need help find out peak amps on a transfomer????????????

[prorms]

how do you find the peak amps in a transfomer
example 45VCT + 45VCT 6.94 AMPS VA 625 PART #Y236857

DATASHEET LINK
http://avellindberg.com/pdf/avel_y23_range.pdf

IAM GETTING ABOUT 33AMPS PEAK ON MY MUILTIMETER
HOW I DID THIS WAS PUT AN 1 OHM RESISTIOR ON THE POSTIVE AND NEGITVE LINE AFTER THE RECTERFIER DIODES
AND THEN I USE OHMS LAW
DOES ANY ONE HAVE A SPEARD SHEET OR THE MATH EQUATION
TO FIND THIS OUT BEFORE HAND

[prorms]

If you are drawing 2.88A rms from a Y236603, assuming and input of approx 115V input, with primaries in parallel, you should be reading approx 40V + 40V rms on the secondaries. If you draw less current, the secondary voltage will be higher.

so my guess would be that va rating just adjust with it?

[MikeB]

Why are you doing that to your poor transformer ? Do it often enough and it will be dead.

Your readings mean only that your transformer puts out 1kw when shorted.

Mike

[prorms]

what transfomer would you use for this amp???

[Stuart Easson]

Hi,

The 'peak' capacity of a toroidal transformer is only 'limited' by the impedance/resistance of the windings. By doing a load test, as you have, you can gauge what the combined resistance of the secondary and primary is and guesstimate the absolute maximum current from that...

Rounding numbers for convenience: Assuming you tested with a single 45v secondary rectified to give ~60v: when you connected the 1ohm resistor, the secondary voltage dropped to ~30v (30A/1ohm). Some math tells us that the resistance of the secondary (and the reflected impedance of the primary) has to be ~1ohm, so the absolute max. into a short is 60v/1ohm, lets call it 60A...

Beware, testing in this way is pretty dangerous...you will probably damage your rectifiers if you short the rectified output, and the transformer will be damaged (as in bursting into flames) if the rectifiers survive long enough.

To answer your other question, the 45v secondary voltage you have is slightly high for the rails specified on the schematic, but otherwise it's probably OK. One transformer per channel would give the full output of the amp, but the transformer will get pretty hot at the amps full output, Avel specify the 625va rating at +53c, so you'd have a transformer at approx 75c (175f), more than enough to hurt you or fry the rest of the amp. I'd consider using the next size up (same voltage, bigger VA), it will run cooler and last much longer.

HTH

Stuart

[prorms]

nooooooooo way go up any higher lower the transfomer is 90 vac
and 6.94 amps it get extremly high i sell you the transfomer i got now if want it to stong amps for me just wonder how i can determine the right transfomer peak volts 130 amps 60

[kubeek]

seanmacss, please use at least a little bit of interpunction, I didn´t understand your last post at all!

[Stuart Easson]

Hi,

The amp schematic shows 55v rails, and a 350w rating, I think that is into 4ohms, since 350w RMS into 8ohms needs ~75v rails.

To get 350w into 4ohms, the rms current is going to be ~9.25A, so a 625VA transformer per channel with 45-0-45 secondaries would be too small for continuous full power use, but probably fine for 'normal' music.

If you are planning to make something that is bulletproof, you'd want a larger transformer, 800va or more per channel. You could try the 625va part with 40-0-40 to reduce the peak power output and get more current from the transformer.

HTH

Stuart

[AndrewT]

Hi,
350W power output requires a VA rating of about 550VA.
350W into 4r requires a voltage of about 53Vpk at the load.

The +-55Vdc rails are going to be too low for this.

As Stuart said a 40-0-40 transformer is probably right.
It will give about +-58Vdc when quiescent loaded (about+-59Vdc unloaded) giving some chance of getting nearer your 350W but still well short.

A 625VA 40-0-40 transformer will exceed the +-55Vdc requirement for a single channel.

1kVA would be required for a two channel amplifier.

BTW. the transformer tries to supply the continuous requirement that the amplifier needs.
The smoothing capacitance does it's best to give you the peak current that the amplifier needs.

Between the two is your power diode bridge. It works hard so bolt it to a large metal heat dissipator.

[Nordic]

So no "nice" way of testing this... I have the same scenario...

Sounds like you have to use sharper and sharper needles to find out what the bluntest needle is that wouldn't pop a baloon...

I have a tranny that puts out 35.5VDC x 2 rectified (71V rail to rail). would love to use it with an LM4780 for 2 60W channels... just don't have any way of telling if its enough until I try it...I assume bass will be somewhat lacking if it can't supply enough current.

The amp it came from is so dubious I could not even find it using google... I suppose I could look at the TDK chip it had in to see what kinda power it needed.. that amp was dead when I got it, but I measured 60V on the rails when I powered it up. Could this be a clue in terms of voltage unloaded and loaded...