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Energy/Electricity Storage and Use/Grid Connection => Off-Grid, Batteries & Inverters => Topic started by: woodi on January 31, 2016, 10:28:48 AM



Title: Two battery banks
Post by: woodi on January 31, 2016, 10:28:48 AM
I've got two completely separate banks of batteries - a main 1000ah 2v tubular plate one @24v, and a backup of 1000ah 6v trojans. I've been trying to come up with a sensible way to utilise the backup, for instance when we get a few dark, still days and I want to save the main bank. Rather than use our incredibly loud generator, it'd be as good to call on the second battery bank, which can then recover in between times.
How best to use them?
cheers
Steve


Title: Re: Two battery banks
Post by: camillitech on January 31, 2016, 11:01:29 AM
I've got two completely separate banks of batteries - a main 1000ah 2v tubular plate one @24v, and a backup of 1000ah 6v trojans. I've been trying to come up with a sensible way to utilise the backup, for instance when we get a few dark, still days and I want to save the main bank. Rather than use our incredibly loud generator, it'd be as good to call on the second battery bank, which can then recover in between times.
How best to use them?
cheers
Steve

Let me know when you find the answer Woodi, two battery banks is 'double trouble' and nowhere near as efficient as one. However I suspect you've inherited one and want to make the best use of it, like me. I have three of them and have yet to come up with a solution. A 450Ah 24V forklift pack that I just use on my generator, bit of a waste as it rarely runs. An 800Ah 48V bank of Rolls cells that power the house and a 950Ah forklift pack in my 'Bunker' (plant room) with an Outback GVFX 3048 attached. I'd like to do something with the latter but can't think what.


Title: Re: Two battery banks
Post by: woodi on January 31, 2016, 11:14:55 AM
Yep, the second set didn't cost me, but I don't want to let them sit too long. We've two buildings here, so what I should do is get yet another inverter, and devote a bit of solar to it. But that involves money I'm loathe to spend, hence the idea of switching them in and out to the main inverters. Also have to get around the fact that it would take a bit of explaining to the battery monitor, so I'd probably end up duplicating that too.
Presumably one option is a bloody great big switch somewhere. The trouble with this sort of setup that manually disconnecting and reconnecting inevitably means plunging the place into darkness, usually in a force 10 gale, at night :)
Plus I have the non-grid-grid tie turbine watching out for the voltage, and you know well what fun is to be had when the AC uncouples and can't recouple.....


Title: Re: Two battery banks
Post by: billi on January 31, 2016, 11:16:34 AM
A few thoughts .....

connect the second battery to a small GTI and Ac -couple  to the other system  on the AC out
connect the second  battery to a cheap Taiwan off grid  inverter and  feed the Victron s  from the AC in , where usually the generator is  connected




Title: Re: Two battery banks
Post by: biff on January 31, 2016, 11:24:39 AM
Hi Steve,
         The 2 bank system was something which I tinkered with for a few years. It is a load of bother for very little return,
 At one time, I had 20 x 100ahx 12v Yousa (excellent)and then another 20 x 105ah yellow powersafe agms,(useless). The trick was in keeping them topped up to the gills before switching over and that requires quite a lot of electrical trickery which in the end defeats itself.
 My voltage is as you know a 120vdc system and i went and installed 60 forklift cells in series that had a minimum 600ah. But,,but,,before that, I had a reserve set aside of another 1200ah x12 volt solar and a 400ah solar in 48volt,each independant of the other but available to power the house in any emergency by just swopping over the normal household 13amp plug in the control house down the garden.
    Then one day, while I was recovering from an illness, I sat down with my wife and explained that I was going to have to map the whole system out properly because if anything went wrong and I was not about, it would be all junk in the eyes of anyone else. So I shut down the 48v system and the 12v system, (I even had another 24volt system for a while) Moved the house geni to a better location and simplified the whole set-up. I marked the plugs clearly and extended the house system down to the shed so that my wife could manage it easily when I was away.
 The system has been totally automatic for a few years now, apart from having to top up the cells. However, if for some reason we have no sun or wind for more than 48 hours, then the geni can be switched on and the house plug switched over manually, very very simple and fool proof. The bank never drops below 124vdc anyhow.
  The high voltage makes it possible to series the 60 cells and get a decent result, We are talking 2 ton+ of lead here and 2 days @ a max of 400watt is only tickling it, so even though they are old cells they do a great job and are never stressed. I tried the two banks and the volt meter was never out of my hands.The forklifts are also very forgiving.
   If i had been scientifically minded, I could have arrived at my present position a lot quicker but my "Suck it and See" methods did throw up a few nice surprises.
  I guess, at the end of the day, you just have to find the method that suits yourself. I never did have any pleasure until I installed the forklift cells and reduced the size of the prop on our wind turbine but it runs beautifully now. I would love a bank of 60 new forklift 1000ah cells, Now that would be quite something :genuflect. No harm in wanting, ;D
                                                                           Biff


Title: Re: Two battery banks
Post by: Justme on January 31, 2016, 12:39:40 PM
Unless you need military or medical grade back up then just combine into one bank.


