Renewable Energy Questions/Discussion > Renewable Energy Q&A
dis -charging capacitors
artv:
hi all, if i charge caps to 40 vdc ,then connect them to a battery..........the caps will drop, to battery voltage... on a 12volt battery....does this mean 28 volts were dumped into the battery??...........but the amps are limited to the "uf" capacity??? the more "uf" the more amps??? KVL ....from what i understand ....says there is only x amount of voltage ,....the amps only come from the resistance...........?? If I can charge caps in the blink of an eye and discharge them into a battery, in the blink of an eye........but stay at ~40vdc ..... does this mean i am dumping 28 volts into the battery ,on a contiuious basis??..............but limited to the "uf" ...amount of amps????...............maybe i should get another wobbly pop..........lol..........artv
WooferHound:
A pulse charger does what you are talking about.
It's a different way of charging but it isn't better
Charging with pulses is the method that desulfators use
Try not to charge a battery any faster than 10% of it's capacity
oztules:
Artv, there is some confusion here.
"hi all, if i charge caps to 40 vdc ,then connect them to a battery..........the caps will drop, to battery voltage... on a 12volt battery....does this mean 28 volts were dumped into the battery??...........but the amps are limited to the "uf" capacity??? the more "uf" the more amps??? "
We cant dump volts anywhere... because the volts are only a pressure figure. We need to drive/dump electrons into the battery. Each electron will give us 1 single molecule of change on the plates.... so the more electrons pushed into the battery by the voltage, the better.... it's not the voltage that does the charging. It delivers the pressure to push the electrons where we want them... but it is not what charges the plates in the battery.
The higher the uf, the more charge we can accumulate. It wont matter if it is at 1 volt or 100000 volts, the charge will still be 1 farad of electrons for a 1 farad capacitor. I think a farad of charge is about 6x10^23 or near 100000 coulombs. A coulomb is 1 amp of electrons flowing past a point in one second... about a 6x10^18 figure.
So can you see that the capacitor simply "stores" charge.... and that charge is just electrons.
The voltage gives it pressure to move those electrons. This voltage and charge can be equated to energy by
E=1/2 Capacitance X voltage squared.
Now, if we charge a 1 farad capacitor, we know how many electrons we have ready to go somewhere....... but we need pressure to push them around our circuit. So if we charge at 1farad at 1 volt.... they won't run up hill and try to get into the battery. If we charge it up at 40 volts, we have 40 ^2 (1600) times more energy stored..... but the same number of electrons..... but now they have a pressure value which if it is higher than your battery means they will flow.
We can see how many amps will flow by your ohms law..... where the amps = voltage/resistance in the circuit.
So it is not the uf that will drive higher current, it will be the volts/resistance that will determine amps.
So your 40-12v gives us a 28volt differential to work with.... so 28/resistance of the circuit is the current.
Of course, as we discharge the cap, we not only use up our electron store, but our pressure will drop too. So as it discharges, it will be like a balloon with a leak, not only do the air molecules get out and leave less in the balloon as a time function, but the pressure will drop as well, until we end up with no air in the balloon, and no pressure either.
The higher the resistance, the longer it takes to discharge....
Looked at another way, the uf tells us how many folks are in the room, and the voltage differential tells us how fast they can get out of the room in a stampede... more voltage , the more frenzied the stampede.
Does that help at all to see what happens?
..........oztules
artv:
Thanks for the replies...
So the higher the uf rating on a cap the longer it takes to charge?, because the more uf means more available electrons, which in turn mean more amps??
I'm not sure if that even makes sense :-[
I have 2 identical caps paralelled....12000uf, 56wv....Once charged to 40vdc,..then discharged into a 12 volt battery,...
The caps drop to battery voltage....so I used 28 volts....so is it E=.5 x 24000uf x 28vdc squared,.....or the 40vdc squared.....
just not sure....artv :-\
rossw:
--- Quote from: artv on January 24, 2012, 06:24:18 pm ---So the higher the uf rating on a cap the longer it takes to charge?, because the more uf means more available electrons, which in turn mean more amps??
--- End quote ---
They will all try to charge at a (nearly) infinite rate. The current could be scary though. So usually there is (some) series resistance, by design or just by nature. It is this resistance that limits the current that in turn affects the charge time.
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