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120VDC in to appliances and devices?

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lufihengr:
Has anyone tested what happens if you put 120VDC in to a TV that has a switchmode PSU meant for 120-240VAC?

In theory it should work, no?

Asking because I would like to avoid using inverters, and modifying appliances like TV's with integrated power supplies is too time and cost intensive.

Thanks

AVGresponding:
In theory yes, but bear in mind you're putting one half of the diode bridge on 100% duty cycle. Depending on the design specs, this might be problematical. In the unlikely event it's a half-wave rectified primary side, you'd have to get the polarity right.

lufihengr:
Would it be better for the appliance to have 120VDC or 240VDC if the PSU is capable of taking 120-240VAC?

And would it technically be even better to have a 100% duty cycle polarity switching DC supply to it? Like have it switch polarity at 10, 50, 60Hz, essentially just a square wave going from +120VDC to -120VDC? Or is that worse than a pure sine wave? It would be easier to make than even a modified sine wave inverter.

Gyro:
If it's a modern, reasonably large TV, you may need to consider how the PFC circuit would react to DC. I have a vague memory of this being discussed on the forum before, but not the outcome.

Ian.M:
You are going to run into severe problems with switches and fuses, as they are extremely unlikely to be rated to break a >30V DC circuit.  Squarewave  AC isn't much better, as there is no 'dead' time round its zero crossings.  OTOH sinewave 120V AC has nearly a millisecond under 30V round its zero crossings, making low energy arcs much easier to quench.  Therefore, you'll probably need to replace fuses with DC rated ones and avoid powering with DC any devices with a mechanical or relay mains switch.

Then there's the issue of PFC circuits - some will be very unhappy with any input waveform that isn't somewhat sinusoidal.

On the subject of switching polarity, see https://www.quora.com/What-is-Quasi-Square-wave-or-Modified-Square-wave-Inverters
Even with dead time at zero crossings, and both peak and RMS voltages equal to sinewave mains, many appliances will run hotter or even fail if run from such a supply.

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