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  1. #1

    Default Relay WTF In Regard To Powering A Wideband

    Okay, I am officially stumped. My Innovate wideband instructions says you're supposed to power and ground it straight from the battery by way of a relay such that it will only power on when the car is on. I had a new relay kicking around, so I thought I would use it. It's single pole, double throw, whatever that means.

    Anyway, what they want you to do is have one of your switched power circuits run the coil side of the relay. Okay, seems easy enough. So, I mocked it up and tested it, and it did power up the wideband when I turned the key to on. So then, I made the connections permanent and put the terminals into a nice plastic connector so everything would stay together and be reliable. Hooked the battery back up, turned the key on and.... nothing. I had hooked the switched power radio circuit to the relay coil. I checked the radio fuse, and it was popped. This is fuse 11, that it shares with nothing else. Replace fuse, try again, fuse is popped.

    Well, I don't know that much about relays, maybe I did something wrong. Here's how I had the relay:

    85 - Ground
    86 - Pwr from radio circuit
    87 - run to the Red power circuit on the wideband
    30 - Power straight from the battery

    Found the page below.



    Okay, does the relay have a diode?



    Yes it does. So, what side is what?



    So, I'd had the switched power from the radio circuit on pole 86 (since it had a plus by it and everything, but how silly of me ), so that wasn't right. I thought I would try switching 85 and 86. Hooked the power up, turned the key on and it popped the &%$# fuse again! I have NO idea what the problem is at this point.

    Does it maybe have something to do with the amp rating of the relay? It's a 30 amp relay, the fuse 11 radio circuit is 15 amps, and the wideband power circuit is 5 amps (THAT fuse never blew, by the way).

    Should I not have run the negative side of the relay coil to ground?! Is that it?! I've done relays like this in the past and never had a problem.
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
    '17 Ford Focus ST
    '14 Ford Fusion SE Manual

  2. #2

    Default

    When I used to mess with relays a lot, I bought one of these

    https://www.amazon.com/dp/B002MCX6LY...osi&th=1&psc=1
    79 Zephyr, 4.6L 4v/4r70w swap, with team z front and rear suspension, 8.8 and upgraded brakes and coil overs. Running Holley Terminator X Max.

  3. #3

    Default

    You had it right the first time, positive to pin 86. The diagram that shows negative at the cathode is assuming that you want the diode to conduct. In this application you do not want the diode to conduct when you apply power to the relay. The diode is meant to conduct when the relay is turned off, shorting the flyback voltage from the coil to ground.

    If you unplug the relay, does the fuse still blow? That would indicate a short in the wiring.

    The 30 amp rating of the relay is for the contacts. The coil itself should only draw 0.04 amps (or so).

    If you are daring, with the relay removed, jumper pin 86 directly to the positive battery terminal and pin 85 to the negative battery terminal. If the relay is working correctly you should hear a little "click". If it is internally shorted then it may explode or melt the jumper wires. Uh... on second thought you may want to try this test with a fuse inline.

  4. #4

    Default

    In your application, the diode is not necessary. Try popping the cover off the relay and clipping the diode out of it. The diode is probably bad now anyway since you hooked it up backwards. Check the relay coil with an ohm meter before hooking it to a battery to test it. Should be around 100 ohms or more.

  5. #5
    FEP Senior Member
    Join Date
    May 2016
    Location
    Lake City Pa 16423
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    510

    Default

    When diodes fail, they will fuse and conduct power like a dead short. You can test the coil side with an ohm meter to verify if it is shorted. You will see a very low ohm reading just as if you touch the meters probes together. Just try removing the relay to see if there is a short, If none, than try another relay.

  6. #6

    Default

    That's exactly what I was thinking was that it was acting like a short.

    You had it right the first time, positive to pin 86. The diagram that shows negative at the cathode is assuming that you want the diode to conduct. In this application you do not want the diode to conduct when you apply power to the relay. The diode is meant to conduct when the relay is turned off, shorting the flyback voltage from the coil to ground.
    That makes a lot of sense. I'd seen something about that reverse voltage elsewhere. Seems like a good thing that diode is there for that reason. I don't need a bunch of voltage going into my radio. If that diode is fried, I think I will just get another relay. I will test it. Maybe not blow myself up though.

    What I don't get though, is why it worked the first time I had it hooked up right, but not the second time. I think maybe the difference was the first time, I did not have my radio plugged in, but the second time, I did. I'm not 100% sure of that though.

