Advice sought on why 6.8A USB charger melted USB cable today

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?? The definition (or one of them :) ) of watt is W=VxA (or VA). Are you saying they are different ? ... if so, why ? :) https://en.wikipedia.org/wiki/Watt
(snip)
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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.
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:)
And the difference between 35 and 40 W is so small as to be irrelevant too I suggest. :)
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Bruce Sinclair wrote, on Tue, 01 Dec 2015 03:38:14 +0000:

You've got to be kidding. It's huge the difference.
15% is a huge lie on something so simple to calculate.
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As I said. Tiny. Not even a factor of 2 (that engineers routinely use), let alone a factor of 10 (that starts to make things interesting). :)
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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.
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a circuit breaker? It may not trip below 40 amps but don't expect it to trip at 41 amps, not for a very, very long time anyway!
--
Chris Green
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cl wrote, on Wed, 02 Dec 2015 10:27:09 +0000:

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?
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Agreed. Conversationms would be had. :)
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On 01/12/2015 09:32, Danny D. wrote:

But they don't really even tell you what it is.
It doesn't say "Maximum output wattage".
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Brian Gregory (in the UK).
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Uncle Monster posted for all of us...

.com> wrote:

Another one off the rails into the ravine and this one is burning...
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Uncle Monster posted for all of us...

mail.com> wrote:

Correct, now I am all amped up (for what I don't know)
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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.
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On 01/12/2015 00:30, Danny D. wrote:

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.
--

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On Mon, 30 Nov 2015 19:00:30 -0000 (UTC), Danny D. wrote:

In electronics, +/-15% isn't too far off :-) . Cheers, -- tlvp
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tlvp wrote, on Tue, 01 Dec 2015 05:32:44 -0500:

It depends. 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 40 watts.
Given they sell for about the same price, which would you choose if you did not know that the 40Watts was a lie?
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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
--
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tlvp wrote, on Wed, 02 Dec 2015 01:30:49 -0500:

If I bought a precision resistor, and it was off by 15%, I'd be upset.
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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.
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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.
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