Newbie System Advice

Shieldsy · March 2013

Hi all,

First of all, I want to apologise for posting such a newbie topic without properly searching through the threads, but I have the opportunity to get some 150Ah batteries and was hoping I could get some advice as time is of the essence. Feel free to point me in the direction of any informative threads

The batteries are 5 x Ritar RA12-150F's. They're 150Ah at 10hr. They came out of a computer UPS and are around 3 years old. They'll only cost me about 50c per Ah, which is much better than the going rate here in Australia ($1-$2/Ah). So my question is, should I grab them while I can?

I also have another 95Ah Deep Cycle AGM, which I neglected a little and am not sure of it's condition. Could I use this with the other batteries or would it detract from the whole system? Is there any way I could rejuvenate it?

I was also hoping on some advice for my system sizing, as I'm trying to get all the necessary pieces together at the moment. Things like what voltage should I run, how should I wire the batteries, what solar panels, etc, etc.

At the moment, it will only be used as a battery backup to my Aquaponics setup, in case the power goes out so the fish won't die. So I was just going to run an inverter (Any suggestions on an inverter?) rather than buy 12V pumps, etc. Is there any problem in this? Would it be more efficient to buy 12V pumps?

In the future, I would like to use the batteries to - at least partially - power my house in an off-grid arrangement. So any advice, and suggestions on a setup with that view in mind, would be appreciated.

BB. · March 2013

Re: Newbie System Advice

It all depends on your loads... If your power usage is small, you could stay with a 12 volt battery bank and use a 300 watt TSW MorningStar inverter (very nice with search mode and remote on off--you hardly ever see this on inexpensive inverters). Oops, seeing you are in Australia, you will need the 230 VAC 50 Hz version (or something similar).

Getting used UPS batteries... Many times, there is not a lot of life left in 2-3 year old UPS batteries. I see those batteries are supposed to have 10 year life... I would just make sure how much it will cost you to get rid of them if/when they fail.

Anyway, back to the system design. We have several ways to proceed. First, based on your (AC) loads--This is the best way. Note that even smaller loads operated 24 hours per day become quite large--Needing a larger battery bank, solar array, backup battery charger, etc.

Otherwise, we can design a system around a battery bank (xx AmpHours at yy voltage), or you only have room for ZZZ watts of solar array (and based on how much sun you get in your region), or even you only have so much money you want to commit to the project.

Lets say you want to start with a smaller system that will power 300 watts (AC) of pumps 24 hours per day. Then working towards the battery bank. 1-3 days of backup power, 50% maximum discharge (for longer battery life). Pick 2 days as a healthy value:

300 watts * 24 hours per day * 1/0.85 inverter eff * 1/12 volt battery bank * 2 days backup * 1/0.50 max discharge = 2,824 AH @ 12 volts

Yikes--That shows what happens when you have a continuous load running 24 hours per day. You would need around 19 of those batteries. That is no "small" system at:

300 watts * 24 hours per day * 1/0.85 inverter eff = 8,470 WH = 8.5 kWH per day

That is quote a bit of power. And, with that size battery bank, I would be suggesting a 48 volt configuration at ~ 706 AH (or 5 parallel strings of your batteries, 4 each in series, with 20 of them). And I would suggest no more than 1-3 parallel strings. More than that can become a battery management nightmare.

And just to finish off the calculations, an off grid solar power system with a minimum of 4 hours of sun per day (perhaps 9 months of year), such a system would need in solar panels:

300 watt load * 24 hours per day * 1/0.52 system eff * 1/4 hours of sun "break even" per day = 3,462 Watt solar panel array

Note--this all goes back to the loads you expect to supply--And shows that conservation is very important, and doubly so for 24 hour per day loads. I have no idea if you need 30 watt or 300 watt worth of power for your fish--So that gets back to your expectations and needs. A Kill-a-Watt type meter is a great place to start. You can plug your loads in and measure them for a few days to get the average consumption.

The basic math above is where to start your planning... You if you only need 30 watts*24 hours per day, the battery/array sizing would only be 1/10th the size of a 300 watt load.... etc.

-Bill

Cariboocoot · March 2013

Re: Newbie System Advice

Welcome to the forum.

The thing about used batteries, any used battery, is that it's a pig-in-a-poke. You have no way of knowing how it's been treated during its lifetime. With a sealed battery you can't even check the specific gravity. These are possible even gel type, which aren't suitable for RE anyway.

What you have got here is really cheap batteries, so it might be worthwhile to get them for experimenting with. If it were a critical "the power is needed" application it wouldn't be worth the risk.

Your 95 Amp hour AGM is probably quite down in capacity if it hasn't been properly looked after. Even if it weren't, its capacity is significantly different from the 150's so mixing them is inadvisable even for experimenting; the 'new' batteries will waste some of their potential trying to charge the 'old' one all the time.

As far as sizing the system goes the thing you start with is knowing the loads. What is the total Watts used and how many Watt hours per day? That is the basis for getting the right inverter and battery bank. From there you can figure out what is needed to keep the batteries charged.

