LiFePO4 - The future for off-grid battery banks?

[karrak]

In doing so, I did notice the warm feeling in the saddlebags where the batteries were. To try and get more data as a baseline, I used an infrared heat gun at the terminal posts, the temperature on all 16 cells in the 48 volt series pack would climb from about 75 degrees starting temp - to 96 or so at the end of the complete charge cycle. NOTE: This would be after using the trike with the pack voltage depleted and then resting at 48-48.5 volts (roughly 3 volts per cell). The recharge time would take a few hours with the supplied 6 amp output charger - significantly less time (about 1 hour and 15 mins using 600 watts of solar - more on that in a bit..)

Thanks Jerry for all the information, there is allot to digest. All very interesting and informative.

I might have missed some information and am unclear about some details of your charging procedure and temperature measurements. I have a few questions.

Did you charge the whole 48 volts battery or split it up into its twelve volt battery modules and charge each one individually?

Were your temperature measurements done using your solar charger or the 6 amp 110volt charger?

Would I be right in calculating the charge current from the solar charger to be around 11 amps(0.6C)

Thanks
Simon

[PNjunction]

Jerry - sounds like you are on the ball, although I read your posts with some trepidation when I saw the E-bike application. Many of those cells in that arena are used, abused, and murdered before their time.

Now that you are running with conservative values, you may want to do as I do when planning your next setup - purposely de-rate the ah specification by 20%. That is, my 20ah battery is really only 18ah, and the 40ah batt only 32ah.

When running conservatively, such as only reaching 3.5v at the high end, and just dipping under 3.2, say 3.19v at the low, this seems to dovetail nicely into what I plan for when doing my power budget based on the 20% nameplate de-rating.

Like you, since I'm running in the so-called "sub-c" environment, there is plenty of time to manually check cells when dropping just below 3.2v for any rogue cells out there - but I certainly wouldn't want to run with as many cells as you are, but understand the repurposing of your original e-bike setup cells. And of course hoping that you have an LVD in use just in case.

If you do go with new cells of larger capacity, but still need to parallel some, remember that with LFP, you build up your capacity first with parallel sets, and then series connect these "sets" or groups of paralleled cells to obtain your target voltage last.

So that's three of us now running GBS - you, me, and Sunking. I only picked GBS for the safety reasons of having the individual cell-terminal covers come with them, as opposed to making your own top-covers with say Winston or CALB.

[CrazyJerry]

GBS 20ah Lithium batteries: Part 3

GBS 20ah Lithium batteries: Part 3.

9 Main started out with 2000 watts of solar – those panels are batch dated 1999. They still perform excellently. During the last 13 years my electrical demand continues to drop due to habits and better appliances – but the solar panel count continues to rise. This is due to the aging Surrette 1700ah lead acid bank. I have generators but really don’t wish to run them – so I’ve added panels. The tally is now 2750 watts.

To replace the Surrettes today would be roughly over $5,000 and they are good batteries – but since 2011, so are these small GBS cells.

The winter months here presented a new challenge for the small batteries with no lawn to mow and a velomobile that was ill equipped to handle snow covered roads.

I thought it would be a novel idea to separate the DC circuit that runs DC appliances in the house off the Surrettes, to a separate battery bank – enter the GBS 20ah cells. These are pretty easy to work with – so one can wire them for nearly any application. I decided to use all 32 cells to make a 160ah 12volt pack. This would easily run the refrigerator, ceiling fans, radio, led lighting, computer, cell phone charge ports, etc..

Taking the individual cells out of their plastic containers required a little fiddling around. The first step was removing all 32 balance boards and the little busbars. Once that was done, careful use of two flat-tip screwdrivers and with equal pressure to each side of an individual 3.2 volt cell to walk it up out of the case. Once one cell is out the rest are easily pulled out by hand. Every other cell was twirled around 180 degrees so that all of the positive terminals are inline as well as all the negatives. (As 12 volt batteries, GBS supplies them 4 cells in series and the terminals alternate + - + - ).

Once that was completed, all individual cell voltages were checked to make sure they were very close in voltage – a mismatch might mean problems if a higher voltage cell was to dump its voltage into a lower voltage cell when wiring them up. I’m getting to old for fireworks in the house. Once checked and given the thumbs-up, braided strap was used to make all the connections and then the beloved balance boards were all reinstalled. But who knew paralleling four cells at a pop was a pretty good way stabilizing cell voltage drift!

