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How to Build an Uninterruptible Power Supply for Home Devices

38 points by synergy20 4y ago

ccvannorman 4y ago
Or you can be lazy like me and buy 3-4 hr battery backup / surge protector bricks at Costco for $50-100.
- NavinF 4y ago
  I checked Costco and they only sell one UPS: A $50 CyberPower “625VA” (lol) “Simulated Sinc Wave” (sine wave?) model. The datasheet says its real power output is 375W and only lasts 2 minutes at that power draw: https://cdn.cs.1worldsync.com/syndication/mediaserverredirect/d7d7f61256d36bf04a6120012559f0c5/original.pdf https://cdn.cs.1worldsync.com/syndication/mediaserverredirec... It’s certainly better than nothing, but at 12.5Wh (worst case), it has less capacity than most Li-ion USB power banks or even phones. Goes to show how far battery tech has advanced since the days when SLA batteries like the one in your UPS were the only option. For comparison, the iPhone 13 Pro Max in my pocket has a 16.75Wh battery.
  - megous 4y ago
    Can your iPhone battery supply 375W? :)
    - NavinF 4y ago
      That’s a discharge rate of only 22.4C; Most LiPo packs can do 30C for 1 minute as long as it’s mounted to a metal plate or has good ventilation. So yes, almost certainly. For comparison a typical $35 RC LiPo is rated for 50C or 1850W (!): https://www.amainhobbies.com/gens-ace-2s-stick-50c-lipo-battery-w-tstyle-connector-7.4v-5000mah-type-1-gea50002s50d1/p530214 https://www.amainhobbies.com/gens-ace-2s-stick-50c-lipo-batt... (first search result; not a recommendation)
      - megous 4y ago
        Is that the battery you have in your iPhone? That must look splendid. :D
  - pomatic 4y ago
    Nice article. For those less handy, I have the following unsolicited recommendations: * APC have a special offer on Amazon for a 1.4kVA UPS for £130. It's a nicely made piece of kit that will run a PC setup with monitor for an hour or so (depending on power consumption, obviously). * For 12V equipment, a CCTV camera power supply can be had off ebay for £30 or so. Nice steel case, floating battery charger included. 12V to USB adapters are the same as those used in cars, so USB equipment can be readily charged/supplied if necessary. * Lastly, low end switches such as the likes of Netgear are often constructed around a power supply brick that is simply enclosed in a case with the IEC connector exposed. It's simple to remove it, and power it direct from a 12V supply.
20after4 4y ago
Although this is really easy to do and works quite well, I'm not sure a car battery is the best choice with the alternative battery chemistries that are available now. lifepo4 is probably the better choice but I'll just talk about lead acid batteries: Lead acid batteries are, at least IMO, no longer the best choice for a backup power source. I can think of several reasons to avoid using a car battery as a backup: 1) lead battery recycling is very environmentally unfriendly. 2) These batteries have pretty poor performance in deep cycle applications. 3) They require constant charging to maintain their voltage so power use goes up just to keep your backup battery topped up. 4) This constant charging, however, degrades the battery and reduces it's useful life. 5) Almost all lead acid batteries on the market are significantly lower quality than what used to be available a few years ago. They have an even shorter life expectancy than what's easily achievable because they are essentially designed to fail after a year or two.
- the_biot 4y ago
  Your first point is kind of negated by the fact that he specifically says he used a second-hand battery from a scrapyard. Indeed, what he's doing is a very good way to keep it away from any environmentally unfriendly process. I expect that in the somewhat near future, used EV batteries will have a similar second life as house electricity storage. You don't want an EV that's got half the range it used to have, but install it in a house and it's just useful.
- bcrl 4y ago
  Lead acid batteries are widely available, cost effective and have an extremely good safety profile. Getting similar capacity from lithium ion batteries is expensive, and the failure modes are quite nasty in comparison (nobody wants a high capacity lithium ion battery that undergoes thermal runaway, and yes, lipo helps). Maybe that will change over time as better battery chemistries are developed. Lead acid batteries have been around for ages and are well understood. I agree that if you're cycling your batteries, li-ion chemistries have advantage, but lead acid are great for standby use in UPSes.
kalleboo 4y ago
I wish USB-C mobile power banks supported supplying power while being powered, they could be a very cost-efficient UPS for low-power devices like WiFi routers or even LED lighting.
- eternityforest 4y ago
  Some of them do. Romoss calls it endless mode I believe. Unfortunately they almost never have USB-C passthrough, just a single C port and a few As for outputs. LiFePo4 solar generators may occasionally have that kind of feature.
  - rapjr9 4y ago
    Zendure calls it "pass-through charging": https://smile.amazon.com/gp/product/B07HB1B4DB https://smile.amazon.com/gp/product/B07HB1B4DB It only has one USB-C port, but it can also be charged via a micro-USB port, so you can charge it (if you have a hefty power adapter) and run something from the USB-C port at the same time. I think it will handle up to 18W of power. I use one as a backup power supply for a Raspberry Pi4 and it works quite well. I've never timed how long it lasts but it seems to run for around an hour or two when the power goes out.
abrugsch 4y ago
This "UPS" solution is missing a key block though. A charging/BMS circuit for the battery. This would otherwise rely on having to manually attach a car battery trickle charger (don't even get me started on 20after4's comment regarding battery composition choice...) every so often. But then using the original router 12v wall wart as the primary PSU would be unlikely to handle charging the battery as well. A cleaner solution would involve something more like: Mains supply->14-20v/5-10A rated PSU (such as a meanwell unit) -> BMS (battery management system) for chosen battery chemistry -> LiFePo4 battery pack (in a 3s config to give 14.4v nominal output, and however many times parallel to give the desired wattage) -> then feed into the circuit provided in the OP and then you have a fully self contained UPS for the devices covered. Though I might add a 5v/2A buck converter or two for being able to charge some USB devices as well...
turtlebits 4y ago
Solar all-in-one inverters also fit the bill, they hook up to AC for charging and you can prioritize AC over battery for redundancy. Solar isnt required. You can get 3kw ones for around $800. Just add your own 48v battery.

