Let's say you are out trailing and for some reason your battery dies. If you take the belt off and you spun the shaft of the alternator by hand for about an hour could that charge your battery enough so you could start it back up? Just thinking about a last resort if you were in the middle of no where.
I never tried it but would like to know if this theory could work. Thanks

 

You would have cramps way before the hour was up! LOL

Bring an extra battery if you are worried about it.

Then again, if your battery dies, most likely its the alternator or battery.

 

Just to be clear i dont plan on using this theory and i would keep an extra battery if i go on a trail by myself, my point was if you were out in the middle of nowhere and you left the radio or lights on, and your battery died, could the theory above work, just by spinning the alternator by hand, thank you guys for sharing your advice.

 

You would have to spin the shaft at about 700rpm. Aint gonna happen.

 

So if you had a cordless drill spinning it, could it happen*

 

for some reason, breaking bad comes to mind with this question.

in theory it works yes.

 

Your correct with breaking bad,

 

awesome

 

If your battery is truly dead, an alternator will not bring it back, however a generator will.

 

It would be a nice little thing to know if your ever in a very tight spot, i was just thinking that an alternator has to spin to make power, and an engine spins an alternator at pretty high rpms just at idle, so i was thinking if you spun it for an hour or so by hand would it produce any charge to the battery, but if the battery is abosultely dead then no but if wasn't all the way dead i think you may have a chance, and also figure it would be a neat thread so people can explain how it could or could not work, i think it could work but you would have to have time and dedication to make it happen, but i truly dont know if it would work.

 

More like ~3,000 rpm to get a decent charge.

And, you'd have to have power fed into the field coils - which is not RPT NOT full battery voltage! (Typically either 0.5-4.0VDC for the old DC regulators. New regulators are PWM - Pulse Width Modulated - which means a variable square wave of +12VDC. Either way, it is not a constant +12VDC with no modification, that's a good way to melt down electronics...)

 

The pulley radio between the engine and alternator is not 1:1. It's probably something between 1:2 and 1:3. Let's assume it's a 1:2. If the engine is running at 700 rpm, the alternator is spinning at 1400 rpm and making 13.8V. Now let's say it's a good day and your hand cranking that alternator at 60 rpm. That's roughly 23 times slower than the engine. Say it takes the engine running for 30 min to revitalize the battery to where it can crank the engine, it would take you 11.5 hours of turning to do the same.

Now, think of voltage as a pressure, current as a rate of flow, and resistance as a resisting force. Say you have a hose full of water/air/helium, pick your fluid, and it's flowing at a set rate with a certain amount of resistance. Now you increase the resistance by putting your thumb over the end of the hose, the pressure increases. If you increase the flow of fluid, the pressure increases. If you add current or resistance to a circuit, the voltage increases.

To fill an a tank of oxygen/acetylene/air , pick your fluid, you generally use another tank. The tank had to have more pressure in it than the one your filling though. The two tanks will want to equalize, greater pressure will flow to the lesser pressure. Batteries are just tanks for voltage, they charge much the same way. The greater the pressure difference, the quicker the fill.

Back to the hose example. When your current goes to zero, so does your pressure. A motor is a device that converts pressure and flow http mechanical power. The unique thing about it, it's reversible. When you put mechanical power into the same device, you generate pressure. When dealing with fluid, it's called a compressor and when dealing with electricity it's called a generator (alternators are slightly different but the principle is the same, the current is just alternating).

I bet your asking yourself why this big long explanation of what is seemingly useless examples and information. Well, so you can understand that when you stop to reposition your hand on the pulley of the alternator, the flow rate of current goes to zero (therefore the voltage goes to zero) and if you haven't made it above the battery's voltage level you haven't put any energy into the battery and have just wasted your own energy...

 

In other words, it ain't gonna work.

 

Well would a cordless drill work if you was able to get it on the alternator and spin it?

 

That was the first thing I thought of when I read this post!

This scene: