understanding capacitors

[electrondady1]

i have been trying to understand capacitors.

i want to rectify the output of my alternators to direct current and place a capacitor in series with a resistor (heater) so that the windmill can start under load.
others have done this so i know it works.
capacitors have voltage and farad values marked on the outside.


what i don't understand is,
if i feed a capacitor 14 volts,  (one that says 100 volts )
what sort of voltage is the resistor seeing?
14 volts or 100 volts ?

[jvnn]

I don't know beans about starting under load, but if this is the circuit you are considering I can tell you a little bit about how it works.

At the instant your power starts up, you will get a burst of current flowing through the resistor.
Then after a very short time, your current will taper down to zero.
The voltage your resistor sees will initially be your full 14 volts, then taper to zero.

The voltage rating on the capacitor is simply the maximum it can be exposed to before it blows up.

The interesting question is how much current flows during the short burst, and how much time it takes before the burst ends and tapers to zero.  That is dependent on the voltage of your circuit and the microfarad rating of the cap and the resistance of your resistor.

I will leave it to someone who knows more about wind power to discuss starting under load.

[ghurd]

The cap will stop DC from flowing after a second or 2.

The cap ideas other used are done with AC.
G-

[kurt]

Zubbly did what you are talking about but with the variable ac of a 3 phase motor conversion and he used large dc caps wired back to back in series instead of motor run caps as he could not find enough large microfarad motor run caps to get the microfarads he needed for the current he was making.

he found that the caps got excessively warm doing that and was nervous they would eventually fail and just before he died he switched to a conventional dump load system using some scrap batteries and a diversion controller until he could come up with a better idea but he got to sick to soon to make any further modifications to the  system.

it is all here somewhere if it made it over from the old board i remember talking to him about it extensively on irc.

[electrondady1]

yes i used to have all those threads on my hot list
including some from Putte and Janne.
i saved my hot list to  my documents  in preparation for this new board
but i found after awhile the links would not work any more.


i have been informed that to do what i want,
 i need non polarized capacitors on each of my alternators
up stream from the rectifiers.

[BrianSmith]

They also need to be a larger value cap so they will pass the low frequency AC from the mill.  Lookup capacitor impedance calculators on Google and put in your AC frequency (I think this will be (at cutin) (# magnets / 2) * (cutin RPMs / 60).  Put in your capacitor value and it will tell you the effective impedance of the cap.  You want to keep this really low if you don't want them to get hot.  The faster the mill spins, the higher the frequency, the lower the impedance of the capacitor.  I would think you need a pretty big cap if you want to run any power thru it....

[electrondady1]

perhaps this question could be placed in storage but i had an idea that could use some light on it

wondering ,if a guy was in a position to harvest energy in one location and store it in large capacitors .
then transport the charged capacitors to another location where the energy could be down loaded so to speak.

you could do the same with multiple battery banks i was just wondering since caps can unload in a hurry
it might be practical?

[ghurd]

It takes huge value caps.  And I mean astronomical values.
What most people would call an astronomical value would not be enough usable power to boot up a laptop running Vista.   

Might find something interesting here,
http://fieldlines.com/board/index.php/topic,143309.0.html

G-

[DamonHD]

Booting Vista requires 1Mb, I believe, ie the Mega (metric) buttload, covered by a new SI unit.

Rgds

Damon

[Bruce S]

perhaps this question could be placed in storage but i had an idea that could use some light on it

wondering ,if a guy was in a position to harvest energy in one location and store it in large capacitors .
then transport the charged capacitors to another location where the energy could be down loaded so to speak.

you could do the same with multiple battery banks i was just wondering since caps can unload in a hurry
it might be practical?

E1;
 That is being done in a smaller sort of way. The USB crowd is making Joule thief circuits. They basically use discarded batteries, that have the appearance of being dead to most circuits down into the 0.3Vdc arena .
These Joule Thief circuits by use, of coil and transistors grab what's left in the batteries, and either use it to charge up a RC network to light LEDs or to recharge mobile phones ( i.e. Altoids tin Joule Thief) the circuits are a snap to build and work even if built with hot glue  .
Google the Joule Thief and you should get tons of hits.
When using Caps, you could certainly charge them up and then use them to recharge batteries. BUT I don't think I would use them to recharge at a high rate, though you could if your battery bank could handle the high rate of charge.
Hope this helps
Bruce S

     

[joestue]

perhaps this question could be placed in storage but i had an idea that could use some light on it

wondering ,if a guy was in a position to harvest energy in one location and store it in large capacitors .
then transport the charged capacitors to another location where the energy could be down loaded so to speak.

you could do the same with multiple battery banks i was just wondering since caps can unload in a hurry
it might be practical?

E1;
 That is being done in a smaller sort of way. The USB crowd is making Joule thief circuits. They basically use discarded batteries, that have the appearance of being dead to most circuits down into the 0.3Vdc arena .
These Joule Thief circuits by use, of coil and transistors grab what's left in the batteries, and either use it to charge up a RC network to light LEDs or to recharge mobile phones ( i.e. Altoids tin Joule Thief) the circuits are a snap to build and work even if built with hot glue  .
Google the Joule Thief and you should get tons of hits.
When using Caps, you could certainly charge them up and then use them to recharge batteries. BUT I don't think I would use them to recharge at a high rate, though you could if your battery bank could handle the high rate of charge.
Hope this helps
Bruce S

    

capacitors: up to 30wh/kg, more like 3 IRL.  
lead acid: 0.14MJ/kg
gasoline: 44MJ/kg.

at 457 ton-miles per gallon of diesel fuel for a train.. its possible to do the math and say that
457 tons of capacitors is about 8.2Gwh at 5wh/kg, and you'd be able to ship this about 186 miles under its own charge, or 100 yards before a transmission line is less investment.  

[electrondady1]

i wasn't thinking about train transportation.
i live in town and can't build a big 20' dia . windmill.
but if i had one on land out in the country.
say, 3 miles away
with a truck full of capacitors parked at the base.
once a week ,i drive the truck back home and unload my capacitors.

joestue has pegged  the carrying capacity at ether 30wh/kg or 5wh/kg
so 300lb of capacitors could carry 300/2.2=136kg x 30wh =4090wh
enough juice to run four base board heaters for and hour.
oh well, just a thought.

[joestue]

i don't even know if its that high.

just did the back of napkin numbers for some mylar caps i have, 9uf, 4Kvdc works out to about 70Joules/kg.
super caps are significantly higher.


its really not worth transporting batteries either.