38 points by synergy20 4y ago

ccvannorman 4y ago

Or you can be lazy like me and buy 3-4 hr battery backup / surge protector bricks at Costco for $50-100.

NavinF 4y ago
I checked Costco and they only sell one UPS: A $50 CyberPower “625VA” (lol) “Simulated Sinc Wave” (sine wave?) model. The datasheet says its real power output is 375W and only lasts 2 minutes at that power draw: https://cdn.cs.1worldsync.com/syndication/mediaserverredirect/d7d7f61256d36bf04a6120012559f0c5/original.pdf https://cdn.cs.1worldsync.com/syndication/mediaserverredirec... It’s certainly better than nothing, but at 12.5Wh (worst case), it has less capacity than most Li-ion USB power banks or even phones. Goes to show how far battery tech has advanced since the days when SLA batteries like the one in your UPS were the only option. For comparison, the iPhone 13 Pro Max in my pocket has a 16.75Wh battery.
- megous 4y ago
  Can your iPhone battery supply 375W? :)
  - NavinF 4y ago
    That’s a discharge rate of only 22.4C; Most LiPo packs can do 30C for 1 minute as long as it’s mounted to a metal plate or has good ventilation. So yes, almost certainly. For comparison a typical $35 RC LiPo is rated for 50C or 1850W (!): https://www.amainhobbies.com/gens-ace-2s-stick-50c-lipo-battery-w-tstyle-connector-7.4v-5000mah-type-1-gea50002s50d1/p530214 https://www.amainhobbies.com/gens-ace-2s-stick-50c-lipo-batt... (first search result; not a recommendation)
    - megous 4y ago
      Is that the battery you have in your iPhone? That must look splendid. :D
- pomatic 4y ago
  Nice article. For those less handy, I have the following unsolicited recommendations: * APC have a special offer on Amazon for a 1.4kVA UPS for £130. It's a nicely made piece of kit that will run a PC setup with monitor for an hour or so (depending on power consumption, obviously). * For 12V equipment, a CCTV camera power supply can be had off ebay for £30 or so. Nice steel case, floating battery charger included. 12V to USB adapters are the same as those used in cars, so USB equipment can be readily charged/supplied if necessary. * Lastly, low end switches such as the likes of Netgear are often constructed around a power supply brick that is simply enclosed in a case with the IEC connector exposed. It's simple to remove it, and power it direct from a 12V supply.

