Hi I have a transformer that I want to increase the output voltage by extending the secondary windings
the transformer has taps at 20.4-16.5-0-16.5-20.4 vac
so if I wind back and cut off the copper wire back to the 16.5vac tap on both secondary windings counting the number of turns as I go
the number of turns = 4v ( 20.4-16.5= 3.9)
if I then attach a length of the same gauge copper wire to the tap at 16.5 and triple the amount of turns per side will this give me about 28vac x2 ?
also the transformer is 50mm x 100mm any guess at the VA rating ?
the transformer has taps at 20.4-16.5-0-16.5-20.4 vac
so if I wind back and cut off the copper wire back to the 16.5vac tap on both secondary windings counting the number of turns as I go
the number of turns = 4v ( 20.4-16.5= 3.9)
if I then attach a length of the same gauge copper wire to the tap at 16.5 and triple the amount of turns per side will this give me about 28vac x2 ?
also the transformer is 50mm x 100mm any guess at the VA rating ?
An externally hosted image should be here but it was not working when we last tested it.
why not just add it to the 20volt tap instead?
seems easier to just add some turns than to dismantle and then add to get to 28 volts...
seems easier to just add some turns than to dismantle and then add to get to 28 volts...
yes I think that would be the best option
I was thinking about removing the wrapping and soldering the extra wire to the 20v tap and cut off the fiy leads to the 16v and 20v tap so I only have 4 secondary fly leads
then re wrap the transformer with black cloth handlebar tape
I was thinking about removing the wrapping and soldering the extra wire to the 20v tap and cut off the fiy leads to the 16v and 20v tap so I only have 4 secondary fly leads
then re wrap the transformer with black cloth handlebar tape
is the hole in the middle free? if so, no need to remove anything, just wrap additional turns and you are good to go...
yes it is free
cool so I can just add to the 20v tap until I get my 28v I will be using the same gage wire
cool so I can just add to the 20v tap until I get my 28v I will be using the same gage wire
I guess glen does not know the turns-per-volt rating for this particular transformer and tries to find it out that way.
No need to go that far, just wind, say, 10 or 20 turns of *any* wire, even plastic hookup wire around that core, measure voltage and then divide t/V (turns/Volts).
Then it´s easy to calculate needed turns to reach desired voltage.
No need to go that far, just wind, say, 10 or 20 turns of *any* wire, even plastic hookup wire around that core, measure voltage and then divide t/V (turns/Volts).
Then it´s easy to calculate needed turns to reach desired voltage.
done
job done just need to get some black cloth self adhesive tape to wrap it in both winding are at 28.8vac
job done just need to get some black cloth self adhesive tape to wrap it in both winding are at 28.8vac
amps
not sure if my meter bottomed out at 10 amp as this is as high it will go!
any guess at what va I am getting ?
An externally hosted image should be here but it was not working when we last tested it.
just rigged up a load to see how many amps I can draw from it and very surprised at the results not sure if my meter bottomed out at 10 amp as this is as high it will go!
any guess at what va I am getting ?
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
your secondary VA = 2 x 28 x 10.6 = 593,
keep in mind that that is the current into a resistor load...
with the rectifier and psu and amp loads, that will change...
you may also want to put that ammeter in the primary leg,
you can then know the traffo efficiency at such loads...
keep in mind that that is the current into a resistor load...
with the rectifier and psu and amp loads, that will change...
you may also want to put that ammeter in the primary leg,
you can then know the traffo efficiency at such loads...
Looking at the case with both windings in series.
You measured 10.16Aac around the circuit.
The load is 8r0||8r0 = 4r0.
The voltage across the 4ohm load is 10.16*4 = 40.64Vac. Did you measure this?
The output during the test is 10.16Aac * 40.64Vac = 413VA
The regulation is ({28.8+28.8} - 40.64) / 40.64 = 41.7% This should be somewhere between 5% and 9% @ maximum rated output.
