Horsepower to spin alternator?
 

Has anyone seen any tests on how much horsepower it takes to spin a loaded alternator?
Reason I'm asking is I have seen test done where it takes 15-30hp to spin a manual cooling fan (depending on type). So everyone says go electric. But with the added demand of the electric fans and most likely larger alternator, how much hp is really freed up??

I could be mistaken, but I believe there is an Engine Masters episode that covers this topic. I don't recall the specifics, though.

There was I can’t remember what season

I saw one where they tested different fans but didn't see any testing with electric fans and alternator

Engine Masters episode #35 covers a variety of accessories and their HP effect. Alternator 4-5 HP, mechanical water pump, 4 HP, engine driven fan was like 18 HP, that was a surprise. Watch the episode to get exact numbers. Going from memory here.

Well, 4-5 hp is a lot better than 22 hp required for both water pump and fan.
Wondering what the difference would be with a 36 amp alternator going to a 100 amp alternator.

This was a thread mostly about cooling fans but I posted some magazine tid bits that were related to the alternator in post #4 here.....

https://forums.maxperformanceinc.com...t=electric+fan


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We saw at least 10 years ago, a 6 HP draw on our Hydrogen Buses with a custom 190 amp alternator. So a 120 amp alternator is going to be close to the 4 HP number posted.

Tom V.

"At 4500RPMs the alternator averaged over the 4 tests a measily 1.28 hp loss."

http://www.carnut.com/ramblin/dyno.html


"Since the 1950s race cars ran on battery only for drag races and short duration round track races ( where magnetos we not permitted). This saves about 4.5 Horsepower on typical V8 engine. Alternators and earlier generators are notoriously inefficient. It takes about 1 HP to make 25 Amps in a perfect world. So dynometer results since the 1960s say you gain about 4.5 HP with the alternator removed."

https://www.physicsforums.com/thread...torque.693576/
Reference: https://www.physicsforums.com/thread...torque.693576/

"Spending the money on a high-quality alternator made for a racing application will save you a lot of headaches on race day."

"You want to make sure the alternator you select can charge well at idle and low RPM. Think about it: how much time do you spend with the car idling in the staging lanes and driving through the pits? That's the time you want the alternator doing its best work."

https://www.dragzine.com/tech-storie...racket-racing/


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Using round numbers we've seen five horsepower when adding a Moroso electric motor driving the water pump compared to a belt.

Twice we removed the fan and made a quarter mile pass and didn't not see anything noticeable with the time slip.

Many years ago Car Craft did a fan shoot out and one clutch fan wailed the crap out of every other fan they tried. Lots of folks ran out and bought that winning fan. Years later the Editor let the world know that the clutch was defective and never locked up causing the increase in power.

I think that was the same issue they let us know the secret about using Chapstick to keep Holley brown gaskets from sticking. :D

Cooling Fan Shoot-Out! - Engine Masters Ep. 20

https://www.youtube.com/watch?v=ZXdLgaFXZzs

Keep in mind the tid bit I posted in the link in post #7. From the Car Craft testing article.....

There is no common industry standard for rating electric fans. Most companies use a cfm rating, often expressed in free-flow and not when placed behind a radiator. You can never know for certain about different cfm ratings or how a company has rated their fan since they can be tested by different criteria and methods. In comparison between brands using cfm ratings alone is difficult, typically not apples-to-apples.


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Regarding the alternator....

"Its pretty minimal. You can calculate it by knowing that 1 HP = 750 Watts. So for example, let's say that you are changing from a 60 amp alternator to a 200 amp alternator. That is a difference of 140 amps. Let's also assume your charging system is putting out 14 volts. Power in watts is equal to current (amps) multiplied by voltage. So, 140 amps X 14V = 1960 watts. 1960 divided by 750 is 2.61 HP. If your alternator is only 50% efficient, that's about a 5 HP difference. And the alternator is probably a lot more efficient than 50%. Plus, your 200 amp alternator is not putting out 200 amps all the time, it is only delivering that amperage when it is required."

Source if interested:

http://fepower.net/simplemachinesfor...&topic=4879.15



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1 hp = 746 watts.

Assuming 100% efficiency in the alternator (all physical energy used to spin the alternator is converted to electrical energy output, no losses to heat, friction or the alternator's fan) an alternator supplying 50 amps (at 14 volts = 700 watts) would need 0.93 HP.

It shouldn't make any difference if it is a 62 amp alternator or a 94 amp alternator. The 50 amps either would be supplying would require the same HP input.

Instead of 50 amps, taking current demand down to a more typical 20 amps would reduce the horsepower requirement down to 0.375 horsepower.

Start adding dual electric cooling fans, sound systems that break windows the next block down the street and low riders using electric-powered hydraulics to hop down the street, then electric demands go way up. But even with a 130 amp alternator providing its fully rated output the horsepower demand would only be 2.44 hp.

All these numbers are based on 100% efficiency. If the actual efficiency were 50% (it is likely more) the HP numbers would only double,

Twice you removed the fan? What type of fan?

From my charging systems days, a 62A alt at full output, 5000 shaft rpm, output is 1.16 Hp (as before 62 x 14v = 868 W / 746 = 1.16 Hp out. This will require approx 3 Hp to drive, including waste heat, friction and fan loading. (From actual testing).

So the 50% efficiency number is very close.
George

Two different outings. Clutch fan one time and I can't remember for sure the second time but pretty sure it was a clutch fan also.

The math holds for : HP lost = (14.4V x 130A /0.65 efficiency) / 746

That's interesting that you saw no difference.
I remember my dad having issues throwing belts on the Firebird one time, it would throw the belt probably somewhere between the 330 and 660, with the belt it ran mid 12.6 when it threw the belt it picked up a tenth to mid 12.5s. I know that the water stopped also but I'd think the fan would be worth more than the pump?? Maybe not?

Non-racing application but going from a 160 amp alternator to a 320 amp Mechman alternator costs me like 2 miles per gallon in my Tahoe. It definitely has a significant draw.

To generate 140 amps at 13 volts requires 2.44 hp. Volts times amps divided by 745.7 equals HP.