Supercaps and ESR

Logic would dictate it would discharge quicker but my logic is usually flawed.

Considering that the draw on these caps is usually measured in microamps, I doubt the higher ESR is going to effect how well it works.

Maybe might make a bit of difference in how long it takes to fully charge though.

Jeff

That's one of those *depends* questions. How much of a voltage drop will you get at the current draw of the circuit and will that have any effect on operation? I wouldn't think that as 30 ohm resistance is going to bother a RAM that draws 6uA or so.

Meat Plow Inscribed thus:

I would have thought that the cap, same value, wouldn't be able to provide the same peak current because of the higher ESR. Other than that, physical size might be an issue !

I don't think peak current is an issue however size might be. In such a device I would look for a taper off of charge as long as possible in order to sustain programmed memory until the bitter end. Otherwise with proper charge the device is pretty much transparent.

Supercaps are also used as batteries in those quick charging micro rc cars where they supply current for about a minute to a small motor and the steering servo. Those models could probably have a lower internal resistance.

"DaveC" schreef in bericht news: snipped-for-privacy@news.eternal-september.org...

Well,

As its says itself it's a Equivalent Series Resistor so it can be considered a resistor in series with the capacitor. As such it dissipates some energy during charging and charging takes some more time. On discharging the resistor will also dissipate some of the energy and lowers the on the cap available voltage by the voltage drop over the resistor. So a high ESR gives a less power efficiency and will earlier be "empty".

petrus bitbyter

I once bought two of those little toy RC cars for about two bucks apiece from the clearance bin. It was fun, for a little while, but frustrating because there was no throttle or proportional steering. It was either stop or go-as-fast-as-you-can, and straight or lock left or lock right, so it was almost impossible to actually steer it, especially over anything but a totally bare hard smooth floor. The tires were about 1/4" diameter.

Some months later, they hired some new kid in the shop, and he bought one of them for ten bucks. >:->

Cheers! Rich

Depends on the application. Some are designed to provide backup power at low currents for long periods. Some are designed to provide high power at high currents for short periods. The latter type won't like an increase in ESR.

Huh!

The higher the ESR the lower the peak current you can draw from it and the longer it will take to fully charge with a given source.

Huh? (Again!)

The draws are usually measured in the 10s of Amperes. In some applications, the 100s of Amperes (such as when a super cap is used to help start something.)

That but also how much the cap heats when both charging the discharging. If it's being used in a power supply filtering function, a high ESR will both reduce the filtering effect and increase the heating of the cap.

I think it depends on application. I haven't done detailed measurement but I would postulate that the low-ESR supercaps have more surface area and higher leakage, and the higher-ESR supercaps have less surface area and less leakage.

Tim.