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 -----Original Message----- From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of Don Sent: Monday, March 05, 2007 10:03 PM To: [email protected] Subject: [Repeater-Builder] DC Power Supply Test Load Sometimes I wonder how in the World did I get a Ham Radio Lic , 25 Yrs ago , Anyway here is what I need Help on I bought a 40 Amp Power Adjustable Power supply with Volt and Amp Meters , I would like to make something to test it Before putting it on a Expensive piece of Communications Equipment Like My Kenwood TS-2000 , I tried a Car Battery Tester but that is a 100 Amp non Adjustable Load , Pined the Amp Meter and Voltage Dropped to 6 Volts . To Much Load, Maybe I will try a Car headlight but that will be Unknown as to how many amps at 13.8, and that is what I need to know Exactly a load that will tell me that, anyone that has done this or has any Ideas I would appreciate it Thanks Don KA9QJG
