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Guest Message by DevFuse
 

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clever electric fan override


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39 replies to this topic

#1 MilesFox

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Posted 12 February 2004 - 06:47 PM

the electric fan is turned on by a thermoswitch in the radiator, near the drain plug

when it reaches a set temp, the switch closes and thus trips the fan relay

but what if you wnat to turn the fan on yourself? easy. on the 2 wires that go to the switch, splice in 2 wires, each to the 2 terminals on a toggle switch

you can turn the fan on , and if the temp switch kicks on, the fan is on anyway

if you forget to turn the fan on, dont worry, the thermo switch will still come on

an easy low amp wiring solution, no relays involved

#2 nutt7

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Posted 12 February 2004 - 08:29 PM

I was just going to do that on my wagon...simple.effective.failsafe. genious!

#3 Skip

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Posted 12 February 2004 - 09:06 PM

This is not a true statement

"when it reaches a set temp, the switch closes and thus trips the fan relay"

The thermoswitch in the radiator side tank does NOT control a relay.

It is a direct connection from the fan fuse (#15) to the radiator fan, through the thermoswitch to ground.
(Did you ever see on an EA81 rad. the grounding strap?)

This means it carries the entire current of the fan (which can equal up to 10 amps). Not, as you allude, a small relay coil current.
This is one reason why the thermoswitches go bad so often.

If some one takes your sage advise, thinking it is just controlling a relay and runs a thin gauge wire, it could over heat and - well possibly cause other problems.
Clever, I don't think so -- genius - hardly
foolhardy - more like it.
A relay can be added as I have done,
with an over ride switch plus an ON light to observe when the fan is running.

If anyone questions my statement please email me, I will provide you with a wiring diagram from the FSM


#4 MilesFox

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Posted 12 February 2004 - 11:14 PM

skip, i must PROVE YOU WRONG, as we have a WORKING EXAMPLE in the RX

the thermoswitch wires off the radiator, is pretty much "shorted" by a toggle switch, and has an in-line 20A fuse

the thermoswitch has some 18ga wire, and the FAN wires are FATTER. no high draw thru this. and it will kick the fan on in the ACC position

#5 nutt7

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Posted 12 February 2004 - 11:18 PM

Skip, thanks for lookin out, I guess thats what the board is for. Glad I didnt do it yet, I have the diagrams at home so I will derive a manual circuit based on that info...I guess your sig proves true. thanks again.
Miles, can you get a diagram to show how you say this will work?
thanks
eric

#6 MilesFox

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Posted 12 February 2004 - 11:27 PM

skip, lets see the schematic for comparison, i devised this circuit from what i have read from the board, how the fan works

works for the RX no problem

#7 Snowman

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Posted 13 February 2004 - 02:06 AM

Miles, I have to side with Skip on this one. I looked at this quite thoroughly when wiring a manual switch on mine, and unless your car came from the factory different from mine, the thermoswitch directly controls the current through the fan with no relay or anything. In the future, I think I may hook it up with a relay just because I think that would be a better setup, but here is what mine currently is, with the only thing changed from stock being the addition of a toggle switch:
Posted Image

#8 MilesFox

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Posted 13 February 2004 - 02:26 AM

the way i have it hooked up, i am using thesame gage wire that is on the thermoswitch plug, something like an 18ga (by eyeball), so if the circuit has the same size wire, whats the problem, and the toggle switch is fused

ok, if there is no relay(i assumed) my bad. but the toggle is doing the same thing as the thermo switch in the "same location" as on a schematic

either way, the fan still has fatter wires on its plug

87 RX MPFI TURBO

#9 Snowman

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Posted 13 February 2004 - 02:51 AM

Okay, I can see doing this as long as you are sure that the wire you are running is at least as big as the wire that's already there. However, I would advise running larger gauge wire for a run that long to avoid as much resistance as possible.

Skip, how did you hook up the indicator light?

#10 MilesFox

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Posted 13 February 2004 - 09:32 AM

the way we have ours, same size wire, 20 amp fuse. maybe we should go 15 if anything

the switch is one of the LIGHTED variety, but the way we have it connected, of you ground the switch, the fan comes on. kight wont work that way.

but i had the idea of an INDICATOR on the dash, connected to the hot side of the FAN ITSELF, so whenever the fan is getting juice, the lught comes on. ground the light to the body

#11 Skip

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Posted 13 February 2004 - 09:56 AM

Back to electronics 101 Donald.
The fan always has +12V to it any time the key is on.
Lots of good that light will do... it will tell you the key is on.

