What's with loads that kills the capacitor in AC adapters?  - Page 1
Forum section: electronics / projects

author: turbo!
author_rank: Regular Contributor
timestamp: August 12, 2014, 06:31:23 am
content: It's well known that the adapter that comes with 2wire Gateway fails, but maybe it is the gateway killing it. The original wall adapter that came with the modem failed, which was 5v 2A SMPS.I chopped the wire off and replaced it with a 2.5A 5v adapter from another router. Just now, I noticed my internet was out and it smelled a bit funny. I checked the router and lights are flashing funny, then I noticed the adapter had bulged as the capacitor got hot, expanded and softened the case.One of the capacitors in the D-link adapter I used was bulging on top and melting the case. The other capacitor that I can see inside the adapter opened and vented on the top and these are 16v 105C capacitors. Is it the 2wire that has some way of overloading the capacitors and destroying them?

author: mariush
author_rank: Super Contributor
timestamp: August 12, 2014, 07:05:53 am
content: No, it's just plain heat from the losses in the power supply killing the capacitors.Such power supplies are about 65-75% efficient. 5v @ 2A = ~ 10w. You have about 2-4 watts wasted as heat inside a closed case, the insides are probably at 60-80c all the time.If you don't keep the power adapter somewhere with water or humidity, just drill a couple of holes into the plastic for ventilation.

author: tautech
author_rank: Super Contributor
timestamp: August 12, 2014, 07:30:47 am
content: QuoteI think your assumption is correct.Failing caps overloading the SMPS.Likely all will be OK with new caps.

author: Rerouter
author_rank: Super Contributor
timestamp: August 12, 2014, 07:38:01 am
content: Equally a large portion of plug-packs use very cheap branded capacitors as they are tacked on towards the end of a project with most devices (find one with the right plug and voltage, at the lowest reasonable price)If your cracking it open i would suggest replacing the 4 diodes that make the diode bridge as well, i have encountered an increasing number of modem / telecoms plug-packs where the bridge rectifier fails shorted phase to neutral,

author: turbo!
author_rank: Regular Contributor
timestamp: August 12, 2014, 10:12:45 am
content: Quote from: Rerouter on August 12, 2014, 07:38:01 amIt's the low voltage side capacitor that blew up. Both the one before and after the EMI choke. A lot of people are having the same exact adapter failures on their 2wire routers. Maybe its the way they run the router that pulls highly repetitive and impulsive demand that wreaks havoc on the power supply.

author: amyk
author_rank: Super Contributor
timestamp: August 12, 2014, 01:37:33 pm
content: Quote from: turbo! on August 12, 2014, 10:12:45 amIf you have a current probe you might be able to measure the peaks. a load that draws current in pulses will definitely stress the output capacitors more if the current demand is high, since the ripple current will go through the cap and its ESR causes heating.Caps should not be getting hot enough to melt plastic. Replace them with low-ESR units, see how much they heat up, adding more in parallel could help.

author: SirNick
author_rank: Frequent Contributor
timestamp: August 12, 2014, 07:54:40 pm
content: You could try a bigger power adapter. A 5A supply can take a bit more abuse from a <2A nominal device, for e.g.Although, even 2A is quite a bit from a SOHO router. Does it get hot?