Anyway, using 600 watts of solar through the same MX60 controller only needed a couple of programming changes to make it work with the combined 12 volt pack. Back then, Bulk was set to 14.2volts, Absorb to 0 hour, Float to 13.4 and end amp setting to 0amps. With these settings, sun shines on panels, 600 watts enters charge controller and brings up pack voltage to 14.2 volts (3.55 volts per cell). Absorb timer is disabled at 0 hours, and with 0 end amps, as soon as the pack reached the 14.2 volts setting charging was over and controller goes to float.

Initially I liked the idea of solar carrying day loads if it was available so hence the float setting. I used the infrared temperature gun on these cells during float at 13.4 volt and didn’t see any notable heat difference than if the charge was just plain terminated so I figured the cells should be ok .

Every week I would check the paralleled cells for cell voltage drift and there isn’t any. This revelation is what made me question the use of ALL the balance boards (remember - half of them are of a differing value) so they were all removed. I check the cells about once a month and they’re fine with no adjustments needed. Typical values fall in the range 3.41 – 3.44. Under a heavy blast of solar the numbers spread s bit more like 3.41 – 3.46, but after the burst they settle right down. An hour or so after charging they are nearly spot-on 3.410 – 3.425 – same for discharging which is seldom more than 20 amps max.

This is the scenario of where these cells are housed today. They’ve been in a trike, a mower, and now powering the DC side of the house. None of the cells have failed in 4.5 years. The capacity has dropped. In April of 2014 they capacity tested at 90%. To be fair, the capacity test was per each 12 volt pack and not each cell individually.

There are 32 cells if one wanted to test them all individually, and I’m not quite that ambitious anymore. I hesitate to make a prediction with these cells regarding capacity because unlike the velomobile and mower where the depth of discharge was repeatedly to the 3 volts per cell mark, as an off-grid house pack they aren’t stressed at all. Depth of discharge is at most 12.8 volts per pack (3.2 volts per cell). The DC stuff is all doing fine with the flat power curve of these cells.

On a side note (and as previous eluded to in another post), I’m already testing some new cells here as the Surrettes are just too hungry for my tastes. It was taking about 200 amp hours of solar daily just to maintain a decent specific gravity in them. This is significant since there is minimal (like almost no) usage at night.

Also, there are references on this forum that a very conservative charging approach may provide long-term benefits. I am taking those suggestions seriously and applying them to both the old GBS 20ah cells and the newly acquired “Lithium-Based” cells. I say “Lithium Based” to avoid possible retaliation for not listing the exact proprietary chemistry within the cells… Lol!

Once I get a bit more data and experience with the new cells I’ll post it.
In the meantime - the countdown is on to September 29th, 2016 - the 2000 day and 2000 cycle milestone!!!

~CrazyJerry

[CrazyJerry]

Dax - what's up with all the ra-ra about Australia vs yanks? I don't get it. I will tip my hat however to Professor John Lions formerly at the NSW dept of computer science!

/* You are not expected to understand this */

Seems like lifepo4 is following in the *nix tradition.

Actually jerry's right, although I did see an edit changing the values. But thanks for bringing that up. Here's the lowdown for the lurkers:

A lifepo4 cell is known as a "nominal" 3.2v cell. The top end of voltage charge specs is commonly 3.7v, although you don't *have* to go there.

ANY OTHER lithium chemistry cell is a "nominal" 3.7v cell. It has a typical top-end charge spec of 4.2v.

*** LFP EXCEPTION *** : IF you are charging at .05C current or less, then you STOP at 3.45v max. Why? Because for the lack of a better term, you are "end-current absorbing" yourself to a full charge when you reach 3.45v. Strange way to say it I know - .05C is the typical absorb end-current from most manufacturers, and if you start out that way, you should stop sooner than what they indicate as the max voltage. If you measure your capacity with this test, you'll see. I recommend .05C as the base minimum charge - and that worries me from a sudden weak-solar standpoint and non-intelligent charge controllers that don't take this into account.

"LIPO" is a misnomer. It is a container material, and can hold any chemistry, although it is most commonly associated with non-LFP batteries, although there are exceptions. In other words, know what you are getting.

