Do AC adapters have fuses inside?

Comments

• Bruce Bates Posts: 3,045

  2007-10-16 15:09 edited 2007-10-16 15:09

  RDL2004 -
  
  Generally speaking no, and those that do often have the fuses inaccessible, so they can't be changed if they blow. Fusing on the low voltage side of the adapter, just after it plugs into the "device", should provide all the overcurrent protection you might need, and it also opens up the possibility of using either fuses or circuit breakers of an appropriate size.
  
  Regards,
  
  Bruce Bates
  
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• RDL2004 Posts: 2,554

  2007-10-16 15:24 edited 2007-10-16 15:24

  That's pretty much what I've found out after a lot of Googling and Wiki reading. Everthing I've ever built, I fused on the mains side. Many of the devices I've seen that us AC adapters have no fuses on the low voltage or DC side. I was going to use an AC adapter on my current project and was trying to figure out how to provide fuse protection or if I even need to.
  
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  - Rick
• Mike Green Posts: 23,101

  2007-10-16 16:06 edited 2007-10-16 16:06

  In the case of a regulated AC adapter, the regulator itself normally will limit the output current, either due to over-current or over-temperature limits. The only reason you'd need a fuse is in case of a regulator failure, not impossible, but very unlikely. As with all protection schemes, at some point, the likelihood of a particular failure is so small that the cost or difficulty of further protection or the cost of the failure itself is modest, that it's not worth adding the protection.
• LoopyByteloose Posts: 12,537

  2007-10-17 15:01 edited 2007-10-17 15:01

  Mike Green points out the reality. For low voltage and under an amp, there isn't much reason for fuses. All the wall wart powered commercial devices no longer rely on fuses - not my cell phone, not my PDA, etc.
  
  Nonetheless, for bench work, I use an 8VDC, 9AH battery. Since a short at 9 amps can do serious damage to whatever I'm building or playing with, I have a 1 amp fuse in line. I have blown the fuse several times, but avoided any harm to my BasicStamps or other chips.
  
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