Just a quick question!
I'm new to using mains transformers. I'm making a car battery charger just to practice and test myself out seems quite simple to do. The circuit I'm using requires 18vdc so I've picked a transformer that goes from 240vac to 18vac 1.5va now to change that to dc I'm using a bridge rectifier. Will this drop the voltage below 18vdc or will it stay at 18vdc?

Thanks in advance

 

A rectifier will allow peak pulses of almost 24 volts.
A bridge rectifier can get you almost 48 volts, depending on how you wire it.
You need to study first and buy later.

 

As #12 noted, rectifying 18VAC (RMS) gives more than 18VDC . The rectifier DC output is nearly equal to the peak AC voltage, which is 1.4 times the RMS. Obviously it's not as simple as you thought.

 

Maybe this will help you decide what your next step will be
http://www.hammondmfg.com/pdf/5c007.pdf