Power supply accuracy - Page 1
Forum section: electronics / testgear

author: jeanguypataterub
author_rank: Contributor
timestamp: September 20, 2014, 02:02:59 pm
content: I have an instek psp405 and I am not sure about its accuracy. When I set 10 V it outputs 10.2.When I set 15 V it outputs 15.2. Etc...Is this an acceptable for electronic work or is this within tolerance?Thanks in advance for your help.PVSent from my iPad using Tapatalk

author: jeanguypataterub
author_rank: Contributor
timestamp: September 20, 2014, 02:23:00 pm
content: I made error on the readings it's actually:30v:30.314v:14.1410v:10.15v:5.05Thanks for the help.PVSent from my iPad using Tapatalk

author: hlokk
author_rank: Contributor
timestamp: September 20, 2014, 03:40:48 pm
content: Are you running a load on it? Does it vary with load?

author: rdl
author_rank: Super Contributor
timestamp: September 20, 2014, 05:29:42 pm
content: Those readings are all fairly good, but how are you measuring? The error could be in the measuring device.

author: grumpydoc
author_rank: Super Contributor
timestamp: September 20, 2014, 06:54:47 pm
content: QuoteI'd agree we need to know how you are measuring the output.The Instek PSP series is supposed to have an accuracy of ± 0.05% for voltage which is actually pretty tight - 30v should be between 29.985V and 30.015V so 30.3V, which is 1% high, is out of spec, as are your other measurements.However these power supplies don't have remote sensing so can only provide their specified accuracy at the output terminals, not at the load - usually this means you will measure lower at the load due to voltage drops in your cables.So, how, where and with what are you measuring the output. Is your multimeter accurate to at least 0.05% - many cheap ones are not.Seehttp://www.gwinstek.com/en/product/productdetail.aspx?pid=38&mid=75&id=164for the specifications.

author: jeanguypataterub
author_rank: Contributor
timestamp: September 22, 2014, 11:22:23 am
content: I was using two multimeters and I also measured it under load. I hooked up an old cb radio and keyed the microphone while I checked the values at 12 v. It maintained the voltage very steadily. I was just trying to decide if this is fairly typical or another unit would likely do better.Thanks again for your input.PVSent from my iPad using Tapatalk

author: jmoreland79
author_rank: Regular Contributor
timestamp: September 22, 2014, 03:25:49 pm
content: I have a BK Precision 1671A, measured with an HP 34401A and no load I get these values:30V: 30.15914V: 14.08410V: 10.05835V: 5.0460

author: LaurenceW
author_rank: Frequent Contributor
timestamp: September 22, 2014, 08:01:31 pm
content: Hold on - we may be confusing two instruments, here.A power supply's job is to supply power, so that your circuit willwork. If that circuit is designed to work at (say) 30V, I would expect it to also work at 25V to 35V, without much by way of a complaint. Otherwise, your design is going to be overly sensitive to small fluctations in the power supply, that could occur from a number of causes, many of which you won't see coming from the comfort of your test bench (user operates equipment out of your temperature range, guy next door switches on his spot welder, lightning strikes the substation down the road... )Precision voltage and current sources are available with very closely specified outputs, typically for calibrating other equipment, not necessarily powering them. Watt for watt, these pieces of test gear are MUCH more expensive than even a decent quality bench power supply.So what I am saying is this. Just about any half-decent power supply should be accurate enoughas a power supplyfor all practical purposes. If your circuit objects to being supplied 30.5V when the power supply reports it is sending 30V, well, you have a bigger design problem right there. And it's hardly the power supply's fault!So, I wouldn't get hung up on the numbers. Those you quote are just fine (unless you have developed a hobby of chasing precision for the sake of it - some have!! Not me.). If it happens that you DO need to know the precise voltage or current, just wack your multimeter into the circuit - assuming that it is correctly calibrated, of course.Having said all that - !! I did select my main power bench power supply, becuase the voltage display goes down to two places of decimals (10mV) and the current down to three (1mA). Many supplies manage with a digit of resolution less than this. This allows me to set or see smallchangesin voltage or current, but I never waste time trying to tweak it spot on to 12.00V for my 12V projects - you are going to lose some in the hook-up wire, anyway.One key measure of a good quality power supply is how much thevoltage drops under load(again, even before your hook-up wires drop another few undred mV). But in practice, in any regulated supply this figure should be too small to bother a tollerantly designed load.That's my (practical) opinion. Others may have a different opinion - they're just wrong, that's all

author: Christopher
author_rank: Frequent Contributor
timestamp: September 22, 2014, 08:20:40 pm
content: It's fine unless you need the accuracy!A typical micro can take +- 0.5V at least.

author: DanielS
author_rank: Frequent Contributor
timestamp: September 22, 2014, 09:05:35 pm
content: Quote from: LaurenceW on September 22, 2014, 08:01:31 pmI bet most of those wide-input circuits are simply voltage regulators for something else which has much tighter tolerances - most digital ICs have 5% tolerances on their power supply rails and you will often want to have better than 5% tolerance on your analog supplies too if you want predictable performance.

author: jeanguypataterub
author_rank: Contributor
timestamp: September 22, 2014, 10:32:12 pm
content: Thanks guys for the reply. I'm gonna keep it. It's a nice power supply for the money.PVSent from my iPhone using Tapatalk