Jerry - the 20ah GBS cells are not the best of breed. Their single cell terminal screws indicate the older "GEN 1" versions. Formulations have improved since then in the Gen2 and Gen3 models, along with the connectors (4-screw nickel plates vs single screw) with the 40ah and higher models.

In addition, if you are playing with the older style 20ah models, check your internal resistance as they may not be as tight as the newer models. For instance, even after cleaning the terminal links and terminals themselves, the internal resistance values on my GBS 4S set was 1/2/1/3 mohm each. This lead to some interesting variances while trying to top balance manually. In other words, my spread is not perfectly even at the top, and trying to make them so is a fool's errand with widely varying IR. Each cell was pretty close in capacity however. an iCharger 306B is what I use as a non-lab instrument for measuring and base-lining stuff like this, although I normally run with a Samlex charger set to 14v for my 4S batts. And um, NO balancers after an initial sanity check, but that's me.

My 40ah GBS battery cells have much tighter tolerances, and the measured IR values was 1/1/1/1 mohm. Manual balance on these after single-cell charging consisted of tiny manual 30 second discharges on the cells once or twice trying to go higher than 3.6v. AND normally I run at 3.5v anyway, but the balance (also a misnomer, but for our purposes we'll stop here) was done very high in the charge slope initially.

In other words, for the 20ah GBS cells, I would treat them with conservatism, and run no more than 0.5C to maybe 0.75C. Thing is, now that you've hammered them with an E-Bike application, they may not be suitable test subjects for a house-bank. If you are going to do that, I recommend getting the 40ah versions or higher and starting over, as these are Gen2/3 models. Or choose another manufacturer perhaps.

Note that the most common housing for the small 20ah cells is seen as a "drop in replacement" for the usual UPS-style agm batteries which is just a plastic surround. The 40ah and higher models are strapped and banded like they would be for a real house-bank setup.

Those that do make a major investment should know that upon special request, you may be able to get a documented printout of each cell's capacity and internal resistance upon purchase. I did not make that request.

PNjunction,
Thanks for your very informative reply. Like you, I do try and get baseline measurements as they are useful especially as our gadgetry ages. The 2011 20ah GBS cells have been used in the house for sometime now and only up until recently (like two months ago) have I adopted the even more conservative charging profile as you and others have suggested. It was over a few forums (including this one) that were validating things I had experienced over time with these cells. One thing I did notice upon delivery in 2011 with these cells was the terminal contact area and before incorporating the "balance boards" I cleaned them all.

In spite of the use/abuse to these cells they are still doing a great job and I am cautiously optimistic they will make it to the proverbial 2000 charge cycles (and days) milestone. Assembled a 180ah group, they are discharged nightly only 10-15% so this is like summer camp for them compared to the days of the trike, and they are staying in balance exceptionally well without all the Christmas lights attached.

The voltage edit you mentioned was the reference to the 3.625 volts per cell. I originally had it at 3.265 volts per cell which was incorrect for the total output of the 29volt pack charger.. One thing I find useful even for my own notes is to include volts per cell along with overall voltage so I try to include them.

I kinda laughed when you recommended he newer Gen2 or Gen3 as a starting over point. Not because there's anything wrong with that, but because you're getting ahead of my posts. (Spoiler alert - already there and in service - Surrette replacements). One more post of the 20ah history and then the story of the bigger versions will be compiled.

Have a great day!
~CrazyJerry

[PNjunction]

Here's another reason why no one here seems to have a clue about lifepo4 technology and where's it's at, what you have posted has no relevance to lifepo4 cell packs, you're talking about another lithium technology and this is a lifepo4 thread, not li-poly,li-ion. Anyone using the voltage parameters you're quoting will destroy their lifepo4 cells quickly and is incredibly misleading.

Dax - what's up with all the ra-ra about Australia vs yanks? I don't get it. I will tip my hat however to Professor John Lions formerly at the NSW dept of computer science!

/* You are not expected to understand this */

Seems like lifepo4 is following in the *nix tradition.

Actually jerry's right, although I did see an edit changing the values. But thanks for bringing that up. Here's the lowdown for the lurkers:

A lifepo4 cell is known as a "nominal" 3.2v cell. The top end of voltage charge specs is commonly 3.7v, although you don't *have* to go there.

