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Power rating factors for the dummy load kit?

craftxbox
 

Hello, I'm planning to purchase the 20w dummy load kit, and got curious, What are the power limiting factors? Certaintly, the resistors would be, but what about the capacitor or diode? To get to a higher power rating, would you just need to replace the resistors, or would those other parts need to be replaced aswell?
The Crunchbird
 

Heathkit used to make a dummy load called "The Cantenna." It used a pretty small resistor that was submerged in a paint can full of either mineral oil or transformer oil which was better if one could find it. This would effectively make a 20W dummy load work to the 100 watt level. Mineral oil removes the heat from the resistors about five times better than air. It would be interesting for someone to buy an empty paint can from Lowes or Home Depot and try submerging Hans 20 Watt dummy load in mineral oil. It would be even more interesting if Hans were to come out with a modification of his kit that fits into a paint can that the buyers can easily obtain along with some mineral oil. The only modification to the can would be to drill a hole in the lid but a pressure relief valve would be a good thing to add. One word of caution, older transformer oil often contains PCBs or Polychlorinated biphenyls so one is better off using unscented mineral oil (the type used for massage etc.) from the drug store. 

On Sat, Aug 22, 2020 at 5:28 PM spam via groups.io <spam=craftxbox.com@groups.io> wrote:
Hello, I'm planning to purchase the 20w dummy load kit, and got curious, What are the power limiting factors? Certaintly, the resistors would be, but what about the capacitor or diode? To get to a higher power rating, would you just need to replace the resistors, or would those other parts need to be replaced aswell?

Gregg Myers
 

November 2018 QST describes such an oil submerged dummy load. They are easy to make. If you want to maximize the wattage, you can artfully arrange the resistors in a way that encourages oil circulation through the resistors. I like to keep my Hans QRP dummy load ‘dry’ (and small) so I would not submerge mine in a can full of oil. For the one I made in a can full of mineral oil, I just purchased 20 1k 3w resistors and a BNC connector, just the article in QST. That’s all it is.

73,
Gregg

On Sat, Aug 22, 2020 at 4:16 PM The Crunchbird <pulsedevil@...> wrote:
Heathkit used to make a dummy load called "The Cantenna." It used a pretty small resistor that was submerged in a paint can full of either mineral oil or transformer oil which was better if one could find it. This would effectively make a 20W dummy load work to the 100 watt level. Mineral oil removes the heat from the resistors about five times better than air. It would be interesting for someone to buy an empty paint can from Lowes or Home Depot and try submerging Hans 20 Watt dummy load in mineral oil. It would be even more interesting if Hans were to come out with a modification of his kit that fits into a paint can that the buyers can easily obtain along with some mineral oil. The only modification to the can would be to drill a hole in the lid but a pressure relief valve would be a good thing to add. One word of caution, older transformer oil often contains PCBs or Polychlorinated biphenyls so one is better off using unscented mineral oil (the type used for massage etc.) from the drug store. 

On Sat, Aug 22, 2020 at 5:28 PM spam via groups.io <spam=craftxbox.com@groups.io> wrote:
Hello, I'm planning to purchase the 20w dummy load kit, and got curious, What are the power limiting factors? Certaintly, the resistors would be, but what about the capacitor or diode? To get to a higher power rating, would you just need to replace the resistors, or would those other parts need to be replaced aswell?

jjpurdum
 

I remember that article! It also had an OLED watt meter, too.

Jack, W8TEE

On Saturday, August 22, 2020, 6:36:45 PM EDT, Gregg Myers <gregg.w7grm@...> wrote:


November 2018 QST describes such an oil submerged dummy load. They are easy to make. If you want to maximize the wattage, you can artfully arrange the resistors in a way that encourages oil circulation through the resistors. I like to keep my Hans QRP dummy load ‘dry’ (and small) so I would not submerge mine in a can full of oil. For the one I made in a can full of mineral oil, I just purchased 20 1k 3w resistors and a BNC connector, just the article in QST. That’s all it is.

