Ultrasonic cleaning bath project...

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jonescg
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Ultrasonic cleaning bath project...

Post by jonescg »

For lack of a better place to put this thread, I figures starting here might be a good place.
Ultrasonic bath.jpg
Ultrasonic bath.jpg (189.73 KiB) Viewed 969 times
https://www.bjultrasonic.com/shop/power ... aner-130l/
A friend bought an ultrasonic cleaning bath from China for about $3000 landed. Not knowing what to expect, and given it looked identical to every other ultrasonic bath on offer, it seemed like a worthwhile gamble. It arrived in a wooden crate with not much regard for the product, but it should be fairly robust. We filled it up with water and plugged it in. Turned it on at the wall and it promptly tripped the RCBO.

OK, time to open it up. Oh. My. Dog.
Chinese quanlity.jpg
Chinese quanlity.jpg (178.56 KiB) Viewed 969 times
I think I counted two cable ties in the whole mess. Nothing tied down or secured, and the heatsink which was supposed to soak heat from the FETs was suspended by two badly aligned long M3 screws. A bit more troubleshooting revealed that the output of the board with the three red capacitors was shorted! Disconnecting it revealed the short was at the transformer, which seems to have been wired up incorrectly. We re-wired it, tried it again, and is seemed to be OK. Reassembled, turned it over, filled it up, turned it on... tripped the RCBO.

Clearly there was a short somewhere. We repeated the process until it turned on and the LED display on the front lit up saying mostly garbage... It's OK, as long as it works right? Pressed the On button... Bang. Tripped again.

SO I conclude this is a dangerous, badly made piece of junk which has no place near humans. However, there's no reason it can't be made to work with a new ultrasonic generator.

All the transducers are fixed to the stainless steel basin which is otherwise acceptably made. However the black wire on all paralleled transducers is common with the chassis. I wonder if this was the problem all along? I attached the 32 paralleled transducers to a 24 V, 50 Hz AC supply and the unit softly hummed. So they seem to be working.

Would it seem reasonable to attach the paralleled transducer to a new 40 kHz, isolated generator and amplifier? Could I just get one as a spare from a reputable supplier?

If it costs $500 to make it useful, a $3500 ultrasonic bath is a good deal. It's a waste of metal otherwise.
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lobster
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Re: Ultrasonic cleaning bath project...

Post by lobster »

Ultrasonic Generators & Spare part assemblies, all below $420

https://www.bjultrasonic.com/category/u ... price-desc

Cheers, Steve
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jonescg
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Re: Ultrasonic cleaning bath project...

Post by jonescg »

I think that's the same place the bath was bought from. And if the generator is the same, it too might blow up on switch-on.
I guess I'd like to know that the transducers aren't stuffed, and if not, then maybe a more reputable supplier can fit the bill?
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lobster
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Re: Ultrasonic cleaning bath project...

Post by lobster »

Chris,

as an ex Elec/Nav/Com/Radio Tech I would suggest some simple elimination checking could find an easy fix.

Can you measure the AC supply side to determine is it tripping on earth leakage or over current, the bath may have a marginal earth leakage or your RCBO breaker may be feeding another device on the same circuit also with a low leakage current?

Can you disconnect various components, transformers, contactors or modules to enable some parts to be powered up?

Multi-meter resistance to earth and diode checks and close visual inspection of components for burning or rupture can find a surprising number of electronic circuit faults without much effort.

Cheers, Steve
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Re: Ultrasonic cleaning bath project...

Post by jonescg »

Yeah I did a stack of that snooping, but the tell-tale was the spark once I pressed the On button. It seems strange to me that the two transformers are wired up in series, but maybe that's just part of the circuit. I'm wondering if the neutral-earth arrangements in Australia are not conducive to how this thing is wired up? The breaker is good - only one thing on it being a 15 A GPO. I haven't spotted any failed FETs, but it's more likely a chassis thing. I'm also surprised that the output of the generator which leads to the transducers is grounded to chassis - but of an oversight?
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Re: Ultrasonic cleaning bath project...

Post by jonescg »

Anyway, I abandoned the existing ultrasonic generator and ended up buying a new generator which could be wired up externally to the bath.

So far so good, although it seems a bit underpowered. Draws about 6 amps max from the mains, so barely 1100 W.
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Re: Ultrasonic cleaning bath project...

Post by jonescg »

This is probably the best place to put my backyard chemistry efforts...

So over the years, I have built lots of things with Li-ion battery cells, and while some are still in use, many have been put out to pasture. And by put out to pasture, I mean discharged and safely stored in a bin in my shed. Two Voltron battery packs and a few Prelude pouch cell modules are in there waiting to be recycled, while I have a wide selection of variously stuffed hobby LiPo pouch packs in need of recycling.

