Hi Anne,
We run 12 off 600AH sonnenscheins here and they have been going for near 8 years with quite a few deep cycles. I have programmed the inverter to cut out at 22 volts so the deep cycle isn't too deep to destroy them. When our AERL900B MPPT went I got a new FlexMax 60 Outback MPPT and the rep was told I had sonnenscheins so he programmed the MPPT to suit them. He did say to me NEVER take those batteries over 29 volts (2.41 volts per cell).

As far as running those 2 independent banks 500AH is decent amount of storage ( we live on a 24 volt 600AH array) so by having a smart controller that can switch banks will be the easiest method. This sounds like an easy project to do in basic with a pic micro.

An inverter does come to mind that would suit you down to a tee as you have the grid connected and that is the SP range from Selectronic. That inverter will do everything but make your toast on a morning ( eh but you can program it to turn the kettle on) It is a stand alone/ grid tie / generator backup and Aussie made for our conditions. They aint cheap but bang for buck there isn't anything on the market close to what this baby can do.

You could still get away with that 500AH original bank, use that SP inverter and have a backup generator.

Cheers Bryan

P.S. I did mention to mate over in WA about those inverters so he bought 2 of them and he has fooled one into thinking the other one is the grid and runs his coolroom for his passionfruit farm off the second one.

The 12.6 to 12.8 voltage would be considered very well charged.
The 2.41 volts per cell equates to a maximum charge voltage of 14.46 v
(2.41v x 6 batteries = 14.46v)

My flooded batteris max charge is 2.58 Vpc or 31v total

In my charge controller there is float, boost, absorb and equalize, you will need to ensure the settings in the controller are for your new batteries they will be different to your old ones.

The controller should be able to do the equalize etc, I do mine manually.

Ruddy i have flooded batteries, 24v system and had a minor nervous breakdown yesterday when my batteries got down to 24v, I would have a heart attack if they got to 22v.

Thanks very much both of you

But a lot of what you say is above my knowledge ....... I need to do some study ........

Anne

G'day Bala,
With every different battery there will be a different charging regime, flooded cells are designed for a higher voltage too. It is important when getting a new battery array to know the set point voltages and program the MPPT or inverter to those parameters.

Hi Anne,
I have been thinking about that suggestion of using 2 battery arrays and switching between when the voltage goes down on one bank. As inverters here in Oz work on 50hz and the micro-controller I would use for the switching runs on 20mhz the time frame between switching banks would be quicker than the inverter would see. But due to the high currents taken from the batteries a IGBT would be needed and it would take someone knowledgeable in electrics to hook it up. As putting the terminals wrong would see that magic smoke appear in a huge display.


Now are those fridges 240 volts AC or low voltage DC ones and what current draw at what voltages do you also do? Also your inverter what brand is it and capacity.

I would love to help out if I can as I am sick of seeing people being ripped off $$$$ by shonky so-called experts.

Cheers Bryan

The first thing you should look is is the settings in the charge controller for the batteries that you have, you should be able to get the settings form your supplier specific to your batteries and charge contoller.

The question you are asking about more batteries, 2 banks etc will not be an easy one to get a straight answer on.

It looks like you have grid power and a battery charger as well. So the batteries are for backup.

If it were me, an i realise its not, I would just use the batteries you already have and use the money from the second ones you were looking at to buy a good genset for back up. You can get a genset hooked up to auto start at a preset battery voltage so even if you are away and the mains goes off for an extended period you freezers will always be on.

For you to study stand alone systems is your best option, a lot of money gets spent on systems and mostly no good help is close. Internet forums can produce more questions than answers so the more you know the better off you will be.

Thanks again your help is appreciated very much. I am realsing how little we really know ..........

