Ultrasonic Washing Ceramic Power Resistors - Yes or No? - Page 1
Forum section: electronics / beginners

author: KirstyA
author_rank: Contributor
timestamp: February 20, 2023, 04:51:02 pm
content: Hi everybody,I aquired a large quantity of new and used ceramic power resistors from eBay but a lot of them are rather grubby.So I wanted to clean them up and I thought let's put them in my ultrasonic cleaner with some cleaning solution and clean them up.Then I read that some ceramics are quite porous and wondered if the ceramic cement these power resistors are made of is porous or not?Yes I could put them in a bowl of isopropyly alcohol and give them a good scrub but considering how many there are it would use up a lot of IPA and I think that's too wasteful.Are they safe to put in my ultrasonic bath with some general cleaning solution or not?I could always bake them dry in the oven at say 100 deg centigrade for a couple of hours afterwards to dry them out.What do you think??

author: MarkS
author_rank: Unknown
timestamp: February 20, 2023, 05:04:07 pm
content: It entirely depends on the porosity of the ceramic. My best guess would be to use IPA, but I don't know if it's advisable.

author: Gyro
author_rank: Super Contributor
timestamp: February 20, 2023, 05:10:09 pm
content: Please don't double post, especially when you leave 20 minutes between them. Be patient, otherwise you will be unpopular with members and mods alike.https://www.eevblog.com/forum/beginners/ultrasonic-washing-ceramic-power-resistors-yes-or-no/

author: bdunham7
author_rank: Super Contributor
timestamp: February 20, 2023, 05:23:41 pm
content: Ultrasonic cleaning is appropriate even for porous ceramics, so I'd go with that. You can bake them a lot hotter than 100C and if you have any especially high values where you might be concerned about leakage, you can always dip them in IPA one at a time after the US cleaning and before the bake.

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: February 20, 2023, 05:39:07 pm
content: Hi KirstyA,At first sight, I would be reluctant to wash those resistors in an ultrasonic cleaner.On these models, the resistive wire is sometimes wound on a ceramic bar. The latter is held inside the main body with a very brittle and porous cement.Actually washing the parts is only half of the job : don't forget to dry them.In the case of porous ceramic, every residual humidity must be removed : when the power resistor gets hot, the produced steam would break the part.Perhaps, give it a try with a small batch and report the results.I would avoid water, and only use alcohol. This means you will need to work outside because of the vapors that could easily ignite.Drying can be done in the kitchen oven at @50°C, for 3 hours.Then test the resistors at nominal power.

author: KirstyA
author_rank: Contributor
timestamp: February 20, 2023, 05:50:47 pm
content: Hello Gyro,I only posted once but it said 'database error' and to try again.So I did, and then there were 2 posts the same.I tried to remove one of the posts and it said I couldn't remove my own post, so there was nothing I could do.

author: Simon
author_rank: Unknown
timestamp: February 20, 2023, 05:51:34 pm
content: Those are pretty clean to be honest. These resistors were never made to look pretty. The "dirtiest" ones I would say are older and were never white to start with. These days they get made nice and white so I'd not worry too much about calling them dirty.

author: Simon
author_rank: Unknown
timestamp: February 20, 2023, 05:51:55 pm
content: Quote from: KirstyA on February 20, 2023, 05:50:47 pmAll taken care of. Don't worry about it.

author: KirstyA
author_rank: Contributor
timestamp: February 20, 2023, 05:57:47 pm
content: They are all low values, so no worry about leakage.I am quite happy to leave them in the oven for hours to dry out afterwards.They are not immediately going into use, I bought them for stock, so what with the oven baking and then leaving them naturally to further dry out over most likely several months before I have a need to use one, would that not be OK?

author: Gyro
author_rank: Super Contributor
timestamp: February 20, 2023, 06:01:27 pm
content: Ah, the dreaded database error, sorry.You tend to find that when you have a loose bag of ceramic resistors like that, they are abrasive enough to rub some of the tinning from adjacent leads. You're unlikely to shift that with either IPA or ultrasonic cleaning. You might be best just living with it.

