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analogmanca
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# Posted: 28 Oct 2013 15:22 - Edited by: analogmanca
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First I should say there are no bad voltages, 12, 24, 48....they all work!
But the 12 volt is sure taking a beating these days.To listen to some you would think its even unsuitable to start a car .
I read a post about someone who's load is around 3kwhs a day being advised to go to 24vdc when such needs and smaller can be well served by 12vdc. Now I admit to being partial to simple, durable, hackable,and largely repairable so maybe that colours my judgement as I am my own warranty, and tech support....
Now I was setting up way back in the old days(2000), back when panels had terminal boxs and not MC4 connectors. Here is what I have and run. Up to this year just 1150 watts of panels, all used when I bought them,mounted on a stand sitting on the ground, tiltable roughly 250 degrees through a hand crank(petal of kids bmx bike). That 1150 watts is feeding 10 T105 type clones, a c60 controller, a xanatrex 1800 watt (3000watt surge) inverter.
I run a 6cuft frezzer, a electric fridge, all the lighting I want, music on all the time, a laptop on 24/7 , a pressure pump for water, another big pump for moving water from the cistern to other tanks, a septic pump,microwave,toaster, coffee maker, (dont watch tv but could) ,stove is propane but I do use electric crock pot, electric frying pan, and I have a full size normal washing machine, electric alarm clock....all the normal stuff...and all on 12 volts and I do not take my batts down below 12.4 volt (other than the odd brief dip under a heavy load) so I pretty much only use 20-25% of my battery capacity.I also have no 240 volt loads.
Rough cost for this basic system today, c60-150,inverter 1000, batteries 1500,at todays panel prices 1000.00 So thats 3650 for the lions share add in 1000 to 2000 more for other needed stuff (fuses, Disconnects,Wiring, Plywood for bat box etc). 5000+ for complete energy independance and all on the lowly 12 volts!
Now let me say regardless of the system voltage you really need to look at your loads and I dont mean reading the often wrong name plate info, get a killowatt meter! Trust nothing! nothing!
Time of use can be just as important as what something draws.
I suggest getting a piece of graph paper, down the left side write the hours of the day (1 through 24), across the top list every load you want to run,fill in values displayed by the killowatt meter. This piece of paper when filled out will be like having a guide/starting point as to your useage at any point in time...if you dont know where you are, you wont know where to go.(some of what you will learn will take you to trying load shifting for greater effeciency).
Lessons learnt,
Use the smallest inverter you can.
Use the smallest battery bank you can.
Use the smallest generator you can.
Time shift your loads when possible
Buy the most panels you can now that the price is so good.
Get a turbine to help in the winter
Its a sunny day...Batteries are floating,think Im going to go out, crank my array at the sun, turn on my miller maxstar 200 and tack some steel together.....all on my 12 volt system.... nothing like the smell of molten steel on a sunny day...
(all the above is how I have run for years, but do to good pricing on panels this year my system is being changed around, Still staying at 12 volts but adding way more panels, and changing how I use them)
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Dillio187
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# Posted: 28 Oct 2013 16:58
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the most difficult thing about a big 12 volt system is charging and discharging the batteries equally. Any difference in the resistance of the batteries themselves, or the connecting mediums leads to imbalances. I tried and tried with a small 4x6V battery bank to keep them equally charged, but I always ended up with 2 batteries discharged more than the other 2, even when using buss bars and equal length cabling. Not saying it can't be done, but I opted to punt and make my bank 24V.
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analogmanca
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# Posted: 28 Oct 2013 17:29
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Wait a minute, you had 4, 6 volt batteries for your 12 volt system,and you could not keep them balanced?
I just dont understand, it would be impossible to have them unbalanced (we are talking new batts right?)
I will try to explain. negative lead ......_ ...._
+ +
_ _
+....+.........positive lead
I do not know how to draw the series connection between the _ and + so just imagine it there.
