# PSU for BA-1

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#### AllenB

Paid Member
To answer these questions what is the voltage of the supply before the coil, will it be in the first position or after a cap, what is the current draw of the amp and is it constant?

#### Ryssen

Changed my mind on this thing BUT it would be interesting to know the answer.
The voltage at the cap would be 25v the coil would be after the cap.
The current draw would be 3,5 amp/channel if I`m not misstaken

#### AllenB

Paid Member
Mostly DC will flow through this coil and it may be a little light with regards to resistance. I guess the 2mH has a resistance of 1.2ohms and would drop 4V across this and dissipate 15W.

Ok,thanks.

#### AndrewT

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The current draw would be 3,5 amp/channel...........

Mostly DC will flow through this coil and it may be a little light with regards to resistance. I guess the 2mH has a resistance of 1.2ohms and would drop 4V across this and dissipate 15W.
3.5A/ch and 1r2 giving ~ 15W of dissipation in the coil is going to be a mighty hot coil, especially in the middle.
If you run two channels (7Adc) through the coil, the dissipation could increase to around 70W ! Because the copper has become too hot.

For minimum resistance (of the winding) the coil outer diameter should be roughly four times the width of the coil. And depth should roughly match the width. i.e. the hole in the middle should have a diameter that is roughly twice the width and depth of the coil.
That pic shows a coil that is too fat and as a result has a higher resistance.

eg for minimum resistance start with a bobbin that is 2" diameter. Set the cheeks at ~1" apart. Wind on a coil that is ~1" high, giving a final outer diameter of 4". You end up with a 4" diam, by 1" thick by 1" wide coil. Now adjust the wire diameter and turns to give your required Inductance.

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