LiFePO4 - The future for off-grid battery banks?

[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.

[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

[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

[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.

[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

[CrazyJerry]

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.

PNjunction,
In the beginning I was unaware of this forum and its only been recently I discovered it. Before registering I've read a ton on here, and a couple other forums too. It's amazing how the comments in many cases, reflect different things I've also experienced along the way with these cells. What I never sat down and charted, was the upper and lower "knees" although I witnessed the sharp rise and drop-off on a meter. Going by the battery spec sheet, I was none the wiser but was suspicious due to heat build up and cells drifting... The knee graph speaks volumes when you know what you're looking at.
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Moving forward, yes, I already have the second bank installed and it follows both the AH derating as well as the very conservative charge/discharge points. At the risk of inflaming some folks on here I do believe you, SunKing and a few others bring quite a lot to the table to include differing views. And, as evidenced by the 2011 20ah spec sheet, this has also been reduced to more conservative figures... Coincidence?
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The Surrette replacements are the 200ah GBS cells. I do like the terminal cover design, but also wanted to try their GenIII recipe. I like the idea of the terminal on both ends of the cells but am having little luck downloading and reading through some of the mega studies where this has definitive benefits.
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This is an interesting experiment and will share anything - good or bad - along the way.
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~CrazyJerry

[Sunking]

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.

Well Jery you have discovered Lithium cells do not drift and there is no need to for them. In fact the Balance Boards are the root of the problems. Most notable destruction. If you want to eliminate the possibility of over discharging the cells, you have acquired the skills and knowledge to Bottom Balance the cells making it impossible to over discharge them and drive them into reverse polarity.

[CrazyJerry]

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

You're welcome Simon and I hope it may be of use to someone, or at least to help paint a bigger picture.
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Bouncing back-n-forth a bit I can see where I could've cleaned up the post a bit.
Initially I charged the 48 volt pack as a whole with the supplied GBS listed 48v 6amp charger. It would bring the pack up to an advertised 58.2 volts. When using that charger on the second 48 volt pack (purchased about a month later) I noticed the balance boards came on way sooner (3.55 volt versions). After digging around on their website I noticed the spec sheets on the batteries and balance boards had changed. So, that's when I began to pay attention to the heat build up from charging with the supplied charger. At the end of the charging cycle with the supplied charger, ALL 16 of the 3.7volt balance boards would be lit (red) and would stay on for some time after. If those board turn on voltages were accurate (3.7 volts) then the charger was putting out more than the advertised 58.2 volts me thought. The only other way I could charge the 48 volt pack was through the solar/mppt so I hooked up the charge station. You are right in the ballpark with your reference to 11amps (0.6C) from the solar. Depending on sunlight/conditions/time of day it would be lower at times. I had 101pv in and the output to battery set at 58volts(approx same as GBS charger). After continuing to observe heat from both saddlebags, I lowered the figure to 56volts and then downward to 54volts.
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Going beyond 11 amps into the pack was pretty easy. I could use both the solar and the supplied charger simultaneously to charge the pack, and just shutoff the supplied charger when things got close and let the solar finish it off. Right or wrong, this is what I did and the cells continued to survive.
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With the string of 16 cells drifting (actually 32 cells since both packs were drifting), I resorted to charging individual 12 volt modules (like you were mentioning.) I reconfigured the solar panel wiring and could see approx 42 amps or so. Charging by 12 volt module was pretty time consuming until I found the the hobby market / Celllog8. After building the monitor, I went back to charging the entire 48volt pack. I could then give an individual cell a jolt or a discharge through the corresponding speaker jacks in an attempt to get the cells back to a closer relationship.
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In lowering the upper charge voltage limit I did notice the lowering of the heat at the terminals so that's what I ended up staying with. The added benefit was "less" cell drift. Reducing upper charge voltage further like PNjunction and others have suggested has settled these cells of drifting although I do check them about once a month.
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So, that's a lengthy post to your question, and in summary, I charged as a 48volt pack as well as by 12volt module. I used the GBS charger and I also charged directly from the solar panels through the MX60.
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~CrazyJerry

[PNjunction]

The only thing I've seen about the 200ah cells is that the positive and negative are on opposite ends to try and help current distribution and avoid hot-spot crowding at the terminals.

This may not be anything noticeable in a "sub-c" solar housebank environment.

Re the Cellog - do power it from a *separate* power source, and avoid the temptation to tap off the battery itself. Again, another point of failure, de-balancer. I would verify the accuracy of each channel with a separate reading from a Fluke or otherwise comparing terminal voltages to the cellog 8 display.

I know T1 Terry and others have used them, but keep an eye on it and do a pm comparison once in awhile.

