constructing a UPS

 I am in the market for a larger UPS for my computer, and decided that rather than being normal and just buying one, I'd like to assemble one that could potentially have a PV array added to it someday and/or upgraded without having to discard the whole thing.  (Yes, I know just buying a normal UPS would be cheaper.  Consider it a form of expensive enternainment.)  I'm completely new to the whole solar power thing, so I wanted to run this past everybody to make sure I'm not picking incompatible components or otherwise making poor choices for some reason.
 The UPS does not need to run for any significant length of time; I want to be able to survive weird power fluctuations, and if the power goes off, I want to be able to have time to save whatever I'm doing and shut down.  I don't anticipate needing more than 5 minutes of run time.   While my current system uses significantly less than this, I'm aiming for the eventual possibility of 1000 watts of equipment.  Shutdown will be manual, not automated, so no interface between the UPS and the computer is required.
 I was thinking of going with the following:
Exeltech XP-1100 12v sine wave inverter.
Iota DLS-75 12-v 75-amp charger, with the built-in IQ4 option.
1 Concorde PVX-340T 12v 34AH sealed AGM battery.

 The Exeltech inverter was chosen primarily becuase of the claimed 21.5 year MTBF,  but also becuase it is supposed to be quieter than 45dBA, is pure sinewave, and is apparently reasonably efficient.
 The Iota charger was chosen mainly becuase I'm vaguely concerned about unexpected incompatibilities between products and an Exceltec rep recommended them; any added for/against advice would be appreciated.  I can't locate any noise rating on this one (I've just emailed Iota, but they haven't responded to a previous question, so my email might not be getting through.)  I'm also a little confused about the combination of listed maximum wattage and amperage on the Iota chargers.  I assume I want to matching the charger output wattage to that of my inverter (so batteries aren't used significantly unless the power goes out), hence the choice of the DLS-75, which can continuously put out 1000 watts.  But it says it can't draw more than 22 amps, so what does the 75amps of output refer to?  Or is that a brief surge capability provided by capacitors or something?
 The battery was chosen as an average between cost and lifespan.  Something that lasts a lot longer would be preferrable, but I didn't really want to fork over $1600 for a pair of Surrette batteries that I will probably find a way to fry before they expire from old age.
 Speaking of frying, is there anything special I should be doing for surge protection?  Can I just plug the charger into a Brick Wall surge supressor, or would that interfere with anything in some way?
 Is a 12v system really what I want if I want to someday add a solar panel? I was originally thinking about a 24-volt system (supposedly more efficient if the panels aren't right by the batteries?) but went down to 12v to reduce the cost.
 Last but not least:  I'm assuming both the inverter and charger will always be connected to the battery with the charger charging all the time to keep the batteries topped off and the inverter being switched on/off as needed, so when turned on the inverter is just pulling power straight from the charger.  Is this setup horribly inneficient because I'm always going through the battery, or is that ok becuase the charger is capable of supplying all the current as long as I have grid power?  I was originally looking at a combination inverter-charger until I found out how much they cost and went to this configuration.
 Thanks for any info anybody can supply!

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,717 admin
    Re: constructing a UPS

    Personally, I would go look around a computer salvage company/auction house for an APC, Triplite or other good brand of continuous conversion UPS. A few years ago, I was wheeling dozens of 3-5kW units out the door for 10 cents on the dollar. These include everything you need for 15+ minutes of battery operation, cheap and reliable--and will give you a automated computer shutdown ability--don't sell this short. The chances you will be at your computer ready to do a manual shut down, vs being across the house/street or on your way somewhere else and forgot to save your work will happen. And if you are after such high hardware reliability, it only makes sense to automate the "wet-ware" side of things too (where all of the mistakes are usually made).

    If purchasing an (a?) used UPS--plan on replacing the batteries--they will not be any good after a few months without power.

    You may have some issues with getting the battery to charge correctly in a home-brew situation... The charger needs to sense the battery condition (voltage/temperature) and with the heavy (1kW+ load), a standard charger (unless it has remote sensing) may not quite cut it. Another reason I would go with the above suggestion.