ANY OTHER lithium chemistry cell is a "nominal" 3.7v cell. It has a typical top-end charge spec of 4.2v.

*** LFP EXCEPTION *** : IF you are charging at .05C current or less, then you STOP at 3.45v max. Why? Because for the lack of a better term, you are "end-current absorbing" yourself to a full charge when you reach 3.45v. Strange way to say it I know - .05C is the typical absorb end-current from most manufacturers, and if you start out that way, you should stop sooner than what they indicate as the max voltage. If you measure your capacity with this test, you'll see. I recommend .05C as the base minimum charge - and that worries me from a sudden weak-solar standpoint and non-intelligent charge controllers that don't take this into account.

"LIPO" is a misnomer. It is a container material, and can hold any chemistry, although it is most commonly associated with non-LFP batteries, although there are exceptions. In other words, know what you are getting.

Jerry - the 20ah GBS cells are not the best of breed. Their single cell terminal screws indicate the older "GEN 1" versions. Formulations have improved since then in the Gen2 and Gen3 models, along with the connectors (4-screw nickel plates vs single screw) with the 40ah and higher models.

In addition, if you are playing with the older style 20ah models, check your internal resistance as they may not be as tight as the newer models. For instance, even after cleaning the terminal links and terminals themselves, the internal resistance values on my GBS 4S set was 1/2/1/3 mohm each. This lead to some interesting variances while trying to top balance manually. In other words, my spread is not perfectly even at the top, and trying to make them so is a fool's errand with widely varying IR. Each cell was pretty close in capacity however. an iCharger 306B is what I use as a non-lab instrument for measuring and base-lining stuff like this, although I normally run with a Samlex charger set to 14v for my 4S batts. And um, NO balancers after an initial sanity check, but that's me.

My 40ah GBS battery cells have much tighter tolerances, and the measured IR values was 1/1/1/1 mohm. Manual balance on these after single-cell charging consisted of tiny manual 30 second discharges on the cells once or twice trying to go higher than 3.6v. AND normally I run at 3.5v anyway, but the balance (also a misnomer, but for our purposes we'll stop here) was done very high in the charge slope initially.

In other words, for the 20ah GBS cells, I would treat them with conservatism, and run no more than 0.5C to maybe 0.75C. Thing is, now that you've hammered them with an E-Bike application, they may not be suitable test subjects for a house-bank. If you are going to do that, I recommend getting the 40ah versions or higher and starting over, as these are Gen2/3 models. Or choose another manufacturer perhaps.

Note that the most common housing for the small 20ah cells is seen as a "drop in replacement" for the usual UPS-style agm batteries which is just a plastic surround. The 40ah and higher models are strapped and banded like they would be for a real house-bank setup.

Those that do make a major investment should know that upon special request, you may be able to get a documented printout of each cell's capacity and internal resistance upon purchase. I did not make that request.

[karrak]

It took an additional month before it really hit me about the difference in the balance boards. On a hunch, I manually balanced the cells and then started charging that pack at the lower value of 3.55 volts per cell and for the most part – every cell in the problem pack was now steady and not voltage drifting apart…. One month later the cells were all very close in their voltages, so out of interest I decided to try once again charging up at the 3.7 volts per cell mark. After just three charge cycles 9 of the 16 cells were drifting. Once a total of 15 charge cycles had been completed the entire pack was a mess. The lowest cell voltage was 3.28 and the highest was 3.70. The distribution was interesting although I’m not sure I can draw any concrete conclusions from it. All but 3 of the original 16 cells that used the 3.70volt balance boards reached 3.70 long before the 16 cells that had the 3.55volt balance boards. Could charging each pack at their recommended (and different) voltage be responsible? And there was a measurable heat difference charging at the higher rate.. Was I seeing damage to those first set of batteries? To this day those cells from the first batch will climb faster IF separated from the pack and charged singly.

Thanks for sharing all the information, I think your trike look great! We have put 1kW electric motors on our mountain bikes so we can get across the paddocks and up some of the steep hills with all the shopping.

It does look like charging up to 3.7 volts was damaging your batteries, I would be interested to know what current your charger was pushing into the battery at 3.7 volts before it started to current limit.

