# Non-HA related theoretical question about AC/DC (not the musicband ;)

As some technical german forums tend to get a little bit “bitchy” when asking theoretical questions (simple don’t do it, if you don’t know; dumb question, trolling) , I’d like to ask this non-homeassistant related question here.
I don’t want to fight. I’d like to discuss this theoretical question here, because I only had positive experience in this community.

VERY IMPORTANT:
So this only a theoretical question. DON’T DO IT. DON’T TRY THIS OUT. Let’s just think about. AND PLEASE DON’T EXPERIMENT ON THINGS WITH HIGH VOLTAGE/POWER IF YOU DON’T KNOW WHAT YOU ARE DOING. DON’T RISK YOUR LIFE!
Thanks!

So know my question:

Some days ago I was asked if it was possible to power an AC powered device with DC.
I personally don’ know if a simple “No” is the right answer for that. I’d like to discuss that.
Maybe “No” ist the right answer for most AC-powered device, but I could imagine some will also work with DC.

As I learned years ago you only need three electrical parts to go from e.g 230V AC to 5V DC.

Those parts are:

• rectifier
• transformer
• capacitor

So lets take the Sonoff Basic as an example. On the input side you have AC. The microcontroller is powered by 3.3V DC.
So what would happen, if you would feed the AC-Input with 3.3V DC.

The only component of those three party that could think of could make troubles is the transformer. I have to less knowledge about that, as I don’t know how it transforms the voltage.

1. If it transforms the input voltage by a certain value lets say 1/70 (230/3,3) and input of 3,3 would lead to an output of 0,05V.
In this case nothing would happen, the mcu doesn’t power up.

2. If it transforms the voltage to a certain value (to 3,3) than (I think) you could power it with DC because the output would be a little less than 3,3V.

Would be glad to hear someone with better understanding on this one, as this is on my mind for a few days now.

That’s why i love this community here!

Nothing, because the transformer needs AC power.
http://www.hobby-bastelecke.de/bilder/schaltungen/netzteil12v.gif

Thanks for your answer. Could we go a little deeper? So the coil of the transformer needs ac, right? Why does it need AC power?

In conclusion this would mean it is not possible to transform DC to DC, right?