Relays - Usage & Protection

[IRTSYSOP]

Very nice write up. I think I will go the diode route from now on with my relays. I'll just say it's VooDoo if anyone asks

[LandCruiserSteve]

NCFJ previously said:

Shhhhhhhhhhhhh that was not for public knowledge, and I want his greatest hits tape back too Steve

As soon as I'm done with it, Stan . . . . .

[Moontime]

Can I ask a couple other relay questions?

I have a set of PIAA 510xt mounted in my expedition one bumper, they have recently stoped working and all i can guess is the relay is bad. I have power at the switch (green/red led is working), i have power going in to the relay (multimeter tested) and no power coming out of the relay.

Just out of curiosity, shouldn't a relay last longer than 8 months?

is there a relay that will last longer?

how do i know what relay to replace the original (PIAA #33086(PL5FB) with?

thanks

[doublejfj]

Sure, it does sound like the relay is bad.

Here's another test: take the relay out and put your meter to measure resistance. Measure the resistance between the coil's positive and negative. That should give you the resistance of the coil. If the coil is shorted, it'll be very, very close to zero. If the coil is open, it'll be infinite.

Relay lifetime is hard to gauge, it's a combination effect of a few things. Motion/vibration, quality of the relay, heat/cold and other things can definitely shorten or lengthen the lifetime of a relay. Out of curiousity, do you use a diode with your relays? I looked at the PIAA product page and it doesn't say anything about an internal diode. This could contribute to a shorter lifetime, but I'm still not completely sure in your case. 8 months is a little slim though, I agree. You might have just got a weak one...

I'd probably just replace it with a nice Bosch 30A or 40A automotive relay or something. I don't know what the PIAA relays cost, but it can't be too good. For comparison purposes, a Bosch relay here is about $3.50.

[DEWFPO]

I like to use high quality relays like Bosch, I always try to mount them with the connections at the bottom, and try to weatherproof them as much as possible. I have had good luck with all of mine.

DEWFPO

[FJandFU]

These are the times I wished I had payed attention in school.

[Moontime]

doublejfj previously said:

Sure, it does sound like the relay is bad.

Here's another test: take the relay out and put your meter to measure resistance. Measure the resistance between the coil's positive and negative. That should give you the resistance of the coil. If the coil is shorted, it'll be very, very close to zero. If the coil is open, it'll be infinite.

Relay lifetime is hard to gauge, it's a combination effect of a few things. Motion/vibration, quality of the relay, heat/cold and other things can definitely shorten or lengthen the lifetime of a relay. Out of curiousity, do you use a diode with your relays? I looked at the PIAA product page and it doesn't say anything about an internal diode. This could contribute to a shorter lifetime, but I'm still not completely sure in your case. 8 months is a little slim though, I agree. You might have just got a weak one...

I'd probably just replace it with a nice Bosch 30A or 40A automotive relay or something. I don't know what the PIAA relays cost, but it can't be too good. For comparison purposes, a Bosch relay here is about $3.50.

thanks, i will try to find a bosch here locally. The piaa relay runs between $15-25 depending on the website ($25 from PIAA)

the relay i have now does not have a diode, can i get those at my local radio shack?

Any idea how to determine if a 30A or 40A would be the appropriate one?

[doublejfj]

WOW, yea that's an expensive relay!

Yes, you can get them at radio shack (see the original post in this thread discussing them). You should have no problem finding that Bosch relay locally.

The only way to really determine which is the appropriate is to add together all of the current draw from your lights (see the original post). That will give you the total, but I can't give you anymore specific info because I don't know what you've got running off that relay. FYI: There isn't much coil draw difference between the 30 and 40A versions. I'd probably just go with the 40A one because it won't hurt if you don't use the extra capacity.

[jeshua]

OK my question is how do you wire up a relay? I still need to wire my roof lights so when I run all my wires where will they connect to the relay?

86=positive (to power or lights)
85=negitive (to ground of lights)
30=?
87=?
87a=? (guessing to ground)


Thanks, great write up so far,I know I will be using it.

[doublejfj]

Here ya go:
86=positive side of the coil (your positive supply to make the coil turn on)
85=negative side of the coil (your negative supply for turning the coil on)
30=connect to the source of the load
87=connect the load (your lights)
87a=nothing (this is only active when the relay is not powered. 30 and 87a are connected when no power is flowing)


See here from the original post for an explanation:

"When there is no difference of potential (voltage) across terminals 85 and 86 (the coil), the relay's movable contact (connected to terminal 30) is held, by spring tension, against the electrical contact which is connected to terminal 87a (the normally closed contact). In other words, when no voltage is applied the the relay coil, terminal 87a is connected to terminal 30. When 12 volts is applied to the relay coil (terminals 85 and 86), the movable contact (connected to terminal 30) is pulled down/in by the electromagnet (coil) so that it physically contacts the electrical contact which is connected to terminal 87. Again, in other words, if battery voltage is applied to the relay coil (terminals 85 and 86) terminal 30 will be connected to terminal 87."