Supercaps and ESR
DaveC
Original:
<http://www.newark.com/cooper-bussmann/b0810-2r5105-r/capacitor-super-1f-2-5v-
0-4ohm/dp/78K7800?Ntt=B0810-2R5105-R>
I can find local replacements rated 1F/5V but the ESR is ~30 ohms instead of
0.4.
I presume that supercaps aren't applied to filter applications -- their
specialty being an alternative to batteries to power memory or such -- so
ripple current shouldn't be an issue.
My question: what's the impact of replacing a supercap with one with a higher
ESR?
Thanks,
Dave
Meat Plow
Logic would dictate it would discharge quicker but my logic is usually
flawed.
--
Live Fast, Die Young and Leave a Pretty Corpse
Jeffrey Angus
> On Tue, 22 Feb 2011 12:21:55 -0800, DaveC wrote:
>
>> My question: what's the impact of replacing a supercap with one with a
>> higher ESR?
>
> 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
WangoTango
inv...@invalid.net says...
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.
Baron
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 !
--
Best Regards:
Baron.
Meat Plow
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.
petrus bitbyter
"DaveC" <inv...@invalid.net> schreef in bericht
news:0001HW.C9895AE3...@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
asdf
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.
Rich Grise
>
> 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.
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
Andrew Gabriel
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.
--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]
John Gilmer
"Jeffrey Angus" <jan...@suddenlink.net> wrote in message
news:4d6423bb$0$4302$bbae...@news.suddenlink.net...
> On 2/22/2011 2:52 PM, Meat Plow wrote:
>> On Tue, 22 Feb 2011 12:21:55 -0800, DaveC wrote:
>>
>>> My question: what's the impact of replacing a supercap with one with a
>>> higher ESR?
>>
>> Logic would dictate it would discharge quicker but my logic is usually
>> flawed.
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.
>
> 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.
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.)
>
> Maybe might make a bit of difference in how long it takes to
> fully charge though.
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.
Tim Shoppa
> Trying to find a replacement for a 1F/2.5V supercap.
>
> Original:
>
> 0-4ohm/dp/78K7800?Ntt=B0810-2R5105-R>
>
> I can find local replacements rated 1F/5V but the ESR is ~30 ohms instead of
> 0.4.
>
> I presume that supercaps aren't applied to filter applications -- their
> specialty being an alternative to batteries to power memory or such -- so
> ripple current shouldn't be an issue.
>
> My question: what's the impact of replacing a supercap with one with a higher
> ESR?
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.