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Author Topic: How much battery is too much?  (Read 2682 times)
fourfootfarm
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« on: March 01, 2016, 11:40:14 AM »

Recently I purchased a forklift which had 36 500ah cells. They're all in good condition and holding on to their voltage. I've not load tested them yet but will do after they've had a few days to rest. So 36kwh's in total.

Now, most battery sizing calculators work on the assumption that you're starting off with lots of electrical junk which you need to power. We are at the opposite end where in we have almost no electrical loads currently, a 12v tv/dvd, lighting, internet router and two laptops is roughly it, with the occasionally power tool recharge. But my parents have been living like that now for 6 years and would appreciate some of the decadent creature comforts like a fridge.

My main worry is not having enough incoming juice to charge the battery bank properly and end up having to fire up the generator all the time to get them topped up. Though I appreciate this is a luxurious position to be in.

Also we're stuck at 24v for the time being, and having three packs in parallel could cause balancing issues.

I am tempted make up a 12s2p pack and sell the other 12 cells to make back some of the cost of the initial purchase.

Any thoughts?
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Outback FM60. EPsolar 30a MPPT and a bunch of Tristar 45's. Hodge Podge of solar ~ 4500w. Various generators and 1000ah 24v forklift battery.

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Fionn
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« Reply #1 on: March 01, 2016, 12:19:23 PM »

What's your daily usage in kWh?
I would think that 6x that figure would be optimum for lead acid, allows you for 3 days with little renewable input to 50% discharge.
Sell the remainder as you say.
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camillitech
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« Reply #2 on: March 01, 2016, 12:32:13 PM »

My thoughts FF for what it's worth.

Seems to me, that at the moment just 12 in series would be more than ample, probably too much judging by your usage. You don't say what size your generator charger is but I'd say that there's little point having a battery bank that you cannot fully charge in six hours with it, unless of course you drastically increase the size of your PV. Personally I'd hang on to all of them but perhaps pick through the best 24, sell 12 and use the money for more PV. Many many years ago (1989 to be precise) I fecked 6 good forklift cells because my Rutland Windcharger and pathetic battery charger just couldn't keep them topped up, they just sulphated and died. They really do need a good regular EQing to keep them healthy and I think 1kW of solar and a small turnip is just not going to do it in the winter. Perhaps if you've got a whacking great 24V mains charger you could use that with the genny but that kinda defeats the purpose. Get more PV, then get more PV, then add more cells then get more PV, no point living like a hermit with all that energy in the sun  Cool

Good luck, Paul
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'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,
fourfootfarm
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« Reply #3 on: March 01, 2016, 01:04:36 PM »

Hi Camilitech and Fionn,

Daily use in kwh I honestly have no idea as its not metered (I should really get on that). When there is less electricity we just use less power! In the region of 1kwh in all likelihood.

I'd like to expand our current usage though to provide some of lifes little luxuries like running a normal washing machine instead of a camping twin tub and the like.

As for chargers we have a 30amp clarke booster charger and the invertercharger is supposedly capable of 80amps charging but I will believe that when I see it as its a china special.

I'm going to try and swap the 72v charger that came with the forklift for a 24v one. I'm on the look out for a 24v alternator or generator to hook up to an old genny who's 230v side is broken. Using dinojuice does seem to defeat the object but if its necessary to keep the batteries happy then its necessary...

Basically I've been bumbling along for the last 5-6 years messing around and learning. But I think now is the time to stop mucking around and build a decent system that I can leave with minimal supervision.

The limiting factor till now was our battery bank, it was charged by about 11am most days so getting more solar was pointless. But now is the time to start filling up that barn roof!
« Last Edit: March 01, 2016, 01:13:53 PM by fourfootfarm » Logged

Outback FM60. EPsolar 30a MPPT and a bunch of Tristar 45's. Hodge Podge of solar ~ 4500w. Various generators and 1000ah 24v forklift battery.

Turkish Turnip
billi
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« Reply #4 on: March 01, 2016, 10:32:49 PM »

Hi , that sounds about the size  of a bank we have , now in total about 13 years old

i split the 48 v  750 AH  bank (bought on ebay  5 years old)  into 2 x 24 volt in parallel  8 years back ,  ok i ave not recently  checked the acid level , but   the parallel  config seem to work ok ...

But we have 4000 watt PV , and   rarely need a generator  to fully charge  / or charge to 80% in winter with genny  and let the sun do the rest


 all  depending on your el. and heating consumption  , but i guess i would keep the 3x 24 V  banks   and increase PV
, if you can sell one ,  ... would that make much money ?




