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dropping power from 12v to 6v... how to? 

 

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 Post subject: dropping power from 12v to 6v... how to?
Posted: Sat Nov 29, 2008 1:55 am 
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hey all, im looking to throw my spare set of thermo's into the EB but due to issues im having in my fairlane im looking to run 1 fan constantly at about 6 volts (basically doing the same job as a clutch fan would, only a lil slower) then when it heats up the 2nd fan will kick in and the 1st boosts up to 12v.

simple in my head and on paper, but i just need to find a way of somehow cheaply dropping the power from 12v to 6v. anyone know how to?

 

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Posted: Sat Nov 29, 2008 10:07 am 
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well yer u could use a transformer

or use AU fans with an AU relay set which do this auto

 

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Posted: Sat Nov 29, 2008 10:12 am 
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cheers i might look into that. but i have a feeling the 6v output would come from the the ECU, not the relays. but i will definately look into it

 

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Posted: Sat Nov 29, 2008 3:19 pm 
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Being DC you will need a regulator if the load varies, but in your case the same thing can be done with a resistor equal to the value of the fan resistance and a power rating equal to the fans power rating.

 

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Posted: Sat Nov 29, 2008 5:09 pm 
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haha you lost me there... im not that smart with those things lol

 

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Posted: Sat Nov 29, 2008 5:51 pm 
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you can run the fans in line so they will be on 1/2 speed..(it would be like each fan is running 6v each)

if you wire it up like the el fans you can have the fans like above running in line through a switch over relay and when the temp gets high the trigger switch the relay over putting the fans on full..??

Last edited by TROYMAN on Sat Nov 29, 2008 5:55 pm, edited 1 time in total.

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Posted: Sat Nov 29, 2008 5:54 pm 
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Posted: Sat Nov 29, 2008 6:05 pm 
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I'd suggest you look at the factory EL or AU setup (3 relays) - as mentioned, it may be a good idea. Figure out how it works, and apply some of it to your setup.
The fans draw a fair amount of power, so a dropping resistor will radiate plenty of heat, not to mention waste power as well.
I'd think it would be better to run both fans in series, while the car normally runs, then have your davies craig switch or whatever, control some relays, to switch one over to full speed, and shut the other down. If the temp still heads towards full overheat, have a manual switch to turn the other fan on to full speed.
This is a few quick ideas, but put your thinking cap on, and come up with a system that will suit you.

 

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Posted: Sat Nov 29, 2008 10:29 pm 
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this is what i was thinking of...

the first shows how i was going to do the setup, 6v to one relay then 12v to the other 2. so basically the 12v would override the 6v.

the 2nd in the probebly better setup, the diodes IN4004 basically stop power running backwards up the lines (one way vavle type thing) so added that to each setup before they join and then that way i can switch between the 2 setups, one is the fans running in series then when the temp rises the fans switch to full 12v. only issue i would have with this would be getting the first setup to turn off when the 2nd turns on. unless it would be safe to run both at the same time...

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Posted: Sat Nov 29, 2008 10:32 pm 
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actually id need to add another in4004 diode inbetween the 2 fans so that when the power goes to the 2nd fan it wont travel backwards... hmm im not sure now

 

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Posted: Sun Nov 30, 2008 6:11 am 
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In a series / parallel arrangement I doubt that you will need any 1n4004 diodes at all and you certainly won't be able to run both systems at the same time it will need to be a changeover switching style.
I will see if I can come up with a circuit for you so it will switch over correctly while I am at work today....

 

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Posted: Sun Nov 30, 2008 8:57 am 
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cheers, the reason id use the diodes is so that i can have both setups wired up to the 2 fans and that way the power would only travel the way i wanted it to and not the other way around.

but thst would be awesome if someone could work out a way.

 

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Posted: Sun Nov 30, 2008 11:19 am 
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I don't know if the 4004's will handle the power.
I did a quick sketch of a setup with 2 relays and a diode that stays off normally, both fans at half speed with A/C on, both fans full speed on overheating, or whatever the temp s/w is set at.
I'll see if someone comes up with something better.

 

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Posted: Sun Nov 30, 2008 12:35 pm 
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this might help with the 3 relays

a chart igrabbed of teh BA manual


fan speed relay 1 relay 2 relay 3 fan 1 fan 2
off off off off off off
low on off off low low
hi on on on hi hi




just work out the realy pins and u be set :)

 

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Posted: Tue Dec 02, 2008 5:51 am 
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It can certainly done with 3 relays and no diodes required, I just need to figure out how to do a diagram to show the connectionss....

 

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