[AMPS] Choke input supply

[Tom Rauch]

> Art says:
> 
> >Can two identical chokes be ran in parallel to increase the
> >overall current capacity of just one of the chokes 
> 
> Yes, but......you need to make sure that the two DC resistances are the
> same, or the current will divide unequally. 'Identical' chokes may well
> have different DC resistances. They need to be mounted such that the
> magnetic fields don't interact, or the inductance could be wildly
> different. They also need to be mounted such that they are at the same
> temperature, or the resistances will differ.
> 
> 73
> 
> Peter G3RZP

They ideally should have the same resistances, reactances, 
reactance slopes with current change, and twice the inductance 
you actually need if you intend double the current rating. 

A major problem is inductance always varies to some extent with 
current, being reduced as current increases. That means the choke 
with least inductance, or that loses inductance fastest with 
increased current, draws more current. That further decreases 
inductance of the lowest inductance choke, and makes that choke 
reduce inductance even further.

Because of that, two iron-core chokes should never be parallel to 
increase current rating unless the AC content of the voltage 
impressed across the choke is low compared to the DC content.

It is OK to parallel two chokes as described in the mid or output 
section of a pi-filter, but they should never be parallelled at a point 
where there is considerable ripple content...like the input of a filter 
or the mid-point if there is a considerable percentage of ripple.

In other words, if you pretty much don't need the choke it's OK to 
parallel them at that point.

73 Tom
73, Tom W8JI
w8ji@contesting.com

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