Hey everyone,
Ayy.. so... I recently shipped about a dozen little widgets that are powered by a 16VAC adapter. The voltage inside gets rectified and turned into a +/-15VDC rail (LM317/LM337). I was measuring the current draw of the actual rails and never bothered to measure the current draw out of the 16VAC adapter until one of the first recipients of my widget said that their wallwart died after 20 minutes.
During testing, I left it on for weeks and my wallwart was fine so I never thought I was approaching the limit of the 16VAC adapter. Sure enough after testing it, I noticed I'm drawing 950mA from the wallwart that is rated for 1000mA.
Wallwart data sheet:
https://www.jameco.com/Jameco/Products/ProdDS/100108.pdfThe wallwart shows a thermal fuse, so I assumed if there ever was a problem that would trip and then return back to useable state after it cooled down, but this was not the case. I'm waiting for the blown wallwart to be returned so I can do an autopsy, but in the meantime I have a few questions:
How bad is it that I'm drawing 950mA from a 1000mA rated AC wallwart? I know I'm not leaving a smart margin of error, and the widget definitely needs to be redesigned to lower the current - but I'm curious about the fate of the dozen widgets already out in the field.. maybe the one that blew was just a runt / weakest link? Or maybe I should expect all 12 to eventually give up the ghost?
I know, I'm definitely stupid for not measuring this before shipping.