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120VDC in to appliances and devices?

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tom66:
I've tried this to some extent with a few devices.

Rigol scope - works fine 50V upwards.  Draws 10W, so unlikely to wear the diodes even at the lowest input voltage.  Below 40V, once started, scope shuts down suddenly with no apparent side effects.  Current draw is minimal until startup works.

LCD TV - works ok up to 100V DC (had a PFC circuit) but below this power supply makes some very unhappy sounds and backlight/sound flutter badly.  Eventually LCD TCON lost its mind and started drawing all sorts of random patterns on the display in place of video, whilst sound continued OK.  Did not break anything.

various AC-DC PSUs - all seemed to work OK

Dell laptop PSU - did NOT work correctly, output pulsed on and off, laptop refused to charge.

amyk:
120VAC is RMS so you should probably be aiming for ~170VDC instead (or 340 for 240VAC).

Zero999:

--- Quote from: amyk on September 07, 2023, 01:40:05 pm ---120VAC is RMS so you should probably be aiming for ~170VDC instead (or 340 for 240VAC).

--- End quote ---
No, the switched mode power supply will be designed to work at a much lower steady DC volage, because the smoothing capacitor will discharge, during the zero crossings.

My Rigol DS1054Z oscilloscope works perfectly down to 36V. I even considered making a battery pack for it, but lost interest because I bought another oscilloscope with a rechargable battery.
https://www.eevblog.com/forum/testgear/battery-pack-for-rigol-ds1054z/msg717702/#msg717702

I'm not saying this will be the case for all switched mode power supplies, but I would expect it to work from a lower DC voltage, than the peak mains. As mentioned above, there are potential pitfalls, to running AC switched mode supplies off DC, but I've found most mains switched mode power supplies work perfectly well.

lufihengr:
As a followup then, is there a point where it would just be easier/better to use DC power from batteries to spin a DC motor, that is connected to a generator? That would at least be a perfect sine wave :D

As you have probably gathered, the situation is a case where grid connection is not available, but the use of regular appliances is wanted.

BeBuLamar:
I work on a machine which has a PC used as the operator interface. They power the standard power supply with 220VDC and it works. I really don't know why they do it that way as they could feed the 220VAC directly to the power supply but they use a bridge rectifer and a large capacitor to create the 220VDC (actually it's more than 220VDC) to run the computer.

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