A. O. Smith Water Cooled High Power Dummy Load?

[W1VD]

What does one do with a four year old hot water heater that has a slow leak up top? Obviously replace it - especially when it's still under warranty.

Wonder if anyone has made a low cost, high-power, water-cooled dummy load with a discarded hulk? It'll never be a Bird...but with 2) 12.7 ohm 4600 watt elements one could perhaps:

Use one element with a 4:1 broadband transformer...if it looks fairly resistive.

If not, feed it with an antenna tuner...maybe two elements in series.

Find two additional elements from another dead unit and mount all four in series in a more compact unit. Oil instead of water maybe.

Recall past impromptu high power dummy loads like the Heath Cantenna in the bathtub...nice oil slick...probably pcbs...

[WA1GFZ]

Jay,
Get a smart water heater if you need a new one. It monitors your use hours and shuts itself down when it learns when you sleep. I'm kicking myself for not putting one in the new place. Then my neighbor across the street put one in. My brother had his go bad so I talked him into spending the extra $30 for the AI heater. The cal rod heater must change resistance as it heats up.
A good jug to store your drain oil. I think elements are 3600 watts so 16 ohms.
Still not bad at 64 ohms.....provided you have the juice to get it hot.
Check Home Depot. They have the wattage rating on new elements.

[w8khk]

Jay, about ten years ago I did something similar to what you are considering.  I had to replace the element in our electric water heater when we noticed it took a long time to recover after a shower, only one of the two heaters was functioning.  I was surprised that a replacement element was only $8.99 at home cheapo.   So I got an extra and did some measurements.  Took a while to find my old notes, but here is what I measured:

One element, 13.3 ohms, with 117 VAC applied, measured 8.8 amps with clamp on amprobe.  I went back and got three more.  With four in series, almost exactly 52 ohms.

I had a five gallon container with less than a quart of Thompsons Water Sealer, which I drained off into another container.  I cleaned the 5 gallon metal container.  Then I took a 1/4 inch thick metal plate and bored holes for the four elements, slightly undersize, and threaded the holes using the steel element threads as self-tappers in the softer aluminum, with lots of lubricating oil.  (When servicing HP flat bed plotters, 1/4 inch plates were disposed of quite regularly, I thought they were too nice to recycle for the aluminum.)  I cut hole in the top of the Thompsons container lid, but left the extendable plastic spout in place.  (This makes it easy to fill the container almost to the top.)  I mounted the aluminum disk on top with several 10-32 machine screws and nuts, with silicone sealer between the aluminum and the sheet metal container lid.

I wired the elements in series, and measured between 52 and 53 ohms.   I filled the container with cooking oil, cheapest I could find was Wallymart gallon containers.  I connected the Bird 43 between my HT-32 and the dummy load, and measured about 1.5-1 SWR on 40 meters.  At 2700 plate volts on the PL-172, I loaded it to a full KW out, and after about ten minutes of continuous loading, the container started to get uncomfortable to the touch.  I plan to use this load for the BTA-1MX on 75 in the near future.  I have not tested it higher than the 40 meter band, but I suppose it could be used with a tuner, as you suggest, if the SWR is unacceptable at higher freqs.   Probably would not be good above 10 meters.

My thought is to check and see what the cost of replacement heating elements is today, as used ones can be pretty nasty, and there is probably a good bit of corrosion or contamination on the element and threads in a used water heater.

[WA1GFZ]

Gee 4 in series must be pretty inductive, maybe just a series cap??

[w8khk]

Gee 4 in series must be pretty inductive, maybe just a series cap??

Might be worth a shot.  Didn't have the MFJ-259 when I threw it together.  Might be a good idea to measure it on each band and see what it does.  Could throw a variable cap in series with it and see if that tames it. One thing I did notice when testing with 60 cycles, is the resistance is relatively static even as they heat up.  I know you are supposed to have them immersed to sink the heat when applying power, but short tests out-of-water with 120 volts did not hurt it, and hot or cold the resistance didn't vary more than a tenth of an ohm.

[W1VD]

Frank...I've been running an old Intertec clock timer on the water heater for a while now. On time just 1-1/2 hrs morning and night. 

Rick...figured someone had already looked into this. Good info. Elements are still available for relatively short money.     

[Steve - WB3HUZ]

Someone told me many years ago that they used electric oven elements for a dummy load. I think it was mostly at AM BC frequencies.

[WBear2GCR]

The Heath Cantenna trick was to put a capacitive sleeve around the elephant in the can... dunno but it might work here to extend the bandwidth...

               _-_-bear

[K1ZJH]

The Heath Cantenna trick was to put a capacitive sleeve around the elephant in the can... dunno but it might work here to extend the bandwidth...

               _-_-bear

Waters did that in their oil cooled wattmeter. I think their concept was to have a taper on the shield which essentially turned the resistor into a transmission line with a varying impedance.

[Opcom]

I wondered about that taper. It is found in other dummys as well. Instead of filling the old water heater with oil, why not a mix of water, rust preventive, and antifreeze? it might be less expensive than oil and just as good.

[K1ZJH]

I'd suggest a pressure relief valve too!  It would dangerous to fill one of those and to plug of the ports. The original PRV will also release on temperature, if the thing ever gets that hot! I'm seen videos of hot water heaters blowing up, like having a cruise missile going vertical outta the cellar!

[KB2WIG]

hmmmm   It seems to me that ya can get a automotive heater core and a 'lectric pump to cool down yer Thompson dummy load... 

cheep  cheep happy new year

klc

[K1ZJH]

You can pipe the coolant back to the finals, and oil cool them too. Kinda like a heatexchanger for the klystrons in an analog UHF TV broadcast TX.

What kind of power do you AM'ers run "key down" or on the "swing side?"

[K1JJ]

An old broadcash dummy load trick - quick and dirty:

Fill a large plasdick garbage can with water.  Mix in a lot of salt.  Stir and dissolve.

Hang two large metal plates into the water facing each other like a capacitor.  Connect standard coax directly to the plates. Adjust the plate spacing for 50 ohms... or use an L network to match, if needed, on the ham bands.

This system should take 20kw+ for a few minutes before the water boils, or 1500w indefinately, caw mawn.... :-)

T

[WA1GFZ]

Tom Vu,
I thought you used the air cooled dummy load on off hours.....The dipole

[N5RLR]

The Heath Cantenna trick was to put a capacitive sleeve around the elephant in the can...

I thought that was to create a "closed loop fountain" effect for the cooling oil, similar to a coffee percolator.

[WA1GFZ]

Jay,
That was my plan to add one of those timers. One my neighbor across the street came out of his basement with his water heater on a hand truck. I ran over to help him load it into his truck. He then told me about this computer controlled thing that learns your habits. Thinking about it 1 1/2 hours in the morning and evening is plenty of time and it would be easy to adjust life to the timer. This summer we started doing the same thing with the oil furnace.
The water stayed pretty warm most of the day. 

[wb1aij]

Just fix the leak, disconnect the 220 vac,connect to your transmitter,fill your bathtub with the heated water, and voila, a supercharged ultrasonic cleaner. You will come out REALLY SQUEAKY clean.

[W3RSW]

N5RLR, I did too.  ...a chimney effect to boost circulation by the vertical resistor with recirculation down the outside in the ;greater world.'  I was just getting to write this when I read your post.   I guess my thermo course didn't teach capacity freq. equalizers