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

Yes, the supply/charger is using a total of 40 watts, some of which gets lost with in itself the remainder used for the connected devices. One could say it's 85% efficient.

Many devices can link up to things like PCs. The USB port has more than just power/charging wires. They also have data wires. Its posible the charger could be detecting basics about the device and selecting a current via the data lines.

On devices that it can't determine the ratings, it may deside to give it all!.

Jamie

M Philbrook wrote, on Mon, 30 Nov 2015 15:18:19 -0500:

While the *input* wattage could be 40Watts, given the input voltage and maximum input current, the *input* is something like 80VA:

That's 100-240VAC (RMS) times 800mA, which is about 80VA.

If the package wanted to say it was input power, it would have stated the 40 as 40VA and not 40W, wouldn't it?

So it's only about 50% efficient if we believe that the max input power dissipation is 80VA while the max output power is 40W.

The 40 Watts listed on the package doesn't match either the input volt-amperes nor the output wattage calculated from the specs off the device itself. This description has the same discrepancy:

I called the company that makes the product but only could speak with sales who didn't know what the reason for the discrepancy was:

195 Raritan Center Pkwy Edison, New Jersey 08837-3650 (718) 499-1000

So, I'm still left with 40 Watts listed on the package, while no numbers listed on the device for either input volt-amperes or output watts is anywhere near that number.

The official spec for USB says its limited to 500mA at 5V.

As long as the 5V is rock steady and within spec the current draw should be whatever the appliance normally takes.

The highest I've seen offered for sale was 2.1A.

You should probably get them checked out before you burn down anyone's Christmas tree.

Ian Field wrote, on Mon, 30 Nov 2015 21:40:17 +0000:

That's old information. Here is newer information:

How USB charging works, or how to avoid blowing up your smartphone

The article says there are three types of USB 3.0 ports:

1. Standard downstream port (900mA at 5VDC = 4.5Watts)
2. Charging downstream port (1.5A at 5VDC = 7.5Watts)
3. Dedicated charging port (1.5A at 5VDC = 7.5Watts)

In addition, tablet-charging USB ports typically are 2.1 Amp minimum, and some are as high as 2.4 Amps per port like this charger says it is.

The problem I have is that it says it's 40Watts, which it can't be if it's also limited to 6.8 Amps per port for 5 ports.

I guess it boils down to how badly you want to ruin peoples Christmas.

If the one you tried melted the USB cable and overheated the appliance, something is clearly wrong.

Being experienced with such electronics, most of the designs out there do not specify inrush currents over normal. It's better to specify the max it could be at, even if only in milSec. Completely drained capacitors in the input can cause an inrush while charging for the initial on cycle, but the rating on the input does not mean it will remain there. Most of those things have a form of time delay fuse and thermal resistor that will help with the inital start.

I did the math and from my point of view, it looks correct.

I don't know where all this is leading to but, I beginning to think it has more to do with just being unhappy due to package confusing.

P.S. I don't think they will be replacing your charging cord or tablet..

Jamie

It seems to have melted some plastic or rubber.

Can you still use the cable?

Isn't the better goal to be figuring out why it overheated so maybe you can continue to ucse the charger, if possible?

Maybe there was a bad connection at that USB connector. Bad connections generate heat, though in practice , I've only seen that at a plug/receptacle connection for a 1100 watt room heater (where a

40-year old receptacle made the plug so hot the hard-rubber plug caught on fire) and a car battery/battery cable junction that was powering a whole car (minus the alternator, which should have been plenty so that's confusing) which was hot to the touch and that's how I realized it was loose.

I can't really imagine this happening on 5 volts, but then again, it did. I think it was a bad connection even though the amperage was within range.

I don't think a good connection would generate any noticeable heat even if it was putting out twice the proper amperage.

M Philbrook wrote, on Mon, 30 Nov 2015 17:08:19 -0500:

You make a fair enough point of where things are going, which, for this issue, is simply to *understand* what is happening.

I think the melted cable is merely a bad cable (with a low resistance short between internal wires perhaps).

I don't (yet) understand the 40Watts of "power".

