-3
\$\begingroup\$

I recently found out I'd need to pay upwards of $2k in order to supply my entire house with automated blinds. I feel like I can definitely do it myself for a fraction of the cost.

For this purpose I'm looking into what would be the cheapest way of powering small 2W/3W 12V/24V motors like those ones, which are pretty easy to get a hold of for a couple of bucks:

enter image description here

I stumbled across this video, which shows something like this:

schematic

simulate this circuit – Schematic created using CircuitLab

Yes, I replaced the motor with a bulb because I couldn't find a symbol for it, sorry.

As far as I understand, the diode will chop it into a half wave, and the resistor will limit the current to:

$$ 220 / 1.414 / 2 / 1000000 = 77 uA $$

Which would probably not be enough to do any work, but let's say I can replace the resistor with a 500 ohm one to get around 155mA, or whatever other value it needs to be in case my calculations are incorrect.

Yes, I'm aware that the produced voltage will not be DC but it should be OK as in it won't introduce damage the motor, and yes, I will need to add a couple of relays between the motor and diode/resistor to be able to switch the direction. I'm really just looking for the cheapest working solution.

I'm not sure what the purpose of the capacitor is and what its value has to be.

\$\endgroup\$
13
  • 6
    \$\begingroup\$ No, stop before you set fire to your house, and electrocute yourself. For 12V/24V motors, buy 12 V or 24 V power supplies, off the shelf, CE / UL marked for safety. \$\endgroup\$
    – Neil_UK
    Sep 26 at 12:07
  • 6
    \$\begingroup\$ $2k sounds like a bargain to me. Unless you place no value on your own time, and have low standards about safety and how the final installation will look. Not to mention that if you don't know what the capacitor is for, you're way outside your skillset for this job. \$\endgroup\$
    – Dave Tweed
    Sep 26 at 12:19
  • 5
    \$\begingroup\$ @php_nub_qq it's up to you. No responsible EE around here would approve such a hazardous solution. Not only do you risk yourself, you will end up burning several motors which in the end will defeat your purpose of saving money. Follow what Bryan said at the very least. Use a DC power supply. Motor shields for Arduino are readily available and easy to code. \$\endgroup\$
    – Daniel Melendrez
    Sep 26 at 12:19
  • 4
    \$\begingroup\$ There are also plenty of people who do not have automatic blinds in their homes. What's your point? \$\endgroup\$
    – Dave Tweed
    Sep 26 at 12:22
  • 5
    \$\begingroup\$ I would feel free not to respond, except that your proposed actions will put other people at risk, starting with your own family, and ending with any future owners of your house. If you want to learn something new, you start with the basics and work your way up from there. You don't dive into the deep end with a non-isolated mains-powered project! \$\endgroup\$
    – Dave Tweed
    Sep 26 at 12:36

1 Answer 1

Reset to default
5
\$\begingroup\$

Do NOT do what you are suggesting!

You are planning to connect uninsulated motors, to the mains, with no safety barrier or protection. This is extremely dangerous.

12V & 24V power supplies, complying with local safety standards, are availability at minimum cost for a wide variety of sources. Use these instead.

As an aside, the resistor in your circuit is to discharge the capacitor, not to carry the main current. The current is limited by the capacitor whose AC impedance would be given by \$1/(2.π.f.C)\$ .

You would also need a reverse diode (in parallel with the first diode and motor) to allow the capacitor to discharge during alternate half-cycles.

\$\endgroup\$
1
  • 1
    \$\begingroup\$ I didn't know there's Aprils fools day. (@php_nub_qq) \$\endgroup\$
    – MiNiMe
    Sep 26 at 12:22

Not the answer you're looking for? Browse other questions tagged or ask your own question.