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Is it bad if a cable is higher current rating than a charger?

1 Answer
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11

No, only the device should not draw more current than the adapter and the cable can handle.

So the device defines how much current will flow through the circuit (which consists of your adapter and cable).

If the device draws more current, the adapter or the cable may overheat (with a fire hazard).

Btw, it's better to be safe and not use exactly a 2A but at least more, so you are safe with a cable of 3A.

Remarks from others
Also, this yields for most (cheap) adapters. See the comment of Jarrod Christman for an exception.

For USB, there is a negotiation protocol. See the comment of Yakk below.

share|improve this answer

answered 2 days ago

Michel KeijzersMichel Keijzers

21116

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I don't think this is right. If the device tries to draw more than 2A, the adaptor should drop the voltage to keep the current down (until it reaches the point where the voltage is so low that the adaptor cuts out altogether).
  
  – Martin Bonner
  2 days ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @MartinBonner I don't have the theoretical knowledge, but afaik an adapter just 'gives' the current the load needs, and if the load requests more, the adapter delivers more, even if it cannot handle it. Of course, it might be possible there is some kind of safety circuit built in the adapter, but this is not common (for cheap adapters at least).
  
  – Michel Keijzers
  2 days ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @MartinBonner, that depends entirely on the adapter design and intent. Some power supplies will attempt to keep voltage constant and allow more current even beyond their own spec and die. This coupled with intentionally underrating for a safety buffer (a 3A power supply may actually do 3.5A fine), it is best to assume the worst case. Thus your power supply and cables should be oversized to some extent for your use, so you're not constantly against their max rating.
  
  – Jarrod Christman
  2 days ago
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Are you aware of how USB-C devices "negotate" with USB-C cables to determine how much current they can draw? Your answer seems to completely ignore this issue, which is at the core of the OP's problem. I believe 56k resistor in the cable communicates to the attached USB device how much current it can safely draw; barring something I don't know (which is plenty) that cable might convince the USB device into thinking "ok, drawing 3A is ok from this", frying the charger. This isn't a "dumb cable"; for a dumb cable your answer seems correct (more A=more safe)
  
  – Yakk
  2 days ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  (note: I am not an expert at this. Possibly there is a way that the other end of the USB connection (the charger) communicates to the USB-C device the current it supports, and/or handles being asked for more power than it is rated for gracefully)
  
  – Yakk
  2 days ago
  

  
  
  
  

 | 
show 9 more comments

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11

No, only the device should not draw more current than the adapter and the cable can handle.

So the device defines how much current will flow through the circuit (which consists of your adapter and cable).

If the device draws more current, the adapter or the cable may overheat (with a fire hazard).

Btw, it's better to be safe and not use exactly a 2A but at least more, so you are safe with a cable of 3A.

Remarks from others
Also, this yields for most (cheap) adapters. See the comment of Jarrod Christman for an exception.

For USB, there is a negotiation protocol. See the comment of Yakk below.

share|improve this answer

answered 2 days ago

Michel KeijzersMichel Keijzers

21116

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I don't think this is right. If the device tries to draw more than 2A, the adaptor should drop the voltage to keep the current down (until it reaches the point where the voltage is so low that the adaptor cuts out altogether).
  
  – Martin Bonner
  2 days ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @MartinBonner I don't have the theoretical knowledge, but afaik an adapter just 'gives' the current the load needs, and if the load requests more, the adapter delivers more, even if it cannot handle it. Of course, it might be possible there is some kind of safety circuit built in the adapter, but this is not common (for cheap adapters at least).
  
  – Michel Keijzers
  2 days ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @MartinBonner, that depends entirely on the adapter design and intent. Some power supplies will attempt to keep voltage constant and allow more current even beyond their own spec and die. This coupled with intentionally underrating for a safety buffer (a 3A power supply may actually do 3.5A fine), it is best to assume the worst case. Thus your power supply and cables should be oversized to some extent for your use, so you're not constantly against their max rating.
  
