[Boatanchors] Parallel Operation of HV Power Upplies

[Carl]

I have done it both ways over the years quite successfully but there are 
caveats.

First, measure the DC resistance of the secondaries; in your case they 
should be identical within a few percent. If they are reasonably modern 
transformers designed for SS and just a capacitor filter the resistance 
will be quite low, in the <50 Ohm area. If the resistance is in the 100 
Ohm and up range you have old iron designed for 866's and either choke 
or capacitor input LC filters. These CANNOT be used with just a fat C 
filter

Any old E&E Handbook will walk you thru the impedance discussion and LC 
requirements to extract maximum power from the transformer without 
frying them. The ARRL HB's are rather spotty in their explanations altho 
the best discussion on transformers and filters was in a 33 QST.  SS 
diodes can be used and modern diodes such as the 1N5408 dont require any 
external C or R. and are darn near bullet proof at about $.25 each.

A single rectifier/filter assembly will work fine. Paralleling the same 
leads from each transformer will "almost" guarantee correct phasing but 
do this and test before hooking up the filters.

No resistors or extra diodes required, treat it as a single supply.

Carl
KM1H


----- Original Message ----- 
From: "Byron Tatum" <bjtatum1 at att.net>
To: <Boatanchors at mailman.qth.net>
Sent: Saturday, February 14, 2009 12:06 AM
Subject: [Boatanchors] Parallel Operation of HV Power Upplies


A Quick Question-
        I need about 800 mA at 2KV. I do not have a single transformer 
to supply this. I do have two identical transformers that will supply 
400 mA at 2 KV.
        I have been studying parallel operation of transformers, but had 
these questions:
                Would just paralleling the transformers be sufficient, 
or should there be low value resistors isolating the HV windings?
                Would it be better to use two identical power supplies 
(transformers, rectifiers, filters) and connect the HV DC leads together 
and parallel them in this fashion? (I have full power supplies already 
containg the 400 mA at 2 KV transformers)
                If I went the complete power supply paralleling route 
would there be any benefit in passing each HV DC lead through a HV diode 
before actually tying leads together?
                                                                Thanks, 
Byron WA5THJ



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