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Old 15th August 2009, 03:13 PM   #1
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Default quick question about 240 to 220 volts transformer.

Dear diy friends,

I want to buy a 80va toroidal transformer, but the problem is, it has 240volts input primary and our local voltage is 220volts. Will it be ok? what is the disadvantage of this setup?

thanks.
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Old 15th August 2009, 03:37 PM   #2
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Indeed!

The disadvantage is possibly a bit heavier transformer than necessary but nowadys much electric gear (in Europe at least) is designed for 220-240 VAC.
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Old 15th August 2009, 03:40 PM   #3
Stu is offline Stu  Australia
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Shouldn't be a problem at all.

The only disadvantage is that the maximum power you can get out of it will be very slightly less. Not enough to worry about, anyway.
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Old 15th August 2009, 03:43 PM   #4
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Thank a lot ,

The transformer will be feeding a regulator for a Pass class A preamp, So the power loss is practically none issue...I guess.

Thanks.
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Old 15th August 2009, 03:44 PM   #5
Akita is offline Akita  Malaysia
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It should be fine.

Incoming ac supply may fluctuate sometime. To avoid it, you may need a regulated supply.

The ratio of your trans difference for 240 and 220. Let say, secondary is 12v then

1)12/240= 0.05 ;
2)12/220 = 0.0545 ;

If the supply for the trans no.2 is 240vac then the secondary will be 240 x 0.0545 = 13v
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Old 15th August 2009, 03:57 PM   #6
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My regulator needs 18V AC to produce a 15V DC , Do you think there is still enough headroom for the regulator to regulate, When you factor the slight voltage drop, Due to the primary mismatch? If I buy a transfo. with 240V pri./ 18-0-18 secondary plugged into a 220 outlet?

Thanks.
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Old 15th August 2009, 05:17 PM   #7
Spiny is offline Spiny  United Kingdom
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At 220v in will give 16.5 - 0 - 16.5, that might just save your regulator, rectified the 16.5vAC will give 23V peak instead of 25.5V a saving of 2.5watts dissapation per amp drawn from the regulator.

Bit simplistic and others will do the full maths with transformer regulation and diode drop taken into account - It will do

You have measured your AC line voltage I take it? As the 220V is nominal in europe, and can vary quite a bit - also depends on how near the substation you are and how heavy are the other loads on the substation are. Carefull measuring it though - it can bite
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Old 15th August 2009, 06:54 PM   #8
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Worst case is likely be to approximately

(18*(220/240)*0.9*0.9*1.4)-2 = 16.7V DC so it may not always be able to provide 18V DC for the regulator input.

If the transformer is only lightly loaded then the voltage will likely be somewhat higher.
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Old 15th August 2009, 11:46 PM   #9
wwenze is offline wwenze  Singapore
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Heh... people in my country have it the other way round, trying to use 230-240V supply with 220V China products.

Not much hiccups. Maybe the regulators run hotter.
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