EFI fan relay driver polarity change question?
#2443919
01/31/18 07:31 AM
01/31/18 07:31 AM
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Joined: May 2008
Posts: 5,399 Aurora, Colorado
451Mopar
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Posts: 5,399
Aurora, Colorado
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What I have: FAST XFI 2.0 EFI controlling cooling fans. The EFI module provides a sink (negative) to ground output signal. What I am working with: Cooper Bussman Relay/Fuse module with five fused 35 Amp Relays and an additional 5 constant hot fuses. The Problem: The Relay/Fuse box is designed so the relays are triggered with a high/hot +12 volt signal, and the ground side is designed into the negative bus bar. I think I could make the negative bus bar a positive bus bar and the relays will activate on the low side signal, but I also wanted to use the relays to drive the Low and High Beam head lights which would be high side triggered, so I need a way to invert the signal to the relay trigger?
I know of many way to do this in theory, like using another relay, or a transistor driver circuit, but is there a better / easier way?
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Re: EFI fan relay driver polarity change question?
[Re: 451Mopar]
#2443927
01/31/18 08:35 AM
01/31/18 08:35 AM
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Joined: Jan 2005
Posts: 2,540 Milwaukee WI
TRENDZ
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Milwaukee WI
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Cut the bus bar. Divide it as you need. Solder a wire or stud to the cut off section, and power it from one of the fused side circuits. There is a potential problem with doing this though. Some relays have an internally configured suppression diode. Since you will be firing the coil from a reversed polarity standpoint from which it was designed, the suppression diode wont do it’s job. (if it is so equipped)and will short circuit. Using a non suppressed relay will allow doing this. The diode is there to prevent flyback voltage from making its way back to the control unit. You could easily add suppression diodes to the bar itself in the required polarity. Google “suppression diode in relay” for more detail on why/ what/ how.
"use it 'till it breaks, replace as needed"
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Re: EFI fan relay driver polarity change question?
[Re: TRENDZ]
#2444029
01/31/18 01:35 PM
01/31/18 01:35 PM
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Joined: Jan 2003
Posts: 7,490 Minnesota
Hemi_Joel
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. Some relays have an internally configured suppression diode. Since you will be firing the coil from a reversed polarity standpoint from which it was designed, the suppression diode wont do it’s job. (if it is so equipped)and will short circuit. Using a non suppressed relay will allow doing this. The diode is there to prevent flyback voltage from making its way back to the control unit. You could easily add suppression diodes to the bar itself in the required polarity. Google “suppression diode in relay” for more detail on why/ what/ how. I found out about these things the hard way last year when wiring my coupe. After years of using relays that had no polarity preference, somehow I ended up with some of these diode relays. My fuel pumps didn't work because the polarity was backwards. Reverse polarity instantly burns up the relay. I burned up up about 3 relays before I figured it out. Beware of the diode relay!
[img]http://i.imgur.com/boeexFms.jpg[/img]31 Plymouth Coupe, 392 Hemi, T56 magnum RS23J71 RS27J77 RP23J71 RO23J71 WM21J8A I don't regret the things I've done. I only regret the things I didn't do. "Wise men talk because they have something to say; fools because they have to say something. ~ Plato"
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Re: EFI fan relay driver polarity change question?
[Re: TRENDZ]
#2444046
01/31/18 02:21 PM
01/31/18 02:21 PM
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Joined: May 2008
Posts: 5,399 Aurora, Colorado
451Mopar
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OP
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Joined: May 2008
Posts: 5,399
Aurora, Colorado
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Cut the bus bar. Divide it as you need. Solder a wire or stud to the cut off section, and power it from one of the fused side circuits. There is a potential problem with doing this though. Some relays have an internally configured suppression diode. Since you will be firing the coil from a reversed polarity standpoint from which it was designed, the suppression diode wont do it’s job. (if it is so equipped)and will short circuit. Using a non suppressed relay will allow doing this. The diode is there to prevent flyback voltage from making its way back to the control unit. You could easily add suppression diodes to the bar itself in the required polarity. Google “suppression diode in relay” for more detail on why/ what/ how. The relays do not have the suppression diodes, so no issue there. The Relays are PICKER PC785-1C-12S-R-X http://www.pickercomponents.com/pdf/Relays/PC785.pdfThe relay bus is molded into the block and connects to pin 86 of the relays, and there is no easy way to cut the bus. This is an EATON #15305-2-6-4 https://www.mouser.com/catalog/specsheets/eaton_01242018_1530X-X-X-X-SALES_RevA.pdfI got this pre-built, wired and populated with the relays and fuses from Amazon https://www.amazon.com/gp/product/B01FWILL20/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1Link to the sellers description: https://www.teamconcours.com/#!/Universal-Waterproof-Relay-Fuse-Distribution-Box-Cooper-Bussmann/p/65063101/category=13963121
Last edited by 451Mopar; 01/31/18 02:25 PM.
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Re: EFI fan relay driver polarity change question?
[Re: 451Mopar]
#2444123
01/31/18 05:11 PM
01/31/18 05:11 PM
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Joined: Jan 2003
Posts: 8,027 Tulsa OK
Bad340fish
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Tulsa OK
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I heard the newer Holley untis can switch polarity which would be a nice feature. My mega squirt triggers the ground for everything so got an oversized relay panels that was half ground and half positive trigger relays because I didn’t know exactly what I would need since I was redoing almost the whole car.
68 Barracuda Formula S 340
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Re: EFI fan relay driver polarity change question?
[Re: 451Mopar]
#2444761
02/01/18 05:59 PM
02/01/18 05:59 PM
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Joined: Jan 2003
Posts: 27,421 Balt. Md
383man
Too Many Posts
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Balt. Md
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It don't surprise me as I know when Mopar started using TIPM modules (Totoally Indegrated Power Module) they started using high side drivers which as a dealer tech I had not seen that from the factory before on factory cars. They would just ground the relay coil all the time and then the high side drivers send 12 volts to the other side of the relay coil to turn on that circuit. They started doing this on a few circuits instead of controlling the ground which I thought was the easier way to control a circuit. Ron
Last edited by 383man; 02/01/18 06:00 PM.
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