Yes.
I didn't check for a voltage drop across the DMM when using it to measure current, though I noticed a significant impact of the series resistance value used when I tested that way, ie. measuring only the drop across that resistor. Eg: using a value of 1R3 showed closer to 150mAac compared to the 400mAac with 0R14.
I didn't check for a voltage drop across the DMM when using it to measure current, though I noticed a significant impact of the series resistance value used when I tested that way, ie. measuring only the drop across that resistor. Eg: using a value of 1R3 showed closer to 150mAac compared to the 400mAac with 0R14.
I don't understand.
Auto transformer! These are not usually adjustable. Maybe different discrete tappings for fixed voltages?
Or is this a Variac?
Are you using two transformers?
One with a variable output voltage?
and a second one ( the Device under test) that has an open secondary with the primary connected to the previous auto transformer?
I can't understand why changing the resistor changes the measured current.
The out of phase component of the resistor voltage drop is so small, it can't significantly affect the overall phase.
What are the actual Vdrop and resistor value when you do the test?
Auto transformer! These are not usually adjustable. Maybe different discrete tappings for fixed voltages?
Or is this a Variac?
Are you using two transformers?
One with a variable output voltage?
and a second one ( the Device under test) that has an open secondary with the primary connected to the previous auto transformer?
I can't understand why changing the resistor changes the measured current.
195mVac across the 1r3 test resistor, 56mVac across the 0r14 test resistor.
The out of phase component of the resistor voltage drop is so small, it can't significantly affect the overall phase.
What are the actual Vdrop and resistor value when you do the test?
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I can see the folly, but under the circumstances?
The multimeter I used is a Fluke 8025A which can withstand its fuse blowing within a circuit presenting up to 600Vrms. Drop across the ammeter is less than a Volt IIRC.
I was using a variac, adjusted under load. Checked again today.. 210mAac.
Transformer weighs 50kg.
So what are the implications of this... Is there a minimum load I should be putting on the secondary? Power factor concerns?
..and of course if I split the primary the losses will change so is there a recommended recourse/compromise if I ensure I will only draw a few hundred VA, that will minimise losses/waveform/noise issues?
210mAac when using 240Vac gives
Xl (X little L) = 240Vac / 0.21Aac = 1143ohms
Xl = 2PiLf
therefore L = Xl / 2Pif = 1143/2/3.142/50 = 3.64H
This is the leakage inductance of the transformer when using 240Vac.
I would expect this to be different if using a different drive/supply voltage.
Did you see Mark's post yesterday for transformer characterisation testing?
BTW,
that 210mA is just bigger than 1% of the maximum primary current of >12Aac
I don't have experience of big 400Vac transformers, but that seems OK to me.
Xl (X little L) = 240Vac / 0.21Aac = 1143ohms
Xl = 2PiLf
therefore L = Xl / 2Pif = 1143/2/3.142/50 = 3.64H
This is the leakage inductance of the transformer when using 240Vac.
I would expect this to be different if using a different drive/supply voltage.
Did you see Mark's post yesterday for transformer characterisation testing?
BTW,
that 210mA is just bigger than 1% of the maximum primary current of >12Aac
I don't have experience of big 400Vac transformers, but that seems OK to me.
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No. I tried searching, which thread would that be? I've been following the diode recovery thread...
So far I'm thinking I'll need a case, IEC socket, fusing at the input, an accessible switch, noise filtering with its own shielding, and an indicator light. Earth from the input bonded to the case, shield and transformer core, and to each output receptacle which would be parallel connected.
Maybe I should fuse the outputs. Maybe I should damp the transformer at the secondary against oscillation. I'd also find it useful to leave the outputs floating with respect to earth. I may further assume that this transformer lacks a thermal fuse but I'm not sure it would be essential here.
first off, did you really intend to say leakage inductance?
secondly, we don't really care what the inductance calculates out to be, because the magnetizing VA's and Watts are measured in watts or VA's per kilogram.
at 120vac input it will probably be 60 milliamps and calculate out to be 7H.
50 watts lost for a 50 kilogram transformer is right on the money for an old E core transformer of that size, running at half the line voltage.
when he takes it up to the intended 465 volts on the stock primary those amps will increase 4 fold and 200 watts no load iron loss is probably expected.
its your choice where to run the core at.
VA "capacity" follows flux density squared. so do eddy and hysteresis loss..
if you don't like the 500VA's of wasted primary magnetizing circulating current you need.. a 6 uf capacitor to cancel it out.
24 uf for the 240v rewind version.
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I did mean to type "leakage inductance".
Now that you have prompted, I see that the shorted secondary test reveals the leakage inductance.
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