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Calculating VA for a toroidal transformer

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m7mood

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I want to know how to calculate VA for a toroidal transformer given that the loads are:

(Heaters 200W -24VAC) + (Fan 12VDC - 1 Amp) + (Microcontroller & LCD 1Amp)

Please help me!! Thanks
 

Heaters: 200W = 200VA
Fan: 12V * 1A = 12VA
Other: ???V * 1A = not much, probably less than 10VA

Total = about 220VA.
So a transformer rated at 250VA should be OK, 300VA would be better.
 

I think he under Microcontroller & LCD 1Amp consider control electronics with thermostat.

Yes 300VA should be fine. Always is good to avoid trafo full load.
 

For bridge rectifier+ filter cap DC supplies you should assume a VA/W "form factor" of 1.6 respectively 2.0 for half-wave rectifiers. Losses of linear voltage regulators add.
 

Thanks for your attention and fast reply!!

Should I separate digital loads (microcontroller & LCD .....) and analog loads (fans & ...........)? so i need to use toroidal transformer with two secondary or not??
 

Depends on the power supply concept. If you are using switched mode voltage regulators or linear voltage regulators for supply nodes with low current consumption, a single secondary could work for the application.
 
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    m7mood

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FvM said:
Depends on the power supply concept. If you are using switched mode voltage regulators or linear voltage regulators for supply nodes with low current consumption, a single secondary could work for the application.
Click to expand...

i'm using linear voltage regulators, so noise from the analog loads like fans will not affect digital loads like microcontroller??
 

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