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 Basic building block question 
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Joined: Sat Jun 16, 2012 3:00 pm
Posts: 15
Post Basic building block question
Just bought Kit 83, Universal dual polarity 1 amp power supply, and even though writing that seems to answer my question, reassurance would be good. Directions state a 7VA transformer with center tap should be used for the AC side. So I'm thinking a 120 VAC input, to +/-12 VAC with center tap out at 1 amp, should work for say a small box of 4 euro rack modules.


Sun Dec 08, 2013 10:10 pm
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Joined: Sun Nov 09, 2008 2:49 pm
Posts: 726
Post Re: Basic building block question
Here's a transformer listed on the Mouser website and suited for the regulated twelve volt outputs you require:

http://www.mouser.com/ProductDetail/Ham ... 5C3LH2U%3d

They will also stock the 7812 and 7912 TO-220 style voltage regulator ICs needed to complete the project as a dual polarity 12V DC power supply.

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Mon Dec 09, 2013 10:52 am
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Joined: Sat Jun 16, 2012 3:00 pm
Posts: 15
Post Re: Basic building block question
Thanks Scott,

I think there must be voltage drop across the kit I am not considering, that's why you recommend the 161H34 and not the 161H24.

Also if I were to use the 161 series, I assume tying pins 4 and 5 together as ground leaving pin 3 as +, leaving pin 6 as -.


Mon Dec 09, 2013 9:14 pm
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Post Re: Basic building block question
Yes, there are drops as the AC voltage passes through the rectifier diodes.

When the dual secondaries are series connected, with terminals 4 and 5 joined, this node becomes the center-tap.

Terminals 3 and 6 are the AC voltages and after the rectifier diodes and voltage regulators on the K83 board, result as the positive and negative DC supplies.

Connect 4/5 to the point labeled CT and 3 to one point labeled AC and 6 to the other AC point (either can go to either AC point).

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Tue Dec 10, 2013 11:28 am
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Joined: Sat Jun 16, 2012 3:00 pm
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Post Re: Basic building block question
Thanks alot Scott,

Your advice gives me confidence in my build.

I know it may be a little off subject but what does 1 amp at 24 volts turn into in VA.

I think this is a common point of confusion for many DIYers.

Best regards.


Tue Dec 10, 2013 6:25 pm
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Post Re: Basic building block question
VA and Watts are roughly interchangeable. VA is Volts (RMS) times Amps (RMS), AC terms.

In DC terms, volts times amps is Watts.

Both ways of expressing power availability or consumption.

An internet search listed this site with more detail:

http://electronicdesign.com/energy/what ... lt-amperes

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Scott Lee
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Wed Dec 11, 2013 12:59 pm
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