In reference to the factory fan/thermoswitch wiring. I have seen melting and other indicators of too much current on the factory wiring. I guess it is possible that dirt, dry bearings or other debris could cause the fan to "drag" thus increasing the currant draw.
I agree with Snowman on his assessment, looks like he made it through E 101 just fine.

I use an auxilary relay mounted in the area of the thermoswitch.
This relay is fed a 12 v fused hot wire from my main auxilary power system (which is connected to the battery through a large amperage circuit breaker)
The relay contacts control the fan.
The thermoswitch and the dash switch control the relay coil.
(much like Donald thought it worked)
This affords a place to pick up a switched hot wire for operating the dash indicator.
BTW
I don't buy into this "trashwagon" Trash.
If you have seen my dashboard I believe it speaks for itself.
All wiring diagrams available upon request.
Hope this helps avoid a fire or worse.


#12 MorganM

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Posted 13 February 2004 - 12:22 PM

I spend the extra time and effort to wire up a relay under the hood and install a lighted switch in the cabin. Bleive I used your old schematic Skip?

Anyway I'm very happy with the results. I just completly bipased the thermo switch since 2 of them had gone out.

#13 MilesFox

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Posted 14 February 2004 - 06:13 PM

Originally posted by Skip
Back to electronics 101 Donald.

I don't buy into this "trashwagon" Trash.



Skip, that is out of line. let it be known that i AM EDUCATED in AUTOI ELECTRICS. so just cause i didnt know something doesnt mean i cant figure it out.

and this was on the RX, not the trashwagon
as far as trashwagons go, and with my posts telling how i did things, that is what works for me

surely i have enough sense to wire something that would not be a hazard, you just dont know. suppose if you have SEEN MY PROJECTS IN PERSON, you would think differently and see that i know what im doing

and besides, wheres your ej22 project. its all about how crative you can be, rather than how much book knowledge you know. at least im driving my projects, cause they work!

#14 bushbasher

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Posted 15 February 2004 - 02:20 AM

Skip take your anger or bouts of poor character out on something other than the message board. I agree that there is no relay, however I don't see any problem running wires to a switch to cut current on/off when you want to. I have done this same thing to my subaru. Since the wires being run are both grounds, accidental contact with any other ground will only cause the fan to be permanantly grounded at the most. To create a short circuit, one of the wires would have to somehow come in contact with another hot wire. Which is pretty hard to do. Even if it manages to find a positive wire, it still isn't a huge deal because the fan circuit is already fused from the factory. Of course nothing is ever failsafe, but I'm pretty confident that this is safe enough.

BTW motors, switches, and relays are not electronic, they are electrical. Electronics involves the use of semiconductors.

-I've edited out some more offensive things I said, I was having a "bout of poor character" myself. I guess I can't blame ya, and I apologize

#15 Rooinater

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Posted 15 February 2004 - 03:16 AM

no, by wiring a switch straight into it you are asking for some trouble. not major trouble but your switch to open up and not work. or worse yet short across and always be on no matter switch position.

is it going to kill you no. is it gonna wreak a switch yes it can. do to running high amps through a toggle switch. they tend to fry switches. over time and prolonged usage. other than that it's fine. that's why using a relay on a higher current system is a preffered method to do this. relays hold the current a lot better. by using a low current sytem to use the switch in. so that the switch does not fry. and using a relay to close the switch and handle the grunt of the current running to the fan. it's not as straight forward but better for overall longevity and current handling. i've fried 30amp switches on these fans. but not any 30amp relays. do to the way they are designed.


Yes, motors, switches and relays are electronics, they are part of electrical systems, but are electronics.

