On Sun, 27 Sep 2009 21:46:35 +0100, "Calvin Sambrook"
Like an oversize phone charger?
Oh, I don't like them. 8-))
And I don't like the bevy of low quality adapters they come with.
I've seen new routers, not necessarily the latest one, by reputable
manufacturers starting at £16 on "one day only" sales.
My current modem - router has mains psu built in. It's predecessors
all had wall warts but I think three of them on the trot had
overheating problems (as does this one) causing disconnections.
So personally now I don't deviate from the standard setup.
NB of the two VIGOR routers I had one had an AC power supply and the
other was DC.
Oh and since I got shot down on one group who accused me of "cooking"
my routers I live in a normal modern house maintained at normal
temperatures, although the modem - router is, for the moment,
unavoidably on a shelf above my desk directly above my LCD monitor.
Probably noisy as hell and could possibly cause the router to lose
connection if it's an ADSL modem/router combo. 3Com had a major problem
a few years ago with a cheap plugtop SMPSU they supplied with one of
their ADSL routers.
I keep looking at them, wondering if I should buy one but then I think
of the box full of 'useful' bits n bobs under the stairs.
Depends, plenty of routers use MC34063 switch mode chips (or similar)
for their internal regulators, if you drop the input voltage the switch
has to stay on for longer and thus it dissipates more power, probably
not enough to overheat it but...
For a linear regulator the opposite is true, the lower the voltage the
less power it has to dissipate.
As I had my Silly Scope out for other, much scarier, reasons I took a quick
look at the Tesco SMPS running my doorbell. Set to 6V and driving only two
LEDs at about 30mA it had about 50mV of essentially unstructured noise.
Fastest rise/fall times in the 1nS region so probably no components over
500kHz. I don't know what it takes to upset a router but if any of my guys
designed anything which fell over because the incoming power had that sort
of noise on it I'd cry.
On Tue, 29 Sep 2009 22:22:05 +0100, Calvin Sambrook wrote:
An ADSL "router"...
ADSL2 uses carriers from around 25kHz to nearly 1.1MHz, ADSL2+ goes
up to 2.2ish MHz. MF broadcast stations can reduce the data rate,
interference at night from foreign MF stations knocks a good 512kbps
to 1Mbps of my link.
OK it's only 50mV on the power rail but the bit of wire connecting
PSU to router will radiate nicely and ...
Load it up somewhere close to rated output, preferably with something
other than a simple LED or resistive load and check again. I'm not
saying it's a bad PSU in the grand scheme of things but that it's a
little too cheap to be really good.
I wouldn't expect a noisy PSU to cause the router to fall over unless
the PSU was exceptionally bad and you'd probably have problems with
anything else you powered from that PSU (perhaps not your doorbell or
ADSL is a fairly special case though, RF interference picked up by the
telephone line can cause a modem/router to lose sync, it's not the case
that it falls over because of the noise, it's that the ADSL 'signal'
gets swamped by the noise, reducing the SNR to a point where it's
500KHz is almost smack bang in the middle of the band of frequencies
ADSL uses so if it's close to the phone line (which is a given because
you're powering the router with it) then it could cause problems.
The power dissipated by a linear regulator is the product of the
current through it and the differential voltage between input and
If the input voltage is lower, for a given output voltage, less power
is dissipated by the regulator.
Ahh, perhaps I wasn't quite clear enough, I should have said 'the lower
the *input* voltage to the regulator the less power it has to dissipate'
but given the context I thought my meaning would be apparent.
F'rinstance, if you have a 5 volt linear regulator passing 1 amp and an
input voltage of 10 volts then the regulator will have to dissipate 5
watts, if you have the same regulator but with a 15 volt input then it
has to dissipate 10 watts.
Linear regulators dissipate power as heat so feeding one with a lower
input voltage will generate less heat.
With the proviso that they need a certain amount of head room to work
properly. So a 5V regulator will behave as you describe, but an input
voltage of less than say 7V may prevent it from working correctly at all.
Exactly where I was going. Most 'normal' (as distinct from low
drop-out types) actually require an overhead of 2.3V, plus you
have to consider mains variations, so a starting target input of
about 8V (possibly even more) is more like it.
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