73,
Gregg

On Sat, Aug 22, 2020 at 4:16 PM The Crunchbird <pulsedevil@...> wrote:
Heathkit used to make a dummy load called "The Cantenna." It used a pretty small resistor that was submerged in a paint can full of either mineral oil or transformer oil which was better if one could find it. This would effectively make a 20W dummy load work to the 100 watt level. Mineral oil removes the heat from the resistors about five times better than air. It would be interesting for someone to buy an empty paint can from Lowes or Home Depot and try submerging Hans 20 Watt dummy load in mineral oil. It would be even more interesting if Hans were to come out with a modification of his kit that fits into a paint can that the buyers can easily obtain along with some mineral oil. The only modification to the can would be to drill a hole in the lid but a pressure relief valve would be a good thing to add. One word of caution, older transformer oil often contains PCBs or Polychlorinated biphenyls so one is better off using unscented mineral oil (the type used for massage etc.) from the drug store. 

On Sat, Aug 22, 2020 at 5:28 PM spam via groups.io <spam=craftxbox.com@groups.io> wrote:
Hello, I'm planning to purchase the 20w dummy load kit, and got curious, What are the power limiting factors? Certaintly, the resistors would be, but what about the capacitor or diode? To get to a higher power rating, would you just need to replace the resistors, or would those other parts need to be replaced aswell?

The Crunchbird
 

What was the power rating for the resistors in oil in the QST article? The Cantenna was supposed to be able to handle 1KW. 
Gregg Myers
 

Ha, ha, you should! It has your name on it, Jack! :)

On Sat, Aug 22, 2020 at 7:55 PM jjpurdum via groups.io <jjpurdum=yahoo.com@groups.io> wrote:
I remember that article! It also had an OLED watt meter, too.

Jack, W8TEE

On Saturday, August 22, 2020, 6:36:45 PM EDT, Gregg Myers <gregg.w7grm@...> wrote:


November 2018 QST describes such an oil submerged dummy load. They are easy to make. If you want to maximize the wattage, you can artfully arrange the resistors in a way that encourages oil circulation through the resistors. I like to keep my Hans QRP dummy load ‘dry’ (and small) so I would not submerge mine in a can full of oil. For the one I made in a can full of mineral oil, I just purchased 20 1k 3w resistors and a BNC connector, just the article in QST. That’s all it is.

73,
Gregg

On Sat, Aug 22, 2020 at 4:16 PM The Crunchbird <pulsedevil@...> wrote:
Heathkit used to make a dummy load called "The Cantenna." It used a pretty small resistor that was submerged in a paint can full of either mineral oil or transformer oil which was better if one could find it. This would effectively make a 20W dummy load work to the 100 watt level. Mineral oil removes the heat from the resistors about five times better than air. It would be interesting for someone to buy an empty paint can from Lowes or Home Depot and try submerging Hans 20 Watt dummy load in mineral oil. It would be even more interesting if Hans were to come out with a modification of his kit that fits into a paint can that the buyers can easily obtain along with some mineral oil. The only modification to the can would be to drill a hole in the lid but a pressure relief valve would be a good thing to add. One word of caution, older transformer oil often contains PCBs or Polychlorinated biphenyls so one is better off using unscented mineral oil (the type used for massage etc.) from the drug store. 

On Sat, Aug 22, 2020 at 5:28 PM spam via groups.io <spam=craftxbox.com@groups.io> wrote:
Hello, I'm planning to purchase the 20w dummy load kit, and got curious, What are the power limiting factors? Certaintly, the resistors would be, but what about the capacitor or diode? To get to a higher power rating, would you just need to replace the resistors, or would those other parts need to be replaced aswell?

jjpurdum
 

:>)

Jack, W8TEE

On Saturday, August 22, 2020, 9:59:05 PM EDT, Gregg Myers <gregg.w7grm@...> wrote:


Ha, ha, you should! It has your name on it, Jack! :)

On Sat, Aug 22, 2020 at 7:55 PM jjpurdum via groups.io <jjpurdum=yahoo.com@groups.io> wrote:
I remember that article! It also had an OLED watt meter, too.

