On Sat, 8 Jan 2005 22:30:42 -0800, DaveC wrote:

On Sat, 8 Jan 2005 15:06:53 -0800, John Fields wrote
(in article ):

OK, I posted a circuit for you on abse.

If you need a circuit description let me know and I'll post one over
there.

John, I'm having trouble downloading it. The file is 1K, which looks
suspiciously small. Can you retrieve it?... it might just be my newsreader.

---
I can retrieve it. Send me your email address and I'll email you the
schematic.

--
John Fields

On Sat, 08 Jan 2005 22:30:42 -0800, DaveC wrote:

On Sat, 8 Jan 2005 15:06:53 -0800, John Fields wrote
(in article ):

OK, I posted a circuit for you on abse.

If you need a circuit description let me know and I'll post one over
there.

John, I'm having trouble downloading it. The file is 1K, which looks
suspiciously small. Can you retrieve it?... it might just be my newsreader.

1K doesn't seem exceedingly small for a simple PDF - but I'm using Pan,
which doesn't interpret inline PDFs either; this could be a configuration
setting I haven't got to yet. So, yeah, it's probably the newsreader.

Cheers!
Rich

wrote:

wrote:

In alt.engineering.electrical wrote:


The 85 cent ones (CBC-125) are 1 F, 2.5 V.

No, the CBC-125 is not the one I had in mind. I should have made it
clearer. It is CBC-131, which is 85 cents in qty 10 and is .1
(point one) uf at 5 volts, not 1 uf at 2.5 volts. The CBC-125 is
$1.00 each in qty 10



Ah. I need a newer (paper) All catalog - I wasn't checking their site.



What I didn't know is implied in your next sentence:





Some of these capacitors are made for very low current (microamps,
CMOS memory) and not the tens to hundreds of milliamps you'd need
for a relay or the 10-20 milliamps you'd need for an optoisolator
or solid state relay.


What happens if you place a 10 to 30 ma load on one of those caps?



The voltage collapses. Another way to say what I said above is that
the caps have a high internal resistance / impedance / ESR.

As an example, look at pages 872 and 873 of the current Digi-Key
catalog, T051. On 872 are the Cooper PowerStor capacitors. The "A"
series has a 1 F 2.5 V cap with 0.090 ohm ESR (@ 1 KHz). DC will be
different, but: if you charged one of these caps to 2.5 V and then
shorted the leads, the initial current would be 2.5 / 0.09 or 28 A.
The "B" series (what All sells) has a 1 F 2.5 V at 0.4 ohm ESR: 6.3 A.
At the top left of page 873 are the Panasonic memory backup type
capacitors. One is 1 F 5.5 V with 30 ohm ESR, or 180 mA max short
circuit current. (As a fairer comparison with the Coopers, charging
this one to only 2.5 V would yield an 83 mA short circuit current.)
So, 10 to 30 mA might be doable with the memory backup capacitor,
but not too much more.



As is typical with OP's we may never hear how he makes out.



I don't know... now he's trying to avoid falling down a well...

Matt Roberds



Matt,

Thanks! Good info. I'm wondering what he is really trying
to accomplish, too. I'll post the results I get, once
the parts arrive.

Ed

The parts arrived. I tested the 1 farad/RLY-635
circuit and it yields 4 minutes,45 seconds. + or -
measurement error. I connected the open points
of the relay in series with a 1.5 volt battery
driven analog clock and measured the time that
way. Did it 3 times. Don't know how accurate
the clock is, but it agrees with my wris****ch,
and precision was not important in any event.

I still have to test with the other relays -
I ordered & received RLY-639 and RLY-405 but haven't
tested them yet, or the opto idea. The 639 and 405
relays should not last nearly as long - they have
145 ohm coils, while the 635 has a 500 ohm coil.
I have the .1 farad caps, the opto and the relays,
so testing now is just a matter of time. I realise
the op has changed his request, so this is just
follow up, but I'll post the results when I can.

In sci.electronics.design wrote:
The parts arrived. I tested the 1 farad/RLY-635
circuit and it yields 4 minutes,45 seconds. + or -
measurement error.

Thanks for posting the results! As you noted, the original poster has
moved on, but I might use something like this in a UPS I'm designing.

