protection features of lab psu - Page 1
Forum section: electronics / beginners

author: RyanS
author_rank: Newbie
timestamp: October 01, 2011, 09:23:49 am
content: I'm a newbie hobbyist just going into learning with a Arduino. To explain I have a physical disability so usually I get someone to set up the hardware on the breadboard and connect it to my computer. Then I can work in the Arduino IDE self sufficiently.I was trying to get this example working the other dayhttp://arduino.cc/en/Tutorial/MotorKnobwith a bipolar stepper motor. Whether it was the cheap unregulated 12 V plugpack/wall wart as the motor psu or dodgy breadboard set up I don't know, in any case the power supply started to smoke which is never a good sign. In any case I had to yell to my assistant for a very quick power cord disconnect. so this has led me to think it's time for a proper powersupply as too much time is wasted searching for the correct voltage plugpack.First things first the type of circuits I'm interested in is optoelectronics, motors of various types, robotics (slightly above my head at this stage) or perhaps switching and environmental control devices that can assist me. a lot of things with wheelchairs are 24v so 0-30v, maximum of 5A would be good. I wonder whether a switch mode lab psu (as something compact would work with limited desk space around my PC) with its inherent ripple is a problem for these sort of circuits? or whether I need to consider linear/hybrid regulation supplies or indeed single or multiple outputs?Although you can power the logic level stuff via the Ardiunos USB or barrel socket, do I need multiple outputs on the power supply if I ever want to breadboard a project away from the actual arduino PCB? another possibility is to simply use plugpacks for logic level voltages and a lab powersupply which (hopefully) can be setup to shut down if anything goes wrong with the circuit for higher current parts.I'm wondering if anyone could recommend a particular manual PSU that if something goes wrong in my circuit will automatically shutdown its outputs (if I go overcurrent, overvoltage short-circuit etc) without physical intervention, and do the cheap import models even have this functionality?Alternatively a PC programmable power supply is perhaps more suitable? not because I'm likely to need complex programming functionality, but in order that I can set voltage, current, etc and most importantly switch the outputs on or off via my computer without having someone stand by to tweak knobs. in fact if I could get away with it PC controlled absolutely everything would be perfect for me! I can give you a budget for the power supply of like $300, but I've rarely seen that sort of functionality for that price except perhaps the B&k one Dave reviewed.sheesh, this post has gotten rather long, Cheers for reading if you got this far!

author: Unknown
author_rank: Unknown
timestamp: October 01, 2011, 11:06:18 am
content: Ripple doesn't sound like a big deal for your applications. Almost all but the cheapest power supplies have an adjustable current limit so you can limit the current to a safe level that won't kill your circuit. Some power supplies have a 5V output with fixed current limit for (5V) digital stuff. It may be convenient to be able to disable both power rails at the same time, which is not possible when using the Arduino as digital supply.

author: saturation
author_rank: Super Contributor
timestamp: October 01, 2011, 02:00:28 pm
content: I concur with alm, also it need not be expensive. The linear PSU Mastech I own, search the archives for reviews and my posts, has both short circuit protection and CC and CV limits, to prevent such things from occurring.

author: RyanS
author_rank: Newbie
timestamp: October 03, 2011, 06:08:06 am
content: Does the 5V output shut down if you overload the main rail, given that it is fixed current? I'm guessing current limit is not particularly necessary for 5V digital circuits?The datasheet for this one:http://au.element14.com/caltek/psd30-3b/psu-laboratory/dp/1270468describes the PSD30/5C, which is 5A, and has an additional 5V output. Has anyone come across that model? element 14 don't appear to stock it.I'm not sure I've seen the Mastech ones available in Australia and I'm a little reluctant to order a heavy item from overseas.

author: saturation
author_rank: Super Contributor
timestamp: October 03, 2011, 03:36:09 pm
content: Yes, a properly designed short circuit protection will shut down the output on a short. You can easily test it yourself, simply short the input terminals. The Mastech are copies of copies, can't tell who the OEM or ODM originally was. You probably find a clone locally; a key item is KISS, so a good basic PSU should provides CC, CV, and output protection and old style analog technology is well established & reliable. No need for progammable output, remote sensing, memories, digital controls etc.,Quote from: RyanS on October 03, 2011, 06:08:06 am

author: Unknown
author_rank: Unknown
timestamp: October 03, 2011, 05:10:43 pm
content: A short on the main rail will not usually shut down the 5V rail, the 5V is often just a simple 7805, which is independent of the other rails (except a possible output enable button). I like adjustable current limits on all my outputs, but that requires a much more complex circuit.