Sorry bushbasher. i got 2 screen names mixed up

#16 bushbasher

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Posted 15 February 2004 - 03:21 AM

hey no problem. Yeah the switches can stop working because they can get carbon deposits from being switched on and off and getting little electrical arcs on the contacts. The difference between the study of electronics and electrics is that electronics involves semiconductors. Sure motors and switches are electronic in nature, as in they deal with electrons, and motors and switches can be involved in electronic circuits, but there is a distinction. I play around with electronics and electrics alot, lifegaurding is just a part-time job :D

#17 Rooinater

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Posted 15 February 2004 - 03:41 AM

i play around with them 14+ hours a day. and even more when the gov't loves me enough to make me work even longer!!

snowman-
by lowering resistance you automatically increase the amperage. which can increase the heat on the switch. the more resistance in the wires the less amps that will travel through the switch. so matching the wires is a real good idea if not using a relay.

as for making an indicator that's easy. find the 12v bulb you want to use. or colored indicator from radio shack. on the gound side of the switch splice in the indicator. that way when the circuit is completed you'll create a parrallel circuit and the light bulb will light up. when the switch is off no power will travel to the indicator

#18 Turbone

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Posted 15 February 2004 - 04:03 AM

A SC is a switch, it just does it in pulses of what? Magic Juice? No, electricity.
Most of your CNC machines are run by computers, but with out electricity to run things, its a dead weight.
Better keep your day job BB.

#19 Snowman

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Posted 15 February 2004 - 04:10 AM

Rooinator:

Increasing the size of the wires over the bare minimum needed to pass the current will not increase the amperage (this only increases the maximum POTENTIAL current flow). The wires themselves are never supposed to have any resistance. If you were to use wires small enough to create enough resistance to lower the current flow, not only would the fan slow down because of the reduced current, but the wires would heat up and probably melt their casings.

Thanks for the help with the indicator though. I'll set it up like that once I wire in a relay (currently, I have the thermoswitch and the high-amp toggle switch separate, so i couldn't do it now). I can't believe I didn't think of that:rolleyes: .

#20 Rooinater

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Posted 15 February 2004 - 04:29 AM

i'm not talking about a high increase in current. only small amounts. but enough to tax out that switch even more. if you want i'll get out the formulas for when you change resistance. even by minute amounts you will increase the current. wiring has resistance wether it's supposed to or not. they teach you not to worry about it. in classes. i remember my auto electronics courses. you assume that there is no resistance. but in reality there is some. i'm not saying it's gonna jump it sky high and fry it instantly. it will allow for more current and a little more heat. not tremendous but enough. to help tax out the switch.

Resistance goes up = Amps go down = voltage stays constant
Resistance goes down = Amps go up = voltage stays constant
resistance goes down = amps stay the same = voltage will change

i'll get the actual formulas for it if i can find them or need to.

#21 Snowman

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Posted 15 February 2004 - 04:37 AM

Are you talking about I=E/R?

#22 Rooinater

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Posted 15 February 2004 - 04:40 AM

yes and no. there's a couple other ones too that show the relation. but yes that's one way to look at it.

#23 bushbasher

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Posted 15 February 2004 - 05:06 AM

sounds like i=e/r. Turbone, electronics involves semiconductors. Of course that involves electricity, semiconductors work on the principles of electricity. But that does not mean that electricity involves electronics. That is what I am saying. A circuit is electrical if it uses electricity and controls the electricity through mechanical means such as relays and switches. A circuit is electronic when it uses electricity and uses a semiconductor to control the flow of electricity. If I couldn't figure that out It'd be hard to imagine that I'm playing with PIC-chip based robotics or building guitar effect pedals!

#24 Skip

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Posted 15 February 2004 - 08:28 AM

Nobody has mentioned the back EMF generated by the collapsing magnetic field in the relay coil.
Okay so..
Lets wire a diode across the coil to thwart this.
Also no one talks of the arc produced when the relay contacts open or close.
So we wire a capacitor across the relay contacts
to dampen this in to a more contact friendly ripple as the contacts do bounce slightly. Okay let fix it by incorporating a Schmitt Trigger. It has two possible states just like other multivibrators.
We could use an IC 555 in this endeavor.
Now.. we have semi conductors and "electrical" components and all is well??
Anyone ever hear of "line loss" in DC circuits?
Is the circuit suffering from hysteresis?


#25 MilesFox

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Posted 15 February 2004 - 11:02 AM

Originally posted by Skip


Now.. we have semi conductors and "electrical" components and all is well??
Anyone ever hear of "line loss" in DC circuits?
Is the circuit suffering from hysteresis?



and if no one has, then what?

magnetic inductance, when a magnetic field is generated across a coil, and then is cut iff of electricity, the magnetic field will collapse, and therefore induce current across a smaller coil with more turns, and thus generates a current of higher volotage, but less amprerage

someone DID mention carbon from the switch contacts ARCING

wouls line loss have to do more with voltage drop, or loss of an rf signal?




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