Bruce Sinclair wrote, on Tue, 01 Dec 2015 01:56:02 +0000:
We both agree that an AC VA is a watt just as much as a DC
volt time amps is a watt.
I found out later that the 40Watts is almost certainly a lie or
a misprint, since the same part number "HC363-5U" also fits an
exact duplicate looking device, only under a different brand
name, but with the wattage listed as a more reasonably close
35Watts to the calculated 34 Watts maximum output.
So, the input AC power factor is just a red herring, totally unrelated
to anything being discussed here.
Bruce Sinclair wrote, on Tue, 01 Dec 2015 23:43:08 +0000:
Let's agree to disagree.
We're not talking "safety" factors (where a doubling is routine).
We're talking specifications.
If I gave you a 40 amp circuit breaker and it kept switching at
34 amps, you'd not be so cavalier about the huge difference.
Likewise, if I told you something was 34 dollars a month, but it
turned out to be 40 dollars a month simply because I lied, you'd
again not think to be so nonchalant about it.
But that was what I was trying to get at.
If a 40A breaker consistently tripped at 34 Amps, you'd likely be upset.
To me, when watts are not only expensive, but 5 Watts is the typical
output of *many* single USB ports out there, so, to mis-state the power
by 5 Watts is a big deal.
Do you ever wonder why they never underestimate the wattage?
For example, you'll almost never see it listed as 29 Watts.
Why is that the mistake is almost always an over statement?
On Monday, November 30, 2015 at 8:07:53 PM UTC-5, Danny D. wrote:
That is not correct. Volt x amps are equal to watts only if
the power factor is one. That's true for a resistive load.
But for a load with inductance or capacitance, like your
charger, VA <> watts and the actual power in watts will be
less than the VA rating.
It could be the input power.
VA is if you measure the RMS input voltage and then separately measure
the RMS input current and multiply them.
But depending on what is inside the charger the voltage and current may
not be in phase so the power, in watts, drawn from the mains might be
less than the VA value.
Brian Gregory (in the UK).
To email me please remove all the letter vee from my email address.
In this case, you compare the exact same model number to
a part that says it's 35 watts and another that says it's
Given they sell for about the same price, which would you
choose if you did not know that the 40Watts was a lie?
On Tue, 1 Dec 2015 20:42:21 -0000 (UTC), Danny D. wrote:
Bought any resistors or capacitors lately? Resistors are commonly sold with
nominal values +/- 20%; capacitors, with +100/-50%. +/-15% may not be high
precision, but it's better than common precision :-) .
And anyway, 35 isn't a whole 15% less than 40, it's only 12.5% less, if
we're going to try for highest arithmetic precision here :-) . No big deal.
Cheers, -- tlvp
On Wednesday, December 2, 2015 at 11:16:27 AM UTC-5, Danny D. wrote:
But you didn't buy a precision USB charger either. You bought a
typical made in China widget, marketed not by Apple, Sony, etc,
which typically vets those products, maintains some control over them,
but by a company called "Hype", which could be run out of someone's
bedroom for all we know. It's typical that these have documentation
errors, language translation errors, etc. And some of them are just
junk on top of that.
You said you bought over half a dozen. Have you tried another one?
If it works, send the bad one back. If it doesn't work, send them
all back and get another product.
Some of the China stuff is junk, but some surprises me. I bought some DC
volt metes that were mainly a circuit board with a display on it. Good from
0 to 99.9 volts. Out of the 4 that I bought for about $ 6 total including
shipping all but 1 followed my Fluke meter up to about 30 volts which was
the limit of the poewr supply I used to test them and the other one was off
by the last digit most of the time which is often normal. That was reading
to the tenth of a volt.
My $ 27 ham band handy takey from China works as well as any other one form
Japan that costs 5 times as much.
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.