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Transformer specs. (Answered)
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MUDGEL:
I want to build a linear power supply.

I’m in Australia so mains voltage is 240 VAC, 10 Amps. I want to have an output of 30 VDC, 5 Amps.

What transformer specs are required to meet my desired output? I did a google search using a variety of the keywords used here but don’t understand about Volt Amps and their significance in spec’ing my desired transformer.

By all means just tell me to get “xyz” transformer or teach me how to work it out for myself.

I hope I asked the correct way. 

Thanks. Mike V.
Jwillis:
 Single phase transformers are wired according to supply either 120 Vac (2 primary connections with single winding),240,Vac (2 primary connection with single winding)or both (4 primary connections with 2 windings). The 4 connection transformers are wired either in parallel for 120Vac or in series for 240Vac.The resistance of both winding's should be equal or very close. The output secondary will have 2 or more connections depending on how its wound and how many individual winding's there are  .Since you only need 30 Vdc at 5 amps you need a transformer with 2 output connections (single winding )with 150 VA minimum and usually is marked according to output(secondary ratings)

S(VA) = I(A) × V(V)

S is apparent power measured in  Volt Amps (VA). I(A) is required out put Amps and (V) is required output Volts.

Generally you want to have a bit more Volts amps to compensate for losses so I would suggest 200 VA -300 VA at 30Volts.I insures you don't over load the transformer at full load.  Having a higher VA won't effect how you power supply operates.But it will be more stable.

Hope this helps.
fourtytwo42:

--- Quote from: MUDGEL on November 16, 2018, 04:38:06 pm ---I want to build a linear power supply.
I’m in Australia so mains voltage is 240 VAC, 10 Amps. I want to have an output of 30 VDC, 5 Amps.

--- End quote ---

The key issue here is you want a DC output, so you will have to rectify and filter the AC output of the transformer depending upon the requirements of your load. So in order to help you fully we need some information about the load.

The rectifier and filter will also effect the required transformer secondary voltage to achieve 30V DC output so is rather important to your transformer specification.

I assume were talking about an unregulated supply here so the operating voltage range of the load also needs to be taken into consideration.
Audioguru:
We need exact specifications, not assumptions.
30V at 5A is a high power of 150W. What will this power supply power?
1) Do you need the voltage to be variable with a voltage adjustment?
2) Do you need the voltage to be regulated?
3) Do you need the maximum current to be regulated with variable adjustment or simple 5A fixed current limiting be OK?
paulflan79:
As stated above, more information is needed as the transformer will provide an AC voltage output that will then need to be rectified and smoothing capacitor's used to make a stable DC voltage however this DC voltage will be higher than the AC voltage coming from the transformer depending on the load and and it's demand's on the power supple and the size of filtering capacitor's used however normally speaking, the higher the better if you've already got them ready to use,

here's a common pic of a full bridge rectifier you will need to use with the transformer,

https://www.dropbox.com/s/6hoiulykbf78iwx/full%20bridge%20rectifier%201.jpg?dl=0

however a quick Google search will provide more information on this matter

Here's a starting point...

https://www.google.com.au/search?source=hp&ei=PhPvW7P8I8jDwQKxiq-wBA&q=increased+VDC+when+rectifying+a+transformer&oq=increased+VDC+when+rectifying+a+transformer&gs_l=psy-ab.12...3864.3864.0.5013.1.1.0.0.0.0.143.143.0j1.1.0....0...1c.2.64.psy-ab..0.0.0....0.CH-_8iaTSxQ
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