In this video we're going to commit random acts of destruction and learn a few
things about capacitors along the way.
Recently "Electronic Goldmine" had a good price on some ultracapacitors
and I bought a lot of them.
Ultracapacitors are like regular capacitors
except they can hold much more energy.
Here's an example:
This is a 560 microfarad 200 volt electrolytic capacitor.
It is about as big as you will ever see on a consumer circuit board.
The energy stored in a capacitor is given by this formula.
If I apply the formula to this capacitor I can see that it can store
a maximum of 11.2 joules.
In certain circumstances that's enough to do some serious damage.
Now the ultracapacitors I bought are 2600 farads (and that's not a mistake)
2600 farads
with a maximum of 2.5 volts.
That means that one of these ultracapacitors can store 8100 joules
of energy which is a huge difference.
So let's see what a few kilojoules can do.
Here I have the ultracapacitor charged to 2.35V and you can
already see this thing means business.
Let's start out by burning some soldering braid.
Now let's melt an inductor.
Here I'm shorting the capacitor across a five cent coin.
Wow, that beaver really took a pounding.
And I thought it was fun to make these PCB traces light up like glow wire.
Finally let's make some random sparks again just for fun.
After all this, the capacitor is still charged to 1.7 volts.
If you apply the capacitor energy stored equation before and after blowing things
up you can see that I used up 3370 joules of energy.
So there's a lot left over.
Now you might be wondering "how did I do all that with just 2 volts?"
If you take two AA batteries and put them in series
you get 3 volts with 2.5 amp-hours of capacity
which is equivalent to 27000 joules of stored energy.
That's more voltage and more capacity
than the ultracapacitor has
and yet there's no way you could do all the things I just did
with two AA batteries. So what's the difference?
The answer is a non-ideal property called "equivalent series resistance"
"ESR" for short.
Batteries, capacitors and a lot of other electronic components will have a
small internal resistance
which limits the amount of current that can flow.
For a typical AA alkaline battery the equivalent series resistance is
120 milliohms.
When you put a load on the battery this resistance will cause a drop in voltage
and generate heat within the battery.
For example a low power device like a television remote control might draw
20 milliamps.
This would cause a 2.4mV drop (which is nothing)
and generate 48 microwatts of heat in the battery. (This is also tiny.)
But if I try to draw 10 amperes from the battery, there will be an
internal voltage drop of 1.2 volts.
And 12 watts of heat will be generated within the battery.
So at higher currents the battery voltage is unreliable and things get
hot enough to be very unsafe.
Now let's see how the ultracapacitor would perform.
This capacitor has an incredibly low equivalent series resistance of 0.7 milliohms.
So with a ten ampere load,
the internal voltage drop is 7 millivolts and only 70 milliwatts of heat
are being generated.
That's nothing.
Even at 100 amperes there's only a 70 millivolt drop and 7 watts of
heat are being generated.
For a capacitor this big that's not a problem.
So you can see that because of the extremely low ESR
these ultracapacitors can charge and discharge hundreds of amperes no problem.
So anyway I'd say that was pretty impressive for a 2 volt supply.
Now let's see what happens with a higher voltage.
If I put 4 of these ultracapacitors in series
the maximum voltage becomes 10 volts.
With a higher voltage I can deliver more power into a given resistive load.
More power means bigger explosions!
Here's what the ultracapacitor array looked like wired up.
But when I tried to charge it up I ran into a bottleneck.
My bench power supply is limited to 5 amperes and for capacitors this big
it's going to take a really long time to charge them up.
Since I have some time to waste,
let's estimate how long it will take using this formula.
5 amperes divided by 650 farads gives me a charge rate of
7.69 millivolts per second.
Since I want to charge my array up to 10 volts... 10V / 7.69mV/s
equals 21.7 minutes.
Okay now we're at 9.65 volts and let the fun begin!
Ooh this is going to be good...
Now the PCB traces don't melt anymore they just vaporize.
And it turns out that the insulation on magnet wire is flammable...
I didn't know that.
Let's try it with 10 cents.
(Looks like this ship has sailed)
Finally let's vaporize a nail.
And after all that the capacitors were still charged to 9.33 volts.
If I use the same energy storage formulas as before,
you can see that I used up about 2000 joules of energy.
In conclusion, ultracapacitors are awesome and if you care about safety
don't do anything I did in this video!!!