> how do I deal with those big 800 to 1000 plus watt power amps?
Bigger resistors, obviously.
1,000W resistors are available; IIRC DigiKey lists to 3,500W (not cheap!!).
Seems to me that iron fence-wire would work. Cheap enough.
TractorSupply sells 17 gauge galvanized "electric fence wire", 1/4 mile (1380') for $13.
I do not know why it is 17 gauge.
#17 Copper is 5.16 Ohms per 1000 feet.
Steel is 6 to 10 times the resistance of copper.
So #17 Steel is 30 to 50 Ohms per 1,000 feet.
Say we want 16 Ohm units (for a 4-8-16 array). Each would be 533' to 320'.
The whole array (one channel) would two rolls tops.
Fusing current for #17 Steel in open air should be >10 Amps, or 160V 10A or 1,600 Watts per 16r unit, 6,000+ Watts for a 4r array.
For $26 and a pair of wood fence-posts to wind a few thousand feet of wire around. (Lace some bamboo stakes vertically, this could be a dandy garden-fence.)
A bit bulky. So you would need a long run of heavy speaker-cable to run from the bench to the garden. (OTOH you could zig-zag it across the rafters in the garage or shed you use for a shop.)
It looks like the fusing current for #17 Copper is 98 Amps. Steel will throw 6 to 10 times the heat per ampere, but has a higher melting point.....
But wait. Metal resistance changes with temperature. You do not want to run it too hot or your "8 Ohms" becomes 10, 12, 20 Ohms. (It is not unusual to run PA speakers hot enough for the VC resistance to double.)
Possibly a smaller gauge leads to an acceptable mix of size and power. I have a spool of nasty iron wire that I probably picked-up in the cement aisle, possibly sold for tying rebar steel rods. If it is half the diameter we would need a quarter of the length, maybe 100 feet for 16r, 10 runs across a 10 foot span, which would fit on a shop wall.
A sturdy plywood box and a 24" box-fan would allow a compact design with higher dissipation.
Doing a load-soak test on a 2*1000W amp may be nice in the winter but very uncomfortable in the summer.
> When do I need a load
You can always run them without a load. Proves it swings. Does not prove it can carry the weight. If an amp has 20 output devices, and all but 2 are blown, it will do fine at infinity or 40 Ohms but fail to swing 4 Ohms to full power. If the amp depends on fan-cooling and the fan is gummy, it may "seem OK" (if you don't know how the fan sounded new) but over-heat or shut-down after many seconds of 500W-1000W into a load.
The last 150W amps I beat-on, I held them in slight clipping for hours at a time. I used a 44W resistor in a can of water.... test was interrupted when too much water steamed off.
Topic: building a dummy load with these parts... (Read 7239 times)