high-watt systems rob horsepower?

Ok, this is just a question out of curiousity.  I noticed that 1 hp=746 watts.  Supposing you were running 1500 watts rms you could assume that it is going to be more like 2000 watts drawn because the amps effeciency, or lack there of.  So could you safely say when you have the stereo tapped out you are going to hurt the available horsepower by about 2.6 ponies using this example?

I havent noticed any lack of horsepower from installing a bigger alternator if thats your question...besides that the electrical system in a car really shoundt add any horsepower nor take anyaway

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2009 0-1000 Trunk WR 154.0DB 2009 1001+ Trunk WR
2007 USACI World Champion
2007 World Record
2006 USACI Finals 2nd Place

I'm studying for the MECP Advanced Installer test right now and the book actually talked about that.

It basically says that a 200-ampere high output alternator requires about 7-8hp from the engine to make the full 200 amps at 14 volts.

Absolutely. You can't get energy (the power for the system, including all waste in the form of heat IS energy) from nothing. The alternator is connected to the crank of your engine BECAUSE it has to rob power from your engine to work.

Larger alternator, more power "borrowed" from your engine. However, an alternator is AT BEST 66% eficient at converting input to output, so 746/.66=1130 watts of MECHANICAL energy in, or 1.5HP, just to convert the mechanical to electrical, and generate 746 watts. These losses include the energy required to set up the field in the stator, also. 200A*14.4v=2880 electrical watts out. 2880 electrical watts out*1.5=4320 machanical watts, or 5.8HP in... minimum.

This is basic physics... ALL energy can only be converted from one form to another, with all of it's associated losses.

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

I guess I just didnt nitice any horsepower loss because of the motor work I did on our latest CRX.

Added the GM large case Alt   300 amp Irragi   But also added

1988 honda CRX factory 83WHP   from dyno testing

D15B2 lower end. Rebuilt with new rods and pistons. rings ect ect

d16y8 SOHC VTEC head, Mild Port and polish job, crower stage 2 cam with titinimum springs and retainers.

DC Sports full motor back 2.5 in exhaust

Edlebrock intake manifold, accord throttle body (18MM bigger)

AEM V2 cold air intake

PM6 ecu reprogramed for mid range power output for normal driving.

192WHP after about $2300 worth of goodies into the motor, I still have some more work to do there, but I need to start focusing on the audio system, this is supposed to be a SPL vehicle!   haha

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2009 0-1000 Trunk WR 154.0DB 2009 1001+ Trunk WR
2007 USACI World Champion
2007 World Record
2006 USACI Finals 2nd Place

It's called parasitic losses.  Anything operating while your vehicle is running whether it is electrical like a stereo system or mechanical like your A/C compressor use energy from the engine to operate, which means they require some of the engine's horsepower and also they cause your engine to use more fuel.  Like haemphyst said, you can't got something from nothing.

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Alright thanks.  That's kind of what I expected but I had no idea on the efficiency of an alternator.  Kind of interesting.  If you think about it the power losses from the alternator draw and the added weight of the sub, box, amps, speakers, damping, etc. there is going to be considerable performance losses,.  I've never really thought about it, and I doubt many people do.

Its amazing how many people don't belive how much these enclosures/amps etc..weigh alone.  I have an install coming in next week to fit 4 12's in the trunk of a grand prix, when its done I guarantee it will be sagging. Maybe I'll post some pics if I get time and figure out how to shrink them.

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