On 4/6/25 14:55, Mike Hammett via NANOG wrote:
I'm trying to find something that keeps my customer's network gear online for a meaningful amount of time. The challenge is that an ONT, firewall, switch, AP, and some IP phones doesn't add up to be very much load. Most normal UPSes get terribly inefficient at lower load ratings. Add up all of the network devices a customer may have and we rarely break 50 watts of load. Normal, small UPSes are lucky to break 50% efficiency at those loads whereas they may be 95% efficient at say 100 or 200 watts. Get a bigger unit with a bigger battery and now you're even less efficient. Get a big enough unit to have extendable batteries and now you're spending thousands of dollars for such a small request.
This is still cheaper than doing a DC plant. A basic telco rectifier, fuse panel and batteries will be in the 5k+ range. Do you need network monitoring too? A UPS will have a standard SNMP interface which can be a huge plus. At my house I had a 400w load between routers, cameras, telco, and was able to get a 240v APC UPS which was rated at 6kva/5kw. The issue was, this equipment all ran with .7 power factor at best, which is about 550 kVA. I discovered the UPS has a 16s of 12v 5Ah batteries with no real balancing between them. I can see why you have to replace them every 3 years in normal service. What I did was rework the external connector to an external string of 16 50a (9.6kw) and added a BMS to level the charge between the batteries. This would give me about 7 hours to 20%. Recharging took about a day after this rundown. I had about 800 for the UPS, 1200 in batteries, 330 for the BMS, and about 250 for cables/connectors/etc to set it up. $2,600 total, I'm sure it would be a bit more today given inflation. In general it worked well and provided the runtime needed, but it was a bit bulky. The real advantage is the lifetime extension of the batteries, as at full load the battery would see a 26 amp draw, which on a 50a/h battery is .5C discharge rate, vs 5.2c on the stock pack. At my load this was .1C, which is just a trickle, so between this and the BMS, I greatly expanded my battery life, and expected 5-7 years out of the SLA. As I had extra power on this, I ran a 10/3 romex with an L14-30 inlet from the network closet to my office and then powered the office from 240v UPS. This worked very well, and the breaker in the UPS tripped when the water flooded my office, but still kept the network up in the main house which was at a higher level. Eventually we were able to watch empty 5 gallon water jugs float down the hallway and until the water rose over batteries which were on the floor. IMHO you can't beat a used APC UPS with an external pack. -- Bryan Fields 727-409-1194 - Voice http://bryanfields.net