transformer identification. need help.

[MrMckSPAZZY]

I was given this transformer, but I can't find anything about it anywhere on the net.

Am I correct in assuming that this is rated at 700VA?

 

[JonSnell Electronic]

I would say 30 v at 6 A = 180V/A

 

[MrMckSPAZZY]

That's what I thought at first too, but I hooked it up with a 2 amp fuse and it blew it when I powered it on. It is working fine with a 6 amp fuse.

 

[dchisholm]

I would say 30 v at 6 A = 180V/A

Power transformer ratings depend on how hot you can allow the thing to get, and whether it must operate on 50 Hz (or lower frequency), but that one is physically too small for 700 VA. As a first approximation you can judge the VA rating of a transformer by comparing its weight to units with known ratings (e.g., http://www.signaltransformer.com/sites/all/pdf/Rectifiers.pdf ). The cross-section area of the core's center leg is also a good gauge, but that information is more difficult to come by.

If it blew the fuse at power-up with NOTHING connected to the secondary it likely has a faulty winding. If you had a rectifier and capacitor connected to the secondary, they might be faulty - or high inrush current may be a normal characteristic of the design.

Dale

 

[Elvee]

Some leads:

http://www.diyaudio.com/forums/power-supplies/240849-how-know-transformer-power-rating.html
http://www.diyaudio.com/forums/powe...ansformer-ratings-cross-sectional-area-2.html
http://www.diyaudio.com/forums/power-supplies/156030-trafo-unknown-power-rating.html
In the case of a multiwinding transformer, you can use this method:
http://www.diyaudio.com/forums/powe...r-each-winding-multi-winding-transformer.html

 

[MrMckSPAZZY]

It just looks small in the picture, it actually stands about 5in. tall.
I called the guy that gave it to me and he said the 6 amp rating is for the primary. I decided to just put a huge load on it and find out. I bridged the +42 and -42 from the caps with a 10 ohm load (a piece of carbon-graphite from a pencil). The graphite immediately turned white-hot and broke in the middle after about 5 seconds. If the secondary was rated for 6 amps it should have burned up, but the transformer was barely even warm so i am pretty sure it is 700VA.
Thanks for the help anyways guys!

 

[AndrewT]

The fuse rating for inductive loads like motors and transformers is:

Fuse in Amps = VA of load / Vac of supply * three.

If you want to close rate the fuse you generally must fit a soft start.

 

[BobEllis]

So you loaded it with 650 W for 5 seconds, it didn't burn up and that "proves" that it is 700 VA? Are you sure you want to stay with that assumption? Transformers can take short term overloads of 2-3 times rated current without damage. What happened to the voltage across your load as you engaged it? How much did it drop?

The 6A notation is between the labels for the secondary. Does it make any logical sense to put the primary current rating there?

You mentioned height. What are other dimensions and weight? I strongly encourage you to follow the links provided above and get a more educated approximation of your transformer's rating. Especially if you intend to use it anywhere near the rating.

 

[gmphadte]

If you can lift 50 Kgs for some time, doesn't mean u can do it all the time.

Gajanan Phadte

 

[pitbul]

Form me, answer is simple:
Secondary voltage is 2x30V=60V, secondary amp=6A, so apparent power is 60x6=360VA.
28V output is part of 30V winding, easely checked with ohmmeter, if there is connection between 30V and 28V output then my assumption is correct.

 

[johansen]

no, that really does look to be a 700va transformer, provided its big enough to be wound with 10 or 9 awg wire for the secondary, and actually measures 5 inches tall.

what are the actual core dimensions in mm?

 

[sonata149]

I too need help to identify (even a guesstimate of) the current capability of the HT section in my multi-winding transformer. I read this thread but being a novice in such matters I would like to know your informed advice.

It is a vintage enclosed-type transformer with the following windings:
Primary: 0 -240V with 5 intermediate taps;
Secondaries: 5.0V @ 2A; 6.45V @ 4.5A; 690/345 (345-0-345) without any current rating indication.

External dims. are: 103 x 106 mm at a Height of 130 mm. It weighs at 5Kg (11lbs) on my commonplace kitchen scales. I measured the dc resistance of the CT sections: 83.3 and 78.3 ohms. I tried the formula Vsq/R using the above data but the result seemed ridiculously high.

From the above data, can someone give me a rough indication as to the current capability of the HT winding. I'm hoping for 160mA to use in an SE project with 2x 807 and 3x 6SN7s as in Triode Dick's 807SE circuit.

Thanks a lot for your help.

 

[Elvee]

From the available data, it looks like the total VA rating is in the 200VA range, and the HV winding ~150VA, around 200 to 250mA AC.

You could cross check the values by also measuring the primary resistance and the core area, if it is accessible enough

 

[sonata149]

Many thanks Elvee for that information.

I checked the resistance across the full primary (0-240V) and it is 9 ohms. Now I always thought that the dc resistance of the primary winding is always greater than that of any secondary winding in a multi-winding transformer. Does this reading match up to your calculations?

Unfortunately I cannot measure the core area as the transformer is completely shrouded and all taps are connected to lugs fixed to the the bottom cover of the unit.

Best regards.

 

[Elvee]

Many thanks Elvee for that information.

I checked the resistance across the full primary (0-240V) and it is 9 ohms. Now I always thought that the dc resistance of the primary winding is always greater than that of any secondary winding in a multi-winding transformer. Does this reading match up to your calculations?

It points to a higher power, perhaps 250VA or 300VA.
Anyway, you are perfectly safe if you draw 160mA.