need cap. charge indicator

[DJ Delorie]

What can I use as a charge indicator? All I really need is for an LED to
light or something like that. Can someone please suggest a circuit or an
idea that would work for this application?

There are two ways - measure the voltage across the cells, or the
current flowing from the charger to the cells. Try just putting a
plain old voltmeter across the cells and watch it until it stops
moving.

 

[Phil Allison]

"Jim"

I built a battery tab spot welder using multiple 5 volt 150,000 uf computer
grade capacitors in parallel, as the heart.

** Who makes 150,000 uF caps rated at only 5 volts ???

The capacitors are charged
using a small 5 volt unregulated charger.

** Bet it puts out a lot more than 5 volts when unloaded.

This works well, except I am not
sure when the capacitor bank is fully charged up, as it takes a long time.

** Should take only 4 seconds with a 1 amp charger.

What the heck are you using ?

What can I use as a charge indicator?

** So you do * not * have a DC voltmeter ?

All I really need is for an LED to
light or something like that. Can someone please suggest a circuit or an
idea that would work for this application?

** A red LED and a 3.3 volt zener would do - but you have more serious
problems than that.




.......... Phil

 

[Chris]

I built a battery tab spot welder using multiple 5 volt 150,000 uf computer
grade capacitors in parallel, as the heart. The capacitors are charged
using a small 5 volt unregulated charger. This works well, except I am not
sure when the capacitor bank is fully charged up, as it takes a long time.

What can I use as a charge indicator? All I really need is for an LED to
light or something like that. Can someone please suggest a circuit or an
idea that would work for this application?

Thanks
Jim

Hi, Jim. One easy newbie way to do this is to rely on the pull-in
voltage of a small DIP package reed relay.

If you were to get, say, a Magnecraft W107-DIP1 (Mouser P/N 528-107-1),
you'd find it has a nominal coil voltage of 5V, with a guaranteed
pull-in voltage of 3.8V and a coil resistance of about 500 ohms. If
you were to place the coil in series with a 1K ohm pot, and adjust the
pot so the relay just clicks in at your desired voltage, you'd have a
reliable and very simple method of indicating charge voltage (view in
fixed font or M$ Notepad):
| ___
| o--------o-|___|--o--------o----------o----o-- . .--o
| | | R | | | | |
| | \ o | | | | |
|6V +| \ | .-. | | |
| --- CRY1\. Vz /-/ .->| |1K | | |
| - o 5.1V ^ | | | | | |
| | | | | '-' +| +| +|
| | .-. | | | --- --- . . .---
| | 220| | | '---o C --- C--- C---
| | | | | | | | |
| | '-' | RY1 C| | | |
| | | | C| | | |
| | LED V ~ | C| | | |
| | - ~ | | | | |
| | | | | | | |
| '--------o--------o--------o----------o----o--. . --o
|
(created by AACircuit v1.28.5 beta 02/06/05 www.tech-chat.de)

While the relay is guaranteed to pull in at 3.8V, it will probably pull
in at around 3V. You should tweak the pot so the relay just turns on
when the caps reach the specified voltage (you might want to use a
meter for this if you have one). This pull-in voltage will remain
fairly stable over time and temp, so you can set the pot, and forget
it. And your very simple, reliable indicator circuit will draw less
than 10mA from the caps.

The relay will let go by itself when you discharge the caps. Vibration
may affect the pull-in of the relay, so be sure to mount the piece of
perfboard on something stable.

If you find another 5V relay that has a different coil resistance, just
measure it, and use a pot with a higher resistance than the coil.
Tweak it to the right pull-in point as above, and be sure to take the
extra current draw from the caps into account.

Questions of this type usually find a good response on s.e.b., too.

Good luck
Chris

 

[John_H]

I built a battery tab spot welder using multiple 5 volt 150,000 uf computer
grade capacitors in parallel, as the heart. The capacitors are charged
using a small 5 volt unregulated charger. This works well, except I am not
sure when the capacitor bank is fully charged up, as it takes a long time.

What can I use as a charge indicator? All I really need is for an LED to
light or something like that. Can someone please suggest a circuit or an
idea that would work for this application?

Thanks
Jim

Look for voltage monitor circuits normally used for keeping a processor
in reset until the voltages are at reasonable levels. You can probably
still find many that are built for 5V rails (triggering at 5% or some
other nominal voltage below rail). These are designed for good behavior
on power-up so you should get a nice LED-style indicator without worries.

