Salvaging components from old UPS - Page 1
Forum section: electronics / beginners

author: Antonio90
author_rank: Frequent Contributor
timestamp: June 19, 2024, 09:21:29 pm
content: Hello,I have an old UPS mainboard. There are relays, big inductors, power resistors, MOSFETs, a transformer, etc. Which I would like to salvage.The ground planes are rather big, and covered in additional solder. The transistors I can desolder with a big soldering tip and/or used copper braid to join the legs. However, with the big inductors and components in the middle of the ground plane I'm at a loss. I don't have a desoldering gun.Any ideas?Thanks,Antonio.

author: Roehrenonkel
author_rank: Frequent Contributor
timestamp: June 19, 2024, 09:53:19 pm
content: Ola Antonio,if you don't want to use a blowtorch or stove-plate,try sawing/cutting the pcb apart.Good luck

author: Antonio90
author_rank: Frequent Contributor
timestamp: June 19, 2024, 10:05:20 pm
content: Thanks!I might try a heat gun or a blowtorch, although I'm a bit afraid of the electrolytics boiling off.Cutting the board might be an option too, or drilling with a small crown bit around the toughest ones.Will have a try tomorrow. Thanks again.

author: BrianHG
author_rank: Super Contributor
timestamp: June 19, 2024, 10:15:09 pm
content: A paint stripper heat gun to the back of the PCB will eject all the heavy components. You will need some to secure the PCB upside-down and pliers to pull the smaller components.First use the paint-stripper gun at a distance to uniformly heat up the PCB, then once everything is hot just below melting the solder, go close-up with the heat gun to the components you want to release.Depending on component type and hole size, many items will just fall off the PCB.

author: golden_labels
author_rank: Super Contributor
timestamp: June 19, 2024, 10:31:00 pm
content: In general it’s best to keep a few such PCBs around and use as donors as needed. Not remove parts all at once. This way you know, how the part was used. If you don’t have datasheets — in particular transformers and inductors — PCB tells a lot about their parameters.The big transformer is generally not worth the effort. Not useful for replacement, not general-purpose, very hard to remove. You’ll spend half an hour working on one and then it’ll collect dust for years. While breaking up a PCB or heating it in a flame works, it’s a health hazard. Respect your health: you can’t buy a new one.Resistors, inductors, relays, and mosfets can be easily removed with a soldering iron. Just use a fat soldering tip. Transistors, inductors, and relays may need a wick. Or, if you prefer not to use it, wiggling. This works particularly well for inductors, which take mechanical and thermal stress well. Be particularly patient with relays: don’t pull, don’t overheat.The small transformer should let go by just adding solder to heat up all pins on one end at the same time. Then wiggle it out.Items you missed: fuses and fuse holders. Fuses are removable by hand, clearly marked. The holders are dirt cheap, but also trivial to remove. The screw terminals: nice for good wire attachment, but often the store doesn’t have the one you want or you must spend an hour searching for the exact shape.Avoid: small or low-voltage transistors, diodes (unless they’re big or in transistor package).Sometimes a radiator, to which a cheap transistor is attached, is worth more than the transistor. Don’t be afraid to wiggle them out at the cost of destroying the transistor. Can’t spot any on this board, but worth knowing.Salvage your time. Unfortunately this is probably something one just must learn by oneself as the life progresses.

author: Xena E
author_rank: Frequent Contributor
timestamp: June 19, 2024, 10:39:03 pm
content: Wear a respirator.Work outside.Fasten board securely.Use a heat gun as suggested to heat the solder to meling point.Used compressed air and dusting gun to blow the solder away from the component pads!

author: MathWizard
author_rank: Super Contributor
timestamp: June 20, 2024, 02:38:17 pm
content: I've desoldered a lot worse than that with a "40W" ebay soldering iron. That was on a computer PSU with a bunch of stuff on big heatsinks. One in particular had high temp solder too. I diluted down the solder a few times with 30/70 solder (or whatever the common leaded stuff is), and wicked away some, and used a soldering pump.I might have used Bismuth alloyed solder, and overall I wouldn't trust most those parts anymore for anything serious, but with it all back together it still works.

author: Antonio90
author_rank: Frequent Contributor
timestamp: June 20, 2024, 04:21:46 pm
content: Thank you for all the advice.I'll try with a heat gun outside. I need to buy a respirator first, though.As per the mere use of soldering iron and solder wick, that's what I'm using for MOSFETs IGBTs and power resistors, however, tips and wick aren't cheap, and I'm not sure many components are worth that much. Also, some of the planes are literally bathed in solder, so the amount of braid needed would be way too much.Quote from: golden_labels on June 19, 2024, 10:31:00 pmThere are a few diodes in TO package or similar, behind the transformer, and they are attached to small, crude heatsinks (just a chunk of metal). I might just snap those off, the leads are full lenght.

author: David Hess
author_rank: Super Contributor
timestamp: June 20, 2024, 04:45:41 pm
content: When I do not want to apply a torch, I use a 100 watt Weller temperature controlled iron:https://www.amazon.com/Weller-W100PG-Farenheit-Soldering-Degree/dp/B002I7X7ZS/

author: Gyro
author_rank: Super Contributor
timestamp: June 20, 2024, 05:37:06 pm
content: I recommend keeping old PCBs in a box and salvaging parts when, and if, you need them. Not only is it easier to remember what parts as you have. You know where to find them too! Otherwise half the stuff you spend your precious time removing, you'll never get around to using.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: June 20, 2024, 05:38:48 pm
content: Two comments.1. Protecting your health is important. But it is easy to over or under do it since no one really knows how much is enough. I have been using heat guns and torches with modest precautions for this type of thing for over 50 years with no obvious problems, but the same thing applies to cigarette smokers. Some folks develop cancer just from being in the same house as a smoker, and others are heavy smokers for seventy or more years with no obvious damage.2. A respirator will protect you from particulates and possibly some types of fumes, but only provides a false sense of security against other things that might evolve from a heated PCB.I would recommend picking a somewhat breezy day and doing your work either outdoors or in a space that the breeze blows through, and work with your back to to wind. Some thought about how wind flows around an obstacle plus observation of any smoke that is generated will let you fine tune your position to best avoid exposure.Also be mindful of those who might be downwind. Because of the small quantities generated by hobby activities I wouldn't worry too much about raising overall pollutant levels in the area, but if your effluent plume is going to where someone else is within a few handfuls of meters the neighborly thing to do would be to do something to mitigate the problem. Pick a time when they aren't home, or when the wind is different, or move your work site so the plume misses them.

author: Xena E
author_rank: Frequent Contributor
timestamp: June 20, 2024, 11:53:28 pm
content: Yeah, look after your health. I feel that soldering is a fairly low risk activity, probably the worst problem is the fumes from the flux.However I will point out that using my method in reply 5 does turn the molten solder in dust... so just beware...X