Need Sparate Fan Control Switch

[WaltH]

I would like to have a separate, manual switch to turn on the engine cooling fan when I think it is needed. This would happen when I am in a traffic jam, or when I am sitting too long with the engine running, or when traffic is slow. I would turn off the switch when I felt it was no longer needed. I had such a switch on one of my Harleys (police fan) and it worked beautifully.

In order to get this job done I need some advice from the Spyder community. Please feel free to tell me anything you think I should know.

I could run the output wire from my switch to the triggering terminal on the fan control relay. This would cause the relay to close and the fan to start running. Normally, the triggering voltage is provided by the Engine Control Module (ECM) in response to a reading of the engine temperature. With this approach I am concerned that my independent voltage may cause a back-feed to the ECM which could harm it in some way or at least get it confused. I could possibly prevent back-feed by placing a diode in the line to the ECM. I am concerned that this could change the impedance in the line which would be noticeable to the ECM with unknown results.

Alternatively, I could run the output wire from my switch directly to the fan. This would require a heavier line. When the ECM closes the relay I could possibly have a potential back-feed situation. I don’t know if this is possible, or not. I could put a diode upstream in the line coming from the relay. I don’t know what, if any, the implications of this would be for the ECM. I don’t know if there are diodes that would handle the required amperage. The fan relay is paired with a 15 amp fuse.

Obviously, I need some advice. Please help.

 

[Big Arm]

Alternatively, I could run the output wire from my switch directly to the fan. This would require a heavier line. When the ECM closes the relay I could possibly have a potential back-feed situation. I don’t know if this is possible, or not. I could put a diode upstream in the line coming from the relay.
.

I think you got the answer right here

 

[Lamonster]

On my blower bikes I would run a wire from the sending unit to the switch to ground. Worked great for me.

 

[Magic Man]

On my blower bikes I would run a wire from the sending unit to the switch to ground. Worked great for me.

Wow Lamont I did not know you had a moped?

MM

 

[Firefly]

I think you got the answer right here

Just put a relay in line that will cut off your extra power line whenever the ECU turns the fan on itself - that way it won't matter if you leave your manual fan switch turned on or not.

 

[mjw930]

Just put a relay in line that will cut off your extra power line whenever the ECU turns the fan on itself - that way it won't matter if you leave your manual fan switch turned on or not.

I don't think that would work, power is applied to the fan relay at all times, the ECM supplies ground to close the relay and switch power to the fan.

Like Lamont said, all you need to do is run a separate switched line to the ECM side of the fan relay to simulate the ECM applying ground. I might consider using a small diode to prevent a ground loop back into the ECM when the switch it on and the ECM also supplied ground but that's all you would need.

The beauty of this is you can run the fans after you shut the ignition off to help cool the radiator too.

 

[Rando]

I would like to see NMN come up with a "plug-n-play" type of device. How about it MM?

 

[Firefly]

I don't think that would work, power is applied to the fan relay at all times, the ECM supplies ground to close the relay and switch power to the fan.

Like Lamont said, all you need to do is run a separate switched line to the ECM side of the fan relay to simulate the ECM applying ground. I might consider using a small diode to prevent a ground loop back into the ECM when the switch it on and the ECM also supplied ground but that's all you would need.

The beauty of this is you can run the fans after you shut the ignition off to help cool the radiator too.

I'll have to check the schematics - but it sounds like you're saying the negative is the switched side? That would be strange - but I've found some pretty goofy things on the Spyder wiring.

Whether it's on the positive or negative side - you could isolate the new switched power feed with a simple relay and toggle switch. Avoiding a loop would be my main concern.

 

[WaltH]

I don't think that would work, power is applied to the fan relay at all times, the ECM supplies ground to close the relay and switch power to the fan.

Like Lamont said, all you need to do is run a separate switched line to the ECM side of the fan relay to simulate the ECM applying ground. I might consider using a small diode to prevent a ground loop back into the ECM when the switch it on and the ECM also supplied ground but that's all you would need.

The beauty of this is you can run the fans after you shut the ignition off to help cool the radiator too.

Is it possible that the ground loop current might go in the other direction, that is, out of the ECM when both grounds are in use simultaneously? My diode would not prevent this from occurring, assuming it is possible.

 

[Firefly]

I don't think that would work, power is applied to the fan relay at all times, the ECM supplies ground to close the relay and switch power to the fan.

Like Lamont said, all you need to do is run a separate switched line to the ECM side of the fan relay to simulate the ECM applying ground. I might consider using a small diode to prevent a ground loop back into the ECM when the switch it on and the ECM also supplied ground but that's all you would need.

The beauty of this is you can run the fans after you shut the ignition off to help cool the radiator too.

Okay - thinking straighter today--- I get what you want to do - but the looping is a concern - but the idea of a simple switched line to the ECM side would be a very easy install.

