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Forum Index : Solar : Solar Panels and Battery charging
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GWatPE Senior Member  Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
I have an RE system with Solar Panel and Windmill and grid recharging. I have many years data collection on the recharging characteristics of Lead/Acid batteries connected to my system. I have noticed that my batteries operate well in the 50-80% stored capacity range. To recharge the remaining 20% takes about 20 hours. The charging current tapers OFF to 0 amps, indicating recharging is complete. My system has boost charging to 29.4V, then Absorbtion charging at 29V for 2 hours and then float charging at 27.6V to try and fully recharge the battery. Even with grid trickle recharging, the battery is not always recharged fully overnight, following a full day of solar recharging the previous day. I was wondering if others had noticed significant decreased battery capacity, indicated by reduced days autonomy following periods with low recharging capacity. I have observed that even with huge excess in solar charging capacity, that this is not able to be effectively stored. The recharging system shuts down the array for much of the solar day and there are not enough solar hours to effectively recharge the battery before discharging begins. The only way seems to be turning OFF all the loads and skipping a discharge cycle every week or so, so the battery can be fully recharged, hopefully by the end of the next solar day. I have observed that my battery hybrid RE system operates closer to ideal with the grid trickle recharging and the windmill recharging schemes in addition to the solar. The system life is determined by the percentage of time, the battery spends away from the float voltage, and the number of times and discharge depth it is subjected to. I hope to investigate other options with batteries. I hope to reduce the need for large solar arrays that spend a lot of time backed OFF during recharging. Others may wish to air their experience with RE Solar battery systems. Gordon. become more energy aware |
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Greenbelt Guru  Joined: 11/01/2009 Location: United StatesPosts: 566 |
Gordon wrote I have noticed that my batteries operate well in the 50-80% stored capacity range. To recharge the remaining 20% takes about 20 hours. The charging current tapers OFF to 0 amps, indicating recharging is complete[/]. check this pdf for a clue 3.5 Time has proven that I am blind to the Obvious, some of the above may be True? |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
Read the .pdf and couldn't find the clue to your problem. I was aware of the first issue in 3.4.1 but the second issue raises some concerns. It seems to suggest that every day (or week or hour) you should make sure the battery is fully charged before taking more energy out it. So, if you have a cloudy day you should fire up the petrol generator to top the batteries up before using them the next night?? 3.4.1 Cycle Life, Depth of Discharge Batteries that are cycled to a lower depth of discharge (say 30% of the battery capacity used versus 50%) will provide more cycles. If the energy per cycle is calculated, then multiplied by the number of cycles, a lower depth of discharge results in more total power being delivered during the battery’s life. If the battery is discharged, but then not completely recharged before being discharged again, this will have a bad effect on total cycles available. Batteries should always be recharged fully. It is Very Poor operation to cycle the batteries between two partially discharged levels. i.e., discharging the batteries down to 60%, then charging back to 90%, then discharging again is much worse for the batteries than discharging to 70% then charging back to 100%, then discharging again. |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
Skimmed through a copy of The Battery Bible found here and the only comment that seemed relevant to your situation is: batteries should be charged at a topping rate for the last 30% and that they can lose the ability to get that last 30% in due to sulphation. He deals with all battery chemistries, with a focus on consumer products (cellphones and two-way radios) so doesn't talk a lot about lead-acid batteries. Are your batteries SLA? He has more to say about them. Cheers, Dave |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi davef, My main question is related to the use of lead/acid batteries with RE Solar setups. There don't appear to be enough hours in the solar day to effectively recharge these batteries given the manner in which the battery is used to supply power to a home in an OFF grid arrangement. I am interested in whether other readers experience the problems of a battery not seeming to give performance like was calculated from sizing estimates predicted before purchase. Gordon. become more energy aware |
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| windlight Guru Joined: 03/03/2007 Location: AustraliaPosts: 331 |
