[R-390] Isolation Transformer update
Barry Hauser
[email protected]
Thu, 6 Nov 2003 12:36:07 -0500
Don't know how typical that is -- doesn't sound unreasonable. But then,
that's why power is switched at the primary .... except for a lot of new
stuff.
Wherever wallwarts are used, there's a constant drain even when the devices
connected to them are turned off. Originally, these were mostly for use
with small devices that were otherwise battery operated and mostly on a
part-time basis.. However, there are many AC only as well as portable
equipment with wallwarts whether they make sense or not. That's so the
manufacturers don't have to design for mains voltage and UL/CSA/CE approval
for the unit itself which only "sees" low voltage AC or DC. Also makes it
easier and cheaper to provide for various domestic supply voltages by simply
packing the appropriate wallwart in the box.
Though well forgotten by now (pre-9/11), one of Dubya's early speeches
about energy conservation called these things "power vampires" that consume
even when not in use. And that's because the primary is connected 24/7.
Look around -- most computer accessories, even tabletop communications
receivers, cordless phone bases, you name it. Probably average about 10-20
of these things per household. Leave 'em all plugged in, turn everything
else off, then go read your meter. I suppose it can add up. (Touch some --
see how warm some of them run on idle.)
While most of the wallwarts have some kind of approval marking, most all
have no internal fuse or thermal breaker. If they fail, most will begin to
burn up well before tripping a 15 or 20 amp breaker.
Gettin' old here. Just mention something about primary windings drawing
current with no load .. and I run off at the keyboard on a wallwart rant.
Don't you just love the ones that don't have the manufacturer's name or
model number, so when you disconnect a bunch .... nevermind. I'm starting
to sound like Andy Rooney.
So you were saying? 350 ma unloaded? Don' t look know but .... ;-)
Barry
----- Original Message -----
From: "Scott, Barry (Clyde B)" <[email protected]>
To: "R390 (E-mail)" <[email protected]>
Sent: Thursday, November 06, 2003 9:46 AM
Subject: [R-390] Isolation Transformer update
> I did some experimentation last night. With no load and the primaries
> connected in parallel at the 120V tap, the primary drew about 350mA. At
the
> 110V tap, it drew almost 500mA.
>
> I then connected the series 75W light bulb. The 120V tap caused a dull
glow
> while the 110V tap produced about twice that brightness (although still
> quite dull).
>
> I didn't attempt the primary at the 104V tap. I did notice the
transformer
> produced a bit more hum at full voltage when at the 110V tap than at the
> 120V tap. I did not notice any heating, but I didn't leave it on very
long
> either.
>
> Do these results sound typical? I've never examined the primary current
> draw on a transformer at no load.
>
> Thanks,
>
> Barry(III) - N4BUQ
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