Jack, W8TEE

On Saturday, August 22, 2020, 6:36:45 PM EDT, Gregg Myers <gregg.w7grm@...> wrote:


November 2018 QST describes such an oil submerged dummy load. They are easy to make. If you want to maximize the wattage, you can artfully arrange the resistors in a way that encourages oil circulation through the resistors. I like to keep my Hans QRP dummy load ‘dry’ (and small) so I would not submerge mine in a can full of oil. For the one I made in a can full of mineral oil, I just purchased 20 1k 3w resistors and a BNC connector, just the article in QST. That’s all it is.

73,
Gregg

On Sat, Aug 22, 2020 at 4:16 PM The Crunchbird <pulsedevil@...> wrote:
Heathkit used to make a dummy load called "The Cantenna." It used a pretty small resistor that was submerged in a paint can full of either mineral oil or transformer oil which was better if one could find it. This would effectively make a 20W dummy load work to the 100 watt level. Mineral oil removes the heat from the resistors about five times better than air. It would be interesting for someone to buy an empty paint can from Lowes or Home Depot and try submerging Hans 20 Watt dummy load in mineral oil. It would be even more interesting if Hans were to come out with a modification of his kit that fits into a paint can that the buyers can easily obtain along with some mineral oil. The only modification to the can would be to drill a hole in the lid but a pressure relief valve would be a good thing to add. One word of caution, older transformer oil often contains PCBs or Polychlorinated biphenyls so one is better off using unscented mineral oil (the type used for massage etc.) from the drug store. 

On Sat, Aug 22, 2020 at 5:28 PM spam via groups.io <spam=craftxbox.com@groups.io> wrote:
Hello, I'm planning to purchase the 20w dummy load kit, and got curious, What are the power limiting factors? Certaintly, the resistors would be, but what about the capacitor or diode? To get to a higher power rating, would you just need to replace the resistors, or would those other parts need to be replaced aswell?

Gregg Myers
 

The wattmeter from the article in an Altoids tin. I spy Jack, W8TEE ... 🙂

On Sat, Aug 22, 2020 at 7:59 PM Gregg Myers via groups.io <gregg.w7grm=gmail.com@groups.io> wrote:
Ha, ha, you should! It has your name on it, Jack! :)

On Sat, Aug 22, 2020 at 7:55 PM jjpurdum via groups.io <jjpurdum=yahoo.com@groups.io> wrote:
I remember that article! It also had an OLED watt meter, too.

Jack, W8TEE

On Saturday, August 22, 2020, 6:36:45 PM EDT, Gregg Myers <gregg.w7grm@...> wrote:


November 2018 QST describes such an oil submerged dummy load. They are easy to make. If you want to maximize the wattage, you can artfully arrange the resistors in a way that encourages oil circulation through the resistors. I like to keep my Hans QRP dummy load ‘dry’ (and small) so I would not submerge mine in a can full of oil. For the one I made in a can full of mineral oil, I just purchased 20 1k 3w resistors and a BNC connector, just the article in QST. That’s all it is.

73,
Gregg

On Sat, Aug 22, 2020 at 4:16 PM The Crunchbird <pulsedevil@...> wrote:
Heathkit used to make a dummy load called "The Cantenna." It used a pretty small resistor that was submerged in a paint can full of either mineral oil or transformer oil which was better if one could find it. This would effectively make a 20W dummy load work to the 100 watt level. Mineral oil removes the heat from the resistors about five times better than air. It would be interesting for someone to buy an empty paint can from Lowes or Home Depot and try submerging Hans 20 Watt dummy load in mineral oil. It would be even more interesting if Hans were to come out with a modification of his kit that fits into a paint can that the buyers can easily obtain along with some mineral oil. The only modification to the can would be to drill a hole in the lid but a pressure relief valve would be a good thing to add. One word of caution, older transformer oil often contains PCBs or Polychlorinated biphenyls so one is better off using unscented mineral oil (the type used for massage etc.) from the drug store. 