Simon

[karrak]

For some reason the Reply with Quote is not working? WillyT We all bemoan the anecdotal bench tests that are out there as not anything you can hang your hat on, it's just as bad trying to decipher the data from regular users. I reached my one year anniversary this week and it's milestone if the fact they made it a year makes a difference. I consider all my data worthless for a couple reasons, one the temperature exposure during the summer was above 90° and I have now made the decision to put them into a storage mode this winter.

Your data is not worthless. As we know there are a huge number of variables, some we have control over and some we don't that will determine how long our LFP batteries will last and how well they will operate. Because of this, the data from your system alone can't be used to make any definitive statement about how long an LFP battery will last, but when amalgamated with data from others can be used to infer how long an LFP battery will last and what factors affect how long they will last. This is rather like having to do epidemiological studies to work out factors affecting peoples health. The more data the better.

The basic internet contention is to drop the SOC to 50-60% and leave them alone to self discharge. It then becomes that 5 months could present some problems in a remote location and un-monitored. The choices are, remove everything and let the cells sit naked, maintain a low float voltage or use a VCS and have a low set point and raise the voltage to a high point within a given range.

I think the safest approach is to remove the balancing boards and disconnect all external cables from the battery.

I wouldn't think there is much risk if you did leave the balance boards connected. If they draw 4mA I calculate they will they will only draw 14.4Ah (.004*24*30*5) from the battery over the five month period.

If you did leave the balance boards connected and one of them did fail having an external power source connected would not stop damage to the battery.

Simon

[Willy T]

To some degree all the manufacturers use a little different make up in their LiFepo4 family of cells as far as I can tell and have patents to prove it. Winston is LiFeYP04 and GBS is LiFeMnPO4, the charging and discharging specifications seem to be all the same. Winston claims the Yttrium extends cycle life. Manganese no clue. Some of it is to enhance the temperature range. I am not really a chemist and I don't sleep in a Holiday Inn Express.

PNJ has made this his quest in life, I'm sure he'll be along to tell us how it all works.

[CrazyJerry]

Here's another reason why no one here seems to have a clue about lifepo4 technology and where's it's at, what you have posted has no relevance to lifepo4 cell packs, you're talking about another lithium technology and this is a lifepo4 thread, not li-poly,li-ion. Anyone using the voltage parameters you're quoting will destroy their lifepo4 cells quickly and is incredibly misleading.

The average consumer like myself may choose to look at the specs provided buy the vendor.
Here's what I see:

LiFeMnPO4 chemistry
Operation Voltage Range: 11.2 to 14.4V

http://elitepowersolutions.com/products/product_info.php?cPath=25&products_id=146

-------------------------------

CALB EV Lithium LiFePO4
MAX CHARGE VOLTAGE - 3.65

http://www.electriccarpartscompany.com/100Ah-32V-2C-br-CA100FI-br-CALB-EV-Lithium-LiFePO4-br-UL-Certified-br-Prismatic-Cell-Batteries-br-USA-Stock-br-56L-26W-86H-in-br-142-67-219-mm-br-75-lbs-34-kg-br-For-Quantity-Pricing-and-Specifications-See-Details_p_38.html

The writing I'm doing is to an earlier response if you took the time to review. If it needs to be moved to a more relevant spot then by all means move it. The info contained within may be valuable to someone else even if you find it of no use.

Best,
~CrazyJerry

[dax]

GBS 20ah Lithium batteries: Part 2.

To expand the use of the batteries, I simultaneously adapted them into a 20” electric push mower: Homelight Model UT13126. This was a 24 lead acid mower and extremely heavy as factory equipped. Two 12volt GBS 20ah packs fit nicely into the same bay as the factory lead acids. The velomobile has one 24 volt pack in each saddlebag (Two 12 volt units wired in series.) A single 24 volt pack was plug-n-play between the two. The runtime with the mower was 50 minutes to an hour depending on the sharpness of the blade and thickness of the grass. With four 24volt packs at my disposal, there was never a problem finishing the lawn. The packs are numbered so I would use these in sequence every time the lawn needed to be mowed and they were always discharged to 24 volts (3 volts per cell) when used. For better or worse, EVERY time the packs were used they were always recharged up promptly. To accomplish this on the separated 24 volt packs, I purchased a GBS ac powered 24 volt charger that charged to 29 volts or roughly 3.625 volts per cell.

