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Author Topic: Two battery banks  (Read 3455 times)
woodi
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« 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
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camillitech
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« Reply #1 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.
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woodi
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« Reply #2 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 Smiley
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.....
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billi
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« Reply #3 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


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biff
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« Reply #4 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, Grin
                                                                           Biff
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Justme
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« Reply #5 on: January 31, 2016, 12:39:40 PM »

Unless you need military or medical grade back up then just combine into one bank.
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woodi
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« Reply #6 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.
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« Reply #7 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  wackoteapot   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
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camillitech
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« Reply #8 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
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woodi
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« Reply #9 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?
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« Reply #10 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
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http://lifeattheendoftheroad.wordpress.com/

'Off grid' since 1985,  Proven 2.5kW, Proven 6kW direct heating, SI6.OH, 800ah Rolls, 4.75kW PV ,4xTS45, Lister HR2 12kW, , Powerspout pelton, Stream Engine turgo, 60 x Navitron toobs and a 1500lt store. Outback VFX3048 and 950ah forklifts for backup,
woodi
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« Reply #11 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.
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« Reply #12 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.

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woodi
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« Reply #13 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.
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« Reply #14 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.
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