A lot of plc power supplies that i see have a toggle switch for 115vac/230vac. Its only used at initial startup to select the correct voltage level. Its never toggled when power is turned on. I think if you downloaded a PDF on one of these power supplies you would get a better idea how its used in the system.

The product uses control valves that are 120VAC valves. The control needs to remains 120V. The only difference is that we need to be able to configure the product so that it can work on either 120V or 230V

Autotransformer at the supply intake. 240V tap, 120V tap. Connect supply appropriately.

If you want it automatically switching, you can simply hook up a voltage sensor to a relay

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OP mentioned, "The product uses control valves that are 120VAC valves."

Better add frequency (60Hz vs 50Hz) to your list of things to consider. Solenoids designed for 120 VAC are often intended for 60Hz. If a transformer is used with 230VAC (and perhaps 50Hz) to provide the lower voltage, then solenoids might be unhappy with 50Hz (risk of overheating). Something to check, if you plans to use a transformer.

Is this something that needs to change on the fly or something that can be done in production? If in production, you could use a regular transformer for 230V operation (secondary 120V). There are many out there to choose from since this transformer is often used in power conversion equipment for foreign travelers.

This needs to be configured in the field, either manually, or automatically (preferred). We will not know whether the power will be 120 or 230 when the product is shipped.

If you provide an auto-transformer with two taps, one marked 120V and one marked 230V, then surely the local electricians can make the correct connection?

Can you use 24V or 110V DC as the valve control voltage and provide a universal power supply at the input (typical input range of 85V - 265V AC or thereabouts)

What is power needed for this system?

Power is roughly 150 to 300 VA

So an auto-switching UPS might do this?

Ah heck, that little power?!

Just build this into your product and then you plaster a label across the power switch that the user reads before powering up the unit the first time. The label directs them to set the voltage in the little window to their local voltage.



You flip down the top little cover with the window in it which can only be done with the power cord removed (no shock possible) then you pop out the red fuse carrier and rotate it 180 degrees so the correct voltage will be seen thru the little window. reinsert the fuse carrier. Close the hatch. Plug the power cord back into the power entry. And, they're in business.

You do need to include the correct fuses for your product.

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Keith Cress
kcress - http://www.flaminsystems.com

The last place I worked used something like that, but the ones they got sucked. The problem was that there was a bad design that adapted to the different fuse sizes and would not ramp the fuses into place, so the techs would bend the contacts to let the US fuses fit so they could do unit burn-in. They would put in the Euro fuses, which would be loose and not make contact, so the European field techs would have to replace the fuse holders, which aren't available separately. Since the units weren't bought directly from the maker, the maker washed their hands of it and refused to acknowledge or fix the problem.

Maybe they are OK if used with only one fuse size, but if they are qualified on one fuse, but used in the other configuration I would check carefully and make a lifetime buy to avoid problems from the maker changing the design. I would also make the installation into a replaceable plate so that an alternate form factor could be used.

As it was there was quite a shock when the new, out of the box, fully tested, QC'd and QA'd, FDA approved design box failed to function because of the f'd up fuse holder that was badly designed.

(why does almost every electrical item seem like the mechanical design was handled by someone who took a drafting course but paid little attention?)