Output @ Idle

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Melissa Stephens Jones

CarAudio.com Recruit
QUESTION:
When an "Alternator Manufacturer" gives you an "Output at Idle" number - What do you want to hear? Most people just want to hear a high number and they're happy from that point on out.... Until they have 12.4 volts at a stoplight and 14.8 when they drive... Do you think they have been “deceived” lied to?

The industry standard for an "Idle output" test is 2400 ROTOR rpm. That's approximately 800 engine rpm if you have a 3:1 pulley ratio. It’s been that way for years...& as far as today that number should really be 2000 Rotor RPM instead of 2400 because crank pulleys have got way smaller on most vehicles which makes the "Output at idle" rating even LESS. Personally, I do not feel that any passenger car alternator on the planet will do 220 amps at 2000 rotor rpm.
To my knowledge there is not a single manufacturer that rates their alternators by this method. They all use the "Boss Audio Amplifier" rating method. (1000-watt amplifier rated at "4000 Watts".)

Do you want to be deceived and be told what the "best case scenario" is? Such as "XX amperage" alternator will do "230+ amps at idle" On "XX car"... which idles at 1000 rpm and has an 8" crank pulley which is typically a 4:1 ratio...
ANY THOUGHTS?...
 

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One of the biggest problems I've seen related to idle output is with smaller, higher revving engines, where the alt isn't even on or is barely producing power at idle, like with a 6000 rpm or higher motor.

I know my EA alt, with a small pulley, would do like 80 amps at idle ~600ish motor RPM. Would do a solid 300 amps at 1800-2000 motor RPM. Redline for that vehicle was ~5200 rpm or so.

I think idle ratings should be relevant to what the vehicle actually idles at from factory. It genuinely seems like a fairly simple thing to calculate; you just have factory motor RPM at idle (full engine warm up idle, not cold idle) with whatever diameter crank pulley, then that turns the ratio'd alt pulley, and that should be the idle rating. IMO, there shouldn't be a industry-standard rotor idle speed; it should be directly relevant to the specific vehicle conditions.

The difference between alt output at idle between big push-rod v8's or a diesel's idle and a DOHC i-4 or i-6 idle is going to be quite different, due to the maximum RPM differences.

What would you say the max alt rotor speed is, in general? From my understanding, there's generally only so fast an alt rotor can spin before it would damage itself, so if your vehicle has a super high redline, then the idle rotor speed is going to be significantly lower than a vehicle with a lower redline, correct?
 
I wonder if a manufacturer could come out with an alt that has a variable-sized alt pulley or like a CVT gearbox? You could make the pulley small at lower RPMS, to try and get more idle output, and then grow the pulley as the motor revved up, so the alt wouldn't over-spin itself. That could possibly provide a lot more power at lower RPM's and more consistent power across the RPM range. Not sure if that would be worth the costs, though.
 
One of the biggest problems I've seen related to idle output is with smaller, higher revving engines, where the alt isn't even on or is barely producing power at idle, like with a 6000 rpm or higher motor.

I know my EA alt, with a small pulley, would do like 80 amps at idle ~600ish motor RPM. Would do a solid 300 amps at 1800-2000 motor RPM. Redline for that vehicle was ~5200 rpm or so.

I think idle ratings should be relevant to what the vehicle actually idles at from factory. It genuinely seems like a fairly simple thing to calculate; you just have factory motor RPM at idle (full engine warm up idle, not cold idle) with whatever diameter crank pulley, then that turns the ratio'd alt pulley, and that should be the idle rating. IMO, there shouldn't be a industry-standard rotor idle speed; it should be directly relevant to the specific vehicle conditions.

The difference between alt output at idle between big push-rod v8's or a diesel's idle and a DOHC i-4 or i-6 idle is going to be quite different, due to the maximum RPM differences.

What would you say the max alt rotor speed is, in general? From my understanding, there's generally only so fast an alt rotor can spin before it would damage itself, so if your vehicle has a super high redline, then the idle rotor speed is going to be significantly lower than a vehicle with a lower redline, correct?

Output at idle issues really aren't related to engine size, it's more crank pulley diameter which there are many V8 motors with 5" crank pulleys and 4 cylinders with 7" crank pulleys. It's impossible to give in vehicle numbers when a given case style fits multiple vehicle models. The real answer is to give rotor rpm and educate the customer to be able to make their own calculations when they are basically "engineering" their sound system. Max rpm really isn't the problem with rotors, it's the abrupt changes in rpm during hard shifts that break rotors
 
One of the biggest problems I've seen related to idle output is with smaller, higher revving engines, where the alt isn't even on or is barely producing power at idle, like with a 6000 rpm or higher motor.

