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Discussion Starter · #1 ·
I have Deralle twin 4000 cfm fans on my 69, when they come on the motor looses about 300 RPM?
I have them wired through two relays pulling power from a fuse block I installed.
The fuse block gets it's power from the alt. via a 8 gauge wire.
It's all wired according to the Madd website, My question is:
If I run a 6 gauge wire directly to the battery from the fan relays, will this eliminate the RPM loss?
Of course I would use a fusible link and the relays are already by triggered the dash switch.
I was thinking it mite take the load off the Alt. wired that way?
But then common sense tells me it wont make any difference?
Any input is welcomed......
T.C.
 

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what happens if you unhook one of them?
maybe if you could stagger when they come one at a time- say, one at 180, and the other if it gets up to 190 or whatever.
or maybe do what the car stereo guys do- run a big capacitor and hope it doesn't explode.
 

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I have Deralle twin 4000 cfm fans on my 69, when they come on the motor looses about 300 RPM?
That could very well be normal. There can be many reasons for this, but those fans pull a lot of power (their website quotes 265 watts per motor, x 2 = 530 watts which equals about 40 amps @ 13 volts. Thats just for the fans and doesn't include anything else (ignition system, battery charging rate ect...) so you might have a 60+ amp load at idle. If you have a performance engine, generally they don't make as much torque at idle then a smooth idling stock engine, so they heavy load from the alternator may pulling the rpms down. If everything is wired correctly and you are not getting excessive voltage drop, larger wires won't help. About the only thing that might help is changing the pulley ratio so the engine has more power against the alternator ( this could cause the alternator not to keep up with the load at idle) or try a A/C solenoid, and wire it to bump up the idle speed anytime the fans are on. I have never tried that but it would work at least in theory. Even with my 540, if I turn everything on, the alternator will pull the rpms down some at idle.
 

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Yup,its the heavy load on your alt thats lowering idle rpm.

Those fan need alot of amps (40-50 amps) so either send your current alt out for an upgrade to approx 80-100 amps which can be done or you can just buy one new or completely rblt thats already upgradded to 80-100 amps which i have seen on ebay .

Scott
 

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Discussion Starter · #7 ·
Thanks for all the replies:
Good question Dean, I guess it wouldn't matter though as long as it was a consistent draw instead of on and off like I have now.
As for my system I have a 105 amp Alt that has been tested at just a little above the 105.
I have a very small alt. pulley 1-1/6" from March, I also have "two" adjustable fan controllers and have them staggered, but once you get over 180 they both run .
That's why I was looking at the wires, or maybe it's my fuse block isn't heavy enough? (nothing is getting hot, no blown fuses)
Or the (+) lead going to it, it's 10 gauge coming from the distribution block at the firewall, witch is where I have my sensor wire and alt. wire from the starter hooked up to.
I guess maybe I need to get the meter out and look for a voltage drop?
To be honest I'm not real happy with the Deralle controllers, I am thinking of buying the Spal, but I don't think that will solve my RPM problem, I'm sure it will help the operation/moisture problems the Deralle has .
T.C.
 

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so you don't have the fans wired DIRECTLY to the battery?
that might explain things.
 

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Discussion Starter · #9 ·
No I don't, I have replaced my horn relay buss bar with a fused buss bar and have it wired as per MADD directions.
That's what got me thinking if I wired them direct to the batt. maybe the amps of the batt. would overcome the draw and I may not get the RPM loss?
The head lites and fans are wired through relays but get there power from a firewall junction block that goes directly to the starter and then the alt.
Make any sense?
Thanks for the reply T.C.
 

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That's what got me thinking if I wired them direct to the batt. maybe the amps of the batt. would overcome the draw and I may not get the RPM loss?
That won't work. If that were to happen, then the alternator would not be keeping up, and voltage would drop off. The alternators job is to supply power to everything and charge the battery. Also the battery charge wire would have to carry the current for the fans and the battery charge rate, which its not meant to do.

Dean said:
Do the higher output alternators take less horse power to produce the same 40-50 amps?
I believe it takes the same amount of "power" to produce a "X" amount of current. How much power the alternator takes from the engine is a variable because of the crank to alt pulley ratio. High output alts do make more power at a lower alt shaft RPMs, but one you get below a certain speed, output drops off drastically.
 

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I think the best you can do is live with it. Many people change over to electric fans thinking they draw less power than mechanical fans. Actually, the opposite is true. The same fan needs the same power to spin it no matter what the power source. A mechanical fan is direct drive, so it is the most efficient. An electric fan suffers from the power conversion loss from mechanical to electric and back to mechanical. Simply physics tells us that there is no 100% conversion.
 

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Discussion Starter · #12 ·
Thanks for the replys
I think I will talk to my alt guy tomorrow, see if we can turn my CS130 into a 140-150 amp?
T.C.
 

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just try hooking the power feed wire to the relays up to the battery, and put a wire the same size as your battery cables from the alternator directly to the battery.
this is the way new cars are wired, and they have all sorts of stuff drawing on the electrical systems.
 

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Discussion Starter · #14 ·
I don't think I could get a wire that size to fit on my alt?
My batt. cables are as large as your thumb something like 4/0?
That would also defeat the sensor wire system I have ?
Although it doesn't seem to sensor very quickly?
T.C.
 

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I just installed Dual fans in my 70 velle .. 300 rpm drop at idle in gear and 150 rpm drop out of gear at idle.. Fans are wired directly to battery and alternator feed to battery is via 6 guage wire .. And still the drop is there .. I believe the resolve would be either in a throttle solenoid that would be used in an air conditioning car to bump up the idle ,, triggered by the temp sensor that triggers your fans or some fine tunning on your carb and ignition timming.. Changing to a bigger alternator is not the answer .. I just changed from a 75 amp to a 120 amp and the problem is still there..I hope that this might help save you a few bucks anyway buy not purchasing an alternator.. My rpm problem is still there .. looks like a good tune up guy is the answer
 
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