I've got two capacitors that I need to use as a power source, but I don't know how to charge them properly. Is there a circuit that I can build to charge them to max and then indicate it with an LED or something? I'd like to use the two caps as a power source for a basic robot I'm building, since its cheaper (in the long run) than batteries.
edit: Come to think about it, I've never even used capacitors before and don't really know how to use them as a power source. Can I just wire them in series like a battery?
It won't be much of a robot trying to run it on capacitors, their capacity is tiny in comparison to even the most basic batteries. Think single figure milliamps for around an hour for a 10F capacitor. 3 Alkaline batteries in series will provide around 2-300 times more capacity than 2 of these.
On the plus side, they don't need much of a charging circuit and yes you can wire them in series. They are intended for short term battery backup (like keeping memory alive whilst the batteries are changed). Thye can't provide any real amount of power for any time.
I'd estimate they would keep an arduino nano running providing you don't connect anything else to it for maybe 10 or 15 minutes. Their voltage drop is linear unlike batterys so they gradually fade out, the arduino will die with a brownout when around half their capacity is used. To charge them you just supply them with their running voltage though a resistor to limit the current. Running motors and servos as used in robots - forget it.
That is unfortunate. I had hoped to eliminate the need for batteries. Sparkfun lied to me I am assuming that if I connected them in series to a USB port through a resistor that they wouldn't overcharge somehow and explode? I've accidentally made caps explode before and haven't really used them since then.
They couldn't keep an arduino nano powered for a reasonable amount of time? Regardless, how would one go about charging them?
Not for a reasonable amount of time (what I consider reasonable). However if you know the total current draw of your nano plus any loads wired to the output pins, it can be calculated, research R/C time constant.
A problem with using caps as a voltage source, even if they hold enough charge, is that their discharge voltages decreases linear with time, not a flat discharge curve like a battery. They are only really useful for micro-amp loads.
To charge a cap you wire wire it to a series resistor to a voltage source. For your 5v rated cap, just use a 10 ohm resistor and a 5vdc voltage source. The 10 ohm resistor will limit the initial current charge to 500ma and the charge current will taper off as the cap gains charge until it matches the voltage source value.
Capacitors don't like over voltage or too much current being pulled out or pushed into them or they do have a habit of exploding. 10 Farads at 5 volts is 50 Coulombs, an AA battery is measured in 1000's of coulombs. 3 of them (4.5 volts) in 10,000's. Halfway through the discharge, the capacitor will be at half volts, the battery almost at its starting voltage.
You can't over charge a capacitor. When it gets up to the charging voltage it just stops. However, you can charge some capacitors too quickly and exceed the maximum charging current, that can generate heat and an explosion but is not normally a consideration. What size capacitors are we talking about here?
... but words convey meaning and in electronics it is important to be precise because there is so much going on you are best not assuming what is meant.
As my manager puts it "Assumptions are the mother of all F*** ups"
OK, but can you show an example of how to overcharging a cap where there isn't a voltage source that is above the voltage rating of the cap or a reverse polarity involved?
So since I can't use these things as a power source for a reasonable amount of time... I've decided to use them to make a joybuzzer. However, before I do this, do you think it would be fatal?
but can you show an example of how to overcharging a cap where there isn't a voltage source that is above the voltage rating of the cap or a reverse polarity involved?
No that is why I said:-
You can't over charge a capacitor.
Having said that I will prove us both wrong. When the inrush current exceeds the capacitors ripple current.
However, before I do this, do you think it would be fatal?
I am assuming that if I connected them in series to a USB port through a resistor that they wouldn't overcharge somehow and explode? I've accidentally made caps explode before and haven't really used them since then.
