Eric, Don, and All,
I have done something similar using RV light bulbs which are rated at 12
volt nominal. Wattages available are typically 60 and 100, which consume
approximately 4.3 and 7.1 watts respectively. The bulbs are cheaper and
fit any common household lamp socket (although wire gauge must be
considered). For mine, I used porcelain open terminal sockets screwed to
a 1x6 board, which I ultimately mounted to the wall of the shop. The
bulbs are cheaper, and don't require fan cooling. I usually try to save
P.S. load checking until the winter months when it serves as
supplemental heat source ;-) ... And it brightens the days...
Bill
N9SII
------ Original Message ----------
Don,
It may be overkill to fabricate a load tester for just your 40A power
supply, but it can be handy to have around. Here's what I suggest: Buy at
least six 2 ohm 100 watt wirewound power resistors, and connect each one in
series with a toggle switch such as might be used for controlling a ceiling
light in your home. Connect each resistor-switch combination in parallel,
and connect the array to the power supply output terminals. The resistors
are available from Digi-Key or Mouser for less than $7 each in small
quantities, and the switches are less than a buck apiece at Home Depot. Rig
the resistors on standoffs so that a fan can blow on them for cooling.
Here's how this "load bank" works, assuming 14 VDC output:
1 switch closed = 7 amps load = 98 watts
2 switches closed = 14 amps load = 196 watts
3 switches closed = 21 amps load = 294 watts
4 switches closed = 28 amps load = 392 watts
5 switches closed = 35 amps load = 490 watts
6 switches closed = 42 amps load = 588 watts
7 switches closed = 49 amps load = 686 watts
8 switches closed = 56 amps load = 784 watts, and so on.
If you wanted smaller increments of load, use 4 ohm resistors rated at 50
watts. Such resistors are about four bucks each. You could also wire up a
matrix of resistors so that several 2 ohm resistors handled increments of 7
amps, some 4 ohms resistors for 3.5 amp increments, and some 10 ohm
resistors for 1.4 amp steps. With careful selection of resistor values, you
can build a load bank that can cover a wide range of current with steps as
small as you want. Just remember that a load bank will generate a lot of
heat, so appropriate heat sinking and forced air cooling is mandatory.
73, Eric Lemmon WB6FLY