Sorry, balance with 4 is perfect does not get any better. I know people with 12 wired up...no problems
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analogmanca
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# Posted: 28 Oct 2013 17:31 - Edited by: analogmanca
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When I posted, the drawing shifted hope it still makes since..that is how you wired it?
negative off the upper left, positive off the lower right
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MtnDon
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# Posted: 28 Oct 2013 18:42
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The potential issue with a 12 volt system arises when there are two or more series connected strings placed in parallel.
For example if you have 6 volt batteries it takes 2 in series to make the 12 volts. If that one series string does not have sufficient amp-hour capacity we would then connect a second or a third series string in parallel. Connecting the negative to one "corner" of the battery bank and then connecting the positive to the opposite "corner" helps to alleviate the balance problem. A better solution is to have longer series connections, whenever possible. The best solution is to have a single series string; no parallel at all, with the capacity set by the choice of batteries. You can disagree and obviously do. That is fine.
The fact remains that if you talk to a solar system designer with years of experience of designing and installing systems for "ordinary folk" who simply want the system to make their "stuff" work when they flip a switch, they will tell you that series is King and parallel Sucks when it comes to long lived batteries. I'm not saying that because I read a book that says so; I'm saying that because a good friend is a pioneer of sorts in the alternative energy field. With 20 years experience ranging from sailboat size systems to those that seamlessly run 2500 sq ft homes I trust his opinions on alternative energy systems much more than anyone else I know.
Many of his systems do not even have a generator included. Of course it does help when the locations are in the SW USA or similar sunny locations in other countries.
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Dillio187
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# Posted: 28 Oct 2013 20:31 - Edited by: Dillio187
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Quoting: analogmanca Wait a minute, you had 4, 6 volt batteries for your 12 volt system,and you could not keep them balanced? I just dont understand, it would be impossible to have them unbalanced (we are talking new batts right?)
yes, for the reasons Don mentioned above. All of the batts were the same brand and purchased at the same time. I tried the 'cross' method you mentioned, and when that didn't work I went to copper buss bars to connect everything to. This worked better, but still wasn't perfect, I frequently had the same two batteries that required more water to top off, and when I measured the SG, were discharged more than the other set.
Yes, as Don mentioned, I had 2 parallel strings of 2x6V batteries to make a 440ah, 12V bank. I now have them wired all in series as a 24V 220ah bank.
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MtnDon
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# Posted: 28 Oct 2013 20:51 - Edited by: MtnDon
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Quoting: Dillio187 2 parallel strings of 2x6V batteries to make a 440ah, 12V bank. I now have them wired all in series as a 24V 220ah bank.
Same watt hours; just better. 
The difference in battery performance stems from the fact that the batteries are imperfect. Batteries from the same manufacturing batch are not identical. Slight differences in the alloy, in the plate thickness, in the internal connections all conspire to make "identical" batteries have differences. This is manifests itself in different internal resistance. Everything goes downhill from there and parallel connections make it worse.
I built my system before I knew my friend Dave. That is how I ended up with parallel strings.  The replacement set for this one, whenever it becomes necessary will be a series only configuration. I am already running 24 volts so that should not be too difficult, although not necessarily cheap. My ideal at present would be to use Trojan L16RE-2V, 2 volt batteries. Cost effective comparisson to Rolls/Surette. One series string and we would have plenty of capacity for an electric refrigerator (with the addition of another string of PV modules.)
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analogmanca
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# Posted: 28 Oct 2013 22:28
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I am not in dissagreement that a series string of whatever voltage batteries is prefered, if it can supply the required amphrs needed. I find this concern to be overrated (just my 2 cents), likely showing up closer to the end of a battery banks life, and can be mittigated by good practices (such as rotation).
I suspect many things conspire to wear on a battery bank including a baby sitter who drove the banks voltage down to LVD as happened to a friend.
You are fully right a designer will spec a system with likely 3 maybe 5 days autonomy(huge expensive bank, with a expiry date), a inverter charge controler maybe with gen support all built in to one unit (expensive,complicated all eggs in one basket, likely requiring on line tech support, some even requiring a factory tech on site to commision the system) But let me ask you is such a system really needed or desired for those remotely set up, clearly capable, and handy with modest requirements (less than 3kwhrs), Simple has merrit so long as it meets the needs of the user.
