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Old 15th January 2012, 03:24 PM   #1
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Default Power Transformer Question

I'm considering a transformer for a project requiring 400mA of current(Edcor)
but the closest one they have in stock is 325mA. How much of an effect in power output will this have? I will enquire for a custom wind,but not sure of the cost difference. Thanks
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Old 15th January 2012, 03:48 PM   #2
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If you use an underspecced transformer, you can expect early failure.

The transformer will do its best to supply what you are asking but it aint big enough.

If cost is an issue, try using modern smaller transformers in seies.
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Old 15th January 2012, 03:48 PM   #3
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The transformer might overheat.

When loading hard the output voltage will drop.

400mA isn´t a to big current must be a standard unit available some where ?

What specs do you need ?
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Old 15th January 2012, 03:56 PM   #4
DF96 is offline DF96  England
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For a rectified supply you may need a bigger transformer than you think.
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Old 15th January 2012, 04:49 PM   #5
M Gregg is offline M Gregg  United Kingdom
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Quote:
Originally Posted by denny9167 View Post
I'm considering a transformer for a project requiring 400mA of current(Edcor)
but the closest one they have in stock is 325mA. How much of an effect in power output will this have? I will enquire for a custom wind,but not sure of the cost difference. Thanks
You need to give more information..

What is is powering...(OK its a project)..what part of the project B+ heaters power amp pre-amp...Voltage required...type of rectifier..etc..

The reason is..

If you under spec you will get sag..then it will run hot and the sound will be "bad" because it will clip early...great for a guitar amp (overdrive)..
It could blow open with inrush at start up with cold heater elements or capacitor inrush..

Regards
M. Gregg
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Old 15th January 2012, 05:10 PM   #6
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More information on the planned PS design is needed, if you plan for capacitor input, you'll need significantly more current capability due to the sharp current spikes charging the first cap. With choke input, the AC current capability does not need to be higher than the DC current you want to get from it, and so on...

So please, more details!

Greetings,
Andreas

EDIT: I always tried to avoid custom wind, but ordered my first custom-wound transformer last year and was very pleased with it. You get exactly what you need, and (at least here in Europe) for a price that is acceptable.

Last edited by Rundmaus; 15th January 2012 at 05:12 PM.
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Old 15th January 2012, 09:31 PM   #7
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Quote:
Originally Posted by denny9167 View Post
I'm considering a transformer for a project requiring 400mA of current(Edcor)
but the closest one they have in stock is 325mA. How much of an effect in power output will this have? I will enquire for a custom wind,but not sure of the cost difference. Thanks
Some people use a Antek toroïdal power transformer and hide it in a car wax can for the look ... Those transformers are very cheap and also have one or two 6,3V secondary for the heaters. Look at their PDF specs for the real output voltage with your project current needs. Shipping is only 11$ in USA for unlimited weight ...

Don't forget with a two diodes fullwave rectifier with capacitor input, IDC = IAC but with a bridge, IDC = 0,62 x IAC ... Also, the deep bass often need much more current than the medium frequency and it is better to choice an oversize transformer.

Alain.
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