I need to explain more about our system and what we are trying to achieve etc etc and will work on posting it ASAP but I type very slowly so it my take while

regards
Anne

ok it took awhile but this explains what we have done and make things a bit clearer ( I hope )

We are pensioners, me disabled hubby my Carer. When hubby left ALCOA in 1998 to look after me he got a super payout which we are gradually putting into self sufficiency as we are “doomers “
We do also live in a bad area for bushfires and usually the power goes off in a fire. We do have a genny and can connect it to a caravan plug to run the house. But in a fire the genny needs to run a water pump. I can’t actively do anything in a fire being disabled but I would not leave and need to be able to keep my air purifyers running in the house.
We have grid power and in 2007 we put in a GF system – 2.5kw Sunpower panels SMA inverter- with a state govt rebate that payed for 50%. In 2008 we also put in a pumping system using a Lorentz pump and 2 trackers with Unisolar panels
Since 2004 we have also “dabbled” with running a small stand alone system to run a few things in the house – some lights , composting toilet fan, 12v TV, and when the weather is good a 12v pressure pump to run the house.
We originally had a 24v system and 4 6v 200 ah Supercharge batteries. Panels 4 x 52 w BP Solarex and 2 x 64 w BP. Prostar regulator.
The 12v stuff was run through a converter and we also had an inverter ( 600w Excel ) to run the air purifier for a couple of hours ( draws 25w ) and the computer or 2 hours in the afternoon when power is expensive. We are on Smart power ( time of use pricing ) This system died in about 12 months as mentioned above - our fault - didn’t calculate 12v ah correctly – cheap batteries.
We put that down to experience and bought 2 x Trojan 220 a/h ( T 105s ) ditched the inverter and just ran the 12 v stuff. This system ran well for about 4 years but from late late year we knew we needed new batteries.
In June we purchased 6x 2v Sonnnshein batteries and a Latronics 1000w inverter. We also had a Plasmatronics PL60 regulator and the 8 Uni solar panels that we bought from a guy who had them sitting in his bedroom never used ! The idea eventually is to move the batteries which are now on the north side o the house and put the under the back verandah on the south side and set up the new panels on a frame along the north side. We have also purchased a “plug and play board “ on which we mount the inverter, charger and new regulator and which has fuses.
For now the batteries are just connected to the old system – BP panels and Prostar regulator.

Anne

RuddyCrazy wrote:
I dont understand this at all ....... even what is an IGBT

I didnt mention in my other post but back in June a company called Aussie solar did a mail drop here mentioning stand alone and aslo battery backup for GF systems, WE contacted them wanting a quote either for a Sunnybackup or making our stand alone system bigger. They originally suggested doubling the sonnenshein battery bank to 1000 ah and said it could be done up to 12 months after intalling the first battery bank.

We decided against the Sunnybackup it didnt seem worth the money and tere is no way you can tell when you are running on batteries.

We wanted a quote to upgrade the stand alone and feed the trackers in to that system in winter but they kept making exuses about bing too busy so we gave up and ordered the batteries our selves from EM

Over here there just doesnt seem to be any companies that know what they are doing we recently had trouble with our GF inverter and the company that originally installed it had been taken over. The new people didnt know what they were doing. It was eventually fixed under warranty but only after I rang Sunpower and they advised them what to do.


The freezers are Vestfrost 240v -the smaller 225 l uses 600 wh a day and surges at 166w.

The 300l is only new - it uses 700 wh by the manufacturers data and 800 by Energy ratings site. we havent yet measured th surge

The inverter is a Latronics 1000 w

Cheers Bryan[/quote]

Anne

this is my second go at replying the first one went into space!!

To work out your system properly is beyond me but if you want to post on either of those solar sites i suggested you will get answers. if you do post i will watch and help you through this site if i can and if you wish me to do so.

you will need the amount of power you would be using per day in watt hrs or Kwhrs, i think you may have a khwr meter??, run all the stuff you would be running off the batteries and measure how much you use per day.
this is used to check the battery size is big enough

because it is a back up system the batteries can possibly be smaller as they won get discharge all that often, (only when the mains is off?)

