I've never used a supercap before, though I have had one kicking about
here for a long time, a 5v 1 Farad. I have an old code entry lock,
which I am looking to install, which runs on 5v and needs a battery to
maintain its code memory at 5uA.

I don't expect the mains supply to ever be off for long, but with no
supply at all available to the lock, it reverts to a not very secure
entry code of '0'.

Would the cap do the job? Anyone any experience of using them?

On Sun, 21 Jul 2019 16:29:48 +0100, Harry Bloomfield wrote:

Would the cap do the job? Anyone any experience of using them?

The R/C constant for voltage decay doesn't magically change just because
you're using "supercapacitors" - just do the math as usual and work it
out for yourself as if you were using common-or-garden electrolytics.



--
Leave first - THEN negotiate!

Erm what is wrong with a good old battery like the ones in computers for the
comes?

Brian

--
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This newsgroup posting comes to you directly from...
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Note this Signature is meaningless.!
"Harry Bloomfield" wrote in message
...
I've never used a supercap before, though I have had one kicking about
here for a long time, a 5v 1 Farad. I have an old code entry lock, which I
am looking to install, which runs on 5v and needs a battery to maintain
its code memory at 5uA.

I don't expect the mains supply to ever be off for long, but with no
supply at all available to the lock, it reverts to a not very secure entry
code of '0'.

Would the cap do the job? Anyone any experience of using them?

Brian Gaff submitted this idea :
Erm what is wrong with a good old battery like the ones in computers for the
comes?

I just thought I had one on the shelf, put the cap to some use.

Cursitor Doom formulated on Sunday :
The R/C constant for voltage decay doesn't magically change just because
you're using "supercapacitors" - just do the math as usual and work it
out for yourself as if you were using common-or-garden electrolytics.

I'm just not sure how the self discharge works, I have no experience of
these caps.

On 21/07/2019 20:18, Tim Streater wrote:
In article , Harry Bloomfield
wrote:

I've never used a supercap before, though I have had one kicking about
here for a long time, a 5v 1 Farad. I have an old code entry lock,
which I am looking to install, which runs on 5v and needs a battery to
maintain its code memory at 5uA.

I don't expect the mains supply to ever be off for long, but with no
supply at all available to the lock, it reverts to a not very secure
entry code of '0'.

Would the cap do the job? Anyone any experience of using them?

Well you need to do the sums. How much charge is stored in it when its
up to 5v? Then, at what lower output voltage will the code memory lose
its data? How much charge does that equate to? So your "available
charge" is the difference, and given you said 5µa, you can work out how
long you can get that current before the output voltage drops too low.

I expect the formulae you need are in Winky somewhere.


http://www.learningaboutelectronics....calculator.php

On 21/07/2019 20:18, Tim Streater wrote:
In article , Harry Bloomfield
wrote:

I've never used a supercap before, though I have had one kicking about
here for a long time, a 5v 1 Farad. I have an old code entry lock,
which I am looking to install, which runs on 5v and needs a battery to
maintain its code memory at 5uA.

I don't expect the mains supply to ever be off for long, but with no
supply at all available to the lock, it reverts to a not very secure
entry code of '0'.

Would the cap do the job? Anyone any experience of using them?

Well you need to do the sums. How much charge is stored in it when its
up to 5v? Then, at what lower output voltage will the code memory lose
its data? How much charge does that equate to? So your "available
charge" is the difference, and given you said 5µa, you can work out how
long you can get that current before the output voltage drops too low.

I expect the formulae you need are in Winky somewhere.

Charge in joules is, IIRC, ½CV²...

--
€œIt is hard to imagine a more stupid decision or more dangerous way of
making decisions than by putting those decisions in the hands of people
who pay no price for being wrong.€�

Thomas Sowell

On Sun, 21 Jul 2019 20:27:30 +0100, The Natural Philosopher
wrote:

On 21/07/2019 20:18, Tim Streater wrote:
In article , Harry Bloomfield
wrote:

I've never used a supercap before, though I have had one kicking about
here for a long time, a 5v 1 Farad. I have an old code entry lock,
which I am looking to install, which runs on 5v and needs a battery to
maintain its code memory at 5uA.

I don't expect the mains supply to ever be off for long, but with no
supply at all available to the lock, it reverts to a not very secure
entry code of '0'.

Would the cap do the job? Anyone any experience of using them?

Well you need to do the sums. How much charge is stored in it when its
up to 5v? Then, at what lower output voltage will the code memory lose
its data? How much charge does that equate to? So your "available
charge" is the difference, and given you said 5µa, you can work out how
long you can get that current before the output voltage drops too low.

