This may be a stupid question, but if i have 2 indentical +/-26VAC tranformers and i want to build a powerful gainclone (BPA200 type) yet i dont think the transformers up capable of delivering the power on thier own...
Is it possible to parallel them somehow to double the supply current?
Thanks...
Is it possible to parallel them somehow to double the supply current?
Thanks...
in theory you can, especially when the two windings are "identical".
In reality, it is always probamatic to parrallel such low impendence devices as they are usually not identical. In that case, one winding ends us acting as a (low-impedence) load to the other winding.
The way to go might to use a full-wave rectification on one of the transformers to generate the positive rail and a full-wave rectification on the other transformer to generate the negative rail.
In reality, it is always probamatic to parrallel such low impendence devices as they are usually not identical. In that case, one winding ends us acting as a (low-impedence) load to the other winding.
The way to go might to use a full-wave rectification on one of the transformers to generate the positive rail and a full-wave rectification on the other transformer to generate the negative rail.
joan2 said:
No one will not load the other. What will happen if the output voltage is not = is that the transformer/bridge with the higher voltage output will provide all of the current to the load untell the voltage sags down to the voltage of the lower output voltage transformer/bridge. The bridge rec prevents the one transformer from loading the other. If the transformers are the same (same manufacture and part number) this just will not be a problem.
Later BZ
If unequal impedances are likely to be a problem perhaps you could put a 1 ohm resistor (10W sandcast?) in series with each lead of the two transformers. You will loose some power this way but I wouldn't think it would be that much.
If this is a dumb idea, I imagine someone will point that out. I'm only speculating - i.e., I've never tried this.
If this is a dumb idea, I imagine someone will point that out. I'm only speculating - i.e., I've never tried this.
Guys, I've done this lots of times building high current 13.8 volt supplies for HAM radio gear. The biggest one used 4, 10amp., 18 volt AC transformers to feed a series pass regulator. If you use a bridge rec for each transformer and parrellel the output of the bridges it will work just fine. The transformers don't even have to be identical and Optical said that they were so no problem. The resistor in series will work but at a loss in output voltage and is not needed.
Later BZ
Later BZ
sam9 said:
I am not sure if that is needed. As HDTVman had correctly pointed out, in theory, a dominant winding (one that has the highest output voltage) will provide all the current, everything else being equal.
However, in reality, all windings will have some internal resistane / impedence. As that dominant winding provides more of the current, its output voltage will decrease, increasing the chance that other windings may produce current. In essence, the internal resistance of a winding works like a current equalizer to share the load amongst all windings.
If you insist, put the 1ohm resistor ahead of the rectifiers, and make sure it has enough wattage.
Well, I didn't much care for my own suggestion, as you would then have one or two more things to worry about (matching resistances and selecting a high enough watage rating). I like what HDTV man writes because he has actually done the deed, which is always more reassuring than just speculation.
Come to think of it I have a transforer stashed away in the garage I've been trying to find a use for -- maybe this will provide me with a way to do something with it. Hmmmm . . .
Come to think of it I have a transforer stashed away in the garage I've been trying to find a use for -- maybe this will provide me with a way to do something with it. Hmmmm . . .
Hmm, ok i have paralleled 2 transformers each with its own rectifier, but at low volumes the transformers heat up quite a bit and if i put my ear to them they are humming quietly..
They are supposed to be identical but perhaps they are slightly different.. Any idea what could be going wrong?
Should i put a series resistor after each +ve and -ve rectifier output?
(I havent observed what happens yet at high volumes.. its 1am.. -will post my findings tomorrow)
They are supposed to be identical but perhaps they are slightly different.. Any idea what could be going wrong?
Should i put a series resistor after each +ve and -ve rectifier output?
(I havent observed what happens yet at high volumes.. its 1am.. -will post my findings tomorrow)
Volume shouldn't matter. the higher the volume, the higher the current draw. this shouldn't affect heat. i have only had a problem with transformers when my amp was fried and the power was shorted. but it got HOT!
what kind of transformer did you use? torrid or standard (sorry, i don't know the correct name). i have 2 transformers, don't know what kind of them, and have 1 120V primary and 1 8V and one 16V secondary. i connected two of the transformers together in serial, to get +-50V. they hum slightly when in use, but it is normal. they don't get warm until they've been on for about an hour, but only a couple of degrees. the other reason transformers have buzzed for me is when i connected them backwards, to get 120V from 10V. it was actually vibrating and jumping on the table. if you had it backwords, you would have a chip blown up in your face, not a warm transformer.
that info above is based on my experiences, but should be accurate.
what is your transformer rated and what is your amp? you could be trying to draw too much power from the transformer. i have had a 26VCT 1A transformer get warm when powering 2 lm1875 (which it couldn't do). so, unless the thing is like a giant soldering iron, i wouldn't worry about it
what kind of transformer did you use? torrid or standard (sorry, i don't know the correct name). i have 2 transformers, don't know what kind of them, and have 1 120V primary and 1 8V and one 16V secondary. i connected two of the transformers together in serial, to get +-50V. they hum slightly when in use, but it is normal. they don't get warm until they've been on for about an hour, but only a couple of degrees. the other reason transformers have buzzed for me is when i connected them backwards, to get 120V from 10V. it was actually vibrating and jumping on the table. if you had it backwords, you would have a chip blown up in your face, not a warm transformer.
that info above is based on my experiences, but should be accurate.
what is your transformer rated and what is your amp? you could be trying to draw too much power from the transformer. i have had a 26VCT 1A transformer get warm when powering 2 lm1875 (which it couldn't do). so, unless the thing is like a giant soldering iron, i wouldn't worry about it
Heh, it hot enough to worry about, almost too hot to touch, and that was on a very low volume, i tried them out on high volume this morning and they seemed to cool down (!), they are 26-0-26VAC about 120VA or so..
'normal' type to, i dont know the name either..
im gonna try parallelling the outputs before the rectifier this afternoon and see if that keeps them cooler
'normal' type to, i dont know the name either..
im gonna try parallelling the outputs before the rectifier this afternoon and see if that keeps them cooler
I've seen this in a lot of low cost transformers, I'm sure there is a valid theory behind it. When unloaded the transformer gets very hot, but increase the load to near its maximum, and the temperatures come down significantly. Unfortunately it is not practical to run the transformer fully loaded all the time in audio (unless it's PA) so one has to live with the heat.
I suppose there's a relationship between this heat and the size of the core/load specifications of the transformer. Usually oversized/generously sized cores suffer from this more than ones which have smaller cores, but the former also behave better under load. I don't know why it happens though, but I'm sure there is a reason.
I assume these are frame transfomers (EI) as these are all I use.
I suppose there's a relationship between this heat and the size of the core/load specifications of the transformer. Usually oversized/generously sized cores suffer from this more than ones which have smaller cores, but the former also behave better under load. I don't know why it happens though, but I'm sure there is a reason.
I assume these are frame transfomers (EI) as these are all I use.
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