# Transfomer secondaries and power distribuition

Discussion in 'General Technical Questions and Answers' started by KK4YWN, Sep 13, 2017 at 11:32 PM.

1. ### KK4YWNHam MemberQRZ Page

How is power distributed accross secondaries if the windings are different? Lets say 1:10 and 1:40? Will the 1:40 get half the input power or no?

Thanks

2. ### AF7TSHam MemberQRZ Page

The turns ratio dictates the voltage ratio. This is still true with multiple secondaries.

IMHO power distribution will be independent of the turns ratios; either coil could take the majority of the power or they could share evenly depending on the connected loads.

The selected wire gauge sets the design current capacity of the coil, so if both coils are made with the same wire then the higher voltage coil (more turns) will have been designed to handle more power. But you could make the low voltage coil with fat wire to balance the power handling.

-Jon

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3. ### WA7PRCHam MemberQRZ Page

^ ^ ^ THIS ^ ^ ^
Also, the total capacity is related to how many turns of wire (vs wire diameter and transformer cross-section area) that can fit, and the magnetic capacity of the core. The wire's DC resistance will cause the temperature to rise. The wire and interwinding insulation's temperature limits may limit how much you can get out of the transformer. At the point the core saturates magnetically, you've reached its power limit. Manfred XQ6FOD has good info regarding magnetic theory (link) and practical rewinding info (link).

I rewound a transformer that came to me with several LV high current windings. I replaced them with a single tapped HV winding (link):

(click for bigly image)

The split bobbin meant I didn't touch the primary windings. After guesstimating the number of primary turns and knowing the needed turns ratio, I then knew how many turns of wire I would need on the secondary. Thanks go to Manfred and a coworker Engineer for their help and info.

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4. ### WB8NQWHam MemberQRZ Page

The primary/secondary turns ratio determines voltage only. Power is determined by the current load and voltage on the secondary winding. Each winding will have a design specification stating voltage and current load - thus power. The total secondary power available will be the sum of all the secondaries. Of course the primary input power will be the sum of all secondary powers plus any power losses in the transformer itself.

Bob
WB8NQW

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5. ### WA9SVDHam MemberQRZ Page

It's NOT quite that simple, (unless you want to disassemble and rewind the transformer.) An example is the typical "computer supply," which may have a 450 Watt rating. But that is TOTAL instantaneous power, and not continuous power. Such a p/s may have a 10 Ampere 12 Volt rating, and the rest 5.0 and 3.3 Volts at many Amperes each. That does NOT mean you can pull 450 Watts @ 12 Volts, even if the 5.0 and 3.3 windings are not used! The supply is STILL only rated for 10 Amperes @ 12 Volts,and drawing more current through that winding will quickly result in exceeding its ratings, excessive heat, breakdown, fire, or worse.

6. ### WR2EHam MemberQRZ Page

never mind...

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7. ### KK4YWNHam MemberQRZ Page

ok well we haven't had a good crack-pot technical discussion in a long time, so i'll just throw this out...

power companies use "tertiery windings" to enforce balance over circuits. they'll often step-down and perform some trickery to make the primary appear balanced despite what happens in the secondary.

the tertiery is a lower-power consumer, according to what-little i've been able to find on the subject.

that got me thinking about feed-point transformers. not chokes but transformers.

three ideas came to mind:
1. a huge step up to a very high impedance on the tertiery winding, terminated into a high value resistor. broadbanded operation with lower power lost to the resistor? just guessing.
2. a huge step up in impedeance to a tank circuit in the tertiery (extreme single-bandedness). the idea here is as you move away from the tank circuits resonant freq the impedance goes down and the tertiery loads down the primary. the goal is to reject out-of-band signals.
3. a 1:1 that acts as a return, leading back to the shack and terminated into a tuner. remote manual tuning.