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# [SOLVED]how to calculate max current that a AC voltage stabiliser can supply?

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#### Mrunal Ahirrao

##### Full Member level 2
I have seen many voltage stabiliser circuits on internet I understood the Buck/Boost principle but I didn't understood how to calculate max current it can supply. I am confused whether the load is on mains or transformer?Please guide me.

Presumed you are talking about a switched transformer stabilizer, it has maximum input and output current. Both ratings must be satisfied. E.g. if the stabilizer is working in boost mode, it's likely that the maximum input current will be exceeded first.

Presumed you are talking about a switched transformer stabilizer, it has maximum input and output current. Both ratings must be satisfied. E.g. if the stabilizer is working in boost mode, it's likely that the maximum input current will be exceeded first.
so you mean to say, that load current depends on max output current of transformer?

That's not what I said.

The transformer or autotransformer rating is always given in VA, and rated to the primary.
Divide that figure by the voltage to obtain the current.

So for a ac voltage stabiliser(tap switching) the max current the stabiliser can supply depends on the Buck/boost transformer?

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That's not what I said.

so what you intended to say? please clarify.

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watch this video I understood the principle from this video. But I am confused that after voltage stabilisation is the LOAD current is drawn from 230VAC mains supply? or Transformer?

As a power supply cannot generate power then Pout cannot be bigger then Pin. In a good switched mode PSU, Pout will be 90 % of Pin. The voltages and currents within the PSU could be anything but the above relationship will hold.
Frank

1. A transformer transforms both voltage and current. If the transformer ratio is different from 1:1, input current (the current drawn from the mains) and output current (the current consumed by the load) are also different. If we neglect magnetizing current and transformer losses for the time being, the currents can be simply calculated Pout = Iout*Vout = Pin = Iin*Vin.

2.If you look at the specification of a stabilizer transformer, you probably find different ratings for input and output current, or may be both are the same. If you determine the available output current for a specific voltage ratio setting, you have to check both ratings. In boost mode, it's likely that the input current is reached first. In other words, the higher the boost ratio, the lower the available output current.

Mrunal Ahirrao

### Mrunal Ahirrao

Points: 2
Thank you FvM now I understand at some point...

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So for example I have 18V transformer with 1A max rated output current and I use it in boost mode to stabilise 200V to 218V , and I want to use this stabiliser with my refrigerator which draws 700mA so this arrangement can supply that much current to run a refrigerator?

It can supply 1A. In an autotransformer circuit, the transformer needs to transform only output current * voltage difference.

Mrunal Ahirrao

Points: 2