Billi

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1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
knighty
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« Reply #5 on: March 01, 2016, 10:54:12 PM »

they still need a decent EQ charge now and again

but big advantage of lots extra capacity is you'll hardly use any of that capacity... you don't need to EQ charge them nearly as much if you're only using 20% of the capacity

plus, fridge and washing machine later on will be nice to put some load on them now and again



also means if some are a bit duff, or you do lose some capacity... it doesn't really matter because you've got so much more than you need anyway
(you lose capacity not efficiency so it's no big deal for you)
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MR GUS
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« Reply #6 on: March 16, 2016, 03:25:20 PM »

Billi, question for you! (no catch) ...IF you were replacing "IF" theoretically, how would your set up differ in all aspects if it were Lithium ion batt pack based like the leaf, i'm curious, based on how you as an existing off gridder would deal with sizing based on useage & lifestyle & what headroom you'd opt for based on all your other kit, the solar, hydro etc ??

not to poke fun of course just to compare selection process etc, all input is good for an impending tech becoming more the norm.
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fourfootfarm
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« Reply #7 on: March 18, 2016, 02:34:34 PM »

Update: Ended up selling the 3rd string of batteries for about as much as I paid for the lot in the first place. People will pay a premium for easy it seems.

They've been gently floating for a while now and not used for very much yet, and won't be until my new fuses arrive. On the scout for a good strong charger so I don't run into sulphation issues. Got some bits of copper to make bus bars.

Generators we have several. A Petter one of unknown power, but I will guess about 3kva a chinese yellow box job which is nominally 5kva but less than that in reality and a 25kva one the size of a large car. Very seldom used but as its three phase very useful for the feed mill and other seldom used bits of agricultural kit.

The yellow box gets used the most as it has an okay silencer and electric start. Usually to run the washing machine.

Any advice on fuse sizing? Inverter is supposedly 5kw. But thats doubtful in reality. 3500/24=145amps I've played it safe and got a couple of 100a and 150a ones.

edit: I dont unit good
« Last Edit: March 19, 2016, 05:54:46 PM by fourfootfarm » Logged

Outback FM60. EPsolar 30a MPPT and a bunch of Tristar 45's. Hodge Podge of solar ~ 4500w. Various generators and 1000ah 24v forklift battery.

Turkish Turnip
johnrae
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« Reply #8 on: March 18, 2016, 09:37:40 PM »

Have you considered trying to find an electrically heated Electrolux gas absorption fridge.  Normally these work from the heat of a small gas flame but many years ago we had quite a large one "salvaged" from a warship (ex RN) that worked with an electric heating element.  Since there is no compressor motor to drive, they may be somewhat less greedy on wattage.
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biff
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« Reply #9 on: March 19, 2016, 09:27:05 AM »

Hi Johnrae,
            If my own experiences with a small 65ltr electrolux fridge are anything to go with, I would give the dc element a miss,
   Mine ate the juice in the 12volt dc side of the 3way supply,,gas,mains and 12dc.
  I found that running the fridge through the12v inverter was a lot more economic on the juice.
 Of course if it were to be used as a dump load,that would not matter and would be of benefit.
                                                           Biff
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An unpaid Navitron volunteer,who has been living off-grid,powered by wind and solar,each year better than the last one.
Justme
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« Reply #10 on: March 19, 2016, 09:27:59 AM »

Have you considered trying to find an electrically heated Electrolux gas absorption fridge.  Normally these work from the heat of a small gas flame but many years ago we had quite a large one "salvaged" from a warship (ex RN) that worked with an electric heating element.  Since there is no compressor motor to drive, they may be somewhat less greedy on wattage.

These use MORE energy than pumped ones.
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fourfootfarm
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« Reply #11 on: March 19, 2016, 10:09:34 AM »

Fancy low voltage fridges are available but they are rather dear.

I've got a three way fridge in my camper van and they are very hungry on power. On 12v they can't draw enough power to actual refrigerate stuff, just maintain existing temp. (My experience anyway) we've got a few more floating around too I think from various caravans that have been salvaged for their goodies. (The farm feels a bit like a wannabe scrapyard at times)

I've got a thermostat wired up and ready to go for a chest freezer as fridge set up. Just need to finish wiring everything together and get a chest freezer.
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Outback FM60. EPsolar 30a MPPT and a bunch of Tristar 45's. Hodge Podge of solar ~ 4500w. Various generators and 1000ah 24v forklift battery.

Turkish Turnip
camillitech
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« Reply #12 on: March 19, 2016, 10:55:02 AM »

Aye, FF, steer well clear of gas fridges and freezers for sure. We had a lovely Swiss upright fridge freezer in the early 'off grid' days. It was a life saver and did us proud for some 16 years. It wasn't until I got an electric one to replace it that I realized how thirsty it was. We went from one 47kg propane cylinder every three months to less than three 19kg cylinders a year!!!!! I now use it as a cupboard in my shed  Grin
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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,
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« Reply #13 on: March 19, 2016, 12:06:46 PM »

You have a 5MW inverter?!  Shocked
Impressive  Grin
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