I am confused about a bench power supply that I just bought. - Page 1
Forum section: electronics / beginners

author: Hextejas
author_rank: Frequent Contributor
timestamp: March 05, 2018, 09:10:55 pm
content: What I need is a PS that provides +15, -15, and GND.So, after I plugged this in I was expecting to be able to read +15 and-15 by connecting one probe to gnd and the other probe to either + or -.That is not what I see and let me see if I can show it.+G = -2.6-G = -15.6+- = +13.01Is this correct, did I buy the wrong PS ?And if this is correct, I think that i will have a lot of trouble when it comes time to wire my circuit.

author: helius
author_rank: Super Contributor
timestamp: March 05, 2018, 09:18:07 pm
content: On a single supply, the GND post is simply a connection to the ground pin of the outlet, it has no function inside the supply. If you want the supply output to be earth-referenced instead of floating, you insert a shorting bar between GND and the (-) post, or between GND and the (+) post. With no shorting bar, the output is floating and the voltage between (-) or (+) and GND is meaningless.To supply +15 and -15 you would want a dual supply capable of tracking.

author: PA4TIM
author_rank: Super Contributor
timestamp: March 05, 2018, 09:26:44 pm
content: Yes, you bought the wrong supply. If you buy a second one you can set them in series to get a symmetrical supply.What you need is a double supply that has the option to set both in series. If you want both rails to behave symmetrical you need one that does tracking.

author: w2aew
author_rank: Super Contributor
timestamp: March 05, 2018, 09:58:05 pm
content: As others have stated, what you have there is a single-output power supply, whose output is floating/isolated from ground. Very common bench power supply configuration - allows you to make is a Positive or Negative supply, but not *both*. It will create the regulated output between the + and - terminals. You're free to use it "floating", or reference one of the terminals to your circuit ground, the supply ground, or elsewhere.Maybe my video will help:

author: Wimberleytech
author_rank: Super Contributor
timestamp: March 05, 2018, 10:02:57 pm
content: What you wanted was something similar to this:https://www.amazon.com/Tekpower-Switching-HY5005E-2-Parallel-connection/dp/B00N0I2JJ4Or as Pa4Tim suggested, buy another one and you can achieve the +/- outputs you need.I am a fan of HP power supplies, like:https://www.ebay.com/itm/HP-6235A-Triple-Output-Variable-DC-mA-Power-Supply/282802272118?epid=2254405040&hash=item41d8543776:g:pEIAAOSwXf1aU81J

author: tautech
author_rank: Super Contributor
timestamp: March 05, 2018, 10:06:38 pm
content: Quote from: Wimberleytech on March 05, 2018, 10:02:57 pmYes, but you need to strap them to get the full 30V between the +/- 15V rails

author: Hextejas
author_rank: Frequent Contributor
timestamp: March 05, 2018, 10:31:46 pm
content: Quote from: w2aew on March 05, 2018, 09:58:05 pmW2, your video helped more than a lot. I happen to have another PS that puts out 14v and I am wondering if the op amp will be too picky re the voltages.Thanks

author: Hextejas
author_rank: Frequent Contributor
timestamp: March 05, 2018, 10:34:49 pm
content: Quote from: Wimberleytech on March 05, 2018, 10:02:57 pmWow, they get a pretty penny for those.

author: Stray Electron
author_rank: Super Contributor
timestamp: March 05, 2018, 10:40:04 pm
content: Even a CHEAP HP supply will still be working when that Chinese piece-o-crap is dead and forgotten. I have aHP supply that was made in 1961 that still works fine and have never had to be worked on or recalibrated.

author: Ian.M
author_rank: Super Contributor
timestamp: March 05, 2018, 10:53:12 pm
content: It will go up to 30V and has a floating output so another option for a +/-15V supply would be to use it with a rail splitter. (If your supply isn't fully floating, you cant ground the rail spitter output.)If you only need a small current, into/outof the 0V rail, theTLE2426IC will do the job. Otherwise you need two equal resistors forming a potential divider across the supply to get a 0V reference and a power OPAMP (either single chip or an ordinary OPAMP with a discrete output stage following it) configured as a unity gain voltage follower. CAUTION: excessive decoupling capacitance between the derived 0V rail and either of the +/- rails will probably cause instability - decouple the potential divider, not the power OPAMP output.

