CuriousOnlooker
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Transformer for VEVOR SH-2 Hotplate/Stirrer ??
My VEVOR SH-2 died on me.
A quick check showed that while mains power is going into the transformer there's none coming out.
Rather than immediately scrap it I'm hoping that the transformer can be replaced.
Does anyone out there know what the output of the secondary winding should be?
Condemnant quo non intellegunt.
Never fire a warning shot. It is a waste of ammunition. ~ Hunter S. Thompson
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Twospoons
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Check for a part number on the transformer. You may also find the voltages are labelled too.
Helicopter: "helico" -> spiral, "pter" -> with wings
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CuriousOnlooker
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Unfortunately there are no markings of any kind on either the transformer nor underneath the PCB.
I will take it to a nearby electronics shop and see what they say.
Condemnant quo non intellegunt.
Never fire a warning shot. It is a waste of ammunition. ~ Hunter S. Thompson
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MrDoctor
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i was not aware that those had transformers. or should. it shouldnt.
a 200W transformer would be a brick occupying most of that space. i think perhaps thats just for the magnetic stirring. either that or its a small 1:1
isolation transformer. But if its for the stirring, thats just a 10W transformer, the heating element should be getting switched by mains directly.
the stirrer transformer is most likely just 12 or 15v, if the primary and secondary look the same then its an isolation transformer for safety
purposes.
one other thing, try measuring the resistance on the primary and secondary, also, test both DC and AC voltage measurements on the secondary if it
doesnt read a megaohms/infinite resistance (dont measure resistance while its powered tho), i dont know your knowledge level or how good your
multimeter is.
my suspicion is something has happened and blown an inline fuse somewhere, and the design is one such that it can trick your multimeter, especially if
you measure it wrong like you would something DC, like negative to earth then positive to, any given part of the circuit connected to mains
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bnull
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See if the transformer case is a little bloated. There was a situation last year where the stirrer wouldn't work properly. It took a long time to see
what was wrong because no one noticed a bubble on the transformer case. Look for a post about an IKA HS-7 mag stirrer; I listed some replacements and
it is possible you will find a suitable one on the same site.
The heater is mains-powered and the transformer services only the DC motor and the controller. Transformer output 12 VAC rectified to 15.5 VDC
(there's a drop of about 1.5 V due to the rectifying bridge). There's another drop of a few volts in the controller circuitry (some 3 V or more
depending on how the control is made). The motor is a 12 VDC; easy to find, cheap to buy, why would VEVOR use something else? A shaded-pole motor
would add more to the manufacturing costs.
Could you please take some pictures of the innards of the stirrer? Both sides of PCB, a close up of the transformer, preferably in a place with good
lighting.
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CuriousOnlooker
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Solved/Resolved
Firstly, thank you to those of you who took the time to reply.
The transformer was shot -- power was going in but nothing coming out. The PCB itself looked pristine.
The only clues were the components on the PCB, of which a couple of power transistors and a current regulator had the only identifiable codes on them.
I looked up their specifications and then purchased a small generic multi-voltage transformer.
 
Both stirring and heating returned. The rate of heating wasn't particularly fast, but it wasn't to begin with and I'd often put an aluminium shield
around it. Solder the connections and all seemed good in the World, but I forgot the carpenter's adage of "measure twice, cut once". The transformer
was too big for the inner cavity of the device. Fuck!
Back to the electronics shop to get the little 9V transformer. As luck would have it this transformer fit perfectly into the mounting bracket that
held the previous one. Once again temporary connections, and everything is running, so fixed into place and permanently soldered. Being lower voltage
it may take some time to heat up, but it never was particularly suited for production or lengthy operations.
Getting functionality back was certainly better than just scrapping it.
Once again, thank you.
Condemnant quo non intellegunt.
Never fire a warning shot. It is a waste of ammunition. ~ Hunter S. Thompson
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MrDoctor
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oh, i know what happened. that transformer was supplying power to the heater-controller, i just assumed it used a mechanical thermostat for some
reason, since they are so damn cheap and low quality that a digital circuit couldnt possibly be cheaper than a mechanical thermostat.
With no transformer supplying the controls, it cant choose to turn on which is why heat and stirring failed together.
Anyway good to hear your hot plate is up and running again, and thanks for posting these pictures im sure theyll be helpful to others
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bnull
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Mechanical thermostat in a digital hotplate? Not likely. They'd set up a phase controller (I forgot the right name) using a triac, a diac, and a
potentiometer, or a dedicated IC.
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