When you know it's time to get a DC Load... - Page 1
Forum section: electronics / general

author: ruairi
author_rank: Frequent Contributor
timestamp: July 07, 2017, 06:40:49 am
content: I'm repairing a mixing console power supply for a friend and needed to test under load, to get to around 10 ohms for each rail I had to run 4 power resistors in series! It was all I had that was high enough wattage, I'm dissipating just over 30 watts on the working rail and more (for short test runs) on the faulty rail.Finances don't allow right now hopefully I can pick up something in the near term, the new Rigol is promising although most of my work is dual rail audio so I'd need a pair. I might be better looking into something used.

author: WastelandTek
author_rank: Frequent Contributor
timestamp: July 07, 2017, 06:59:22 am
content: needs moar fans

author: ruairi
author_rank: Frequent Contributor
timestamp: July 07, 2017, 07:01:42 am
content: Quote from: WastelandTek on July 07, 2017, 06:59:22 amThe supply actually has ridiculously uprated fans that are blowing across the load. That said I'm only running it for very short periods while I probe and figure out what's going on.

author: Muxr
author_rank: Super Contributor
timestamp: July 07, 2017, 07:07:18 am
content: I have one of those Maynuo DC loads. Picked it from eBay from China. Was relatively affordable, and does a decent enough job. I don't use it often, but every once in a while it comes in handy.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 07, 2017, 07:12:31 am
content: Warning, those resistors are only good for a fraction of their headline power, without heatsink. And you need a beastly large heatsink, since they can't take any more temperature than semiconductors can. Unlike semiconductors, the plastic end caps are placed inside a barrel, so when they blow up, they blow out...But as long as you're using them within ratings -- I don't see anything wrong here. Nothing wrong with a pile of resistors when you need to burn some heat.Tim

author: ruairi
author_rank: Frequent Contributor
timestamp: July 07, 2017, 07:13:52 am
content: Having seen the issue Dave had with his BK Precision load I worry about cheaper loads inducing noise in the PSU under test. For a repair like this it wouldn't matter but for design projects it might have me chasing my tail. I could be worrying unnecessarily.Looking at used Agilent and Kikusui things get expensive quickly. I'll have to sell my Tek TDS620A and some Sencore LCRs to raise some funds.

author: CJay
author_rank: Super Contributor
timestamp: July 07, 2017, 07:19:26 am
content: Quote from: T3sl4co1l on July 07, 2017, 07:12:31 amAbsolutely, they need a chunky heatsink and some airflow to keep them in the style they are accustomed to if you want to use them to thier specs and no, not a thing wrong with a bunch of resistors to load up a PSU, many hundreds if not thousands of PC power supplies went through my hands, initially tested in just that way before being 'live' tested in a PC.I'm really pleased I don't repair things for a living nowadays, I'd be pilloried for just getting on with the job and not spending the GDP of a small African nation on test gear.

author: ruairi
author_rank: Frequent Contributor
timestamp: July 07, 2017, 07:19:46 am
content: Quote from: T3sl4co1l on July 07, 2017, 07:12:31 amAbsolutely Tim, I read the data sheet on these when I bought them and was surprised how much they need to be derated without a larger sink. I've got 4 x 100 W resistors in series per side, a 6.8 ohm and 3 x 1 ohm so I am well within the safe zone. A variable load would make it easier to test under various conditions but I'm working with what I have.I bought 8 of the 1 ohms to make a load for testing power amps. They are slightly inductive but not enough to cause issues what I'm doing.

author: ruairi
author_rank: Frequent Contributor
timestamp: July 07, 2017, 07:21:28 am
content: Quote from: CJay on July 07, 2017, 07:19:26 amWhat about the third way? Where I get on with the job but talk myself into buying more test gear too?

author: CJay
author_rank: Super Contributor
timestamp: July 07, 2017, 08:59:32 am
content: Quote from: ruairi on July 07, 2017, 07:21:28 amOh absolutely, I'm not anti test gear at all and it's not aimed at you at all, I work on the principle that money earned is for buying more of the toys we all like and I would happily buy more if I had funds, but there's group of people who seem to believe you can't do anything unless you've got tens of thousands of test gear sitting on a shelf when in fact a box of resistors and a ratty old 3.5 digit DMM are more than good enough for checking the PSU you repaired.Simplicity is elegant, any fool can make a job more complex and probably confuse the hell out of themselves with all the data they gather, 'getting by' with a minimal set of test gear is actually a great way to learn to think and hone your skills because you have to understand and become good at what you are doing, when you get there you are so much better equipped to make good use of the high end kit.If you've a need for the DC load outside of trivial repairs or just have the funds sat there begging to be spent then go for it, I will be suitably envious and of course, please come and torment us with testgear porn and details of projects if you can.

author: RoGeorge
author_rank: Super Contributor
timestamp: July 07, 2017, 09:16:27 am
content: Literally, a bucket of load:

author: idpromnut
author_rank: Unknown
timestamp: July 07, 2017, 11:43:49 am
content: I believe it was mikeselectricstuff that tested a DIN rail power supply using a bucket of water and speaker wire. Make sure the wire is fully submerged. Never underestimate the energy it takes to heat a bucket of water

author: Rolo
author_rank: Regular Contributor
timestamp: July 07, 2017, 12:37:28 pm
content: Creative solutions ! I did make simple a dummy load from parts I had in the drawer. It's not going to win any beauty contests but it does the job. I do not need it much. Don't know the exact specs but I have used it to test my bench PSU with 12V at 3 Amps for a long time. At 18V 3Amps I put an old computer fan against the heatsink.

author: Muxr
author_rank: Super Contributor
timestamp: July 07, 2017, 02:59:45 pm
content: looks pretty to me

author: ruairi
author_rank: Frequent Contributor
timestamp: July 07, 2017, 05:08:53 pm
content: Quote from: CJay on July 07, 2017, 08:59:32 amYou are absolutely right! You can go a long way with a handheld multimeter and some skills and in the field that's all I usually have. I love test gear and some of my gear is more than I need, but I get a disproportionate amount of pleasure from having good tools.I don'tneeda DC load but it would be very useful, that's the point of the thread I guess, how we talk ourselves into such purchases.Cheers,Ruairi