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Old 06-09-2008, 12:43 AM   #1
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Default What's the maximum current draw on OEM fan circuits?

Searching for 12" fans as the OEM fans won't fit with the super thick radiator I have. I need to know the maximum current the factory fan circuits can handle. 1996 Miata. Thanks.
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Old 06-09-2008, 01:05 AM   #2
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I know guys running 7 amp fans, though they're not wired in parallel so each fan has its own relay circuit. I don't suggest the "relay jumper" method of parallel fans for people that have high current draw fans.
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Old 06-09-2008, 10:46 AM   #3
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Originally Posted by cjernigan View Post
I know guys running 7 amp fans, though they're not wired in parallel so each fan has its own relay circuit. I don't suggest the "relay jumper" method of parallel fans for people that have high current draw fans.
So are you better off to buy a fan controller, or run a bunch of new wiring?
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Old 06-09-2008, 12:33 PM   #4
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If you've got a fan that draws high amps, say over 15, you can connect a relay to the OEM fan wire to engage the relay, then run the power wire to a 30 amp power source in the fuse box on the passenger fender, or directly to the battery. I just don't want to hassle with that stuff right now. I've got 2 ebay 12" fans mounted to a lexan plate right now. Problem is the CSF radiator is 53mm thick, the fan standoffs are tall, and I have a RB hollow swaybar, so there's no room to properly mount a shroud and fan assembly. I had to slot the lexan to move it and the fan assembly as close to the rad as possible. With the lexan so close to the rad core, I am concerned that airflow through the radiator is going to suck, so I want to direct mount a couple fans to the core using aluminum straps bolted to the radiator's fan standoffs. If I do that I want fans that are going to pull enough air to get the job done. That's why I want to know what the OEM circuits can handle so I know what I can get.
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Old 06-09-2008, 12:56 PM   #5
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Quote:
Originally Posted by soflarick View Post
Searching for 12" fans as the OEM fans won't fit with the super thick radiator I have. I need to know the maximum current the factory fan circuits can handle. 1996 Miata. Thanks.
There is no one magical number at which the factor circuit blows up. Way too many variables. Generally speaking, as fan current increases, relay life will diminish, however it's not going to be dramatic and catastrophic.

In your '96, each fan has its own relay and its own fuse. The A/C fan shares its fuse with the A/C clutch, but apart from that they're pretty stout circuits.

If you want to trigger both fans to come on when the cooling circuit triggers, just put a jumper wire between the two relay coils. Black / Green at ECU 1A is the main fan, Blue / White at ECU 1B is the A/C fan. This way, you're letting the relays do their job normally, you're just forcing them both on. This has been covered in my A/C FAQ: https://www.miataturbo.net/forum/showthread.php?t=20954

Also, checkit: http://www.fatcatmotorsports.com/fanshroud.htm
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Old 06-09-2008, 12:59 PM   #6
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Rich, FYI I have 2 of those ebay fans mounted to my rad right now and I havent had any cooling problems. I've spent countless hours in traffic since I installed them and they seem to work just fine.
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Old 06-09-2008, 01:17 PM   #7
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I guess the 1.6 cars with aftermarket fans should just expect to run a seperate relay circuit at the fuse box, right?
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Old 06-09-2008, 01:24 PM   #8
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I guess the 1.6 cars with aftermarket fans should just expect to run a seperate relay circuit at the fuse box, right?

I have been running both of my fans in parallel off of the same circut for a year now and havent had any issues?
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Old 06-09-2008, 01:35 PM   #9
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I have a Hydra so each fan is running off its own circuit. I'll just mount the fans I have and datalog the temps.

Whatcha been up to Phil?
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Old 06-09-2008, 01:55 PM   #10
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Originally Posted by soflarick View Post
I have a Hydra so each fan is running off its own circuit. I'll just mount the fans I have and datalog the temps.

Whatcha been up to Phil?
SOS bro. I called you last week and left a message. We need to talk about your suspension because im about to make a move. Call me.
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Old 06-09-2008, 02:24 PM   #11
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Originally Posted by levnubhin View Post
I have been running both of my fans in parallel off of the same circut for a year now and havent had any issues?
what fans?
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Old 06-09-2008, 03:36 PM   #12
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Is everyone in agreement with this video? I've seen the back and forth thats come up, but doesnt seem to be a definitive answer..

