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DUMMY LOAD ADVICE




 
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July 09, 2020, 06:27:31 AM *
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WD8BIL
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« Reply #25 on: June 27, 2020, 09:40:37 AM »

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It looked very similar to the  dummy loads we used at the Telco I worked at for  34 years.... but the telco  DL's were used
for load  testing emergency generators.....up to  500 kva..( and coils could be switched in /out in parallel  with a tap switch, to change the load).

Were those Avtron loads? We used them at Lorain Products to test the telcom power systems! My lab had enough load banks to pull 15,000 amps at -48VDC!
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VE7RF
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« Reply #26 on: June 27, 2020, 10:29:14 AM »

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It looked very similar to the  dummy loads we used at the Telco I worked at for  34 years.... but the telco  DL's were used
for load  testing emergency generators.....up to  500 kva..( and coils could be switched in /out in parallel  with a tap switch, to change the load).

Were those Avtron loads? We used them at Lorain Products to test the telcom power systems! My lab had enough load banks to pull 15,000 amps at -48VDC!

##  Nope, these loads were for the   208/120 vac  (3 phase)  diesel generators  that  each  Central office had.   The cell sites (only a few of the bigger cell sites  had an emergency generator) ran on  240/120 vac,  single phase, like a home.  The fan on the portable  DL  made a hell of a racket. It was towed behind a truck.

##  Main office  downtown,  was  470 / 271 (3 phase).

##  we only had small DL's  for the  +5vdc (@ 40A)  supplies.   These were  DC-DC  converters, thousands of them. -52 vdc  input..and  +5Vdc output.

##  Think it was around late  70's, when the change came to the  -48 vdc.  It was increased to  -52 vdc.  It's  still  -52vdc to this day.

##  Never did see a  huge  dummy load for the  -52 vdc  rectifiers.  The  -52 vdc rectifiers  came in  25-50-100-200-400-800  amp  sizes.
Huge things in the  400 +  800 amp sizes.   Before I retired in  2009, the  new standard  was the -52 vdc switching type  supplies.   6 x 3.3 kw  units in one  shelf (20 kw /  400A  ccs)...that ran on  208 single phase....  or  240 vac  single phase  (cell sites).  Up to 7-8  shelves in a bay..with a control unit in the middle of the mess.  One bay was good for  140-160 kw.

##  Main office  downtown  sucked  3750 Amps @  -52 vdc.   We bought the power from the power  company at 14.4 kv / 3 phase...  then had our  own 2000 kva  vault  transformer  ( to step it down to  470/271 vac).   The emergency generator on the roof  was 1800 kva, and was a V-16  diesel. 2 x 35,000  litre  underground ( double walled) diesel tanks below the parking  lot.  Fuel lines were the size of fire hoses.

##  We had a myriad of  Lorain products in most offices.  Extremely rare we had issues  with Lorain equipment.

##  On  a side note, apparently the large dummy loads can be rented.  A  buddy had  400 A  (240/120) service upgrade to his home.  The power company wanted to install a 2nd  50 kva  xfmr in parallel  with the existing  50 kva xfmr.....and still feed  9  homes.   Buddy  complained, and they relented,  so the new xfmr is just for his home.   Now the battle is.... a new, dedicated  50 kva  xfmr is only good for 200A, not  400A  !   So he's gonna  rent a  DL,  suck  400A  CCS, and destroy the new xfmr.  Then he will get a 100 kva installed.

## I have  '200 A'  service into my home... but the  50 kva  xfmr is  shared  with a total of  9  homes.  (5.5 kva  per home).   Power company guys came out..said  to just blow it up ( they are over fused  with a 9-11  amp  slow blow).  They said they  have em in  25-50-75-100-125  kva  sizes ( for mounting on utility poles).  They can also be paralleled.  Anything bigger, and it has to be mounted on the ground, on a slab, inside a kiosk.

##  silly really.  My 3-0 cu wire from  200A  panel is spliced into 2-0 Al  drop line ( it might be  1-0 al).   V drop  from xfmr  to B+  supply is bad news.   Once these  100%  electric cars become more mainstream, the  pole pig xfmrs will  start popping offline, massive upgrade required.

sri for the  diatribe.

Jim  VE7RF
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KD6VXI
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« Reply #27 on: June 27, 2020, 10:44:14 AM »

The utility company doesn't have to comply with NEC regarding utility drops to a house. Silly, really.

