[Dale .D]

Hello. I'm hoping to get some advice. I have a rebuilt 71 - 1.9 to 2,0. Combo cam, big valves etc. I have a Kenlowe electric fan drawing 28 amps. A bit more at start up. Also a Gm alternator 105 amps. With the Combo cam the Idle is somewhat loppy which I like. My problem is that when the fan kicks in it puts such a load on the alternator it wants to kill the Idle. Is there a way to wire it so it doesn't draw so bad on the alternator. I have put the fan back on and have the electric as back-up but I'd sure love to take it off.Thanks for any suggestions.

 

[Dale .D]

Glad it's not just me. Some great Ideas. Its a common Alternator so it shouldn'r be hard to find a smaller one. Has anyone done this?

 

[Dale .D]

TWENTY-EIGHT AMPS!!!!! Holy Bejeesus! That's ridiculously huge. You should be down around 15amps max. I run an excellent engine fan, same as PJ, and a separate auto tranny cooler fan on the same controller and fuse and I only use 15amps.

I use a GM SI-style one-wire 105amp alternator. It doesn't begin the charging cycle until 1500rpm. I was running undersized crank and oversized water pump/fan pulleys to increase cooling efficiency, but that makes your alternator run slow and yet I still only needed to rev the engine to 1500 to start the charging and then I can ease off on the pedal and it would continue to charge at the 1000rpm my side draft required. I have an auto tranny that squashes the rpms down to 800rpm when in Drive no matter what you set the idle at and I would still have some charging, albeit a little lower. My FI mod has forced me to go back to the stock pulley sizes, so I should have a faster spinning alt and even better charging. I retain the use of the engine fan and my electrics only kick on at 180*. Under normal circumstances cruising around my engine only gets up to 160*, so my fans seldom kick on. Only when I'm stuck in traffic, a fairly common occurance, does the temp start to spike and kick on the fans. My funny pulley sizes made the water pump turn slower for better cooling efficiency at higher rpms, but at idle this would cause the engine fan and alternator to turn slower than oem. Going back to the oem pulley sizes should make my fan spin a little faster and provide better radiator cooling, plus improve charging at idle.

When I had a Combo cam I also disliked how the lope would mess with my charging at idle. Very annoying. Every time it lopes you're on the verge of stalling.

If I were you I would get a fan that doesn't gobble so much power. I'll see if I can find the fan that me and PJ use....

Great info thanks. Wonder why my fan draws so much. Had to go to a 40 amp fuse too.

 

[Dale .D]

Ok, so what I'm hearing so far that it is in question whether a smaller pulley on the Alternator will hinder or help when the big draw comes in when the electric fan kicks in at idle. I'm also hearing that a a different Fan might be in order. 28 amps is way to much from what I'm hearing. Some have suggested timing but it's running way to well to mess with things now. Great input everyone. Keep it going.Thanks eh.

 

[Dale .D]

In other words:

Let's say, you have a 12V DC motor with 80 Watts. This means, the motor has a power consumption of 80W at 12V. Since power consumption P (Watt) = U (Voltage) x I (Current), as a result your current draw is P / U or 80W / 12V = 6.67A.
Also, the electrical resistance R (Ohm) = U / I, so your motor has a resistance R = 12V / 6.67A = 1.8Ohm. Since the resistance is constant (within our idealized example), you can see that you can rearrange the equation to I = U / R --> Since R is constant, if the voltage drops down, the current drops down in the same relation which will bring the power consumption down even further.
If the voltage drops by factor 2 (to 6V) and the current drops by factor 2 as well (to 3.33A), the power drops by factor 2[SUP]2[/SUP] = 4 from 80W to 20W (6V x 3.33A).

Dieter

Oh ya that cleares it right up Can you put this in laymans terms that relates to the issues at hand.

 

[Dale .D]

As the voltage to the fan drops the fan slows down, uses less power (watts), and draws less current (amps)

As the voltage to the fan rises the fan speeds up, uses more power, and uses more amps.

This is only relevant to your problem with blowing the fuse. You are more likely to blow the fuse when the alternator is charging the battery.

IMO, a smaller alt pulley will still fix your stalling/discharging problem. Even though the fan draws more when the alternator is charging the battery. Your engine rpms will still drop less with a smaller pulley because the alternator will charge much more efficiently at idle and take less engine power to turn.

If you have a one wire alternator like me you might barely be charging at idle right now. One wire alternators are triggered by rpm. There’s a reason they don’t use one wire on anything but tractors anymore.

Thanks Knorm I will give it a try. Actually I don't have a fuse blowing problem now that I went from 30 to 40 amp fuse. If this doesn't help I'll have to change the fan to one with a much lower draw. Thanks for everones input eh.