The Learning Circuit 29: How Capacitors Work

Some Digital Multimeters can test them.  My DMM had a limited range, so I bought a dedicated capacitor tester with a very broad capacitance range.  It is super quick and easy.

To test, you have to desolder at least one leg off the board.

See ya',

Sean

See ya',

Sean

I better understand how they work, but what is the best way to test them to make sure they are still good or if they will are almost at the end of their lifecycle?

Haha! We'll see what happens!

Hi Matthew,

Now that you have posted the request for ideas on the element 14 forum you have 3 to 4 hundred of the best minds on the planet working to come up with a suggestion. I am not one of these minds but I do enjoy seeing what they come up with from time to time. I am not even sure about that number as they are a undisciplined lot and don't always perform on cue. We will just have to wait and see what they come up with. In the meantime we can be working on cool names for the new application. I would guess something like "Flux Capacitor" but that one is already taken. Hmm !

John

I think someone originally tried to turn this bank into a power supply for an arc welder, but abandoned the project halfway in. One of the shop elders bequeathed it to me in the hopes that I will figure out something interesting to do with it. I'm open to suggestions! Maybe we can turn it into an episode of element14 Presents!

My entire life I have dreamed of being able to have a Farad ranged capacitor. Unfortunately I was so absorbed with wanting one I never got around to what I wanted to do with it, The other night I spent some time experimenting with a 160 F 2.7 Volt bank. It felt a lot like playing with a battery with a very low internal resistance. I am still looking for the magic revelation of what to do with this.

John

I've got a huge bank of Farad-magnitude supercaps at the shop just waiting for a project. But what to build...?

Thanksfor the response, will try and get back.

Thanks Karen and John too for the response

Good stuff. In the tank example, I take it there is tank bypass piping circuit that has our pressure regulator and globe (throttle) valve in it.  That piping returns to the pump suction.  In turn, a plan view of the piping circuit looks just like our electrical circuit.

What the heck, let's throw in another load - a paddle wheel that turns a shaft for our 14th century saw mill. Even if the pump shuts off, the paddle wheel will still be driven by a flow of current as the pressure equalizes across the membrane tank allowing water to flow out of the tank down the pump discharge line back around to the tanks other side, thus draining the "capacitor".  So even if the pump surges, the saw speed will be practically constant.

Fun to think about.

See ya',

Sean

Hi Sean,

Analogies can be useful in helping us visualize and relate to our own experiences phenomenon like electrons, voltage and current which are not able to be seen or experienced in the same way. That being said, if we push the analogy far enough we will start to have to describe situations that are as complicated as the one we are analogizing. For example I will take you water analogy one step further and describe a situation that is an analogy for the diode in the circuit. We have a source of water under pressure ( Battery ), We have a tower that we are filling using the water source at the bottom of the tower. If we hook the water source to the tower the water will flow into the tower until the height of the water produces a back pressure equal to the supply pressure. As you have pointed out the introduction of a valve or restriction (resistor) will slow the process of filling the tower but will not limit the level of the water from reaching full equilibrium height. I can think of a couple specialized water controls that would act like the diode does but perhaps the best match is called a pressure regulator. This is a valve that lets water pass until the pressure on the outlet side reaches a preset level. For example we could feed a water pressure of 10 psi into a regulator set at 5 psi and the most the pressure on the outlet side will ever be is 5 psi. Now if we put the regulator between our water source and the tower and set the regulator pressure for a level less than the pressure of the source the water tower will not fill to the original height but to some fraction of the height as controlled by the regulator.  Another analogy for the diode using water is the check valve and in fact certain check valves with spring loaded gates also act like mild regulators so the analogy holds fairly well.

Electrically for a circuit to work it has to be a circuit. The movement of charge in the circuit would be simultaneous. Think, using a water analogy, of a water pump (battery) with a section of pipe hooked from its output back to its input with no breaks. When you turn on the pump, does a molecule of water leave the outlet before a molecule of water enters the inlet? Even at macroscopic levels we would probably say that they both move simultaneously. The water analogy that you described for the capacitor breaks down as you have provided no return pipe for the water to get back to the pump. A better analogy might be a tank with a rubber diaphragm sealing one side of the tank from the other side. The pump's outlet is connected to one side of the tank and the inlet of the pump is connected to the other side of the tank. It is a closed circuit, totally filled with water, and not open at any point. Now when we turn on the pump the pressure on one side of the tank begins to increase as water flows in and the pressure on the other side of the tank drops as water flows out. This can continue until the pressure exerted on the water by the stretched rubber diaphragm is equal to the pressure produced by the water pump. At that point the water stops flowing and the analogy capacitor is full.

John