Author Options:

whats the easiest way to convert 120 VAC from wall to 24 VAC ? Answered

A friend gave me a security camera without power wires. on the back it  has 3 power terminals 

- 24 VAC

- GND ( ground)

- 24 VAC 

should i just try to find a wall adapter that puts out 24 volts DC and then take it apart and take out the rectifier ?     im guessing thats how they work.   THANKS :)


If you're in the USA, Get a transformer from Radio shack.

Add a power cord, and a fuse for safety.

Job done.


24Vac is a standard low-voltage supply. It operates below the 46V cut off, so is considered pet and human safe for accidental contact, and can deliver more power at longer distances than 24VDC.

I thought this 120V system was supposed to be "safe" like that, not heard of 46V thing...


46V is a cutoff voltage for human safety. Can't site the governing doc for you, as my profession has shifted to web dev and the resources are no longer handy, but it's a number I remember quite clearly.

110 VAC will kill you dead as a stone. Safer than 240, no doubt, but it's still a lethal voltage. Unless you're that anomaly guy from India who can pass 3 A @ 240VAC and power a blender...

The only thing that makes either 120 or 240 safe(er) is the recent arrival of whatchamacallit circuit breakers. (sorry, too little coffee this morning)...the kind most local govs now require for bathrooms...

mm, but that's nearly twice 24V - original que-est'ion. ...


24VAC because it has rectification internal to the camera. (I'll almost bet that the camera could be popped open and you'd find a switch or a jumper that would allow it to be used with 24V DC) 24VAC because it was probably designed to be for remote location, say atop a light pole or on a building wall up a few stories...or another location distant from the supply source. 24VAC would be used because 24VDC would present losses that might be unacceptable to consistent use of the camera, due to the length of cabling required to power the camera. 24VAC is a standard low voltage source because...well... idk... because that was some sort of standard low v supply voltage in use at the time it came into fashion to reuse it for low-v outdoor apps, most likely chosen because the components required to make the supplies or the supplies themselves were more economic than reinventing the wheel....but it does meet with safety rules, so that's good enough for me. As I said, I can't recall which reg i'ts governed by, and frankly, it's not all that important to *me to dig it up. I have bigger fish to fry. It's actually about 1.69 times at peak, which still falls below the 46V cutoff. It's single phase.

You have to be careful with this. Rectification cuts the duity cycle in half. A circuit that runs on 24vac after rectified is 12vdc, not 24. Applying 24vac in place of the rectifier will double the operating voltage and release the magic smoke. An easy way to hook this camera up to local power is to use 12vdc on the two 24vac pins. 99% of the time, that works without issue and a lot of these cameras are laberled to use 24vac or 12vdc. Because of the internal rectifier, polarity of the 12vdc will not matter.

Nah, 120 V is NOT safe, our site safety transformers create AC 55V to ground, on "live" and "neutral"

60V to GROUND, because you HAVE to use isolating transformers, the US system is 120V to ground

. In an industrial/commercial installation the camera may be quite a distance from the power source. AC travels better than DC. Plus the AC can provide a synch signal.

My question is why the two separate 24VAC connections. Is that supposed to be out of phase (48V across the pair), or is something else going on? As they say, with an exclamation point, SEE INSTRUCTION MANUAL.

ground is a safety connection Ork. One connects the 24Vac across the 24VAC connections, the ground wire is connected back to...ground.

Ah. Right, of course; "ground", not common. Hadn't occurred to me that a camera operating off low voltage would have any need for a chassis ground.

As a second thought, could also be used to attach shielded cable for noise reduction...but I suspect the principle reason is electrical grounding, ie, safety grounding by any other name.

The easiest way would be to just buy a 24VAC transformer, you can easily find them for under $10, like here for example... http://www.mcmelectronics.com/product/82-1530&CAWELAID=220594904