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USB-C Charging and Overheating?

AMS

Member
Since Day 1, I've been running my SL3 with a USB-C hub to charge it. The fans are nearly always running, and the case is always hot.

This past weekend, I charged it using a Surface Connect power supply, and the fans were silent. I've since verified that with another power supply. Does anyone out there know what's the deal with USB-C charging and why it should cause this kind of behavior?
 

sharpuser

Administrator
Staff member
USB-C is generally unregulated current, at a steady voltage. That is why USB-C chargers (plugs, bricks, adapters) show their wattage. But “bigger” carries a price of efficiency and wear-and-tear. The small conductors (wires, circuit paths) when using a high wattage charger dissipate heat due to the resistance. The fan is trying to cool everything down. And that draws a little more power while you’re trying to charge the battery, making the problem even worse.

In contrast, the OEM Surface charger reaches the battery circuitry with lower resistance (more robust) lines. Charging may be slower, but there is less wear and tear on your machine. Longer time with less heat. Like slow-cooking a roast.
 
OP
A

AMS

Member
USB-C is generally unregulated current, at a steady voltage. That is why USB-C chargers (plugs, bricks, adapters) show their wattage. But “bigger” carries a price of efficiency and wear-and-tear. The small conductors (wires, circuit paths) when using a high wattage charger dissipate heat due to the resistance. The fan is trying to cool everything down. And that draws a little more power while you’re trying to charge the battery, making the problem even worse.

In contrast, the OEM Surface charger reaches the battery circuitry with lower resistance (more robust) lines. Charging may be slower, but there is less wear and tear on your machine. Longer time with less heat. Like slow-cooking a roast.
This implies that the cable and connector would be hot, but they're not. The laptop itself is hot, and the fan isn't working to cool the connector as its temp is not elevated. It could be the battery, however...if the battery is using the extra current to speed-charge. however, the machine is hottest near the motherboard, and coolest near the battery, which makes the battery theory less plausible.
 

sharpuser

Administrator
Staff member
No, the cable and connector can handle the current. The smaller conduits are in the PC.
 
OP
A

AMS

Member
No, the cable and connector can handle the current. The smaller conduits are in the PC.
If that's so, that's rather poor engineering. In fact, it's EXTREMELY poor engineering, since the product is designed to charge from USB-C.
 

sharpuser

Administrator
Staff member
All laptops have this vulnerability, as also do non OEM chargers using the Surface Connector.

Here is a quote from a DELL laptop support website:


The temperature gets really high with a USB-C dock/charger plugged in and no CPU usage. Its very very hot to touch and my measurement suggests close to 65C in the hottest stop.

Can someone from Dell confirm if this is OK? Is there a BIOS fix coming for this? I don't think this is normal and it will ruin the battery/electronics around this area in the long run.


A DELL charged this way burned up the motherboard.
 
OP
A

AMS

Member
All laptops have this vulnerability, as also do non OEM chargers using the Surface Connector.

Here is a quote from a DELL laptop support website:


The temperature gets really high with a USB-C dock/charger plugged in and no CPU usage. Its very very hot to touch and my measurement suggests close to 65C in the hottest stop.

Can someone from Dell confirm if this is OK? Is there a BIOS fix coming for this? I don't think this is normal and it will ruin the battery/electronics around this area in the long run.


A DELL charged this way burned up the motherboard.
The fact that it happens in lots of machines from different manufacturers doesn't excuse it. If the traces on the circuit board are so small as to be unable to reasonably handle the current that the machine may be expected to draw, then it's bad engineering.

Granted that I worked in software, not hardware, but when I was an engineer, we designed our products to deal with user-imposed stressors.

If a port is advertised to be used for charging and the cable can carry the current that the machine demands, then it behooves the people designing the portions of the motherboard that will carry that current to do so--or, in the event that they can't do it because the machine "has to be thinner," or something, to object.

There's no reason that a manufacturer can't say "This USB-C port doesn't support power delivery." In fact, I own a machine in which one of the ports is so designated. If you're going to implement USB-C charging then you ought to do it right. As the Dell support question you quote points out, this kind of heating "will ruin the battery/electronics around this area in the long run."
 

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