To totally avoid any looping, you could have have the toggle switch run the extra ground from ECM to the fan - but throw a relay in so that when the 'real' ground connection from the ECM trips the stock relay it would turn power on the new relay and thus cut your new ground connection off.

But a diode setup should work also - and would be easier.

 

[WaltH]

To summarize what I have learned:

The fan relay activates when the ECM provides a ground connection for the triggering side of the relay. The positive input connections on the relay are always hot.

One solution would be to provide a switched ground connection for the relay to substitute for the ECM. To prevent a possible ground loop from occurring, a diode should be placed in the new ground line.

An alternative solution would be to run an independent switched and fused hot line to the positive output connection of the relay (or anywhere in between it and the fan) to proved current for the fan whether or not the relay is activated. The relay itself would isolate the new line from the ECM in all cases. No diodes would be necessary.

I am not clear as to whether I would need one or two diodes, and where they would go. Should the diode be placed in the new ground line, the line to the ECM, or both?

I would appreciate it if someone would clarify the location of the diode (s) and correct any mistakes in my summary.

I am grateful for all of the advice in your postings. Having you guys on my side is better than having a smart brother in-law.

 

[Firefly]

"An alternative solution would be to run an independent switched and fused hot line to the positive output connection of the relay (or anywhere in between it and the fan) to proved current for the fan whether or not the relay is activated. The relay itself would isolate the new line from the ECM in all cases. No diodes would be necessary."

This would be my plan of action - keeps it simple.

Does the Hot from the ECM stay hot even with Spyder off?
I would want the manual fan hot lead to power down with the bike in cause I forgot to turn it off.


If the other side of the pole on the output of the relay is open (would think it should be) then you can just hook the new hot (manually switched) lead to that and you're as good as gold - like you said the relay would simply change from the manual HOT wire to the ECM hot wire when the relay trips - automatic isolation.

 

[Roaddog2]

Wow Lamont I did not know you had a moped?

MM

:roflblack::roflblack:no separate fan switch for me :lecturef_smilie:

 

[Lamonster]

:agree::lecturef_smilie::yikes:

 

[chris56]

maybe easiest solution for crazy ideas (like mine..)
buy a new (second) fan install it "over" the original one ..longer screws..
and switch it on/off without changing something on the existing system..
chris -

 

[mjw930]

I'll have to check the schematics - but it sounds like you're saying the negative is the switched side? That would be strange - but I've found some pretty goofy things on the Spyder wiring.

Whether it's on the positive or negative side - you could isolate the new switched power feed with a simple relay and toggle switch. Avoiding a loop would be my main concern.

Switching ground through the ECM seems to be common practice with European wiring schemes, I've seen my share of odd grounding systems on older Porsche's.

I double checked and the + side of the fan relay is always hot, it's not switched. The only way to make it fool proof would be to power a switching relay from the ignition output so when you turn off the bike the relay goes to a normally open condition.

 

[chopster]

maybe easiest solution for crazy ideas (like mine..)
buy a new (second) fan install it "over" the original one ..longer screws..
and switch it on/off without changing something on the existing system..
chris -

I simply CNC'd new brackets, bolted in a Perma-Cool hi-performance fan, added a toggle switch and relay and disconnected the factory fan. New fan is not tied into the factoy electrical system at all. When my digital water temp. gauge reads 175 degrees, I flip the switch and turn the fan on. In low 90 degree weather, I seldom see four bars except in heavy stop and go traffic-typically runs at three bars. 2K miles with this setup and no error codes or issues, just a cool running Spyder.

Chopster

 

[chasbadger]

"An alternative solution would be to run an independent switched and fused hot line to the positive output connection of the relay (or anywhere in between it and the fan) to proved current for the fan whether or not the relay is activated. The relay itself would isolate the new line from the ECM in all cases. No diodes would be necessary."

This would be my plan of action - keeps it simple.

Does the Hot from the ECM stay hot even with Spyder off?
I would want the manual fan hot lead to power down with the bike in cause I forgot to turn it off.


If the other side of the pole on the output of the relay is open (would think it should be) then you can just hook the new hot (manually switched) lead to that and you're as good as gold - like you said the relay would simply change from the manual HOT wire to the ECM hot wire when the relay trips - automatic isolation.

It sounds like you know electronics quit well. so what you are saying to do is run a hot wire with a inline fuse to the one side of the toggle switch, then a wire from the toggle switch to the hot wire between the the relay and fan? that way you would still have the convience of auto plus manuel
as well. also how would I know witch wire is the hot from the relay? I could run the bike till the fan comes on but that would make it to hot to work on for some time. or am I missing something?

 

[rleathen]

CHASBADGER did you ever get a response to your question about running a fused and switched hot wire to the hot wire of the fan between the fan and relay. This is the way I am considering doing it and just wanted to know if you received any comments that this is the right way to go.

 

[Tom in NM]

Well . . . . .

Wow Lamont I did not know you had a moped?

MM

. . . . Yes, it was a Moped BEFORE he started modding it.

Tom