In principle is bigger more efficient. - Page 1
Forum section: electronics / projects

author: Simon
author_rank: Unknown
timestamp: July 02, 2018, 06:41:49 pm
content: Say I where to have a number small SMPS, would these be better replaced by one medium power SMPS in terms of efficiency?

author: JS
author_rank: Frequent Contributor
timestamp: July 02, 2018, 06:45:32 pm
content: Not necessary, there are unefficent medium sized smps, limited by thermals on how big and crappy you can go, and small efficient ones for battery powered devices.JS

author: filssavi
author_rank: Frequent Contributor
timestamp: July 02, 2018, 06:51:50 pm
content: It's difficut to judge in your case without more databut usually as power output goes up also efficiency increases, partly it is due to lower impact of fixed losses such as logic or (even if they very slightly increase with power) gate driver losses, also it becomes more and more economically viable to use higher and more expensive component (their higher capital cost is offset by lower operating espenses)it is basically economy of scale appled to hardware

author: Simon
author_rank: Unknown
timestamp: July 02, 2018, 07:21:55 pm
content: I am talking 10's of watts versus 100's of watts

author: CopperCone
author_rank: Super Contributor
timestamp: July 02, 2018, 07:58:57 pm
content: Regardless how are you gonna do load sharing nicely with a whole bunch of DC DC converters? Your going to end up having to do something kinda peicewise in terms of your control loop I think, with startup peculiarities etc, particularly on loads that draw alot or are jumpy.I was dissuaded from tying to load share DC DC converters.

author: BravoV
author_rank: Super Contributor
timestamp: July 02, 2018, 08:18:48 pm
content: Quote from: Simon on July 02, 2018, 07:21:55 pmNot always, for example my recent scores of this DC to DC converters, look at the the top one with 325VDC input, all I need is just AC mains rectification and probably filtering to make a really compact 200 watts module, and these has about 80 to 90% power conversion efficiency.These Vicor modules has power density reaching 50Watts/Inch Cubic, watch closely the TO-220 chip lying on the top one to give you the idea of it's size.

author: Simon
author_rank: Unknown
timestamp: July 02, 2018, 08:29:16 pm
content: Quote from: CopperCone on July 02, 2018, 07:58:57 pmI'm not talking in parallel but single small units for small loads versus one central converter.Putting converters in parallel is not a problem if they have current limiting, I have 6 1.2KW supplies at work and I can put as many as i like in parallel, once one hits it's current limit it starts to reduce voltage and hold current and so another supplies supplies the required current.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 02, 2018, 08:34:59 pm
content: Quote from: Simon on July 02, 2018, 07:21:55 pmGoing from 10s of watt to the 100's of watts range often also is going from no PFC to active PFC. Simply combining several 10 W supplies might violate requirements for PFC in higher power systems. The lack of PFC can help to get a higher efficiency. Other-wise there is a slight tendency for inductors and transformers to get better efficiency when larger. The effect is more pronounced with old style 50/60 Hz transformers, but sill applies to other inductors (e.g. filters).At several 100 W, there may also be a different topology: active PFC + forward converter versus simple rectifier and filter and a flyback.

author: Simon
author_rank: Unknown
timestamp: July 02, 2018, 08:39:23 pm
content: This is DC/DC

author: CopperCone
author_rank: Super Contributor
timestamp: July 02, 2018, 08:40:42 pm
content: just a thought, if you need to sense a bunch of different currents, then you are losing more energy in all the shuntsby load sharing I mean like, disabling/enabling other supplies, if you have 50 supplies doing 100mA each it kind of gets retarded if you have a fixed gate switch when they are running at 1% duty cycle. You really need to know your load to know if you can quickly initalize a bunch of other supplies during a heavy draw as not to overload one to maintain regulation.

author: Simon
author_rank: Unknown
timestamp: July 02, 2018, 08:47:40 pm
content: This is independent supplies with their individual loads versus one bigger converter with all of the loads on it.

author: CopperCone
author_rank: Super Contributor
timestamp: July 02, 2018, 08:51:44 pm
content: I don't know but its easier to design, possibly more reliable if you have loads that short out, and you can spread spectrum the interference.For efficency you have more shunts for current limiting (more graceful failure though) and more transistor gates being driven.

author: CopperCone
author_rank: Super Contributor
timestamp: July 02, 2018, 08:55:30 pm
content: A place to start might be to look at the gate capacitance of the transistors and compare a buncha smaller ones being charged over 1 being charged to achieve the same duty cycle and do an integral on the linear region impedance for switching losses (i think), I doubt the driver supervisor electronics will take much compared to kilowatts of load. I don't really know how to do the losses other then the gate losses and the ON-time losses from RON.This seems almost totally dependent on the switching transistor parameters.

author: james_s
author_rank: Super Contributor
timestamp: July 02, 2018, 10:16:22 pm
content: Generally speaking, a single large device is more efficient than multiple smaller devices, this is true of just about any sort of machine, an extreme example being the huge container ships powered by a single gigantic engine. This assumes though that you are running near maximum capacity all the time. For situations where your peak demand is much higher than the average, it can be more efficient to use multiple smaller units and shut down the ones you don't need at the time.

author: ajb
author_rank: Super Contributor
timestamp: July 02, 2018, 11:36:47 pm
content: Another big factor is distribution, if your loads are spread out then doing individual POL converters allows you to do the bulk of your power distribution at a higher voltage which may provide a substantial reduction in I2R losses. And if that's the case, then doing POL conversion is probably going to give you substantially better power stability as well.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 03, 2018, 03:50:33 am
content: For DC-DC modules in that range, usually yes.Read datasheets and see what efficiency you find in different sizes.Tim