[Larco]

Do any of you know how many HP an alternator robs from a 180HP engine when the charging rate is 50 amps? Thanks, Larry

 

[Larco]

Do any of you know how many HP an alternator robs from a 180HP engine when the charging rate is 50 amps? Thanks, Larry

I should have looked here first but got this answer from Google. Might be interesting for someone so I will leave it here
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I found this formula to calculate how much hp is required to run your alternator.

amps x volts = watts
745.7 watts = 1 hp
hp x 15% = hp loss
hp +hp loss = total hp used
example
55 amp x 14.9v = 819.5 watts
819.5 watts / 745.7 = 1.098 hp
1.098 hp x 15% = 1.26 hp

 

[BillL]

Not to be splitting hairs, but the real world efficiency of the claw pole alternator is only about 60%, so divide electrical power by .6. This makes the HP input about 1.8. I happened to work with these things for a while. When an on highway truck uses a 200 amp alternator, they lose a LOT of power.

 

[simpkinsona]

Keep in mind that the actual load on an alternator is rarely close to the rated output. Unless your battery is dead, the current from the alternator is only the total of your electrical components and a couple of amps to the battery to keep it charged. That being said, of course there are frictional losses in the belt, pulley and bearings to consider. I bet a day VFR airplane is using less than 10 amps most of the time.

-Andy

 

[Low Pass]

I should have looked here first but got this answer from Google. Might be interesting for someone so I will leave it here
--------------------------------------------------------------------------------

I found this formula to calculate how much hp is required to run your alternator.

amps x volts = watts
745.7 watts = 1 hp
hp x 15% = hp loss
hp +hp loss = total hp used
example
55 amp x 14.9v = 819.5 watts
819.5 watts / 745.7 = 1.098 hp
1.098 hp x 15% = 1.26 hp

Are you considering V-belt power transmission loss? I recall reading somewhere years ago this was about 10-15%.

 

[dlloyd3]

V-belt drives are about 97% efficient at rated load, correct tension and a new belt. If you ever hear one squeal it is slipping more than 12%.

 

[RV6airplanePilot]

no extra speed

I turned off my alt field after getting stable in cruise at 6500 msl. Waited several minutes, speed did not change. I was curious, if it gave me an extra knot I would do it in a race; not planning to now. Those who are afraid to turn off the field in flight do not know the difference between a real power dump and just turning off the alternator field. (something the regulator does many times per second).