[Elecraft] Homebrew power supply

[Martin Kratoska]

This one

http://ludens.cl/Electron/Ps20/Ps20.html

I tried it, it is almost perfect and very simple construction, rugged
enough. If you use a high quality toroidal transformer you will probably 
need a soft start circuit (limiting the inrush current when switching on).

This one
http://www.warc.org.uk/proj_psu.php

is more sophisticated construction with all types of protection you 
need. I use now very similar design (mnufactured here by OK2EZ) which 
runs now its 8th year without any problem. There are some notes 
(presumed the above mentioned design used as reference):

- no need of 50R/50W resistor. Use a MOV surge protector (varistor) 
instead (similar type to varistors used in PC switching PS), they 
withstand much more inrush current and won't became very hot in the case 
of faulty RL-1.

- I made very good experience with "smoothing" capacitors 20x 3300uF 
105C Nippon Chemicon, Low ESR, 35 Volts (at least) instead of two big 
33000uF units. This solution is also sometimes cheaper as two bigger 
units. 3000uF per ampere is not bad...

- for usual 100 W radio rate your PS not for 20 Amperes but for 25-30 A 
instead. The four 2N3055 are good enough for 40 A with sufficient 
cooling, alu heatsink block + fan recommended. If fan used, its RPM 
should be controlled. A suitable circuit is here:
http://www.ok2kkw.com/00003016/komparator/pwm_ventilator/pwm_ventilace.htm
This article is in Czech, a link to Google translator is provided.
The thermal sensor can be located on the output transistors heatsink block.
The cooling is a bit tricky. The cooling air path starts at the mains 
toroidal transformer followed by the bridge (a heavy heatsink should be 
used, preferably precisely milled to the bridge shape) and the 2N3055 on 
a heatsink should be located near the air open hole (with a grill). 
There are some poor constructions where the hot air warmed by the 2N3055 
output set warms up the trasformer...

- the output current metering can be done at the primary of the mains 
transformer (clamp ammeter principle). No need of any 0.01 ohm resistor 
in the output path. The measured values must be corrected. This circuit 
is still planned, no schematic available for now.

73
Martin, OK1RR

Dne 16.1.2014 22:40, John Cooper napsal(a):
> Anyone have schematic or plans or know a site that has one for min 20amp power supply to run a k2 at 100watts.  Linear or switching.
>
> WT5Y
>
>
> Sent from my Cricket smartphone
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