Electrical Transformer

[spamonkey8]

I dug a nice big toroidal power supply from a broken 400w RMS speaker set and I'm trying to get it to work to supply low (relatively) voltage and a decent amount of current. It has three leads on one side and two on the opposite. Red/white and yellow/orange/black in case it matters. The resistances I read are as follows:

 

Red - White 2.1

Yellow - Orange 0.9

Black - Orange 0.9

Black - Yellow 0.9

 

(I don't have any way to measure inductors, so this is a rough guess)

 

Now before I tested this out, I hooked the yellow & orange to 110 VAC wall socket and it, of course, flipped the breaker. How can this be used to step down AC voltage if Ohm's law says that the minimum current that would be drawn would be 52 amperes?

 

If pictures help, I can provide them. Thanks!

[Spyman]

When using AC through a transformer there will be an additional resistance by the impedance.

(Which must be added to the resistance before Ohms law can be used.)

 

The AC current through the primary inductor in the transformer creates an magnetic field which in the secondary inductor creates a new current.

 

The number of laps, (of the wires), between primary and secondary determines the transformation of voltage and current.

 

The power in is the same as the power out, (except for heat losses), so lower voltage out means higher current and higher voltage out means lower current.

 

If the transformer is swiched backwards and power is supported to the secondary then it will raise the voltage instead of lowering it.

 

So if it was used to create 2x40 V AC from 110 V AC and You applied power to the wrong side then the other side would have had approximately 300 V AC.

 

Note: 2x40 is just a wild guess, because 400 W RMS output indicates a voltage of this level.

(Also from 400 W and 110 V I guess about 4 Amperes current in and maybe 10 Amperes out.)

 

When power is connected the magnetic field must first be created which draws a lot of power. The power to create the required magnetic field for this transformation was to much for Your fuse.

(Good for You, be careful or toasted. )

 

From Your post I would guess that Red - White is the primary circuit and the others two secondary circuits connected inside the transformer to get a middle point.

(For creating +40, 0 and -40 DC voltage or similar.)

 

Try to connect the Red - White circuit to the mains instead.

[Douglas]

From your description, it seems like the White/red leads are the primary of the transformer, with the orange/yellow leads being the secondary, and the black being the secondary center tap........The problem is.. the yellow.orange resistance should have been 1.8 ohms.

 

Try putting a 100W light bulb in series with the red/white leads, then plug it in. Measure the voltage across the red/white leads, then measure the voltage across the presumed secondary.

[YT2095]

yeah it reads like a center tapped coil to me also.

 

but as it`s from a speaker, I`de be very doubtfull if it`ll take direct household mains!

it may pay you to use a reactive load in series with the primary, such as a 40 or 60watt mains light bulb, that way you at least limit the current and can guage the drain on the secondary without causing any real damage

[Douglas]

yeah it reads like a center tapped coil to me also.

 

but as it`s from a speaker' date=' I`de be very doubtfull if it`ll take direct household mains!

it may pay you to use a reactive load in series with the primary, such as a 40 or 60watt mains light bulb, that way you at least limit the current and can guage the drain on the secondary without causing any real damage [/quote']Yeah YT, I was confused about the "speaker" thing. But since he said..."toroidal power supply from a broken 400w RMS speaker set" ...I figured it might be a power transformer from a power amp with a speaker. I guess he'll have to clarify.

[spamonkey8]

Douglas's got it. It was from the amp/sub cabinet to a 4.1 system that came packaged. I hooked 120VAC to the red/white and the secondaries were 52 volts between the yellow & orange with the black being the center tap for 26. Whew, I was thinking backwards I saw the three cords and without thinking jumped to ac and a ground for some reason.

 

I just would like to know one thing. How could I find out how much current it can deliver? As far as the system goes, it will take 720W max, 400 RMS. This thing weighs a good 7 or 8 pounds at least...

[spamonkey8]

Oh a whim, I punched in some letters on the side of the unit, and it was made by Ten Pao. The part number isn't listed on the site, but it's TOU543001F0, just for reference.

[Douglas]

Oh a whim, I punched in some letters on the side of the unit, and it was made by Ten Pao. The part number isn't listed on the site, but it's TOU543001F0, just for reference.

Well, if you have 52 volts at 400 Watts, seems like it'll deliver 7 or 8 amps.

[spamonkey8]

Yeah, but as far as efficiency, how much would be lost with heat? Also, could I do something to get 26 volts at double the current?

[Douglas]

Yeah, but as far as efficiency, how much would be lost with heat? Also, could I do something to get 26 volts at double the current?

Since the output is rated at 400W, the losses are already accounted for. Yes, 26V at 15 amps is the same as 52V at 7.5 amps, you have a choice.

[spamonkey8]

Sorry, I solved my own problem. As it is, the secondary *will not* supply any more than ~7.7 amperes.

 

If the max current the given wire can handle is ~7.7Amps from one end to the other (52V) and there is a center tap to give you 26V, there is no way to draw more current. Granted, the lower impedance of the shorter coil will allow you a bit higher current, but not double.

 

If I cut the insulation off the side and find where the center tap is, I can cut the coil wire and solder separate leads to give me two separate secondaries supplying 26V and 7.7A each (technically more, as I said above). I can then choose to wire the two in series for 52V 7.7A or in parallel for 26V 15.4A.

 

Thanks for the help in working through this!