You will need the amount of panel wattage you have, this needs to be calculated to ensure the panels are big enough to recharge the batteries in one day

You will need your solar isolation hrs, this will probably be on an chart online some where and is usually the amount of usable sun at the worst time of year. No good saying you have lots off sun, state where you are in the world.

you PL60 will be plenty big enough and good quality,

The inverter is good quality but you will need to check the start up current of the freezers and any other motors you want to run.

if you post and explain your situation and what you already have and what you are trying to achieve you should get some good advice, you may get a bit of a ribbing for not working it all out first but thats ok. better to get is all sorted now so you can rely on when you need to.

Regards

Max

I had a look at the specs for the 1000w inverter, the 5 seconds surge is 3000w so that should handle the start up of your vestfrosts.

Hi Max

It should handle it easily because the meter we have says the 225 l only surges to 166W ! This is one of the advantages of Vestfrost ......... no doubt the bigger one will be higher but I would expect not by much.

I do have all the figures of what we use set out in an Excel spreadsheet ..... I just cant work out how to post it here !!!

I looked at the links but to be honest I am a bit put off by them being US ........ usually overseas based into has limited use due to diferent products and conditions but maybe that doesnt apply to solar ?

BTW we have 7.9 hours average peak sun in summer and 4 hours in winter

regards and thanks
Anne

So the PL60 will be fine and the inverter should be as well, you now need to find your watt hrs or KWhrs of daily use that you would be expecting to use.

From this you/we with some help can work out if the batteries you have will handle what you wish to draw from them,

the next step would be to check the panel sizing,

So if you post your expected usage and your panel size we should be able to come up with some results

green-trust.org/solarcalc/

have a look at this calculator, it will give you an idea of what info is used to size a system and you can play around with the values and see the effect on battery size etc

BUT it is only a guide / for my system it gives the following,

I put in 3kwhrs a day use, i have a 24v system, 1800 ah battery pack and 2240w of panels,

It tells me i will use only 20% of my battery capacity if i use 3kwhrs a day without recharge for 2 days,

Well I dont think thats true at all!!

but it is a good to be able to play around with the figures;

I am getting a better under standing myself so i will look at some manual calculations for my system and see what i come up with

Thanks max

at the moment we are only using 414 wh a day on DC and the calulator says we need 298 amp hours at 12 volts of battery storage and 90 watts of PV panels!

present BP array is 336 watts so we are not draining these batteries much. In Fact my calc say about 7%.

I will try nd work out a way to post my intended usage later but it looks like I may have to type it all in here.

The new array will be 512 watts - 8 x 64 w Unisolar panels. The chart from the site shows we have average sun hours of 8 to 9 ........ info I had from somewhere else says 8 in summer- 6 autumn spring and 4 winter so my calcs are probably on the conservative side

One big factor is that we only need to work on one day usage because having grid power if it is cloudy we can either switch and use 240v or run the battery charger.

I think I confused you before ...... we considered a backup system and decided against it ...........our intention with this system is to run as much as practical of our house on the stand alone and save drawing so much from the grid. It also means essential items (eg freezers )can still run in a power outage.

At present we are not even going to try and run the fridge we have on solar - converter to a chest fridge is a future project !

Anne

I have tried to understand the sizing of my system from the online calculators and manual calculations and none of the answers equal what I have.

Your original question was should you buy more batteries, 99.99% of what I have read and learned is that parralel strings of batteries is not the best configuration for battery life. I would not suggest more batteries unless you are going to 24v in series.

I would connect up what you have. You will learn to get the most from it. Start hooking up one freezer and see how your batteries handle it and depending on the result keep adding more appliances etc until you work out a level of overnight battery depth of discharge you are happy living with and that this balances against how your panels are able to recharge that amount. If your panels can recharge quickly enough you can then start to use more power during the day. For eg I know on a sunny day my panels can recharge the batteries and I can also run the washing machine pump water etc after about 10am. I have been using my system for 5 years now so I know it well and what I can get from it without damaging my batteries.
You to need to learn your system and its limitations.

So feel free to keep asking me questions and compare my answers to other info you find. Keep and eye on those two forums especially the off grid sections, no need to post but there is a lot to be learnt.

Have you checked that the setting in your prostar regulator are correct for your new batteries??