1
\$\begingroup\$

I'm doing a home automation system which uses a RF transceiver(nRF24L01+) paired with an arduino to control the relays. Since these require low power DC to run I was researching on ac to dc when I came across capacitative power supplies. This type of supply is needed as there isn't enough of space to throw in a transformer in a back box.

My only concern here is if such a power supply is safe, cause I don't want my house burning down.

This is the circuit I've found so far : http://www.circuitsgallery.com/2012/07/transformer-less-ac-to-dc-capacitor-power-supply-circuit2.html

\$\endgroup\$
9
  • \$\begingroup\$ You should also be asking whether connecting it to the mains is legal. \$\endgroup\$
    – user207421
    Apr 26, 2016 at 23:27
  • \$\begingroup\$ @EJP Are you aware of any jurisdictions where it wouldn't be legal for personal use? Because I'm not. \$\endgroup\$
    – user39382
    Apr 26, 2016 at 23:52
  • \$\begingroup\$ @EJP I honestly don't see how there's a legal aspect to this. As far as I know, the mains are within the confines of my house for which I pay a monthly electricity bill. OR do you mean the mains being tampered (for lack of a better word) by someone who is not a professional electrician? \$\endgroup\$
    – azhamn
    Apr 27, 2016 at 0:05
  • 1
    \$\begingroup\$ @nappyboi -- most countries have regulations as to what can be plugged into a mains outlet -- these are intended to make sure that gizmos don't fry people with mains AC to the face, go on a rash of burning down folks' houses behind their backs, or spew RF trash all over the powerlines that hoses up your neighbor's radio. \$\endgroup\$
    – ThreePhaseEel
    Apr 27, 2016 at 0:31
  • 1
    \$\begingroup\$ You certainly can build such a thing (I have), but you would never want to sell it. It would be unlikely to get UL approval, which is a legal issue only in that it helps protect you from liability. \$\endgroup\$
    – Mark
    Apr 27, 2016 at 4:35

2 Answers 2

Reset to default
2
\$\begingroup\$

The capacitive PSU is common in many devices like LED lamps,etc..The device shall not have exposed metallic parts, because it is a shock hazard as the part have mains live voltage. As for burning the house: you need to properly fuse the input and there is no big difference between transformer and transformerless PSU regarding fire hazzard.

\$\endgroup\$
1
\$\begingroup\$

There are several safety issues with this circuit:

  1. A "400 V rated capacitor" may be very misleading. A lot of capacitors can withstand 400 V DC, but are not suitable for prolonged operation at 50/60 Hz 230 V AC. You should use a special X or Y rated capacitor.
  2. You must use a fuze even with X/Y rated capacitor.
  3. Equipment connected to the circuit is under the line voltage with respect to Earth. So you are exposed to the electrical shock hazard.
\$\endgroup\$
4
  • \$\begingroup\$ 1. Exactly where to I add the fuse? on the life or neutral side? 2. Is there any way to ground this circuit/the arduino? \$\endgroup\$
    – azhamn
    Apr 28, 2016 at 1:29
  • \$\begingroup\$ I've just found this. Seems better doesn't ? microcontrollerslab.com/… \$\endgroup\$
    – azhamn
    Apr 28, 2016 at 1:45
  • \$\begingroup\$ A fuze in the line wire is slightly more preferable, since it will provide protection from line to ground fault (but not from the electrical shock hazard). \$\endgroup\$
    – dmitryvm
    Apr 28, 2016 at 19:21
  • \$\begingroup\$ There is no way to ground this circuit or the arduino. It is possible to ground (connect to an "earth" wire) an isolated metallic casing around the circuit. A better solution was already mentioned by Marko Buršič: "the device shall not have exposed metallic parts". As for other circuit, it uses half-wave rectifier, so a larger capacitor is required for a given power. Also, the current-limiting 47Ω resistor may be a good thing, but such resistor should be specially designed to act like a fuze (otherwise it will pose the fire hazard) and should withstand high current pulses. \$\endgroup\$
    – dmitryvm
    Apr 28, 2016 at 19:38

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

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