Mislabeled Signal Transformer?

I'm building a run of the mill +/- 18v unregulated power supply. I ordered a 36V transformer with CT from digikey - a Signal Transfomer DST-6-36. Here is the data sheet:

http://www.signaltransformer.com/Data/Datasheets/1.1-36.pdf

Now, I've got the primaries in parallel, and the secondaries in series, with pins 6 and 7 to ground. The ac off my wall is 125V - the output of the transformer is 48.1V AC, 66.7V DC full wave rectified.

This isn't a 36V CT transformer is it - I think it is the next highest value, a DST-6-48.

Am I getting anything wrong here??
 

error401

Member
2007-03-24 7:54 am
cuibono said:
I'm building a run of the mill +/- 18v unregulated power supply. I ordered a 36V transformer with CT from digikey - a Signal Transfomer DST-6-36. Here is the data sheet:

http://www.signaltransformer.com/Data/Datasheets/1.1-36.pdf

Now, I've got the primaries in parallel, and the secondaries in series, with pins 6 and 7 to ground. The ac off my wall is 125V - the output of the transformer is 48.1V AC, 66.7V DC full wave rectified.

This isn't a 36V CT transformer is it - I think it is the next highest value, a DST-6-48.

Am I getting anything wrong here??
Transformer output voltage is rated under full load. If you're measuring it unloaded, 30% is pretty standard regulation. Under load, the output will drop; at 0.5A you should expect about 36VAC out of it. Unfortunately the regulation is not specified in the datasheet, but I know 30% is a typical value for toroids of this size.
 

AKN

Member
Paid Member
2005-08-01 9:23 am
In the middle of Sweden
cuibono said:
Yeah, it could be unloaded voltage rise, but I doubt it could be that big. Especially when it sits right at 48V, which is the next size up transformer in the series. I think its mislabeled.

I'll power it up soon and see if the voltage drops when loaded...

Hi cuibono,

Hi,

Your unloaded secondary voltage is not impossible at all. I cannot see any regulation specification on the spec sheet you provided so I took numbers from another small 6VA transformer as an example:

Transformer 6VA 2x18V (@170mA), Regulation 25%.

Assuming mains voltage spot on we get maximum unloaded AC:
36*1.25=45V
Add some tolerance and 48V is not far away.