Instructables

Is It OK For Me To Use This Transformer??

I have a few questions about my transformer that I scavenged from an audio amplifier.
I assume this transformer was used to drive big speakers.
This bad-boy weighs in at eight pounds and is pictured below.
The coil has a resistance of 2.2 Ohms. Is that normal?
The Impedance of the transformer @ 60Hz will be higher that 2.2 Ohms, right?


The transformer was wired into the wall outlet (120V AC) with only a #102 (1000pf) ceramic capacitor and a 125V-6.3A fuse in series.
that means that the power comes from the wall goes through a fuse, a transformer, a ceramic capacitor, and then back into the wall.

The fuse was burnt-out so I am bypassing it for now. I fully intend to get one asap.
The #102 ceramic capacitor either isn't working or limits the voltage too much so I am bypassing that as well. What is this capacitor used for?
Some of the voltage levels that I am measuring from the outputs of the transformer are as follows: 5v, 30v, 40v, 60v, 80v, and possibly a 100v measurement. There are a lot of outputs on this transformer so it is hard to remember all of the voltage levels.
Is there anyway to tell how many amperes I can safely draw from this transformer? (I have no datasheet and cannot find one)

Thank you for taking the time to read my plight! I would really appreciate a reply! Thanks!


Picture of Is It OK For Me To Use This Transformer??
pfred23 years ago
 I'd use it. I use this:

http://i.imgur.com/RJS8T.jpg

Your transformer was consuming something like1260 VA when it blew its fuse. That doesn't mean it can put that sort of current out, but something close to it is not out of the question obviously. Being as the fuse is blown, and the transformer lived to tell the tale, minus typical losses of course.

So a ballpark figure of 1000VA wouldn't shock or amaze me. Though good design dictates derating 50% so I think you should be good at 500VA. I'd sure expect about that out of such a device.

I believe the numbers you found were for the entire amplifier unit. So the engineers apparently oversized the transformer a little just to play it safe.

The only way to really know is to load it up and monitor for excessive heat. It can do what it can do.

http://www.engineeringtoolbox.com/nema-insulation-classes-d_734.html

Class A being the worst case. Personally I don't like things to even get that warm, but apparently they can.

Me load testing one power supply I built:
http://img196.imageshack.us/img196/6414/pict0576h.jpg

100 watts no sweat! Based on my observations and what I know about the components 300+ watts would be about what I'd expect. I'd run a fan if I was going to draw that though.

So use your senses, smell, touch and especially your common sense. I mean what's the absolute worst thing that can possibly happen? You can burn your house down and everyone on your block dies? Electronics is more important!

My last mystery transformer session:
http://i.imgur.com/ZmoPu.jpg

Stay wired.

jensenr30 (author)  pfred23 years ago
thank you!
iceng pfred23 years ago
Anyone who uses Simpson 260s is O.K. by me.
Even though the first pic pointer looks like an xfmr
was too close to a smoker then actually self fried :-)

A
pfred2 iceng3 years ago

That transformer is in the tan box in this image:

http://img196.imageshack.us/img196/6414/pict0576h.jpg

See the black zip cord coming off the barrier strip?

See it in this picture?

http://img713.imageshack.us/img713/2244/pict0579s.jpg

Same wire. So no, it isn't fried.

The meter on the right is a 270. Says so right on the scale.
iceng pfred23 years ago
I apologize..... your still O.K.
pfred2 iceng3 years ago
I just back from out there and my still does in fact seem OK to me as of yet. I have it out hiding over by my junk box where those low down dirty revenuers will never find it!


http://img7.imageshack.us/img7/8210/72363334.jpg




iceng pfred23 years ago
Im no clean revenuer either but I see straight deciduous trees. So I figure your
still more South then North in Delmarva where it's soo... dusty one can almost
believe you posed your old simpsons next to the low cost Harbor Freight
CEN-TECH digital red readout and left some finger prints still easy to be traced.
pfred2 iceng3 years ago
When anyone asks me what I make I tell them I make dust, anything else I happen to make is just a byproduct of the dust making process! The Simpsons are magnets for the most rarefied dust it seems. I use them a lot so they mostly sit where they are.

