Re: need cap. charge indicator



budgie wrote:
On Sun, 05 Mar 2006 22:21:07 GMT, Fred Bloggs <nospam@xxxxxxxxxx> wrote:


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.

.

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