Also - look at the Maxwell Powercache capacitors. Only 2.7V but with a
proper balance, two in series would give you 1300 Farads at 5V. Farads!
Perhaps this link:

http://www.maxwell.com/ultracapacitors/index.html
or
http://www.prestostore.com/catalog.php?ref=tecategroup.com&dt=5621&or=&preview=Y

 

[Tom Bruhns]

Charge indicator: volt meter. If you don't already have one and
you're on a serious budget, try something like 90899.2VGA from
http://www.harborfreight.com/. On sale at about $5, sometimes even
less. Should be good enough for what you are doing.

Cheers,
Tom

 

[Jim]

I built a battery tab spot welder using multiple 5 volt 150,000 uf computer
grade capacitors in parallel, as the heart. The capacitors are charged
using a small 5 volt unregulated charger. This works well, except I am not
sure when the capacitor bank is fully charged up, as it takes a long time.

What can I use as a charge indicator? All I really need is for an LED to
light or something like that. Can someone please suggest a circuit or an
idea that would work for this application?

Thanks
Jim

 

[amdx]

I built a battery tab spot welder using multiple 5 volt 150,000 uf computer
grade capacitors in parallel, as the heart. The capacitors are charged
using a small 5 volt unregulated charger. This works well, except I am not
sure when the capacitor bank is fully charged up, as it takes a long time.

What can I use as a charge indicator? All I really need is for an LED to
light or something like that. Can someone please suggest a circuit or an
idea that would work for this application?

Thanks
Jim

How about posting the schematic and pictures of your spot welder.

 

[Anthony Fremont]

"Phil Allison"

** Should take only 4 seconds with a 1 amp charger.

What the heck are you using ?

How did you come/jump to that conclusion? The OP didn't even say how many
caps he was using. Please tell us how you calculated that.

 

[Fred Bloggs]

I built a battery tab spot welder using multiple 5 volt 150,000 uf computer

grade capacitors in parallel, as the heart. The capacitors are charged
using a small 5 volt unregulated charger. This works well, except I am not
sure when the capacitor bank is fully charged up, as it takes a long time.

What can I use as a charge indicator? All I really need is for an LED to
light or something like that. Can someone please suggest a circuit or an
idea that would work for this application?

Something like this in a small *steel* enclosure will work well enough.
It is better if the detector power supply does not get pulled down by
the caps:
View in a fixed-width font such as Courier.

 

[budgie]

I built a battery tab spot welder using multiple 5 volt 150,000 uf computer
grade capacitors in parallel, as the heart. The capacitors are charged
using a small 5 volt unregulated charger. This works well, except I am not
sure when the capacitor bank is fully charged up, as it takes a long time.

What can I use as a charge indicator? All I really need is for an LED to
light or something like that. Can someone please suggest a circuit or an
idea that would work for this application?

Something like this in a small *steel* enclosure will work well enough.
It is better if the detector power supply does not get pulled down by
the caps:
View in a fixed-width font such as Courier.

.
. .----------------[470]-------------------->TO
. | CAPS
.5V>-+-----------------------+----------------+-----.
. | | | | |
. | .----+ | | |
. | | | | | |
. | | | | | |
. | | | | | |
. | | | 555--------- | ---
. | /_ | | VCC/RST | [330] \ / ~~
. | \/| | | | | --- IND LED
. | 50K / === | | | | GREEN
. | /\ 0.1u | | | |
. | | | .---|TRIG DIS|--[220]--|-----'
. | | | | | | |
. | | | | | | |
. | +----+---+---|THRESH | |
. === | | | | |
. 0.1U | | |OUT CONT|---------+
. | | | | | |
. | | | | GND | |
. | | | ----+------ |
. | | | | |
. | | | 1N4001 | |
. | | '--|<|---+ |
. | \| | |
. | 2N3904|---------------|----------------+
. | <| | |
. | | | ---
. | | | \ / ~~
. | | | --- REF LED
. | [10K] | | RED
. | | | |
. | | | |
. | | | |
. '-----+-----------------+----------------+
. |
. ---

I'm with Tom B on this. Why all the fuss when a cheap DMM (or panel meter) will
give the full story?

