2 Sep
2006
2 Sep
'06
8:01 p.m.
On Saturday 02 September 2006 09:58 pm, Chuck Guzis wrote:
On 9/2/2006 at 11:11 PM ard at p850ug1.demon.co.uk
wrote:
This is correct. But the light bulb as a current limiter is a very handy
thing to have, in any case. If you have a transformer that's developed a
short, for example, or some load is connected to it while you're testing,
or a rectifier turns out to be shorted, or all sorts of other things.
I built myself a little box that uses a center-off DPDT switch to select
whether that light bulb is inline with the outlet in the box or not. And I
also have a set of binding posts connected across that switch, which is
labeled "Bypass/Meter/Limit" for no limit, measuring current with the meter,
or using the light bulb to limit it.
This sort of thing is very handy when you're working on, say, solid-state
audio amplifiers, and you've just replaced a whole set of blown output
devices and want to find out if anything else is bad without blowing them
again. Stuff like that.
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, a critter that can
be killed but can't be tamed. --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin
A useful trick is to connect a 100W mains light
bulb in series with the
input to the transformer when first applying power (and with the
secondaries of the transformer unconnected). Such a bulb will easily
handle the magnetising current of a small transformer, anf won't even
glow (or drop much voltage), so you can check the output voltages, etc.
Hmmm, the way I'd do is to hook up one winding to the mains, then tie one
lead of the second winding to either side of the mains supply and measure
the voltage between the other lead and the other side of the mains supply.
If correctly phased, the voltage difference will be closer to 0 than
2xmains.