And So Cal Edison.... What a hoot.  Friend built a house and had to have a new drop to his house.  Goes to engineering, they recommend a new xformer.  He buys a pole pig through SCE, they mount it run service drop to his pole in his property, etc.  75kva as he plans in having a shop w welder, etc.

NO GUARANTEE THEY WON'T CONNECT OTHERS TO HIS PIG!  Even though he purchased it, paid to have the service installed, etc.  It's a shared transformer.

You have to purchase wholesale power to get your own xformer!

I've heard the dame story about having to blow a pig up before they will replace it.

Me, I want 208/120. 

--Shane
KD6VXI
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W2PFY
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« Reply #28 on: June 27, 2020, 07:48:23 PM »

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Future projects = Oiled cooled cigar holder. Moose restraints. Cement chewing gum.

Hi folks, I cannot believe the traction this tread has attracted and the good suggestions that have come from it considering that it was supposed to be an April 1st. spoof. I guess I cannot do it as well as the ARRL has done in many of their publications?

Anyhow lets keep it rolling!     
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VE7RF
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« Reply #29 on: June 28, 2020, 11:02:05 AM »

The utility company doesn't have to comply with NEC regarding utility drops to a house. Silly, really.

And So Cal Edison.... What a hoot.  Friend built a house and had to have a new drop to his house.  Goes to engineering, they recommend a new xformer.  He buys a pole pig through SCE, they mount it run service drop to his pole in his property, etc.  75kva as he plans in having a shop w welder, etc.

NO GUARANTEE THEY WON'T CONNECT OTHERS TO HIS PIG!  Even though he purchased it, paid to have the service installed, etc.  It's a shared transformer.

You have to purchase wholesale power to get your own xformer!

I've heard the dame story about having to blow a pig up before they will replace it.

Me, I want 208/120. 

--Shane
KD6VXI

Shane, did u get the pix I sent u ?

Back to  50 ohm  DL's.   Instead of oil, can  distilled water be used instead ?   IE: if a new / clean  heath /mfj  1 gallon can is filled with
distilled  water,  will it still be  50 ohms resistive   up to  30 mhz ??   What about plane tap water ??   As long as swr stays flat  ( even when  hot),  it occurred to me that  my hb  DL  could be filled with distilled water, instead of oil.  ( it's  empty and clean right now).

I ran through the various formulae, and even with "power level X"  it would take a while to heat up  7 gallons of water, esp with pulse tuning at  30%  duty cycle.

Another thought is to  attach 3/4" garden hose brass  fittings, etc... to lower end of side of 7 gal container..and also upper  end of same container ( but  opposite side).  Then just crank in cold tap  water into bottom portion of  7 gal can....and   route the  hot water  from  upper fitting....over to a drain.  The idea here is... once  7 gallons  get hot, it takes a long time to cool down, esp  oil..which could screw up any   RF testing.  In those cases, the cold tap water could be used to  cycle through the can.   Coaxial  dynamics 15 kw  water cooled load  uses  4 GPM..and plane jane  3/4" garden hose fittings. (  2 GPM on their 5 kw loads).  Coaxial dynamics  uses  3/4"  garden hose fittings.

Jim  VE7RF
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VE7RF
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« Reply #30 on: June 28, 2020, 11:14:02 AM »

Excellent PDF  from  coaxial dynamics.  Everything you ever wanted to know about their  water cooled loads.  They all use  3/4"  garden hose fittings.   Water  goes down the INSIDE of the  tubular  50 ohm resistor ( bottom  end of  resistor, where it's  shorted)... then  comes out the top of the resistor,  loops around,and then makes a 2nd pass, but this time  down the outside of the resistor.... back to the bottom, then exits the DL,  through  3/4"  garden hose fitting  #2.

http://www.coaxial.com/manuals/86000.pdf

The above is fine..as long as you have loads of municipal /  city  water..and it all goes down the drain ! 
For Broadcast sites out in the bush, etc, this is  not feasible, so  either a reservoir is used  (200-1500 gallons)...or an external ( air cooled ) radiator  is used.

One big advantage of water is....  if something leaks, or gets spilt on my  concrete basement shop floor, I don't end up with a helluva mess,  unlike  oil !

Jim  VE7RF
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K6IC
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« Reply #31 on: July 02, 2020, 09:37:30 PM »

AM Load here.   FWIW  Vic


* Bird 8787B Load & QC 007.JPG (1208.07 KB, 2304x3072 - viewed 35 times.)
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