So i built a power supply circuit and had some PCB's manufactured for prototyping.
Everything works.
Only thing is, i've designed this power supply and all these boards to be kind of universal prototyping boards for myself.
I designed the power supply to be able step-down up to 20v to as low as 1.5v, and to supply up to 500mA (actually i think it could handle up to 750mA in short bursts).

Testing voltage output is easy, but i want to crank it up and see how well it does at higher currents. I'm struggling at coming up with ways to test this.

First test was a bank of 1/2w resistors, i dont recall how many mA i was pulling at that time, but it was quite lower than 500.

In case anyone cares the power supply is a MC34063 switcher, configured as a step-down (obviously), with what i believe to be appropriately rated components.
House fires and explosions are acceptable during testing.
I also dont have a lot of tools available.

 

Current is just V / R and power is V * I, so buy a value of power resistor that gives the current you want at the desired output voltage.
You can put a bunch of lower wattage resistors in series/parallel to get the resistance and power you need.

For example 0.5A at 10V would require a resistance of 2 ohms with a power rating of at least 5W.
Thus you could connect five 10 ohm, 1W resistors in parallel to get the desired load bank.

Note that those resistors will get quite hot, so you don't want to run the test for more than a minute or so at a time.

 

The way we used to test power supplies was with 100' spools of 16-18 AWG wire. You can get Ω/100' from tables or measurement. Compute the current draw at the voltage you want and let the power supply drive spool(s) of wire all afternoon. As the voltage increases you might need to add more spools. The wire spools will tolerate several 10's of degrees C temperature rise. I don't recommend exceeding about 20-25 °C over ambient.

So #16 AWG is listed at approximately 0.4 Ω/100' so you can achieve a pretty fine tuned load.

 

Current is just V / R and power is V * I, so buy a value of power resistor that gives the current you want at the desired output voltage.
You can put a bunch of lower wattage resistors in series/parallel to get the resistance and power you need.

For example 0.5A at 10V would require a resistance of 2 ohms with a power rating of at least 5W.
Thus you could connect five 10 ohm, 1W resistors in parallel to get the desired load bank.

Note that those resistors will get quite hot, so you don't want to run the test for more than a minute or so at a time.

Isn't your example off by an order of magnitude. 0.5 A x 2 Ω = 1.0 Volts, not 10 volts
For 10 volts at 0.5A you need 20 Ω. Right?
You did get the power rating correct for 0.5A through 20 Ω at 5 Watts

 

Isn't your example off by an order of magnitude. 0.5 A x 2 Ω = 1.0 Volts, not 10 volts
For 10 volts at 0.5A you need 20 Ω. Right?

Of course.
Dang, I always get confused about that decimal point position when using my ol' slide rule.

 

Cool, I dont have access to rolls of wire, so i guess i'll have to buy some power resistors.

If i want to try and determine ripple current and voltage droop without a scope? All i have is a cheapo multimeter.

Might be worth another post, but if i picked up a $100 cheapo DSO scope
like this
https://www.amazon.ca/gp/slredirect...28718504914980&widgetName=click_within_inline
or
https://www.amazon.ca/SainSmart-Ver...1490875352&sr=8-1&keywords=oscilloscope+ds202
would that be worth it?

or should i save up and get a $300 bench top DSO scope like https://www.amazon.ca/Hantek-DSO507...8&qid=1490875237&sr=8-3&keywords=oscilloscope

 

i guess i'll have to buy some power resistors.

A clothes iron could be pressed into service (pun intended ) as a test load. The elements in electric fires or fan-heaters would be suitable too.

 

Testing voltage output is easy, but i want to crank it up and see how well it does at higher currents. I'm struggling at coming up with ways to test this.

One way to test different current loads, without requiring a lot of different values of power resistors, is to use a variable power supply like LM317. With a few resistor values that you can switch in/out, you can test at about any current load you want.

If you really want to stress test your supply, use a power transistor to briefly short your supply.

When you get your scope, you'll be able to measure ripple under loaded/unloaded conditions.

 

if i picked up a $100 cheapo DSO scope
like this
https://www.amazon.ca/gp/slredirect...28718504914980&widgetName=click_within_inline
or
https://www.amazon.ca/SainSmart-Ver...1490875352&sr=8-1&keywords=oscilloscope+ds202
would that be worth it?

or should i save up and get a $300 bench top DSO scope like https://www.amazon.ca/Hantek-DSO507...8&qid=1490875237&sr=8-3&keywords=oscilloscope

That's really only something you can decide, based upon what you intend to use it for and how many electronic projects you think you will do.

 

That's really only something you can decide, based upon what you intend to use it for and how many electronic projects you think you will do.

Unfortunately I dont know enough about the specifications of oscilloscopes to properly understand the limitations of the cheaper units.

 

Also, as it stands i've ordered and recieved 30 pcs of prototype boards with integrated power supplies, and working on another 10 that will include space for a RTC, USB, secondary Microcontroller (with broken out programming connector), and space for prototyping with some SMD components as well as the requisite through hole spaces.
So either i need to find someone who wants to buy the surplus, or I need to get building stuff.
New dashboard for my motorcycle comes to mind... Automatic feeder for my fishtank....