Title: Re: Two battery banks
Post by: woodi on January 31, 2016, 12:54:47 PM
Hmm, combining a bank of 1000ah 2v forklift batteries with a bunch of 6v trojans is unlikely to do anything any good, methinks, Justme. Biff, I know what you mean, simple is usually better, and I might just wind up splitting the system and might even try one of those Tiawanese inverter/mppts that people have mentioned, to manage the second bank and feed power to our little rental cottage.
Billi's suggestion of running them through the inverter to the output of the multis is a good one, I reckon I might give it a go. I don't know how clean the output of the TW units is, but the multis can be persuaded to be very tolerant when they have to. Our generator puts out lord-knows-what sometimes, and they don't complain too much.


Title: Re: Two battery banks
Post by: billi on January 31, 2016, 01:20:38 PM
.... i once  ran a 350 watt  Victron true sine    into my 2 Victron Multi Plus on the AC in site  ,  as a backup  generator  ( second batteries where on my pickup  truck to get recharge while driving )


It did work fine , but as you know,  the power  is switched through the main Victrons  into the house then   and that lead to an overload problem of that 350 watt  Inverter  , so on the AC in side idea i would go for  a bigger off grid inverter (like these cheap TW units  with 2400 watt) and i am quite positive,   that your Victron Multis would accept that 

If you AC couple  a GTI on the AC- out side  and run a Micro GTI like the AEconversion  units (match a 24 volt bank )   direct connected to your battery , then i would assume you have lesser trouble,  because the 2 Victron Multis you have stay the "Master" then  and  the GTI  supply  house load  and  batterycharging of the main  batterybank in backfeeding into the main Victron Multis



Sounds confusing  wacko   but i did both ,  i guess i would go the GTI road today , even if its only 300-500 watt  output to the house 

Billi


Title: Re: Two battery banks
Post by: camillitech on January 31, 2016, 01:45:46 PM
A few thoughts .....

connect the second battery to a small GTI and Ac -couple  to the other system  on the AC out
connect the second  battery to a cheap Taiwan off grid  inverter and  feed the Victron s  from the AC in , where usually the generator is  connected




Interesting line of thought Billi and one I'd not considered, in option 1 you'd need to shut the GTI down at a certain voltage though? In option 2 you'd have to reprogram the 'Master' to think it was using the grid and not the generator? Needs more thought, I do like this idea.

Definitely a bad idea combining the different cells. Yes Biff two banks are a proper PITA and I'd never condone it but if you've acquired a bank or two for buttons then Billi's scheme has merit.

Cheers, Paul


Title: Re: Two battery banks
Post by: woodi on January 31, 2016, 02:33:57 PM
In the multis its easy enough to tell them that the second inverter is in fact the grid, or a generator - I'm not sure it would make much difference. Its possible to switch it around from the CCGX if you have one. Then tell the multis to use the 'grid' - second battery bank, if demand peaks above a certain amount.The Hub-1 profile in the multis allows you to use the grid without feeding back, and you can set the levels at which it begins to call on the grid input.
That'd do it I reckon. Then the second bank only gets used when demand is high.
Sounds like a plan?


Title: Re: Two battery banks
Post by: camillitech on January 31, 2016, 04:38:56 PM
In the multis its easy enough to tell them that the second inverter is in fact the grid, or a generator - I'm not sure it would make much difference. Its possible to switch it around from the CCGX if you have one. Then tell the multis to use the 'grid' - second battery bank, if demand peaks above a certain amount.The Hub-1 profile in the multis allows you to use the grid without feeding back, and you can set the levels at which it begins to call on the grid input.
That'd do it I reckon. Then the second bank only gets used when demand is high.
Sounds like a plan?

Sounds like a really good plan, must break out the SI manual and check that out, sounds like heavy reading ahead. Thing is, what are you going to do about charging that bank? that's the next stumbling block. The chances are, if you've been given that bank (as I have) then it's not going to be 100% and would probably most efficient if it was cycled regularly rather than charged up and left lying to self discharge.

