Tuesday, February 7, 2012

Unboxing the Beasts

The Winston Battery cells are expensive. This lot of 8 cost me an eye-watering €4096 which translated into £3540 including 20% VAT 2% credit card payment surcharge, 2.5% currency exchange charge (from VISA as it was in Euros to Pounds) and TNT overland shipping (quite quick at 3 days from Prague).  At least when I put the payment in it was the week when all the Euro countries got their credit ratings downgraded and the Euro slumped against Sterling.

Pretty steep, but actually a lot cheaper than good OPz solar cells.  A quick check on the Tanya battery web site shows "12 OPzV 1400 Sonnenschein A600 Solar Battery" cells of 1,400Ah (C100) would cost £822 each (inc VAT but excluding delivery). That's £9,864 for 12 cells to make an equivalent 24V sealed type of lead acid battery pack that might last 10 years and be usable indoors (not a flooded fork lift type battery).

Even the Deka Solar gel batteries were quoted to me at £250 each - £1,000 for 180Ah (C5).  And they only lasted 850 cycles or 2.5 years (although they were 2nd hand when I got them for £50 each, so I can't complain).

Then there's the problem of weight... the A600 bank of cells weigh 97kg each... 1,164kg in total. By comparison, the Winston Battery cells only weigh 14kg for a total pack weight of 112kg.  Even boxed as a whole pack it would be an easy two-man lift.

Just starting to play around with the video recording on my Samsung Galaxy SII phone. So, here's my first video blog entry for this lithium battery project... Enjoy!
Each cell has a factory date code and serial number printed on it.  All the cells I have are in serial number order from 6288-6295 and were all made in October 2011.
I ordered some cell connecting straps with the cells that come with the A2 grade stainless steel M14 2.0mm pitch thread terminal bolts.  You have to order the straps as the cells don't come with bolts.  The sets also include a stainless steel washer and a spring washer.

I only ordered 7 straps (as that's all you need to connect together 8 cells) but the kit rather unhelpfully doesn't include the two additional bolts you need to make the end plus and minus terminal connections.  So I had to source these from a fastening specialist in the UK (Westfield Fasteners).

I ordered:
2x A2_Screwbolt_HexHd_M14_20_THRfull (M14 x2.0 x 20mm fully threaded hex head set screw bolt)
2x A2_Washer_FormA_M14 (large diameter M14 washer - there are 3 kinds of washer)
2x A2_Washer_SprgSq_M14 (a square profile spring washer)

This was £8.75 delivered.

The cell straps themselves are a bit comedy.  They're made from multiple copper plates that have been stamped out and then tied together with heat shrink tube.
 The other thing I ordered was a Junsi CellLog8 cell logger.  This is a tiny device that is designed specifically for monitoring of multi-cell battery packs.  It can do lead, NiCd, NiMH, and all the various types of lithium cells.
What it does is monitor the individual Voltage of each of up to 8 cells (handy as I've got just that number of cells) and then you can set alarms for over, under, and differential Voltage limits on each cell and the pack as a whole.  It will beep on some / any of these conditions and also drive an open collector transistor output for a relay or whatever (either NO or NC mode).  This is going to be one of the key battery protection elements of my plan.

7 comments:

  1. Love the creek as you open the box :-)

    Good luck, Paul

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  2. Hahahaha... Yeah, opening the box was a bit of a Van Helsing moment and I was recording it "live" so that was fun.

    They'd nailed the lids down pretty good and even nailed down steel strapping on the corners. Were they expecting these monsters inside to try and escape???

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  3. Awesome. I'm fooling around with NiFe batteries. I could not get a comfortable feeling with the lack of decent BMS systems for large, house scale Li battery banks.
    ( website diverts to our facebook page, and photos abound there.)
    I've got hints for making your own terminal lugs and stuff. Your blog will keep me busy for a day or so, looking through it.
    Mike
    http://tinyurl.com/LMR-Solar
    http://tinyurl.com/LMR-BigLug
    http://tinyurl.com/LMR-NiFe

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  4. Thanks Mike.

    I've heard a bit about NiFe cells (seen that NiFe association page before) but I think they're main drawback is that they have relatively poor current delivery and charge acceptance and need to be vented, making lots of hydrogen.

    But on the plus side, they don't need much supervision, are very tolerant of over charging, deep discharging, don't mind being left in a flat state and are relatively safe (apart from the gassing).

    The lithium cells exhibit 95% charge efficiency (lead are about 80% and NiFe are about 65%) and can absorb power at 1C rate with no supervision (current limiting or temperature compensation, etc.). They can absorb up to 3C charge rates with temperature supervision. We just don't know yet if they'll last 30 years, like NiFe.

    I keep my batteries behind the sofa in the living room, I see you solved the problem by moving the sofa to your workshop :P

    Curious about the battery caps. They look like they have rubber ball valves. Do they remain sealed until a certain pressure and then pop open (on the hinges I could see in the photo) or do they vent all the time? Are they recombinant? You mentioned heavy gassing in absorption on Facebook.

    Errmm... Luck escape with the molten lead and mixing concentrated KOH in beach-wear :D

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  5. How did you initially go about bottom balancing them? I just purchased 16 CALB 100Ah cells from EVTV for use as a 48V 5Kwh battery bank on solar.

    :)

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    Replies
    1. By hand. Nothing clever. Just used a pack load to discharge the pack to close to the minimum Voltage (using the cell protection monitoring) and then it's just a case of discharging the cells one at a time or in small groups by hand with a multimeter (or the cell monitor) and a 60W 12V light bulb. When the cells are in balance at the chosen Voltage, you can then recharge the pack.

      The smaller the cells you use, the more closely they have to be balanced.

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  6. Just wanted to say thanks for the detailed write up. I'm equipping a small sailboat to make a trip around the "island" that makes up the eastern part of the United States. You can take a look at http://great-loop.us if it's of interest.
    I just picked up a set of 8 400ah Winston lithium cells, and was hunting for the terminal sizes on line to clarify / confirm the dimensions I'd measured. Stainless M14 - 2 x 20mm bolts aren't easy to come by here, but at least now I've got confirmation that those are what I need.
    Now I just need to get past the look on folks' faces when I start talking metric - you know, the one where they look like they just bit a lemon! ;-)
    Thanks again -
    Dennis

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