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Author Topic: New off grid install battery questions  (Read 2784 times)
Stevie D
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« on: August 04, 2009, 04:04:43 PM »

Hi folks - just found this site - love the cross - over experience from different technologies all in one place.

I'm part way through my off grid install here in the Irish Midlands. Currently an occasional / weekend home but that is soon to change in the next year or so - It's a base to refurbish our old 1800's schoolhouse from. It's got a mixed 30 acres of land from good agr / forest / bog

I have a Log Cabin built already with modest electrical needs,24v system and components, 24v cfl lighting installed @ 21watts, small portable tv, sat disch, radio - about 130watts, with the occasional 'big' load powered by eiter wee 2.5kwatt 4 stroke genny or the same sized quasi sine wave invertor / charger(unfrtunatley this doesn't like to poor wave form from the small genset and won't cahreg correctly - but does work well as ups switch). 

Heating & cooking is from an ebay bargain rayburn stove.

I have an absorbtion fridge as well but tent to leav that running on butane rather than th continus 30 ish watt load on 12v purely beacuse of how may battery strings are currently configured.

I have a small 600w pure sine wave invertor that's on line most of the day / evening for the laights etc and power for the solar thermal pumpstation & controller. Low residual current draw.

I'm totally off grid bar the water pipe, so have no means to charge batteries other than generator.  Fell accross acidentally a pair of 24-30v ex mod gensets recently for 150 so now use these to charge the battery bank.  Theyre rated at 1500w each.  Both self contained and sound proffed etc.  Unfortunatley petrol rather than deisel but have my etye on a deisel unit from the same source.

Both gensets are fully control enabled for bulk / float etc albeit mannually, with dial in volatge and or current.

My queston relates to the battery strings.

I've just aquired 16  sonnscien (sp)12v 80 amp hr vrla / gel batts from a ups station refurb - was rude to say no really, was just about to purchase a flt battery when these came up. I know they aren't an ideal battery but funds are tight

I've already got them all stringed together about to connect to busbars with all same lengths of cables.

I think I'll probably struggle to maintain the battery strings on float with my current setup.

RE currently consist of a 1kw wind turbine feeding battery bank via a morningstar tristar 60ish amp controller to  a yet to be aquired load dump, and I'm waiting delivery of 2 sharp 135w solar pv panels going through a similar trisatr 40 amp controller.

Should i configure all the batterys into one common bank or split them into 2 larger banks. Logic may be to keep one on solar the other on the mill and swap over now and again, or have both sources feeding 1 large bank. Is there any advantages??
I only ever intend to discharge to max -20% of capacity - hell 2 110 batterys will keep the place going nearly all weekend at present, but using nearly all the battery capacity.

I have copper bus bar and lots of real heavy cable and managed to aquire a large crimping tool but really need a help in making up my mind before starting to cut up cables and cooper bar.  Only want to do it once this year anyways.

Thanks, Steve
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Off grid 400ft2 log cabin
640ah 24v VRLA battery pack - it was Free :-)
700watt (1000 watt peak) windturbine
60amp Dump load controller
Chinese thermal solar tubes
Resol Solar pump station
50amp ex military dc genset - now coupled to  Lister cs 6
3kw Sterling Invertor
Justme
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« Reply #1 on: August 04, 2009, 04:31:43 PM »

One large bank has a larger capacity than two smaller ones added together. I know it sounds odd but it is true.

Its all down to the size of the load compared to the size of the bank. The small the load is compared to the bank the longer it can last. So say 2 x 100ah bats wired sepperatlly will give a capacity of 200ah but 2 x 100ah bats wired in one bank will give about (dep on load) 230ah.

For the full details look up Puekets  HERE

While you are at it also look up wiring battery strings on the same site HERE as the most common way is not the best way.


