| JazzzSpazzz |
Greetings,
If a transformer has 2 secondaries (12 VAC @ 10A & 6 VAC @ 4A) and I connect them in series I'll get a 18 VAC, but what is the current? I get 8A by my calculations--am I in the ballpark or just all wet? :confused:
Thanks,
Bret Morrow
Here is the link to it:
http://www.sciplus.com/category.cfm...13&category=138 |
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| Sch3mat1c |
No, current is limited by the lowest rated element in the circuit. That's why fuses work. :D
Tim |
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| JazzzSpazzz |
What if I connected the DC rectified current from 2 trannys (18 VAC x 4A) in parallel? Would this give me an 18 VDC 8A source? ...or should I get another towel?? :confused:
Cheers (& Thanks!),
Bret Morrow |
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| Duo |
To my knowledge, if you connect two transformer secondaries in series, you'll be able to feed as much current as the one with the lowest rating. In your case, if they are both 4A, then in series, the current will be still 4A. This is because in a series circuit, the same current will flow through all parts in order to give up all of it's energy before making a complet flow.
This means that if a coulomb leaves the power supply with 4 joules (will be 4 volts), it will return to the negative side with 0 joules per coulomb, this is because to drop 4 volts accross the circuit, the 4joules per coulomb must be used up.
As for parallel, the current in a parallel circuit is always divided in some way betweent the components paths. If you have two transformer secondaries in parallel, each 4A, the total current output would go to 8A, this is because with 4A in one winding, and 4A in the other, the total is 8.
For your case, putting the rectified outputs in parallel will also do the same thing. Two 4A DC circuits in parallel will deliver 8A.
This also explaines why when you connect two same batteries together in parallel, they will give more current per hour, therefore lasting longer for a certain load than one battery would.
I hope I haven't exhausted you with information here, however, this should help describe what's going on. |
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| Sch3mat1c |
Unfortunately, you can't connect supplies in parallel when they have different voltages, so you're SOL on using them together to any usefulness.
Tim |
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| Duo |
That is for certain.
The reason why electricity works! Voltage difference causes current flow through conductors. ;)
Good I guess if you wanna see some serious current flow in a transformer, but yeah, forgot to mention, only parallel sources of the same voltage.
And if you're paralleling transformers, make sure that the windings are in phase. |
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| JazzzSpazzz |
| quote: | Originally posted by Sch3mat1c
Unfortunately, you can't connect supplies in parallel when they have different voltages, so you're SOL on using them together to any usefulness.
Tim |
Thanks all. I understand that I can't use the 12V & 6V secondaries of the same tranny in parallel, but could I use the series output of 2 identical trannys in parallel, right? In case of the tannies in question--it would be two 18V 4A trannies in parallel to yield 18V 8A.
On a second issue brought up by Duo, after rectification, phase shouldn't matter, right?
I am thinking of a cheap GC for my computer at work using a total of 4 of those trannys--2 per channel. At $2 each, it'll be a bargin--of course there is more cost in the diodes. But will it work??
Thanks in advance & Cheers,
Bret Morrow |
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| Duo |
Well, in DC, there is no longer phase to be observed, but polarity.
As long as the polarity is the same, all is well. I'm sure you understand already how that works.
In AC, you know that the current flow is always reversing its direction. In that case, you want the secondaries going positive at the same time and then negative at the same time.
Got the idea now? |
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| JazzzSpazzz |
Thanks Duo & Sch3mat1c! That fills in some blanks in my mind!
Thanks again,
Bret Morrow |
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| rayban68 |
| Are two trannies in parrallel really necessary for a gainclone? some opinions are expressed in this thread, http://www.diyaudio.com/forums/show...&threadid=32286 see what you think of that. But if you plan on using a lm3875/3886 I can assure you that a single 18v / 4A transformer will be adequate. You'd be better off putting the 4 transformers into 4 amplifiers rather than two. If you can have 4 amps, why settle for two? ;) |
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| peranders |
| JazzzSpazzz, I'll suspect that you can take out a little bit more than 4 ampere if you connect the windings in series. The VA rating is a little bit complicated when you connect like this. The only thing which determine the VA is the temperature of the transformer. |
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| Sch3mat1c |
The only problem is that the transformers will likely be slightly off. Even .1V difference will cause one to supply more current than the other to the DC supply. Just how it works. :xeye: Better than paralleling the windings though since the rectifiers prevent them from interacting directly.
Tim |
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| JazzzSpazzz |
| quote: | Originally posted by rayban68
Are two trannies in parrallel really necessary for a gainclone? some opinions are expressed in this thread, http://www.diyaudio.com/forums/show...&threadid=32286 see what you think of that. But if you plan on using a lm3875/3886 I can assure you that a single 18v / 4A transformer will be adequate. You'd be better off putting the 4 transformers into 4 amplifiers rather than two. If you can have 4 amps, why settle for two? ;) |
Re-reading that thread & thinking about it again, you are right. But its worse than you think--I wanted to try 4 trannies per 1 GC to yield 288 VA. It probably is really, really overkill to use 2/channel. I kinda liked the idea mostly due to its complexness. Even so, 1 per channel (2 per GC) is likely the way to go--enough overhead power & completely separate power pathways for each channel (what ever that's worth). The cost of the trannys--$2 each, is so low that the limiting factor for making more GCs are the other components, not the trannys.
Thanks!
| quote: | Originally posted by peranders
JazzzSpazzz, I'll suspect that you can take out a little bit more than 4 ampere if you connect the windings in series. The VA rating is a little bit complicated when you connect like this. The only thing which determine the VA is the temperature of the transformer. |
Thanks. I doubt that I would even get to the 4A level, but I'd like some headroom to avoid heating the trannys up. I kinda like to wear a belt & suspenders, too. :D
Thanks & Cheers,
Bret Morrow |
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| Duo |
Well, in the case of the outputs in parallel being slightly different voltages, low resistances can be put in their path before they are connected together, like in the output stage of a power amplifier with paralleled transistors.
Not sure, but something in the order of less than .5ohms should help a bit.
This is just a bit of a quick-fix though. There are better ways around it. |
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