Switching Power Supply not deliwering full power like it used to. - Page 1
Forum section: electronics / repair

author: Pexy13
author_rank: Regular Contributor
timestamp: October 25, 2022, 11:55:42 am
content: Greetings!I have a lava lamp that worked fine but I noticet recently that when I power it on it's not as bright and warm enough to get the wax floating.I measured the output of a 12V 2.5A PSU and it's 12.1V when no load is connected but when I load the output whit the 12V 20W bulb the output drops to 1.8V and is sloooowly climbing up at around 0.01V per second. I don't know if that's because of the bulb heating up or something regarding the power supply.I tried powering the lamp with a different power supply (12V 1A) for a few seconds and it's a lot brighter then with the old psu.Does anyone have any ideas what might be wrong? I used the lamp whit this power supply for around 3 years and it has a good amount of hours on it. Is there something I can replace or ddo to fix this problem? Any advice is welcome.Cheers!

author: wasedadoc
author_rank: Super Contributor
timestamp: October 25, 2022, 12:05:07 pm
content: Probably the most common problem with switch mode power supplies is deterioration of the electrolytic capacitor(s) on the output of the low voltage rectifier.

author: wraper
author_rank: Unknown
timestamp: October 25, 2022, 12:08:14 pm
content: I suspect bad electrolytic capacitor with such failure. They are not nearly as often faulty as some people tend to blame them for everything, but this is one of those cases where electrolytic cap is the primary suspect.

author: Pexy13
author_rank: Regular Contributor
timestamp: October 25, 2022, 12:11:18 pm
content: Is it worth opening the PSU and replacing the capacitors?

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 25, 2022, 01:24:42 pm
content: If it's just a 12V halogen lamp, replace the PSU with an "electronic halogen transformer", which doesn't filter the output so less to go wrong.

author: wasedadoc
author_rank: Super Contributor
timestamp: October 25, 2022, 01:25:47 pm
content: Quote from: Pexy13 on October 25, 2022, 12:11:18 pmDoes it open up readily or is it a glued /welded case? Problem with the latter type is getting it apart such that it can be closed again and remain safe.

author: Pexy13
author_rank: Regular Contributor
timestamp: October 25, 2022, 01:38:37 pm
content: Quote from: NiHaoMike on October 25, 2022, 01:24:42 pmSo I could just power it with a 12V hahlogen transformer connected directly?

author: Pexy13
author_rank: Regular Contributor
timestamp: October 25, 2022, 01:40:29 pm
content: Quote from: wasedadoc on October 25, 2022, 01:25:47 pmIt is glued shut but i oppened psu like this before with a hacksaw and later glued em back up and wraped them with electric tape so I think they are safe again. And the only one using the lamp is me so there's no danger for anyone else getting shocked.

author: tunk
author_rank: Super Contributor
timestamp: October 25, 2022, 02:19:04 pm
content: Quote from: Pexy13 on October 25, 2022, 01:40:29 pmYou could also try with a vice or polygrip pliers and seeif you can crack the glue/welds. If you open it, post photosof both sides of the PCB.

author: Pexy13
author_rank: Regular Contributor
timestamp: October 25, 2022, 02:32:22 pm
content: You could also try with a vice or polygrip pliers and seeif you can crack the glue/welds. If you open it, post photosof both sides of the PCB.I also used a bench vice to crack a few of them open. I'll post photos over the weekend when I get to the home shop. Cheers!

author: wraper
author_rank: Unknown
timestamp: October 25, 2022, 05:28:49 pm
content: Those are too destructive ways to crack it apart. There are different ways to open nicely. You can put in it a freezer, then take out and quickly (like within 30 seconds) hit with a rubber mallet all around the weld. Freezing temperatures make the weld fragile. Be sure to put it on some hard surface, holding in hand while doing so will likely result in a broken inductor or transformer. Also there is a chemical way. Special solvent mixtures do exist but gasoline, nitro solvents and acetone work too AFAIK, not as well though. And may leave marks on plastic. Usually solvent is applied across the weld, left for around 5-10 minutes and cracked apart with a little bit of force.

author: Pexy13
author_rank: Regular Contributor
timestamp: October 27, 2022, 09:26:20 pm
content: if you can crack the glue/welds. If you open it, post photosof both sides of the PCB.I opened it. Here are a few photos. I can see the output caps bulged at the top so they are probably gone. If I change them it should work like it used to?

author: wasedadoc
author_rank: Super Contributor
timestamp: October 27, 2022, 10:58:32 pm
content: Use good quality, low ESR, 105 degrees caps. I prefer Panasonic ones.

author: wraper
author_rank: Unknown
timestamp: October 28, 2022, 02:22:19 pm
content: For better reliability you can add a 4th cap which is not assembled.