Alternator and HP Loss

[70fireturd]

I was talking to my engine builder about HP loss with viscosity fans and straight fans, which got me thinking what kind of HP loss do you have with electric fans, water pump,fuel pump, bla bla bla. My searches led me to this formula.



Amps x Volts = Watts
Watts / 745.7 (one HP) = Electrical HP Produced by the Alternator
HP x 15% Efficiency Loss = HP Loss
HP + HP Loss = Total HP Used

I put 140 for my one wire Alt and it came out to less than a HP loss. Is that wrong or are the electrical components that good.


Sorry if this has been discussed before. I didn't see it anywhere.

[JRouche]

I was talking to my engine builder about HP loss with viscosity fans and straight fans, which got me thinking what kind of HP loss do you have with electric fans, water pump,fuel pump, bla bla bla. My searches led me to this formula.

Amps x Volts = Watts
Watts / 745.7 (one HP) = Electrical HP Produced by the Alternator
HP x 15% Efficiency Loss = HP Loss
HP + HP Loss = Total HP Used

I put 140 for my one wire Alt and it came out to less than a HP loss. Is that wrong or are the electrical components that good.


Sorry if this has been discussed before. I didn't see it anywhere.

Interesting. All the math is beyond me. I did learn to add and subtract. Thank you public schools

But thinking about the draw for just say the cooling fan. The viscosity fans or clutch fans have alot going for them. When they are in good working order. They pull from the engine when they need to, then free wheel when they have done their job.

And the same with a properly working electric fan. They will only turn on when needed. And only tax the alt at that time,

But..... Then you have to look at parasitic losses. With a large alt it will still have some load on the engine when the electrical load is reduced, say the fan is in its off cycle. Granted, alot lower then when the current is needed and it becomes very resistive.

Same with a clutch fan, it will be more resistive when its engaged. And a whole lot less when dis-engaged. But it still has some drag on the engine when dis-engaged.

So what component has less drag on the engine when its not turning the fan? A free wheeling big alt or a clutch fan dis-engaged? Good question.

And which one has the most drag when the fan is activated? Thats prolly more important to some.

The way I see it, for my car, is I need a large supply of current for all the other operating systems. So I need the large alt anyway. It becomes a dual purpose tool.

And dont get me wrong. I think clutch fans are great, specially if they are working clutch fans, some peeps keep a broken fan in there too long. On a simple car that doesnt have much of an electrical load I will use a clutch fan and a small alt.

But on my car where I have power EVERYTHING including some major power using components, yes, an electric fan and a EFI computer that likes to see a good 13VDC I need a large alt to keep the battery pumped up.

I think it depends on your car, or truck. If it already has a need for alot of electricity then you should use a large alt. If the vehicle doesnt have alot of need for electricity (much more than the engine and lighting) then a clutch fan is a good choice. JR

[70fireturd]

My engine builder was saying he saw the difference of up to 25 HP loss with a fan. The worst one being a non-clutch fan at 8k rpm. What about a electric water pump and fuel pump. These are all items people go to first to cut down on mechanical drag. I am not saying there is anything wrong with mechanical components at all. For these Pontiacs if you tweak the divider plate properly you can get more than enough cfm, but its still not electric. The equation is assuming a consistent amp load which like you said the fans run when they need to.