Go Down

### Topic: Capacitor Question (Read 694 times)previous topic - next topic

#### Alligator

##### Aug 21, 2010, 03:39 am
I have a capacitor rated at 5V, but I have a 9V solar cell that I want to connect to it.

First, I know charging with a voltage above the capacitor rating is bad, but what if I disconnect it when the charge gets to 5V on the capacitor?  Or, is there a way to reduce the 9V to 5V and keep no higher than this voltage?  The only thing I can think of is 7 diodes in a row (0.7 volt drop across each diode).  This seems a little ridiculous.

#### RuggedCircuits

#1
##### Aug 21, 2010, 04:04 am
Do you have *another* capacitor? You can put them in series which will accept 10V (albeit for half the effective capacitance).

Yes, you could disconnect the 9V source when the voltage reaches 5V, but this sounds relatively complicated.

You could put the 9V through a voltage divider to get no higher than 5V, though this wastes current and slows down capacitor charging (any more details on what you're trying to do?)

You could also put a 4.7V zener diode across the capacitor to limit the voltage. Again, the best solution is going to depend upon what you're actually trying to do.

--
Check out our new shield: http://www.ruggedcircuits.com/html/gadget_shield.html

#### TchnclFl

#2
##### Aug 21, 2010, 04:05 am
Yeah definitely don't over voltage a cap.  It's bad.

Also, you really shouldn't get too close to the limit either.  You'd be better off capping it off at about 3.5-4 volts.

#### jackrae

#3
##### Aug 21, 2010, 01:06 pm
Go and get yourself a properly rated capacitor, say 25 volt rating.
jack

#### deSilva

#4
##### Aug 21, 2010, 04:29 pm
(1) Solar cells issue their current at quite different voltage,
http://www.pvresources.com/en/solarcells.php
Is 9V really the max of your "system"?
(2) The energy stored in a cap goes with V square, thus also the price

#### jackrae

#5
##### Aug 21, 2010, 07:51 pm
Some questions for the author
1) what is the watt rating of your solar panel system
2) what is the value of the capacitor you have in microfarads
3) why do you want to put a capacitor across the PV panel
4) what is your PV panel connected to (battery ? etc)

When you've answered these we might have a better idea of what you are ebdeavouring to achieve

jack

Go Up

Please enter a valid email to subscribe