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Car Alternator

Using excess electricity from car alternator
 (-2) [vote for, against]

Has anyone ever considered using the excess electricity from the alternator from the car? When a car is not using all of the electricity the alternator can provide the excess electricity is converted to heat in the voltage regulator. Could an additional battery be connected to "tap" into the excess energy and charge the battery for home use?
 — dogbulter, Jan 31 2007

US Battery http://www.usbattery.com/
lots of good info on ampacity of different size batts [elhigh, Feb 02 2007]

(?) PM alternator using a motorcycle alternator
http://www.dangerouslaboratories.org/altp1.html [n81641, Jun 09 2008]

There isn't any "extra" electricity. By using power from the alternator you are increasing the electical resistance if gives to the engine, increasing gasoline consumption.
 — Galbinus_Caeli, Jan 31 2007

Not by much, [G_C].

[dogbulter], there's a device called a split-charging relay which is used by RV and caravan owners to charge the battery used in the 'home' part. Pretty well baked.
 — angel, Jan 31 2007

Sorry to say, dogbulter, but the control system for a car alternator doesn't work the way you think it works. The voltage regulator doesn't convert all the excess into heat; it makes sure there is no excess to begin with, by varying the magnetic field in the alternator so that the voltage is right.
 — Ling, Feb 01 2007

 But Ling, surely the system is not perfect, and SOME excess is converted to heat.

Of course, getting electricity out of that instead of just entropy will be quite an engineering problem.
 — ye_river_xiv, Feb 01 2007

Yes, a little bit is probably used to heat up the input of an Op-Amp circuit. At least a fraction of a micro-watt.
 — Ling, Feb 01 2007

 The energy available in a typical car battery isn't as much as you might think. In order to get one amp at 120v, you have to convert 11a from your 12v battery - sorry, no free lunch: the inverter eats a bit of your energy.

 A 27TMX size battery from US Battery [link] will supply about 12.5a for eight hours before pooping out. You can take over 60a for one hour, but you're still looking at only 700w on the output end. That's not a lot of juice. And having used all of that stored energy, now you have to shove it back into the battery. A car's voltage regulator is not a sophisticated charge controller and will simply stuff however much current into the battery as the alternator can generate. How long do you have to drive to fill a C/8 100ah battery back to 100%? Depends on the alternator, but it's at least two hours at cruising speed, and a charge/discharge cycle like this is absolute hell on an auto battery.

I saw in a Mother Earth News article about fifteen years ago a guy who was doing this exact same thing, complete with the extra battery. His commute was about an hour each way, and the electricity was for the light in his propane-powered fridge, a couple of small lights here and there in the cabin, a very small black and white TV and a stereo. All those items were 12v.
 — elhigh, Feb 02 2007

Dogbutler has a point.. even though more electricity consumption causes more resistance, there is still a surplus of energy supplied by the alternator. If I were to install a split charging system in my truck and use it to charge 3 separate batteries while driving down the interstate, the amount of resistance and additional fuel consumption would be insignificant. But in contrary to what dogbutler said, the car will never be able to generate enough energy to adequately help power a house.
 — Jscotty, Feb 02 2007

Permanent magnet alternators such as those on some motorcycles and power equipment, DO just make heat once the battery is charged. PM Alternators can be much more efficient that a typical car alternator, until you consider the waste when the power isn't needed. A solution like this might help.
 — n81641, Jun 09 2008

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