AC switch mode power supply connected to DC

[edmundopt]

Is it possible to do so ?
So I am asking because my modified sinusoidal AC wave inverter has an efficiency of 89% at 400w and less then 60% at 30w, this is causing me a problem.
What happens if a ~100v..240v AC switch mode power supply input is connected directly to DC voltage?
 - chances of DC voltage arcing in the inputs of the SMPS ?
 - components before the diode bridge that would be damaged with a DC voltage?
 - SMPS controller chip to be unstable/damaged because too low voltage in its input ?
 - stuff that I am not thinking about?
 - Without actually connecting it, is there some math to calculate its efficiency ?

[CaptDon]

I guess it really depends on the supply. Some automatic dual voltage supplies may not like it as they normally operate in a voltage doubling mode on 120vac and non-doubling at 240 automatically detected. Some of the 120vac SMPS units simply full wave rectify the 120vac making around 140vdc and run from that, if so you could probably run one of those types direct from 140vdc either polarity sine there is a full wave bridge inside the device. You would really have to know the topology of the power supply in question.

[David Hess]

What happens if a ~100v..240v AC switch mode power supply input is connected directly to DC voltage?
 - chances of DC voltage arcing in the inputs of the SMPS ?

No.

- components before the diode bridge that would be damaged with a DC voltage?

No.

- SMPS controller chip to be unstable/damaged because too low voltage in its input ?
 - stuff that I am not thinking about?

Why would the voltage be lower unless you make it so?  Most power supplies are intended to operate with about 340 volts DC produced by the input rectifier and filter.  Power supplies which use active power factor correction should operate correctly with DC inputs from somewhat lower than 170 (90 volts?) to 340 volts DC.

If the voltage is too low, then the negative resistance input characteristic of the switching power supply will draw excessive current and damage the power supply.  Good power supplies have an under-voltage lockout to prevent this.

Some designs with power factor correction are just defective and will not operate on DC at all because they are expecting AC.

- Without actually connecting it, is there some math to calculate its efficiency ?

The change in efficiency will be negligible.