours and the group's time with all that hoo-hah about latching relays. If you meant that there are two contacts marked "COIL," then your relay will fit in the circuit you showed in your link without a problem, as long as those lamps don't draw a combined current of more than 40 amps (i.e., 20 amps each) 'cause they're wired in parallel. Polarity shouldn't be an issue; those reverse-bypass diodes you mentioned generally aren't built-in.

BTW, coil windings generally will operate at 85& of their rated voltage and can usually tolerate up to 110% of it. You can determine the coil's current rating with an ohmmeter because, as this is a DC circuit, its impedance isn't an issue

-- find the coil's DC resistance with an ohmmeter and use ohm's law to determine its current draw. This will tell you what size fuse to put in the switch circuit. Of course, the lighting circuit will need a 40A/FB.

Have fun!

Scotty '99 TJ 4.0L '99 XJ 4.0L '03 BMW Z4

*** WARN> These are rated 40Amps. $3 per at Princess Auto...I finally found the one

Hey don't worry about it. It's information posted for everyone!!

I picked up some cheap fuse blocks along with the relays and switches. I don't know IF I'll need to put a fuse block on both power sides of the relay (light side and switch side)....I figure it couldn't hurt if either end shorted out....

I've seen some links that say to put one on each side and I like the idea of a fuse block better than an inline fuse.

You wouldn't need a polarity marking unless the relay has a diode suppressor, in which case one would expect some manufacturer willing to spend for the diode to spend to mark the polarity.

that being said....do you guys add diodes yourselves?

It does make 'some' difference.

I prefer to put power to the coil at the relay (hook pin 87 to pin 85) and use the switch for a ground only off pin 86 to fire the coil. This means I only need one small ground wire coming through the firewall to the switch. Hit the switch, this grounds the coil and fires the relay. No fuses needed on this side of the wiring, only on the primary power.

You can also make a 'latching' relay if you wire it right so it holds 'on' until the key cuts the power.

No diodes are needed normally with these mechanical relays unless you are playing around with LED's.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

SB wrote:

On Tue, 27 Apr 2004 23:01:48 GMT, the following appeared in rec.autos.makers.jeep+willys, posted by "SB" :

The only way DC relays are "polarized" is if they have diodes across the coils (there to prevent inductive kick when the coil drive opens). If they do, the coil must be connected so that the diode is reverse-biased (cathode to positive, anode to negative). With an ohmmeter, you can usually tell if this is the case, assuming the coil resistance is greater than 20 ohms or so, since the diode will conduct when forward-biased.

Well i picked up those fancy schmancy led switches that light up when on.

4pack for $5....woo hoo sale!! lol

I'm just looking at how I'm going to wire these up....looks like, instead of your ground switch closure being 1 wire, I'll have a powered closure that is still 1-wire to the coil. Still only 1 wire to run!

Are yours connected to ACC or to your battery? I'm looking at hooking up to ACC (except for one convenience cig outlet to the battery).

Battery.

I have an Optima battery with a bolt post for accessories. Canadian Tire now sells generic rolled cell batteries.

Mike

SB wrote: