On Sun, 21 Aug 2011 16:36:05 +0100, Ian Field wrote:

"mick" wrote in message
eb.com...

I've got quite a few of these. They look like 1N400x family but are
marked W642G1, with 540 on a second line. I've been using them as
'4001s but they may well be something else. The W symbol has vertical
sides, by the way. It could be a logo.

If you check Vf on a DMM diode check, generally speaking the lower the
Vf - the faster the rectifier - then there's the jump to the much lower
Vf of SB rectifiers. If you get a Vf measurement actually anywhere near
0.7V, its likely to be a zener.

You can check reverse breakdown voltage with a (2 electrolytic) voltage
doubling bridge rectifier fed by a high resistance (about 68k for 230V)
and monitor the slow voltage rise until it stops, with a DMM.

The fully charged electrolytics are of course pretty dangerous - if you
just add a shorting switch to discharge the capacitors, it will blow the
contacts away - put a NTC surge limiter in series with the switch.


Thanks Ian. Vf is about 0.525 for these. That's why I was using them as
rectifiers. I hadn't thought of doing a reverse breakdown test like that
- nice idea. I will now!

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
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