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: February 20, 2023, 06:04:37 pm
content: Quote from: KirstyA on February 20, 2023, 05:57:47 pmNot reasy to answer, It depends on the ceramic features.If you want to let them dry them naturally, you'll need to wait for months before performing a test at nominal power and verify if they are in good health.

author: RCL
author_rank: Newbie
timestamp: February 20, 2023, 06:13:45 pm
content: A cautionary tale..............I put my eye-glasses in my wife's ultrasonic jewelry cleaner. It did a great job. Later, I noticed it had stripped the UV coating from the lenses.

author: bdunham7
author_rank: Super Contributor
timestamp: February 20, 2023, 06:18:02 pm
content: Quote from: KirstyA on February 20, 2023, 05:57:47 pmI would be mostly worried about corrosion, so you'd want them dry before storing IMHO. 3 hours at 200C would probably do the job. I'm not so worried about the other possibilities of destruction as these types of resistors are notoriously tough and I haven't seen them fail catastrophically even in some pretty dire environmental conditions. I'm pretty sure I could toss them in my swimming pool for a week and then fish them out and give them 100% rated power, all without any steam explosions. Of course I'm just some guy on the internet and I don't have any degrees in resistorology, so take my advice accordingly.

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: February 20, 2023, 06:22:17 pm
content: Quote from: RCL on February 20, 2023, 06:13:45 pmFrom UV to US...Did you use any particular cleaning solution ? (other than water and liquid soap)

author: Gyro
author_rank: Super Contributor
timestamp: February 20, 2023, 06:27:55 pm
content: Just another thought, what about one of those dry 'magic eraser' type pads? They are pretty good at removing surface contamination from matt painted walls etc. Obviously you would need to make sure that you don't repeatedly flex the leads in the process.P.S. I would get them away from that newsprint.

author: KirstyA
author_rank: Contributor
timestamp: February 20, 2023, 06:29:04 pm
content: 'A Degree is Resistorology' sounds interesting bdunham7, lolI recently did an intense 'home study' course in 'Electrolytic Capacitor ESRology'. Conclusion, if you have cheap crappy consumer electronics then ESR is likely a thing to take note of and test for. But if you have decent high quality branded old test equipment like HP, Keithley, Fluke, Tetronix etc. the reason I was looking, then forget ESR, just test for capacitance value and leakage. Reform if necessary. So far I haven't found a bad cap in any of my old aquired test equipment, except the tantalums.

author: KirstyA
author_rank: Contributor
timestamp: February 20, 2023, 06:37:23 pm
content: OK then I think what I am going to do is wash a few of the bad ones down in IPA, and a few more in the ultrasonic bath with a water based cleaning solution.If they don't come up any cleaner then i'll have to accept them as permanently dirty.I do have some new original ones myself which are approximately 40 years old still unused in my parts drawers and they aren't as dirty as these.Yes, they are not white white, they are a cream colour, but they don't look dirty like these.

author: TimFox
author_rank: Super Contributor
timestamp: February 20, 2023, 07:16:36 pm
content: "Rheology" is a real field of study that does not involve "rheostats".

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: February 20, 2023, 07:18:38 pm
content: A friend of mine who was a very good teck, used to wash TV chassis with electronics intact. He did this in a quarter car wash.Dried them in the sun.No failures due to this Process.Another highly regarded teck used to put boards in his dishwasher, good results, until his wife put a stop to it.

author: james_s
author_rank: Super Contributor
timestamp: February 20, 2023, 07:23:59 pm
content: When I was repairing a lot of CRT monitors I would often run the chassis through the dishwasher with only a low dose of detergent, it did a great job and I never had it cause a problem except sometimes stickers or printing would wash off something. Toss a few in for a test run and see how it does, but I would be very surprised if it causes any problems.