Justme

 
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Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
2 x Victron Multiplus II 48/5000/70
Cerbo GX & GX 50 touch
BMV 700
6kva genny
48v 1000ah
Grid Possibly coming soon
peter999
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« Reply #2 on: August 04, 2009, 04:47:31 PM »


 Steve if the attery bank is too big you will never be able to get upto the absorbtion stage of charge let alone through to float, but if the bank is too small you will constantly be either over discharging it or dumping excess charge from turbine /pv which is very wasteful,

i fear its going to be trial and error 16 bats at 80a/h = 1280a/h at 12v =15360kw max discharge say 40 (gell cells) =6.1kw allow for losses approx 5.2ish usable power.

But if you take 5kw out of the you need to put it back 1kw turbine and 270w of pv  flat out 105 amps 1280a/h battery bank charge at c/20 (gell cells) 64 amps MAX, charge time approx 20hrs

all theory trial and error one large bank all batts in parrell full charge up use and see what happens monitor batts daily  see what results you get

best of luck  Peter
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Stevie D
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« Reply #3 on: August 04, 2009, 07:45:52 PM »

Cheers for the response gents.

Already have the batteries configured for the method 3 in the site refered to Justme - cheers. I guess its going to be one big bank then.

I went to see the other genset I've had my eye on this evening to get specs off that - It's got a max 225amp output at 28 volt, massive improvement on my current setup, but perhaps too much for the gel batts - not sure how configurable it is, need to do so research into it - but it is diesel so should be more economical in the long term - red / marked being about 1/2 of a gallon of petrol.

What would be the max charge rate be for these assuming I run them down to 40% - I was assuming the 10% of overall capacity rule of thumb as per normal lead acid.

Quote
i fear its going to be trial and error 16 bats at 80a/h = 1280a/h at 12v =15360kw max discharge say 40 (gell cells) =6.1kw allow for losses approx 5.2ish usable power.

The capacity should be the same for 24v yes?

Maybe I should just go buy a flt battery and be done with it?

Steve
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Off grid 400ft2 log cabin
640ah 24v VRLA battery pack - it was Free :-)
700watt (1000 watt peak) windturbine
60amp Dump load controller
Chinese thermal solar tubes
Resol Solar pump station
50amp ex military dc genset - now coupled to  Lister cs 6
3kw Sterling Invertor
Justme
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« Reply #4 on: August 04, 2009, 07:56:41 PM »

As you have these already you have nothing to loose.

One thing to remember is that as you cant top them up you MUST NEVER over charge them. Find the makers specs & stick to it if poss.

Personally I prefer to be able to top up so use flooded lead acid type (FLT 2v cells) but you have nothing to loose as you got them FOC.
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Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
2 x Victron Multiplus II 48/5000/70
Cerbo GX & GX 50 touch
BMV 700
6kva genny
48v 1000ah
Grid Possibly coming soon
billi
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« Reply #5 on: August 04, 2009, 08:03:32 PM »

Quote
It's got a max 225amp output at 28 volt
 so its a DC Generator   Grin  and can it be regulated  to lower Amp ?  And adjust volt ?

My conclusion is that Dc generators perform smoother in an off grid idea  ( but sure  if something goes wrong  you wouldnot have any AC generator to supply the house )  

But sure gel batteries are more reliant on the correct charge

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
Stevie D
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« Reply #6 on: August 04, 2009, 10:22:15 PM »

Yes Billi the one i'm considering is a dc genset, I already have 2 small dc petrol ones (1500watt) - I'll probably keep one as a backup and sell the other. 

I need to do a bit of research into the bigger one before parting with money to ensure it has a similar control circuit as the others.

I have the option of a flt battery as well- it's 48 v so I'd have a bit of work to do to it to reconfigure, but at least then i could check sg and top up etc.

Steve
Logged

Off grid 400ft2 log cabin
640ah 24v VRLA battery pack - it was Free :-)
700watt (1000 watt peak) windturbine
60amp Dump load controller
Chinese thermal solar tubes
Resol Solar pump station
50amp ex military dc genset - now coupled to  Lister cs 6
3kw Sterling Invertor
billi
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« Reply #7 on: August 04, 2009, 10:26:21 PM »

steve  respect  Grin  you must have a good source / supplier here in Ireland


I sometimes search years for the right gear ......

Have fun

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
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