Power source for A12 Fan signal

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2x0
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Power source for A12 Fan signal

Post by 2x0 » Sun Mar 11, 2018 11:24 am

Wondering if there is a limit to how much current should be used as a source to my fan relay controlled through pin A12 on a p28 ecu

Picture attached shows where I have the power (res wire) coming from in the under hood fuse box. It is a battery hot 12V due to how it is wired, my battery positive from the rear hatch feeds straight to the large terminal next to this one.

Is this going to put too much current through the FANC input and fry the ecu? I’m a newb at electrical.

Thanks,
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'91 CRX, B18c1, T3/T4, 17psi on e85, FIC 1000cc's, S300 V3 P28

forevertrj
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Re: Power source for A12 Fan signal

Post by forevertrj » Sun Mar 11, 2018 11:35 pm

current has nothing to do with how close to the battery you are, the relay will have a current is uses in it's internal coil that will trip the actual 12v feed that the Fan is using. you haven't explained enough of your circuit to have a proper answer of what is drawing what current on what wire, also make sure you have a fuse link on your source wire to the relay if you short it you don't want the battery pumping max current down your wire into the chassis and arching.
Let's not make assumptions, please leave as much detail as possible!

2x0
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Re: Power source for A12 Fan signal

Post by 2x0 » Mon Mar 12, 2018 2:41 am

I have it wired similar to the attached schematic, except my relay is on the ground-side of my fan. The red wire shown before is what goes to 86 on the relay then to the ecu A12. It is not fused right now but I will add one.

Thanks,
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'91 CRX, B18c1, T3/T4, 17psi on e85, FIC 1000cc's, S300 V3 P28

2x0
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Re: Power source for A12 Fan signal

Post by 2x0 » Tue Mar 13, 2018 5:22 pm

Does anyone know if this is a safe source to run power into A12 to switch on my relay?
'91 CRX, B18c1, T3/T4, 17psi on e85, FIC 1000cc's, S300 V3 P28

DA9's
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Re: Power source for A12 Fan signal

Post by DA9's » Wed Mar 14, 2018 7:58 am

2x0 wrote:
Tue Mar 13, 2018 5:22 pm
Does anyone know if this is a safe source to run power into A12 to switch on my relay?
You really should post exactly how you have it wired. "Similar" to the diagram you posted above is not good enough, we need to know exactly how it is wired in order to give good advice. As long as you have A12 connected to the #86 on the relay you shouldn't have anything feeding "into" the ecu. The purpose of a relay is to create a gate that will carry the current you don't normally want running across a switch etc. Why not just wire it exactly as shown in the picture? That is the proper way to wire the relay and I assume all the wires are already ran to the relay so it is just a matter of switching the terminals. Maybe I am missing something????

Ok, I just reread your second post and you said the relay is on the ground side of the fan. Does it work as is? If so I assume #30 is grounded, #87 goes to the fan ground and the positive side of the fan shares the same source as the 12V switched that powers the relay?

2x0
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Re: Power source for A12 Fan signal

Post by 2x0 » Wed Mar 14, 2018 9:06 pm

12V goes to fan, then fan ground goes to #30 then #87 is grounded. 12V to #86 then #85 to ecu is wired just like the diagram.

It does work like this, but last time the relay started fluttering so I either have a bad connection somewhere or (hopefully not) could have damaged ecu possibly? Just trying to rule that out.
'91 CRX, B18c1, T3/T4, 17psi on e85, FIC 1000cc's, S300 V3 P28

DA9's
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Re: Power source for A12 Fan signal

Post by DA9's » Wed Mar 14, 2018 11:09 pm

I would start by looking at the ground side of everything to make certain that all your connections are clean and solid. Unless there was a total failure with the relay (which I have never seen) I'd bet the ecu is fine.

2x0
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Re: Power source for A12 Fan signal

Post by 2x0 » Fri Mar 16, 2018 6:06 am

Thanks! Today I am going to go through every connection and install a fuse on the hot side.

I also realized that I had my max speed for the fan control set to 45mph. I wonder if I was driving right around that speed if it could’ve caused the relay to click on and off that quickly. Going to try increasing it to 100mph or something. And datalog in case it happens again.
'91 CRX, B18c1, T3/T4, 17psi on e85, FIC 1000cc's, S300 V3 P28

DA9's
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Re: Power source for A12 Fan signal

Post by DA9's » Fri Mar 16, 2018 7:37 am

No problem, post back with your results. Good luck!

Just out of curiosity, why did you opt to put the relay on the ground side rather than the positive as shown in the wiring schematic? Do you have the stock source powering (+) the fan (ie the factory wiring and thermo switch) and are using the relay and A12 to override with the Hondata?

2x0
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Re: Power source for A12 Fan signal

Post by 2x0 » Fri Mar 16, 2018 12:48 pm

I used a different schematic someone drew up for me on honda tech. It also made more sense to wire this way, since I could put the relay inside close to the ecu and my ground to the chassis, for less wiring to fish around in the engine bay.

My fan is wired positive straight from the battery basically. OEM fan source is not to be found after the previous owner swapped the engine and had already rewired everything, so my fan circuit is now completely new/custom.
'91 CRX, B18c1, T3/T4, 17psi on e85, FIC 1000cc's, S300 V3 P28

2x0
Posts: 87
Joined: Sat Feb 04, 2017 6:51 pm

Re: Power source for A12 Fan signal

Post by 2x0 » Fri Mar 16, 2018 5:18 pm

Everything working good now. I cleaned my grounds at the thermostat housing, and increased my max speed for fan to 158mph. It cycled several times today with no drama.

Thanks for the help
'91 CRX, B18c1, T3/T4, 17psi on e85, FIC 1000cc's, S300 V3 P28

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