Multiple Grounds With Multiple Buck & Boost Converters - Page 1
Forum section: electronics / projects

author: jmoschetti45
author_rank: Contributor
timestamp: June 27, 2017, 04:32:34 pm
content: Basically, what I have going on here is a giant "12V" UPS/Solar setup.12V Battery bank as one input (solar charging is handled separately), 12V from a power supply.I currently have two solid state relays driven by an esp8266 (and some other stuff) to select the battery bank until it gets down to 11.8V, then fire up the power supply. Once the batteries have recharged enough from the sun, switch back to battery. That part was easy. Keeps electric cost down a lot. Works great for all my unregulated 12V loads right now.Now, to complicate things. I'm going to need 5V, 12V, and 48V outputs. The 12V probably should be an actual solid 12V (some sata hard drives...don't think those will enjoy swinging between 11-15v very much...raid arrays with very vital data).My first thought was simply grab a buck converter for the 5V, and a boost converter for the 48V. Easy enough.They seem to make auto buck/boost converters to make a stable 12V, but those are hard to find with 20A ratings. I could always boost to say 17, then buck down to 12...To get an idea of power consumption here, I'd need 5V 25A, 12V 20A, 48V 2A, and probably 30A of 11-15V with no regulation.Now, that wouldn't be so bad, until I realized a lot of those converters said you can't connect the input and output side grounds or the magic smoke will come out.All these loads need to be switched individually. Things freeze up, and I currently have an RPi set to ping/ssh into everything to see if its alive. If not, I can just have it hard reboot. I was thinking MOSFETs since I have about 100 N-Channels and high side drivers laying around, and I'm trying to minimize current consumption (and physical size) of the controller here, or I'd just go for relays and this wouldn't be an issue.Concerns: If the grounds of the converters can't be connected, I'd have to have separate power rails from there on out. That in itself isn't bad. High side switching is a must...very bad things happen if the ground is switched (things still stay powered via hdmi grounds, audio grounds, mains grounds, etc).Thoughts: I could power the high side drivers off of each power rail, and optoisolate from the esp8266's i2c I/O expanders, but that's going to add a lot of components.Suggestions?

author: Monkeh
author_rank: Super Contributor
timestamp: June 27, 2017, 04:35:18 pm
content: Stupid idea: Mains inverter.Also, if 'things freeze up', your hardware or software needs to go where it belongs: The bin.

author: jmoschetti45
author_rank: Contributor
timestamp: June 27, 2017, 06:03:46 pm
content: I have a mains inverter, but, the goal here is to get rid of the 8 power strips full of wall warts.Things freeze, chinese code isn't perfect, my code isn't perfect.The other reason for switching things. I don't need everything on all the time. Remote control to boot needed things

author: Ian.M
author_rank: Super Contributor
timestamp: June 27, 2017, 06:32:57 pm
content: 12V ( and 24V) automotive voltage range input PC PSUs are readily available. One or two of them could easily supply all your IT equipment loads that require well regulated +5V and +12V rails. You would probably have to put a moderate load on their 3.3V rails for the other rails to be in sspec, but that would almost certainly burn less power than inverting up to 120V AC to use the original mains PSUs.Your only other requirement is boosting to 48V - that's a bit high for the cheap EBAY boost converters but as its a common Telecoms equipment voltage, converters for it are reasonably easy to find. However as the telecoms supply standard is -48V with respect to ground, it would be extremely unwise to connect different models of 48V powered equipment to the same 48V supply. You need to first sort them into positive ground, negattive ground and fully isolated categories then you can connect all the positive ground ones to the same supply which will need an isolated output, and all the negative ground ones to another supply, which can either be isolated or common ground. If you need individual item power control, DIN rail mount or chassis mount relays or SSRs are probably the best option fed by a suitable fusebox or DC rated circuit breakers though if you need mkany individual outputs you may be able to save by desiging and build your own optoisolated power control and distribution board with over-current protection and status monitoring.

author: jmoschetti45
author_rank: Contributor
timestamp: June 27, 2017, 07:01:34 pm
content: Quote from: Ian.M on June 27, 2017, 06:32:57 pmThat's what I was hoping to avoid. It's a viable solution though, 4 modules with MOSFETs and optos isn't too bad.

author: C
author_rank: Super Contributor
timestamp: June 27, 2017, 07:25:01 pm
content: If you have 8 power strips now, you may not need to do all one voltage on one converterLook at aLTC3780 - High Efficiency, Synchronous, 4-Switch Buck-Boost ControllerLinear makes other chips and TI has some chips like this.You can find some prebuilt on EBay and Bang goodhttps://www.banggood.com/LTC3780-Automatic-Buck-Boost-Constant-Current-Power-Module-p-990459.html$15.83By splitting the load you could use many and have options if one fails.This also has the advantage of each having a current limit to protect it's load.From what I see connecting ground should not be a problem with these.From looking at circuit you might be able to modify to more current while using most parts from prebuilt unit.

author: Someone
author_rank: Super Contributor
timestamp: June 27, 2017, 10:38:46 pm
content: Head over to digikey and look at their selection of isolated DC-DC converters, they hover around $1/W (some high volume parts will be lower) and offer complete flexibility. If you break down into segments or individual supplies per load as they are often intended then the enable inputs will save on having to build other switching controls.