Sciencemadness Discussion Board

Using Corning PC-425D on 240V

print118 - 21-11-2023 at 14:41

Hi all,

I've been looking for a new hotplate stirrer, since my old one broke down and browsing eBay, I came across some Corning ones. Now I've heard those are pretty reliable so I'd like to get one of them, but the problem is that all the ones I can find used, are 120v 60Hz, while I live in Europe, where we have 240v 50Hz.

I have found transformers for stepping the voltage down, but not for changing the frequency. Not to mention that a transformer would be a pretty bulky solution.

Now I have heard that many electronics, that are sold in different countries, which have different voltages, have the same internal electronics and that the device recognizes the input voltage and does whatever to work accordingly. But I don't know if Corning does the same with their hotplates, they do have 240V 50Hz models though.

So does anyone know if a 120v model would work with 240v or does Corning have separate electronics for both voltages?

fx-991ex - 21-11-2023 at 15:24

Sometime theres different tap to the power transformer for different line voltage.
Do you have schematic or picture of the inside?

semiconductive - 21-11-2023 at 23:03

I don't have one to check.

But: I know that the 240V corning plate and 120V corning plate have the same model number, but just a different catalog number. That's not the same as a schematic, and could be misleading, but it does suggest the circuit board inside can be configured for more than one voltage.


You don't list a model number, so I can't even search for specific information.
But, I tried to find corning PC200, and they don't have schematic online; so it's possibly moot.

OTOH: Many of those Corning devices are microprocessor controlled stirrers; and if that's what your are looking at, then Microprocessor control generally means the motor must be operated from a rectified DC power supply inside.

eg: anything that is advertised as "closed loop" is pretty much is going to rectify the power in order to run the motor. This usually means the frequency of the line 50Hz vs. 60Hz, doesn't matter. The voltage, however, does.

The step down transformer solution you found (although bulky) by itself is likely to work for a microprocessor controlled stirrer.

On that vast majority of CNC machine's I've installed, 50/60 Hz doesn't matter. On the few that it did matter, because of inductance, running the voltage a little high (140V) instead of (120V) was the solution.

But again, none of this is guaranteed for a Corning; and without access to the schematic, there's no way to evaluate your risk in buying one.

Note:
There are also down conversion switching supplies, that don't have true sine wave outputs; Those are much smaller than transformers; and depending on the wattage of your stirrer, those may also be available. If it's computer controlled, and a transformer would work, then so would a voltage down converter.





print118 - 22-11-2023 at 04:04

I made an error with the model, my apologies. The actual model was the Corning PC-420D.

The listing also included some other model information:
Serial Number: 153520282003
Lot Number: 28220503
Model?: 6795-420D

All that info came from the image of the sticker on the hotplate. If you can find any information about it, then great, since I don't have the skills for it.

Sulaiman - 22-11-2023 at 07:17

Your options will probably be determined by the heating element(s) voltage rating.

The electronics will be powered either by

A small/cheap transformer that may have input voltage selection options,
or will be not too expensive to replace,
Or
A switch mode supply that may be usable with 240Vac

If lucky the heating is done by two re-wirable elements,
in parallel for 120 Vac
in series for 240Vac.
If not then an ac power transformer will be required;
700VA minimum if it is an isolating transformer
350VA minimum if using just the primaries of a common dual-primary transformer wired as an autotransformer.
Using higher VA rated transformers is ok, even better.

semiconductive - 22-11-2023 at 13:59

Quote: Originally posted by print118  
I made an error with the model, my apologies. The actual model was the Corning PC-420D.

The listing also included some other model information:
Serial Number: 153520282003
Lot Number: 28220503
Model?: 6795-420D

All that info came from the image of the sticker on the hotplate. If you can find any information about it, then great, since I don't have the skills for it.


Quick google search yields:
https://www.corning.com/catalog/cls/documents/equipment-manu...
https://41j.com/blog/2018/07/corning-pc-420d-hotplate-stirre...
https://www.sciencemadness.org/whisper/viewthread.php?tid=65...
https://www.youtube.com/watch?v=EEqY-h_j0sA

This may interest you, as well, because the 420D was involved in laboratory fires.
https://www.osti.gov/servlets/purl/1506818

No schematics were available.

Although these links are not sensitive to serial number/lot run changes; it's clear that the design has historically been as I expected. There is a transformer soldered to the main processor board. This is a small power transformer to go from 120VAC down to somewhere around 5-24 volts D.C.

I'll see if I can read some of the chip part numbers off the photos, and get an idea of the voltages used; and see if I can trace the heating wires out. I don't see, at first glance, four heater wire connections.

But, since this is computer controlled; it's quite possible the heating element is the same for both 120VAC and 240VAC. Only the on-off time used by the computer would have to change in that case. SInce you are going "UP" in voltage, as long as the heating element can take pulses at higher voltage (which many can), the design may be able to use 240V directly after just replacing the small transformer inside.

Of course, any changes you make to the device have to meet the standards of your country; U.L., VDE, etc, or you can never resell it; and it might affect things such as your house insurance. I can't give you any guidance on those issues. (I don't know.)

semiconductive - 22-11-2023 at 14:17

After looking at the pictures, I'm going to say the answer is NO. You will have trouble using this unit on 230-240VAC in Europe. The reason is that it's a triac driven design. I've used the MOC series opto-isolator chips, and the ones that are in there will fail in Europe on a 240V line.

You must lower the voltage to 115 to 120VAC for it to work.
( The heating element is also two wire, and not re-wireable manually to raise the resistance. )

I've put MOC chips in several electric kilns I designed, and to be honest, I hate the chip's reliability. It's just shy of garbage in my opinion.

I'm not at all surprised these hot plates have failed.

Corning is attempting to minimize cost by purchasing chips for the absolute lowest possible voltage setting. In the end, I think they end up wasting more money on handling stock room inventory than they save. This is a typicial engineering trade-off decision.

The main board is running the processor and support chips at five volts. I can't tell if it also uses lower voltages; but this is typical.
There's no reason the circuit can not run using 50Hz power except that Corning may have programmed the processor to give an error code if you attempt to do it.

I'll read a bit more; but I think I ought to discourage you from trying it at this point; the design is using parts I've had bad experience with and there's evidence in the design style that they are intentionally making the device non-operable in any situation it wasn't configred to be used in during manufacturing.


[Edited on 22-11-2023 by semiconductive]