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: February 20, 2023, 08:53:13 pm
content: Quote from: Wallace Gasiewicz on February 20, 2023, 07:18:38 pmWell, if it is forbidden to use the dishwasher to clean electronic boards, then it is almost useless to have such a device at home.

author: SeanB
author_rank: Super Contributor
timestamp: February 20, 2023, 09:04:57 pm
content: Simplest is to take a heavy plastic bag, drop them in it, and fill with IPA, then put that in the IPA and use the ultrasonic. Will likely strip off the lettering on them though. Good enough just to leave them as is, or a scrub with a toothbrush in a bowl with water will get a lot of the crud off. Then bake at 150C for an hour to dry off.

author: amyk
author_rank: Super Contributor
timestamp: February 20, 2023, 10:51:14 pm
content: Those don't look dirty to me at all.

author: EPAIII
author_rank: Super Contributor
timestamp: February 22, 2023, 08:40:51 am
content: Back in the day we had an ultrasonic cleaner with Freon TF in it. It did a great job of cleaning almost anything electronic. I remember a photo of a oscilloscope, powered on and running, with a trace displayed, while completely submerged in that solvent. It also evaporated very rapidly so no heat and very little time for it to dry.But that was then and this is now. I don't think you can even get Freon TF today without Presidential permission. And perhaps not even then.I am probably dating myself.If you use IPA in an ultrasonic cleaner I would suggest that the alcohol be placed in a plastic, zip lock bag with the parts and ordinary water be used to fill the rest of the cleaner's tank. You don't want to fill the room with flammable fumes. I would also suggest the 91% IPA to keep the water content down. Most IPA sold is only 70% or even as little as 50%.

author: Haenk
author_rank: Super Contributor
timestamp: February 23, 2023, 11:43:56 am
content: I agree this is mostly from the tinning of the leads, IPA probably won't help.Maybe try some wiping with acid first.

author: donlisms
author_rank: Frequent Contributor
timestamp: February 24, 2023, 03:42:46 am
content: In earlier days, Tektronix would routinely wash entire oscilloscopes in warm water and detergent. The procedural details are documented with pictures in official Tek documents.Yes, really. :-)(Sorry I don't have any links; there is at least some discussion at groups.io.)

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: February 24, 2023, 05:48:57 am
content: Hi donlisms,Quote from: donlisms on February 24, 2023, 03:42:46 amYou are right.Setup, required tools, chemicals and procedure is describedhere.Nice TE wash station, probably including a lazy-susan to ease the handling of the displayed boat anchor.Don't know if the two lights at the top are really waterproof...

author: vk6zgo
author_rank: Super Contributor
timestamp: February 24, 2023, 07:34:20 am
content: Quote from: Simon on February 20, 2023, 05:51:34 pmYeah, the old ones looked like cement.If you wash them by complete immersion, either in a ultrasonic cleaner or more traditional ways, it is a good idea to cook them in a normal domestic oven, which will dry them out.Many years ago, we washed a unglazed porcelain insulator from a TV transmitter, then soaked it in alcohol to hasten its drying.Unfortunately, even though it looked dry, when we turned the Tx on, it went "bang" & shut down, so in the end, we had to cook the insulator in the lunchroom oven.We learned just how porous unglazed porcelain was, but I doubt that the ceramic coating on resistors would retain as much fluid.

author: vk6zgo
author_rank: Super Contributor
timestamp: February 24, 2023, 07:37:07 am
content: Quote from: KirstyA on February 20, 2023, 05:57:47 pmThe oven baking should be quite sufficient.

author: EPAIII
author_rank: Super Contributor
timestamp: February 24, 2023, 09:05:01 am
content: If it it corrosion on the leads that you are worried about, you are probably going to need some form or abrasive. I always keep small pieces of extra fine (200, 320, 400 grit) sandpaper at my electronic benches. With the sandpaper folded in half it only takes a few seconds to have old leads cleaned down to bare metal. Then flux and tinning and you are set to go.And there is no sense in doing this before you are ready to use them. If you are like me, you probably will never use 75% of your collection of e. parts.

