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I am fairly unfamiliar with the different types of capacitors besides the small ones used for small circuit boards, so I want to be sure I am purchasing the right thing.
I will be running experiments with frequencies of 1-5kHz, and require capacitances of a few hundred uF. I anticipate powers of around 5W, possibly up to 10W if things go well. My power supply is theoretically rated up to 10V, but most of our operations have been well under that.
So currently I am just looking for some capacitors to get our experiment started, so these don’t need to be optimized. It just has to not burn out. I am told that electrolytic capacitors won’t work at such frequencies, and we might be pushing the limit on ceramic ones, is that correct? On the other hand, film capacitors seem to be rated for well over what I’m looking for. What would be recommended?
Eventually, I am also going to be looking for capacitors that would work in the MHz range, so if you have any recommendations there, I would also be interested. In that case, the power and voltage may be smaller.
This document may prove a useful guide to the various capacitor types available.
The polar/nonpolar question is one to start with; like microwave cheeseburgers, nonpolar 'lytics do exist but have many less than appealing qualities…
After that constraints on acceptable C, V, and $ values narrow the options quickly. 5kHz is no longer fast for many 'lytics (polymer types particularly), films rated for 600V won’t protest if operated at 6V, and increasing frequency by a decimal place or two will likely require the question to be revisited all over again, not leastwise because many devices sold as capacitors are actually inductors at higher frequencies.
So do you think that, to create a proof of concept experiment, I could utilize aluminum capacitors? The article does say that it is electrolytic capacitors can work in the kHz range; so which ones should I purchase that are available on digikey? I think I can put off the MHz question until later.
I was really considering the purchase of a few of the ceramic capacitors rated for 100-600 uF, but the article says very little about ceramic capacitor use in AC conditions. Is there a bit more information you could offer me there, or are they just going to fail in any AC conditions?
I can definitely hold off on film capacitors if they aren’t necessary. Also, they don’t seem to work well into the MHz range anyway, so that would be a waste of resources if that’s what I’m looking to do with them. Am I mistaken there?
Maybe: if their polarized nature can be accommodated and devices with suitable voltage ratings have sufficiently low ESR for your purposes, they’d be an option. Aluminum polymer types tend to have lower ESR, but have a more limited range of offerings.
The intent was to explain the construction of the different device types, in order to offer an explanation of -why- some devices are better suited to a given application than others.
Which would you expect to have greater sensitivity to reversal of applied voltage: a capacitor whose dielectric is a ceramic slab, or one whose dielectric was made electrochemically by applying a voltage of a specific polarity?
Few capacitors in the 100uF+ range DO work well in MHz+ territory, be they film, ceramic, or otherwise; big C values mean physically large devices, which mean more parasitic inductance. Beyond some point, the impedance expected of an ideal C is less then that of the parasitic L, less than the resistance of the solder joints, or of the conductors leading to/from the device. As frequencies increase, a person starts having to account for the invisible components of a circuit just as much as the ones that get soldered into place.
Characterization sheets for ceramic capacitors are often available, which give insights into some of their non-ideal behaviors. Example for CL32A107MPVNNNE here. The DC bias characteristic is one that often catches the uninitiated by surprise.
Thank you again Rick, there’s definitely a lot of considerations I had never thought about before.
I think for now, I will just ignore the MHz experiments and let that be a problem for the future.
How would you accomodate for a polarized capacitor? Though this is mostly for future reference. I think I will purchase a few film capacitors since I do not know exact parameters for my experiment yet, and they seem to work in approximately the range I am expecting.
Do the following seem reasonable for use in resonant RLC circuits? Or others that are similar to that. I will probably purchase a few just to be able to get a range of capacitances.
(I have a few more, but I am limited to two links per post)
Usually by designing a circuit that doesn’t apply voltage in the wrong direction. Use of two connected “back to back” in series is essentially how the nonpolar 'lytics are made, but half the C and twice the R doesn’t do favors for Q.
One’s not likely to find a much lower ESR for the ratings, so they could be a decent choice. There’s no “right” answer per-se, only tradeoffs.
Welcome to the rabbit hole. It’s been suggested there’s a bottom, but nobody’s found it yet…