 

[John Jardine.]

I built a battery tab spot welder using multiple 5 volt 150,000 uf computer
grade capacitors in parallel, as the heart. The capacitors are charged
using a small 5 volt unregulated charger. This works well, except I am not
sure when the capacitor bank is fully charged up, as it takes a long time.

What can I use as a charge indicator? All I really need is for an LED to
light or something like that. Can someone please suggest a circuit or an
idea that would work for this application?

Thanks
Jim

The LED starts to come on with about 4.8V across the capacitor. This is 96%
of full charge and the equiv' of 6.9 Joules of stored energy. If you're
using a 'wall wart' 1/2 amp type PSU then the caps could easily charge to
say 6.5V and store a much higher 12.7 joules. Charge time to 99% of final
voltage can easily be 60sec.
Much faster to charge the caps from a charged 6V sealed cell battery via a
low value resistor.
john

o------------------o----oo-----o-----------o
| | | |
| 5V | .-. |
| Charger | | |10k |
.--o--. | | | |
| 5V | | '-' PNP |
| | | | BC556 |<
| | --- o---------|
| | --- | |\
| | | | |
| 0V | 600000u | | |
'--o--' | z Zener .-.
| | A 4.3V | |
| | | | |
| | | 330ohm'-'
| | | |
| | | |
| | | V
| | | Red LED -
| | | |
o------------------o----oo-----o-----------o

(created by AACircuit v1.28 beta 10/06/04 www.tech-chat.de)

 

[Jim]

I can do better than that. Here is a link. Mine uses different components
but operates the same.

http://www.philpem.me.uk/welder/


Jim

 

[Anthony Fremont]

"Phil Allison"

: time.


** Should take only 4 seconds with a 1 amp charger.

WTF? You don't even know how many caps he's using and you can calculate
the charge time? Please show us how you did it.

 

[Anthony Fremont]

"Phil Allison" long

WTF? You don't even know how many caps he's using and you can calculate
the charge time? Please show us how you did it.

This reply wasn't supposed to be posted, oh well.

 

[Fred Bloggs]

I built a battery tab spot welder using multiple 5 volt 150,000 uf computer
grade capacitors in parallel, as the heart. The capacitors are charged
using a small 5 volt unregulated charger. This works well, except I am not
sure when the capacitor bank is fully charged up, as it takes a long time.

What can I use as a charge indicator? All I really need is for an LED to
light or something like that. Can someone please suggest a circuit or an
idea that would work for this application?

Something like this in a small *steel* enclosure will work well enough.
It is better if the detector power supply does not get pulled down by
the caps:
View in a fixed-width font such as Courier.

.
. .----------------[470]-------------------->TO
. | CAPS
.5V>-+-----------------------+----------------+-----.
. | | | | |
. | .----+ | | |
. | | | | | |
. | | | | | |
. | | | | | |
. | | | 555--------- | ---
. | /_ | | VCC/RST | [330] \ / ~~
. | \/| | | | | --- IND LED
. | 50K / === | | | | GREEN
. | /\ 0.1u | | | |
. | | | .---|TRIG DIS|--[220]--|-----'
. | | | | | | |
. | | | | | | |
. | +----+---+---|THRESH | |
. === | | | | |
. 0.1U | | |OUT CONT|---------+
. | | | | | |
. | | | | GND | |
. | | | ----+------ |
. | | | | |
. | | | 1N4001 | |
. | | '--|<|---+ |
. | \| | |
. | 2N3904|----[10K]------|----------------+
. | <| | |
. | | | ---
. | | | \ / ~~
. | | | --- REF LED
. | [10K] | | RED
. | | | |
. | | | |
. | | | |
. '-----+-----------------+----------------+
. |
. ---

I'm with Tom B on this. Why all the fuss when a cheap DMM (or panel meter) will
give the full story?

Part of the problem with USENET is that the OPs blind you to their
narrow view of things which results in suggestions that compound the
p.o. crap even more. Then of course the whiners complain they never get
a decent response from the NG. The long charge time is due to the
exponential decay of charging current from a supply open circuit voltage
not much greater than the final value. The charging should be done from
a 9 or 12V supply that is cut off at 5V+/-5%, and the threshold
detection should not be corrupted by the I x ESR product. Let's see your
friggin VM do that I added a 10K in the base circuit of transistor.

