Putting regulated power supplies in parallel? - Page 1
Forum section: electronics / beginners

author: Infraviolet
author_rank: Super Contributor
timestamp: July 29, 2022, 11:59:38 pm
content: Just been pondering, not for any specific application yet, if it is possible to parallel up regulated supplies to give greater current capabilities. I know parallelling batteries of any kind is bad for the battery life expectancy, and likely to go boom if one is silly enough to try with lithium, but is it possible to parallel up power sources after regulation to a known voltage? Are there ways one could put in parallel say the outputs of several 12 volt regulated switch mode DC-DC converters (buck, boost or buck-boost depending on other details, each fed by its own fully separate battery)(rated for maybe 1A out each), or say several 5V USB powerbanks (rated for maybe 2A each)? Is this sort of thing feasible ever? Are there circuit designs which let current from multiple regulated switching supplies be combined without harming the other supplies? I am going to say here, for the purposes of eliminating clever tricks like "use one power supply for this board, one for this motor, and yet another one for that LED array..." that you want all the supplies current brought together to power one big simple thing like a high current DC motor which draws an amount of current which would be n times greater than a single regulated supply is capable of, for n in the range perhaps 3 to 10.Not in any hurry, but would be interested in thoughts on it.Thanks

author: MathWizard
author_rank: Super Contributor
timestamp: July 30, 2022, 02:52:24 am
content: Unless they were designed for it, everyone would say no, don't do it. It will probably burn out something sooner or later. Some op-amp circuit will try and fight the other op-amp circuits, and get the power transistors or their drivers, killed.If u took 2 random 12V regulated PSU's and put them together with only contact resistance between them, their control loops would be fighting each other for control. IDK what would happen, I bet there's utube video's on it, people in their sheds or something.There's video's of people bolting 2 and more, car engines together, and getting it working, but not great, and they did other mods to control them together.Now there are things like multi-phase PSU's , which are more like multi-cylinder combustion engines, but they have the controller made for it.And I bet u can get purpose made separate PSU's, where u can parallel them, but again, they are made to do it.I bet some cheap random SMPS, could be made to work as a multi-phase configuration, IDK how hard that would be, but it's not impossible.

author: Psi
author_rank: Super Contributor
timestamp: July 30, 2022, 03:06:20 am
content: You can do some Diode OR'ing to combine them without them 'seeing' each other.Normally you'd at least want some LC filtering on each to decouple them a little from each other.The issues tends to happen when the output noise from one gets detected by the regulation loop of another one.You may also want a little series resistance to allow them to share the load better.You want the voltage drop across the series resistor at max amps to be a little more than the voltage variations you expect across all the supplies.So if one draws more current that causes more of a Vdrop for that series resistor which brings the voltage down to the point that another one has a higher voltage and therefore takes some of the load. eg, it will seek out a balance. This isn't a problem if you have a tight voltage tolerance of say +/- 100mV for all supplies but can be annoying if its very wide like 4V from 10-14V etc..

author: IanB
author_rank: Super Contributor
timestamp: July 30, 2022, 03:17:01 am
content: I believe it can be possible with compatible regulated laboratory power supplies. I've seen this mentioned, for example, by TTi.Let's suppose you have a load that requires 3 A at 12 V.What you do is you set the first supply in current limited mode to 2 A with a high compliance voltage greater than 12 V, such as 15 V. By itself this will deliver 2 A to the load, but the voltage won't reach 12 V yet.Then you set the parallel supply in voltage mode at 12 V, with a high current limit greater than 1 A. This supply will now deliver additional current to the load until the voltage reaches 12 V, where it will regulate.The net outcome is that the load receives the desired 3 A at the a regulated 12 V.This would probably work best for passive loads, and only if the supplies are designed for it.

author: MathWizard
author_rank: Super Contributor
timestamp: July 30, 2022, 03:17:08 am
content: I used to run 12V computer fans, between the 12V and 5V rail, for 7V. I learned a lot more about how the PSU's work, but not enough to say if thats really a problem or not.

author: EPAIII
author_rank: Super Contributor
timestamp: July 30, 2022, 08:46:51 am
content: I would not do this unless the OEM's specifications and instructions specifically say that the exact two supplies being used can be connected and used in this manner. For one thing, most regulated supplies use series regulation so the current from the larger supply would not flow through that regulating element and therefore could not be regulated by it. And if it is feeding backwards in the regulating element of the smaller supply, it may generate more heat than that element was designed to dissipate. The infamous smoke is the likely result.I have used two supplies in parallel, but they were isolated with steering diodes so, as someone stated above so nicely, they don't "see" each other. And this was done for redundancy, not for extra current capability. Although, doing it for extra current is also possible. But they MUST be isolated from each other.Quote from: IanB on July 30, 2022, 03:17:01 am

author: IanB
author_rank: Super Contributor
timestamp: July 30, 2022, 09:28:42 am
content: Quote from: EPAIII on July 30, 2022, 08:46:51 amThis is a sensible approach, but some manufacturers may indeed say it can be done. For example, this is what my TTi instruction manual says:Quote

author: Ian.M
author_rank: Super Contributor
timestamp: July 30, 2022, 09:44:27 am
content: Many types of PSU *really* don't like being back-fed. At best it confuses the control loop railing some part of it resulting in very poor transient behavior at any step change of load current and at worst, it lets the magic smoke out. Unless its a CC/CV power supply and the manual/datasheet explicitly permits paralleling, you *NEED* a series diode for each, between the output and the paralleling point as 'Psi' suggested. This of course degrades regulation, even if you use high current Schottky diodes. You could of course use MOSFET Ideal Diodes, but be wary of their reverse recovery transient response, which potentially could let a pulse of enough current through to damage the PSU.Balancing the load between multiple parallel PSUs is *difficult* without introducing excessive voltage drop.(PSUs designed and intended for paralleling probably already have droopy output regulation to aid balancing.)Therefore its likely that some of your PSUs will be running at their current limit, and others virtually unloaded, with only one or two supplying current in CV mode, so check that continuous operation in CC mode is permissible - you may need to de-rate. Some series resistance can help a bit e.g. run separate wires from each supply and only combine them at the load. Tweaking their output voltages for better sharing can help, but keep a good eye on the combined voltage, and don't expect the current sharing to be stable with respect to large changes in load current or temperature.

author: armandine2
author_rank: Frequent Contributor
timestamp: July 30, 2022, 09:45:07 am
content: Kikusui PMX-A user manual says you can connect in parallel for the same model - i.e. say, two PMX-A 18V 5A modelssee caution aboutConnecting the load

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: July 30, 2022, 10:19:36 am
content: I wonder if any consideration should be given to circuit protection. Even if stringing all these monsters together does work, would the resulting circuit be able to handle a direct short?One disobedient capacitor could melt the wires and PCB traces leading to it, if given the opportunity.