HomeRoast Digest


Topic: 12V Outdoor transformer wiring (2 msgs / 54 lines)
1) From: Mark Cravatts
I was told that 130V was what I needed for a safe boost. Rather than 
buying an expensive variac, or step-up transformer, I thought of using 
an inexpensive consumer grade transformer wired in series with the 
incoming 120VAC.
I discovered that outdoor lighting transformers output AC voltage and 
are isolated.  I did this by purchasing one, taking it home and checking 
it out.
I purchased a 200W unit.  This is good enough for 200W/12V = 16 2/3 
Amps.  The Baby George draws a lot less than 16 Amps with even 132V 
coming in.  It is true that it is important the way the output is wired 
to the 120VAC, as pointed out by David.  In one way, you end up 
subtracting 12V from 120V, leaving you 108V.  The other way, you end up 
with 120V + 12V = 132V.  The only way to know for sure is to either use 
a load that you can notice the difference, such as a light bulb, or by 
measuring the resultant voltage.
This is how it's wired: http://www.cravatts.com/BabyGeorge/transformerwiring.jpg
I wired up a separate outlet so that I didn't have to cut any of the 
power cords.
So there you got it, a $50 12V voltage booster rated at 2200 Watts (132V 
* 16 2/3 Amps)
-Mark

2) From: Aaron
Oooh, the only problem i see with this is.
You are using the 12 volt windings to put your power through, which is 
roughly 120 volts applied. 
Many of the transformers, especially cheapo's like this have insulation 
on the low sided barely rated for the 120 on the other side.
In other words you could end up with a meltdown and a mushroom cloud if 
you are not careful.  Not to mention power up and power down, the 
'spikes' that will go through it as the field collapses can punch tiny 
'holes' into the insulation which eventually will lead to breakdown as well.
Be careful with this thing.
aaron


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