# Consider a transformer with winding ratio of 1 : 10

1. Feb 5, 2010

### Curious007

Just out of curiosity : Consider a transformer with winding ratio of 1 : 10.

What happens when AC 120 v is applied on primary and on secondary we apply DC voltage of 120 v from a battery source is series or in parallel? What will be the output in both cases?

2. Feb 5, 2010

### waht

Re: Transformer

It's going to blow up.

3. Feb 5, 2010

Re: Transformer

Well, certainly putting any battery in parallel with a transformer secondary sounds like a recipe for trouble. Typically large DC and AC currents would flow, and probably both transformer and battery would be destroyed. This is not something you should try at home.

The battery might more safely be put in series with the secondary, as long as anything completing the circuit had sufficiently high impedance / resistance to restrict the current to a safe level.

4. Feb 5, 2010

### Curious007

Re: Transformer

What if the secondary of that transformer is designed to withstand against the very very High Current and Voltage?

5. Feb 5, 2010

Re: Transformer

I suppose that's possible, e.g. in the case of a transformer with very large current ratings relative to the battery short-circuit current. Transformers can be quite intolerant of DC current though, as it tends to cause core saturation.

However, in the case of a huge transformer and small battery the transformer might survive, but the battery would pass a large DC current due to its own voltage, limited only by its own internal resistance and that of the secondary winding. There would also be an AC current, perhaps about ten times as big from the figures you quoted.

The battery could be expected to heat up rapidly, generate gas internally, and probably boil its electrolyte. Actually I think the last poster summed it up pretty well. DO NOT TRY THIS.

6. Feb 5, 2010

### sophiecentaur

Re: Transformer

This sounds a pointless question. It's yet another "What happens when an irresistible force meets an immovable object?" question. If you were to state the specs of the transformer and the battery then it might be possible to tell which will die first but to what end?
There are so many ways of constructing a smoke-making machine which are more convenient. Try a bonfire in the back garden.

7. Feb 5, 2010

### waht

Re: Transformer

Assuming the input AC can supply unlimited power, 1200V AC will be induced in the secondary coil.

There is no standalone 120V battery. Such voltage would have to be built up from many battery cells in series, and each having its own internal resistance. So lets assume the total internal resistance adds up to 10 ohms. To AC voltage, the impedance of the battery appears as a short having only internal resistance.

So the AC current through the battery would be approximately 1200V/10 ohms = 120 Amps AC

It would destroy the cells well before delivering 120V DC.

8. Feb 7, 2010

### m.s.j

Re: Transformer

Regardless some mentioned quantity, conceptually if transformer has enough capability for withstanding of over current and over voltage (without any saturation), the problem can be simplified to connection of (parallel or series) two ideal ac and dc voltage source. In practical view it is related to voltage sources technical characteristics and their ability for over current withstanding.

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9. Feb 10, 2010

### MThornton

Re: Transformer

I have seen some larger commercial battery chargers (old designs) which incorporate a heavy-gauge DC series winding from the output, into the main transformer. The idea was that as the charger's DC current approached the charger's design current limit, the transformer iron was deliberately saturated, and provided a magnetic voltage regulator of sorts.
Modern electronic chargers are much better.