  – Jarrod Christman
  2 days ago
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Are you aware of how USB-C devices "negotate" with USB-C cables to determine how much current they can draw? Your answer seems to completely ignore this issue, which is at the core of the OP's problem. I believe 56k resistor in the cable communicates to the attached USB device how much current it can safely draw; barring something I don't know (which is plenty) that cable might convince the USB device into thinking "ok, drawing 3A is ok from this", frying the charger. This isn't a "dumb cable"; for a dumb cable your answer seems correct (more A=more safe)
  
  – Yakk
  2 days ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  (note: I am not an expert at this. Possibly there is a way that the other end of the USB connection (the charger) communicates to the USB-C device the current it supports, and/or handles being asked for more power than it is rated for gracefully)
  
  – Yakk
  2 days ago
  

  
  
  
  

 | 
show 9 more comments

11

No, only the device should not draw more current than the adapter and the cable can handle.

So the device defines how much current will flow through the circuit (which consists of your adapter and cable).

If the device draws more current, the adapter or the cable may overheat (with a fire hazard).

Btw, it's better to be safe and not use exactly a 2A but at least more, so you are safe with a cable of 3A.

Remarks from others
Also, this yields for most (cheap) adapters. See the comment of Jarrod Christman for an exception.

For USB, there is a negotiation protocol. See the comment of Yakk below.

share|improve this answer

answered 2 days ago

Michel KeijzersMichel Keijzers

21116

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I don't think this is right. If the device tries to draw more than 2A, the adaptor should drop the voltage to keep the current down (until it reaches the point where the voltage is so low that the adaptor cuts out altogether).
  
  – Martin Bonner
  2 days ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @MartinBonner I don't have the theoretical knowledge, but afaik an adapter just 'gives' the current the load needs, and if the load requests more, the adapter delivers more, even if it cannot handle it. Of course, it might be possible there is some kind of safety circuit built in the adapter, but this is not common (for cheap adapters at least).
  
  – Michel Keijzers
  2 days ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @MartinBonner, that depends entirely on the adapter design and intent. Some power supplies will attempt to keep voltage constant and allow more current even beyond their own spec and die. This coupled with intentionally underrating for a safety buffer (a 3A power supply may actually do 3.5A fine), it is best to assume the worst case. Thus your power supply and cables should be oversized to some extent for your use, so you're not constantly against their max rating.
  
  – Jarrod Christman
  2 days ago
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Are you aware of how USB-C devices "negotate" with USB-C cables to determine how much current they can draw? Your answer seems to completely ignore this issue, which is at the core of the OP's problem. I believe 56k resistor in the cable communicates to the attached USB device how much current it can safely draw; barring something I don't know (which is plenty) that cable might convince the USB device into thinking "ok, drawing 3A is ok from this", frying the charger. This isn't a "dumb cable"; for a dumb cable your answer seems correct (more A=more safe)
  
  – Yakk
  2 days ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  (note: I am not an expert at this. Possibly there is a way that the other end of the USB connection (the charger) communicates to the USB-C device the current it supports, and/or handles being asked for more power than it is rated for gracefully)
  
  – Yakk
  2 days ago
  

  
  
  
  

 | 
show 9 more comments

No, only the device should not draw more current than the adapter and the cable can handle.

So the device defines how much current will flow through the circuit (which consists of your adapter and cable).

If the device draws more current, the adapter or the cable may overheat (with a fire hazard).

Btw, it's better to be safe and not use exactly a 2A but at least more, so you are safe with a cable of 3A.

Remarks from others
Also, this yields for most (cheap) adapters. See the comment of Jarrod Christman for an exception.

For USB, there is a negotiation protocol. See the comment of Yakk below.

share|improve this answer

answered 2 days ago

Michel KeijzersMichel Keijzers

21116

share|improve this answer

answered 2 days ago

Michel KeijzersMichel Keijzers

21116

answered 2 days ago

Michel KeijzersMichel Keijzers

21116

answered 2 days ago

Michel KeijzersMichel Keijzers

21116