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
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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
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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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jonescg
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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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