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question about multiple transformer wiring on primary side
question about multiple transformer wiring on primary side
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Old 7th March 2021, 09:40 PM   #1
CharlieLaub is offline CharlieLaub  United States
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Default question about multiple transformer wiring on primary side

I have some harvested amp boards and transformers that I would like to make use of. The transformers have a single 120VAC primary and multiple secondaries that are used to power multiple amp modules. All these parts were obtained from a multi-channel Crestron CNAMPX-16x60 power amp.

The question I have is how I might be able to use (or not) the same transformers on 220/230VAC mains (European standard). If I will be using two of these transformers, can I simply connect their primaries in series so that each one sees half the AC mains voltage? If I do that, can I leave some secondaries "unused" on one or both transformers?
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Old 8th March 2021, 11:09 AM   #2
duncan2 is offline duncan2  United Kingdom
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A researchgate.net answer---I have never tried it myself but the same question below is from Martin Amegnave- University of Lome.


Its answered by Igor Ivankovic Croatian Transmission System Operator & Michael Hermann -University of Leibniz -Hannover .


For DIY Audio posters they answer Yes but with "qualifications"--please read the qualifications .-


Hello. Can we put the primary of 2 transformers in series and connect them on on network of 220V?
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Old 8th March 2021, 11:37 AM   #3
FauxFrench is offline FauxFrench  France
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In principle yes with the two primary windings connected in series. BUT, there are some very important restrictions! In practice it is not advisable.
The voltages across each primary winding are divided according to how much the secondary windings are loaded. This meaning that if one transformer is loaded less than the other, it has a higher primary voltage, and accordingly also secondary voltage, than the transformer with the highest loading. Then it starts getting really difficult to balance the voltage sharing of the input voltage.
If you have two identical transformers and you connect the primary windings in series (they are assumed identical) and also the two secondary windings in series (they are also assumed identical), then the loading of the two transformers is the same and they share the input voltage pretty well. With two different transformers it is very difficult to control.
So in conclusion - don't do it.

Last edited by FauxFrench; 8th March 2021 at 11:40 AM.
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Old 8th March 2021, 02:47 PM   #4
CharlieLaub is offline CharlieLaub  United States
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I think FauxFrench is getting at what I am concerned about: current flow.

So, yes I have multiple identical transformers of around 800VA-1kVA each. Each transformer has a single 120VAC primary and four (eight wires) identical secondaries which are around 45VAC each or so IIRC. The secondaries are completely independent of each other.

The amp that these were taken from has eight two-channel amp boards. Four of these are powered by one transformer, and the other four by another (identical) transformer. I have both the two transformers and eight amp boards from an amp that I disassembled a couple of years ago, and I also have two other intact amps of this model.

So, here is my dilemma. Let's say I want to use these in Europe on 220/230VAC mains. Apart from getting a step-down autoformer, can I use the two identical transformers, with their primaries wired in series? Each would see 120VAC, half of the mains AC voltage. That seems to pass the sniff test.

What I don't understand for that arrangement is how current is flowing on the primary side of these transformers when current is drawn from the secondary side(s). Since the transformer primaries would be in series, current flow would be identical for both, but not necessarily the current draw from the secondaries. In fact, how does this even work for a single transformer of this type, where there are multiple secondaries which might draw vastly different current at any given time? This I cannot quite figure out in my mind, so I am looking for some background and info about it. Saying "dont' do that" is good, but I am always interested in WHY. I might, you know, learn something.
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Old 8th March 2021, 03:12 PM   #5
scottjoplin is offline scottjoplin  Wales
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Transformers Part 1 - Beginners' Guide to Electronics
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Old 8th March 2021, 04:43 PM   #6
CharlieLaub is offline CharlieLaub  United States
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Quote:
Originally Posted by scottjoplin View Post
You are the absolutely least helpful person so far, by far.
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Old 8th March 2021, 05:06 PM   #7
scottjoplin is offline scottjoplin  Wales
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There are three more parts.
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Old 8th March 2021, 05:13 PM   #8
CharlieLaub is offline CharlieLaub  United States
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Yes, I scanned all of them. It's yet another great Rod Elliot overview for sure, but I didn't see anything for my question per se. Can you be a little more specific perhaps???
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Old 8th March 2021, 05:14 PM   #9
PRR is offline PRR  United States
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question about multiple transformer wiring on primary side
The primary voltages in series will split according to the secondary loads. (Like any series string.) Have you addressed that?
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Old 8th March 2021, 05:21 PM   #10
scottjoplin is offline scottjoplin  Wales
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I thought if you learned how transformers work it would become evident. He writes very well thought out articles that deserve study in my opinion.
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