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!!)