Gordon you do not say how old the batteries are, but in an article by Sandia they make reference to the cost of topping off batteries that last little bit, in brief they question the cost effectiveness. The forth report down. One not published way to wake up batteries is to give them a full (to 1.85V/cell) discharge, this is also a great time to do a discharge at rated capacity test. Then after a full recharge and equalizing for say 5 hours they will not be so lazy. I also like to run mine up to 31.5 volts for equalizing, mind full of battery temp and current. allan Sandia laboratories "I like this place and willingly could waste my time in it" - (Act II, Scene IV). |
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| phred01 Newbie  Joined: 16/09/2009 Location: Posts: 10 |
Couple facts about Pb acid batteries. Ordinary Pb batteries like in cars are are designed for Hi currents to crank engines. So the discharge is very shallow and the alternator tops up the battery fairly quickly. Say a particular batter if discharged to zero capacity then recharged straight away the recovered capacity is 99%. So after 100 cycles the battery is dead. In the case of a car battery the discharge is 0.01% then 99% of 0.01% is 99.9911% so the number of cycles 10,000. So if one starts the car 6 times a day that's 2000 times a year. Therefore giving a battery life of 6 yrs. What one need's is a deep battery which can be easily recharged from a deep discharge. These batteries are no good for cranking engines. Hope this helps |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi I had a problem like this with ex standby batteries SLA type and have fitted desulphator to both packs 24v 1000 ah after a few weeks I have noticed a improvement in absorbsion and power delivery no exact figures but looks like 12 to 15% but is a slow process due to large capacity and the batteries are 5 and 7 years old/ Also tried it on nearly dead battery in my car and it has kept it going through winter and still stars after 12 months May the power be with you Bob Foolin Around |
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| pdave54 Newbie Joined: 12/05/2008 Location: AustraliaPosts: 3 |
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KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
I am a believer in whatever kind of battery giving them an occasional beating. EG a huge load, this seems to "wake them up" as someone else quoted. Battery testers are good for this as they make the battery crack out 700A or more for 30 seconds or so. you're local battery guy will have one of these. painful but load them all up in the ute and get him to load test them for you free. I did lots of work at Boeing trying to extend the life of forklift batteries that had been previously abused. operators were told NOT to recharge the fork until the battery was dead.....MISTAKE!!!! Lead acid batteries do not develop a memory like Ni-Cads BUT, some simple rules should be followed. 1) monitor individual cells if you can one dead cell will quickly stuff the whole battery 2)keep them in a high state of charge as much as you can. (as you are doing) for your grid battery charger, if you can disconnect the load and charge individually every once in a while (monthly or so) thats good for them too. Do some r&d into your charger a simple cheap charger has a pretty rough DC output as seen on a scope, I dont know how they do it but better chargers have cleaner DC (like your solar input) which works better. Im thinking at 20Khz you're f&P must be good for them too as it produces a cleaner DC after rectification... I dont know about the AXFX.. presumably a much lower frequency than the f&P or the grid.... I dont know how battery desulfators work but on the fork batteries a good whack of load certainly came up with higher voltages post charge than could be obtained before the big load. Batteries in the fork were big and the charger would readily pump 80A into them when discharged, falling off as you describe as float voltage was attained... Hence constant current charging is difficult as you need more voltage to get it causing ill effects of gassing etc. old school batteries will take much more beating than VRLA cells, just ask Trev who successfully destroyed them in his EV at $700 a pop!!. SO my question..... why batteries at all when you have the grid? My tip, grid tie the solar, keep the batts as grid out power only. a PVE1200 or for your AXFX perhaps the PVE 2500 and 96V+ could be the solution..... Phill's solution with the Ni-cads is OK but I do worry what pumping in 3KW whilst only extracting 1200W from the PVE and 600W from the dump load is doing to them.. I have seen Ni-Cads explode in a Jetranger Helicopter when the volt reg died on the starter/generator....lets just say cleaning up the mess was the least of our problems. disposing of it much tougher! so for the time being as woeful as they are they are still cheap energy storage... Luck favours the well prepared |
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| KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