Incidentally, for RE purposes batteries are sized by the "20 hour" rate. This will be slightly more than the 10 hour rating given. All things considered though, it won't be a significant factor in this case (old batteries, used for hopefully short-term back-up).

westbranch · March 2013

Re: Newbie System Advice

Go for those used ones, you will learn a lot about charging and what constitutes a failing battery ... cheap learning and you will also go through the growing pains of a too small system before you lay out 'real' money, good learning.. ps 5 batteries iin parallel (12V) is not a good design, see if you can go 3 max or consider 24 v , its more expensive though

Shieldsy · March 2013

Re: Newbie System Advice

Thanks for the replies, it's given me a lot to think about.

As far as my load goes, at the moment I have:

50w AC Water Pump
25w AC Air Pump
18w AC UV Sterilizer

All of which run 24 hours a day.

Would I be better off trying to get my hands on 6 batteries, so I could have 3x2 @ 24v? Or 2x3 @ 12v? What kind of loads could I expect to run per day with a 900A battery bank and an appropriately sized array to go with it?

How big of an array would I need to keep things running? At this stage I'd be happy to run a backup charger as a fail safe. I currently have a 3000mA Smart Charger, would this be adequate to keep things topped up in the meantime?

I can get my hands on 120w Poly or 80w Thin Film panels for a reasonable price (65c/w). Any suggestions on which one to go for? I'm guessing Poly, but I don't mind using the extra area if Thin Film would be better in the long run.

I'd like to have the ability to periodically remove 1 or 2 batteries from the system to power my DC fridge when I go away camping. Is there any problem with this? Do I need to set things up in any special way to cater for it?

Cariboocoot · March 2013

Re: Newbie System Advice

Let's see, 93 Watts worth of load running 24 hours a day that's 2,232 Watt hours per day. Add consumption from a small inverter like the MS 300 (6 Watts * 24 hours = 144) you get 2376, call it 2.4 kW hours per day. That's bout what my whole cabin uses.
On 12 VDC that's 200 Amp hours. At 50% DOD it would bee a 400 Amp hour battery bank, so that's at least three of those 150's in parallel (450 Amp hours).

This is acceptable due to the nature of the over-all system. It's for back-up, not constant use right? Going to 24 Volts means a different inverter, one that would probably have more self-consumption. Three parallel batteries isn't impossible to keep balanced. I go with that from your five and keep the other two separate to take with the 'frige.

Recharging 450 Amp hours @ 12 Volts would require at least 22.5 Amps peak current so you'd need a 30 Amp charge controller and about 400 Watts of panel (check both the Imp and Vmp on the panels as Wattage alone is not telling for a PWM controller). Again you can get away with minimum charging as this is not a daily use system.

How long do you usually have outages for? If it's several days at a time you might want to rethink the whole thing. If it's occasional blips then small will work.

Don't expect to be able to "scale up" this system to something larger.

Shieldsy · March 2013

Re: Newbie System Advice

Thanks Cariboocoot.

It is just a backup at this stage, but with so many batteries, I wouldn't mind gathering the pieces I would need to switch over to full time once I've got everything together. What would I need to do different in order to have the solar powering the pumps full time, with the mains power backing it up instead. Kind of a vice versa situation.

We don't often get outages at all, so looking toward powering everything via solar full time was always my long term goal, I guess.

How do you get away with such a low usage in your cabin, by the way? I wouldn't mind doing something similar...

Cariboocoot · March 2013

Re: Newbie System Advice

Shieldsy wrote: »

How do you get away with such a low usage in your cabin, by the way? I wouldn't mind doing something similar...

I keep the fish in the lake, not in a tank.

If you want to convert that system set-up to "full time" you basically double everything; reduce the DOD to 25% (increase to 24 Volt system @ 400 Amp hours as trying to manage 800 Amp hours @ 12 Volts is difficult) and increase the charge rate to 10% so you get 1250 Watts of panel and an MPPT controller.

Look at that carefully and you'll see it basically says "throw everything out and start over".

BB. · March 2013

Re: Newbie System Advice

If it is for backup--You could probably use a small genset (a Honda eu2000i or eu1000i -- 1,600 watt / 900 watt) genset and a couple gallons of gas per day.

The batteries give you 24 hour backup protection, and time to get there and start the genset if there is a long term outage. 20 gallons of fuel on hand, and that will give you enough backup power for 10 days (use fuel stabilizer and recycle back into your vehicles once per year).

The Hondas are nice because they also have a small fuel pump that allow you to build/buy a new fuel cap with a hose attached, and they will draw fuel from a 5 gallon fuel can (don't have to refill every 10 hours of use).

There also propane conversion kits for the small Honda (and others like Yamaha) if that is a useful fuel for you.

If you need electric/automatic start--Then you are looking at a whole different level of genset (and fuel usage--very difficult to find a full automatic genset in the smaller wattage range).

In general, for emergency backup, a good genset + small battery system (with or without solar panels) is going to be more cost effective.

-Bill

Newbie System Advice

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