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Old 12th January 2011, 12:56 AM   #1
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Default Edcor Transformer Specs

I'm starting this thread to add measurements I've performed on some Edcor output transformers, so that desingngers can refer to this thread when considering a given Edcor transformer for a design. Other folks are more than welcome to chip in with their measurements.

To roughly characterize a transformer, I throw it on the bench and apply 50V, 300 Hz to the primary. The 50V input voltage ensures a good flux swing so that I can get an inductance reading applicable to real working conditions. I use 300 JHz to ensure that the input excitation is in-band, so that I can get a reasonably accurate number for the turns ratio. Anway, I feed the primary with a 50V, 300 Hz signal, read the output RMS voltage with a DVM, and read the no-load excitation current using a Yokogawa WT210 wattmeter. The transformer primary inductance can be calculated from the excitation current, and the excitation voltage and frequency. All this gets me the turns ratio, so that I can calculate the transformer primary reflected impedance. The turns ratio is also an important number in it's own right, and I generally use that number rather than the impedance to calculate operating end point. for a given design.

Anyway, the first set of numbers is from an Edcor GXSE15-8-5k. With 50V, 300 Hz excitation, the output voltage is 1.998V, so that the turns ratio is 25.02 :1. For the rated 8 ohm output, the reflected impedance at the primary is 5010 ohms, pretty much right on the money. No-load excitation was measured as 1.59 mA. The formula Lp = Vin/(6.28*fin*Iin) was used to calculate primary inductance. Vin = input voltage =50V. Fin = input frequency = 300 Hz. Iin = excitation current + 1.59 mA. This yields a primary inductance of ~17.7H, fairly respectable for a small sized transformer, and no doubt a compromise between low frequency extension and primary current handling capability, limited by saturation rather than overheating.

Next up, I'll post some numbers on one of the bitty XSE transformers.
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Old 12th January 2011, 01:07 AM   #2
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Thank you Wrenchone! Click the image to open in full size.

My experience with Edcor calls for measurement of stray inductance for big transformers. Can you do that?

Also, some small 15K:600 Ohm line level transformers have too low for 15K inductance... Is it a joke, or I misunderstand something?
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Old 12th January 2011, 01:21 AM   #3
tomchr is offline tomchr  United States
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Shorting the secondary and measuring the current would give you the total leakage inductance referred to the primary. Obviously, you'd have to limit the drive signal amplitude when you do this.

I measured some Edcor transformers on an HP 4194A Impedance/Gain-Phase Analyzer and used its equivalent circuit function to calculate the L, R and C from the impedance sweep. I measured the primary impedance when loaded by 8 ohm on the secondary. DC resistances were measured with a 6-digit DMM using a 4-wire setup (Kevin connection). Here's what I came up with:

XSE15-8-5K: Lp = 2.43 H; Cp = 233 pF; Lleakage = 4.66 mH. Primary impedance magnitude when loaded by 8 ohm on secondary: 5.10 kOhm @ 2 kHz. R(DC) of primary: 87.44 Ohm. R(DC) of secondary: 0.264 Ohm.

CXSE25-8-5K: Lp = 13.86 H; Cp = 1.541 nF; Lleakage = 10.32 mH. Primary impedance magnitude when loaded by 8 ohm on the secondary: 4.42 kOhm @ 2 kHz. R(DC) of primary: 80.83 Ohm. R(DC) of secondary: 0.361 ohm.

I'm surprised the primary impedance is 4.4 kOhm not 5.0 kOhm as specified. I ordered two transformers. They both measure 4.4 kOhm. It doesn't make a big difference in real life, I'm just surprised...

~Tom
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Old 12th January 2011, 01:42 AM   #4
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I find that inductance numbers measured at low level excitation aren't too repeatable, and also vary with frequency. That's why I use a high level sinewave source to apply a healthy voltage with real current capability to the transformer primary. I started out using our usual inductance meter, and the numbers I got were way low. We also have an HP4194A at work. I find it very useful for other measurements and for SMPS transformers, but I dont trust the low level measurements with 60Hz transformers. Driving the transformer with a good healthy signal and using the 4194 to measure parasitics may be useful.

I've been wanting to build a saturation tester to apply a fixed voltage to a transformer primary with a mosfet switch in order to look at the current ramp, with a protective current-actuated shutdown to protect the transformer, along with a healthy voltage clamp across the primary. This would be useful to determine the real current rating for a given transformer primary, as well as a way to sort out NOS/unknown transformers. This could be used to evaluate SE transformers as well as determining the volt-seconds rating for a push-pull unit.

Last edited by wrenchone; 12th January 2011 at 01:43 AM. Reason: sp
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Old 12th January 2011, 01:46 AM   #5
tomchr is offline tomchr  United States
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To accurately reflect performance in the circuit, the transformer should have a DC bias applied to it as well.

I haven't had any issues with repeatability of my measurements on the 4194A, though. LCR meters, that's another story...

~Tom
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Old 12th January 2011, 09:11 AM   #6
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Talked to the guys at Edcor the other day and they specified the 25W 5k having 50H primary inductance at 1kHz. Quite a bit from the measured above. Also max current 125mA.
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Old 12th January 2011, 10:52 AM   #7
JLH is offline JLH  United States
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Its seems to me that most of the Edcor designs don't always have as much inductance as I'd like. I had some custom SE transformers wound that have a 15% cathode feedback winding. It was a small 10W model 3.5K : 16/8/4. I used it for a small Class A2 amp for my desk. Anyway, the primary inductance measured in at 13H. Thank goodness for the CFB, otherwise I would have had zero bass.
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Old 12th January 2011, 11:53 AM   #8
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Quote:
the primary inductance measured in at 13H.
If this was the 10W it shouldn´t be to farfetched that the 25W would have the double or more.
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Old 12th January 2011, 11:55 AM   #9
PWR RYD is offline PWR RYD  United States
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I realize this thread is about Edcor's output transformers, but how good are their power transformers? The particular one I was looking at was quite a bit cheaper than the same spec'd Hammond. Thanks.
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Old 12th January 2011, 01:55 PM   #10
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PWR RYD, I have purchased about 4 or 5 power transformers from Edor. Of there 2 were custom to my design. All have been quality built products that have performed right on to where they were sped'd. I believe they are a real quality built product. Mickeystan
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