    I'll do more testing and get back to you.
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
    '17 Ford Focus ST
    '14 Ford Fusion SE Manual

  7. #7

    Default

    Quote Originally Posted by ZephyrEFI View Post
    Seems like a good thing that diode is there for that reason. I don't need a bunch of voltage going into my radio.
    The diode is only necessary when the relay is being switched by a transistor or tiny micro-switch that can be damaged by the flyback voltage. Automotive electrical systems are notoriously "noisy" so your radio has filtering built in to deal with the voltage spikes.

  8. #8
    FEP Super Member gr79's Avatar
    Join Date
    Jun 2009
    Location
    SE Michigan
    Posts
    5,141

    Default

    Am not triggering my added accessory relay with any wire directly with KO or acc power.
    Is triggered indirectly via a switch.

    Circuit plan:
    Add a second fuse panel for more accessories. Control the panel with a relay. Mount behind glove box.
    Power this second fuse panel direct from battery and fuse for safety. Panel power on/off control by relay.
    Control relay on/off with a switch.
    Use existing Ford Premium Sound push-pull under dash switch, with AMP LED, for relay low current on/off trigger control.
    Idea was copy basic Bosch fog light power circuit wiring. Fog lights were already installed and work good.

    Circuit design:
    Instead of fog lights, relay powers an eight spade fuse panel box for accessories. Radio, amp, two power points.
    Similar to fog lights, wanted to turn the second fuse panel power completely on and off at any time via a relay.
    Repurpose Ford amp switch to turn a new relay on/off.
    Amp switch's 12v power source wire or fuse circuit feed for relay trigger is unknown (forgot).
    Amp switch power is KO or ACC position dependent.

    Parts description:
    4 pin Dorman 30a 84601 relay with relay pigtail. Has no diode. Has tab with screw hole for mounting.
    30a Maxifuse with holder and cover, located near battery, weather protection cover.
    Buss 8 fuse panel
    Ford Premium Sound push-pull switch with matching LED light panel.

    Operation:
    Relay trigger switch off- no power to trigger the relay. No power to accessory.
    Relay trigger switch on- sends trigger power to relay. Relay turns accessory on.
    The 'AMP' LED is working good as a running indicator and diagnostic of 12v power to relay circuit.

    Connections:
    30- Receives fused high current 12v from battery
    87- Supplies high current 12v to accessory (in my case, the extra accessory fuse box).
    87a- n/a, not used. Used to turn accessory off if relay is energized. Opposite action of terminal 87.
    85- Receives 12v trigger power from low current switch. Controls high current 30/87 (or 87a) circuit.
    86- Grounded

  9. #9

    Default

    Couple of test results:

    turn on key without relay DOES NOT blow fuse.

    Put relay in again with power at 86, ground at 85, fuse DOES blow.

    Relay reads .3 ohms across the coil with leads in either position.

    Sent from my SM-G960U using Tapatalk
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
    '17 Ford Focus ST
    '14 Ford Fusion SE Manual

  10. #10

    Default

    I tested the coils of a couple other relays I had, and they were 83 and 67 ohms. I put one in my connector and the radio and wideband powered up successfully!

    So, here's the question. Is that not a good place to get my switched power?

    Sent from my SM-G960U using Tapatalk
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
    '17 Ford Focus ST
    '14 Ford Fusion SE Manual

  11. #11

    Default

    It’s been a few years since I installed my LC-1, I don’t recall using a relay with that unit.
    79 Zephyr, 4.6L 4v/4r70w swap, with team z front and rear suspension, 8.8 and upgraded brakes and coil overs. Running Holley Terminator X Max.

  12. #12

    Default

    Oh you know, I just like to make things complicated for myself.
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
    '17 Ford Focus ST
    '14 Ford Fusion SE Manual

  13. #13

    Default

    Are you using an LC-1?
    i thought you were using something newer
    79 Zephyr, 4.6L 4v/4r70w swap, with team z front and rear suspension, 8.8 and upgraded brakes and coil overs. Running Holley Terminator X Max.

  14. #14

    Default

    It's an MTX or something.

    Sent from my SM-G960U using Tapatalk
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
    '17 Ford Focus ST
    '14 Ford Fusion SE Manual

  15. #15

    Default

    Okay, so I ended up changing the switched power circuit to one of the airbag module power. Only the wiring is left from that system, so it's a good choice, I think. And I'm keeping the Ford relay in there. I'm not sure where I got it, but I think it's from a time when I pulled all the fuses and stuff out of a car in the junkyard.

    I think the airbag circuit is a bit safer because there's less chance of radio interference, anyway. Things seem to be all good now though! Thanks for the help, all!

    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
    '17 Ford Focus ST
    '14 Ford Fusion SE Manual

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