The balance boards that came with each battery remained affixed from the time I put them into service. Within the first 6 months I did notice another difference between the first set of batteries (that used the higher voltage engage point of 3.7 volts in the balancing boards) and the second set of batteries (that used the lower voltage engage point of 3.55 volts in the balancing boards). The difference was the red led balance indicator on the boards was no longer consistent in lighting up together at basically the same time on the higher voltage ones. Two or three lights would come on, then minutes later a few more and so on. The pack with the higher voltage boards was cell voltage drifting. The pack with the lower 3.55 boards was pretty much perfect in that all lights turned on within a 10-30 second span.

My understanding was the balance boards were supposed to balance these cells but that didn’t seem to be happening. I decided to continue to let them do their jobs anyway. I tried using the supplied lithium charger to correct this – but that charger had no communication with the pack so the boards would mostly just glow red until the charger shut-off. Using the charge controller from incoming solar, I could fine-tune the charge a little better and manually pull the leads to let a balance board bleed down a high cell. This was time consuming and really didn’t accomplish much.

I did some digging on the internet and discovered the hobby market. Using a couple cell-log8’s, a project enclosure, speaker jacks, trailer lighting whips, two fuse panels, shoe-goo, and some low voltage chargers from portable equipment, I made a pack monitor and the speaker jacks corresponded to the cell-log cell values, so I could individually apply a charge or discharge to any cell(s) and watch them. This worked great once I got a procedure down. What I didn’t quite piece together at that time was using the balance boards as a primary indicator of nearing full charge. Using the 3.7 volt units as the indicator were creating more problems then they solved. The 3.55 volt balance board equipped cells were pretty rock solid. The homebrew monitor I built can be seen online here:

http://diesel-bike.com/Aurora/aurora_files/Cell_Log8_Charge_Panel_800x638.jpg

http://diesel-bike.com/Aurora/aurora_files/Cell_Log8_Charge_Panel_Close.jpg

It took an additional month before it really hit me about the difference in the balance boards. On a hunch, I manually balanced the cells and then started charging that pack at the lower value of 3.55 volts per cell and for the most part – every cell in the problem pack was now steady and not voltage drifting apart…. One month later the cells were all very close in their voltages, so out of interest I decided to try once again charging up at the 3.7 volts per cell mark. After just three charge cycles 9 of the 16 cells were drifting. Once a total of 15 charge cycles had been completed the entire pack was a mess. The lowest cell voltage was 3.28 and the highest was 3.70. The distribution was interesting although I’m not sure I can draw any concrete conclusions from it. All but 3 of the original 16 cells that used the 3.70volt balance boards reached 3.70 long before the 16 cells that had the 3.55volt balance boards. Could charging each pack at their recommended (and different) voltage be responsible? And there was a measurable heat difference charging at the higher rate.. Was I seeing damage to those first set of batteries? To this day those cells from the first batch will climb faster IF separated from the pack and charged singly.

Life was great for the velomobile and mower but could these batteries serve a third purpose and be used in the house?

This was worth considering since the 1700ah of Surrette lead acids had seven years on them at that point and were starting their decline….

More in Part III..

~CrazyJerry

Here's another reason why no one here seems to have a clue about lifepo4 technology and where's it's at, what you have posted has no relevance to lifepo4 cell packs, you're talking about another lithium technology and this is a lifepo4 thread, not li-poly,li-ion. Anyone using the voltage parameters you're quoting will destroy their lifepo4 cells quickly and is incredibly misleading.

[CrazyJerry]

GBS 20ah Lithium batteries: Part 2.

GBS 20ah Lithium batteries: Part 2.

To expand the use of the batteries, I simultaneously adapted them into a 20” electric push mower: Homelight Model UT13126. This was a 24 lead acid mower and extremely heavy as factory equipped. Two 12volt GBS 20ah packs fit nicely into the same bay as the factory lead acids. The velomobile has one 24 volt pack in each saddlebag (Two 12 volt units wired in series.) A single 24 volt pack was plug-n-play between the two. The runtime with the mower was 50 minutes to an hour depending on the sharpness of the blade and thickness of the grass. With four 24volt packs at my disposal, there was never a problem finishing the lawn. The packs are numbered so I would use these in sequence every time the lawn needed to be mowed and they were always discharged to 24 volts (3 volts per cell) when used. For better or worse, EVERY time the packs were used they were always recharged up promptly. To accomplish this on the separated 24 volt packs, I purchased a GBS ac powered 24 volt charger that charged to 29 volts or roughly 3.625 volts per cell.