    In theory, other than the price of the inverter, a 12v or 24v system should cost you about the same to build (solar panels are pretty much priced per watt in any voltage--once you get to the larger sizes. And the the same charge controller frequently can charge multiple voltages and types of batteries with a configuration switch change or two. And at higher currents (1kW at 120vac => 100 amps at 12 vdc), the 24 or 48 vdc system, with its smaller wires and less issues with voltage drop, would be a better design.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: constructing a UPS
    I was thinking of going with the following:
    Exeltech XP-1100 12v sine wave inverter.
    Iota DLS-75 12-v 75-amp charger, with the built-in IQ4 option.
    1 Concorde PVX-340T 12v 34AH sealed AGM battery.

    Sean,

    Although the Exeltech 1100 inverter will work for your intended purpose, this combination of equipment otherwise doesn’t make sense from a strictly technical perspective.

    Exeltech's published noise spec is indeed 45 dBa. I suspect that is valid for the XP line when they're convection cooled, but my XP 600 is noticeably louder when its cooling fan kicks in. Fortunately, it's in my garage.

    Assuming a 1000 W load and 85% full-power inverter efficiency, the inverter will draw upwards of (1000 W / 12 V) / 85% = 98 A. (Note the inverter’s rated input current is 107.8 A. :-o ) This will require BIG cable (1/0 AWG or larger) from the charger to the battery(ies) and inverter, and, allowing for the NEC’s 125% multiplier, it will require a fuse or circuit breaker rated at ~125 A, or the next size up. DC-rated breakers of this size are available, but they’re expensive.

    The 75 A charger will not meet the current requirements of the inverter's 1,000 W load (~90 A - 100 A). Accordingly, the battery -- assuming it’s healthy and fully charged -- will make up the difference while it can. For a 34 Ah battery being discharged at ~15 A - 25 A, it’ll last for ~ one or two hours. After that, the charger will overheat and shutdown, and the system will have no UPS capability at all. Instead, you’d need a 12 V charger rated at 100 A or more.

    Even if the charger were large enough to handle the inverter's 1,000 W net steady-state load and charge the battery, the 34 Ah battery will almost certainly be woefully undersized. In the event of a power failure, the heavy load from the inverter will cause the battery voltage to drop dramatically, and it may briefly drop below the inverter’s low voltage cut-off (10.4 V). This action would instantly shut off the inverter and defeat your UPS intent.

    Finally, overall system efficiency will be dismal. Assuming 80% charger operating efficiency and 85% inverter efficiency, the system will suck almost 1,500 W out of the wall while powering a 1,000 W load.

    Assuming you still want embark on this project, I recommend you consider an Outback FX 2012T backup inverter-charger with >100 Ah of 12 V battery, an FX2524T with >50 Ah of 24 V batteries (2 each 12 V x 50 Ah wired in series) or an FX3048T with >25 Ah of 48 V batteries, any of which with the appropriate DC circuit breaker. You could add a PV array and charge controller at a later date.

    HTH, and good luck!
    Jim / crewzer
  • BrockBrock Solar Expert Posts: 633 ✭✭✭✭
    Re: constructing a UPS

    I agree with what Bill and Jim said and will add to it,

    First I have to say I am extremely impressed with iota chargers. They can put out their full amperage they are rated all day long. I have dual DLS-55's connected to my beat-up old 3kw gas genset. They charge my 2000 amp 12v bank, which in turn powers my dual SW2412 inverters. In an outage I have run the genset 12 hours with both charges putting out the full 55 amps the whole time. They limit themselves to what ever they are rated for and stay there as long as the voltage doesn’t come up to the point of reducing amperage to not overshoot voltage. Very nice.

    My big concern is the idle loss with this setup as Jim mentioned. Let’s just say you only have a 500w load running. I believe the inverter is 85% so a 500w load would pull 590w, now the iota charger would have to supply 590w and is about 75% or 790w so now your 500w load is consuming 790w and making 290w of heat or loss. You would be far better off with even a small older used SW or Plus line Xantrex (trace) inverter. Then if the power goes out they automatically switch over to battery as fast as most UPS's with no idle loss while the grid is up. Then just trickle charge the battery bank with solar. By the way this is exactly how I got in to all this in the first place, doing exactly what you’re trying to do.

