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Author Topic: New battery needed....  (Read 4355 times)
Jonah
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« on: March 15, 2016, 07:15:46 AM »

Hi all,

I've finally had enough of my old batteries as after a life of abuse I'm finally happy to admit I've ruined them and they need renewing...

The system used to run our off grid farm but now we have mains. I have 4kw of Pv, midnite solar charge controller and 2 Victron inverters and 1100ah of 48v lead acid batteries and use the system to run all the day to day stuff and the Victron use the main every time the kettle or washing machine goes on. 

Question is, lead acid or lithium ion?  I know that financially it probably doesn't make sense but I happy to play and tinker. I've been looking for a leaf battery or something but nothing has turned up and I'm a little concerned about bms.

Can anybody advise please based on experience with their systems?

Thanks

Marc
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Fionn
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« Reply #1 on: March 15, 2016, 08:14:40 AM »

I know where you can pick up a leaf battery for 2200 + delivery with low "mileage" on it.

Hard to look past lithium in my opinion, great cycle life, more compact and far easier to manage.
Just set up redundant dump loads to ensure it never goes above 4.1v/cell and a low voltage disconnect at 3.7v per cell and you're done really.
Loads of cheap BMS systems about and easy to configure it for 48V (LA equivalent) operation with 7 modules in series.

Lithium is really far easier to use than LA, the sole disadvantage is it's not tolerant of over charge or discharge, protect against both of these and it's very straightforward.
No need to worry about charging rate, discharge rate, sulfation, toppping off water, boost charging.
You can leave it indefinitely at mid capacity with no capacity loss - in fact it's ideal to keep it mid way for optimum shelf life.
Determinging state of charge is as simple as checking resting voltage per cell.
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baker
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« Reply #2 on: March 15, 2016, 08:42:05 AM »

where
and do you get the bms system and charging leads?
baker
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billi
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« Reply #3 on: March 15, 2016, 09:39:28 AM »

...My  0nce  40 kWh   Lead acid battery is now about 12 years old   ,  would  consider it again ,  but with electrolyte string idea  , a 30 kWh bank is about 2000
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Fionn
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« Reply #4 on: March 15, 2016, 09:45:10 AM »

If you look up there's a thread on here by user Offpiste IIRC that did it.
The easiest way to hook them up is to use 7 modules in series for a 14S battery which will give an operating voltage range similar to a 48V lead acid system.
You would have 6 strings in parallel if you used 42 modules or a 21kWh battery with 6 modules left over.
There are lots of BMS systems available.
Personally I'd buy 12 of these:
http://www.progressiverc.com/celllog-8m.html
They are highly accurate cell monitors.
You would have monitoring of every individual cell on all 6 strings.
The alarm outputs of the monitors can be configured to operate at precise low and high cell voltage limits.
The paralleled alarm ouputs could then drive your disconnect contactor through some fairly simple circuitry.

There may be better / cheaper off the shelf options available nowadays, it's a while since I looked at it.
For a total belt and braces solution you could put in place a secondary LV/HV disconnect monitoring system that looks at the overall pack voltage and operates slightly above / below the limits of the cell monitors.
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freddyuk
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« Reply #5 on: March 16, 2016, 03:07:37 AM »

Consider AHI Aquion. No drama they just work. If you have floor space (30 x 30cm per stack) you can fit and forget. Work well with Victron and will latch onto your existing PV installation and take any spare power for charging. If no dump load facility the Victron can throttle back power of the PV. Nothing greener out there to my knowledge. With 100% DOD potential you only need 50% of FLA capacity so numbers stack up.
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readiescards
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« Reply #6 on: March 16, 2016, 06:18:22 AM »

From my limited research the Aquion has higher internal resistance so leading to much reduced maximum output current and likewise longer charge times.  Meaning you need more than double the capacity of the lead acid to achieve the same kWp/h, along with the need to run the generator, or have the sun available, for longer.

Given they are already jolly expensive (along with I suspect zero scrap value), they need to fall in price significantly to be a true competitor to the alternatives.


