UPS constraints

Seems to me that you're talking about disconnecting the UPS's internal battery and substituting considerably larger external capacity. In which case the UPSs own float charger is quite possibly not going to be up to the task, and you'll need to disable it, and implement a separate float charge mechanism, especially if you don't want to wait days for your batteries to recharge after use.

Your existing 24V 50AHr is nowhere near enough if you envisage a 1.5KVA load for five hours, and the fact that you have it should probably not factor into your purchasing decision.

Sylvia.

On larger units, the internal battery can be augmented with external "add on" packs. Regardless, I don't expect to cram my batteries into the existing enclosure.

The internal charger typically tops off the "factory supplied" battery in ~3 hours. With 5-10X that capacity, I figure I can still get a final charge in about a day.

[to have two outages within 24 hours of each other would be exceptional; recall, also, that I can always fall back on the genset for prolonged outages -- but, that is far less convenient than a UPS that's up and running at the push of a button!]

However, I am not sure how "smart" the controllers in these devices are. They could, conceivably, complain that the battery isn't "taking a charge" if the battery is *too* oversized for the charger!

"I.e., it seems prudent to oversize the UPS if I intend to have it running for 4 or 5 hours at a time."

UPS's seem to have a sweet spot at about 30-40% of rated (load) capacity. Any lower and you suffer from conversion efficiency. Any higher and the battery depletes disproportionately quicker. I.e., run it at a lower load to increase battery life; or a higher load to increase converter efficiency.

My concern is that running at ~30% of rated load the UPS's typically expect to ONLY operate for 30-40 minutes. "Adding battery packs" is typically only supported on larger units (presumably, if the unit is designed to accommodate additional battery packs, it has been designed to take into consideration extended operating times at higher loads).

So, at what point does the LACK of support for external battery packs change from "saving the cost of a connector" to "saving the costs of a more robust design"?

After a while, people object to having to use $300 batteries and/or AWG 0000 battery cables. :)

If it were me, I'd look at some of the inverters you can get for RVs/ motorhomes. Not the $50 "500 watt" ones in the brightly colored extruded aluminum cases, but the ones in stamped steel enclosures that are designed to go in the electrical cabinet and integrate with the 120 V system. They are designed to be run for (potentially) extended periods of time; many people object to their RV burning down in the middle of the night. These inverters cost several hundred dollars, on up.

I think some of these are just inverters and the battery charging is done "by others" when either shore power (AC) or vehicle power (DC) is available. In your case, this would let you pick a charger to suit your recharge time and battery-life requirements.

There may be electrical code issues with integrating the AC side of one of these with a home electrical system. If you can tolerate the short outages involved with "unplug appliance from normal wall socket, plug it in to inverter socket", then that's the simplest thing to do.

If you don't already have it, consider a large fuse or circuit breaker on the battery pack, plus maybe an automotive-type battery isolator switch. The garage you save may be your own.

Matt Roberds

Yup. Usually a wide range of discarded UPS's to choose from as folks decide they aren't worth the cost of the replacement batteries!

And, teh (obscenely) larger ones (i.e., the size of a refrigerator) have their own, special "lack of appeal"! :>

Yes. I've played with a couple of 2"KW" units in the past. They typically don't do anything besides power conversion (usually with little to no instrumentation, etc.). I'm not even sure how they respond to a depleted (failing) battery condition!

Exactly. I use UPS's on each workstation -- but, primarily to span short outages (i.e., "lights blink" events). In the event of a real outage, I pick a UPS that has been "off", power it on and plug into it. When it gets to the end of its useful life, I move on to the next "unused" UPS and repeat the process.

Slightly inconvenient but not a major hassle given that we can still do things in the house (besides read books). E.g., this computer (plus internet modem) will stay up for a bit over an hour in an outage. Or, I can switch it off and put a few CFL's on the UPS and light these two rooms for several hours.

Already in place (the batteries are housed in a large plastic "battery case"). Watch a (large) battery get shorted *once* and you don't quickly forget the amount of energy within! :>

push of a button? you mean manual activation? have you considered an inverter instead? they're rated for continuous running, but you'll need a separate charger.

--
umop apisdn

Yes. No reason to leave a standby power source running when it's not needed. (Also, recall that this is sited out in the garage so I'd even have to wander out there to connect loads to it)

UPS's are (apparently) rated to run for the durations I am describing. This can be seen by the support for external battery packs to lengthen the available up-time that the bare UPS itself would provide.

But, those packs tend only to be (physically) supported by the larger units. Larger units tend to want to run off 48V.

