Last night, I picked up a huge copier someone in my neigbourhood had thrown out. One of the many useful parts is a transformer I'm hoping to use to power up a T-amp. It has 3 secondaries, 26V at 1A, 26V at 1.5A, and 10V at 1A.
I'd like to connect the two 26V in parallel to get 2.5A. AFAIK, there's only ONE RIGHT way to do it, so that I don't end up with the coils connected in the opposite way. I will use an autotransformer to identify the secondaries, but how do I figure out which ends of the 26V coils to connect together?
Sorry for the noob question. 😱 TIA - ardo.
I'd like to connect the two 26V in parallel to get 2.5A. AFAIK, there's only ONE RIGHT way to do it, so that I don't end up with the coils connected in the opposite way. I will use an autotransformer to identify the secondaries, but how do I figure out which ends of the 26V coils to connect together?
Sorry for the noob question. 😱 TIA - ardo.
It doesn't matter which way you hook it up, either way will hurt the transformer.
What you want to do is run each secondary into it's own bridge diode set and then you can connet the two DC lines together.
What you want to do is run each secondary into it's own bridge diode set and then you can connet the two DC lines together.
Hi Ardo
If both secondaries have exactly the same voltage (same number of turns), it is perfectly acceptable to connect them directly in parallel.
Here is how you can proceed to make sure it is the case and to find the right phase of the windings.
You pick one wire of each winding and you connect them together; you measure the voltage between the two remaining wires: you have two possibilities, either you read 52V, meaning the windings are in series (NOK for you), or you read approximately 0 (OK for you). If the residual voltage is small (<200mV~), it means both windings have the same number of turns, and it's OK to to short the wires together (the residual mV's are due to flux heterogenoities and are harmless).
If on the other hand a difference exists and is below 1.5V, you can use two rectifier bridges and a small resistor in series with the winding having the highest voltage; something around 0.47ohm would be suitable.
LV
If both secondaries have exactly the same voltage (same number of turns), it is perfectly acceptable to connect them directly in parallel.
Here is how you can proceed to make sure it is the case and to find the right phase of the windings.
You pick one wire of each winding and you connect them together; you measure the voltage between the two remaining wires: you have two possibilities, either you read 52V, meaning the windings are in series (NOK for you), or you read approximately 0 (OK for you). If the residual voltage is small (<200mV~), it means both windings have the same number of turns, and it's OK to to short the wires together (the residual mV's are due to flux heterogenoities and are harmless).
If on the other hand a difference exists and is below 1.5V, you can use two rectifier bridges and a small resistor in series with the winding having the highest voltage; something around 0.47ohm would be suitable.
LV
Seeing as one is 26v at 1A and one is 26v at 1.5A I don"t think each secondary has the same Turns (or maybe the same Turns but different Gague Wire).......
😉
😉
Hi,
two identical bi-fillar wound secondaries can be paralleled.
I would not parallel two non identical secondaries, even if they are the same voltage.
I recommend that you add a small series resistor (0r1 to 0r47) in each secondary and then rectify each secondary separately. Then parallel the outputs into the smoothing capacitors.
The total VA of the transformer is 26+39+10=75VA. But you are using only part of that. Would it be better to buy the correct transformer?
two identical bi-fillar wound secondaries can be paralleled.
I would not parallel two non identical secondaries, even if they are the same voltage.
I recommend that you add a small series resistor (0r1 to 0r47) in each secondary and then rectify each secondary separately. Then parallel the outputs into the smoothing capacitors.
The total VA of the transformer is 26+39+10=75VA. But you are using only part of that. Would it be better to buy the correct transformer?
no.
= somewhere in the range between 0r1 and 0r47.
Try a variety, starting with the highest value and see what voltage drop you get. You may find it works just fine at either end of the range. It may be that the lower VA winding requires a resistor about 50% higher value than the higher VA winding. That way you should get about the same voltage drop across each resistor when drawing proportional currents from the respective windings.
Andrew:
I guess I didn't phrase that clearly. I am not that familiar with that style of labelling.
By 0r1 do you mean a 0.1 ohm resistor or a 1 ohm resistor?
And by 0r47 do you mean a 0.47 ohm resistor or a 47 ohm resistor?
I'm guessing the larger numbers but just trying to make sure. 🙂
I guess I didn't phrase that clearly. I am not that familiar with that style of labelling.
By 0r1 do you mean a 0.1 ohm resistor or a 1 ohm resistor?
And by 0r47 do you mean a 0.47 ohm resistor or a 47 ohm resistor?
I'm guessing the larger numbers but just trying to make sure. 🙂
AndrewT said:
Paralleling non-bifilar windings is no problem; the difference with the bifilar situation is the higher leakage inductance between the windings, but far from being a problem, it is rather an advantage: in some cases a difference of one turn can be accomodated without excessive circulation currents.
LV
OMG, the e-mail notification didn't work,I'm glad I just decided to browse this thread. Thank you all for responding. I didn't expect anything but a simple Yes or No answer, but I was wrong... 😉
The problem with buying a new transformer is very simple: $70 or so Canadian. The transformer I scavenged may not be ideal, OTOH, I don't mind seeing it go up in smoke. As long as the amp is OK, of course.
Actually, the 65VA that I can get out of it is less than perfect, what I really need is 160VA.
Next step: take apart that blown Sony 600W receiver & see what it has. 😀
Thanks again - ardo
The problem with buying a new transformer is very simple: $70 or so Canadian. The transformer I scavenged may not be ideal, OTOH, I don't mind seeing it go up in smoke. As long as the amp is OK, of course.
Actually, the 65VA that I can get out of it is less than perfect, what I really need is 160VA.
Next step: take apart that blown Sony 600W receiver & see what it has. 😀
Thanks again - ardo
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