 

[Fred Bloggs]

The LED starts to come on with about 4.8V across the capacitor. This is 96%
of full charge and the equiv' of 6.9 Joules of stored energy. If you're
using a 'wall wart' 1/2 amp type PSU then the caps could easily charge to
say 6.5V and store a much higher 12.7 joules. Charge time to 99% of final
voltage can easily be 60sec.
Much faster to charge the caps from a charged 6V sealed cell battery via a
low value resistor.
john

o------------------o----oo-----o-----------o
| | | |
| 5V | .-. |
| Charger | | |10k |
.--o--. | | | |
| 5V | | '-' PNP |
| | | | BC556 |<
| | --- o---------|
| | --- | |\
| | | | |
| 0V | 600000u | | |
'--o--' | z Zener .-.
| | A 4.3V | |
| | | | |
| | | 330ohm'-'
| | | |
| | | |
| | | V
| | | Red LED -
| | | |
o------------------o----oo-----o-----------o

(created by AACircuit v1.28 beta 10/06/04 www.tech-chat.de)

Nah- that led starts coming on at about 4V across the caps or 0.64
storage energy at 5V. SPICE zener models stink.

 

[budgie]

I built a battery tab spot welder using multiple 5 volt 150,000 uf computer
grade capacitors in parallel, as the heart. The capacitors are charged
using a small 5 volt unregulated charger. This works well, except I am not
sure when the capacitor bank is fully charged up, as it takes a long time.

What can I use as a charge indicator? All I really need is for an LED to
light or something like that. Can someone please suggest a circuit or an
idea that would work for this application?

Something like this in a small *steel* enclosure will work well enough.
It is better if the detector power supply does not get pulled down by
the caps:
View in a fixed-width font such as Courier.

.
. .----------------[470]-------------------->TO
. | CAPS
.5V>-+-----------------------+----------------+-----.
. | | | | |
. | .----+ | | |
. | | | | | |
. | | | | | |
. | | | | | |
. | | | 555--------- | ---
. | /_ | | VCC/RST | [330] \ / ~~
. | \/| | | | | --- IND LED
. | 50K / === | | | | GREEN
. | /\ 0.1u | | | |
. | | | .---|TRIG DIS|--[220]--|-----'
. | | | | | | |
. | | | | | | |
. | +----+---+---|THRESH | |
. === | | | | |
. 0.1U | | |OUT CONT|---------+
. | | | | | |
. | | | | GND | |
. | | | ----+------ |
. | | | | |
. | | | 1N4001 | |
. | | '--|<|---+ |
. | \| | |
. | 2N3904|----[10K]------|----------------+
. | <| | |
. | | | ---
. | | | \ / ~~
. | | | --- REF LED
. | [10K] | | RED
. | | | |
. | | | |
. | | | |
. '-----+-----------------+----------------+
. |
. ---

I'm with Tom B on this. Why all the fuss when a cheap DMM (or panel meter) will
give the full story?

Part of the problem with USENET is that the OPs blind you to their
narrow view of things which results in suggestions that compound the
p.o. crap even more. Then of course the whiners complain they never get
a decent response from the NG. The long charge time is due to the
exponential decay of charging current from a supply open circuit voltage
not much greater than the final value. The charging should be done from
a 9 or 12V supply that is cut off at 5V+/-5%, and the threshold
detection should not be corrupted by the I x ESR product. Let's see your
friggin VM do that I added a 10K in the base circuit of transistor.

I'm not sure what your native language is, but my take on the O/P's request for
a charge indicator meant just that. Let's not obfuscate the task by suggesting
improvements to his charging arrangement, regardless of the scope.

A voltmeter is a perfectly good indicator of the state/progress of charge of his
cap bank. If you think otherwise, please support your view with cogent
argument.

 

[Fred Bloggs]

I'm not sure what your native language is, but my take on the O/P's request for
a charge indicator meant just that.

What did I just tell about that simple-minded interpretation of posts
written by simple-minded people?

 

[John Jardine.]

[...]
Nah- that led starts coming on at about 4V across the caps or 0.64
storage energy at 5V. SPICE zener models stink.

Indeed.
Measured a few Zeners for real. Total crap, like bendy resistors. My drawn
circuit was shite anyway. (neat self destruct .
regards john