Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Connecting transformer right way round.

Status
Not open for further replies.

revans

New Member
Ok I've got a 12v SLA battery charger which typically plugs into a wall power plug. For my reasons, I'm mounting it inside an enclosure, and connecting it to power via a IEC-320 socket and cable.

Having (somewhat vigorously) stripped off the stock plastic casing, I found that I'd managed to disconnect the two wires connecting the charger's transformer to the mains plug pins.

Problem: I don't know which pin to reconnect which wire too... I'm using an NZ power plug: 240V powerplug datasheet and only the neutral and active wires are required. The two wires from the transformer are both red, so I have no idea which connects to 'neutral' and which connects to 'active'. I'm not to keen on connecting 240v mains with the wrong polarity... :D

Thanks for any help with this.
 

Diver300

Well-Known Member
Most Helpful Member
It doesn't matter which way round you connect the transformer.

Live and neutral are only different for other stuff. Live and neutral are usually marked on IEC sockets, and the switch and fuse should be in the live side.
 

revans

New Member
Oh really? Thanks for clearing that up Diver :)

Yeah, I've seen the L and N pins on my IEC socket... so I can connect the transformer to the either way round... that's handy.

I assume you were talking about the "switch and fuse being on the live side" in general terms (ie. not specifically relating to this... the charger doesn't have any external components like that).

Again, thanks for helping me out.
 

Diver300

Well-Known Member
Most Helpful Member
I assume you were talking about the "switch and fuse being on the live side" in general terms (ie. not specifically relating to this... the charger doesn't have any external components like that).

Again, thanks for helping me out.

No problem.

Yes, I was just speaking in general terms. There is no need to have either.

Some transformers have some marking the indicates live and neutral, like brown and blue wires or labels of 230 / 0 on the terminals. I try to stick to those, but that is only to avoid confusion later on, as there is no technical difference.
 

Mr RB

Well-Known Member
You would like to think so, and I would ALWAYS wire it like that, but quite a lot of modern equipment has the switch and fuse in the neutral - I've no idea why?.

Wow. That would actually be illegal in Australia. :eek:
 

Burningmace

New Member
I'm intrigued as to why it matters (to the point of being illegal!?) which wire you put it on. It's AC, so it's not like there's any difference at all as to which wire you choose.
 

grim

New Member
switching/fusing the neutral, means the equipment is still live and dangerous when it's switched off.
 

Burningmace

New Member
--- EDIT ---
Sorry, I was misinformed. You're correct. Wiring it to the neutral would be hazardous because if you short the live to earth within the appliance the wire would melt and cause an electrical fire. The neutral doesn't supply a voltage (ok, it might carry 20V or so due to impedance from the load within houses, but not enough to shock you) so it's in no danger of causing a fire.
 
Last edited:

revans

New Member
New transformer question: Do transformers ever make sounds when in operation? When the charger is in operaton there's a weird buzzing/crackling/indescribable low noise you can only hear when you're right next to it...

I'm guessing it's the transformer... because I wouldn't imagine other omponents like resistors etc would generate a sound??

Just a bit confuzzled as to what/why it's there...
Assuming it's nothing major, although maybe it could be :confused:

EDIT: The noise actually continues once power to the charger's been cut... though it does slowly trickle off over a few minutes.
 
Last edited:

Diver300

Well-Known Member
Most Helpful Member
It seems you have a switch mode power supply. They rectify the mains, and charge a capacitor with the rectified mains. The high voltage DC from the capacitor is fed to the transformer for a very short time, then disconnected. As the high voltage is disconnected, the energy in the transformer core is transferred to the output as a short pulse. The pulses of DC to the input of the transformer are only sent when needed.

You can probably hear the pulses in the transformer. The magnetic fields cause forces in the transformer, so any flexibility results in movement and then audible noise.

The noise will continue until the input capacitor is discharged, which can take a long time if there is no load.
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top