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LTO for SailBoat
#21
So despite balancing all the the cells in parallel to start.. I found that same strange behaviour that occurred with the 5cell test pack.

As end of charge neared.. and the cells were all about 2.6V, the cell forming the +ve terminal suddenly spiked to 2.75. The charger promptly stopped putting in any current and it flipped from absorption to float. The lowest voltage was now on the cells forming the -ve terminal.

Put the QNBBM's on and despite the relative size of the battery they soon balanced this out.. I discharged the battery partially then recharged.. once again , right at the end this unbalance appeared and the QBNNMs kicked in.

What's the impact? Probably not much. Instead of setting the total full charge voltage at 15.6 V , setting it at 15.2 seems to address it (without the QNBBMs). Though one un-answered question is does this unbalance at the end of charge continue to creep up with each successive charge...

For these packs the QNBBMs will stay on. They work.

As for a discharge test .. I found a large clothes iron.. 2.1 kW.. and connected that to the inverter. Thats pretty much at its full capacity (3kVA/2.4 kW). Wow. Next thing you know 200+ DC A are flowing! But never missed a beat. The battery voltage dropped to 11.8V under this load but no issue. None of the bus bars got hot. (The jumper cables I'm using to temporarily connect did get a little warm). The best I'm currently able to draw out of my current boat setup is 50-60A , so this single LTO is way better than the 3 lead acids ..
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#22
This is normal behaviour for any battery pack in series, this is why balancers, at least top balancers, are important. The power is pumped in from the +ive end first, hence the first pack charges first.

This is also the reasoning behind Jim Jr's directions regarding resistance and AH testing and pack assembly, to best arrange the packs so that the first pack takes slightly longer to charge so that they all arrive at full around the same time.

I'm intrigued that your cells stabilise nicely around 2.5x volts, I have found the OSN cells sit more in the range of 2.18-2.28 although out of 215 I have about a dozen that will self drain down to 0v over an extended time period. These will be assigned to high abuse purposes, start batteries, camping power packs, etc
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#23
(12-22-2018, 02:26 AM)BaronVonChickenPants Wrote: This is normal behaviour for any battery pack in series, this is why balancers, at least top balancers, are important. The power is pumped in from the +ive end first, hence the first pack charges first.

This is also the reasoning behind Jim Jr's directions regarding resistance and AH testing and pack assembly, to best arrange the packs so that the first pack takes slightly longer to charge so that they all arrive at full around the same time.

I'm intrigued that your cells stabilise nicely around 2.5x volts, I have found the OSN cells sit more in the range of 2.18-2.28 although out of 215 I have about a dozen that will self drain down to 0v over an extended time period. These will be assigned to high abuse purposes, start batteries, camping power packs, etc

BVCP.. my miscommunication...   The 2.5V (or actually 2.57V) seems to be what I can target as the final charge voltage and not worry about balancing.   If the cells are balanced at the start of charge and I start charging , without balancers, then if I charge to that amount , 2.57 or 15.4V total then that serial pack phenomenon (ie the positive cell spikes) does not occur and the cells stay in balance.

So there is not a lot of value in my statement other than as an observation.  I can charge to that voltage and probably dont need balancers.  This probably means some capacity is not used, but it doesn't appear to be a lot of amps.

As I've bought balancers I will likely install them anyway and then decide if I tweak the final charge voltage up to 15.6 or so from 15.4V.

Still too early for me to confirm the parasitic quality.. the first 5 (Kylin) I noted earlier and were good.   You mentioned 10/215 (5%)  of yours are not so good. I have 60 in this batch (Kylin not OSN)  so will be looking for 2-3 I guess to not end up so good.

I did not measure capacities or IR for these cells.  I think elsewhere in Jims notes he mentions that simply by having multiple individual  cells forming  one parallel set mixes / averages the capacities : meaning each final cell should have similar capacity.  I did figure out a simple way to measure the IR of the cells, but not the capacities yet.  Any recommendations?  At the moment my approach will be to get them installed in the boat and fully load and drain them and see if there is any unusual cut-off (ie one cell with less cap)  toward the end of discharge.  A pretty crude approach.

Today I got my second set together.. after sorting out the frozen nuts. Also seems to be ok though looks like 1 of the balancers is faulty (1 of 12).  Supplier already offered to issue replacement so cant fault them.  Have ordered a cheapo 12mm tap and die set as that seems mandatory to work with this aluminium.

So my guess is that this project is 65% done.  I need to go back and re-read all the input (especially that capacity / IR items) but as of now I feel confident enough to declare  that this will all work and not be a waste of money.  The significance of this is that I will now do 2nd project which is 20kWh on a farm in Australia starting April next years.

My thanks for all the support.
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#24
I have just tested my 0v cells after a month since they have been charged to 2.80.

I was surprised, most are between 2.3-2.4v, 1 is 2.10, 1 is 2.47.

A lot better than I expected.
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#25
I'd cycle them a few times then run that self discharge test again. I have had li-lion cells that were just left too low a bit too long come back and be good performers.
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#26
The aluminum used for the terminals is " Dead soft" , you need a good electrical grease to lube them ,also coat the connection
 between the buss bar and the battery. This will prevent oxidation of the aliminummm (Hillbilly spelling ) , it will keep out the
 salt air also.  Oxidation of the connection can escalate to arcing quickly .
 The lube will also prevent galling of the aluminum .
Aluminum starts oxidizing as soon as it is made , unless it is coated with something to prevent it , I have been exposed to the
  extrusion industry , ever since I was able to sit in a high chair with my dad ,for @ 55 years

The new test setup I have for single cells is 100 amp meter with a external power supply and several 1 ohm 50 watt resistors .
  The resistors pull @ 5 amp at 2.4 volts , just connect a couple together , in parallel ,to get the load you want . Just watch out
  they get toasty .

I appreciate the references but Grasshoppers , You have learned enough to fly out on your own. But you still need to pick
  up that red hot cast iron bowl with your forearms  Big Grin Kung Fu (TV series)
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#27
Cost.. Something is happening with the cost of these.. when I started in October 2018 .. the 40AH were USD17 / pc.. By December they had jumped to USD30.. and if I'm reading things correctly this evening (Jan 20, 2019) they just popped to 50+. Looks like no more projects
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#28
Ouch, that sucks Sad
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#29
Got some more feedback this morning .. from Kylin.. they indicated that Yinlong had been releasing unused cells (I assume Grade B per Jim Jr ) for some time for cash flow.. however that need was now gone .. so the cells on offer now from Kylin (and presumably OSN and a few others) are now new Grade A.. wiht no further large price rises expected..That said, they are now a fairly pricey cell so any project will have to be well funded and really need cells with this kind of lifespan. Outside of ESS I cant think of many and even then you'd have to wonder.. so instead use lifepo4 and assume those prices will come down in 10 years or there will be a cheaper alternative.
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#30
My understanding is that Yinlong do not and have never sold new cells externally to the BYD group (Tesla style) as they do not have enough new cells for their existing group products so any and all cells on the "market" are recycled/recoverd. Just like trying to get new cells from Tesla...

What I have come across is resellers saying the cells are "new" because they think the cells are still in a "new" state because the internal calacity (Wh) is very close to spec when the internal resistance is way way way above spec at over 1mOhm..
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