    I would also recommend upsizing the battery as well. A 34 amp battery will likely drop so much voltage under even 500w of load the inverter will shut down thinking the battery is dead. I would recommend at a minimum of 100 amps of battery, but would suggest about 250amps.
    3kw solar PV, 8 L16's, xw 5548, Honda eu2000i, iota DLS-54-13, Leaf EV, 4 ton horizontal geothermal, grid tied - Green Bay, WI
  • System2System2 Posts: 6,290 admin
    Re: constructing a UPS

    I have two best power axxium 1500 rack mount ups's. They have 4 12 volt 7ah battery's internally and also has an external connector for adding more battery capacity. They are 48 volt and I have used them with solar panels. They are tru sine also.
  • System2System2 Posts: 6,290 admin
    Re: constructing a UPS

    Thanks for all the advice. Always better to find out before, rather than after, that it won't work as expected!

    Also, just in case anybody was curious, I received a response from Iota concerning the DLS-75 12-volt, 75-amp charger volume question: "We do not measure the noise in decibel levels that our units create, they are normally not loud enough to create an issue."

    I looked at the some of the Outback inverters, and found that the worst-case transfer time from AC for some of them is around 8 milliseconds to 16 ms. That got me wondering exactly how long my PC can go "without power" anyway. Searches mostly turned up 2-4ms as the longest hold-up time for a typical power supply, although a lot of those seemed to be duplicates of the same statement and I don't know where the number originated. I noticed that one of my power supplies was listed on NewEgg.com as having a hold-up time of 17 ms (haven't yet been able to confirm that with the manufacturer though) and a few others randomly examined were listed there as between 8 and 16ms, if the rating was listed.
    If anybody is interested in the details on the Outback inverters (or just has nothing better to do on a friday night), here's what I've heard from others:
    http://www.outbackpower.com/forum/viewtopic.php?p=6712#6712
    http://www.outbackpower.com/forum/viewtopic.php?t=839&highlight=switch
    This also led to me spending way too much time reading up on UPS systems; didn't realize there was more than one type (standby, online, and a hybrid of the two) or that a UPS could potentially not always transfer in time either. I always assumed a UPS always transfered in time. Here's a section out of one of the many randomly discovered documents discussing it: http://www.jetcafe.org/~npc/doc/ups-faq.html#0204 although I'm sure there's more and better info out there elsewhere.
    Fun with technology.
  • BB.BB. Super Moderators, Administrators Posts: 29,717 admin
    Re: constructing a UPS

    Yep, on a UPS that promissed 1/2 cycle (8ms) cutover--I would SWAG (guess) that about one out of ten times, the average PC would crash on switchover... On one project I supported, we used continuous conversion type UPS's (Triplite). Never looked into it deep enough to figure out if it was the PC power supply or the UPS that messed up on the transfer... One of the problems seem to be a real power failure is not a nice clean event (brownouts, surges, etc.)... Seemed to confuse the standby type UPS's at times....

    But if I had a choice between standby or no UPS--I have a cheap standby UPS connected to my home PC. (I like laptops--2+ hours of standby--continuous conversion).

    I spec. my custom system designs for 1 cycle dropout at 50 cycles (20msecs)... Never had reason to do exhaustive tests--but never had any complaints either.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BrockBrock Solar Expert Posts: 633 ✭✭✭✭
    Re: constructing a UPS

    Sean the iota are really quiet even with the fan running, they make less noise then the inverters or charge controller. Without the fan they make absolutely no noise.

    And as I posted over on Outback I ahve never had a computer lock or crash on inverter transfers if that helps any.

    3kw solar PV, 8 L16's, xw 5548, Honda eu2000i, iota DLS-54-13, Leaf EV, 4 ton horizontal geothermal, grid tied - Green Bay, WI
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