My simple original, bullet proof (150 dollar)C60 controler works without fuss, Two knobs on it , one to set bulk, another float. With some of the new panels I set up I tried a "newer designed controller" Guess what? Bank of dip switches to set, unlabelled, god help me if I lose the book (or my glasses),with flashing light error codes that makes learning brail easy, the thing can be hooked up to a laptop for custom programing.....like I need that.(going back to a C60)
I am saying 12 volts and simple works fine, put the money you would spend on expensive batteries, expensive all in one controllers, and buy panels. You can run a heavy load on 12 volts, I cut all my firewood for the year with a electric chainsaw, run a 16 inch chop saw for steel, all on my 12volt system. Once your batteries are at float (in my case 13.4 volts and usually by 11am) the controler will then pass all current to the load. As in my first example, that 1150 of panels nets me roughly 58 amps...58 x 13.4 =777 watts, thats free power not having to come from the batts. As happens the batts will kick out more if needed by the load. Now that panels are so cheap I suggest buying as many as needed to get up to 2000 + as I have done. This now gives me a second array putting out 56 amps, so together I can run 1500 watt loads for hours at a time, all on a 12 volt system , without hammering my batts. I am not saying my way is the only way, only that 12 volts works fine, and such a system can be cheaper to put together than higher voltage systems with their often more complicated controlers.
Just occured to me with panels lasting 25, 30+ years, how many of those expense controlers, and batteries will you have gone through in the same time frame, for some it wont matter, but for those like myself cost vs performance is always looked at.
Dillio187, you have me stumped. makes no sense to me, the wiring I descriped with 4 batts should be equall to a series string.....I would have suspected a manufacuring irregularity.....how long have you been using them?
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creeky
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# Posted: 29 Oct 2013 09:56
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i'm with you analogmanca. more panels. get your batteries to float and then bring on the dishwasher, washer, chop saw.
tho I love my banks of dip switches and internet "live" data. you only set the switches once. currently my 12v system is 13.16v at 9.1 amps. someday I'll cut down that tree (in the winter my panels get shade for an hour in the mid a.m. and that tree ain't gettin' any smaller).
i also like mppt and the higher voltages my ts-mppt 60 charges at. keeps my plates in good shape I believe. batteries are at 5 C and headed to 15.3v for absorb.
i too fail to see the benefit of 3-5 days of backup battery capacity. go out and start your generator in the morning while you boil water for coffee and make breakfast. after an hour. turn it off. there. for .50 of gas you replaced 2k of batteries.
tho, where I live, i only run my genny for charging in oct/nov/dec. the rest of the time i get enough sun to get by. this oct I have run my genny three times. I could have reduced my loads, but it's oil change time and the gens been mostly sitting.
i think some folks forget that "perfect is the enemy of good"
or call in the babysitter a lot.
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Dillio187
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# Posted: 29 Oct 2013 10:24
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This bank is at my house, and about 2 years old, I ran it for about 9 months as a 12V bank, and switched it over to 24V and it's been that way for about 15 months now. All of the batteries charge and discharge fine now. It's quite a common problem actually, I read about it almost daily over at the Arizona Wind/Sun forums., that's actually where I found out why this was happening. Once I thought about it, it made a lot of sense.
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toyota_mdt_tech
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# Posted: 29 Oct 2013 11:24
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Couldnt a guy have a large voltage system, lets say 48 volts, this keeps wires small from solar panels, or small on those long runs where the panels are away fromt he home, then have your sereies 12V batterys set up to charge at the cabin in a safe ventilated area, then you could tap offf of each 12V battery individually, break it up into circuits, loads etc (trying to keep it overall even) in other words, a heavy load could get its own 12V battery, say a fridge, while lots of lighting can have its own 12V battery, but they would all charge in series. Could this work? I know it would work, I'm just curious if the batterys would remain even all the way across being charged in sereis.