author: Gyro
author_rank: Super Contributor
timestamp: February 24, 2023, 12:39:06 pm
content: I would still just leave them alone. They are reasonably low value so any surface leakage isn't an issue, and they are designed to run hot. Just take them out of the newspaper, store them where they won't rub together to much and stop worrying about it.

author: TimFox
author_rank: Super Contributor
timestamp: February 24, 2023, 02:56:30 pm
content: Some of the "dirt" on the rough surfaces may be just newspaper ink that rubbed off.

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 24, 2023, 05:14:12 pm
content: Quote from: Wallace Gasiewicz on February 20, 2023, 07:18:38 pmI sometimes put PCB's through the dishwasher. The latest one of note was PCB's from a nicotine flavoured TDS 700 series Tek scope.Came out sparkly clean and after a good dry, and a blow with some compressed air and hairdryer to get water out from under the chips, it works fine.

author: james_s
author_rank: Super Contributor
timestamp: February 24, 2023, 07:58:23 pm
content: Just keep in mind it can take surprisingly long to get all the water out from under large ICs. Also if you are in an area that has minerals in the water it's a good idea to give it a good rinse in alcohol or distilled water prior to drying.

author: DavidKo
author_rank: Frequent Contributor
timestamp: February 27, 2023, 02:10:09 pm
content: Quote from: EPAIII on February 24, 2023, 09:05:01 amI use steel wool for such a purposes. In case of sandpaper, than 200 is still quite rough. With sandpaper I usually start with 600-800 grit and go down if the rust is deep.

author: EPAIII
author_rank: Super Contributor
timestamp: February 28, 2023, 05:57:05 am
content: No sense in arguing over the grit size. My point is abrasive is the best way to remove corrosion from the leads. 200, 400, 800, I even have 2000 grit. And perhaps a scrap of 10,000 grit. Start where you will.As for steel wool, it can leave whiskers behind. Steel whiskers which will be conductors. Sand paper leaves dust which is an insulator. I will stick with the sandpaper.Quote from: DavidKo on February 27, 2023, 02:10:09 pm

author: EPAIII
author_rank: Super Contributor
timestamp: February 28, 2023, 06:26:00 am
content: A lot is being said about washing PCBs and even whole electronic devices in water and aqueous solutions. I have done this and probably worse.BUT care must be used in the decision to do this. Boards or devices with electro-mechanical parts can be very difficult to dry. Relays, switches, variable resistors and capacitors can admit water to their interior where it can remain for days or longer. And membrane switches are almost impossible to dry out except by complete disassembly if that is even possible.A high purity alcohol is your friend here. 91% or better.Even the use of solvents intended for electrical or electronic use can carry foreign substances into the interior of these parts where those substances remain after the solvent itself has long since evaporated. I learned the hard way that flux remover would carry the flux into switches and relays where it coated the contacts turning them into insulators. It took many additional washings with the solvent to remove that flux from those components. The lesson is, if you use flux remover, be very careful where it flows.One more point: ICs and other components in plastic packages are NOT hermetically sealed. Gasses and liquids can get inside and possibly cause damage. And the damage may not be immediately apparent. This is one reason why there are ceramic packages.

author: DavidKo
author_rank: Frequent Contributor
timestamp: February 28, 2023, 09:05:17 am
content: You can get similar result when you use solvent to remove the "fat" on the PCB. Fat will be only dissolved in the solvent and after evaporating it create thin fat film everywhere.Our approach (for cleaning and degreasing) in ultrasonic cleaner was:- clean with detergent (industrial - do not have "special" ingrediencies) which "breaks down" fat to be washable- clean with distilled water- clean with pure alcohol (99.9%) - probably can be replaced with IPAAfter cleaning the last step was flushing the surface with pure alcohol.We have used it to prepare substrate for vapor deposition.