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oil pan 4 08-29-2015 12:26 AM

Alternator delete switch
2 Attachment(s)
Just turning power off to the alternator isn't good enough for me.
No I want to stop the alternator from turning and sever its electrical connection, with the push of a switch, because I am lazy.

Just removing the electrical load is only removing half the over all load at best. Since vehicle alternators are around 50% efficient at their peak efficiency (max amp draw for that RPM).
So most of the time the vast majority of the engine power sent to the alternator is used to beating on the air around the alternator.
This is why you want to stop it.
Then you must cut power to the voltage regulator, With the alternator stopped and the voltage regulator powered up it will still draw 2 to 3 amps. I found this out the hard way when I rewired my charging system to use the high amp output post on the alternator and put one of the wires in the wrong spot. It slowly drained my batteries.

I have seen people put A/C clutches on an alternator. Only problem with that is you put a bigger pulley on, reducing amp out put. For some applications that larger alt pulley is great. Not mine.
When I need power, really I need power.

How then?
I believe I should take the alternator, make it pivot. Install a spring to bring the alternator belt under tension. Then counter the spring tension with a pneumatic linier actuator when alt power is not required.
But that would allow the belt to fall off the pulleys.
Not unless I install a guard around the belt holding it in place. Just like on a riding lawn mower. The guard holds the belt just off the alternator drive pulley when tension is relaxed.
Since its riding lawn mower technology I think it could work.

All it then needs is a source of compressed air.
I have that at least.

How to control the air? The smartest way to do it would be non electronic. Something like this.

Frank Lee 08-29-2015 12:54 AM

I like the train of thought. But being opposed to Rube Goldberg complexities, I think I'd want an all-mechanical solution, like a cable or lever.

Then what happens to the other stuff on the belt drive? (water pump, pwr str + a/c if you have 'em)

oil pan 4 08-29-2015 01:59 AM

Its a lever, spring and pneumatic actuator. The simplest Rube Goldberg device in the history of Rube Goldberg devices.
The alternator is the only thing being driven by this v belt.
The coolant pump is electric.

Frank Lee 08-29-2015 02:32 AM

OK Carry on.

Baltothewolf 08-29-2015 02:44 AM

Just have an electric motor turn alternator, creating it's own energy, therefore cresting an infinite power source. Great Scott!! Why didn't I think of this sooner!! Infinite renewable energy!!

OK seriously though, why not just use an A/C clutch, but upgrade your alternator to compensate for the bigger pulley size?

GhostWolfGT 08-29-2015 08:36 AM

I can't see it making all that much of a difference. I've seen a homemade wind generator spin out of control because there was no load on the alternator being used. Almost no resistance. Put 1 light on it and it comes down to a safe speed. You could probably test it before rigging it all up by observing engine load at idle with and without the belt.

I do like Frank's idea if it was worth splitting hairs, though. A parking brake lever and cable from a car would be perfect. A trampoline spring holds it loose and you pull up on the parking brake to tighten it up and activate the alternator. Locking it in place. Less weight. Less room for a failure later on. And you could find an even better use for the actuator.

You could even wire the switch in the parking brake to a relay that turns the alt back on when pulled up.
Alternatively, a spring loaded idler pulley would probably work best so not to wear out the pivot point on the alt. But use the cable to release tension when pulled up instead of create tension.

oil pan 4 08-29-2015 01:32 PM


Originally Posted by Baltothewolf (Post 491522)
OK seriously though, why not just use an A/C clutch, but upgrade your alternator to compensate for the bigger pulley size?

A typical A/C clutch is so much bigger than a regular alternator pulley that the alternator over drive ratio would go from a 1:3 over drive down to a 1:2 or 1:1.5 over drive.
Then at idle being over driven at 1:2 the alternator would only spin 1200 to 1400 RPMs and make almost no power. Getting a bigger alternator would not fix this.

This is on a 6.5L mechanically injected diesel. I cant hook a computer up to it and look at the difference in load. The only way to see how much the load changes with out the alternator hooked up is to watch for the RPM increase at no load with the injector pump metering lever set in a fixed positions. Such as idle and fast idle.

All the air compressors I have built and rebuilt use a idler tensioner. This is my preferred method but I don't think loosening an idler can prevent the belt from rubbing on the crank pulley.

I would use spring to tension the alternator so that if the cable broke, the actuator or its air supply failed or what ever mechanism I used failed, the alternator's belt would go to tension and start supplying power.
This is a fail safe mode.

oil pan 4 08-29-2015 01:44 PM


Originally Posted by GhostWolfGT (Post 491533)
I can't see it making all that much of a difference. I've seen a homemade wind generator spin out of control because there was no load on the alternator being used. .

Most vehicle alternators red line at 15,000, they can exceed this speed, but not for extended time.
Those small turbine alternators only have to turn a few hundred RPM to make power because of permanent rare earth element magnets. They spin "out of control" at under 2000RPMs because of the huge relatively unbalanced blades attached to them.
You are correct, it does take almost no power to turn an alternator 2,000RPM, but in a vehicle the only time the alternator in a vehicle spins less than 2,000RPM is at idle.
At cruise speed the alternator is typically spinning between 6,000 and 10,000 RPM.
Every time you double the speed, aero dynamic drag on the alt increases by 4 times.
This is why vehicle alternators are not very efficient.

Frank Lee 08-29-2015 02:33 PM

I slowed mine down and it does the job.

markweatherill 08-29-2015 03:13 PM

If you want to mechanically disengage and re-engage the alternator at will, I feel a more reliable solution would be to adapt things so it is driven by the outside of the belt, and just needs to pivot towards or away from the belt surface.

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