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Dillio187
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# Posted: 29 Oct 2013 11:35
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no, because then you would have 1 set of 12V batteries heavily discharged, and others without hardly any discharge. Then if you try to charge them as a large bank, you cook the barely discharged batteries while shoving amperage into the discharged batts.
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toyota_mdt_tech
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# Posted: 29 Oct 2013 21:56
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Wouldnt the low battery naturally pull the voltage down and consume more current till the state of charge is even with the other batteries?
So lets say a battery bank of 12V X4, all wired in series for charging, one is used more, (even though I said to spread the load around evenly, but for the sale of argument) OK, so now a good charging voltage on a 48 volt system would be 56 volts.
The single low battery pulls the bank voltage down to lets say 52 volts, thus, allowing more current, but to the low battery. (keep in mind, full charge is 56 volts, so at 52, its really not charging all battery's. As soon as the bank is charged up and voltages climb to the regulated (off) of 56 volts, then current or charge rate tapers off.
So wouldnt it charge the low battery, getting them all somewhat even, then topping them all off at the same rate when they are equally charged, condition of battery is perfect and all even for this scenario.
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MtnDon
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# Posted: 29 Oct 2013 23:22 - Edited by: MtnDon
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It would be next to impossible to divide the loads on individual batteries in a manner that would keep the state of charge as equal as possible. IMO. You'd be sweating it out every time you turned something on or off. Again, IMO.
Quoting: toyota_mdt_tech battery bank of 12V X4.....
.... as Dillo said, No.
Ok for simplicity 4 - 12 volt batteries wired in series. 48 volts
Battery A is at lower state of charge than B and C. Battery D has not been used at all... state of charge is quite high.
If they sit there with no charge going in and nothing being drained, the low battery A will "leach" some current from the others. But this will happen very slowly. Once the peak voltage from the last charge is dissipated the overall voltage of the bank will be something like maybe 50 volts...
In order to get a decent charge going on a 12 volt battery needs 14 volts, 13.8 can work, but our common chargers use 14.4 or so. Remember a full 12 volt lead-acid battery has a voltage around 12.7 volts. So with 50 / 4 = 12.5 volts, the transfer from the higher batteries to the low (A) will be slooow.
Not only that, but when a proper charge current is applied to the A, B, C, D series string, battery D (the full one) will start to do some serious bubbling and overcharging right away. The full battery can not reject the current it does not need. It is in series with the other three so the current passes through. The same voltage and current is being applied to the entire string. If the charge time went on long enough the lowest battery (A) will become fully charged. The other three will have suffered various degrees of overcharging. The battery D that began as full will likely be quite hot and eventually be much lower on fluid than the others.
It's a don't go there situation if you want to prolong each batteries life to the maximum.
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analogmanca
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# Posted: 30 Oct 2013 11:09 - Edited by: analogmanca
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Quoting: creeky i think some folks forget that "perfect is the enemy of good
That is what I have failed to articulate, and perfect is not achievable anyway, and the costs of going for perfect will shut some out of trying.
I am not a luddite regarding technology but wiegh its costs/complications against performance, and ease of use...Take MPPT....great techology... lots of magic in those controlers and in the real world you will net more amphrs from your panels. I am only going to talk about quality ones (not L cheapo/chinese, off e bay,may burn your place down) like a classic 150 for example, cost up here last time I looked was 800.00. vs 150 for a C60 800-150=650.00. Panels can be bought for .78c a watt (right now). I can have a Classic 150 controler and O power.......... or aC60 controler, and 825 watts of power!! where is my money better spent! ofcourse you dont hear that from those selling the controlers as there is more profit in the higher priced sale....but I am going off on a tangent not related to my 12 volt comment.
