Semi cold start

[Shawn Everette]

I think if it kicked on after a charge or big temp loss you might have some trouble, but otherwise it might run for a while. I keep meaning to check the wattage, and just thought about measuring an amp pull at the different %'s. For the length of power loss in the boonies it might not be able do much, at least when not paired to a generator.

[Eric Trulson]

So I got curious and did some back-of-the-envelope math about this last night. For this UPS and this squirrel cage blower (both about $150, pretty standard stuff for a small furnace blower and good-but-consumer-grade UPS):

Blower draws 0.85A, and say the furnace controller needs 0.15A to make the math simple, so that's about a full amp or 110 watts for the always-running aspects of the furnace controls.

UPS has a 12V, 9A-hr battery, so it's got ~108 watt-hours of charge that it can store up.

So you've got basically 110W-hr of power stored, and 110W of power draw. The discharge isn't perfectly efficient, more like 60-80% in this case, so you won't get a full hour of runtime. But by the numbers, you'd get somewhere between fifteen minutes and a half hour of blower & controller runtime before the UPS ran out of juice. That pretty much matches up with my gut sense on it as well - a normal UPS running a small blower would have enough storage to outlast a 5-10 minute outage, but not an hour-long one.

[Shawn Everette]

.85A is full draw, mine is significantly smaller and idols at 30%. I could make it even more efficient by opening the butterfly past half, but then I lose some minute control. If I can separate the wire I'll take readings from 0-100% tomorrow. As long as it's actually uninterrupted, 15 minutes is more than I need in the vast majority of my circumstances. 4am phone calls are plenty of incentive to spend $150.

[Shawn Everette]

Preliminary results are that after a usual charge my blower doesn't go above 70% and the full system pull is 1.25A. The highest pull I read was actually at 55% about 5 later and didn't get above 1.5A. By a half hour in we were down to a 30% idol at .5A, and it looks like anything below 40% is less than half amp with the lowest read at 24% @.3A right before I charged again at the 1.5 hour mark.

If I'm in tomorrow I'll take another read of the full tank with a long soak, which I would assume to be the most efficient. Either way, it looks like unless I'm charging a 1500w UPS should be more than enough for short outages.

[Art Freas]

The other thing about putting things on a UPS is that you don't want a furnace to run too long without your shop blowers running . CO can build up fast and because of the way it binds in the body you can get CO Poisoning with surprisingly low CO levels.