Cheers, Paul


Title: Re: Two battery banks
Post by: woodi on January 31, 2016, 05:30:05 PM
Well, I'm willing to punt 300 and try one of those Taiwanese Inverter/Charger/MPPT jobbies that Billi has mentioned, then it can take enough solar to keep the batteries happy. Long term I suppose I could consider yet another multi, and mppt, but thats the thick end of 900 trade for the multi, and another 150 for the mppt. Then another battery monitor - BMV-700. So its either 300 and establish that it works, and see how long the kit lasts, or the thick end of 1100 to keep it all Victron. Chances are, the first option will win for now. If it blows up I'll not cry too hard.
I've only limited experience with the Sunny Island, and I know my Victron kit well, but programming the SI seemed an awful lot less intuitive, though it may be grand if you use it all the time.


Title: Re: Two battery banks
Post by: Justme on January 31, 2016, 05:48:48 PM
Hmm, combining a bank of 1000ah 2v forklift batteries with a bunch of 6v trojans is unlikely to do anything any good, methinks, Justme.

Are they the same tech IE both open FLA?

If so then the fact that some are 2v cells & some are 6v batts is not an issue.

Assuming that both sets are in full working order & if they are not then your pissing in the wind anyway.



Title: Re: Two battery banks
Post by: woodi on January 31, 2016, 05:53:18 PM
Yes they're both FLA and in good condition, but one set are tubular plate and the other aren't.  They are different ages and capacities though, and everything I've ever read tells me that mixing batteries in that way isn't a great idea. Going to go with the inverter feeding the current setup and ac coupling. If nothing else it will be an interesting experiment.


Title: Re: Two battery banks
Post by: knighty on January 31, 2016, 05:55:51 PM
Hmm, combining a bank of 1000ah 2v forklift batteries with a bunch of 6v trojans is unlikely to do anything any good

ok it's not perfect, but joining them into one big bank is your best bet

you'll end up with a 2000ah bank

so even if you're drawing off/charging at  200amps it's only 0.1C rate - you'll hardly touch them



just need to make sure you give them a decent equalisation charge once in a while to even them all out and keep the happy


anything else you do you'll struggle to keep them evenly used - you'll end up with one bank hardly being used while the other does most of the work

better off with one big battery hardly doing anything


you might lose a couple of % efficiency but you'll save at the same time because you're not adding in chargers/inverters etc. etc.


Title: Re: Two battery banks
Post by: camillitech on January 31, 2016, 07:21:05 PM

ok it's not perfect, but joining them into one big bank is your best bet





I'm with Woodi, really bad idea mixing different cells, ages and capacity. I've looked after many battery banks at home and work and mixing them always ends in tears. Especially something like Rolls (I bet Trojans are the same) as they like a much higher voltage than others. My main bank sits around 60V much of the time, don't think that would go down well with other types. Certainly one bank is better than two, but if someone has given you half decent bank then you don't want to turn your new good bank into another half decent one.

 The sane thing to would be to sell the half decent one on eBlag, combine it with the money you would save on an extra inverter and buy more PV or a quieter generator  horror: (hides from Billi) However, sometimes it's more fun and a lot more interesting to be a little insane  ;D

I already have a spare Outback inverter/charger and really fancy working on Billi's idea of AC coupling into the main system. I'm working on using a spare Tri Star I have and using it LVD mode on the forklift bank. Not read the Outback manual fully yet but it may have similar features to the SI and Victron so may not be necessary. Trouble is that to do anything on an Outback you need a 'Mate' and I'm not for forking out on one of those unless it's going to really improve my system.

Cheers, Paul


Title: Re: Two battery banks
Post by: woodi on January 31, 2016, 07:45:58 PM
Well the cycle life and general durability of the 2v traction batteries is way above the Trojans - the 2v are 60kg each, and a single 6v trojan is what - 20kg? I'm very nice to the traction batts, so I reckon they'd outlive the Trojans quite considerably.
Selling the Trojans and getting some more PV is probably a sensible proposition if they are worth anything, but part of me can't resist the idea that more storage is a Good Thing, and adding another AC coupled inverter offers the chance to play around. Plus I can always separate the 2 systems, which at some point might be useful as I'm powering 2 separate buildings....
Camilltech makes a good point about voltages. The traction cells have an absorbtion voltage of 30v because of their height, and subjecting the trojans to that would (I assume) end in tears.


Title: Re: Two battery banks
Post by: camillitech on January 31, 2016, 07:58:29 PM
Well the cycle life and general durability of the 2v traction batteries is way above the Trojans - the 2v are 60kg each, and a single 6v trojan is what - 20kg? I'm very nice to the traction batts, so I reckon they'd outlive the Trojans quite considerably.


