navitron
 
Renewable Energy and Sustainability Forum
Welcome, Guest. Please login or register.

Login with username, password and session length
News: Anyone wishing to register as a new member on the forum is strongly recommended to use a "proper" email address. Following continuous spam/hack attempts on the forum, "disposable" email addresses like Gmail, Yahoo and Hotmail tend to be viewed with suspicion, and the application rejected if there is any doubt whatsoever
 
Recent Articles: Navitron Partners With Solax to Help Create A More Sustainable Future | Navitron Calls for Increased Carbon Footprint Reduction In Light of Earth Overshoot Day | A plea from The David School - Issue 18
   Home   Help Search Login Register  
Pages: [1]   Go Down
  Print  
Author Topic: Off grid - One the cheap - need to start again and learn ... Ground up.  (Read 2325 times)
Dyslexicbloke
Full Member
***
Offline Offline

Posts: 159


Blue sky thinking ...


« on: December 15, 2010, 07:00:26 AM »

Hi folks,

I live off grid and in the process up upgrading things including my generator but wanted to plan my battery installation.

I have circa 300w of PVís and a 600W continuous inverter and when Iím done a generator and charging circuit that will be microprocessor controlled. I will probably add more alt energy as I go on but it will require money I currently donít have so for now it is what it is.

OK so you have a little background what I need to learn is how to manage batteries in this environment so I can design a system that will do it for me, I can probably handle the electronics but right now I donít know what I should be trying to achieve.

I can state Ö.
The condition of my batteries is poor, but they only owe me scrap value anyway.
I donít know how to test them properly
I donít know how to charge them properly, strategy I mean.
I donít know if my charger creates too much ripple on top of the nominal voltage
I probably donít have enough real time measurement going on
I cant calculate how long they should be running things for

As you can see I know practically nothing of use and defiantly wouldnít know how to plan an installation so I donít want to scrap these and spend money on any others until I do !

Please help if you can, and please donít feel you need to spare my feelings or pull any punches
[Not doing it isnt an option, paying somone to do it probably isnt an option ... its just how it is, on me whatever happens]

I look forward to your comments, good or bad
Thanks for reading
Alistair
Logged

Off Grid - Big Caravan and huge enclosed gazzebo.
300W PV 12V system.
400Ah of AGM Absolyte GP cells. (Second hand)
600W Inverter (Maplin's finest :-) )
CHP in the works - Chinese Horisontal Diesel [S195 Generic - Kukje]
VAWT testbed flying - Back to that when its warmer I think.
KenB
Hero Member
*****
Offline Offline

Posts: 2694


Energy Self Enlightenment


WWW
« Reply #1 on: December 15, 2010, 08:16:02 AM »

Alistair,

There are some scrapyards that receive a lot of redundant back-up batteries from IT installations.  Only last week I walked past several tonnes of sealed lead acid batteries in almost new condition which had been discarded from a server UPS system and date stamped 2007.  I could have had the UPS inverter charger units too for the price of scrap steel.

If your existing batteries are beyond redemption, you could take them to such a yard, and for a small payment equal to the difference between scrap lead buying and selling price, exchange them for something considerably newer.

Testing batteries should be done under load. A couple of car headlamp bulbs connected in paralllel will put a 10A load on a battery. Measure the voltage across the battery with this load connected and check that it stays around 12 to 12.5V - quickly allowing you to assess the state of the battery.



Ken
Logged
Dyslexicbloke
Full Member
***
Offline Offline

Posts: 159


Blue sky thinking ...


« Reply #2 on: December 15, 2010, 09:54:20 AM »

Interesting ... I am finding that batteries are a complicated subject.
The more I learn the less I seem to know, I just read a recent post talking about the 10% rule as a rough guide charge / discharge at no more than C/10 makes sense but how would I know where 10% of C per day fell or what to do I reached it.
Wouldnt that involve constantly logging the current and voltage ........  surrender

And whilst I am thinking about t how would I go about detecting when I reached some % of C as an overall state of charge I mean.
I see that deep cycling is not a good thing to be doing but I expect that my current asumption that terminal voltage alone will allow me to control that is wofully inadiquate ... Embarrassed

Its no wonder my bats dont work well ..... Ah well on and up I guess, given that I need to bring opertunity charging to the mix as well, much reading to do i think.

