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I've moved a lot of my home computing to home-brewed 12V UPSes using these. LFP charger --> Battery --> 12V or 5V DC-DC buck or boost/buck regulator --> device.

by dgacmu 2y ago

I've moved a lot of my home computing to home-brewed 12V UPSes using these. LFP charger --> Battery --> 12V or 5V DC-DC buck or boost/buck regulator --> device. Most UPSes are designed for high wattage, short runtime, but things like my firewall or small proxmox box for SDN+DNS benefit from low-wattage, long-runtime, and getting the inverter out of the picture substantially improves runtime. Said proxmox box uses under 10W and gets about 20h of runtime from a $50 battery.

kijiki 2y ago
What charger and battery did you use?
- dgacmu 2y ago
  For the moment some random cheap ones from Amazon - I haven't run it long enough to see if it will last more than a few months of full-time use. The battery was a freebie, so I don't actually recommend it; the charger is an "ULTRAPOWER 4a". We'll see. What it's augmenting is a pretty cheap AIMS power brand modified sine-wave inverter/charger (meh, should have gone pure sine, it causes some of the power supplies to make funny noises) hooked up to a Litime 2kWh LFP battery (very happy with the big battery). TODO on the experiment is swapping out the inverter part with direct 12V conversion for some of the things on the inverter, but I wanted to test the regulator approach with a non-critical component for a month or two first before hooking it to something that can deliver 100A, obviously with a fuse. :-)
thehappypm 2y ago
Does it outperform a $50 UPS?
- dgacmu 2y ago
  Kinda depends what you're asking. There are IP camera 12V UPSes you can get that are ok -- I have a few TalentCell 98Wh units -- but they don't actually deliver regulated power, they just tap directly off of the li-ion cells. Those are about $65. With an inverter UPS, $50 gets you a unit with a single 12V / 8ah or so lead-acid cell; 90 or so watt-hours _could_ be reasonable except that the inverter draws upwards of 10-15W while running, so these units actually won't run even a router for more than a couple of hours. Also, lead-acid dies after about 3 years, and then you're in for another $15 or and a bit of a pain replacing it. I'm really sick of doing surgery on old UPSes at this point and trying to move entirely to LFP for the 10 year lifespan alone. If you want really long runtime, you basically have to DIY, but it's fortunately quite straightforward. Larger LFP batteries are about $250 per kWh, sometimes less. DIY'ing it, you can pick your capacity/runtime independent of your wattage, vs pre-packaged UPSes that frequently couple the two. (I have a big pile of APC UPSes of various sorts, some with external expansion battery packs, and it's quite a hassle to get truly extended runtime from any of them -- I don't want to have a generator, I want 20 hours of extended runtime. I realize I'm a little weird, but I like to hope I'm just ahead of the curve a little on switching. :-)
namibj 2y ago
Interestingly, many universal power supplies (as in, works in the US and in Europe without doing anything to the PSU) are naturally capable of digesting 200~300V unregulated DC. Beware though that DC arcs above 500mA will not easily extinguish, so devices should not be plugged under load (and if it can't be helped, a rapid yoink keeps the arc from burning the contacts). Circuit breakers have to be used with 2 poles in series and mechanically linked to switch together. Check the datasheet for details. Mains fuses with a suitable DC rating on their datasheet are readily available, though.
- user_7832 2y ago
  I believe that's because many power supplies' first step is to rectify the DC into AC, so if you feed in DC directly it "just works".
  - namibj 2y ago
    Well, yeah, but this actually goes beyond those that first rectify. E.g. bridge less totem-pole designs where rectifying and the active power factor correction stage are fused, would also work unless the firmware gets confused by the lack of input polarity flipping. And yes, that topology can also go into a flyback transformer or pretty much any other unipolar magnetic of an SMPS.

by dgacmu 2y ago

kijiki 2y ago

What charger and battery did you use?

dgacmu 2y ago
For the moment some random cheap ones from Amazon - I haven't run it long enough to see if it will last more than a few months of full-time use. The battery was a freebie, so I don't actually recommend it; the charger is an "ULTRAPOWER 4a". We'll see. What it's augmenting is a pretty cheap AIMS power brand modified sine-wave inverter/charger (meh, should have gone pure sine, it causes some of the power supplies to make funny noises) hooked up to a Litime 2kWh LFP battery (very happy with the big battery). TODO on the experiment is swapping out the inverter part with direct 12V conversion for some of the things on the inverter, but I wanted to test the regulator approach with a non-critical component for a month or two first before hooking it to something that can deliver 100A, obviously with a fuse. :-)

thehappypm 2y ago

Does it outperform a $50 UPS?

dgacmu 2y ago
Kinda depends what you're asking. There are IP camera 12V UPSes you can get that are ok -- I have a few TalentCell 98Wh units -- but they don't actually deliver regulated power, they just tap directly off of the li-ion cells. Those are about $65. With an inverter UPS, $50 gets you a unit with a single 12V / 8ah or so lead-acid cell; 90 or so watt-hours _could_ be reasonable except that the inverter draws upwards of 10-15W while running, so these units actually won't run even a router for more than a couple of hours. Also, lead-acid dies after about 3 years, and then you're in for another $15 or and a bit of a pain replacing it. I'm really sick of doing surgery on old UPSes at this point and trying to move entirely to LFP for the 10 year lifespan alone. If you want really long runtime, you basically have to DIY, but it's fortunately quite straightforward. Larger LFP batteries are about $250 per kWh, sometimes less. DIY'ing it, you can pick your capacity/runtime independent of your wattage, vs pre-packaged UPSes that frequently couple the two. (I have a big pile of APC UPSes of various sorts, some with external expansion battery packs, and it's quite a hassle to get truly extended runtime from any of them -- I don't want to have a generator, I want 20 hours of extended runtime. I realize I'm a little weird, but I like to hope I'm just ahead of the curve a little on switching. :-)

namibj 2y ago

Interestingly, many universal power supplies (as in, works in the US and in Europe without doing anything to the PSU) are naturally capable of digesting 200~300V unregulated DC. Beware though that DC arcs above 500mA will not easily extinguish, so devices should not be plugged under load (and if it can't be helped, a rapid yoink keeps the arc from burning the contacts). Circuit breakers have to be used with 2 poles in series and mechanically linked to switch together. Check the datasheet for details. Mains fuses with a suitable DC rating on their datasheet are readily available, though.

user_7832 2y ago
I believe that's because many power supplies' first step is to rectify the DC into AC, so if you feed in DC directly it "just works".
- namibj 2y ago
  Well, yeah, but this actually goes beyond those that first rectify. E.g. bridge less totem-pole designs where rectifying and the active power factor correction stage are fused, would also work unless the firmware gets confused by the lack of input polarity flipping. And yes, that topology can also go into a flyback transformer or pretty much any other unipolar magnetic of an SMPS.