Building a power supply load

snapJaw

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I have a boatload of switchers that I intend to go through over the holidays.

I would like to build a test rig to hook each switcher up to and check voltages. What resistance should I use?

Do all 3 voltages require a load or just the +5? I noticed Randy Fromm's guide mentions using a 1ohm 50 watt resistor. I have a bazillion resistors - all 1/4 or 1/2 watt - is there a way I can make a large series resistor that can serve as a load?

Thanks for any input.
 
Never mind - I don't know what I was thinking.

I have an old harness and pcb that I can use for this.
 
You don't need much of a load, hence the 1 ohm resistor. It is just that at 1 ohm, it is going to draw a lot of power, which if you remember Ohm's Law (I=V/R) gives you 5 AMPs with a 1 ohm resistor. That will burn up those smaller resistors.

One way to draw a load that I use is to take a #44 or #47 bulb and put it across the terminals of the switcher (I actually have a socket with the bulb mounted and terminal leads on wires soldered to the socket lugs). This works for + and - 5 volt. For + and - 12V swap the #44 out for a 12 volt bulb (the number escapes me at the moment).

The bulb should draw enough current to stabalize the switcher and bulbs are designed to dissipate that kind of load.

ken
 
Peter Chou screw terminal power supplies do not need a load.

However, the Peter Chou computer style ones do need a load on the +5 and +12 volt lines.
 
i used a IIRC 12v 18w auto tail light/blinker/brake lamps to put a fair load on the 5v rail (18/12=1.5A) and:
- run more in parallel to increase the load as needed (reduction in resistive load by additional bulbs in parallel = higher current draw)
- run more in series to decrease the load (increase in resistance by adding more bulbs in series reduces current draw)

just calculate the desired load first & therefore number of bulbs either in series or in parallel before you attach to psu so you dont draw more current than the rated rail by mistake and use thick wire to suit. if you are going to test a 15Amp 5v rail at 15Amp dont use 10Amp wire on its own

as ken suggested, easy to buy bayonet sockets for pinball machines (and cheap) with associated lamps so you can rig up a permanent test rig with switches or banana plugs to change combinations of current load

i would include a current meter and voltage meter as well for monitoring (digital or analogue, meh)
 
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