Electric fan stalling Idle
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    1000 Post Club Dale .D's Avatar
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    Electric fan stalling Idle

    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.
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    Quote Originally Posted by Dale .D View Post
    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.
    My alternator and AC does this at idle. The problem is the alternator is not hardly charging anything at idle. We need a smaller pulley on our alternators to get our fancy modern alternators to work. I have my idle set to 1200rpm to combat this, but my AC will drop my engine to 750rpm at idle.

    I’m working on making a fast idle solenoid or a smaller pulley to increase the rotations of my alternator to fix this.
    "Mira," 1970 Opel GT Working ARA AC, European 2.0L and Midikit
    "Kara," 1972 Opel GT Targa, Welded Doors, Rhinolined, 40 DCOE SSD

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    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?

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    Senior Member The Cub's Avatar
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    I just installed a 2,000 cfm pusher yesterday that only draws 10 amps, not much compared to the 28 like the one you have yet that’s exactly why I was playing around with my old idle cut off solenoids yesterday, I had to cheat my idle speed to bring the idle up too. Unfortunately you then start drawing too much fuel at shut off and risk occasional desiling, I’m just running the stock alternator for now until I can step mine up, an observation that I didn’t think of, I believe that the FSM says the stocker’s rated output takes place around 2,000 RPMs so mine was even noticeably sluggish on the idle transition when taking off from a stop light. Much better now. So what makes today’s cars handle loads so smoothly? Is it differently designed alternators or the computerized management systems make quick compensation for the loads put on the generators?

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    Just Some Dude in Jersey The Scifi Guy's Avatar
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    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....

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    Here, this appears to be the one. 3000cfm:

    https://www.ebay.com/itm/A-TEAM-14-H...oAAOSwkfJdSMFN

    Nice and cheap at $35. The fan blades are connected together with a ring at the outer circumference, this contains and directs the air flow better. It blows like a freakin' tornado and it's nice and quiet.
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    For a high amp. draw like you are having (28 amps) you need to have the bat. wire from the alternator wired directly to the battery terminal (10 gauge) and not through the amp gauge. Use a voltmeter in place of your amp gauge.
    HTH
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    If you are using the 105 amp alternator, for a high amp. draw like you are having (28 amps) you need to have the bat. wire from the alternator wired directly to the battery terminal (10 gauge) and not through the amp gauge. Use a voltmeter in place of your amp gauge.
    HTH
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    A smaller alternator pulley will make the alternator output higher at idle.. but that will make the power draw of the fan WORSE when it turns on. So that is moving this problem the wrong way.

    OP, you might improve your idle response to loads like this fan by better tuning. There tends to be a lot of interaction between ignition advance and idle opening in the carb. Too much ignition advance at will result in a very small throttle opening at idle, and that will be much more effected by changing loads. The main point is that part of what you may have is in the engine's tuning.

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    Quote Originally Posted by guyopel View Post
    For a high amp. draw like you are having (28 amps) you need to have the bat. wire from the alternator wired directly to the battery terminal (10 gauge) and not through the amp gauge. Use a voltmeter in place of your amp gauge.
    HTH
    Exactly. Mine is done that way and I have yet to have my idle drop when my pusher fan comes on. I have to listen for the fan to cut on. It will cycle when the car is cut off, but no problems when the car is running. Jarrell
    You lose your dreams, you lose your mind. (The Rolling Stones)

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    Electric fan stalling Idle

    Quote Originally Posted by Manta Rallier View Post
    A smaller alternator pulley will make the alternator output higher at idle.. but that will make the power draw of the fan WORSE when it turns on. So that is moving this problem the wrong way.

    OP, you might improve your idle response to loads like this fan by better tuning. There tends to be a lot of interaction between ignition advance and idle opening in the carb. Too much ignition advance at will result in a very small throttle opening at idle, and that will be much more effected by changing loads. The main point is that part of what you may have is in the engine's tuning.
    I think you may be mistaken (but I’m open to correction).

    The alternator charges the battery to a higher voltage whenever the pulley is moving faster at idle (since it’s currently not with a stock sized pulley). The power draw from the fan does not change. An 80W motor is an 80W motor for example.
    Since the battery voltage is higher the amp draw from the battery will be less.