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Fionn
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« Reply #7 on: March 16, 2016, 08:27:23 AM »

To be fair, the leaf cells "just work" too.
I have a 4 module pack that I've been using myself for over a year.

They're a really conveninent form factor and there are plenty of comprehensive BMS systems on the market that could be used with them.
They can be charged at about 2C and discharged at at least 4C too, so ideal for high powered inputs like wind or generators.
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MR GUS
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« Reply #8 on: March 16, 2016, 09:17:56 AM »

Fionn, any threads i've missed regards your leaf batteries, till off-piste gets back off his leaf battery assisted yacht / cruiser trip (no joke) I think you may be lead person for any battery pack high jinks!  Smiley
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Fionn
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« Reply #9 on: March 16, 2016, 09:42:32 AM »

Hi Gus,
           I only have 4 modules that I picked up from a seller in the states some time ago.
I haven't shared much on them. Ideally I would get 3 more modules and make it into a 48V system, it would be more useful for me then.

Just this morning a pack from a 2011 car was listed on eBay UK for 1500, no detail on mileage though.
More and more should become available over the coming years.
As early cars are crashed, even light damage will make repair uneconmic with the residual value of the battery packs.
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nowty
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« Reply #10 on: March 16, 2016, 09:46:38 AM »

Jonah how old are your fecked batteries ?

I am interested how long they lasted with your said abuse.
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Jonah
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« Reply #11 on: March 16, 2016, 11:15:34 AM »

Thanks all, I really want to go the leaf battery route but just a bit scared on the second hand bit although not as scared as the price of new...

I was looking at some leaf batteries in Norway which I'd be happy to drive and get although if I could get a cheap set here and they are easy enough to work with id go for that.

Fionn, where are the first batteries you mentioned?

Nowty, in all fairness I cooked my batteries, they were excellent for two years then I moved house and didn't put them on my new place for another 18 months ish and just left the battery sat full but just abandoned and when I went back to it loads of cells were empty, sg levels all over the shop etc etc but it still works excellently in the longer days when it can have the solar all day but it take a lot more in than it give out. I did try getting some acid to add back in to see if I could fix things but that's as far as it went.

Thanks all


Marc
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Fionn
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« Reply #12 on: March 16, 2016, 11:24:58 AM »

Hi Jonah,
               Sorry, I should have clarified, it's the same seller that has the 2014 pack for 2200.
He hasn't listed it directly but it's listed with the engine he has for sale item 281944970610.

I'm sure delivery on a pallet wouldn't be too expensive, I think the seller is in Latvia.
If you go that route I'd happily buy 3 modules from you (you'll have 6 left over if you go 48V).

I wouldn't be overly concerned about buying second hand so long as there is no mechanical damage to the pack.
The Nissan BMS is excellent obviously and there have only been 2 recorded Leaf battery failures in Europe to date AFAIK. Most likely even these would have been single module failures so wouldn't have a big impact on you as you could easily swap out a bad one for a spare.

Fionn.
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Jonah
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« Reply #13 on: March 16, 2016, 11:28:47 AM »

Ok thanks, I did email these guys a few months ago about a set they had and have just emailed about the 1500 ones. What is the dod on them? Would I have to treat them like LA battery? Do they give off much heat? Should they go inside building or outside?

Thanks again.

Marc
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Fionn
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« Reply #14 on: March 16, 2016, 11:37:09 AM »

Hi Marc,
            In the leaf I think the usable portion is about 21kWh so a DOD of about 87%.
In 48V configuration with 42 modules you'd be down to about 22kWh anyway.
If it's enough for your needs I would set them up for about 15kWh of usable capacity, clipping the top and bottom 15% of the charge cycle.
You can keep them where you like, I'd keep them indoors, about 15C would be a good temperature to keep them for lifetime and performance.
They will give out next no no heat at the typical charge and discharge rates of a stationary storage application.
In the car they can be charged at 22kW and discharged at 90kW, they will have a very easy life with you compared with their original use.
Fionn.
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