testing/loading a homemade power supply without speial equimpent? - Page 1
Forum section: electronics / beginners

author: dentaku
author_rank: Frequent Contributor
timestamp: March 26, 2014, 05:55:26 pm
content: I know some people have special equipment for testing power supplies. Dave just did a video about testing power supplies for and had the right equipment to do it.QESTION: if I finally build a power supply with a 317/337 how can I test I without any special equipment beyond an analog scope and a multimeter.I want to put a load on the outputs, while it's still just on a breadboard and see what it's limits are.

author: Phaedrus
author_rank: Frequent Contributor
timestamp: March 26, 2014, 05:57:04 pm
content: Pick up some power resistors. You can usually get 5-10 ohms 10-50W fairly reasonably.

author: dentaku
author_rank: Frequent Contributor
timestamp: March 26, 2014, 06:11:55 pm
content: Quote from: Phaedrus on March 26, 2014, 05:57:04 pmI found a cement 10ohm 10W resistor in my bins. The next biggest is a 3W resistor but it's about 12Kohm.

author: Phaedrus
author_rank: Frequent Contributor
timestamp: March 26, 2014, 06:21:10 pm
content: I love those 10ohm/10watt jobbies. I use them for discharging 400V capacitors.Figure out what resistance and power you need, then plug those into Digikey here:http://www.digikey.com/product-search/en/resistors/chassis-mount-resistors/66696?k=power%20resistorShould give you some results. Keep in mind that most of these are designed for use with heatsinks; I put my 3x500ohm (166.65ohm) load (meant for 120VAC) on a CPU heatsink with a fan meant for servers, seems to manage fine for up to 5 minutes at least.

author: linux-works
author_rank: Super Contributor
timestamp: March 26, 2014, 06:33:42 pm
content: I bought one of these but have not tried using it yet:http://www.ebay.com/itm/ELTEST-EL2A-LC-DIGITALLY-PROGRAMMABLE-ELECTRONIC-LOADS-DTL2A-LC-COMPATIBLE-/121302512918its not too expensive and I plan to have a cheap arduino controlling it.my dc load tester (background in photo) does the job now (needed one for a project and didn't have time to build this module):but at some point, I do plan to get this serial programmed dc load up and running.

author: eneuro
author_rank: Super Contributor
timestamp: March 26, 2014, 06:50:26 pm
content: This above is rather special equipment-but sometimes such car H4 light bulbs do the job well when connected in pararell at 12V about 55W each , so 2 gives me about 10A and 100W load

author: electronics man
author_rank: Frequent Contributor
timestamp: March 26, 2014, 06:54:32 pm
content: some good ideas

author: miguelvp
author_rank: Super Contributor
timestamp: March 26, 2014, 07:12:20 pm
content: Quote from: electronics man on March 26, 2014, 06:54:32 pmMaybe for a post somewhere else but probably not for a beginners thread.Meaning if you are very careful, have total control of your lab environment and not clumsy at all, nothing against Mike since it's a clever load, but very dangerous nevertheless.

author: edpalmer42
author_rank: Super Contributor
timestamp: March 26, 2014, 07:20:07 pm
content: Just look around your house and see what you've got for electrical heating appliances. Kettles, frying pans, space heaters, irons, etc. These are nothing but big power resistors. Calculate the resistances and see what kind of series/parallel combinations you can come up with. Old and dumb is better than new and smart because there won't be any electronics involved, just bimetallic thermostats.Some years ago I picked up a few heating elements from an electric stove. 208/240V @ 1000/1325W means it's a 43R resistor. 208/240V @ 1765/2350W is a 25R resistor. So if you've got a 30V power supply, 25R would give you 1.2 amps @ 36W. I think it can handle that power!Note that I'm not suggesting that you disassemble your stove. Your significant other might not be impressed. They also might not like seeing a bunch of appliances connected together with clip leads, so proceed cautiously!Ed

author: linux-works
author_rank: Super Contributor
timestamp: March 26, 2014, 07:34:46 pm
content: I would not use 'some random heating appliance' as a load.a good load stays stable and does not vary. as you heat up a heater, its resistance will vary. you do NOT want that!you also don't know if there are thermostats or other things going on.if you have to go very low-cost, a bunch of power resistors in parallel is the best way to go. some banana plugs and sockets would be good so you can add/remove some from your series or parallel combo to change load values.

author: Bored@Work
author_rank: Super Contributor
timestamp: March 26, 2014, 07:40:12 pm
content: Quote from: dentaku on March 26, 2014, 05:55:26 pmDon't. You likely have no proper cooling of the 317 on the breadboard. It won't reach its max specs. Not by several miles. No need to test this.

author: edpalmer42
author_rank: Super Contributor
timestamp: March 26, 2014, 08:29:18 pm
content: Quote from: linux-works on March 26, 2014, 07:34:46 pmDo you really think that a 1000 watt heater is going to notice if you put 50 watts through it? Not a chance! Thermostats?? It'll barely get above room temperature. You're only feeding it 5% of it's rated power! We're not talking about parts per million accuracy here. If you can get the resistance values you need, this is a zero-cost solution that works. It's particularly appropriate for a one-time test.Ed

author: dentaku
author_rank: Frequent Contributor
timestamp: March 27, 2014, 12:01:40 am
content: Quote from: Bored@Work on March 26, 2014, 07:40:12 pmI probably never will max it out anyway. I just need something that's handier than using two 9V batteries all the time and that can give me at least +/- 15V but +/- 18V would be nice too of course.I'm not short on heatsink material so I'll be sure to use enough.

author: pickle9000
author_rank: Super Contributor
timestamp: March 27, 2014, 12:48:20 am
content: If you have some 12 volt computer fans wire 2 of them in series. That will give you something to power. The current draw will vary so you will need to measure it. Typically a single fan will draw between 100-200 ma. This should be within the limits of your supply. If you want to load it down more a couple more fans in parallel with the first one.- The fans will spin slower at lower voltages.- If a fan is forced to spin slower (by a finger or because it's bearing is gummed up) it will draw more current.- measure the current with you meter- If you have a temp probe measure the temp of the regulator.- Regulators blow so make sure you have one handy just in case.- Keep the magic smoke to a minimum but if it blows you just need to fix it.

author: dentaku
author_rank: Frequent Contributor
timestamp: March 27, 2014, 01:32:46 am
content: Quote from: pickle9000 on March 27, 2014, 12:48:20 amA 12V 1PC fan is actually the second thing I tried powering with a simple regulator circuit. The first was an LED of course, just to see if it worked