Maintaining a 48V battery, here, is impractical. OTOH, I already have the need to maintain a 24V battery (so, it could do double-duty with the UPS).

I've seen high quality power inverters come with a UPS feature, but I don't recall from where. You supply your own charger.

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I will not see posts from astraweb, theremailer, dizum, or google 
because they host Usenet flooders.

If you have a genset, why don't you just use it as your "big" UPS? You'll spend less on a transfer switch (if you don't already have one) than you will farting around trying to use a UPS in a task it's not designed for.

Put little UPS's on your 'puter, cable modem (or whatever) and router, to keep everything alive through the blink-off events. Then whenever the power just flat goes out, switch over to the genset and fire it up. If firing up the genset is an adventure every time, well, get the stupid thing fixed!

As an alternative, get a UPS that's designed for external batteries, from a reputable company. By implication, such a gizmo is designed to let you determine how long it'll run, so it should run for a good long time.

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com

Because a genset is overkill for most of these needs. I can run *this* computer with ~100VA -- why fire up a 10KW genset for that purpose? If the outage proves to be just an hour or so, then the UPS's can already address that need.

[Genset is geared towards keeping *big* loads operational -- loads that can't be "pared down" like the loads that you'd put on a "big" UPS (e.g., turn off the TV if you want to conserve battery)]

SWMBO can push a button on a UPS to have power available (she ALSO knows how to plug a cord into an outlet!). If tasked with bringing up power via a genset, she'd probably just sit in the dark.

Genset is outdoors, by necessity. Even a large UPS can operate *indoors*.

Genset requires fuel to operate; UPS's battery can be maintained from *tiny* PV and MPPT charger (which is how the battery is currently maintained in its role powering the irrigation pump).

Fuel degrades over time. I.e., either don't keep the genset's tank full

*or* plan on running through the fuel in it periodically (even if not needed). *And*, keep "fresh" fuel available (siphon from car tank?).

No need for -- nor desire -- a transfer switch and the associated inspections, etc. We're not trying to power the whole house -- or even a significant portion thereof.

It also doesn't lend itself to helping others through those prolonged outages. I can load a genset (or UPS) onto a pickup and bring it where needed. Transfer switch stays with the house and is useless if the genset isn't there as well.

Already have six (seven?) 1.5KVA UPS's to handle the small/transient outages. What I want is something that lasts longer, can handle larger loads and doesn't have to sit *in* the living room/dining room/den/etc. along with it's chemical energy store (because those larger loads will require something "more substantial" than a little consumer UPS to tuck under a desk/dresser)

That is exactly the case! But, the larger UPS's tend to want 48V stacks. I'd prefer to stay with a 24V battery because I already have and need that capability. Installing *two* 24V driven UPS's run off the same battery seems foolhardy (and, buying a second set of batteries for a second 24V UPS is silly given that I could use the TWO sets to power a single 48V UPS).

Presumably, the larger (48V) UPS's are designed with higher margins so would be more comfortable operating in higher ambients (at derated loads). I want that sort of margin but with a lower voltage battery as supply.

I'll just bring some home and see how they fare. I'm sure if I throw them in a closed box, I can quickly get them operating at higher effective ambients and see where they crap out.

You always find APC being scrapped or in the surplus shops, but that is probably because they sell more units than anyone else. I never find anything but APC in the surplus shops.

The comment I made about Eaton is based on someone who uses them in a government facilities and has found them to be crap, as in "Why do we keep buying this shit when they don't last." They haven't had issues with other brands. However if you troll fbo.gov, the US still buys a lot of Eaton UPSs.

48V is the standard in the data centers. I would presume your most reliable gear is on 48V. I've seen 48V computer power supplies in the surplus shops. I believe the voltage goes back to the Bell system, which determined 48VDC is a safe voltage regarding shocks.

Good point about the fuel degradation. That is why most radio shacks use LPG for backup. Supposedly LPG also starts more reliably.

I have no first had experience with LPG generators, but I was surprised to find a cellular shack running totally on LPG. Figure on at least half a KW for the shack, easily in range of a generator. But I wondered how often they have to refill the tank. It can't be very profitable to run a shack like that, but AT&T apparently didn't have any qualms.

You can get 24V inverters. I presume they are meant for continuous duty, but it is a question I never asked when buying one.

It is the UPS that I wonder about regarding continuous duty since most are designed to provide time to shut down a computer system.

Note that a double conversion UPS is designed to run at the rated power since by definition it has to do so. That is, you are always running the inverter in the box unless you switch it to economy mode.

