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Old 01-26-2018, 10:02 PM   #1
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quality of relays

What do you guys think of the quality of relays that are available? Is there a source of relays that are not some junk that are going to burn out in a few months?

I've been thinking about some modifications for the truck using relays, including the headlight mod and a kill switch, and wiring my electric choke that uses a signal from an oil pressure switch, and perhaps some other stuff. The thing is I don't know if I can trust that some Chinese manufacturer is going to really give me a 20 or 30 amp relay, or are they just going to stamp that rating on the plastic housing of something crappy and call it good. Since everything is now made in China and is cheaply made, I'm hesitant. Needless worry, or am I right to be concerned?

Somewhat related: At one time I read a post where somebody described how to pick wire that was suitable for under the hood, and there were specifications, gauge, and all sorts of other things discussed, but now I've searched to death and can't find it. I recall that it was in a discussion about the headlight relay mod. Any pointers on type of wire?
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Old 01-27-2018, 07:29 AM   #2
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Re: quality of relays

Surprisingly I have been using cheep relays for years and never had one fail . Not to say they cant , but I do keep one in the glove box just in case . Never had to use it .
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Old 01-28-2018, 05:23 PM   #3
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Re: quality of relays

The purpose of the relay determines the type of relay. GM during the 90's into the 2000's use a standard relay with terminal of .250 or 1/4". The "Micro" type uses the metric 280 or 2.80mm width. I get all of the relays from the bone yard, while picking the relay from it's location that I plan to use it. A coolant fan will have a rating of 35-40 amps while a horn relay is rated at 15-20 amps. Also inside the relay, in parallel with the pull-in coil is either a resistor or diode. The resistor will help dissipate inductive voltage spikes when the circuit is shut off, but is primarily used by the PCM or ECM to perform required OBD-II circuit checks using a voltage drop or resistance check. Color, brand and part number will change a GM used several vendors. Check online for specs using the P/N. If you suspect a relay of being faulty, use jumper wires and place them between the socket and relay. Use a good DMM to measure voltage drop across the switching terminals, plugged in, turn on, in the circuit it was intended to function. With current passing thru the internal contacts, the DMM should read below 0.050 Vdc. Try several times until you are happy that the contacts are good. As for custom wiring, remember to use terminal 86 for B+ in, while 85 is ground. Id the relay uses a diode, it matters. Try using fused voltage to power the relay to terminals 85 & 30 or common. Depending on the relay, it can be closed or open to terminal 87 and open to 87a. Yours will very. Always check with your DMM first. ISO 9000 relays have the schematic on the case with common terminal numbering. Controlling the relay using 85 a ground will reduce the amount of current thru the circuit, wire, connectors and switch. Why? The coil is a current limiting device. Using ohms law, a cold copper coil will allow more current to pass thru it, yet it heats up very quickly, reducing current. This increases the life of switches. Remember, in a series circuit, the device is to consume all of the voltage. The DMM across a device, in a working circuit will show almost B+. But each component in the circuit, from B+, wire, connector, switch, device, connector to chassis ground, back to the negative battery will have small voltage drops, but need to be checked. Red led or Blk, either way is the same reading, you just get a (-) symbol in front of the reading.
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Old 01-28-2018, 05:44 PM   #4
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Re: quality of relays

Bosch and Hella come to mind first when I think of high quality relays..

omron and some others are possibly more common but may not be as robust..

you may want to consult with an electronics component house like Mouser or Newark for more technical advise on load and duty ratings, moisture resistance, or whatever criteria you're most interested in..

remember to consider duty cycle, continuous ratings, intermittent ratings, etc. while designing your system..

good luck!
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Old 01-28-2018, 09:52 PM   #5
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Re: quality of relays

Good info, I'm learning. I believe I am interested in finding some suitable general purpose relays. The applications I have in mind will not require much current. One application involves switching on and keeping on the power to the HEI distributor. The relay will be energized by a microprocessor-controlled kill switch circuit. So, the current will be 2 amps and the duty cycle will be continuous while the truck is running. The headlight mod will require about 8 amps and duty cycle will be continuous while the headlights are on. I want to incorporate automatic daytime running lights into my headlight relay mod, so the duty cycle will be continuous while the engine is running and switched on a few seconds after the oil pressure sensor switches.

Last edited by dmjlambert; 01-29-2018 at 11:11 AM.
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Old 01-29-2018, 03:22 AM   #6
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Re: quality of relays

I haven't had issues with relays in the passed. I typically pull a bunch from the junkyard because they usually haven't been swapped out. I know all the ones I have are Omron and no issues.

If you are planning on redoing a bunch of circuits, you should consider a fuse box that contains your relays and fuses. Waytek wire carries a few different versions. I have used 4 of the smaller boxes on 3 different projects and they work great and are completely sealed (cavity plugs, cable seals, and a lid seal).

As far as wiring goes, I typically stick to 12 awg for any power circuit (distributor, starter, etc...), 14 awg for headlights, 18 awg for relay control and marker lights. Unless you are willing to order a bunch of wire, you aren't going to have much of a choice on type of wire. Even most cheap auto parts store wire will hold up well if you protect it from abrasion, damage, and heat. I almost always using wire conduit or loom, and secure it in place.
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Old 01-31-2018, 06:03 PM   #7
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Re: quality of relays

I typically only use TYCO or Omron. I do use some Hella relays although some are now coming from China ��
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