I know my EA alt, with a small pulley, would do like 80 amps at idle ~600ish motor RPM. Would do a solid 300 amps at 1800-2000 motor RPM. Redline for that vehicle was ~5200 rpm or so.

I think idle ratings should be relevant to what the vehicle actually idles at from factory. It genuinely seems like a fairly simple thing to calculate; you just have factory motor RPM at idle (full engine warm up idle, not cold idle) with whatever diameter crank pulley, then that turns the ratio'd alt pulley, and that should be the idle rating. IMO, there shouldn't be a industry-standard rotor idle speed; it should be directly relevant to the specific vehicle conditions.

The difference between alt output at idle between big push-rod v8's or a diesel's idle and a DOHC i-4 or i-6 idle is going to be quite different, due to the maximum RPM differences.

What would you say the max alt rotor speed is, in general? From my understanding, there's generally only so fast an alt rotor can spin before it would damage itself, so if your vehicle has a super high redline, then the idle rotor speed is going to be significantly lower than a vehicle with a lower redline, correct?
Bro most stock everyday engines idle at about the same rpm, 600-800 rpm, whether it's a V8, V6, or four cylinder. Redline and idle rpm are two completely separate things and one has nothing to do with the other. Only race engines with massive cam timing overlap and giant carburetors have high idle rpm. They simple won't run any slower. Big alts usually aren't run on those engines anyway because it eats horsepower.
 
Bro most stock everyday engines idle at about the same rpm, 600-800 rpm, whether it's a V8, V6, or four cylinder. Redline and idle rpm are two completely separate things and one has nothing to do with the other. Only race engines with massive cam timing overlap and giant carburetors have high idle rpm. They simple won't run any slower. Big alts usually aren't run on those engines anyway because it eats horsepower.
You missed Buck's point. He's comparing idle rpm to max rpm and assuming that alternators have a maximum pulley rpm before they are damaged. Otherwise the easy answer would be to just spin it faster at idle.

Melissa, are you suggesting Iraggi takes a different approach to idle ratings than other manufacturers?
 
I wonder if a manufacturer could come out with an alt that has a variable-sized alt pulley or like a CVT gearbox? You could make the pulley small at lower RPMS, to try and get more idle output, and then grow the pulley as the motor revved up, so the alt wouldn't over-spin itself. That could possibly provide a lot more power at lower RPM's and more consistent power across the RPM range. Not sure if that would be worth the costs, though.
I imagine a clutch or torque converter would be much more simple and reliable.
 
You missed Buck's point. He's comparing idle rpm to max rpm and assuming that alternators have a maximum pulley rpm before they are damaged. Otherwise the easy answer would be to just spin it faster at idle.

Melissa, are you suggesting Iraggi takes a different approach to idle ratings than other manufacturers?
If that was his point then yes I missed it.
 
You missed Buck's point. He's comparing idle rpm to max rpm and assuming that alternators have a maximum pulley rpm before they are damaged. Otherwise the easy answer would be to just spin it faster at idle.

Melissa, are you suggesting Iraggi takes a different approach to idle ratings than other manufacturers?

No, I'm suggesting ALL Alternator companies use the industry standard and give rotor rpms so the customer can educate themselves and make their own calculations and not be just be given a random number for a random fictitious application just to make them not have to understand what's going on and feel happy making a purchase based off data that doesn't apply to them
 
Yeah, that would be awesome but will probably never happen, .. it would be to expensive compare to a simple $5 steel pulley
Thinking out loud for the fun of it here: Engines rarely turn more than 3-4k when you're driving normally, so why not implement a clutch and WOT cutout relay like they do with a/c compressors? Then you could spin it faster at idle and prevent damage and eliminate the extra load when you need the power. I know from experience that a good battery will start and power a vehicle for several days of driving before it drops low enough to not start the vehicle (I forgot to install a fuse after a motor swap).
 
Thinking out loud for the fun of it here: Engines rarely turn more than 3-4k when you're driving normally, so why not implement a clutch and WOT cutout relay like they do with a/c compressors? Then you could spin it faster at idle and prevent damage and eliminate the extra load when you need the power. I know from experience that a good battery will start and power a vehicle for several days of driving before it drops low enough to not start the vehicle (I forgot to install a fuse after a motor swap).
Seems like it would be easier and cheaper to just build alts that can spin faster at idle and handle high wot rpms. A/c compressors are expensive af! I think alts would double in price to be honest.
 
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Melissa Stephens Jones

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