oops i missed the key "I have observed that even with huge excess in solar charging capacity, that this is not able to be effectively stored. The recharging system shuts down the array for much of the solar day and there are not enough solar hours to effectively recharge the battery before discharging begins." This happens as the voltage reg (PL20??) is thinking the batt is recharged as the recovery rate is quick... this is an inherant problem with deep cycle batts, they must be charged slowly or the voltage will rise without actually properly charging the battery, thus the charger thinks they are charged when actually they are not.... Lots of stuff in 4WD forums on this one, EG fridge batt 50% discharged put in parallel with main vehicle batt, volts come up quick, so you think its charged but get to camp and fridge dies an hour later..... have a look, often they go into great detail on this Luck favours the well prepared |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi Karl, An 80 panel solar with 3 x Sunny Island 5048 inverters into 2 x 650 AH @48V battery was the system. The solar was AC coupled with Sunnyboy through the inverter/charger to the battery. After several weeks of good sunny days, the battery has finally recharged. Gordon. become more energy aware |
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| KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
wow, thats a serious set up. Top work, trust the govt gave you stuff all towards that! when you say 80 panels do you mean 80x 100W? 8000 watts is some really serious $$. Im green with envy.. Karl Luck favours the well prepared |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi All I am still playing with desulpators and having some interesting results, I started with Jaycar units and found that they are only good on small batteries below 250 ah I am now trialing some rated at 1000 ah but they are very slow and need to be shifted from group 24v to next on the bank to get results, on one bank with 12 volt sealed SLA i shift the 12 v desulphator from battery to battery these are old standby batteries 5 years old and have come back to full capacity. When I got them they where nearly dead showing 10.5 static volts, they wouldnt spin my tester {12 volt starter on a diesel tractor] which reminds me a good battery tester is a starter with a disk brake rotor on the shaft old bendex drive one is the best, use a caliper with a trailer master cylinder to provide load and a 300 amp or more meter to read amps and volt meter to watch for droop and week cells. Can be made for $50 and works as good as one costing heaps but n bells abd whistles after two days on desulphator it spins up as good as a new battery. Once all the cells are treated the commercial unit may keep sulphation at bay but not do the 1000 ah bank all at once, Looks like I will have to bite the bullet and build a big one High Energy pulse to do that. In the old days when I serviced 32 volt units I found that I could use a half wave rectifier to ressurect dead batteries the pulsing effect was better than smooth DC that lacked penetration, also I used a Lincon welder DC generator with good success. in the CROscope it was steady dc with a lot of spiking and I now believe that was what re converted the sulphation crystals as the desulphator does now. I would crank it to 40 volts and 100 to 120 amps for four hours being carefull not to overheat cells, it also worked in single cells at low volts if there was a stubben one. The big bang method tends to blow a lot of active material off the plates to clean them but it dosn't reconvert the sulphate crystals they just end up as sludge in the bottom of the cell, My system is using grid feed as battery load over 27.5 volts so they feed the grid till voltage drops to 26 v then disconnect, This can be switched out to equalise at 30 v but must be careful with SLA and Gell cells, I found it is better to equalize with the desulphator I hope this will give them alzhermers from batt memory. across a low 2v cell at present I dont have a 2 volt unit so have to shift cells to make up 12 volt pack. Combine cells with same or close voltages/ If one had the money to buy new cells and fit desulphator from day one all these problems would go away, but with pension as only income that is a pipe dream. Sorry to waffle on All the best Bob Foolin Around |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Update on desulphators After three months the batteries have increased their capacity noticably before with 40 amps input it would push them to 30.2 volts to equalise now I have trouble getting them to 29 volts need more input to equalise to me means more capacity. The desulphators I am using are to small in reality as I had to shift them around to get best result, Also found a 12 volt one acrossd lazy 12 volt batteries brought them up. Conclusion fit one desulphator per 500 amp cells. These are old batteries for all intents past use by date and it has made them a useable power source, on a new set of good batteries I am confident it would extend th working life as the maker promotes. Also my dead car battery is still going. All the best Bob Foolin Around |
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