Large battery backup, but not solar

System · February 2007

I'm trying to build a 948AHr battery bank from 12 x 79AHr 12VDC batteries. I live in a 220 volt area. I'm having trouble finding high amp DC power supplies to plug in to the charge controller. My plan is to use a a solar charge controller but power it with the regular power supply rather rathern than solar cells. Am I going about this the wrong way? Should I just wire several smaller power supplies in parallel? Also looking for a good pure sine 220V inverter.

Thanks,
Kris

mike95490 · February 2007

Re: Large battery backup, but not solar

Power supplies will not cut it. They will overcharge, and kill your expensive batteries.

There are some good combo inverter/chargers someone here should point out their faves for you.

Are you looking for a 48v or 96V bank ?

System2 · February 2007

Re: Large battery backup, but not solar

This doesn't always work. The good news is that you can charge the 12 volt batts individually with 12 volt chargers, being careful not to overcharge if they are VRLA or AGM type (sealed). This can get the string out of order so to speak, but if you look at it as separate strings and don't power them on the main buss all at once it is probably less critical. You probably already know that if you have different age of batteries this can be a problem. Are they of differing ages?

I have hooked power supplies through Trace / Xantrex C-40 chargers with varing results. I have had good luck with hooking up 54 volts of batteries and put chargers on the batteries while feeding the output of that to the C-40. The batteries seem to stabilize the charging and not make the C-40 go into a low amperage mode too soon. I use an extra bank of 4 12 volt batteries plus a 6 volt T-105 to get the voltage and it works pretty well, in fact much better than hooking 4 12 volt chargers in series. My guess is that this will reduce the ripple, but I have not checked that theory out.

There is Lots of surplus -48 volt telephone stuff that can be had for pennies on the dollar and is a good investment.

Good Luck

Skip

System2 · February 2007

Re: Large battery backup, but not solar

Mike: I WILL be using a charge controller. I want to run a 12V bank.

Eargasm: All the batteries will be new. Is it not possible to charge them all at once? I've seen systems like this in action before I'm just not sure what parts were. We call it a whoel building UPS. I don't need an especially fast charge time. 24 hours would be alright.

crewzer · February 2007

Re: Large battery backup, but not solar

I'm trying to build a 948AHr battery bank from 12 x 79AHr 12VDC batteries. I live in a 220 volt area...Also looking for a good pure sine 220V inverter.

See: http://www.outbackpower.com/Export.htm and http://www.outbackpower.com/pdfs_manuals/Export%20Manual%20rev%207%201.pdf These units can charge batteries from 220 VAC / 50 Hz and can invert DC to 220 VAC / 50 Hz. They offer a couple of models for 12 VDC.

HTH,
Jim / crewzer

mike95490 · February 2007

Re: Large battery backup, but not solar

bokado wrote:

Mike: I WILL be using a charge controller. I want to run a 12V bank.

Eargasm: All the batteries will be new. Is it not possible to charge them all at once? I've seen systems like this in action before I'm just not sure what parts were. We call it a whoel building UPS. I don't need an especially fast charge time. 24 hours would be alright.

12V is a bad idea. 48V is much better.
Why?

Say you need to power a whole building, I'll assume that at some random point, a car will hit a power pole, knock it down, and your building looses power. I'll assume the bldg load is 30A @ 240V (240 is what they have in the USA, usually) That comes out to 7200 watts, that you need, instantly. Do you want this to switch automaticly, like a UPS would? How well balanced are the 2, 120V legs of your building ? (one leg has the space heaters, coffee pots, and mini-fridges, the other leg has the overhead lights - this would be unbalanced)
So you load is 7200 watts, and you need to take that from your battery bank. That would require over 576 amps @ 12.5V. What size cable will carry that load?
If you used 48V it would only be 150A. (that's still a Yikes!)
If you can stand to manually transfer, and shut down the stuff that does not matter, and only leave the server room and it's air conditioner on, then you will not have the whole building load to deal with. I'd wire the inverter into the circuit for just the server room, and add a couple of small overhead lights to it, so you can find your way around the server room, and the battery / inverter room.

System2 · February 2007

Re: Large battery backup, but not solar

Crewzer: Those Outback products fit the ticket almost perfectly. The only problem is that I only need to draw 300 - 400 watts. I undestand inverters are less efficient when being used at too high or low of their rated capacity. Is this so and do you know of a similar product rated for less watts?

Mike: My load for the UPS is only going to be about 300 watts so 25A at 12V. Still, you're right, it seems it would be more efficient to use 24 or 48 to lower the loss due to resistance in the wires.

System2 · February 2007

Re: Large battery backup, but not solar

You can charge them all at once and I have done it in several different ways. The best is to charge the buss all at once, and depending on the amount of charge, it might end up being just a way to trickle charge the bank.