The bats I have now, well 4 of them, were scrapped unused and date stamped 4 years ago. leasure cranking combe 110Ah I think.
They read 12.8 with no load when I collected them from the yard. Perhaps one realy abusive charge followed by some TLC may just help ... nothing to loose I guess.

Keep it comming folks .... THere is Sooooooo much I dont know
Thanks
Al
Logged

Off Grid - Big Caravan and huge enclosed gazzebo.
300W PV 12V system.
400Ah of AGM Absolyte GP cells. (Second hand)
600W Inverter (Maplin's finest :-) )
CHP in the works - Chinese Horisontal Diesel [S195 Generic - Kukje]
VAWT testbed flying - Back to that when its warmer I think.
stephendv
Hero Member
*****
Offline Offline

Posts: 928



WWW
« Reply #3 on: December 15, 2010, 10:37:45 AM »

Most off-grid inverter/chargers use the IUoU charging process: http://en.wikipedia.org/wiki/IUoU
I = Constant current, also called Bulk charging, this is where generally you should drive a current of more than 10% of the capacity.  E.g. 100Ah battery, max 10A.  The battery manu can be more specific about this, some can go as high as 20%.  This stage is done at a given Absorb voltage, around 2.4V per cell - once the batt reaches this voltage voltage then this stage finishes, and the charges moves to the next one:

Uo = Constant voltage, decreasing current, also known as "Absorb" stage.  This phase is limited by time and preset in the charger - see this discussion on the topic: http://www.navitron.org.uk/forum/index.php/topic,12411.0.html  You can work out the end of this phase by measuring the specific gravity.  If it stops rising over a 2 hour period, then it's done.  You can also detect it by measuring the current going into the batt, if it stops decreasing over 2 hours, it's done.  AFAIK, none of the off-grid inverter/charger units do this, they just allow you to set a predefined time.
In general it's better for battery life to have a longer absorb cycle to make sure the batt is charged, if you leave it too long all that happens is that the batts gas more and you need to refill with water more often.

U = Float, a lower voltage of around 2.23V per cell is applied just to replace the self-discharge.  I know many off-grid installers don't use float at all, they just extend absorb to a very long time as generally it's preferable to have a longer absorb than undercharge the batt (Check justme's comments in the thread listed above).  The former costs fractionally more in maintenance and water, while the latter can cost you years in battery life through chronic undercharging and sulfation.

Another phase is Equalisation which is done periodically to bring all cells to the same charge level and mix the electrolyte around a bit to prevent stratification.  Uses constant high voltage, e.g. 2.6-2.7V per cell with not much current to induce gassing.  It's hard on the plates, so is only recommended infrequently, e.g. once every 3-6 months.

Some handy links:
http://www.windsun.com/Batteries/Battery_FAQ.htm
If you google "Battery Technology Handbook" you'll find some links to "free" PDFs of the book.
Logged

http://www.casanogaldelasbrujas.com
2.8kW PV, SMA Sunny Island 5048, 5 PzS 700 battery bank, stinky diesel.
Justme
Hero Member
*****
Offline Offline

Posts: 3575


« Reply #4 on: December 15, 2010, 12:38:03 PM »

No point starting with cr*p bats.

The total losses in a good designed & well functioning system are bad enough. Add in cr*p bats & its just not worth it. The extra cost of running the genny to try to fully charge them will make you cry.
Logged

Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
2 x Victron Multiplus II 48/5000/70
Cerbo GX & GX 50 touch
BMV 700
6kva genny
48v 1000ah
Grid Possibly coming soon
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.20 | SMF © 2013, Simple Machines
SMFAds for Free Forums
Simple Audio Video Embedder
Valid XHTML 1.0! Valid CSS!