Getting the right power XF

hobiesound

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that is a 225 VA transformer. NOT a 225V AC transformer. 225/(2x18V) = 6.25 amps per secondary. Do you really need that much current for 2 x ssl9k ? the primary is rated for 230Vac btw. Look for something with about 50VA. That's about 1.4 amp per secondary so that should be more in line with the ssl9K current requirement. Maybe even a little too much but i don't know the current requirement so jus guessing. Usually you choose a transformer that can supply the current needed for the circuit + about half more.

greetings,

Thomas
 

G-Sun

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Thanks a lot!
It's surly something I don't understand about power transformers.

What's the difference between 225VA and 225V AC?

And why is 225/(2x18V) = 6.25 amps per secondary
and not 225/(2x18V) = 12,5 amps per secondary?

Anyway, 50VA on primary: All three transformers fit in 1U :)

BTW: When I want 18VDC, 18VAC on the power xF secondaries are right, right?

BTW2: Anything I should look for when buying power transformer, regarding quality and hum?
 

Harpo

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G-Sun said:
What's the difference between 225VA and 225V AC?
225VA is the transformers secondary rating as a product of voltage (in RMS) times current.
225V AC is the voltage difference between two potentials, in this case measured in Voltage of AlternatingCurrent.

And why is 225/(2x18V) = 6.25 amps per secondary
and not 225/(2x18V) = 12,5 amps per secondary?
Because this transformer is rated 225VA. Divide this 225VA by the transformers secondary Voltage (in this case 2 separate windings, each with a primary:secondary ratio that delivers 18VAC when the primary winding is fed with its stated input AC voltage), giving 12.5A for the total secondary windings max.current (both secondaries wired in parallel) or 6.25A per each secondary winding. This 12.5A or 2x6.25A is the max.avail.current for 18V AC. The amount of max.avail. DC current is a lot less and depends on the type of rectification used.

Anyway, 50VA on primary
50VA max. as the sum of the secondary AC load.

All three transformers fit in 1U :)
Maybe. Measure the inner dimensions of your case, for usual less than the frontpanel HE minus thickness of case top and bottom panels.

BTW: When I want 18VDC, 18VAC on the power xF secondaries are right, right?
Maybe, but most often yes. (Depends on the amount of your AC mains voltage on a bad day or at an open-air venue, what type of rectification is used, what is the voltageregulators dropout voltage to maintain regulation, what amount of ripple voltage is allowed?) 



(1000 nonsense posts in 6 years and still not kicked off board ::) , thanks to all for tolerating me that long)
 

G-Sun

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Harpo said:
1000 nonsense posts in 6 years and still not kicked off board  , thanks to all for tolerating me that long
Well, not a lot nonsense here. Very helpful indeed.
Thanks a lot!
 

G-Sun

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So..

How do I determine the size of the power-transformer I need for my projects?

I need to sum up the Amper-draw for each component, right?
So, for ssl9k, 2ch with JLM Gobetween it's: Channel-boards x2, Go-between x2, balancing-board x1.
But, how to I calculate that power-draw?
Then I time it with voltage, right? Getting the total VA needed.
The, how much is minimum extra? What's recommended extra? (It's a little more for preamps than other stuff, right?)
 

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