In the video he goes as far as saying that fans are the primary source of air to the rad, and that the next best would be to fully expose the entire rad by hacking up the fascia...

However I'm not totally sure how I feel about the exercise he did since it was only with the shroud in place...Before and after wouldv'e been a little more convincing...

Whats the verdict on this or is the jury still out?
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Old 06-09-2008, 03:55 PM   #13
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Originally Posted by tvalenziano View Post
Is everyone in agreement with this video? I've seen the back and forth thats come up, but doesnt seem to be a definitive answer..

In the video he goes as far as saying that fans are the primary source of air to the rad, and that the next best would be to fully expose the entire rad by hacking up the fascia...

However I'm not totally sure how I feel about the exercise he did since it was only with the shroud in place...Before and after wouldv'e been a little more convincing...

Whats the verdict on this or is the jury still out?
At $400 for a chunk of lexan and $50 ebay fans, I don't think so. I'll make my own.

Don't forget that a properly molded shroud on the front-side of the rad ideally conformed to the shape of the mouth will be superior to just sticking a head exchanger out front. I looked at a bunch of $$$ race cars and they all do this. Look at the size of the vent on racecars, the molding, and the pressure differentially behind.
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Old 06-09-2008, 04:02 PM   #14
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I also didn't see anything on that guy's cardomain page about the undertray or shrouding. I assume that yet another person decided that rather than build a shroud to force air through the radiator, they just put fans on it to pull it through.
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Old 06-09-2008, 04:03 PM   #15
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Oh i NO way was I considering paying for something like that...I have a sheet of ABS that I was thinking would work nicely as a shroud..
Ideally, my thought is to shroud as you said from the opening of the mouth, the sides of the rad, and also the fans behind it...

But again, heard nothing bad about the mouth/sides being shrouded...the dispute seems to be over doing a fan shroud... I'd also think some of the info gathered from people doing hood extractors would apply here no? I could EASILY be misunderstanding this, but it seems related to where one of these works and the other not so much no?
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Old 06-09-2008, 04:08 PM   #16
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I'm no expert, but I'm going to fiberglass a shroud for the front side of the rad to the mouth, then work on the undertray, then new fans and a shroud, then cut the hood as a last resort.

I just wanted to point out that this guy built the fan shroud before he looked at the undertray or directing air into the heat exchangers. I hope this plays out in my favor because I'm tired of spending money.
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Old 06-09-2008, 04:13 PM   #17
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I hear ya, I feel the same. I'd rather look into shrouding everything so I know the heating isnt due to a lack of air... Also not to keen on cutting my hood (aka *****)...

I have my undertray started, and thats going in soon. I've been waiting for my GS rad to do anythign else (shrouding, fans, etc..).

I'm trying to do things piece by piece so I can judge what kind of difference each solution/suggestion makes...I wouldn't say I have the worst overheating problems, but I think ANY is too much at this point...

Guess this basically falls into trial and error...
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Old 06-09-2008, 04:25 PM   #18
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I've always thought that the heat exchangers should do their job without the fans, that's what race cars do. The fans are for street driving. Hopefully a fat lip on the undertray and the front side shrouding will get the job done.
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Old 06-09-2008, 04:29 PM   #19
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I can't see how a leaf blower with a focused jet of air is going create an accurate representation of the oncoming air at speed. I honestly think the best approach is to install the fans first and then see what happens. If you're getting high temps in traffic and at stop, then the shroud probably will help. But at speed the air is being forced through a much smaller exit area.
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Old 06-09-2008, 04:34 PM   #20
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Originally Posted by m2cupcar View Post
I can't see how a leaf blower with a focused jet of air is going create an accurate representation of the oncoming air at speed. I honestly think the best approach is to install the fans first and then see what happens. If you're getting high temps in traffic and at stop, then the shroud probably will help. But at speed the air is being forced through a much smaller exit area.
Yeah, this is what I was getting at. I talked to a guy about that this about 1-year ago at the track, but never really put 2+2 together. He said that his legends car was overheating and no matter what he did, it ran hot at best. So he took off the shroud on someone elses recomendation and the car ran fine at 96* or so on the track.
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