I expect the formulae you need are in Winky somewhere.

Charge in joules is, IIRC, ½CV²...

Er, that's the stored energy. The charge Q (in coulombs) is simply CV.
For the example given, the available charge is C(Vmax - Vmin).
As a first order approximation, and ignoring any self-discharge, it
would seem reasonable to assume a linear decay rate, so I = C(Vmax -
Vmin)/T. (From I = dQ/dt).
Rearrange to get T = C(Vmax - Vmin)/I.

Call yourself a 'natural philosopher'? Sheesh!

On Sunday, 21 July 2019 18:24:21 UTC+1, Cursitor Doom wrote:
On Sun, 21 Jul 2019 16:29:48 +0100, Harry Bloomfield wrote:

Would the cap do the job? Anyone any experience of using them?

The R/C constant for voltage decay doesn't magically change just because
you're using "supercapacitors" - just do the math as usual and work it
out for yourself as if you were using common-or-garden electrolytics.

He can't. First it's necessary to know V_min for continued remembering and what v the cap charges to. I don't suppose he knows those figures.


NT

Hmm well the cmos batteries seem to be being sold in packs of 2, seems a
little odd since by the time you need the second one either the machine will
be too old or died.

Brian

--
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This newsgroup posting comes to you directly from...
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Blind user, so no pictures please
Note this Signature is meaningless.!
"Harry Bloomfield" wrote in message
...
Brian Gaff submitted this idea :
Erm what is wrong with a good old battery like the ones in computers for
the comes?

I just thought I had one on the shelf, put the cap to some use.

On Monday, 22 July 2019 00:08:08 UTC+1, tabby wrote:
On Sunday, 21 July 2019 18:24:21 UTC+1, Cursitor Doom wrote:
On Sun, 21 Jul 2019 16:29:48 +0100, Harry Bloomfield wrote:

Would the cap do the job? Anyone any experience of using them?

The R/C constant for voltage decay doesn't magically change just because
you're using "supercapacitors" - just do the math as usual and work it
out for yourself as if you were using common-or-garden electrolytics.

He can't. First it's necessary to know V_min for continued remembering and what v the cap charges to. I don't suppose he knows those figures.


NT

but all that is trivially skirted. Fit your supercap & see how long it remmebers


NT

On 22/07/2019 00:08, wrote:
On Sunday, 21 July 2019 18:24:21 UTC+1, Cursitor Doom wrote:
On Sun, 21 Jul 2019 16:29:48 +0100, Harry Bloomfield wrote:

Would the cap do the job? Anyone any experience of using them?

The R/C constant for voltage decay doesn't magically change just
because you're using "supercapacitors" - just do the math as usual
and work it out for yourself as if you were using common-or-garden
electrolytics.

He can't. First it's necessary to know V_min for continued
remembering and what v the cap charges to. I don't suppose he knows
those figures.


NT


I don't think it matters if his drain figure is correct as it will stay
at 5V -5% for days.
It will probably drain more if the weather is humid than the device uses.

On 22/07/2019 07:29, Brian Gaff wrote:
Hmm well the cmos batteries seem to be being sold in packs of 2, seems a
little odd since by the time you need the second one either the machine will
be too old or died.

Brian


The CMOS battery in my laptop has just gone and that's a usable i5 two
core machine. So they don't outlast the machines these days.

It was only a 1822 or similar battery though, not rechargeable.

Need to buy one and solder some wires on or keep it in standby mode so
it doesn't forget.

Not that it matters if it forgets its still boots and windows corrects
the time from the internet.

On 21/07/2019 19:59, Harry Bloomfield wrote:
Cursitor Doom formulated on Sunday :
The R/C constant for voltage decay doesn't magically change just because
you're using "supercapacitors" - just do the math as usual and work it
out for yourself as if you were using common-or-garden electrolytics.

I'm just not sure how the self discharge works, I have no experience of
these caps.

I have used them, but not for a while. From memory, the self-discharge
rate is quite high. The main benefit of supercaps is the fast rate of
charge and the high number of charge/discharge cycles.

You say it is 1 Farad at 5v - from memory again (not always reliable
these days!) supercaps operate at 2.7v.

On 21/07/2019 16:29, Harry Bloomfield wrote:
I've never used a supercap before, though I have had one kicking about
here for a long time, a 5v 1 Farad. I have an old code entry lock, which
I am looking to install, which runs on 5v and needs a battery to
maintain its code memory at 5uA.

I don't expect the mains supply to ever be off for long, but with no
supply at all available to the lock, it reverts to a not very secure
entry code of '0'.

Would the cap do the job? Anyone any experience of using them?