I'm about 9/10s the way south in DE.

Recently I needed banana plugs and I ended up paying more for a pair at Rat Shack than I do for those CEN-TECH digital meters, with leads, and plugs. So I could literally save money buying those meters, cutting the plugs off, and throwing the rest out.

Plus I could save myself the annoyance of being looked at funny in the Shack store asking for banana jacks. The kid claimed he'd never even heard of them. But he sure knew all about cell phones.
samaddon1 year ago
okay! you have got a multi power transformer (in simple words) the three bottom wires are ac1 ac2 and ground and i think 2.2 ohms resistance is very very low resistance you are measuring something wrong use a better multimeter ! the ceramic capacitor is used for decreasing it's pulse in hrtz! you can safely use voltage up-to 40volts cause if you will draw more power it's unsafe cause you can easily die with a shock of 100volts dci also have one i had removed it from my vcd player! and it's a good quality transformer i will cost upto 10 to 30 dollars*!
STFU.!2 years ago
transformers
crazy_jim3 years ago
ok first i am not so good in english so i won't be able to use always the right words ... now about the transformer

well i believe if you are confident about to use it ,first use some mathematics and then your sence of smell ....

if you are familliar with electronics you can find through RLC circuits about how much current the transformer coil can withstand . since you know the capacitor value , the coil's resistance and the alternating current frequency you can calculate pretty much everything ...

(As you asked the capacitor is used to eliminate as much Reactive power as it can since the frequency is always the same . Because the coil creates +reactive power the capacitor is used to create -reactive power ... the only thing you must know is if the capacitor is connected in paraller or in series ... )

the second way to find how much current it can withstand is by using tranformer's formulas ... if you know about how many watts the speakers where and their operating voltage ,with ohm's law you can find the current . so if you use this formula you can find the maximum current you can draw ...

U1/U2=I2/I1

U1 >is the high voltage coil 120v
U2 >is the low voltage coil ?v
I1 >is the high voltage's coil current
Ι2 >is the low voltage's coil current

remember the power in the high voltage coil is the almost same in the low voltage coil . ( tranformers effitiency is about 93% )

so this is about it . Hope it helped ...


jensenr30 (author)  crazy_jim3 years ago
thank you!
jumpingcat3 years ago
yes
sooraj6193 years ago
check for the output current using a multimeter and you may draw about 75%of it, and the voltage range given by you will be ac a diode bridge is required to convert it to dc , capacitor or thermistor(post a picture if you can) may be used to reduce the inrush current( when connected to some appliance)
The "capacitor" may well be an inrush suppressor.

I'd guess at 100VA for that transformer.

Steve
jensenr30 (author)  steveastrouk3 years ago
The audio amplifier i pulled it out of said that it was rated for 230W, 300VA.
That means that it can handle 230 Watts of heat and 300Volt-Amperes of energy, right?

when you say "The 'capacitor' may as well be an inrush suppressor" do you mean that the capacitor was used to limit the amount of energy drawn when the transformer is first plugged into 120V AC mains?

thanks a lot for the answer! I hope i hear from you again!
regards, rtty21
Its probably not a capacitor, its a thermistor.

VA are units of power handling, like Watts, not units of energy.

Steve
iceng3 years ago
Yes, the $82 Panasonic transformer Impedance @ 60Hz will be higher then
the DC resistance. No description just out of stock and price.
With the voltages you describe it sounds like a power supply xfmr.

A
jensenr30 (author)  iceng3 years ago
ok. thank you!
+1 re power supply, especially since you say it was originally connected to the power cable.

Re finding specs: You could try contacting the manufacturer of the unit you dismantled, telling them you've got one that you're trying to repair (as an amateur), and asking whether a schematic is available. That might give you the information you're looking for. Or might not.
jensenr30 (author)  orksecurity3 years ago
I'll try that. thanks!