Reliable 5v buck converter recommendations?

[zboblamont]

A 5v UPS is back on my radar to keep the Pi3/HDD/Arduino Controller/Gateway operational through occasional 30 second to 3+ hour power cuts. As the Controller will now be triggering a secondary relay for the central heating it must be 100% reliable, which is not necessarily the case when the Pi reboots, better solved by avoiding them. The existing 2.5A Pi PSU has proved reliable thus far, so 2.5-3A seems a sensible target.
A 12v PSU/Charger and a 7Ah acid gel battery appear the simplest readily sourced combination, a buck converter providing the constant 5v supply more efficiently than a linear regulator.

There are plenty of buck converters on the market from China under various names citing 3A low ripple continuous supply, but does anybody have particular recommendations or sources which have been found to be reliable?

[Yveaux]

@zboblamont said in Reliable 5v buck converter recommendations?:

As the Controller will now be triggering a secondary relay for the central heating

Just thinking out of the box: why don't you power the normally-closed relay from mains, so it will automatically close on power failure?

[zboblamont]

@yveaux A understandable misunderstanding...
The relay is a bistable in parallel with the existing central heating thermostat relay. It is to be triggered by the Controller via a Node at the boiler to maintain minimum temperatures where they decay differently to the location of the main thermostat under specific weather conditions.
Upstairs bedrooms can currently fall below setpoints for several hours while the separate main thermostat is not yet calling for heat.
Additionally, if I go away for a period with the central heating set low, it is possible for some areas to drop further than would be safe, so this is a sort of piggy-back zone control at the expense of a Node and a relay ...
Everything else has battery backup currently except the Controller...

[zboblamont]

Surprised no recommendations offered, so trial and error it will have to be...
Ordered up two XL4015 5A capable 5v boards before Trump modifies free postage . $3 for two (one as a spare), doubt I could build even one at that price, just the 2 week/months slow boat to wait for.
The general idea for the UPS being followed is per link text, the PSU, case and battery are easy enough local sourced, and plenty of time to decide whether USB or direct wiring is the choice of powering up the Pi..

[axillent]

@zboblamont said in Reliable 5v buck converter recommendations?:

Surprised no recommendations offered, so trial and error it will have to be...
Ordered up two XL4015 5A capable 5v boards before Trump modifies free postage . $3 for two (one as a spare), doubt I could build even one at that price, just the 2 week/months slow boat to wait for.
The general idea for the UPS being followed is per link text, the PSU, case and battery are easy enough local sourced, and plenty of time to decide whether USB or direct wiring is the choice of powering up the Pi..

XL4015 will work for you. It is not the best performer but it will do a job.
If I got your question correctly you do need a module to step down from acis battery (nominal 13.2V maximum 14.6) to 5V up to 3A contineous. Right?

Best performers in steping down are so called synchronous rectifiers. The eseest to find as a modules is a module based on MP2307. Also a good selection will be a modules based on MP2315. Both are 3A maximum.

[zboblamont]

@axillent Thank you for that guidance.
The current limit of 2.5A was presumed from the max of the existing supply, others who measured consumption indicate spikes of 2.5A for the Pi3+Gateway+HDD and running current of 1.5A or less.

The selected XL4015 version will be operating well within the 5A limits, and even if not at optimal efficiency, still better than the linear VRs I'm accustomed to.
Your suggestions should cope with brief spikes (HDD spinup) without overheating, locating modules which are NOT poorly fabricated should keep me busy for a few days..

[zboblamont]

@axillent Further to your suggestions, have ordered up a further pair of USB outlet fixed voltage MP2315 types to trial which seem to have been decently reviewed by users as reliable.
Thank you again.

[parachutesj]

I have a powerbank with a USB-DC adapter connected to my RPi. Most likely the battery will die when I do not expect it to happen...
However you spoke about 100% reliability. Whatever you'll build in front of the RPi, it will not be safe enough: At some point, the RPi will fail with its SD-card.
So for me, thinking too much is overkill. There are too many points of failure unfortunately. And if main power is down, a battery powered RPi and sensors don't help much, the pumps, motors and other stuff will be out of service anyway.
Sorry for OT.

[zboblamont]

@parachutesj It's not really OT but don't knock over-thinking, it is a nice diversion in semi-retirement.
The 100% reliability was to do with booting up, the Pi sometimes stalls on power being restored, possibly the hard drive spinning up taxing the power supply. A buffered power supply should avoid a reboot from intermittent outages of variable length common here, and ensure the heating continues when it drops to -20.
SD card is read only and if the HDD fails there is a fallover standby, UPS on the heating, oversized PVs on the water supply if I run out of beer...

[parachutesj]

@zboblamont well, looks like you thought it through. I should move my write access of the RPi also to an HDD, currently just limiting and having a 2nd on standby in case my master fails.
Never had any boot issues though.

Back to the topic:
I have a solar charged weather station and had some issues on reliability. Did quite some testing and ended up building it new. The battery is a simple lion 3.7/4.2 and solar panels usually have much higher output. So bought this and did work well
https://www.aliexpress.com/item/DC-6-24V-12V-24v-to-5V-USB-Output-charger-step-down-Power-Module-Mini-DC/32692500351.html?spm=2114.search0104.3.110.7d863cbbudQu7N&ws_ab_test=searchweb0_0,searchweb201602_2_10065_10068_10890_5730315_319_10546_317_10548_5728815_10696_453_10084_454_10083_10618_5729215_10307_537_536_10134_5733215_5733315_328_10059_10884_5733115_10887_100031_5733415_321_322_5732515_10103_5733515_5733615-10890,searchweb201603_55,ppcSwitch_0&algo_expid=7e5645cc-8270-475b-97a5-d40894e33c53-15&algo_pvid=7e5645cc-8270-475b-97a5-d40894e33c53

not sure if this has enough amps for a RPi

[gohan]

If you don't want to rely on the RPI, you can still use node to node communication and have a node sending temperature to the relay and when it gets a temperature lower than a certain limit will trigger the heating. You can also use a small attyny as an HW watchdog on the pi that will trigger a hw reset if it doesn't detect a certain condition

[zboblamont]

@parachutesj I had two expensive Sandisks blow up before shifting to the HDD, after learning the world is awash with fakes even via reputable companies.... Not sure if spinnup draw current is the cause of the periodic boot hang, but as a UPS is necessary anyway, only a major outage would see it recur.

That buck converter is a dead ringer for the MPP2315 ones I bought after the post by @axillent , aside from "QSKJ" on the back. It was reviewed well elsewhere under the Fine brandname, and should be ample current to fire up and run the Controller/Gateway etc....

[gohan]

SD cards fail faster if you have programs constantly writing to them, I am using dietpi as it has been thought to rely mainly on ramdisk for log and temp files

[zboblamont]

@gohan Didn't think about the hw reset, may incorporate that yet as a belt and braces solution irrespective of the UPS.
The problem with the Node controlling heating lay with human interface to vary conditions, Home/Away, Top floor occupied/Not, ignore that room as the window is removed as my most hated relative is staying in it...
The possibility for later remote secure external access made the Controller the logical choice with the greatest flexibility.