1F @ 5F is 12.5J or 12.5 watts for 1 second. Of course, we don't know
how much of that can be used as we don't know what voltage drop your
lock can bear. It uses a battery at present which is likely to be less
than 5V I'm guessing.

So let's say we can only use 4% of that energy which seems very
conservative and leaves us with 0.5 Ws.

5uA at 5V is 25uW, so 0.5Ws would give you 20,000 seconds or 5.5 hours.

I've no idea what the self discharge of these things is, but it will be
much less than 25uA, so it sounds like a useful thing to do.

Cheers
--
Clive

Brian Gaff wrote

Hmm well the cmos batteries seem to be being sold in packs of 2,

Not always.

seems a little odd since by the time you need the second one either the
machine will be too old or died.

Not when plenty of other stuff uses them now.

My kitchen scales and bathroom scales do.

"Harry Bloomfield" wrote in message
...
Brian Gaff submitted this idea :
Erm what is wrong with a good old battery like the ones in computers for
the comes?

I just thought I had one on the shelf, put the cap to some use.

On Mon, 22 Jul 2019 19:46:11 +1000, cantankerous trolling geezer Rodent
Speed, the auto-contradicting senile sociopath, blabbered, again:


Not always.

Starting another auto-contradicting session, you clinically insane
auto-contradicting senile asshole?

FLUSH the rest of your usual bull****

--
Kerr-Mudd,John addressing senile Rot:
"Auto-contradictor Rod is back! (in the KF)"
MID:

On 21/07/2019 22:51, Custos Custodum wrote:
On Sun, 21 Jul 2019 20:27:30 +0100, The Natural Philosopher
wrote:

On 21/07/2019 20:18, Tim Streater wrote:
In article , Harry Bloomfield
wrote:

I've never used a supercap before, though I have had one kicking about
here for a long time, a 5v 1 Farad. I have an old code entry lock,
which I am looking to install, which runs on 5v and needs a battery to
maintain its code memory at 5uA.

I don't expect the mains supply to ever be off for long, but with no
supply at all available to the lock, it reverts to a not very secure
entry code of '0'.

Would the cap do the job? Anyone any experience of using them?

Well you need to do the sums. How much charge is stored in it when its
up to 5v? Then, at what lower output voltage will the code memory lose
its data? How much charge does that equate to? So your "available
charge" is the difference, and given you said 5µa, you can work out how
long you can get that current before the output voltage drops too low.

I expect the formulae you need are in Winky somewhere.

Charge in joules is, IIRC, ½CV²...

Er, that's the stored energy. The charge Q (in coulombs) is simply CV.

I assumed what he was inteersted was the energy in the charge not the
couloumbs

In my whole career as an electronic engineer I never once used coulombs
for anything.

For the example given, the available charge is C(Vmax - Vmin).
As a first order approximation, and ignoring any self-discharge, it
would seem reasonable to assume a linear decay rate, so I = C(Vmax -
Vmin)/T. (From I = dQ/dt).
Rearrange to get T = C(Vmax - Vmin)/I.

Golly, what a superb skill in cut and pasting you display..


Call yourself a 'natural philosopher'? Sheesh!

Yes, I do.



--
Ideas are more powerful than guns. We would not let our enemies have
guns, why should we let them have ideas?

Josef Stalin

explained on 22/07/2019 :
He can't. First it's necessary to know V_min for continued remembering and
what v the cap charges to. I don't suppose he knows those figures.

V_min is 3v, V_max is 6v, but it will have and charge the supercap to a
rail of 5v. I'm thinking connect the supercap directly across the rail.
I'm just trying to avoid the need to introduce a battery for backing up
the settings. Its a UA3730, I am trying to repurpose as a code entry
lock system, on my garages side entrance - my original code lock has
become unreliable and lacking a circuit, I have not been able to work
out why..

Clive Arthur wrote on 22/07/2019 :
I've no idea what the self discharge of these things is, but it will be much
less than 25uA, so it sounds like a useful thing to do.

I suppose I could just charge it up to 5v and see how long it takes to
drop to the 3v V_min of the IC.

On 22/07/2019 13:54, Harry Bloomfield wrote:
Clive Arthur wrote on 22/07/2019 :
I've no idea what the self discharge of these things is, but it will
be much less than 25uA, so it sounds like a useful thing to do.

I suppose I could just charge it up to 5v and see how long it takes to
drop to the 3v V_min of the IC.

Yes, nothing like a good experiment, after all it may be duff. Make
sure your meter doesn't load it too much, and be aware that it'll
probably discharge more quickly at higher temperatures.

