Energy storage question

jjg53jjg53 Registered Users Posts: 2
hello all and thanks for a wonderful site! im building a kinda "free energy" device using a car alternator and rare earth magnets. im in the beginning stages but just had some questions. i dont have a strong electrical background so i wanted to check a couple things out before i began. i want to run my alternator to a capacitor bank, and use that as my battery. i then would run that power to an Inverter. my questions are...
1. what would be a good starting capacitor size, would run a few of them in parallel. was wondering if a 2.2 farad car audio capacitor would work but im thinking not
2. the alternator (100A) i have does not have a regulator, what would be a good regulator, so im not overcharging the capacitors

thank you again!!!


  • BB.BB. Super Moderators, Administrators Posts: 28,315 admin
    Capacitors (even "ultacapacitors") really do not store much energy compared with a lead acid battery. Here is a bit of math/discussion:

    Don't even bother going down the road with Capacitors vs Batteries. It will not do anything useful for you.

    Another issue with converted car alternators is that they tend to run at high RPM to generate "useful" amounts of power. The blades to not spin fast enough (usually) to turn a converted alternator at "optimum" RPM. And any sort of gear box/belt device to increase Alternator RPM is fairly lossy too.

    And, car alternators can output >100 volts pretty easily, the battery bank actually does the voltage regulation on a short term basis. The voltage regulator is for long term regulation (i.e., battery at 14.4 volts when full).

    A standard alternator uses rotating field coil (and slip rings) to regulate the output voltage (more current to coil, more charging current. Less current to coil, less charging current). With a PM conversion, the "standard" regulator will not work anymore.

    The typical solution is to use a PWM Shut/Diversion/Dump charge controller and resistor bank. When the battery is "full", the dump controller turns on and sends the excess current to a resistor/load bank (heating air/water/etc.). There are some standard solar charge controllers that can be setup as dump load controllers.

    If you are very interested in wind power--I would suggest these links/forums: (good forum for DIY Wind Power)
    Hugh Piggott - Scoraig Wind Electric site for tons of info (from mike90045)
    Scoraig Wind "Recipe Book" for DYI Turbines (added from "russ"--Like here but more wind/less solar)

    Personally, I am not a big fan of small wind... You really need to build your own turbine (or if you can find one of the few good commercially built units)--And fly it a minimum of 60-90 feet above ground level (and over nearby buildings/trees/hills).

    For a project, you can learn a lot. For generating useful amount of energy--Do some more research first. And understand the wind flow at your own site. Most people do not live in areas where there is lots of good wind (windy sites are usually miserable places to live). And you need to fly the turbine above the turbulent layer of air near the ground/buildings/trees. There is very little useful energy in turbulent air.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jjg53jjg53 Registered Users Posts: 2
    hey thank you very much for the reply. ya im just toying around now with the ideas of alternate energy and how to apply them around the house and whatnot just trying to get my feet wet in the area haha...
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