The balance boards that came with each battery remained affixed from the time I put them into service. Within the first 6 months I did notice another difference between the first set of batteries (that used the higher voltage engage point of 3.7 volts in the balancing boards) and the second set of batteries (that used the lower voltage engage point of 3.55 volts in the balancing boards). The difference was the red led balance indicator on the boards was no longer consistent in lighting up together at basically the same time on the higher voltage ones. Two or three lights would come on, then minutes later a few more and so on. The pack with the higher voltage boards was cell voltage drifting. The pack with the lower 3.55 boards was pretty much perfect in that all lights turned on within a 10-30 second span.

My understanding was the balance boards were supposed to balance these cells but that didn’t seem to be happening. I decided to continue to let them do their jobs anyway. I tried using the supplied lithium charger to correct this – but that charger had no communication with the pack so the boards would mostly just glow red until the charger shut-off. Using the charge controller from incoming solar, I could fine-tune the charge a little better and manually pull the leads to let a balance board bleed down a high cell. This was time consuming and really didn’t accomplish much.

I did some digging on the internet and discovered the hobby market. Using a couple cell-log8’s, a project enclosure, speaker jacks, trailer lighting whips, two fuse panels, shoe-goo, and some low voltage chargers from portable equipment, I made a pack monitor and the speaker jacks corresponded to the cell-log cell values, so I could individually apply a charge or discharge to any cell(s) and watch them. This worked great once I got a procedure down. What I didn’t quite piece together at that time was using the balance boards as a primary indicator of nearing full charge. Using the 3.7 volt units as the indicator were creating more problems then they solved. The 3.55 volt balance board equipped cells were pretty rock solid. The homebrew monitor I built can be seen online here:

http://diesel-bike.com/Aurora/aurora_files/Cell_Log8_Charge_Panel_800x638.jpg

http://diesel-bike.com/Aurora/aurora_files/Cell_Log8_Charge_Panel_Close.jpg

It took an additional month before it really hit me about the difference in the balance boards. On a hunch, I manually balanced the cells and then started charging that pack at the lower value of 3.55 volts per cell and for the most part – every cell in the problem pack was now steady and not voltage drifting apart…. One month later the cells were all very close in their voltages, so out of interest I decided to try once again charging up at the 3.7 volts per cell mark. After just three charge cycles 9 of the 16 cells were drifting. Once a total of 15 charge cycles had been completed the entire pack was a mess. The lowest cell voltage was 3.28 and the highest was 3.70. The distribution was interesting although I’m not sure I can draw any concrete conclusions from it. All but 3 of the original 16 cells that used the 3.70volt balance boards reached 3.70 long before the 16 cells that had the 3.55volt balance boards. Could charging each pack at their recommended (and different) voltage be responsible? And there was a measurable heat difference charging at the higher rate.. Was I seeing damage to those first set of batteries? To this day those cells from the first batch will climb faster IF separated from the pack and charged singly.

Life was great for the velomobile and mower but could these batteries serve a third purpose and be used in the house?

This was worth considering since the 1700ah of Surrette lead acids had seven years on them at that point and were starting their decline….

More in Part III..

~CrazyJerry

[CrazyJerry]

Thank you for your replies folks. What I'm presenting is by no means a "be all end all" - not by a longshot. But this off-grid venture is slated for the long-haul so I'm always looking or trying different things. If something works it gets passed on and maybe someone can improve upon that - we all benefit. The final chapters on these topics may never be written though.

Anyway, while I have some time I'll continue the write-up to present day..

Stay tuned.
~CrazyJerry

[lkruper]

Jerry, excellent setup description on the life of your batteries so far. I think we can all make allowances and extrapolate from your data. I re-read it twice to make sure I absorbed all the little nuances. Looking forward to the rest of it.

I knew I was not on ignore

[Willy T]

Jerry, excellent setup description on the life of your batteries so far. I think we can all make allowances and extrapolate from your data. I re-read it twice to make sure I absorbed all the little nuances. Looking forward to the rest of it.

[lkruper]

Can you give me an executive summary?