Two 110V devices on a 220V outlet

Is there a way to wire 2 separate devices made of 110V power transformers to use them on a 220V outlet?
Like for instance wiring the primaries of the 2 devices' transformers in series and supplying them with 220V ?

saint gillis said:

Is there a way to wire 2 separate devices made of 110V power transformers to use them on a 220V outlet?
Like for instance wiring the primaries of the 2 devices' transformers in series and supplying them with 220V ?

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That actually might work but it would require some surgery. You could wire the two primaries in series as you say and then parallel the two secondaries. But you can only have one rectifier. So you would have to basically remove the diodes / rectifier from one supply and then jumper the inputs of the two supplies together. Technically I think that would work. But it's kind of a kludge and potentially dangerous (are you going to put both in the same enclosure?).

Are you sure the primaries don't already have split primaries? That would be cleaner.

No I was just thinking...
It's 2 separate devices, so I will end with a 220 to 110 transformer...

The "two devices" must be IDENTICAL, every bit of current.

Two 115V lamps both same Watts and same brand and lot will work in series on a 230V supply.

Two "same" electronic devices may have slight differences in start-up current surge. A similar problem was the death of many tubes in series-string heater tube TV sets.

Two different devices: once I had a 100W mixer and a 1,000W teapot on a split 230V/115V circuit and the center-tap got loose. The tea was cold and the mixer EXploded. In recreation I observed 160V on the 115V mixer, and it may have been worse in fact.

230V-115V transformers are not THAT expensive. Certainly cheaper than one smoke-bomb.

Back in the day as a small manufacturer I could buy dual primary transformers that had two identical 115VAC windings. We could put them in series for 230VAC markets and in parallel for 115VAC market.

I wouldn't try this with separate transformers on different cores, but with two identical windings in the same transformer it worked fine. 

JR

PRR said:

The tea was cold and the mixer EXploded.

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Hahaha awesome!

saint gillis said:

Like for instance wiring the primaries of the 2 devices' transformers in series and supplying them with 220V ?

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You should not do that in any case.

A transformer with multiple windings can do that.
Let's suppose the 2 devices have exactly the same transformer model. Is the problem that the windings are on separate cores?

I'm rolling around the floor laughing  from PRR's analogy ,  ;D
No such thing as a stupid question in any case ,better safe than sorry when it comes to live mains power.  respect the power .
I think you kinda kicked yourself in the ass by asking the question St Gillis , of course you have to consider V=IxR if you want to share the volts evenly .You knew that too 

Good point about series connected heaters in vintage radios ,I notice the sets that live longest are the ones with a properly engineered heater supply , not 'a puppet on a string' supply  where, as one fails the rest are overvolted then disconnected. I remember as a boy my Grandad had this beautifull 'Bush' radio ,its had amazing big bakelite dials with backlit scale ,it was transformerless , no metal was exposed in order to prevent shock hazard ,my fingers were so tiny I could touch the grub screw on the dials , so I actually used get a little tingle of mains leakage off the radio ocassionally  . I have seen other sets along the way where boot polish or wax was used to fill the holes in the dials  , I have to try and see if that old Bush set still resides in my uncles place , Id fit that out with a nice iso transformer and use it myself for another 40 years.

Morning StG , I think if you have identical transformers with similar loads off them ,its worth a try series connecting them ,power it up and see how the volts divide across the two loads .

Lets suppose you take a pair of 110 volt powered monitors ,and gleefully strap them across the mains , now imagine you play the Beatles mixes with hard panned sources ,one monitor is driven to full power while the other remains silent , its not going to be long before 'Heuston we have a problem' and systems are down . I you do want to load share  ,you at least want two devices that draw the same current,same transformer  and with very little fluctuation in load current .

Maybe a nice analogy here is a see-saw ,as one load draws more power the other gets starved of volts until 'Kaboom'  ;D

saint gillis said:

A transformer with multiple windings can do that.
Let's suppose the 2 devices have exactly the same transformer model. Is the problem that the windings are on separate cores?

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No, the problem is when wired in series they spit the voltage based on how they are loaded. Even two identical units may not always present identical loads... (tea is cold on one leg). 

JR 

saint gillis said:

Let's suppose the 2 devices have exactly the same transformer model. Is the problem that the windings are on separate cores?

Click to expand...

What PRR means is that you can't load the secondaries differently. That's why I said you have to wire them in parallel, remove one rectifier and jump the loads together. Then the secondaries will be loaded evenly.

saint gillis said:

A transformer with multiple windings can do that.
Let's suppose the 2 devices have exactly the same transformer model. Is the problem that the windings are on separate cores?

Click to expand...

Yes. the problem is in separate cores where the loads are never equal. When one core is used, the all power is splitted 
between two primary windings equally (not perfectly but close). 

squarewave said:

What PRR means is that you can't load the secondaries differently. That's why I said you have to wire them in parallel, remove one rectifier and jump the loads together. Then the secondaries will be loaded evenly.

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Yup with two Identical units, you could wire the primaries in series, and secondaries in parallel and presumably get good sharing. You would probably also need to turn both units  on/off by a single switch. Note: if the units are not identical don't try this.

Obviously be careful messing around with primary wiring. An external step down transformer is neater, safer, and preserves the resale value of the gear.


JR

A single box all self contained and where the aformentioned caveats appyling to current are respected  is probably feasible ,trying to span this system across two seperate units would be a poor mans job at best and at worst hazardous to life .

Answer us a simple question ,what voltages and currents do you actually need ?

The view was blurry, now I see the light.
Of course each secondary reflects its load to its corresponding primary.
Whereas on a single transformer with several windings, they all reflect to a one and only primary.

Over here you can find small site transformers very cheaply, yellow ones  , you could get one for 20-30 euros ,good for a couple of killowatts ,so will power all your 110 volts stuff very comfortably  it will also most likely  give some isolation from mains noise from other sources too ,a good thing .

big enough to run almost anything ,very safe with integrated cut out in case of faults , lasts a lifetime in the domestic environment ,job done.

Thanks, I have 110v transformers, I was just asking for the sake of understanding, and now I do better, so thanks to all of you.

Just one last point I thought was worth mentioning ,be aware that most smaller transformer based 110 volt adapters arent in fact galvanically isolated on the secondary side ,its a tapped choke or autotransformer .

Wouldn't it be easier to buy a stepdown transformer