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

[Danny D.]

Zaidy036 wrote, on Mon, 30 Nov 2015 16:30:59 -0500:

That power factor is only for peak to peak voltage, isn't it? Do they use the power factor for RMS voltage?

[Danny D.]

Danny D. wrote, on Mon, 30 Nov 2015 21:37:43 +0000:

I just read up on the power factor and I don't think it applies here:

[Dave Higton]

Of course it applies here. Read again and keep reading until you understand it.

Dave

[Danny D.]

Dave Higton wrote, on Mon, 30 Nov 2015 22:32:11 +0000:

But if you're saying the 40W is actually 40VA, where is the math that backs that up?

All "my" math (given only the printed numbers), come up with

34 Watts (DC) output with about 80VA (RMS) input.

Nothing is even close to 40W or 40VA.

[Tony Hwang]

What is power factor? USB works on DC current.

[Danny D.]

Tony Hwang wrote, on Mon, 30 Nov 2015 17:12:02 -0700:

I don't fully understand the power factor but it only applies, AFAIK, to the AC input voltage time current.

Even then, I think it only applies when you add multiple AC wattages up.

The voltage and current fluctuate so, even if you pick the RMS voltage and current of the one AC signal, if you try to add it to another AC signal with a different phase, then you have to factor in the power factor.

At least that's how I understood it after reading about it, but, I don't think the power factor applies here, as you said, b because we only care about the output power, which is DC.

[Danny D.]

Danny D. wrote, on Tue, 01 Dec 2015 00:20:57 +0000:

This article says the AC power factor plays a role whenever the AC current and the AC voltage are not in phase:

I think the whole power factor thing is a red herring because we're talking output power, which is DC, which has both the current and voltage in phase.

Only if the 40W is for the input power would the AC power factor matter, and, if that 40W was for the input, it wouldn't be called Watts - it would be called VA (volt amperes) anyway.

So, I don't think the AC power factor applies in this question.

[Danny D.]

nospam wrote, on Mon, 30 Nov 2015 15:09:53 -0500:

Thank you for that reference. It's pretty clear from the white faceplate and the lack of printing on the cable that it's not an Apple cable, but that doesn't mean the cable is bad.

I ran down the iPad today and have it on the same charger with a different USB cable (this one I think was from Staples because it's flat instead of being round). So far it's not getting hot, but I will know by tomorrow.

As for the 40Watt figure, I think it's a lie because I googled for the part number that is printed on the side of the unit:

Notice that HC363-5U printed on the unit?

Googling for just that, I find the same unit only with a different set of markings, which is listed as being 35Watts, which is closer to the 34 Watts that 6.8 Amps gets us at 5 VDC:

"Hausbell 35W HC363-5U UL Certified (UL No:E310745) Family-Sized USB Wall Charger Plug Smart Charger, Single USB Output 2.4A Max,Output total 6.8A Max,5P-USB Output for Apple and Android Smartphones,Tablets and More(White) by Hausbell, Price: $59.99 & FREE Shipping"

Here's the same unit, this time for $15:

Here's another, again listing it as 35Watts:

And another:

And another:

So, pretty much, the 40Watts is either a bold-faced lie, or it's not the wattage of the output.

[Savageduck]

Damn! Did you wear out your "Paul M. Cook" sock already?

At least you could have come up with something new and different rather than one of your earlier well worn nyms.

[Savageduck]

Aah! You also noticed that.

[Savageduck]

Then you have a PIA, nymshifting doppelgänger who uses a particular posting style. Hmmm...

[trader_4]

/6000193376994

My guess is that part of the answer to this is that this is a cheap, Chinese no-name product. It probably has all the typical confusing specs, specs lost in translation, etc. Why it burned up the cable, who knows. What kind of support is there for this? I'm betting not much.

[Tony Hwang]

If you understand inductive or capacitive reactance in AC circuit. Most load in AC power has inductive reactance meaning voltage leads current by certain amount depending on how reactive it is. The more phase angle, less power factor losing power as wasted(non energy producing) Power factor is expressed as Cosine Phi So when the angle difference is zero PF factor is 1 which never will be. Less than one, VA and W=V*I are not equal. I just explained it in layman talk. Draw a full Sine wave one for voltage and one for current. In this case voltage wave leads the current wave by few degrees. So both waves does not super impose. The difference in phase angle expressed in Cosine is PF. In the case of capacitive reactance current leads voltage. You should know conjugatory number? +jR is inductive reactance, -jR is capacitive reactance. AC circuit impedance Z is root mean square of DC resistive value plus +/-jR Still Ohm's law like in DC cibut reactance is additional parameter. I hope I made some sense. If I have blackboard I could show you with graphics.....

+jR is 2*pi*f*L (f in Hertz, L in Henry) -jR is inversed 1/2*pi*f*C (C in Farad) Opposite of Impedance Z is called Admittance Y=1/Z

If there is step down transformer involved power can incur some loss due to poor material like heating up the core iron Not only PF is an issue. Any power supply produce heat(lost energy lowering effciency) For an example look at the power supply for desk top or laptop PCs. Good ones have higher efficiency as well as producing clean very stable outputs. You get what you pay for applies here too, LOL!

[Tony Hwang]

We have couple iPADs kicking around in the house. I wouldn't use quality unknown anything with iPAD for the danger of damaging the unit. Look for UL, CSA,EU approval Logo on stuffs like that. I have O'scope at least I'd check how clean output they produce EU standard is quite higher than that of UL.

[Danny D.]

Tony Hwang wrote, on Mon, 30 Nov 2015 17:52:11 -0700:

I think the packaging is telling a lie about the 40Watts.

If you look at the device, you see the model of HC363-5U.

If you type "?HC363-5U" into the URL bar, you find the same device under a different brand name, which lists it clearly as 35 watts!

amazon.com/Hausbell-35W-HC363-5U-Certified-Family-Sized/dp/B00NUREFMO

So, pretty much, I think it's a lie or a "misprint" that the unit is 40Watts. It's more like 34Watts (35W is reasonably close). "Hausbell 35W HC363-5U UL Certified (UL No:E310745) Family-Sized USB Wall Charger Plug Smart Charger, Single USB Output 2.4A Max,Output total 6.8A Max, 5P-USB Output for Apple and Android Smartphones,Tablets and More(White)"

Do you know which authorities to contact?

[Danny D.]

Tony Hwang wrote, on Mon, 30 Nov 2015 18:00:22 -0700:

They print the UL approval on lighting cables?

[Danny D.]

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.

[Danny D.]

Tony Hwang wrote, on Mon, 30 Nov 2015 17:52:11 -0700:

The AC power factor has nothing to do with this problem.

[Danny D.]

trader_4 wrote, on Mon, 30 Nov 2015 16:44:45 -0800:

Hey Trader,

I know you mean "cheap" as in cheaply made, but, try to find a USB multi-port charger that isn't made in China.

Besides, it's sold for $60 here, so, that's not cheap (if anyone is dumb enough to pay that much for it that is):

[Bruce Sinclair]

?? The definition (or one of them :) ) of watt is W=VxA (or VA). Are you saying they are different ? ... if so, why ? :)

(snip)