Mains transformer search

[W DeMarco]

I want to get a new transformer for our SC series 2 psu.  Hope someone might give me the go ahead with the one I picked out.  The manual calls for a 40 volt 150VA secondary.  I have found a triad on digikey that rated at 48 volts 160 VA, can someone doublecheck it for me.  Much appreciated.  http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=237-1349-ND

 

[gyraf]

...what is a "SC series 2" ?

Jakob E.

 

[W DeMarco]

Old soundcraft series 2 console,  the PSU is draining from 40 volts to 2 volts when I plug it into the console.  I think I fried the tranx, heard it making that noise like crumpling tin foil when I rewired the voltage selector/fuse, ooopps.  48 volt is fine but on a seperate transformer.  Its not in the console as our other psu will power it with no problems.

www.vuturevisions.com/series2.jpg

 

[sahib]

Not very much to check. It is a 2 x 24V dual secondary @ 3.33A  each.  If you connect them in series you get 48V @ 3.33A. The VA rating is 48 x 3.33 = 159.84VA.

 

[W DeMarco]

So its a good pick then?  It looks right to me.

Thanks

 

[sahib]

Have you checked the transformer disconnected from the psu board?

 

[W DeMarco]

No, but I know it will provide the right voltage without load.  Im not too sure how to check it otherwise and am not clear what I would check it for.

 

[sahib]

If the primary of the transformer was burnt it would keep blowing the mains fuse and you would get no voltage output at all.

If your power supply is giving 40V without the load but dropping down to 2V under load then I would check the power supply.

Disconnect the transformer secondary from the power supply and check it. If you read 40V then check the power supply.

 

[W DeMarco]

Cool, will do.  The pc board is actually either a prototype or someone must have built it.  Its on breadboard with 317s for regulation where the schemies shows no 317s at all. 

Thanks for the advice!

Will

 

[W DeMarco]

I read up on the 317 regulators and noticed that the max current was around 1.5 amps.  Since the original console supply tranx is at 40v 150VA I am assuming that the maximum current drawn could get up to double the 317s rating.  Would the 317 shutdown if to much current is asked for(40volt at 3.75A)? 

 

[sahib]

If you read the data sheet you should have also noticed that LM317 has overload protection. Hence it is shutting down. However if it was working before then you should also look for why it is not now.

When you thought you fried the transformer did you remove the psu board? One of the common problems of the IC based linear regulators is not tightening it sufficiently to the heat sink and/or insufficient heat dissipation. As soon as you connect the load the case temperature will rise rapidly and it will shut down.

 

[W DeMarco]

Right now the IC's don't have heatsinks.  This psu has never worked for me.  I resort to interchanging the working psu on both consoles.  The supply didnt have a a container screw so I wired a fuse directly in to check that it was operating this is when I heard the tranx sounding off.  Once I got it right the supply seemed to act fine until the load was connected at which point I changed the main caps out and tried to swap out the 317's.  No luck on either.

 

[sahib]

..... The supply didnt have a a container screw so I wired a fuse directly in to check that it was operating this is when I heard the tranx sounding off. 

Once I got it right the supply seemed to act fine until the load was connected at which point I changed the main caps out and tried to swap out the 317's.  No luck on either.

I don't understand what you mean by above.

It is unthinkable not to have a heatsink for the regulator unless you are drawing something insignificant like 50mA. And I do not think it is the case here.

You also have not answered my question. Was this psu supplying the console before? Or have you/somebody else just built it and it is not working?

What are the console supply voltages?

 

[W DeMarco]

OK, I see now.

The console came without a psu.  Our 2nd series 2 has a functional supply that we can use on either console.  The bad supply came from evilbay and was suppose to be a working supply, which it is but someone rebuilt a pcb for it featuring the 317's which makes me think it was used to power one or two modules.  The console requires 48V for phantom and 40 V for everthing else.  Now that I opened it I do see there are heatsinks on the 317's, thought there were not.  On another note a member has offered me the guts of his old PSU for a good price, it will include the original pcb which I hope will just replace the breadboarded one.  He said the regulator is a 3055 mounted to the case through a heatsink.

Will

 

[sahib]

O.K. now.

Maximum ouput voltage LM317 can put out is 37V @ 1.5A. Hence that home made psu is not rated for the entire console.

3055 (2N3055) is a power transistor not a regulator. It functions as a pass transistor to provide the required output current.

Go with the second hand original psu.

 

[W DeMarco]

I think a pic post is in order here.  Ill have to take one when I get home.  LOL, what a shame.  Good ole ebay.  I'll have to look up the function of the pass transistor now.  Thanks for your input, much appreciated.

 

[W DeMarco]

So the pass transistor allows a higher current to be drawn from a linear regulator.  Nice