need cap. charge indicator

"Jim"

** Who makes 150,000 uF caps rated at only 5 volts ??? ** Bet it puts out a lot more than 5 volts when unloaded. ** Should take only 4 seconds with a 1 amp charger.

What the heck are you using ?

** So you do * not * have a DC voltmeter ? ** A red LED and a 3.3 volt zener would do - but you have more serious problems than that.

......... Phil

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

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

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:

or

Charge indicator: volt meter. If you don't already have one and you're on a serious budget, try something like 90899.2VGA from

On sale at about $5, sometimes even less. Should be good enough for what you are doing.

Cheers, Tom

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

computer

not

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

"Phil Allison"

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.

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 | | . | | '--|

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

computer

not

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

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

Jim

time.

to

an

"Phil Allison"

time.

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.

long

calculate

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

will

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.

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

will

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.

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

[...]

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