On Sat, Aug 22, 2020 at 5:28 PM spam via groups.io <spam=craftxbox.com@groups.io> wrote:
Hello, I'm planning to purchase the 20w dummy load kit, and got curious, What are the power limiting factors? Certaintly, the resistors would be, but what about the capacitor or diode? To get to a higher power rating, would you just need to replace the resistors, or would those other parts need to be replaced aswell?

The Crunchbird
 

I just found a link on how to build the dummy load. Here it is for those who are interested. This would work great for those with Hans 50W amplifiers. 
Dave. N2SN
https://www.k4eaa.com/dummy.html#:~:text=Building%20the%20Dummy%20Load&text=It%20uses%20a%20number%20of,during%20tuning%20or%20repair%20procedures.
jjpurdum
 

Al and I tested it at 200W continuous duty for 20 minutes and the oil was approaching the French Fry temperature, although there was no damage to the resistors. Also, I think the Cantenna was a gallon of oil whereas ours was just a quart. That makes me think a KW into our DL is probably not a good idea.

Jack, W8TEE



On Saturday, August 22, 2020, 9:58:40 PM EDT, The Crunchbird <pulsedevil@...> wrote:


What was the power rating for the resistors in oil in the QST article? The Cantenna was supposed to be able to handle 1KW. 
Shane Justice <justshane@...>
 

Do you want fries with that???

73,
Shane
KE7TR



				
					
					

					


On Aug 22, 2020 at 19:07, jjpurdum via groups.io <jjpurdum@...> wrote: 


        
Al and I tested it at 200W continuous duty for 20 minutes and the oil was approaching the French Fry temperature, although there was no damage to the resistors. Also, I think the Cantenna was a gallon of oil whereas ours was just a quart. That makes me think a KW into our DL is probably not a good idea.

Jack, W8TEE




         
        

            

                 
                

                    On Saturday, August 22, 2020, 9:58:40 PM EDT, The Crunchbird <pulsedevil@...> wrote:
                

                


                


                
What was the power rating for the resistors in oil in the QST article? The Cantenna was supposed to be able to handle 1KW. 





            

        






					


				
				
				
			

			
			

				
	

	

	
	

		
			

				
					

				
				

					

						
						
					

				

			

			

				

					

				

			

			
			
				

	



			
		
			
				
	

		
			
			

			
			
			

				

					


						
							
								
	
		
			
		
		
  
	
    jjpurdum
	

	

							
						
					

					

						
							


						
						 
						
							
							
						
						
					

				

			

			

			



        
Nope!

Jack, W8TEE



        

            


                

                    On Saturday, August 22, 2020, 10:16:35 PM EDT, Shane Justice <justshane@...> wrote:
                

                


                


                
Do you want fries with that???

73,
Shane
KE7TR



				
					
					

					


On Aug 22, 2020 at 19:07, jjpurdum via groups.io <jjpurdum@...> wrote: 


        
Al and I tested it at 200W continuous duty for 20 minutes and the oil was approaching the French Fry temperature, although there was no damage to the resistors. Also, I think the Cantenna was a gallon of oil whereas ours was just a quart. That makes me think a KW into our DL is probably not a good idea.

Jack, W8TEE




         
        

            

                 
                

                    On Saturday, August 22, 2020, 9:58:40 PM EDT, The Crunchbird <pulsedevil@...> wrote:
                

                


                


                
What was the power rating for the resistors in oil in the QST article? The Cantenna was supposed to be able to handle 1KW. 





            

        









            
        

					


				
				
				
			

			
			

				
	

	

	
	

		
			

				
					

				
				

					

						
						
					

				

			

			

				

					

				

			

			
			
				

	



			
		
			
				
	

		
			
			

			
			
			

				

					


						
							
								
	
		
			
		
		
  
	
    Shirley Dulcey  KE1L
	

	

							
						
					

					

						
							


						
						 
						
							
							
						
						
					

				

			

			

			


The Cantenna could handle a kilowatt but only for a couple of minutes. If I remember correctly, the maximum power for long term use was 200W. You could probably improve that a bit by sticking a fan in front of it.