Knowing full well that recycling was an iffy proposition in Australia, I've been researching how to recycle them myself to ensure the materials are put to good use. I spent a lot of time pouring through the scientific literature and found a few different methods with various levels of success. They all seem to work on paper, but might require exotic materials or equipment I don't have at my disposal. So Chris Dodd of CD Dodd scrap metals and I decided to work on the first few steps in the recycling process.

I had painstakingly separated all of the Li-ion pouch cells by cutting them open and separating the cathode from the anode and separator, so most of my experimental work has been on dealing with the cathodes alone. But a more streamlined system would be a bit simpler - shred the whole lot and then start the separations. This will probably be the way to go, particularly since you can mix the shredded cells in water and the plastics float to the top while the metals and active material sinks:
float sep plastic.jpg
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The cathodes are mostly Li-CoO2, which is standard faire for RC LiPo. Most research indicates that the cathode is 30% aluminium and up to 50% cobalt, with the rest being carbon and binders.
J Electrochem Soc 164_1_A6184 2017.JPG
J Electrochem Soc 164_1_A6184 2017.JPG (66.35 KiB) Viewed 423 times
Several papers suggest dissolving the binders in N-methyl pyrrolidone, so I ordered a drum and started playing around. Well, this is a mighty solvent which will dissolve any polymer other than polyethylene, but it was no match for the PVDF binder and cathode materials. So I needed another approach. Ultrasonic removal made sense, so we ordered a 130 litre machine (as discussed above). I've probably overloaded it but I'm also trying to keep the liquid volumes to a minimum. So far plenty of black stuff has been removed, but there's heaps left on there, so the digestion is an ongoing process. I've also added some acid to the bath in an effort to get the cathode layers to let go of the active material, but I'm reluctant to get the pH too low as the aluminium will start to react and dissolve.
When the solution is completely dissolved in acid, you get a burgundy red solution which is everything metallic in acidic solution:
acid digested cathode solution.jpg
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Dissolved Al3+ is not too big a deal, but it's a pest to remove from the mixture. At very low pH, it exists as the free ion, but as the pH is increased towards neutral, you get some weird intermediate species including Al(OH)2- and eventually at pH 6.5, solid Al(OH)3 as a fluffy precipitate. This will settle, leaving (hopefully) everything else in solution. Cobalt ions (Co2+) will react with hydroxide ions to form a brilliant blue CoOH2 precipitate, but it soon turns to a brownish precipitate that looks like... well...
NaOH precipitate of acid digest.jpg
NaOH precipitate of acid digest.jpg (67.52 KiB) Viewed 423 times


The thing is, this happens at about the same pH as the formation of Aluminium salts. If it's too alkaline, all the cobalt crashes out and the aluminium goes back into solution. So there might be a two step process here to get rid of the cobalt first before removing the aluminium. I tried bicarbonate instead, which looks a little more promising. Al3+ will react with bicarbonate to form Al)OH)3 with the release of CO2. Trouble is, cobalt also forms an insoluble carbonate which is pink in colour, but I have a feeling most of that is still in solution since the pH is probably around neutral, and there's still a pink solution on top of the pinkish-grey precipitate:
Bicarbonate precipitate of acid digest.jpg
Bicarbonate precipitate of acid digest.jpg (43.92 KiB) Viewed 423 times
I need to get a pH meter as litmus paper is too flakey. Will update on the progress over the coming weeks.
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Re: Ultrasonic cleaning bath project...

Post by Rusdy »

I reckon CSIRO should hire you and fund the research! Surely this is a lucrative future market?
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Re: Ultrasonic cleaning bath project...

Post by 4Springs »

No labels on jars. :shock: Grits teeth...
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Re: Ultrasonic cleaning bath project...

Post by jonescg »

4Springs wrote: Mon, 23 Aug 2021, 19:15 No labels on jars. :shock: Grits teeth...
Hey, I just got myself a pH meter. No more taste testing for alkalinity!

Also: topical webinar:
https://youtu.be/oZ6oFQstRiY
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Re: Ultrasonic cleaning bath project...

Post by 4Springs »

jonescg wrote: Mon, 23 Aug 2021, 20:05 Hey, I just got myself a pH meter. No more taste testing for alkalinity!
Oh, I don't know why you'd bother. You'd naturally get an idea of pH when you mouth pipette wouldn't you?
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Re: Ultrasonic cleaning bath project...

Post by brunohill »

I used to work with an old Scottish bloke that could smell a sulphric acid solution and tell you the w/w % strength to 0.1 decimal place. We gave up doing titrations to prove him wrong because we couldn't.
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