Building a high current 12V power supply.

This is a power supply project for the current hungry!
I needed a good high current power supply to run my Subwoofer amp from.(The amp is a 200Wx2/400Wx1 car amp,that I fixed.)
I used a Microwave Oven Transformer (MOT). I used my dremel tool,and a hammer/chisel to remove the HV secondary winding.
I wound 2 new secondaries,each feeding it's own 25amp bridge rectifier,on a CPU heatsink.Each winding is 10awg wire,the turns ratio will vary with the transformer,but usually 10 turns is a good starting point,measure it with a DMM and see if you need more windings. I get 12.6V with a fair load.It dips as low as 11.0V under heavier loads.I need more turns,but can't fit any more wire in the core! (smaller wire may be advisable!) solid copper house wire will work well,but is pretty hard to work with (I gave up and used stranded 10AWG!). 12AWG primary wire is good,but be sure it has a high temp rating,as the MOT will run rather hot.(you can see about removing the magnetic shunts,etc mine are in the form of two weld's in the core,on either side.)

After you parallel the outputs of the rectifiers with some heavy gauge wire,You will need some filtering caps.Remember,this ain't your average bench supply,you will need mondo filtering.I currently only have a little over 0.12F on there.You could use up to 1Farad for better filtering.Use heavy gauge wire for all connections.Use a 3 prong line plug,with 14awg conductors.Put it all in a metal enclousure for shielding,you may want to consider magnetic shielding around the transformer! Make sure your ground connection is secure,and makes good contact with the transformer frame. Use a heavy power switch,and a 15A circuit breaker or fuse (this can all be scrounged from the same old microwave.) and include a small "PC" fan in the enclosure. And remember,This thing will draw a fair amount of current,and there will be a huge surge when it is first switched on,to charge the caps! (you could use a high power resistor in series,and switch it out of circuit after a few seconds,to limit the surge,and bring the caps up to voltage slowly.)
The bridge rectifiers,or other rectifiers should be mounted on an adequate heatsink. I put each bridge on a small CPU heatsink with some white grease,and they hardly get warm.Under heavier loads they get a bit warm,but a small fan will keep them nice and cool.
The transformer will run the hottest,due to the magnetic shunts.A fan is advisable.

Here's a couple pics of it. It's pretty crude,screwed,and zip-tied together on a plank of pine.I'm still searching for a metal enclosure large enough to hold it all. I have since replaced the bundle of 6 caps,with just two 11,000uf 63V caps. (The other capacitors are mounted on my subwoofer.)


PIC#1  You can see the 10AWG "jumper cables" I made up for battery charging/jumpstarting in the background.
(Yes,I've jumpstarted my old chevy V-8 with it!)

 PIC#2 from the top.

After taking my advice,my friend built up one of these,and uses a 600W amp with his subwoofers!
I think he used #12awg wire (dual secondaries) and 35A bridge rectifiers,along with about 0.1F worth of filtering caps.

These supplies might also be useful for light arc-welding.. *Be very careful not to short out the supply*  Seriously!
A penny shorted across the capacitors "buss bars" would result in a small explosion!!
(Don't ask me how I know this!!)