Electronics > Beginners
Estimating transformer current from L, ESR, R, V for Isolation transformer
(1/1)
lordvader88:
I have a big transformer from a 1970s floor model Zenith TV. There's 3 secondary windings
1 is a 6V heater filament I think. 1 has seven outputs, from 5V to 24, 50, 90, and even 250V
The 3rd is pretty much 1:1, just 2 wires. Using a proper LCR meter I measured it and the primary at 100Hz
The pri is
Lseries=240mH @100Hz
ESR=30.2O @100Hz
DC resistance is 6.2O
The sec. is
229mH
26.6O
4Ohm
I could measure the capacitance but I just put away the meter. There's a lot of transformer eq's, and I don't know anything on the magnetic side of this.
I don't want to burn it out just trying a 100W light blub, but doesn't it look like a lot of the power is meant to go through that winding ?
And should I dead short the other 2 windings (to themselves) and just try a light bulb ?
Jwillis:
Really depends on the gauge of wire used for each winding.Generally the the high voltage secondary will have a very low current.Measuring the inductance and capacitance really won't tell you much.
The measurements you need to do is the gauge of each winding on the secondary.The gauge of the primary will usually be matched to the VA requirements.or a bit better. The core area will will be the maximum VA allowable before core heating occurs.This measurement is higher than the total requirements of the secondary winding's.
Draw a schematic of the winding's .Measure the gauge of the wire for each winding.
You can use the Maximum Amps for Power Transmission of 700 circular mils per amp .Or usehttp://www.litz-wire.com/New%20PDFs/Fusing_Currents_Melting_Temperature_Copper_Aluminum_Magnet_Wire_R2.011609.pdf and calculate 8% of the fusible current rating of the wire gauge.This will give you a ball park figure of a safe workable amperage through the winding.
Measure the width and length of the center core and calculate the area . Download a simple stand alone program called Xformer Designer. Its free and open source.Enter known parameters and it will give you fairly descent information about your transformer. The flux is usually around 50000 to 60000 lines per square inch for laminate cores.
I use this information often and all my rewinds operate within exceptional specifications.
lordvader88:
Yeah this is all sealed up in a nice can.
I ran a 40W bulb and the output drops from 115.5V to 112.5V, I never tried a 100W yet, but I guess this winding won't be much good for much more than that.
I need to let it sit and watch the temp, but I guess that's no real guarantee either. The wire's insulation could be melting off before this massive thing heats up.
Most of the power has to go to the other other rails, I'm just disappointed.
lordvader88:
With a 100W bulb it drops to 104VAC
Navigation
[0] Message Index
Go to full version