Mass USB charging

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I ran into a bit of a problem with a project I am working on and wonder if anyone has any ideas.

I bought a 36 port USB hub that comes with a 5V 4A power supply. After plugging in 25 Huawei S7 tablets the poor power supply nearly melted (in fact, it did become soft in parts) and shut itself down after about 15 mins.

After doing some research I noticed that the max output for one USB port is supposed to be 500mA, which means the max the 36 port hub can charge is 8 (500mA x 8 gives 4A). This is a bit of a bummer, as I need to be able to charge 34 simultaneously :P

Common sense (and that's all it is, have no formal education in electronics) says I need to find a 5V 17A power supply to charge the hub as this should give each port at least the 500mA it needs.

But that is easier said than done, most hubs come with underpowered power supplies and I have yet to find a 5v supply with anything more than 4A.

Any ideas or suggestions?
 
Ideally it should allow for simultaneous charging, as the devices will be charged overnight for use during the day.

During the day the devices will be used as needed, so in that case there will be less devices attached.

I was thinking of perhaps splitting it up into three or four 10 port hubs, but they in turn come with their own underpowered power supplies that only have 2A for 10 slots. It seems manufacturers bargain on users not using the max draw on each port and thus cheap out on the power supplies.

I can use the power supply from the 36 port hub to power the 10 port hub, but then where will I find more 5V4A power supplies for the rest of the 10 port hubs?
 
WARNING: DO NOT PLUG IN A HIGHER RATED SUPPLY THAN THE ONE IT CAME WITH.

The power supply acts like a fuse. The reason they ship under-rated supplys is to protect the components from too much current. Remeber that P=I^2*R. The heat dissapation on the wires is just that. You were overheating at what? 5 amps? Can you immagine what will happen when you try pump even 10 amps in there?
 
Largest I could find with a quick search is 12A for around R900... if it draws too much power it will auto shutdown until it cools down enough, and then it will start again
 
agentrfr said:
WARNING: DO NOT PLUG IN A HIGHER RATED SUPPLY THAN THE ONE IT CAME WITH.

The power supply acts like a fuse. The reason they ship under-rated supplys is to protect the components from too much current. Remeber that P=I^2*R. The heat dissapation on the wires is just that. You were overheating at what? 5 amps? Can you immagine what will happen when you try pump even 10 amps in there?
Click to expand...

Lovely pyrotechnics? :D
 
Thanks Archer, do you perhaps have a link?

@agentrfr Does that hold true of both the V and the A? I thought that perhaps at the same voltage it would just send more amps through and the ports will draw as much as they need?
 
agentrfr said:
The power supply acts like a fuse. The reason they ship under-rated supplys is to protect the components from too much current. Remeber that P=I^2*R. The heat dissapation on the wires is just that. You were overheating at what? 5 amps? Can you immagine what will happen when you try pump even 10 amps in there?
Click to expand...

Um.... The PSU was overheating, not the internal wiring of the hub. So what does wiring have to do with this again? And the PSU is a fuse?? That would be the absolute worst design ever...
 
12A might work, that would give charging to 24 devices at a time, which might be workable. If using more amps on the will blow it up, then yeah, I don't particularly feel like burning down the house ^_^
 
The hub should have been designed to handle a worst case scenario, ie, all devices pulling max load. In fact, if it was designed properly, it would be designed to handle more than that, usually around 120% of max, thats standard engineering practice. Its only the PSU thats struggling. So I would not hesitate to give it more amps. If you are a bit unsure I can prob come have a look at it
 
Archer said:
The hub should have been designed to handle a worst case scenario, ie, all devices pulling max load. In fact, if it was designed properly, it would be designed to handle more than that, usually around 120% of max, thats standard engineering practice. So I would not hesitate to give it more amps. If you are a bit unsure I can prob come have a look at it
Click to expand...

I wish I could give more info, but the hub itself does not have any specifications on the outside. Here is a link to the hub if you want to check it out:

http://www.electromannsa.co.za/shop/?q=node/834

This would really work out well if it could just charge 20 - 30 tablets at the same time. It doesn't even have to charge quickly, just enough so it could be used the next day.
 
The only limiting factor is the size of the tracks/wiring by the power input to the hub. Unfortunately I couldnt find anything more about the HUB either, so I cant say for sure. Past that however, each ports wiring/tracks will handle 500mA, its just the bus that could be an issue
 
Most breakers in the DB board for a plug will only be 16amp so your going to have to plan a bit more and check other things as well.
 
Beachless said:
Most breakers in the DB board for a plug will only be 16amp so your going to have to plan a bit more and check other things as well.
Click to expand...

Thats for 220V, ie roughly 3.5kW. This is 5V, so its only 90W (@18A). The DB will be more than fine
 
Archer:8090754 said:
agentrfr said:
The power supply acts like a fuse. The reason they ship under-rated supplys is to protect the components from too much current. Remeber that P=I^2*R. The heat dissapation on the wires is just that. You were overheating at what? 5 amps? Can you immagine what will happen when you try pump even 10 amps in there?
Click to expand...

Um.... The PSU was overheating, not the internal wiring of the hub. So what does wiring have to do with this again? And the PSU is a fuse?? That would be the absolute worst design ever...
Click to expand...

Maybe I explianed it a bit fast. The PSU is the fuse for the device, because that is where all the current goes in and out. They design the PSU to fuse out (melt) when tbe current is at a level that could harm one of the components. To save building costs, tbis wires or used inside your usb hub. That doesnt matter at low currents, but when you pump up the current to 3 times more it was regulated by the PSU for, you arw going to have problems.

In general, the rule of thumb is 8. The fuse will blow at 80% of the current that will damage the most sensitive component on the device. When that goes, the whole thing stops doing what it is supposed to. That could mean all the current goes into just one of the tablets.

Do you really want unregulated current going into your expensive tablets?

Do. Not. Do. It.
 
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