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Dummy Load for Astron RS35-M

Discussion in 'Radio Circuits, Repair & Performance' started by KD3LT, Jul 26, 2020.

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  1. KD0CAC

    KD0CAC Ham Member QRZ Page

    Since we are talking about 12vdc , or there about Astron 35amp PS .

    Use to be in auto repair [ and a bunch of other jobs / hobbies ] had multiple DC load testers , the cheapest was the toaster / nichrome-wire - but this is a crude all at once button load about $30 - $60 .
    Another but more expensive carbon-pile tester , it use several carbon disks that were separated by springs and a screw system that would give a variable load control , around $300 - $800 ++ .
    New prices .
  2. N9LCD

    N9LCD Ham Member QRZ Page

    Try 12-volt marine incandescent light bulbs -- the kind that screw into a standard socket.
  3. KA9JLM

    KA9JLM Ham Member QRZ Page

    You can make a Load using some Nichrome Wire.

    Do not touch wire while under test. :eek::oops:

    VE3CGA likes this.
  4. KM3F

    KM3F Ham Member QRZ Page

    120 volt surface mount Ceramic light sockets and 120 volt screw in heater elements.
    Set up on a plywood panel board and fire proof underpayment board, connect load resistance combinations as needed.
    Find all at electrical supply.
    Use at least #8 wire size or larger to cover the highest 'reasonable' loads you will likely want.
    May be even consider Asbestos covered wire used in electric stove tops for load inter connects.
    Use high current terminal posts and connecting cable.
    Welder supply cable is a good consideration.
    Don't use any soldered connections. All Crimp or mechanical.
    For example 120v/60 amps= 2 ohms load or pretty close to it.
    You may want to add an amp meter with enough range, in line.
    This load arrangement should be good for both AC and DC loads all the way to 120 volts AC or rearrange for 240 AC if ever needed.
    The Easiest way to get large flexible capacity.
    When you need heat in the shack in winter, just power up the load bank.
    Do the design, then go get the parts and build it.
    Good luck.
  5. VE3CGA

    VE3CGA XML Subscriber QRZ Page

    exactly what I used to test my power supplies.
    they were cc/cv so I ran them at full output 15V@15amps for 8hrs
    then 1V@15amps for a couple hrs.
    I had the nichrome in a bucket of water fed with some #10 stranded
    after the tests the bucket of water was like water from the hot water tap

    If the nichrome was ever out of the water it would glow red for a bit

    I used it 2yrs ago when I built and tested the 35A supply for my IC9100
    KA9JLM likes this.
  6. W8NGA

    W8NGA Ham Member QRZ Page

    Do they still make those 120 volt screw in heaters?
  7. KA9JLM

    KA9JLM Ham Member QRZ Page

    My guess would be NO. But heat lamps are available.

    They are fire hazards, If not used properly.

    You can tap a length of Nichrome wire for any Voltage or Current that you want to test. Plus the price of wire is cheaper than other test jigs.

    I never did the Bucket of water cooling, But I did modify a cheap $20 heater and had fan cooling.
  8. KM3F

    KM3F Ham Member QRZ Page

    The screw in heating elements are available from an electric supply vendor, not HD or those big stores.
    Same as Ni chrome wire and other items for repair and replacement.
    The appliance, as an open face heater using the screw in element, is not available for obvious reasons and liability.
    The encased heaters of all types have a cutoff switch of some type if they are knocked over while On.
    A bonus using resistance wire in coiled form is at 50 ohms DC resistance, you can use a series variable capacitor to tune out the wire coil's Inductance and have a very nearly flat 50 ohm load for RF up to about 10m depending on the value of variable capacity used. There will still be a power limit but should handle 100 watts for a few minutes at a time.
    I have mounted two 100 ohm 50 watt wire wound resistors in parallel with in series variable cap.
    The variable tunes out the inductance anywhere from 160m to 15m.
    Use Antenna analyzer or SWR meter to bring the match to near zero (j) at the driving frequency and you have a flat match for SWR. It's a tunable load.
    Bonus beside this is you now have a load that 'mimics' an antenna for +/- j if you like to play a little and learn.
    The load for the power supply can even be configured to use as RF load if a UHF connector is mounted and a bit of coax supplied to a 50 ohm load resistance with a series variable capacitor, all in one unit.
    KA9JLM likes this.
  9. WA9SVD

    WA9SVD Ham Member QRZ Page

    That can work, but I'd add two (BIG?) caveats:

    1. Purchase and USE distilled water ONLY; tap or other water may well be at least partly conductive.

    2. Using a plastic or otherwise insulated material for the container (bucket, etc.) will prevent "leaching" (even a small amount) of metal ions as would be possible from a metal bucket. ("Paint" type 5 gal. pails are good. available at most H***Depot, L*we's, and many local hardware stores.)
  10. W9WQA

    W9WQA Ham Member QRZ Page

    dont think conductive water is a problem in 14 volts.
    i happened onto a cheap dual carbon pile yrs ago. did a lot of golf car work with it.
    also i have accumulated piles of big resistors for pennies at hamfests. you just gotta look and buy junk for future use !!
    i have a number of big .5 ohm resistors. i make series/parallel units.
    a .5 ohm from 4 of them makes a good load for serious 14 volt supplies.
    tells you what its worth !!

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