Series connecting HP server power supplies to get 100V DC? - Page 1
Forum section: electronics / projects

author: Chris Wilson
author_rank: Super Contributor
timestamp: October 31, 2015, 10:41:15 pm
content: I have a circa 3kW 51V at 57 amp HP switch mode computer server supply that I have used for various projects, but now have the need for a stiff, regulated 100V or thereabouts supply. I have measured 38K Ohms from +50V to ground and 36K Ohms from -50V to ground. Can I assume they are floating and is it pretty safe to put two in series for 100V? Thanks.

author: Richard Crowley
author_rank: Super Contributor
timestamp: October 31, 2015, 11:04:39 pm
content: It SOUNDS like it may be isolated enough.But can you not find some official specification? or even the schematic?You didn't reveal the model number, so you are on you own for Googling.

author: Chris Wilson
author_rank: Super Contributor
timestamp: October 31, 2015, 11:17:30 pm
content: Hi Richard, the one I have is an HP 226519-001 but despite many false leads I have yet to find a schematic for it.It's one of these, sadly here in the UK I have to pay a good deal more for them, but for a near 60 Amp supply they are still remarkable value.http://www.ebay.com/itm/HP-226519-001-253232-001-3000W-48v-Hot-Plug-Power-Supply-BL-P-Class-Enclosure-/371436715147

author: nctnico
author_rank: Super Contributor
timestamp: November 01, 2015, 01:59:17 am
content: I'd take it apart and look how the ground of the case is connected to the outputs. That shouldn't be hard to check.

author: lukaq
author_rank: Regular Contributor
timestamp: November 01, 2015, 07:36:53 am
content: one of the supplys needs to be floating. Many are doing this for their RC chargers, 2x 12v go get 24v at some 70-100A

author: rikkitikkitavi
author_rank: Contributor
timestamp: November 01, 2015, 12:25:16 pm
content: Is it the ESP120? Many of the largish 48V powersupplies are grounded only at chassi when inserted in the bay, and then positive output is connected to ground. Ground here is chassi = protective earth. I have a pile of Dells that are completely lacking earth lugs at the supply, only 230VAC. The bay is earthed.It means of course that the outputs are floating with respect to earth or chassi.I cant see why two in series is a problem, but there is a limit where isolation will fail of course..Starting them might be be tricky if they trip each others protection. Perhaps using a diode in series with the lowers positive output?

author: Chris Wilson
author_rank: Super Contributor
timestamp: November 01, 2015, 04:04:32 pm
content: Yes, I just checked the labelling and it is an ESP120, are you familiar with that model then? I think other makers used the same supply with different logos on them.If it is floating it makes things quite a bit simplerThanks for that.

author: rikkitikkitavi
author_rank: Contributor
timestamp: November 01, 2015, 07:25:25 pm
content: Not personally, but I read up a bit on itbefore I found my present 12 kW...It is well studied , though.https://endless-sphere.com/forums/viewtopic.php?f=7&t=32829Google "ESP-120"You will find a lot of info.The ESP 120 has a earth connection though.

author: Chris Wilson
author_rank: Super Contributor
timestamp: November 01, 2015, 08:46:12 pm
content: That was a great link, only just got through scanning through it, and associated links, many thanks.Seems isolation is sufficient to series two of them without issues, even with casings bonded. They speak of diodes as mentioned earlier. Do they need to be Schottky diodes, or what? Could anyone advise safe ratings for them, as also mentioned earlier there's an issue with start up and one back feeding the other, which would not be good... Thank you!

author: Zero999
author_rank: Super Contributor
timestamp: November 01, 2015, 08:52:09 pm
content: Quote from: Chris Wilson on November 01, 2015, 08:46:12 pmIf you're considering connecting the power supplies in series then it's advisable to connect a diode in reverse parallel with each power supply, as when overloaded they go into constant current mode and the current needs to bypass the PSU with the lowest voltage.

author: Fungus
author_rank: Super Contributor
timestamp: November 01, 2015, 09:51:12 pm
content: Quote from: Chris Wilson on October 31, 2015, 10:41:15 pmConnect a 1K resistor in series with your multimeter and measure current from each output to GND. If the current from both outputs is zero then it's probably safe to assume they're floating.If there's 50mA on an output then the other output must be connected to GND.

author: Chris Wilson
author_rank: Super Contributor
timestamp: November 02, 2015, 03:08:52 pm
content: Just checked on the one unit I currently (excuse the pun) have and they seem isolated. I believe they become un-isolated when put in the mainframe chassis connectors, which won't affect me. I would like specific info on whether I need diodes, where they need to go, what type, blah blah, if series connecting 2 of them. In fact I am thinking of putting two in one cabinet and having switching to enable them to run parallel or series connected, and maybe to just run one on its own for 50V for less noise and better economy. I can't immediately see a future need for 50V at 114 AmpsI am in the motorsports trade and have some big 200 Amp Anderson connectors for the output sockets, with matching plugs. Thanks for all the help!