Cheers
--
Clive

Clive Arthur explained :
Yes, nothing like a good experiment, after all it may be duff. Make sure
your meter doesn't load it too much, and be aware that it'll probably
discharge more quickly at higher temperatures.

No need for the meter to be connected all the time, just a few seconds
to get a reading.

14:00 5.01v
14:20 4.83v

In article ,
Farmer Giles wrote:
I have used them, but not for a while. From memory, the self-discharge
rate is quite high. The main benefit of supercaps is the fast rate of
charge and the high number of charge/discharge cycles.

Thought their main purpose was a very high maximum discharge current for
their size?

--
*How can I miss you if you won't go away?

Dave Plowman London SW
To e-mail, change noise into sound.

On 22/07/2019 14:45, Dave Plowman (News) wrote:
In article ,
Farmer Giles wrote:
I have used them, but not for a while. From memory, the self-discharge
rate is quite high. The main benefit of supercaps is the fast rate of
charge and the high number of charge/discharge cycles.

Thought their main purpose was a very high maximum discharge current for
their size?

There are essentially two types, some for effectively replacing small
batteries for memory etc, and some for supplying and absorbing rapid
short bursts of welly. The former tend to look like ordinary
capacitors, the latter have much thicker tabs to take the current.

Cheers
--
Clive

Harry Bloomfield formulated on Monday :
14:00 5.01v
14:20 4.83v

19:55 4.45v

Its looking very promising.

"Dave Plowman (News)" wrote in message
...
In article ,
Farmer Giles wrote:
I have used them, but not for a while. From memory, the self-discharge
rate is quite high. The main benefit of supercaps is the fast rate of
charge and the high number of charge/discharge cycles.

Thought their main purpose was a very high maximum discharge current for
their size?

That’s just one of their main purposes. The other obvious
one is that they don’t have a limited life like a battery does.

On Tue, 23 Jul 2019 05:10:12 +1000, Swer, better known as cantankerous
trolling senile geezer Rodent Speed, wrote:


That¢s just one of their main purposes. The other obvious
one is that they don¢t have a limited life like a battery does.

Luckily, you 85-year-old senile asshole have only a VERY limited life left!

--
Norman Wells addressing senile Rot:
"Ah, the voice of scum speaks."
MID:

On Monday, 22 July 2019 13:45:59 UTC+1, Harry Bloomfield wrote:
tabbypurr explained on 22/07/2019 :

He can't. First it's necessary to know V_min for continued remembering and
what v the cap charges to. I don't suppose he knows those figures.

V_min is 3v, V_max is 6v, but it will have and charge the supercap to a
rail of 5v. I'm thinking connect the supercap directly across the rail.
I'm just trying to avoid the need to introduce a battery for backing up
the settings. Its a UA3730, I am trying to repurpose as a code entry
lock system, on my garages side entrance - my original code lock has
become unreliable and lacking a circuit, I have not been able to work
out why..

If your figures are correct it's simple to work out how long it'll keep it remembering for. Others have explained.


NT

On Monday, 22 July 2019 19:58:20 UTC+1, Harry Bloomfield wrote:
Harry Bloomfield formulated on Monday :
14:00 5.01v
14:20 4.83v

19:55 4.45v

Its looking very promising.

If that's from 5v, somewhere in the region of 80 minutes then


NT

On 22/07/2019 22:46, wrote:
On Monday, 22 July 2019 19:58:20 UTC+1, Harry Bloomfield wrote:
Harry Bloomfield formulated on Monday :
14:00 5.01v
14:20 4.83v

19:55 4.45v

Its looking very promising.

If that's from 5v, somewhere in the region of 80 minutes then


Most of that drop will be from the few seconds the meter is connected
unless its a very high input impedance. It won't be.

On Mon, 22 Jul 2019 22:57:44 +0100, dennis@home wrote:

On 22/07/2019 22:46, wrote:
On Monday, 22 July 2019 19:58:20 UTC+1, Harry Bloomfield wrote:
Harry Bloomfield formulated on Monday :
14:00 5.01v 14:20 4.83v

19:55 4.45v

Its looking very promising.

If that's from 5v, somewhere in the region of 80 minutes then


Most of that drop will be from the few seconds the meter is connected
unless its a very high input impedance. It won't be.

My meter is 10megohms, so it wouldn't discharge that much ...

--
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wish to copy them they can pay me £1 a message.
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On Tuesday, 23 July 2019 01:11:16 UTC+1, Bob Eager wrote:
On Mon, 22 Jul 2019 22:57:44 +0100, dennis@home wrote:
On 22/07/2019 22:46, tabbypurr wrote:
On Monday, 22 July 2019 19:58:20 UTC+1, Harry Bloomfield wrote:
Harry Bloomfield formulated on Monday :

14:00 5.01v 14:20 4.83v

19:55 4.45v

Its looking very promising.

