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Old 20th Feb 2021, 9:50 pm   #1
cathy_vintage
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Default Ultrasonic power supply for ultrasonic cleaner

I am fed up of replacing the bipolar output transistors on my 40 litre, circa 1990's, ultrasonic cleaner made by 'Ultrawave' in the UK. There are four transistors obviously sharing the output load but when these units were manufactured the transistors were matched in production. In fear of these going obsolete I bought 10 devices a few years back (not matched though). Today a pair of them 'popped' again. I now think the original culprits were the insulating little m3 plastic 'top-hat' bushes that eventually distorted with heat and thus allowed the mounting screws to become slack and the transistor experiencing thermal runaway as a consequence. My problem now is that I no longer have a matched set, so it is possible that the load is not being shared equally.

I have seen very high-quality ultrasonic high wattage power supplies (sometimes termed amplifiers) being sold off cheaply, which are the correct 40kHz frequency and I am thinking about driving the transducers in my cleaner with one of these. However, the manufacturers (such as Branson) typically make both ultrasonic cleaning tanks and also ultrasonic welding machines. Does anyone know if such supplies are application specific ? For instance I found one supply being sold as being suitable for a plastic welding machine but the label on the back warns you to 'make sure tank is filled before switching on ultrasonics', which would suggest it can be used with an ultrasonic cleaner.
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Old 21st Feb 2021, 2:34 am   #2
Maarten
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Default Re: Ultrasonic power supply for ultrasonic cleaner

Seems like an easy fix. Match some (other) transistors yourself (they would have some kind of balancing resistors to even out some of the difference even if they're matched anyway) and use better mounting materials. It will probably last forever without having to go through the trouble of modifying, testing, modifying some more, etc.
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Old 21st Feb 2021, 10:23 am   #3
cathy_vintage
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Default Re: Ultrasonic power supply for ultrasonic cleaner

Thanks for reply .. I did have a thread on this in 2016 the last time I had problems. I got around this by 'robbing' a factory matched set of transistors from a scrap unit PCB assembly.

https://www.vintage-radio.net/forum/...d.php?t=129893

The transistors are BUV48C and they do have ceramic body 1R wire-wound power resistors associated with the output transistors.

If I am honest the more detailed ..... and probably the correct way to go .... matching procedure, detailed in the replies was a bit daunting, even though I do have a digital storage scope and signal gen's etc. Plus I fear that my batch of new transistors is limited to only 10 and the factory would probably have 100's possibly 1000's to use .. so what's my chance of matching 4 out of ten. They cost £8 to £10 each, which makes it prohibitively expensive to buy a larger batch.

This cleaner is invaluable to me.

A word of caution on fixing later large ultrasonic baths units made by 'Ultrawave'. They only have one pair of output power devices (I think they were MOSFETS) BUT the control electronics is done using a PIC micro (there are actually two PIC's but one drives the LCD I think). On the one I looked at fixing, the output devices were dead short but also the +5v power supply had failed taking the control PIC device with it. Ultrawave will not sell you a pre-programmed PIC (not surprising really) So unless you return the unit to them to fix (really expensive and very bulky to ship), the cleaner is not repairable.
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Old 21st Feb 2021, 1:15 pm   #4
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Default Re: Ultrasonic power supply for ultrasonic cleaner

I once had that tab problem with 700W SMPSUs.
The manufacturer had not drilled the holes right in the heat sink and it used to damage the insulators. They were MOSFETs.
My employer at the time never had a drill press so I obtained FETs with factory insulated tabs and lower on resistance.
The massive heat sinks ran stone cold and there were no more blow-ups.
What transistors are in your unit?

They are bipolars and are not easy to get at that voltage now.
I am wondering if the drive circuit will modify to work with FETs?

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Old 21st Feb 2021, 5:14 pm   #5
cathy_vintage
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Default Re: Ultrasonic power supply for ultrasonic cleaner

The circuit used only has the four BUV48C active devices and diodes etc and no high frequency drive IC or similar, so it must use feedback tappings on a ferrite transformer to form the oscillator circuit. Therefore, I would find it difficult to replace the bipolar devices with MOSFETs.

I just checked at work and I have 3 original devices from Ultrawave marked '29' that are OK and two devices marked '27' that are also OK. Plus I have the ten new devices (all made by ST including the factory ones). I am wondering if the '27' and '29' markings from the Ultrawave factory are merely DC gain measurements as the number lies in the centre of the DC current gain range quoted by the transistor manufacturer.
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Old 21st Feb 2021, 6:17 pm   #6
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Default Re: Ultrasonic power supply for ultrasonic cleaner

Try doing a search for Induction Heating.

This is something I am playing with, only theoretically at the moment, But I want to generate 20-30kHz at up to 15kW, and solid state seems the way to go. The idea of a 20kW RF triode at 10kV is not something I want to use.

Try

https://www.rmcybernetics.com/scienc...duction-heater

But Sealy, I think, sells induction heaters for heating rusted nuts, but not cheap. Possibly throw the ultrasonic electronics away and use these. If you get up to 10MHz or so then can set the glue used in laminating wood, might be similar.
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Old 22nd Feb 2021, 1:01 am   #7
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Default Re: Ultrasonic power supply for ultrasonic cleaner

I don't know how the output stage is configured but given that these are switching transistors it may very well be a bridge. If that is the case then all the devices in the bridge should really be replaced as a set and the remaining "good" ones discarded - they will certainly have been stressed beyond their reliable limits during the failure.

