Hi Larry,
<snip>
>I am striving to return to my roots, if you will, where all my equipment
>was built from stuff I found in trash cans around the neighbor hood.
>I.E., free or cheap.
Your neighborhood trash may vary from the norm!
<snip>
>I have cheap electricity so efficiency is really not an issue either.
It becomes an issue insomuch as the heat must go somewhere. An ol' iron
supply is pretty darn efficient.
An inefficient switcher will cost more in terms of larger heatsinks and/or
fans. At just over 90% efficiency, a 3KW supply will exude 250W of heat!
<snip>
> Power factor correction? Why bother?
Because it only costs a couple bucks and gives regulation good enough for
Amateur Radio. It could even be used for fine control between 375 volt steps
of the secondary for continuous coverage.
In my previous discussion, I suggested a PFC front end followed by a "DC
transformer" with only the PFC being regulated
> No matter what, it will be better than the HVAC unit on the house. (and
>so will the start up surge)
A separate soft start will still be required. A few thousand uF directly
across the line will pop your breakers.
<snip>
>The designs offered so far show me no advantage at all over a
>conventional HV supply in terms of cost and usefulness.
Cost depends on where the parts come from. If you're finding 3KW iron
transformers on your curb then no contest.
Several large companies have spent years designing really cute parts for this
application that they sell for only a couple bucks each.
>So far the cores mentioned have been, for me at least, made from
>unobtainium. I have access to Micro-Metals, Fair-rite, and Steward cores
>though the suppliers I normally deal with. It would really be nice to
>see designs using materials made by one or more of those companies.
The core may be easily substituted. Fair-rite's large 78 material cores are
just fine for this application.
>The challenge as I see it is not to produce an "excellent" design but to
>come up with a 750 watt +/- module that can be built from a minimum
>count parts list comprised of components that can be obtained at swap
>meets and/or surplus houses as much as possible. Parts lists that total
>up to the cost of a new Dahl/Harback transformer are not interesting to
>me and I suspect not many others either. Think disposable consumer
>electronics like microwave ovens and not Super Collider projects.
How much does a new 3KW transformer cost now-a-days? $300? $500??
Since cost is one of your primary design criteria let's see what I can SWAG
in that direction...
First, some assumptions:
Let's stay with a single 3KW (3KV@1A) supply, including a conventional PFC
front end, as that will require many fewer parts overall.
This discussion started with a 100KHz operating frequency as that was
employed in the ol' QEX article. Let's downshift that to say 50KHz so that
cheap IGBT's may be employed instead of pricey MOSFETs.
And include overcurrent protection in the event that a tube arcs or a moth
decides to go kamikaze on the HV line.
IC's -- PFC Controller $4
Bridge Controller $7
IGBT Drivers $5
Current sense $2
Soft Start $1
IGBT's -- 6 total $20
Diodes -- Input Rectifiers $7 or less depending on your swapmeet
16 Output Rectifiers $8
Capacitors -- Input Caps $5 at my swapmeet. I got new Sprague:
1200uF@450v for $1ea
Output Caps $7 or less at swapmeet prices. I paid .50
for .1@4KV
Small Caps $10 or in the old junquebox
Resistors -- $10 if all bought new
Cores -- Transformer $40
Output filter $10
Heatsink -- Either a large one, or a small one with a fan
or the free one from the curb unless someone took it to the
aluminum recycling place
Let's say $25
PCB (small quantity) $25
Wire, hardware, etc. $25
I think that totals circa $200 or 7 cents/watt for parts
>I suspect this won't go anywhere, but I need to ask....
Well it went somewhere.... :-)
73 & Good afternoon,
Marv WC6W
http://wc6w.50webs.com/
*
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