All kinds of reasons why some people have had problems with 12 volts, Cant address them all as each situation like each person is unique, Just saying 12 volts can work fine for the smaller systems of say 3kw or less. I can go to 24 volts today if I wanted to, I dont because there is nothing at all to gain....no advantage for me at all! I run everything just fine on my 12 volt system (maybe I lack ambition)....I can take you to 2 other places in the area and same story...running on 12 volts, have been for years (14-15 years the longest I know of), no problems related to 12 volts...
Quoting: MtnDon The fact remains that if you talk to a solar system designer with years of experience of designing and installing systems for "ordinary folk" who simply want the system to make their "stuff" work when they flip a switch, they will tell you that series is King and parallel Sucks when it comes to long lived batteries. I'm not saying that because I read a book that says so; I'm saying that because a good friend is a pioneer of sorts in the alternative energy field. With 20 years experience ranging from sailboat size systems to those that seamlessly run 2500 sq ft homes I trust his opinions on alternative energy systems much more than anyone else I know. Many of his systems do not even have a generator included
I dont always have the highest regard for experts...but thats just me. Their objectives are not solely yours. I too can design a system without a generator...how many panels, and how much lead would you like to buy? I do understand your point though..
Quoting: MtnDon "ordinary folk" who simply want the system to make their "stuff work"
Sadly thats becoming the lowest common denominator in everything...
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analogmanca
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# Posted: 30 Oct 2013 13:48 - Edited by: analogmanca
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Forgot to mention, also lots of interesting stuff to play with when you have a 12 volt system and I dont just mean the 12 volt appliances.
Think inverters are new? quess again, back in the old days they were mechanical.
That black one in the picture could have been from as early as 1911-1912 to 194? when the company changed their name. Sometimes just for fun I will hook it up and run my gameing computer on it....oil the babbit bearings...it will still be working a hundred years from now...will yours?.... Look no dip switches, no lap top interface cable, no waiting on hold for tech support, no firmware upgrades or software bugs, no extended warranty conditions or cost... yet it just simplely puts out a perfect 60 hz 120 volt sign wave....how far have we really come.....just food for thought...
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MtnDon
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# Posted: 30 Oct 2013 14:09 - Edited by: MtnDon
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Quoting: analogmanca I too can design a system without a generator...how many panels, and how much lead would you like to buy?
I can and did too. I happen to dislike generators, period. Even quiet Hondas and Yamaha; I do own a couple too for those times the extension cord is not long enough. One is propane fueled and has an auto start to come on if necessary like when we're away and the grid goes down (home setup, not cabin). What it comes down to is there are different correct answers for different people, different uses. You are happy with yours. I am happy with mine. My couple of grid tied neighbors are happy with their solutions. I have another neighbor with a stand alone system. Then there is our home with grid and batteries.
And there is nothing wrong with simply wanting something to work with no fuss, mess or bother. We can't all simultaneously be experts in all fields though some try harder at that than others. It is what makes the commerce of the world go round.
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analogmanca
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# Posted: 30 Oct 2013 14:43
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MtnDon,
I know you can design one, and probably much more. The target of my post isnt those who can, rather those wanting to try, likely with the eye on costs. Costs, and products built with a expiry date built in work against that. Many ways to get the job done including 12 volts.
Regardless of voltage choosen, and before buying or deciding anything get a killowatt meter(35.00 or less) measure everything, think about each thing used (how/when). experiment, we live in a stunningly wastefull, high energy part of the world when with the littlest effort and thought, the same level of comfort and needs can be met.
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Dillio187
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# Posted: 30 Oct 2013 15:36
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don't get me wrong, I like 12V (my cabin runs on a 12V system with 2 golf cart batteries).
Just like Don said, different strokes for different folks!
BTW, that rotary converter is really cool!
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MtnDon
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# Posted: 30 Oct 2013 18:02
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Quoting: analogmanca The target of my post isnt those who can, rather those wanting to try, likely with the eye on costs.
Unfortunately those trying to cut costs also frequently screw themselves by trying to make do with too little. Too little battery capacity is one of the main failures people make when they design their own systems. Included in the list of causes of system failure and/or owner dis-satisfaction is too much reliance on a generator for charging and too little PV capacity.
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