Basically, I want to switch from AC to battery at the slightest hint of
a problem, but once AC comes back, I want it to have stayed on for some
amount of time before I switch from battery to AC. I'm not too worried
about the exact time, just as long as it meets a minimum. There will be
a big cap in there someplace to handle the switching glitches.

This is for holding up a cable modem and VoIP box during power outages.
I know I could just buy a commercial UPS and plug in the wall-warts, but
it seems wasteful to me to go from 12 V DC to 120 V AC back to 12 V DC.
Besides, for what I pay for a UPS, I can buy a bigger battery and a
couple of support parts that will keep me up much longer than the UPS
will.

Followups to s.e.design.

Matt Roberds

wrote:


The parts arrived. I tested the 1 farad/RLY-635
circuit and it yields 4 minutes,45 seconds. + or -
measurement error. I connected the open points
of the relay in series with a 1.5 volt battery
driven analog clock and measured the time that
way. Did it 3 times. Don't know how accurate
the clock is, but it agrees with my wris****ch,
and precision was not important in any event.

I still have to test with the other relays -
I ordered & received RLY-639 and RLY-405 but haven't
tested them yet, or the opto idea. The 639 and 405
relays should not last nearly as long - they have
145 ohm coils, while the 635 has a 500 ohm coil.
I have the .1 farad caps, the opto and the relays,
so testing now is just a matter of time. I realise
the op has changed his request, so this is just
follow up, but I'll post the results when I can.


I tested with both the RLY-405 and the RLY-639 parts.
Both of them last for 4 minutes. I was surprised to see
them last so long, untl I looked at the datasheet. I tested
each 3 times - same results. Those relays have polarity
sensitive coils. They energize at a little over 2.5 (as measured)
volts as the voltage on the cap rises while it charges. They
stay energized until it drops to about .45 volts, per the datsheet,
which accounts for the longer than anticipated period.

After the relays, I set out to test the opto - and realized I
have no clue as to how to test it, without knowing what the
sense loop specs are. I would welcome some ideas! I
figure the sense loop must be very low current, because the OP
said it runs on a lithium battery. And he indicated he wanted
to keep battery replacement of any added battery to once.
every two years, which implies that the lithiums last that
long.

Ed

DaveC wrote:

On Fri, 7 Jan 2005 16:07:32 -0800, DaveC wrote
(in article et):



Thanks for all the great ideas. All of this makes my (volunteer) job much
easier.



A new twist to the challenge:

The output needs to be a one-shot, momentary-close event. In other words, 5
minutes after power fails, the contacts need to close and open again. This
alerts the alarm to the power out-condition, and clears the alarm sense line
for another event to be reported.

Ideas?


Two relays, two capacitors, one resistor.
Refer to the circuit mentioned in my post above -
a 5.5 super cap and RLY-639 or RLY-405. When power
drops, the relay stays energized for ~4 minutes, then
drops.

Use one of the closed points on the first relay to
complete the circuit to a second relay from a charged
cap.
One point of the second relay is the output. Another
point of the second relay to switch a low value resistor
across the cap that energizes the second relay.
Here's the circuit: (the output point is not shown)

A +-----0 \---relay2coil---+
| R1P(nc) |
+---/\/\/\---o \--+ |
| R1 R2P | |
Cap2 | |
| | |
B +-----------------+------+

+ 5 volts is supplied to point A, ground is at point
B. R1P is the normally closed point of the relay
mentioned in my earlier post and shown in the diagram
below. R2P is one of the normally open points of
relay 2. The other normally open point of relay 2 is
the output you need.

Here's the ~4 minute delay circuit:

A -----+---relaycoil1----+
| |
SuperCap |
| |
B -----+-----------------+

The super cap is a 1 farad 5.5 volt cap
and the relay is RLY-639, both specified
in the earlier post, from Allelectronics.
Use a regulated 5 volt supply with series
diode protection, or a regulated 6 volt supply
with two 1N4001 diodes in series to produce
the supply to points A and B. The diode
protection prevents discharge of the capacitors
back into the supply. Cap2 does not need to
be a super cap. On an untested guess, I'd
say a 470 uf cap with a second RLY-639 would
work. A 100 ohm 1 watt resistor will work for
R1 with that cap. Let me know if you want me to
test it - I have the parts.

Ed