The car type chargers have quite a bit of ripple which will decrease the life of batteries, but the good news is that you can add caps to make the ripple less for not too much money. I just purchased a 48 vdc power supply, (53 volts open circuit) @ 10 amps with great big filters off of ebay for $47 delivered and it is rack mountable. It is cool. It is a telephone type of piece that was never used, at least that is the way it was described, and from the looks of it I believe them. There are great deals on telephone equipment out there that was designed for 48 volt heavy duty service that will probably work for years to come at a fraction of the new cost.

Keep us posted! And we love pics too,

Skip

crewzer · February 2007

Re: Large battery backup, but not solar

The only problem is that I only need to draw 300 - 400 watts. I undestand inverters are less efficient when being used at too high or low of their rated capacity. Is this so and do you know of a similar product rated for less watts?

Bokado,

You’re generally correct about inverter efficiency. Unfortunately, I don’t know of a true sine wave (TSW) inverter/charger combination that's rated in the ~750 W range, which would probably be just right for your needs. Another complication, frankly, is that there’s a limited pool of ~230 VAC/50 Hz equipment to recommend from here in the U.S.

Note that the Outback includes a “search” mode that greatly reduces power requirement when the inverter is not under load, but will switch on the inverter when it senses a large enough load.

Another option might be separate components. For example, the Xantrex TrueCharge 40i charger will charge “12 V” batteries at up to 40 A, which should be enough for your battery bank if its not to heavily loaded. The 40i is the international model that runs on ~220 VAC. The 40+ model is intended for 110 VAC markets.

See: http://www.xantrex.com/web/id/70/p/245/pt/5/product.asp

Exeltech here in the U.S. makes very good TSW inverters. Their XP series is available in a 12 VDC in / 230 VAC / 50 Hz out configuration. The 600 W model might be just right for your expected needs.

See: http://www.exeltech.com/ex_root/ex_products/ex_inverters/ex_xp/ex_xp_series.htm

Both the Xantrex and the Exeltech units are very good products. NAWS sells and ships internationally. You may be able to check with them for prices and availability of these “export” items.

Good Luck!
Jim / crewzer

niel · February 2007

Re: Large battery backup, but not solar

i might be missing something here, but i'm not sure if this is for 50hz or 60hz. 220vac is often what is referenced to here in the usa as it was typically 110/220vac. nowadays the voltages have climbed to as high as 125/250vac, but the 60hz didn't change. europe has 220vac like service, but with 50hz and i don't recall bokado saying exactly which he was looking for.

crewzer · February 2007

Re: Large battery backup, but not solar

Bokado indicated in his initial post that he was "...looking for a good pure sine 220V inverter." To me, that was pretty clear that he wasn't looking for a 120 V inverter or a 120/240 inverter. ~220 VAC inverters are almost invariably 50 Hz, and, except for the overall size, he seemed to like my suggestion of the export versions (230 VAC, 50 Hz) inverters.

But, you're right that he didn't explicitly state a line frequency requirement. However, I think the inference is clear enough. If not, it's up to Bokado to clarify.

Regards,
Jim / crewzer

System2 · February 2007

Re: Large battery backup, but not solar

50hz.

Crewzer: Those both look like good products. Finding 220V stuff here in the US has been a real PITA.

So we agree that running an inverter at low load is inefficient, does anyone know just how inneficient it is? That all in one Outback unit is my ideal item if the efficiency loss isn't too bad. Will give them a call on Monday.

crewzer · February 2007

Re: Large battery backup, but not solar

bokado,

I conducted a quick efficiency test on my FX2524T this morning: 367 W out / 412 W (net) in = 89%. Considering that 367 W is but ~14.7% of the 2524's 2,500 W output rating, that's pretty impressive for a TSW inverter! 8-)

The 12 V Outback inverters are likely 1%-2% less efficient, but these numbers compare favorably with Exeltech's 12 V spec of 87% peak efficiency at 1/3 power.

Tomorrow (Monday, Feb. 19) is a holiday in the U.S. -- my understanding is that Outback will be closed.

HTH,
Jim / crewzer

System2 · February 2007

Re: Large battery backup, but not solar

Was your test while you were running off the batts or off grid power. I assume the FX2524T doesn't run off the inverter/batteries all the time, only when main power fails?
Been calling Outgback today but it seems the tech department is out to lunch.

crewzer · February 2007

Re: Large battery backup, but not solar

My test was run from the batteries. My inverter is presently set up to run only from my battery bank. I will soon set it up to run primarily from the battery bank, but with grid backup if the battery voltage falls too low ("high battery transfer", or HBX, mode).

HTH,
Jim / crewzer

Large battery backup, but not solar

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