The old/current genset is gasoline fueled -- chosen because I figured I could always siphon fuel out of one of the vehicles instead of having to keep large quantities in jerrycans (somehow, 20G in a car's fuel tank seems safer than a bunch of jerrycan's sitting outside the garage).

The new genset is diesel powered (apparently better long term reliability). But, a problem as we have no real way fo routinely consuming any diesel on hand (short of running the genset, wastefully).

Gensets are just a lot less convenient than a UPS. Oil changes, filters that need to be cleaned, fuel that needs to be "rotated out", etc. And, sited outdoors makes them prone to infestations (poisonous insects, pack rats trying to steal wire, etc.).

But, getting that high power density is only practical with them! So, if it looks like you are in for a prolonged outage, UPS isn't going to cut it but genset *will*.

(would be cool to have a PTO on vehicle for this sort of thing!)

It's *clean* and relatively portable (bottled).

Central Offices (telco) tend to use a small jet engine as power source. No idea of the actual fuel choice, though.

We see lots of LPG powered vehicles, here. But, only *fleet* vehicles. I suspect they have their own depot for filling them.

Oh, I don't know about gas can exposure to the sun. A few cans in the garage is probably safe.

Kind of a waste of money, but I have been buying California CARB rated gas cans and just tossing my old ones (perfectly good except for the CARB rating). These CARB gas cans don't emit fumes. When I go off-roading in the boonies, I fill a 5 gallon can at the edge of civilization, and can travel with the can in the SUV and not smell any fumes. [Obviously I need to use 5 gallons in the car tank first before using the can.]

Hard to believe, but the best cans are the ones that Harbor Freight sells. I wait for a sale, use the 20% off coupon plus the free whatever with purchase, then get the replacement can. That makes tossing something perfectly good a bit more acceptable, plus it is good for the environment.

It is from

These guys got the formula down. Air tight!

That said, some people hate the safety features of the spout. What people don't realize is there is a hook on the spout that you use to push open the safety. While there is no manual to RTFM, you do have to be able to comprehend simple instructions.

keep

other

UPSs.

Most Federal agencies and most State agencies that receive Feuderal funding are required by law to use lowest bid purchasing. You can figure out the rest from there.

?-)

reliable

shops.

48VDC

I find that rather surprising. If you actually monitored the battery voltage both during recharge and in long-term float, you'll find that BOTH will generally exceed the battery manufacturer's recommendations.

The recharge behaviour is largely understandable - they want to have recovery after discharge as quick as possible. But the excessive float voltage is a sure way to kill the best of batteries. The observation that most UPS at disposals are "function OK, needs new battery" is testament to this. Although I refrain from collecting them, I have an assortment ranging from tiny 150W/12v through to big-mother 48V units all of which were donated in this condition.

Eaton are IMHO no worse than others in the small end of the market (

I suggest you look into the implications of low fuel usage in a diesel system.

Yes, that was my point. But, the larger units -- by virtual of having support for external battery packs -- are obviously designed to run for much longer (at higher loads). Often the battery pack is the size of the original UPS.

So, the question boils down to: do the smaller units (24V, 1.5KVA-ish) omit the external battery capability as a cost-saving feature (the price of a connector?), as a "positioning" statement, or, as a consequence of the entire design (cooling?) being downsized to a much tighter operating margin?

E.g., the (APC) SmartUPS 1500 supports external packs (AFAICT it is a 24V design) but the 2200 jumps to a 48V design (no doubt easier to downsize the current requirements at those higher levels).

But, there is less "load margin" (for my use) in a 1500VA unit than a 2200VA. Given that I'm already siting the unit in high ambient, it seems like I'd be tempting fate and inviting a thermal shutdown sooner as I move to lower capacity units.

Good point! Most of the smaller "consumer" units I use (to span "light blink" episodes) are line-interactive. I should look at the ones I've been considering and see if that is also the case (there's a 3KVA unit that I know is a true on-line UPS but it's a 220V model... more hassle than it is worth)

Agreed. Along with Tripp-lite (I have two pallets of the former to sort through and one of the latter). I've rarely found a "dead" unit -- all seem to be discarded solely because "replacing the batteries wasn't in the budget" (regardless of consumer or data center models)

Yes, they made the FerrUPS (sp?), IIRC?

Yes, but 48V requires a much larger investment, for me. I.e., I have no other use for a large 48VDC pile, here. OTOH, I have a couple of things that can (do) use the existing 24V pile... The "extra" two batteries represent $100+ that *only* is there to support the UPS functionality.