Higher power dummy loads exist. I remember the demos that the maker of Alpha amplifiers used to do at conventions. They would put a brick on the key and run their amp for the duration of the convention at maximum legal power, so they had to have a dummy load that could handle 1500W for a couple of days. They also ran ads with the brick and key like this one: 


				
					
					

					


On Sat, Aug 22, 2020 at 9:58 PM The Crunchbird <pulsedevil@...> wrote:
What was the power rating for the resistors in oil in the QST article? The Cantenna was supposed to be able to handle 1KW. 






					


				
				
				
			

			
			

				
	

	

	
	

		
			

				
					

				
				

					

						
						
					

				

			

			

				

					

				

			

			
			
				

	



			
		
			
				
	

		
			
			

			
			
			

				

					


						
							
								
	
		
			
		
		
  
	
    John Rabson
	

	

							
						
					

					

						
							


						
						 
						
							
							
						
						
					

				

			

			

			


At Ongar PO radio station in the 1960s, they used 75 ohm carbon tube resistors with water pumped through them as dummy loads for 9kW ISB HF transmitters.

I had a box of these resistors but they went missing in a house move.

John F5VLF G3PAI


				
					
					

					


On 23 Aug 2020, at 07:10, Shirley Dulcey KE1L <mark@...> wrote:

The Cantenna could handle a kilowatt but only for a couple of minutes. If I remember correctly, the maximum power for long term use was 200W. You could probably improve that a bit by sticking a fan in front of it.

Higher power dummy loads exist. I remember the demos that the maker of Alpha amplifiers used to do at conventions. They would put a brick on the key and run their amp for the duration of the convention at maximum legal power, so they had to have a dummy load that could handle 1500W for a couple of days. They also ran ads with the brick and key like this one: 

On Sat, Aug 22, 2020 at 9:58 PM The Crunchbird <pulsedevil@...> wrote:
What was the power rating for the resistors in oil in the QST article? The Cantenna was supposed to be able to handle 1KW. 






<New-Alpha-555x228.jpg>


					


				
				
				
			

			
			

				
	

	

	
	

		
			

				
					

				
				

					

						
						
					

				

			

			

				

					

				

			

			
			
				

	



			
		
			
				
	

		
			
			

			
			
			

				

					


						
							
								
	
		
			
		
		
  
	
    ajparent1/kb1gmx
	

	

							
						
					

					

						
							


						
						 
						
							
							
						
						
					

				

			

			

			


On Sat, Aug 22, 2020 at 03:16 PM, The Crunchbird wrote:


It would be interesting for someone to buy an empty paint can from Lowes or Home Depot and try submerging Hans 20 Watt dummy load in mineral oil.

One of the tricks of oil cooled (or even air) is getting the resistors in the open enough 
for the coolant to circulate freely.  You need convection and no hotspots.
 
What makes it tough to work well to at least 30mhz the lead lengths need to be short.
That makes the resistor array problematic unless one goes to some effort or it starts 
to look inductive.

Heath cantenna makes use of that with the structure around the resistor to aid cooling 
as hot oil will rise and draw in colder oil from the bottom. That structure shape also 
helps keep the resistor looking like a 50 ohm load at VHF and up.   I have a modified 
version with 14 inch long 3/8th copper tube from top to bottom (10 of them) on the outside 
and soldered in place before building to increase the cooling surface.  That one will take 
400W all day and 1500 peak (10 minutes).   The key is both volume and surface area, 
volume is for peak power and surface area limits temperature rise.

The bench dummy uses a pair of 100W caddock resistors mounted to a copper plate 
(soldered!) that is mounted to 3x5 inch heatsink with 1" fins  in a perforated aluminum  
cage.  That can stand 600W for 2 minutes max and 200w all day.   That was built for 
use through VHF (layout and very short leads).

