added UD pulley's, need to change anything?

[Sburn]

Originally Posted by JackandJanet

Some people forget that the power for e-fans HAS to come from somewhere, and that "somewhere" is the alternator that is powered by the engine. Anytime you increase the load on the alternator, you MUST increase drag on the engine. And, since there is a "middleman", sort of, in this system (the alternator), you cannot have 100% transference of power to the fans, since nothing is 100% efficient.
- Jack

OK, to noodle the e-fan business around a little bit more, here are my thoughts and calculations. Feel free to refute, correct, debate:

Looks like the standard twin e-fan set-up (Spal, Derale, F-A-L) makes 4000-5000 CFM and take around 50 Amps (2 fans @ 25A). 50 Amps @ 12 Volts is 600 Watts. 600 Watts converts to 0.8 Horsepower. As Jack said above, there will be some conversion losses. A quick search suggests that belt-driven alternators are not much more than 50% efficient in converting mechanical to electrical power, so the engine has to turn the alternator with 1.6 HP to get that 0.8 HP (600W) out the other side.

I can find very little on how much HP is required to turn a conventional (non e-fan), other than from the folks who are selling e-fans. The often quoted 10-15 HP drag may come from a clutch-engaged fan at 5000 RPM for all I know. And the HP "savings" in that case would be 15 HP less the 1.6 HP for e-fans, in the case of the e-fans fans running full speed.


So, back to the real world:

In summer stop-and-go traffic, the e-fan may prove helpful with the added airflow for the A/C. 1.8 HP gets used to power those e-fans, but I'm not sure I care too much about losing 1.8 HP in stop-and-go traffic anyway. Having the A/C work real well is a fair trade on a hot summer day for me. The conventional fan in this situation is engaged and eating some ammount of HP, but it's likely moving less air than the e-fan, so it's likely using less HP than the e-fan.

Now, traffic clears out and I'm now zooming along at 60 MPH. e-fan are (or should be) completely off and taking zero HP. Conventional fan should have the clutch open and be freewheeling.

So at idle, the conventional fan may win the HP battle, provided you don't care about maximum A/C. And a 60 MPH, the e-fan wins since they should be off. At 60 MPH the conventional fan is disengaged, but it's still taking some HP just becasue of the mass and clutch drag.

Thoughts? Comments?