PSU only 2 terminals not 3 (spikegate) - Page 1
Forum section: electronics / beginners

author: mdronic
author_rank: Contributor
timestamp: May 05, 2015, 09:47:29 am
content: Sorry if these are really silly questions. Searching for a psu and have noted that many psu only have the 2 terminals black and red no green earth. Why? is this safe and should you only buy one that has green for all outputs. Many multi output psu's have only one green for all the outputs. Many single output psu's have none at all. Does this limit the things you can do. and how are they grounded?. Should you add one?Is it possible to make up some leads that sit between the psu and your ? project, that will project it from spikes etc on turn off/ on so you can leave connected with eg an inline toggle on off switch and fuse (? could change fuse depending on...). The idea being that you can leave bannanas connected to the psu and just switch of power via inline toggle, and fuse and ?something else to protect from spikes for the cheaper units where this is lacking or a problem. Rather than taking leads out or turning of the psu. Thanks.

author: electr_peter
author_rank: Unknown
timestamp: May 05, 2015, 10:01:55 am
content: Almost all lab DC CV/CC supplies have floating output. Some also provide earth terminal for ease of wiring. Some don't, because it adds weight/cost and most importantly, size on front panel. You don't need to have earth connection on PSU, especially when you do not understand what it is for.If you are worried about turn on spikes of PSU and still want to keep PSU connected with cables all the time, make adapter cable with switch or relay. Something like this:DUT - cable - switch - cable - PSUThen first turn on PSU, then turn on the switch to power your circuit. This way there will be no spikes.You can add fuse if you like, but why would you need that complexity with constant current PS?

author: Zero999
author_rank: Super Contributor
timestamp: May 05, 2015, 06:38:01 pm
content: Yes it's safe. The output of most lab power supplies is <120VDC which is classified as SELV (Separated, Extra, Low, Voltage) so no earth connection is necessary.Not having an earth is good because it means the power supplies can be connected in series or used for powering things connected to another power supply.

author: feedback.loop
author_rank: Frequent Contributor
timestamp: May 06, 2015, 07:11:24 pm
content: Quote from: mdronic on May 05, 2015, 09:47:29 amWhy? Even half-decent supply shouldn't have significant spikes or overshoots on the output. You can always check that with an oscilloscope.

author: mdronic
author_rank: Contributor
timestamp: May 07, 2015, 02:13:01 am
content: Thanks for your replies. I have been trying to learn some things re: psu's before taking the leap and purchasing one. As my budget doesn't extend to the more recommended ones iam going to have to purchase one of the "other" psu's. Having done some research into these matters here and watched some videos ...these questions come up. There has been threads on eev re spikes with divided opinion about spikes and overshoot the only constant being recommendations that you do not leave things plugged in while switching on the psu. Psu's with a output on\off switch is a good feature to have. The oscilloscope is on the list after psu.While some psu's have an output on\off toggle many do not. So to over come the "design limitation" and add safety it seems logical (to a newbie) to make an inline toggle on\off that did not void the warranty. so a psu--bannana-----cable-----switch------cable-----dut without a fuse will do the job? as suggested.Are there any other things that can be done to protect the psu, project and newbie from being damaged? and things to be aware of , read. thanks.

author: c4757p
author_rank: Super Contributor
timestamp: May 07, 2015, 02:16:02 am
content: Quote from: feedback.loop on May 06, 2015, 07:11:24 pm+1If you get a power supply and it overshoots at startup, return it. It's faulty or faultily designed, and a piece of garbage.

author: mdronic
author_rank: Contributor
timestamp: May 07, 2015, 05:44:37 am
content: Quote from: c4757p on May 07, 2015, 02:16:02 amEg.Posts re spikes with psu's:https://www.eevblog.com/forum/testgear/is-rigol-dp832-output-voltage-spikes-when-unit-is-turned-on-an-real-problem/msg603132/#msg603132This confuses me as there seem to be numerous posts and reviews mentioning spikes or overshooting when switching on psu's, including those suggested to buy. ? there would be a lot of recommended psu's that would be classified as faulty and garbage. From the posts, some psu's have output switches which you can turn on/off with no spike. The main switch (turning on/off) can cause a spike and there seems to have been a lot of discussion regarding this issue. Some spikes have been detected on output? also.Many of the psu's that I can afford do not have an output switch and the question was in part about adding this feature. ? I may have misunderstood the reviews and posts regarding this spikeing business or "spikegate" (news reference). If the criteria above was applied then most psu's would be deemed faulty and garbage as many have spikes apparently.. Thanks.