That's exactly my point Woodi, charge the forklifts at the Trojan (Rolls) voltage and they'll get fecked or charge the dubious Trojans at the forklift voltage and they'll barely hold a charge. OK, perhaps not so dramatic but you get my gist, DON'T MIX em in the same bank (not that you would). Much more fun to play around with inverters and AC coupling  :crossed probably not sensible but far more exciting  ;)

Cheers, Paul


Title: Re: Two battery banks
Post by: billi on January 31, 2016, 11:07:03 PM
no , pairing those 2 different batteries  does not sound right to me ,   what is gained with that idea ? If one weakens the main  bank  of 2 volt tractions cells  that can live beyond 15 years  ( mine are now 13 )  if treated right ( i am  not overprotective  but my system  does seldomly discharge them under 50% )

It does make perfectly sense to me  to create a kind-off back-up generator  with that second battery (that has a shorter cycle life)  to avoid  too often deep discharges of the main Batt bank


We  people  take care of weather forecasts  because of our off grid  lifestyle    and  can switch on  that battery based  back up generator   (or  our main inverters do that automatically )


But i think , i think  i would go the Micro GTI 300-500 watt  idea http://www.aeconversion.de/en/inv350-60.html  ( i mentioned 2 options above)   connected to the Trojan  battery  and feed into my housegrid to take the pressure of the main battery on the AC-out   of the Victrons

It is done and tested that  micro GTI s work on battery power , but as Paul meantioned  , a too deep discharge has to be  avoided ( simple time  perhaps )

This guy  works  a lot with that kind of idea http://www.solarelectrix.de/4_panel_uk.html    of feeding battery into Micro GTinverters




Title: Re: Two battery banks
Post by: Justme on January 31, 2016, 11:19:43 PM
Yes they're both FLA and in good condition, but one set are tubular plate and the other aren't.  They are different ages and capacities though, and everything I've ever read tells me that mixing batteries in that way isn't a great idea. Going to go with the inverter feeding the current setup and ac coupling. If nothing else it will be an interesting experiment.

Everything you have read is wrong.

Age & capacity matter not if they are in good condition. All the stuff you read about splitting banks is due to a faulty bat dragging the rest down.

Think about it.

If you cant join banks then you cant have more than one 12v battery in each bank unless its made up of 2v cells. You also could not have say a forklift battery converted from its original voltage to 12 or 24v as you are linking banks in parallel.

Read THIS (http://www.smartgauge.co.uk/splitting.html) re split banks. The writer is prob the best source re battery info.

Just for clarity I will say again that this is with the same battery type.

Mixing types would be wrong.


Title: Re: Two battery banks
Post by: billi on January 31, 2016, 11:57:14 PM
  ... we are not splitting banks here  , more about how to combine   different  batteries together  , but sure  i would be interested in  an answer  of the smartgauge  guy  , if he would recommend to direct parallel a 600 cycle with a 1500 cycle battery


Title: Re: Two battery banks
Post by: camillitech on February 01, 2016, 12:03:37 AM


Just for clarity I will say again that this is with the same battery type.

Mixing types would be wrong.

But the OP quite clearly says in his first post that they are different types.


Title: Re: Two battery banks
Post by: oliver90owner on February 01, 2016, 06:51:40 AM
I've seen that the ah rating for both is 1000.  I've seen that one bank is 24V (so a group of 12 cells).  I've see that one battery is 6V.  I am given the impresion that both banks are equivalent in power, if not quality/durability.  I've also read that the trojan cells weigh around 6-7kg each (6V battery is 'about 20kg') whie t'others are 60kg/cell.

They are not the same.  What is the battery format of the trojans?  Strings of 4 in parallel for the pack to achieve 1000Ah?

As soon as a high current is drawn the cells with the higher internal resistance will deliver less power as their terminal voltage will fall more than the other set..

At a push, if both were really the same type (traction fla or whatever) they would be acceptable in series - yes, at a push.  They are not, and 48V is not an option,  so they are not compatible for secure long term use.

Seems to me that the word 'type' is being used as a convenient term.  They are both lead/acid chemistry, so of the 'same type'?  Would one mix fla with gel, even if both were of that 'type'?  Even as a series bank newer with older is not good - think here of changing one failing battery, of a pair, for a mobility scooter.  Just not the done thing unless for a short term quick fix (err, bodge).


Title: Re: Two battery banks
Post by: woodi on February 01, 2016, 07:59:34 AM
Ok, for clarity - they are both FLA banks but one is a year old bank of12x 2v tubular plate traction cells - Exide EPZS 1000ah@24v. The other are 8 x fairly regular Trojan 6v 225Ah, (so 2 strings of 900Ah to give 24v @900ah) which are  nearly unused, but approx same age, and have had the odd float to keep them happy. Quick check of specific gravity shows the trojans to be in a marginally better state of charge. 

