Electronics > Beginners
What happens if a transformer that get less voltage then rated for?
<< < (3/5) > >>
FriedMule:

--- Quote from: IanB on May 21, 2018, 02:15:24 am ---If you take a transformer and supply it with one quarter of the designed primary voltage, won't this reduce the magnetic flux in the core by a significant amount? And won't this reduce the VA rating of the transformer proportionally? I do not know the theory behind this, but surely something has to give in this scenario?

--- End quote ---

You are correct, something gives.
If you put less voltage in, you get less voltage out but the current stay the same.

i.e. a transformer to 240V -12V 2A is a ratio of 1:20  (240V/12V = 20) so 120V (120V/20 = 10V) but it can only deliver the same amount of amps so in the end, you only gets half of the power out with halv voltage.
FriedMule:

--- Quote from: Brumby on May 21, 2018, 02:33:31 am ---
--- Quote from: FriedMule on May 21, 2018, 02:05:34 am ---the price difference between a 600VA and a i.e. 750VA seems really high.
But you would mean it is equally good solutions 600VA 300V and 750VA 240V?

--- End quote ---
Ignoring efficiencies for the moment:
 
A 600VA 300V primary transformer will have a maximum primary current of 2A.  When run at 240V, this maximum current should not be exceeded, as that has been the design value for the wire in the primary.  This effectively gives you a 480VA transformer.

Secondary voltages also need to be adjusted.  If you want 30V off your (nominal) 300V transformer, then you need to have nominal secondary voltages of 37.5V  (30 * 300/240).

For this derated transformer (480VA) supplying two 30V secondaries, you will only get 8A out of each of them.  If this matches you needs, then by all means you can run with it.

--- End quote ---

My thought was this:
600VA with 240V in and about 60V 10A out, split in two = 30V x 2.
Therefor 600VA 300V in 75 out, split in two = 37,5V about 10A.

Is that correct?
tautech:

--- Quote from: FriedMule on May 21, 2018, 02:43:44 am ---My thought was this:
600VA with 240V in and about 60V 10A out, split in two = 30V x 2.
Therefor 600VA 300V in 75 out, split in two = 37,5V about 10A.

Is that correct?

--- End quote ---
Where will you obtain 300V from when Denmark mains is 230VAC ?

What do you need 2x 37.5V 10A supplies for ?

Please tell us more.
FriedMule:

--- Quote from: tautech on May 21, 2018, 03:21:06 am ---Where will you obtain 300V from when Denmark mains is 230VAC ?

What do you need 2x 37.5V 10A supplies for ?

Please tell us more.

--- End quote ---

There is no ware in Denmark that you cab get 300V just out of the wall, the standard is 240V.
What I am doing, are to order a transformer that have 1/4 time larger in and out, then I need.
And that way, try to avoid heat, saturation and other of the bad side effects that else would be if you run it by nearly max voltage.
Brumby:
Starting with a transformer rated at 300V primary and 37.5V secondaries.

Run it at 240V primary voltage, secondaries now deliver 30V.

However, to get 10A out of both secondaries, the primary current would have to exceed 2A - which for a 600VA, 300V transformer is more than the design current for the primary.
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod