DC transformer amps.

[hartly]

Why does my 9v D.C. transformer only give a max. amps. of 0.22A?.
I've looked inside it and it doesnt seen to have any resistor in
series to restrict the current.
A 6v. battery charger can give out 4 amps.,which proves its nothing
to do with the voltage of input or output.
Thanks.

 

[Andrew Holme]

Why does my 9v D.C. transformer only give a max. amps. of 0.22A?.
I've looked inside it and it doesnt seen to have any resistor in
series to restrict the current.
A 6v. battery charger can give out 4 amps.,which proves its nothing
to do with the voltage of input or output.
Thanks.

It'll be the rating of the transformer and/or the rectifier diodes.
The transfomer core can only handle so much magnetic flux before it
satures. The windings have resistance and dissipate heat. There are
Eddy currents that also generate heat. The bridge rectifier diodes
will be of a similar rating to the transformer. I should imagine your
battery charger is larger and heavier.

 

[Joe McElvenney]

Hi,

Why does my 9v D.C. transformer only give a max. amps. of 0.22A?.
I've looked inside it and it doesnt seen to have any resistor in
series to restrict the current.
A 6v. battery charger can give out 4 amps.,which proves its nothing
to do with the voltage of input or output.

But everything to do with losses its iron core and the copper
wire that it is wound with.


Cheers - Joe

 

[John Popelish]

Why does my 9v D.C. transformer only give a max. amps. of 0.22A?.
I've looked inside it and it doesnt seen to have any resistor in
series to restrict the current.
A 6v. battery charger can give out 4 amps.,which proves its nothing
to do with the voltage of input or output.
Thanks.

The output current has to pass through the resistance of the secondary
winding. This uses up voltage and produces heat. The output current
(transformed by the turns ratio), in addition to the magnetization
current has to pass through the primary winding. This also drops
voltage and produces heat. A transformer is rated for output current
based on acceptable total voltage drop (called regulation, expressed
as %) and temperature rise. If they build the transformer with a
larger core that has a larger window opening, they can use larger wire
that drops less voltage and produces less heat at a given current,
raising the current rating. It turns out that the rated power (output
voltage times rated current) is roughly proportional to the weight of
the transformer.

You can get more current out of any transformer, if you accept the
lower voltage, and either do this briefly enough that the transformer
doesn't overheat, destroying the insulation, or are willing to put the
fire out.

 

[John Larkin]

Why does my 9v D.C. transformer only give a max. amps. of 0.22A?.
I've looked inside it and it doesnt seen to have any resistor in
series to restrict the current.
A 6v. battery charger can give out 4 amps.,which proves its nothing
to do with the voltage of input or output.
Thanks.

Its price or its weight are pretty good indicators of how many watts
it can deliver.

John

 

[Larry Brasfield]

size of the core, wire, etc...

the wire in the transformer is small, thus creating resistance of its own.
Yes.

Core saturation

No, core saturation does not act to limit the load current.
In fact, load current tends to reduce core saturation.

with inductance etc. etc. etc....

Yes.

 

[Jamie]

Why does my 9v D.C. transformer only give a max. amps. of 0.22A?.
I've looked inside it and it doesnt seen to have any resistor in
series to restrict the current.
A 6v. battery charger can give out 4 amps.,which proves its nothing
to do with the voltage of input or output.
Thanks.

size of the core, wire, etc...

the wire in the transformer is small, thus creating resistance of its
own.
Core saturation with inductance etc. etc. etc....

 

[hartly]

Thanks Andreww, and others.
My low current transformer does have 2 diodes in the circuit, but I
hadnt realized that they also restrict amps like a resistor does.
So that must be why it gives only 0.22 A


Hartly.

 

[John Fields]

Thanks Andreww, and others.
My low current transformer does have 2 diodes in the circuit, but I
hadnt realized that they also restrict amps like a resistor does.
So that must be why it gives only 0.22 A

---
No. The reason you can only get 0.22 amps out of it is because of (to
a first approximation) the resistance of the primary and the
secondary. The diodes will drop a _voltage_ somewhere between 0.5V
and 1V depending on the current going through them. Read John
Popelish's reply again.