Quote:
Originally Posted by Mxfrank
A Allowing for the 80-90% efficiency of the average alternator (where did you get 70%), about 1HP of engine horsepower will be consumed by either alternator.
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The 55% average alternator efficiency number comes from Delco-Remy. The 70% number is from Denso for their proprietary high efficiency hairpin design.
I agree on the efficiency of electric motors and fans in general. I think they make sense if the alternator can handle it. However, they can't approach the efficiency a direct driven fan - too many conversion losses. They work well only because they don't work often.
Decoupling pulleys help with serpentine belt tuning and efficiency. The crankshaft of an engine only spins at an average RPM. Each piston stroke accelerates and decelerates the crank momentarily. The decoupling pulley prevents the mass of the alternator from being decelerated and consequently re-accelerated. This prevents belt flutter and improves efficiency. Even fixed RPM operation is not steady state. Modern alternators are massive and accelerating that mass takes power.
Mike-D: I'm glad your setup works for you and it's encouraging should I ever go that route. On my 220D with all accessories running (no AC) I'm hitting 35 amps - think traffic jam at night in the rain. I'd feel more comfortable with a 55 amp alternator if you add the fan. Easy to do with stock parts.
I looked at the Volvo 850 fan which is a popular choice for conversions. Current on high is 35 amps, low is 28 amps and the starting current peaks at 80 amps. The Lincoln MKVIII fan (another favorite) is even worse. A fan with a running current of only 6 amps can't move much air as compared with these OEM solutions. If you say it keeps your car cool I might give it a try though. Where did you get your fan?
I look at this problem for my 220D from the standpoint of maximum efficiency and simplicity. Adding a serpentine belt drive and an alternator decoupling pulley with an electric fan might yield an efficiency improvement. Serpentine belts have reduced loss because they are thinner and have less power loss with each bend. On a car with a full set of accessories it's possible to replace 4 V belts with a single serpentine yielding definite gains. My 220D has only one belt so the gains are minimal. Especially considering the fabrication costs. Without the serpentine I can't use the decoupling pulley so my only route to improving efficiency is an alternator with the smallest rotating mass.
On a 300D - I'd go electric. The fan clutch is expensive and the engine produces plenty of power. The 300D is efficient for what it is but it's the wrong platform to start with if max efficiency is your goal. A 115 amp alternator, V belts and a Volvo 850 fan make great sense here. AC performance improves too.
The best solution and the one I'd implement if fabricating is the belt driven electric clutch fan from the 190D. Small electrical load and high mechanical efficiency.