author: PA4TIM
author_rank: Super Contributor
timestamp: March 05, 2018, 10:55:55 pm
content: I have a HP powersupply from 1955. Stil spot on

author: Wimberleytech
author_rank: Super Contributor
timestamp: March 05, 2018, 11:08:52 pm
content: HP Power supplies, Chinese meters

author: NivagSwerdna
author_rank: Super Contributor
timestamp: March 05, 2018, 11:29:03 pm
content: It could be worse. You really need to specify how much +15 and -15 you need.It is possible you could turn up the volume to 30V and then use a resistor divider to provide a virtual ground and hence +15 and -15V.Whether that would work or not would rather depend on how much current you need to source and how much you are prepared to burn in the divider.Might allow you to muddle through though

author: buck converter
author_rank: Regular Contributor
timestamp: March 06, 2018, 12:04:56 am
content: or one of these cheap, heavy, power horseshttps://www.ebay.com/itm/GW-GPC-3020-Dual-Tracking-Laboratory-Power-Supply/122937505809?epid=1919387835&hash=item1c9fa57811:g:mc4AAOSw3q5abTRE

author: Old Printer
author_rank: Frequent Contributor
timestamp: March 06, 2018, 02:46:12 am
content: After watching Alan's (w2aew) power supply video I hopped on eBay and bought the nicest HP 6216A I could find. I just picked up my second one tonight so I have a matching pair. They are great little supplies. I have one of the large 3230 units from the ITT sale and it is a great double supply for $60 but big and has a loud fan. It's relegated to the garage bench. The Tektronix CPS250 is a nice supply with 1 fixed 5V and 2 variable and can be had under the BK 1651 badge for less than $100, I got one recently for $50. Be carful, it's a disease, I have bought five of the damned things in the last few months. Gotta get back on scopes

author: Wimberleytech
author_rank: Super Contributor
timestamp: March 06, 2018, 03:27:27 am
content: Quote from: Old Printer on March 06, 2018, 02:46:12 amMy brother from another mother...lol

author: Hextejas
author_rank: Frequent Contributor
timestamp: March 06, 2018, 03:43:30 am
content: Well, thus is what I wound up buying but if you think that I was unwise, I will back out of the deal.https://www.ebay.com/p/GW-Instek-Gpc-3020-Dual-Tracking-With-5v-Fixed-DC-Power-Supply/1919387835?iid=263426024505&_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D50073%26meid%3D978fdce2f4c146fa871ae542b7652b72%26pid%3D100005%26rk%3D1%26rkt%3D6%26sd%3D122937505809%26itm%3D263426024505&_trksid=p2047675.c100005.m1851

author: Hextejas
author_rank: Frequent Contributor
timestamp: March 06, 2018, 04:13:24 am
content: Is there a difference between HP and Agilent ?

author: helius
author_rank: Super Contributor
timestamp: March 06, 2018, 04:15:37 am
content: HP spun off its test and measurement division into Agilent in 1999, which later spun off its electronic T&M division into Keysight in 2013. So the only difference is the age of the equipment.

author: Brumby
author_rank: Unknown
timestamp: March 06, 2018, 04:26:09 am
content: Quote from: Hextejas on March 06, 2018, 03:43:30 amThat is a much better solution - as long as you don't need anything more than 2A from each of the positive and negative rails. Being a "tracking" supply is great too. You only have to change the Master control to alter the voltage onbothrails. The voltage on the Slave side will follow automatically, irrespective of the Slave control position.It has the advantage of separating the two halves, giving you two independent floating supplies as well as switching them into parallel, where you get the voltage of one, but 4A of current capacity.The separate 5V supply can be very useful, too.So - if a split rail supply capable of up to 2A at up to 30V sounds like it will be enough, then this would be suitable.Being able to reconfigure it as two (up to) 30V/2A independent supplies or one at 4A is a bonus.PS don't sell the one you've got unless you really, really have to. You can never have too many power supplies.

author: jh15
author_rank: Frequent Contributor
timestamp: March 06, 2018, 07:37:06 am
content: Why don't these have a "volume" that goes to 16 volts?Just a joke, most climate and media controls in my car go to eleven re "Spinal tap" movie.On the same note, I repaired HP supplies decades a go, and most will have meters with a grey scale above the ratings.The published specs are for at worst case situations, maybe 105 volts in, temperature, etc.You could always go into the "11" area with totally no worries at 120 volts in.Buy a cheap broken HP, come to the forum for help, If you get GAS.Miss working on TE. Consumer crap makes me glad I'll die before I get older. If in my 20's now, would go nuts with today's future outlook.

author: Old Printer
author_rank: Frequent Contributor
timestamp: March 06, 2018, 01:29:32 pm
content: Quote from: Hextejas on March 06, 2018, 03:43:30 amThat is the first real supply I bought. It is very good and should do you well, just on the large side and the fan runs constantly and kind of loud, though that could be changed down the road. I bought mine from the same seller, one of the better ebay dealers. I got a very clean unit, I think you will be happy and you can't beat that price. Now the trick is to stop buying them, if you figure that out let me know