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Transformers - Help please

M

Mack

Jan 1, 1970
0
I have a transformer which says its output at 240 volts to 110 volts will
allow 100 va. Can you tell me what this would be in amps or watts Please.
Cheers
Mack
 
G

Gavin Parsons

Jan 1, 1970
0
That depends on the efficency of the transformer
 
G

Gavin Parsons

Jan 1, 1970
0
Sorry wrong newsgroup delete last reply
Gavin Parsons said:
That depends on the efficency of the transformer
 
A

Andrew Gabriel

Jan 1, 1970
0
I have a transformer which says its output at 240 volts to 110 volts will
allow 100 va. Can you tell me what this would be in amps or watts Please.

100 VA is 100W if the load is a pure resistance, like a heater
or a filament lamp. It will be less than 100W if the load is
not resistive in nature -- it depends on the nature of the
load exactly what the value is. If you give a clue what the
intended appliances are, we can probably guess the watts to
VA ratio (which is known as the Power Factor).
 
P

Perion

Jan 1, 1970
0
If connected for 240 volts its max amp rating is 100 volt-amps / 240 volts which
is about 0.42 amps.
If connected for 120 volts it would be 100 / 110 or about 0.84 amps.

This is just the max amp rating - the transformer doesn't "output" amps. It
supplies an alternating (AC) electrical potential or voltage so the actual
current that would flow is dependent on amount and type of load that the
transformer supplies.

Perion
 
M

Mack

Jan 1, 1970
0
Thank you all for replying - Its a heater which is pure resistance. Can
anyone tell me the formula for working this out please?, if their is a
'simple' rule of thumb, that will do nicely.
Cheers.
Mack.
 
T

Ted Rubberford

Jan 1, 1970
0
Repeating Rifle said:
Your initial statement does not ring true. I would expect a transformer
changing 240 VAC to 120 BAC but not 110 VAC.

Bill

240v to 110v is pretty much a standard step-down in the UK.
Looking at the OP email, it looks like a UK post.
Probably provide just under 1 amp on a resistive load.

Teddy Rubberford..
"The man in the rubber hood"
 
D

daestrom

Jan 1, 1970
0
Mack said:
Thank you all for replying - Its a heater which is pure resistance. Can
anyone tell me the formula for working this out please?, if their is a
'simple' rule of thumb, that will do nicely.
Cheers.
Mack.

The term 'VA' comes from 'Volt-Ampere' which is one rating of transformers.
It means, literally Volts times Amps.

It is useful for transformer ratings because the same number applies to
either the primary or secondary. If you have a 240V to 110 V step down
transformer that is rated 100 VA, then...

Secondary...
100 VA = 110V X 0.909 A

Primary...
100VA = 240V X 0.4166A

The power in Watts is from a formula...
P = V X A X pf
pf = Power factor. For resistive loads it is 1.00, so the power in watts is
equal to Volts X Amps (which is 'VA').

100VA with a resistive load is 100 Watts

daestrom
 
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