    For example at 12V an 80W motor will draw around 6.7 Amps
    At 14V the motor will draw more like 5.5 Amps

    The alternator is also more efficient at higher rpm therefore it won’t have as much drag on the engine with the smaller pulley.
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    Quote Originally Posted by The Scifi Guy View Post
    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.

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    Quote Originally Posted by Knorm65 View Post
    The alternator charges the battery to a higher voltage whenever the pulley is moving faster at idle (since it’s currently not with a stock sized pulley). The power draw from the fan does not change. An 80W motor is an 80W motor for example.
    Since the battery voltage is higher the amp draw from the battery will be less.

    For example at 12V an 80W motor will draw around 6.7 Amps
    At 14V the motor will draw more like 5.5 Amps
    Power draw is not a constant vs voltage in these motors... the example numbers are not correct. Don't confuse the rise in current draw when a motor stalls with running current versus voltage when the motor is running in the normal RPM range. Current in motors like these is related to torque which is related to fan blade, speed, etc. Increase the voltage (from the faster alternator as proposed) and the speed will increase....we all know this from hearing fans slow down when we drop and engine to idle and the fan(s) slow down due to alternator voltage dropping. Torque/load will increase with speed, and current has to increase; it may not increase much, but it won't go down. (This all comes out of the mathematical modeling for motors and involves back-EMF's, etc.)

    With better voltage, the torque load on the engine is higher.
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    There’s also a large inrush current when electric motors first start rotating from a locked/stopped state.
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    Quote Originally Posted by Manta Rallier View Post
    Power draw is not a constant vs voltage in these motors... the example numbers are not correct. Don't confuse the rise in current draw when a motor stalls with running current versus voltage when the motor is running in the normal RPM range. Current in motors like these is related to torque which is related to fan blade, speed, etc. Increase the voltage (from the faster alternator as proposed) and the speed will increase....we all know this from hearing fans slow down when we drop and engine to idle and the fan(s) slow down due to alternator voltage dropping. Torque/load will increase with speed, and current has to increase; it may not increase much, but it won't go down. (This all comes out of the mathematical modeling for motors and involves back-EMF's, etc.)

    With better voltage, the torque load on the engine is higher.
    Ah! Your response encouraged me to look at how DC motors worked. Good lord they are more complicated than I thought.

    You are totally right. Thanks for clearing that up. DC motors do not work like typical DC components like resistors. Fun!

    So speeding up the alternator will indeed increase the draw on the battery from the fan.

    Speeding up the alternator will not help with the blowing fuse problem they are having, but I still think it will help my problem because the alternator works much more efficiently at higher rpms (and I rarely have my cooling fan on).
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    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.

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    Yes, 28 amp draw sounds excessive. My 14" Perma cool draws like 12amps. I can easily start it off idle with very little noticible effect on idle quality with the original 50 year old 35 amp alternator! But my fan is fed directly from my battery...
    Last edited by Vincent; 3 Weeks Ago at 08:09 PM.
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    Quote Originally Posted by Manta Rallier View Post
    Power draw is not a constant vs voltage in these motors... the example numbers are not correct. Don't confuse the rise in current draw when a motor stalls with running current versus voltage when the motor is running in the normal RPM range. Current in motors like these is related to torque which is related to fan blade, speed, etc. Increase the voltage (from the faster alternator as proposed) and the speed will increase....we all know this from hearing fans slow down when we drop and engine to idle and the fan(s) slow down due to alternator voltage dropping. Torque/load will increase with speed, and current has to increase; it may not increase much, but it won't go down. (This all comes out of the mathematical modeling for motors and involves back-EMF's, etc.)

    With better voltage, the torque load on the engine is higher.
    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 22 = 4 from 80W to 20W (6V x 3.33A).

    Dieter

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    Quote Originally Posted by G.v.Mainberg View Post
    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 22 = 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.
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    Electric fan stalling Idle

    Quote Originally Posted by Dale .D View Post
    Oh ya that cleares it right up Can you put this in laymans terms that relates to the issues at hand.
    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.
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