Electronics > Beginners

Convert 220v/50Hz illuminator to 120v/60 Hz. Safe to plug in?

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james_s:

--- Quote from: Yansi on February 17, 2019, 04:27:33 pm ---The input capacitors are what is the frequency dependent component. Too low frequency and it will not filter enough. Too high frequency and you will smoke the diode bridge.

--- End quote ---

Not to any degree that matters. Anything from about 40Hz to 400Hz or more ought to be just fine with a capacitor and rectifier intended for 50 or 60Hz. Sure if you feed it 20kHz you will probably have issues but that's way outside of the frequency of any mains system.

mcfudge:
Yes, the lamp is 24V 150W halogen.

StillTrying:
I'd have plugged the 220V 50Hz device into the 120V 60Hz by now, I'd be surprised if it actually blows up. :)

mcfudge:
Hey Richard,

Uh no nameplate, it's so basic and cheaply manufactured.  And the only identifying marking on the board is underneath the S20LC20U rectifier just above the PFC choke ("BC-150 1407 126531"), image attached.  The obscured components are TL494 PWM control chip, two Toshiba C3306 NPN (left side) and two bridge rectifiers KBPC110 and KBU810.  They weren't captured well in my original photo.  AmScope makes several claims in their brief 3+ page operating instructions pamphlet.  I'll include a couple screenshots of it.

In the case of this board, there doesn't appear to be any intended method to easily switch between 120 V and 220 V.  There are only a few unpopulated locations - CE5, C2, C3, and the rear of the chassis only has a fuse, mains power switch, and that epic mains input connector.

Thanks for the advice re IEC.  I do plan to make that modification.  It probably goes without saying that this device bears no electrical safety certification for NA or elsewhere.

Richard Crowley:
Despite anyone's protestations otherwise, I don't see any way that could possibly be a linear power supply.  That is clearly a SMPS with the added feature of a variable output via the front-panel control.  Neither of the visible inductors are anything but ferrite-core high-frequency design.  You could confirm by looking at the value of those large capacitors.  If they are low voltage (30-60V) then that is a linear supply.  But if they are high voltage (200-300-400V) then that is clearly a SMPS.

And IME, there is absolutely nothing about it that cares about the power mains frequency, 50Hz, 60Hz or anything around that range.

My only question would be whether it would operate with 120V AC mains power input.  IMHO, there is little risk of simply trying it.  I would plug it in with the cover removed for observation and temperature monitoring.  I would turn it on for a few seconds and see if the lamp lights to full brightness and if the control works as expected. 

Best case would be that it will simple work properly and we are done here.  Worst case would be that it won't work and may even overheat one or more of the power supply components.  That is why I would try it for only a few seconds to start with in case the SMPS misbehaves.

Beware of the hazards of mains-powered SMPS. Those large capacitors are probably high-voltage (hundreds of volts) and will retain a good amount of energy even after power-down.  It is always good practice to discharge all of the larger capacitors before poking around inside.

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