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   Home   Help Search  
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Author Topic: air vs oil dummy load ?  (Read 4298 times)
W9IQ
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Posts: 2907




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« Reply #60 on: August 28, 2018, 05:50:54 PM »

I never tried to make an RF dummy load from salt water but I did try to make a dummy load for a power supply project I was working on. I wanted to put a 25 amp load on a power supply and tried salt water. I did not want to use a perfectly good radio until I was sure I had all the bugs worked out.

I quit before I got it "dialed in" after a friend warned me of salt water vapors possibly being dangerous. Does anyone know about that?

Bob

If the salt is common sodium chloride (NaCl) table salt, there is no danger in moderate concentrations. Corrosive to the surrounding environment perhaps, but generally not harmful to humans.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
W9CN
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Posts: 126




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« Reply #61 on: August 28, 2018, 07:27:24 PM »

I never tried to make an RF dummy load from salt water but I did try to make a dummy load for a power supply project I was working on. I wanted to put a 25 amp load on a power supply and tried salt water. I did not want to use a perfectly good radio until I was sure I had all the bugs worked out.

I quit before I got it "dialed in" after a friend warned me of salt water vapors possibly being dangerous. Does anyone know about that?

Bob

If the salt is common sodium chloride (NaCl) table salt, there is no danger in moderate concentrations. Corrosive to the surrounding environment perhaps, but generally not harmful to humans.

- Glenn W9IQ

LOL

Think I will stick to my Altronics and Coaxial Dynamics loads...
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K5LXP
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« Reply #62 on: August 28, 2018, 08:24:39 PM »


One way I test power supplies and batteries is to connect a 12V to 120V inverter, then connect various wattage 120V light bulbs to draw the appropriate test current.  An inexpensive volt/current/Ah meter between the supply/battery and inverter monitors the 12V parameters.  Even a small inverter can put a relatively heavy load on a station supply or small battery.

I test large storage batteries at moderate currents (75A) with a piece of steel wire coiled up in a bucket of water.  The length of wire determines resistance, and thus desired current.  Long tests require some flow of cool water to keep the water from boiling.

Mark K5LXP
Albuquerque, NM
 
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WE6C
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Posts: 105




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« Reply #63 on: August 29, 2018, 05:49:47 AM »


One way I test power supplies and batteries is to connect a 12V to 120V inverter, then connect various wattage 120V light bulbs to draw the appropriate test current.  An inexpensive volt/current/Ah meter between the supply/battery and inverter monitors the 12V parameters.  Even a small inverter can put a relatively heavy load on a station supply or small battery.

I test large storage batteries at moderate currents (75A) with a piece of steel wire coiled up in a bucket of water.  The length of wire determines resistance, and thus desired current.  Long tests require some flow of cool water to keep the water from boiling.

Mark K5LXP
Albuquerque, NM

I did end up doing that. The largest bulb I had was a 200 watt and was trying to get a little more draw, closer to 25 amps. I settled for the 20 amp load.
 
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VK3BL
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« Reply #64 on: September 01, 2018, 08:20:40 PM »

The oil loads also take longer to cool down to the point of running rated power again.

There are often several sizes large commercial loads by Bird and others that can run continuous at 500 to 3000W and at a fraction of new cost.

Mine is a RCA 3000W made by Bird and rated to 1300 MHz found at a hamfest over 30 years ago. No leakage ever from that type.

Carl

This is the best advice one ham can give to another with regards to dummy loads.

My personal dummy load is a Bird 8201 late 90s model obtained from South Korea delivered for around $250usd.

Rated to 1:1.25 to 2.5GHz and 500w continuous COMMERCIAL service, or up to 50,000W for 1 microsecond.

73, Jarrad VK3BL
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J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
KM1H
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Posts: 4722




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« Reply #65 on: September 02, 2018, 07:52:11 AM »

Thanks Jarrad.

With a little creativity an external oil cooler can be used with a fan to increase the duty cycle time. Similar to automatic transmission and oil coolers used on high performance vehicles. I use a pair of fans on my 3KW load since I do not want to have to drain fried PCB fluid which really stinks. I remove the drain plug yearly and take a whiff Shocked

For those who may not understand this there is no RF present in the fluid.

Carl
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KE0ZU
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« Reply #66 on: September 03, 2018, 05:20:07 AM »

I have an old Military 600W 100% duty cycle load I got for $50 off the bay, about eleven years ago.    Just kept watching the new listings.    It has weeped a very slight amount of oil, enough to make a ring around the seal, but never any real "leak".   This thing must be at least 50 years old if its a day.



   
« Last Edit: September 03, 2018, 05:41:55 AM by KE0ZU » Logged

Regards, Mike
https://mikeharrison.smugmug.com/
Pics and bold print are usually links.
G0HZU
Member

Posts: 162




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« Reply #67 on: September 03, 2018, 04:13:26 PM »

Many years ago I managed to get a used one of these Bird high power (air cooled) attenuators and I would definitely recommend them as long as you keep transmissions relatively short and/or blow it with a fan. They do appear on auction sales now and again and an attenuator like this is very useful. This model is very linear so can be used for IMD testing etc.

https://www.birdrf.com/Products/Test%20and%20Measurement/Attenuators/1kW/1000-WA-Series_RF-Attenuators.aspx

They also do a 1500W version but mine is only the 1kW version. It covers up to 2.4GHz with low VSWR and has a fairly accurate 40dB of attenuation across this range. The most mine has ever seen is 450W PEP at a couple of GHz but I usually use it below 100W. The model I have allows the heatsink to be reduced in size as the outer two sections of the heatsink are removeable (with a load of chunky Allen bolts) so it spends nearly all its time like this. Much smaller and lighter and still probably OK to >300W like this. To get an idea of size, it is about 19" from end to end (input connector to output connector).

it is directional so you have to feed the high power into the correct end and it consists of a series of flanged attenuators in series. There are lots of attenuator sections starting at something like 0.5dB and the attenuation value of each section builds up along the length and the idea is that the heat is distributed evenly along the 19" length. So the final attenuator sections are something like 10dB each. But that is just a guess. The total is 40dB for the model I have here although you can get versions with different overall attenuation. 40dB is about ideal in my opinion...
« Last Edit: September 03, 2018, 04:29:29 PM by G0HZU » Logged
AC6CV
Member

Posts: 301




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« Reply #68 on: September 09, 2018, 12:48:53 PM »

The oil loads also take longer to cool down to the point of running rated power again.

There are often several sizes large commercial loads by Bird and others that can run continuous at 500 to 3000W and at a fraction of new cost.

Mine is a RCA 3000W made by Bird and rated to 1300 MHz found at a hamfest over 30 years ago. No leakage ever from that type.

Carl

I have an old Heath Kit oil dummy load from the 70s. It has never leaked. Still use it.
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BOOTYMONSTER
Member

Posts: 95




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« Reply #69 on: September 09, 2018, 03:24:28 PM »

I have a leg up on this poster.
He hangs out or used to on another board where everything/anything  goes.
I have not gone to that board for years so don't know what goes on their now since there was a change.

I would have thought by now he would have an idea about this 'seeins' they know it all their.
Sorry to sound so tough but that's the way I see it.

thanks for the replies folks Smiley
KM3F , don't worry , you don't sound tough . you just sound like a old poop stirring Cb'er hiding behind a keyboard  Smiley take care puddin
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