Alternator clutch
 

I was thinking about the mpg benefit (up to 10%) from deleting the alternator, but with the risk that you drain the battery on an extended journey.

But thinking about how the air conditioning is switched in using a clutch, could the same be done with an alternator?

With this set up, while driving, the alternator pulley would spin with the belt, offering minimal resistance until a sensor detected the battery falling below a set voltage (say 12V). The sensor would then engage the A/C-like clutch to spin the alternator until the battery returned to a set voltage (say 13.5V), and then disengage once more.

Has anyone done this? What do you think - worth a try?

Brian

How does the drag of the clutch compare to the drag of the alternator when the field windings are turned off? there is a reason that it's worth removing the belt from your A/C if it doesn't work or you don't use it ever.
I haven't seen an alternator with a fan on it for years, so if your field windings are turned off then the only drag on the alternator are the carbon brushes, the bearings and the rotor, adding a clutch you will be adding another set of bearings, more rotating weight and more air drag.

One problem with this solution is that the energy has to go in and out of the battery, that loss might be bigger than the savings at the bearings. (At least with lead-acid.)

Oh, they still have fans; they've just moved inside the housing (probably for noise reduction). Except for the liquid cooled ones.

The only potential savings I see from a clutched alternator are from not spinning a cooling fan. The added drag from the clutch itself may cancel out even that meager benefit.

The alternator on my Civic doesn't have a fan at all, inside or out, and I checked the parts diagram to make sure I wasn't missing it, maybe I've just spent to much time around Honda's, but like I said, I haven't seen many fans on alternators any more.

Oh- haven't done a Honda. The ones I've seen have internal fans, not like the old GM fan adjacent to the pulley.

Did a quick handful of google searches on alternators and it would appear that America likes to put fans on their alternators, Japan does not, nor do the VW alternators that I looked at exploded views of, but the American made alternators have a big old crude "fan" right there, ready to chop up whatever comes at it.

An alternator with a clutch on it will still need energy to keep the clutch engaged. This will most likely be anywhere from 24-36 watts worth. You would need to save more than this for this mod to be effective. Plus you would have a clutch assembly that could possibly go out on you too. Some one else mentioned it is harder(takes more energy) to start it spinning from a stand still than it would be to keep it rotating.


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My Golf has a clutched alternator. On cold mornings when the battery is almost dead from previous days EOC you can tell it's cycling off and on rapidly during idle because every 5 seconds the engine sounds loaded, then unloaded. To me it's just another thing to break.