Going only by the printed specs, if that 40W is stating the input power, wouldn't that be double that (at 100VAC rms times

800mA rms)?

And, if the 40W is output power, there's no way that 5VCD times

6.8Amps is anywhere near 40W (it's 15% less, which is a lot).

So, if your numbers matched the 40Watts (whether that's input power dissipation or output power), if you show the math, it would be better understood by me.

Ian Field wrote, on Mon, 30 Nov 2015 22:05:26 +0000:

I think the cable was bad, because it's rare for a charger to put out *more* than the 2.4Amps that it says a port can output.

But that doesn't help explain where the 40Watts comes from since no calculation comes close, whether that's input RMS VA or output Watts.

Micky wrote, on Mon, 30 Nov 2015 18:32:49 -0500:

This is a very fair perspective, especially since I have a half dozen of these 6.8Amp five-port USB chargers (they were on sale for less than $20 each).

I ran down the iPad all morning, by running GPS software and Youtube videos and I put it on a permanent Hangouts video conference call so that the battery ran down to something like 50%.

I then put the iPad on the same charger with a *different* cable, and, so far, the ipad is about at 75% and the (different) cable is *not* overheating yet.

So, at this point, if the iPad charges overnight with the different cable without overheating, I think I would have to conclude it's not a good cable.

I'll know by tomorrow.

Micky wrote, on Mon, 30 Nov 2015 18:32:49 -0500:

This is a good point. So, I'm assuming the cable is bad and I switched cables and at the moment, there is no heat.

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 but it also calls it 35 Watts:

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

And another listing it as 35 Watts:

And another listing it as 35Watts:

So, pretty much, the 40Watts is either a bold-faced lie, or it's not the wattage of the output (which is closer to 34 Watts).

First of all, to melt a wire or connector, there must be an overload. Unless the charger went overvoltage it is not at fault. check what you were charging and its cable.

jurb6006 wrote, on Mon, 30 Nov 2015 16:48:19 -0800:

Even if the charger put out all 6.8 Amps into the iPad, there shouldn't have been resistance AT the cable end sufficient to cause the cable plastic to melt from the power dissipation at the connection point.

So, that pretty much tells me that the cable was bad. It could have started a fire, so, it's good that I pulled that cable out of service.

I have the same charger and a different cable, so I will see if this second cable (this one is from Staples, I think, instead of from Office Max) works without overheating.

If you keep being nice to the people you deal with on Usenet, it will be hard to fight with you. For many people that will ruin the whole experience.

I don't know why this bothers you so much. Maybe it is a lie, they were trying to increase sales. Maybe the guy who said 40 was drunk, but he really thought it was 40. Maybe he made an error. Do you remember the Hubble telescope? 100's of millions of dollars and they ground the mirror wrong because someone miscalculated. If they can do it, so can whoever made the charger.

Based on what you have below, it's probably 35 watts.

Micky wrote, on Tue, 01 Dec 2015 00:12:10 -0500:

Nobody makes that kind of mistake by accident. The difference between 34 Watts and 40 Watts is huge.

I suspect they wanted to compete with the competitor who makes the exact same device (same everything but the name and the lie on the package).

I do have a call in to the manufacturer to find out why they say

40 Watts, and I will report it to Consumer Reports if I can find an email address to do so.

Had you considered it might be putting out more than the 5V its supposed to?

Apparently; the OP bought over half-dozen of these units for stocking fillers.

Probably worth figuring out what the problem is before one wrecks the nice shiny pad someone got for Christmas - or burns down their Christmas tree...................

To quote a paragraph from the OP;

"When I pulled it off the iPad, it was noticeably extremely hot, but it doesn't seem to have damaged the iPad (AFAIK)."

Seems to indicate the iPad was working (and apparently undamaged) - and since the device got hot, a short in the cable isn't that likely.

Maybe mis-wired cable reversing the polarity, or regulation fault in the charger.

Ian Field wrote, on Tue, 01 Dec 2015 18:29:45 +0000:

It could be. What I need is one of those USB DMM tester cables that Jeff keeps recommending.