Your transformer is massively overloaded.
And you are pushing 413VA through 200W of load ! What temperature is inside those resistors? Enormous?
You measured 10.16Aac around the circuit.
The load is 8r0||8r0 = 4r0.
The voltage across the 4ohm load is 10.16*4 = 40.64Vac. Did you measure this?
The output during the test is 10.16Aac * 40.64Vac = 413VA
The regulation is ({28.8+28.8} - 40.64) / 40.64 = 41.7% This should be somewhere between 5% and 9% @ maximum rated output.
Your transformer is massively overloaded.
And you are pushing 413VA through 200W of load ! What temperature is inside those resistors? Enormous?
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Find two more 8r0 100W resistors.
Wire them in series parallel for an effective 400W 8ohms load.
Now apply the 8ohms as a load to the two series secondaries.
measure the AC current and the AC voltage.
Calculate the VA = Vacoutput * Iacoutput.
Calculate the regulation = (Vout open circuit-Voutloaded) / Voutloaded.
A better way to measure output current.
Wire 16 1r0 1% 600mW resistors in parallel. Reff=1/16th ohm = 0r0625
Allow a gap between each resistor.
If the output current is 7Aac, then the loading on the 0r0625 is Iac² * Reff = 7*7*0.0625 = 3.0625W
The loading on each 1r0 is 191mW. These will warm up but should not get hot if well ventilated and should stay fairly close to their rated resistance.
Now measure the voltage drop across the 0r0625 during the test. Expect ~440mVac
Iac = 440mVac/0r0625 = 7.04Aac
Wire them in series parallel for an effective 400W 8ohms load.
Now apply the 8ohms as a load to the two series secondaries.
measure the AC current and the AC voltage.
Calculate the VA = Vacoutput * Iacoutput.
Calculate the regulation = (Vout open circuit-Voutloaded) / Voutloaded.
A better way to measure output current.
Wire 16 1r0 1% 600mW resistors in parallel. Reff=1/16th ohm = 0r0625
Allow a gap between each resistor.
If the output current is 7Aac, then the loading on the 0r0625 is Iac² * Reff = 7*7*0.0625 = 3.0625W
The loading on each 1r0 is 191mW. These will warm up but should not get hot if well ventilated and should stay fairly close to their rated resistance.
Now measure the voltage drop across the 0r0625 during the test. Expect ~440mVac
Iac = 440mVac/0r0625 = 7.04Aac
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while it may appear so, transformers can actually be overloaded,
but thing to watch out for is the core temperature rise.....
and since sine waves are involved, as long as the temp rise is within reason
and the duration of overload is only for a short time, then this can happen...
resistors are easy loads, they do not distort the current waveforms
the way rectifier circuits do...
for audio applications, i doubt that your traffo will ever be overloaded,
clipping will probably set in first and you will have to back down on volume...
thanks guys was going to make 2 transformers but one with a 6x 10,000uf cap bank I think 1 will be enough its only running 2 nap 140 clones
cloth wrap
and as a added bonus the el chepo amp is sounding very good with 100uf wet tants in the feedback
An externally hosted image should be here but it was not working when we last tested it.
wrapped in loom tape very happy with the results and as a added bonus the el chepo amp is sounding very good with 100uf wet tants in the feedback
An externally hosted image should be here but it was not working when we last tested it.
heat removal can be a problem with power transformers - so any electrical insulation used should try to have good thermal conductivity
Sorry if this too elementary but hey, that's my level! I wonder about the original outside plastic wrap. Now that it's covered with more winding and outer tape, is there chance of melt or fire if the transformer is run hot?
Thanks
Thanks
fuses should take care of this...do not worry too much, listening to music draws little current than what was tested using a resistor load....
toroids uses mylar films of about 10mm width all throughout, separators for primary and secondary coils,
they are not even dipped in varnish....dismantling is very easy....at least from my experience..
and the good news is, the dismantled copper can be reused....
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