Over they years I used a BIRD 1KW (continuous) load at work and it was maybe 40 
pounds and looked like a floor radiator.  

Allison
-------------------------------
Please reply on list so we can share.
No private email, it goes to a bit bucket due address harvesting

				
				
				
			

			
			

				
	

	

	
	

		
			

				
					

				
				

					

						
						
					

				

			

			

				

					

				

			

			
			
				

	



			
		
			
				
	

		
			
			

			
			
			

				

					


						
							
								
	
		
			
		
		
  
	
    Steve in Okinawa
	

	

							
						
					

					

						
							


						
						 
						
							
							
						
						
					

				

			

			

			


50 ohm 250w resistors in parallel/series on an aluminum spreader, showing the paint can lid 😅.  It's flat to 30mHz, usable to 50, and with 3 liters of oil I haven't even been able to get it warm with my old FL2100B.  JS6TMW


 

				
				
				
			

			
			

				
	

	

	
	

		
			

				
					

				
				

					

						
						
					

				

			

			

				

					

				

			

			
			
				

	



			
		
			
				
	

		
			
			

			
			
			

				

					


						
							
								
	
		
			
		
		
  
	
    Leland L. Bahr
	

	

							
						
					

					

						
							


						
						 
						
							
							
						
						
					

				

			

			

			



  
  
    
I would think oil seeping/wicking into the coax would change the
      impedance.

    
Lee, w0vt

    

    
On 8/23/2020 1:13 PM, Steve in Okinawa
      wrote:

    

    

				
					
					

					



      
50 ohm 250w resistors in parallel/series on an aluminum
        spreader, showing the paint can lid 😅.  It's flat to 30mHz,
        usable to 50, and with 3 liters of oil I haven't even been able
        to get it warm with my old FL2100B.  JS6TMW

      

       
      
    

  


					


				
				
				
			

			
			

				
	

	

	
	

		
			

				
					

				
				

					

						
						
					

				

			

			

				

					

				

			

			
			
				

	



			
		
			
				
	

		
			
			

			
			
			

				

					


						
							
								
	
		
			
		
		
  
	
    Steve in Okinawa
	

	

							
						
					

					

						
							


						
						 
						
							
							
						
						
					

				

			

			

			


Lee: the dielectric constants of polyethylene and mineral oil are almost identical. 

				
				
				
			

			
			

				
	

	

	
	

		
			

				
					

				
				

					

						
						
					

				

			

			

				

					

				

			

			
			
				

	



			
		
			
				
	

		
			
			

			
			
			

				

					


						
							
								
	
		
			
		
		
  
	
    Leland L. Bahr
	

	

							
						
					

					

						
							


						
						 
						
							
							
						
						
					

				

			

			

			



  
  
    
OK.

    
Lee

    

    
On 8/23/2020 5:40 PM, Steve in Okinawa
      wrote:

    

    

				
					
					

					


Lee: the dielectric
      constants of polyethylene and mineral oil are almost identical. 
      
    

  


					


				
				
				
			

			
			

				
	

	

	
	

		
			

				
					

				
				

					

						
						
					

				

			

			

				

					

				

			

			
			
				

	



			
		
			
				
	

		
			
			

			
			
			

				

					


						
							
								
	
		
			
		
		
  
	
		
			Gregory Winterflood VK8GW
		
  

	

							
						
					

					

						
							


						
						 
						
							
							
						
						
					

				

			

			

			



-- 
Greg Winterflood
VK8KMD
Alice Springs
Central Australia
PG66wh

				
				
				
			

			
			

				
	

	

	
	

		
			

				
					

				
				

					

						
						
					

				

			

			

				

					

				

			

			
			
				

	



			
		
	

	

		
		
		
		
		
	

	

		
		
		
		
		
	

	
	

		
		
		
		
	



	

		
		
		
		
		
		
	

	

	

		

			
	
		

			

				

					
						
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