[Amps] Advice needed for SS amp

[Jim Thomson]

Date: Thu, 06 Jun 2013 05:08:14 -0700
From: Bill Turner <dezrat1242 at yahoo.com>
To: Amps <amps at contesting.com>
Subject: Re: [Amps] Advice needed for SS amp

ORIGINAL MESSAGE:          (may be snipped)

On Thu, 06 Jun 2013 04:24:21 -0500, W4DNR wrote:

>
>If there were no long term effects of dropping the whole circuit down  
>into a tank of water or 50/50 glycol, I think there would be  
>additional cooling benefits for the whole pc board. 

REPLY:

Brian, ZL4AD, just sent a picture of an amp cooled by transformer oil, which
is a non conductor of course. Might simplify things, worth looking into. 

73, Bill W6WRT

##  I would not mess  with a 50/50 glycol water mix.  Sure the boiling point is raised
to 265 F..and the freezing point is at –40 F.   But unless you plan on having the amp
in an UN heated  garage, don’t bother with a 50-50 mix.  100% Distilled water will
remove way more heat than a 50-50 mix.  To prevent spot boiling and bubbles forming,
and for better flow, you could use a few oz’s  of redline water wetter, or Royal purple..
purple ice.  These products just reduce surface tension,and are  used in car engs all the time.

##  Most race tracks wont allow a 50-50 mix to be used.   They instead use a 100%
distilled water + water wetter.  Adding the water wetter agent to the distilled water will
reduce the temps by a huge amount, like 20F.  Dunno if water wetter will increase resistivity
of water or not. 

##  a buddy recently constructed a 50 ohm  dummy load, built from 9 x 50 ohms surface mount
resistors, each resistor rated at 800 watts CCS.  Wired series-parallel  onto a large AL heatsink.
One of the resistors  exploded.  The  fix was to immerse the fins of the heatsink straight down into
a ice water bath...problem solved. 

##  I would not suggest using De-Ionized water either.  The ion depleted water  will attack everything
in site.  Water cooling could be achieved by using  a small 4 to 20 GPM pump, and routing to an
external air cooled radiator.   I use a 4 GPM Bosch 12 vdc  electric pump for my cars  supercharger’s
heat exchanger- intercooler setup.  It only draws 4 A  @  14 vdc.   You can also get em in 8 GPM, 
and all the way up to 55 GPM.     A  120 vac version would be the ticket. 

##  I think 1 watt = 3.15 BTU    So for a 1500w output  RTTY setup, with say 50% eff, the SS  amp
would have a  3 kw input..and 1.5 kw output...and have to dissipate 1500 w as heat.   1500  x 3.15 =
4725 BTU’s.    I just bought a small  7.5 inch tall x 12 inch wide x 3/4 inch thick  transmission cooler for
my car. It is rated for 13,000 BTU.   It is a bar + plate type vs the less eff tube + fin type. 

##  as long as you had a high enough flow rate, like 2-8 GPM, and a pair of fans on the small external
radiator,  water  cooling should be doable.  You can mount the radiator either vert like in a car..OR
horizontal, with air being blown up from below.    Commercial air conditioning roof top units are now
using H mounted rads with fans below em.   For ham use, the rad + pump could be located in another
room, or mount the rad outside. 

##  As for 50 vdc supplies, there are literally thousands of surplus Telco  52 vdc  supplies  across
the usa and canada these days..they can’t give em away.   They come in 25-50-100-200-400-800A
variety, all using xfmrs.  Typ  208/360/480 vac 3 phase for the bigger ones..and  single phase  208/ 240 vac
for the smaller ones. 

##  telco’s  + cell sites are all now using 52 vdc  switching types.  3.3 kw CCS each.  Up to 6 can be 
mounted in a 25 inch wide rack  x 7 inch tall... 19.8 kw ccs.  At the office I worked in, we stacked  em 6-7 high,
used for the UPS  setup.   They barely run luke warm.  They either run on 208 single phase...or
240 vac single phase.   They will operate just fine with anything from 160 vac to 300 vac.   
Any line freq from 40-70 hz.   The slick part is the power factor is always unity.  If 2 or more are used,
they will  talk to each other, such that the load always divides equally between em.  If one craps out,
the remaining units take up the slack.    $475.00  each brand new.    Dunno how many you could string in series.
I have never tried wiring em in series.   You can get em surplus too. 
  .         
I like the idea of a 170 or 340 vdc supply.  Then no xfmr required, just a FWB + filter cap.

Jim   VE7RF