Bench power supply from a G5 PSU and LTC 3780 - Page 1
Forum section: electronics / beginners

author: shobo
author_rank: Regular Contributor
timestamp: November 06, 2017, 08:28:31 am
content: Hi all! I have a behemoth of a power supply from a G5 and i want to convert it to a bench power supply with a couple of LTC3780 modules.Any advice on how i should proceed?some DOs and DONTs? The power supply seems to have 2at least 2 12v rails at 10 amps each at least.

author: Cliff Matthews
author_rank: Unknown
timestamp: November 06, 2017, 03:59:58 pm
content: Are you using the standard 130w units sold on ebay? And expecting each LTC3780 to be galvanically isolated from the other when you're using the same source supply? (the rails are still grounded at the same point..) You may be better off floating the outputs of 2 smaller ATX psu's isolated but inside a safe enclosure (fused of course). On YouTube, others have tested these units:https://www.youtube.com/results?sp=CANQFA%253D%253D&search_query=LTC3780+Buck+BoostYT channel "Onstate LED Lighting" tests a lot of common ebay modules, look in the user comments to glean more info's.

author: shobo
author_rank: Regular Contributor
timestamp: November 06, 2017, 08:17:39 pm
content: Quote from: Cliff Matthews on November 06, 2017, 03:59:58 pmyeah thats the plan.now that you mention it seems logical to have the same ground for both of them.Sent from my SHV-E250L using Tapatalk

author: Cliff Matthews
author_rank: Unknown
timestamp: November 06, 2017, 09:15:05 pm
content: I'm not sure you understand the grounding issue completely.A computer PSU mains ground is most often tied to its output ground. With a bench supply, the outputs should float unless you specifically connect one to a mains ground. So your LTC's need separate floating inputs if you want to arrange their outputs as a split supply (connect the positive of one LTC to the negative of the other, or cascade with other supplies). So in whatever "feeder" DC supply you use, you must ensure it's output ground is NOT mains grounded.

author: shobo
author_rank: Regular Contributor
timestamp: November 07, 2017, 03:46:50 pm
content: Quote from: Cliff Matthews on November 06, 2017, 09:15:05 pmi see.i was not thinking of using then in any configuration (series or parallel)but rather independent.wouldn't disconnecting the cable that goes from the mains cord (yellow green) from the case make its output floating?either way i think for the moment I'll go with one those linear kits from eBay since those i can buy cheaper and localSent from my SHV-E250L using Tapatalk

author: Cliff Matthews
author_rank: Unknown
timestamp: November 07, 2017, 07:22:28 pm
content: A bench supplies usefulness is limited if it cannot be used as bipolar (think of how many op amp cct's usegnd, + and -) and whatever output module or kit you go with, the mains ground is an issue thatwon't go away. Yes, you could disconnect the ground from the case, but it would be safer to have a grounded case with output binding posts floating at the front (if anything goes wrong inside, the case and by extension your body, will never go live..).G5 supply: Have you tested continuity (and capacitance) between the mains ground and the output ground? Did you examine the PCB to see what's required to float the DC outputs ground? Attached jpg is a G5 psu. (yellow line is between primary and secondary, and the red-circled Y-caps are between grounds).

author: shobo
author_rank: Regular Contributor
timestamp: November 07, 2017, 10:57:07 pm
content: My supply is a bit different,it doesn't have the bus bars it has ATX style connectors.for the moment i'll buy a linear kit locally and use it like that.i already found a 100 VA transformer for it and the whole deal will cost around 30 bucks.this is the kit:https://img01-olxro.akamaized.net/img-olxro/146284551_1_1000x700_kit-sursa-reglabila-0-30v-2ma-3a-bucuresti.jpg

author: Cliff Matthews
author_rank: Unknown
timestamp: November 08, 2017, 12:12:22 am
content: You may carefully want to read Soligen's thread on that kit.. because the old greek design needs mods. Cheers! - Cliffhttps://www.eevblog.com/forum/beginners/bangood-psu-enhancements/

author: shobo
author_rank: Regular Contributor
timestamp: November 09, 2017, 08:39:18 pm
content: i read it a few times and some things are clear some are not.either way the most important conclusion i drew is that a 24 transformer is overkill and i'll go down to 18