I'm thinking about DC appliances and energy efficiency.
A common appliance like an air conditioner has a rectifier to convert 230V AC into 50V DC. If I connect the appliance directly to 50V DC instead of 230V AC, what would happen?
If the rectifier is passive, I suppose there's only a 0.7V voltage drop. What if it's an active rectifier?
Thank you everyone!
A common appliance like an air conditioner has a rectifier to convert 230V AC into 50V DC.
Incorrect, to convert 230 volts AC into 50 volts DC requires a transformer with the correct turns ratio and a rectifier with a suitable smoothing capacitor to suit the ripple output requirements under load.
If I connect the appliance directly to 50V DC instead of 230V AC, what would happen?
You'll likely melt the primary winding of the transformer.
If the rectifier is passive, I suppose there's only a 0.7V voltage drop.
If the rectifier is a bridge type like this: -
Image from wiki
Then we usually say it has a volt drop of two forward diodes i.e. 1.4 volts.
What if it's an active rectifier?
It probably won't be but, that's a moot point given your other questions.
If it's an oldskool aircon unit it will have a big AC motor, usually asynchronous, so no rectifier is involved.
If it's a modern "inverter" unit, it'll have a rectifier and power factor correction circuit to turn your mains voltage into some higher DC voltage, about equal to the peak value of your AC. So if you're running it on 230V it'll make about 320V DC. Then an inverter generates three phase power to run the motor, with speed control.
This type of appliance can, in theory, run on DC, if the DC voltage is in the same range as the allowed input AC voltage. In practice, it may or may not, the absence of zero crossings may cause the PFC unit to behave in unexpected ways.
I don't see any reason why your aircon unit would use 50V DC anywhere.
A common appliance like an air conditioner has a rectifier to convert 230V AC into 50V DC. If I connect the appliance directly to 50V DC instead of 230V AC, what would happen?
Here's an example of how it's done.
Telecom and wireless networks typically operate on 48 V DC power, with short-term battery backup for uninterrupted power, till a backup generator takes over after a utility power shutdown.
Utility power is stepped down and rectified to power the base stations and charge the battery bank.
Simplified diagram
The air conditioning units, used in the base stations, are also designed for operation at 48 V DC.
They would operate without any problem with 48 V DC derived from the mains or sourced from the battery bank.
