Hi,
I was reverse engineering the charger for an air mouse and noticed a 1u (50V) electrolytic installed *backwards* at the input. I've checked this twice to make sure I wasn't tracing foils improperly. I don't know, for sure, what it is
*intended* to see across it though the battery in question is ~3V and the line is protected with a 15V TVS -- I'm guessing around 6V based on other components in the signal path.Is there any *intended* reason for this? Or, is it just a stuffing error?
Did you actually measure the voltage across it?
Probably just a stuffing error.
A 50V e-cap could last forever at -3V but I wouldn't bet the farm on it.
It sees whatever the input voltage (wall wart) supplies to the charger. I.e., it is *at* the input (a diode drop below the input voltage). Since I don't *know* what the input voltage is supposed to be (other than the constraints imposed by the other components in the circuit), I can't guess as to what is "supposed" to be across the cap.
That's what I was thinking. But, wondered if there wasn't some bizarre "trick" involved...
Well, it will see at least that much as the battery it is driving (looks like a simple series resistor) is about 3V. I'm guessing it has 5-6 volts across it (it currently does as that is what I am using for a wall wart currently). But "never" more than ~15 (owing to the TVS).
It's lasted this long, I'll just leave it there instead of risking breaking the case trying to get it open again.
Well, wont any electrolytic cap reverse its polarity, when you feed it reversed very gently for a long time,limiting current to a trickle? There will of course be a period, where it does not act as a cap....
Directly across the output of the wall wart hardly seems like it will see "a trickle"... :>
And on at least one occasion I found an artwork error on a board. The cap was properly polarized but the silk screen was wrong.
G=B2
:)
I once found a 16v lytic installed wrong polarity on a 23v psu rail in an amp I'd been using for years without incident. Worked just fine. It was doing psu smoothing for a preamp stage, so was via a resistor must have reformed awful quick.
NT
Someone told of a story here where the company had made such an error, so told the production guys to flip the capacitors on assembly. All is fine and dandy. Then they did a revision, and fixed it, and more than a few boards made it out before the production guys got the message :-)
Tim
Maybe the capacitor was labeled wrong and really, really, cheap because of it?
The Chinese are expert dumpster-divers - they even have a business, with DKK 4 Million turnover (More in other currencies!), sorting the mangled coins out of all the shredded cars they get, filling them in containers and banking them before they melt the scrap steel down.
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