ups for use as full time power inverter

[bahnfeldt]

i have a ups of 10 kva advaiable to me, it is a 240 volt dc input and a double converstion type the spec in manual show it has good efficenty etc, i am happy ot configure a bank of deep cycle to this, is there any issuse with series of battery to such a high dc output (vent cap lead acid type) i know a ups is designed for power outs in normal situation , can any one see any disavantages in using this for a 24/7 off battery bank, do i need any special protection between the battery bank and inverter, the battery bank would be in it own shed, the solar panels allow for a max of 400 volts open voltage, so solar charging as well as my diesel looks like no issuse

any there any thing i am missing for saftey, and long term relabilty

cheers arny

[Usman]

You can use this UPS or another one as an inverter on continuous duty, however,be ware, most of these UPS would have an overheadpower consumption i.e. standyby or operational power consumption, in case of an APC 5KVA UPS, it is 80watts.

Also, the effeciency of such UPS inverters is not that good.

Hope that helps.

Thanks, Usman.

[TomW]

usman;

My experience, exactly. Horrible efficiency and they don't really last in that type use. They do "work" though.

Cheers.

TomW

[scottsAI]

Bahnfeldt,

Double conversion, are always inverting. Full time use therefor should not be a problem.

The efficiency is listed I expect as Full power. What is it at no load?

My 3k and 5k use 48 / 90 w anytime it's on. All APC older units. Cheap.

Does not sound like much, but 90 * 24 = 2.1kwhr / day.

Lightly loaded the efficiency of a 1kw is below 50%. (have not tested the bigger units).

1kw draws 24 w when on. Two CFL = 43 watts lasted the same time as one of the two battery did with a 300w inverter. I would call that poor. For a sin wave output the 1,3,5kw are cheap.

Have fun,

Scott.

[nothing to lose]

Agreed with others, standby power no load is a killer with many UPS's.

 I think Rich and I tested one of my Matrix 5K units as about 156watts from a 48V battery bank no load. That's like 3,744watts to have it turned on 24hrs but not used!

 It did seem there was less loss when a load was actaully on it, some of that 156watts went to the load then, not just losses.

I have not tested my SU22000 rack mount, 24V, 1750V sinewave UPS for losses on batteries yet, but it uses 30watts from the grid just turned on no load. I expect on batteries it more because the fans and such also kick in, load or not.

These UPS's vary a great deal and I never tried a 120Vdc one. Perhaps it would have less losses? I use mine allot as inverters but I turn them on when I want them and off when I don't need them, not a 24hr type thing because of the losses.

 For anything like a fridge/freezer or such needing random 24hr power I will use a real inverter mostly, when I need extra stuff like a computer, TV, stereo, DVD etc... I can run a UPS with less losses under a load and shut it off when done.

[bahnfeldt]

thanks yes agree it design use, the standby power is not much of a issuse, so i wounder if i could modifly it some how  to has very low idle current,

[marvin]

UPS Service Tech here with a few comments:

As mentioned above idle power consumption will probably be the biggest factor in overall operation. If you have a means of turning off the inverter when power is not needed then that should reduce it to zero.

I know of two UPSs that are as you describe, the Liebert AP100/101 and the Deltec 7000 Series. Both are double conversion, Phase controlled SCR Rectifer/DC bus regulator and PWM Bipolar Transistor Inverter. They both also have a Static Switch to direct AC power through them for maintenance/repair without loss to loads.

The problem with the Liebert is that it is microprocessor controlled and uses a multi-positioned rotary switch to go from "Off" to "On Line". I recently picked one of the 5kva units up that I hope to play with to see if I can set up a utility drop out relay. It would work with the UPS's aux contacts on the main switch so that the unit will stay in static bypass until a power outage occurs then turn on the inverter after an adjustable delay to make sure power is realy going to be out for awhile.

The Deltec is a little more friendly as it actually has an inverter "ON" button.

I believe I have full documentation for both units, for sure on the Liebert and I have access to lots of documentation for many other UPSs so if you decide to get this I can probably give you all the info you'd need.

The other problem is that creating the 270vdc to charge the batteries will be tricky from the home built stand point. You will probably need at least 5 amps to be able to keep the batteries charged and 50 amps to operate the UPS at full power.

I would be running mine with utility connected to keep the batteries charged and only use the inverter as an emergency back-up. I picked mine up along with a 25kva 3 phase Deltec and cabinet full of batteries for $150 and sold the scrap 10yr old batts for $250. I'll probably scrap the copper, aluminum and steel from the Deltec.

Let me know if I can help.

marvin