20after4 4y ago

Although this is really easy to do and works quite well, I'm not sure a car battery is the best choice with the alternative battery chemistries that are available now. lifepo4 is probably the better choice but I'll just talk about lead acid batteries: Lead acid batteries are, at least IMO, no longer the best choice for a backup power source. I can think of several reasons to avoid using a car battery as a backup: 1) lead battery recycling is very environmentally unfriendly. 2) These batteries have pretty poor performance in deep cycle applications. 3) They require constant charging to maintain their voltage so power use goes up just to keep your backup battery topped up. 4) This constant charging, however, degrades the battery and reduces it's useful life. 5) Almost all lead acid batteries on the market are significantly lower quality than what used to be available a few years ago. They have an even shorter life expectancy than what's easily achievable because they are essentially designed to fail after a year or two.

the_biot 4y ago
Your first point is kind of negated by the fact that he specifically says he used a second-hand battery from a scrapyard. Indeed, what he's doing is a very good way to keep it away from any environmentally unfriendly process. I expect that in the somewhat near future, used EV batteries will have a similar second life as house electricity storage. You don't want an EV that's got half the range it used to have, but install it in a house and it's just useful.
bcrl 4y ago
Lead acid batteries are widely available, cost effective and have an extremely good safety profile. Getting similar capacity from lithium ion batteries is expensive, and the failure modes are quite nasty in comparison (nobody wants a high capacity lithium ion battery that undergoes thermal runaway, and yes, lipo helps). Maybe that will change over time as better battery chemistries are developed. Lead acid batteries have been around for ages and are well understood. I agree that if you're cycling your batteries, li-ion chemistries have advantage, but lead acid are great for standby use in UPSes.

kalleboo 4y ago

I wish USB-C mobile power banks supported supplying power while being powered, they could be a very cost-efficient UPS for low-power devices like WiFi routers or even LED lighting.

eternityforest 4y ago
Some of them do. Romoss calls it endless mode I believe. Unfortunately they almost never have USB-C passthrough, just a single C port and a few As for outputs. LiFePo4 solar generators may occasionally have that kind of feature.
- rapjr9 4y ago
  Zendure calls it "pass-through charging": https://smile.amazon.com/gp/product/B07HB1B4DB https://smile.amazon.com/gp/product/B07HB1B4DB It only has one USB-C port, but it can also be charged via a micro-USB port, so you can charge it (if you have a hefty power adapter) and run something from the USB-C port at the same time. I think it will handle up to 18W of power. I use one as a backup power supply for a Raspberry Pi4 and it works quite well. I've never timed how long it lasts but it seems to run for around an hour or two when the power goes out.

abrugsch 4y ago

This "UPS" solution is missing a key block though. A charging/BMS circuit for the battery. This would otherwise rely on having to manually attach a car battery trickle charger (don't even get me started on 20after4's comment regarding battery composition choice...) every so often. But then using the original router 12v wall wart as the primary PSU would be unlikely to handle charging the battery as well. A cleaner solution would involve something more like: Mains supply->14-20v/5-10A rated PSU (such as a meanwell unit) -> BMS (battery management system) for chosen battery chemistry -> LiFePo4 battery pack (in a 3s config to give 14.4v nominal output, and however many times parallel to give the desired wattage) -> then feed into the circuit provided in the OP and then you have a fully self contained UPS for the devices covered. Though I might add a 5v/2A buck converter or two for being able to charge some USB devices as well...

turtlebits 4y ago

Solar all-in-one inverters also fit the bill, they hook up to AC for charging and you can prioritize AC over battery for redundancy. Solar isnt required. You can get 3kw ones for around $800. Just add your own 48v battery.