If that's from 5v, somewhere in the region of 80 minutes then


Most of that drop will be from the few seconds the meter is connected
unless its a very high input impedance. It won't be.

My meter is 10megohms, so it wouldn't discharge that much ...

AFAIK all digital multimeters are high R_in.

formulated the question :
If your figures are correct it's simple to work out how long it'll keep it
remembering for. Others have explained.

Yes, I am well aware of that - it was the self discharge I was stuck
on, I had no figures and no experience of.

My tests suggest it will do the job more than adequately. The spec. of
the IC says that when it fails to be maintained by its backup battery,
it defaults to an entry code of 0 (a single press of the zero button).
Simple plan is to disable zero button and not use a zero in the access
code. I have other ways to get in, if the code lock fails.

On Mon, 22 Jul 2019 17:34:32 -0700, tabbypurr wrote:

On Tuesday, 23 July 2019 01:11:16 UTC+1, Bob Eager wrote:
On Mon, 22 Jul 2019 22:57:44 +0100, dennis@home wrote:
On 22/07/2019 22:46, tabbypurr wrote:
On Monday, 22 July 2019 19:58:20 UTC+1, Harry Bloomfield wrote:
Harry Bloomfield formulated on Monday :

14:00 5.01v 14:20 4.83v

19:55 4.45v

Its looking very promising.

If that's from 5v, somewhere in the region of 80 minutes then


Most of that drop will be from the few seconds the meter is connected
unless its a very high input impedance. It won't be.

My meter is 10megohms, so it wouldn't discharge that much ...

AFAIK all digital multimeters are high R_in.

Which means "won't be" is nonsense.


--
My posts are my copyright and if @diy_forums or Home Owners' Hub
wish to copy them they can pay me £1 a message.
Use the BIG mirror service in the UK: http://www.mirrorservice.org
*lightning surge protection* - a w_tom conductor

On 23/07/2019 01:11, Bob Eager wrote:
On Mon, 22 Jul 2019 22:57:44 +0100, dennis@home wrote:

On 22/07/2019 22:46, wrote:
On Monday, 22 July 2019 19:58:20 UTC+1, Harry Bloomfield wrote:
Harry Bloomfield formulated on Monday :
14:00 5.01v 14:20 4.83v

19:55 4.45v

Its looking very promising.

If that's from 5v, somewhere in the region of 80 minutes then


Most of that drop will be from the few seconds the meter is connected
unless its a very high input impedance. It won't be.

My meter is 10megohms, so it wouldn't discharge that much ...


50micro amps at 5v how many meg?

dennis@home pretended :
Most of that drop will be from the few seconds the meter is connected unless
its a very high input impedance. It won't be.

It is a 25 year old LCD digital meter on the 20v range, so what will
that be - 1M Ohm?

28 hours later, it is showing 3.94v.

On Tue, 23 Jul 2019 00:11:14 +0000, Bob Eager wrote:

My meter is 10megohms, so it wouldn't discharge that much ...

It's okay, Dennis the Dunce doesn't have a clue what he's talking about.



--
Leave first - THEN negotiate!

In article
,
says...


I have used them, but not for a while. From memory, the self-discharge
rate is quite high. The main benefit of supercaps is the fast rate of
charge and the high number of charge/discharge cycles.


I recall an article in Elektor magazine a few years ago which
usewd them in conjunction with a cycle dynamo lighting system
so that when the dynamo voltage dropped, the supercap turned a
pair of high efficiency LEDs until the bike moved again.

(Cycle dynamos were still very popular until only about 5 or 6
years ago on the continent - not surprising when you could buy
them for as little as ¤5.)



--

Terry

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On 23/07/2019 19:31, Cursitor Doom wrote:
On Tue, 23 Jul 2019 00:11:14 +0000, Bob Eager wrote:

My meter is 10megohms, so it wouldn't discharge that much ...

It's okay, Dennis the Dunce doesn't have a clue what he's talking about.




CD still doesn't understand anything I see.


But then he probably doesn't even know what a micro amp is.

On 23/07/2019 19:50, Terry Casey wrote:

snip

I recall an article in Elektor magazine a few years ago which
used them in conjunction with a cycle dynamo lighting system
so that when the dynamo voltage dropped, the supercap turned a
pair of high efficiency LEDs until the bike moved again.

Yes, a clever idea. A bridge rectifier made from LEDs was driven by the
dynamo with another LED and supercap on the bridge output providing the
backup.

Cheers
--
Clive