SMPS in parallel for 24V - Page 1
Forum section: electronics / beginners

author: delicado
author_rank: Contributor
timestamp: May 26, 2020, 12:02:21 pm
content: HiI'm trying to power a 24V 10A motor with a 500W ATX PSU by boosting the 12V rail to 24V. Is there anything I should be aware of? I've heard that having two SMPS interacting with each other may not be a good idea because of potential oscillation events, but is there a way to mitigate that? I know I could use a Meanwell instead, but having exposed mains wires isn't a good idea in my current setup.Thanks

author: tooki
author_rank: Super Contributor
timestamp: May 26, 2020, 12:26:23 pm
content: Do you mean just using a DC-DC boost converter? That’s a totally normal thing to do.

author: delicado
author_rank: Contributor
timestamp: May 26, 2020, 12:31:59 pm
content: Quote from: tooki on May 26, 2020, 12:26:23 pmYes. AFAIK most DC-DC boost converters are switching regulators. If the PSU and the boost converter aren't synchronised, won't something nasty happen?

author: PKTKS
author_rank: Super Contributor
timestamp: May 26, 2020, 01:57:25 pm
content: Quote from: delicado on May 26, 2020, 12:02:21 pmYou SHOULD NOT USE ATX for this.I usually (daily and for a fairly long time) deal with ATX andSMPS PSUs. Your problem is very typical.The relevant points are:- ATX PSUs are **VERY DIFFERENT** from each other- none of them are suited to drive MOTORS.- Although you can use 2 or 3 ATX on "COMPUTERS"...- THEY MUST BE SEPARATED - one for CPU - one for GPU - one for RAID- They should also be ISOLATED from the mains using proper equipoThis will ensure safe proper operationDriving MOTORs is a fairly different problemSMPS are sensitive to LOAD (type of load)You just ca not drive a too inductive or too capacitive loadwith some type of SMPS ( example: pure boost or pure buck)they will probably go wacko oscillating or misbehavingDO NOT USE A BOOST FOR THIS.Try to buy a FLYBACK type (ISOLATED TOPOLOGY) withdecent supervisor (vary among fabs.) capable of drivinginductive loads.SIMPLE EXAMPLEhttps://www.aliexpress.com/item/4000151682100.htmlGet a proper one and hope for the better as somewill not drive highly inductive loads that easyPaul

author: tooki
author_rank: Super Contributor
timestamp: May 26, 2020, 02:06:04 pm
content: Quote from: delicado on May 26, 2020, 12:31:59 pmI don't think so. That topology is extremely common in modern electronics. In a modern computer power supply, nearly all the power is supplied as 12V, which then uses DC-DC converters right at the load ("local regulation") to drop it down to the various voltages needed. In fact, Intel is pushing a standard (ATX12VO) where the power supply is 12V only, meaning that essentially all components will be using a local DC-DC converter.Similarly, in every single laptop, you've got an external switch-mode power supply (charger), and in the computer, DC-DC converters produce all the various voltages.I'm sure there are some types of SMPSs and DC-DC converters that could induce oscillation between them, but I really don't think it's an issue with anything that's even halfway decently designed. And I'd guess that a few extra caps would probably solve the vast majority of them.Quote from: PKTKS on May 26, 2020, 01:57:25 pmBut the question here is about using an ATX PSU to feed a DC-DC boost converter, in which case it's the output characteristics of the boost converter (and not of the ATX PSU) that need to be happy with the motor load, right??The question is not about using multiple ATX PSUs in series to produce 24V. (The thread title is indeed misleading, since the question involves neither putting multiple PSUs in series nor parallel, but rather of daisy-chaining a DC-DC converter onto the output of the PSU.)

author: PKTKS
author_rank: Super Contributor
timestamp: May 26, 2020, 02:13:04 pm
content: Quote from: tooki on May 26, 2020, 02:06:04 pmyes I have got the point very well.I had a problem with several s-360 and s-540 and s-1000trying to have some economy and smaller bench footprintby just adding BOOSTs to themExample I tried to put a 24/10A boost to a s-360-30Awhich typically drives my BENCH GIZMOS for repair.They do not do soft start when INDUCTIVE LOADS are"overloading" the inserted boost.It is safer and cheaper just to buy a proper s-360-24Vand directly try to soft start the motorPaul