Don't ask me how I know!
Been there, done it, got the T shirt

I'm wondering if there is an altogether more robust transistor you could use as a replacement?

Steve.
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Old 22nd Feb 2021, 1:01 pm   #8
cathy_vintage
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Default Re: Ultrasonic power supply for ultrasonic cleaner

The PCB design, in terms of thermal considerations, isn't good (see attached pics). Which is bad really, as they were on issue 5 by this time, several years down the line of production and the units were very expensive when new.

The PCB was originally mounted inside the cleaner itself and therefore subjected to any inevitable tank leaks so, I mounted it in a separate box. After I did his, the unit gave probably the longest period of fault free operation. I did plan to mount the 4 transistors on four separate heatsinks with fan assisted cooling and direct contact of the heatsink tabs onto the main heatsinks. If I can ever get a full set of matched transistors again, that is what I will do. I think the relaxation of the transistor insulating bushes killed it this time and I kick myself for not addressing this weakness in the manufacturers design sooner.

Sadly, from past experience, if I just fit a set of unmatched transistors it goes pop the instant I switch it on.
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Old 22nd Feb 2021, 2:14 pm   #9
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Default Re: Ultrasonic power supply for ultrasonic cleaner

Yeah, you're right, that is very crowded round the power stages! Judging by the scorch marks on the cooper side of the board it looks like it's the resistors and diodes that are getting hot.

Steve.
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Old 25th Feb 2021, 6:23 pm   #10
cathy_vintage
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Default Re: Ultrasonic power supply for ultrasonic cleaner

Well I gave up with the Ultrawave unit for the time being (500 watts US power) and in desperation I dug out another cleaner I was given years ago as being BER. This one is a Decon FS400 (400 watts) ... made by Decon Ultrasonics in Hove, who are no longer trading. The fault with this unit was the digital ultrasonic timer and temperature controller no longer worked and the control board itself was long gone .. I bypassed all of this and just wired up the ultrasonics to come on permanently. The general construction of this unit is generally better than the Ultrawave unit and has a large toroidal isolation transformer, which powers the ultrasonic circuits and low voltage regulator.

I got thing working and left it buzzing away with a Honda CB500/4 cylinder head in it and kept checking it and all seemed OK, initially. Then I left it for a good while and it stopped working and there was a horrible acrid smell like burning phenolic in my garage, so I was thoroughly disheartened, fearing the worst. However, after stripping it all down again I found that the IEC mains input filter had burned out, so I bypassed it temporarily and all is well again... touch wood.

Does anyone know how the 'disc' type transducers directly bonded to the stainless steel bath like on this Decon made unit, compare with the 'horn' type as fitted to the Ultrawave unit.
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Old 25th Feb 2021, 8:47 pm   #11
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Default Re: Ultrasonic power supply for ultrasonic cleaner

Those transducers bonded to the tank have been about for a few years before your unit was built.
My valve bath has one.
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Old 25th Feb 2021, 9:23 pm   #12
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Default Re: Ultrasonic power supply for ultrasonic cleaner

Hi the horn type, that look like a miniature Dalek are more expensive to manufacture but are much more robust and normally operate at a higher power (as used on the Kerry Pulsatron system.
The smaller modular Kerry units operated with a simple power unit, run from an autotransformer from the mains and used a pair of BDY93/01 transistors in PP.
Additional protection against customer abuse was provided by overvoltage protection on the transistors by means of gas discharge tubes

Ed
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Old 25th Feb 2021, 11:14 pm   #13
cathy_vintage
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Default Re: Ultrasonic power supply for ultrasonic cleaner

I have to say that the ultrasonic cleaners I have encountered with the bonded disc type transducers seem to survive really well, without major blow ups. However, I have seen all sorts of problems with the 'Dalek' ones e.g with the transducer mounting pad de-bonding from the stainless steel base of the tank and serious localised pitting of the tank around the transducer mounting areas. The general build quality of even the expensive Swiss made (Sonoswiss) ultrasonic cleaners, that we use where I work, isn't brilliant either.. the Swiss ones have control pots that look like the ones Sinclair used to use in his late 1960's amplifiers and they also have crabby little plastic clips which are used to mount the main PCB that break off very easily. Diabolical for a unit that costs over £2k new. One of these days I might take one apart and have a 'wow that's more like it' moment, like when I 1st took the back off a Sony Trinitron TV.
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Old 26th Feb 2021, 10:12 am   #14
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Default Re: Ultrasonic power supply for ultrasonic cleaner

I did a test with aluminium cooking foil and results were good after a short period in the bath. see pic. I also left the unit running for a long period without any disasters. I think I will settle on using this Decon one on my motorcycle stuff, rather than persevering with the Ultrawave unit. I think I will look out for a 500 watt plus ultrasonic power supply from the likes of Branson etc. and try to adapt that to the Ultrawave bath (well two because I have two large Ultrawave units now with identical duff main PCB's).

Ed D. ... I found this link interesting re: Kerry Ultrasonics .. I bet we have all encountered people like this guys MD in our careers .. I certainly have.

https://simonhawketts.co.uk/2020/08/...y-ultrasonics/
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