Question about electricity

[AZ Nomad]

How would it be any problem at low voltage.

[Mark Lloyd]

[snip]

A transformer is an AC-only device. Maybe you're (incorrectly) referring to a power supply which contains a transformer and a rectifier. The transformer is on the AC side.

There might be some conversion table around, something like use xVAC for a yVDC relay. Still, I'd rather not do that.

Most of the relays I use are made for 12VDC and work with small DC wall-warts.

A half-wave rectifier has an even greater need for filtering. The capacitor needs to store enough electricity to fill in the gaps. With a half-wave circuit the gaps are half as frequent but much longer.

BTW, most wall-warts contain a full-wave rectifier that uses only 2 diodes. This is possible with a transformer with double the secondary voltage and a center tap.

[Mark Lloyd]

That's what I thought.

Of course, there's still the term "average current", that describes what an analog meter responds to.

[Don Klipstein]

Halfwave rectification also causes a DC component to flow through the transformer's secondary winding. That may cause the core to saturate when the primary's "magnetizing current" is in the same direction.

I have seen fullwave ones. The 2-diode-center-tap scheme has higher ratio of RMS to average current in its secondary windings since the secondary windings are used only half the time. Copper has gotten really expensive over the past 3 years and diodes are cheap.

- Don Klipstein ( [e-mail])

[TWayne]

Because what you are calling "low voltage" doesn't have anything to do with the IR abilities to start a fire and/or get very hot. There are still safety issues related to fire.

[AZ Nomad]

If you're only dealing with a few hundred milliamps, it can't generate more than a few watts of heat and beside, it would be inside an electrical box.

[TWayne]

OK; go for it then. But fault current on the secondary of a transformer is much more than a few hundred milliamps as is the resultant primary side draw. Safety issues don't bother you, so ... don't look up UL or CSA requirements or anything; just do it.