As Billi says, they have very different cycle lifes and are physically very different beasts. Info about mixing them together is very interesting but I'll let someone else experiment with their two and a half grands worth of battery :)


Title: Re: Two battery banks
Post by: billi on February 01, 2016, 08:44:05 AM
.... the  one batt is rated  at C5 1000 ah  capacity ,   the Trojan  900 ah  at C20.......  at C5 that would only be about 650 ah



Title: Re: Two battery banks
Post by: biff on February 01, 2016, 10:37:41 AM
Hello Woodi, ;D
                 How are ya doing over there.? We are having a right old breeze at the moment and it is set to get going properly around 3ish this afternoon.
   The sun is shining now. We are going to have to get out of the house and move into a tent down the garden because the water is that warm, the house is too comfortable and we want the excitement but,
  maybe we will wait until this after noon till the dance really gets going.
   Years ago, I defeated the laws of physics on this very forum, I mixed a whole clatter of different type batteries, different Ahs, different compositions and different brands, 24cells forklift cells were 850ah and 36 cells were 650ah. I stuck the lot together and hoped for the best. I got the best. Then in the name of science, i boiled them dry for good measure Twice,!!. Now I can excuse myself (no bother to me) on the grounds that I was very ill and batts and things never entered my head for over 6 months,,but,,but the system still kept running till I was able to stand and walk. So down the garden I went and gave them a big long drink of the purest bluestack rain water, which Eleanor said could be full of that Atlantic salt :'(  but,,but They are still going strong and are being pumped full of lovely lecky as i type.
 I was due to make some alterations to the AH recently by adding more to the mix but the bad weather scuppered that. I need a nice calm day and will have to wait a while longer,
 Yes,they are still performing well. These cells would have put in a hard time in their previous job, so that is my experience of mixing 60 cells..However, my voltage is 120vdc and the cells are in series. I still have to add a 48pack at the end,in parallel. wackoold, all in the name of science of course.
 Now, in fairness,, I would not recommend that you do what I have done. I am beginning to sound like my old man, who used to get quite serious when I was young. he would say, " Don,t do what I dii but dii as I tell yee"  especially after a few days consulting with Johnny Walker and Black Label. He only lived till he was 94 and would have taken another 94 if he could have gotten it but that is a totally different story and has nothing at all to do with banks and cells and batteries.
    I will make one quite serious hesitation, if you get my gist, You have some very good stuff and even I would not bring them down to the level of your "Not quite so good stuff"
 Was it Paul who said,"stick them on fleabay"  Yes!!, and use the cash to buy into a new pack like the good ones that you have already.
          Cheers,
                     Biff.


Title: Re: Two battery banks
Post by: woodi on February 01, 2016, 10:49:14 AM
Still oddly calm here. We're relatively sheltered, but average windspeed hasn't risen above 25mph this morning, and biggest gust has been 43mph. Plenty to keep the power coming though - be a good chance to equalise the batteries, and turn the dump off for an hour. By the looks of the satellite, the storm has gone south a little, so you could be in for a bumpy ride.
My turbine isn't coming down any time soon, as the winch mount broke, so I've to drill out a bit of plate to make a new one. All my previous 'incidents' with turbines have been when taking them down anyway - never had one fail in the air, its always been down to some mishap with winches and/or supports.
Good to hear about the longevity of your batteries - when I got these, it was with the intention that I wouldn't have to do it again for a long time - I try and keep them above 70% at all times, and they've never been below 50%.
Part of me can't resist the lure of more boxes to play with, so not decided what to do yet.


Title: Re: Two battery banks
Post by: Justme on February 01, 2016, 10:59:47 AM


Just for clarity I will say again that this is with the same battery type.

Mixing types would be wrong.

But the OP quite clearly says in his first post that they are different types.

No he did not.

By types it means FLA or sealed or jell or ect ect. Not if the are dif capacities or 2v cells or ready assembled 2v cells.

He only mentions that one bank is 2v cells & the other 6v batteries. They could be the same type.

Again all the talk of if one is failing & how it will affect the rest, well then you should not even be using it.

Re load sharing, if correctly set up the load will be split proportionately to the capacity.



Title: Re: Two battery banks
Post by: DaveSnafu on February 01, 2016, 11:30:11 AM
Just for clarity, 4 x 6v 225ah batteries in series to make 24v is still only 225ah, thus 2 strings would make 450ah, NOT the 900ah stated, and then as has been pointed out, at trojans rather optimistic rating @c20.