[karrak]

With the string of 16 cells drifting (actually 32 cells since both packs were drifting), I resorted to charging individual 12 volt modules (like you were mentioning.) I reconfigured the solar panel wiring and could see approx 42 amps or so. Charging by 12 volt module was pretty time consuming until I found the the hobby market / Celllog8. After building the monitor, I went back to charging the entire 48volt pack. I could then give an individual cell a jolt or a discharge through the corresponding speaker jacks in an attempt to get the cells back to a closer relationship.

The CellLog8 is a great little device but it does have its issues. The main one being that unless it is modified it draws its power from only the bottom six cells so will unbalance your battery. I have fixed this by powering it via an external switch mode power supply. There are other ways to fix this problem and other information on the CellLog8 can be found here Cellog 8 hacking. Let me know if you want more information about my fix.

It can be calibrated and I have found that it seems to hold its calibration.

Simon

[CrazyJerry]

Well Jery you have discovered Lithium cells do not drift and there is no need to for them. In fact the Balance Boards are the root of the problems. Most notable destruction. If you want to eliminate the possibility of over discharging the cells, you have acquired the skills and knowledge to Bottom Balance the cells making it impossible to over discharge them and drive them into reverse polarity.

Thanks SunKing. Some time ago when I discovered this forum I was initially quite entertained by your label of "vampire boards" however, it is a great way to remember what they do well. Currently, they are in a small box not far from my antiquated Frontier bag phone.
The new pack that runs the other side of the house is bottom balance (again thanks to this forum).
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~CrazyJerry

[CrazyJerry]

The CellLog8 is a great little device but it does have its issues. The main one being that unless it is modified it draws its power from only the bottom six cells so will unbalance your battery. I have fixed this by powering it via an external switch mode power supply. There are other ways to fix this problem and other information on the CellLog8 can be found here Cellog 8 hacking. Let me know if you want more information about my fix.

It can be calibrated and I have found that it seems to hold its calibration.

Simon

Simon, I remember that post (actually right where you referenced) and I left it on the to-do list someday mainly because the celllog8's are only powered on when I check the cells. When I was using the velomobile there wasn't room for anything else so pack monitoring at a pack level was it. Now, the home unit normally just sits on a shelf all rolled up.

When it is hooked up to the repurposed cells that are now part of the house bank it no longer has to monitor 8 cells per celllog meter (there are two separate meters in the box). The setup now is that each meter only "sees" 4 cells. This is a result of how they are all wired up (4p4S)... Basically the first group (or 16 cells in series @ 48V) that I purchased is still together as a happy family but now in it's own 12volt pack. The second group is also wired identically. So each group has it's own celllog8 that's now only seeing 4 cells each. I used the flat trailer whips plus a separate ground wire for quick connect/disconnect capability. I don't watch much tv.
~CrazyJerry

[CrazyJerry]

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.

PNjunction,
So today in looking at the new pack monitoring (this place is now starting to look like (Frankenstein's lab!) I thought you might get a kick out of this. Very interesting that at just 13.46 volts (3.36-3.37 per cell) matches up with 95% capacity. They may even be a little more conservative than you - lol! (Take with a grain of salt)
-

-
~CrazyJerry

[PNjunction]

Pretty cool - although I think what I'm seeing are *rested* voltages, not while under charge. Most GBS cells, especially Gen1's rest (4 hours or more) at 3.38 / 3.39 when considered 100% fully charged. So that meter is relatively accurate.

I'm using something similar, but just a bit smaller:

http://tecmate.com/products/ts-126/

Tested against a Fluke, and a bit more convenient than a chart taped on the wall. It isn't lab-quality, but close enough for daily checks and so forth. Note that it too draws a bit of current, so I don't leave it attached.

Although rested voltages are not always the most convenient way to deal with things. But I do use it from time to time to judge the effectiveness of various voltage and current tests with lifepo4.

Example tests of charging (>.05C current, .1C or more typical) and later evaluation of rested voltages:

1) Charge to 3.5v and stop.
2) Charge to 3.6v and stop.
3) Charge to 3.5v and allow absorb current to drop to .05C.
4) Charge to 3.6v and allow absorb current to drop to .05C.

It was easy to find that options 3 and 4 both result in a "fully" charged cell, but option 3 merely takes longer.

[CrazyJerry]

Pretty cool - although I think what I'm seeing are *rested* voltages, not while under charge. Most GBS cells, especially Gen1's rest (4 hours or more) at 3.38 / 3.39 when considered 100% fully charged. So that meter is relatively accurate.

I'm using something similar, but just a bit smaller:

http://tecmate.com/products/ts-126/

Tested against a Fluke, and a bit more convenient than a chart taped on the wall. It isn't lab-quality, but close enough for daily checks and so forth. Note that it too draws a bit of current, so I don't leave it attached.

Although rested voltages are not always the most convenient way to deal with things. But I do use it from time to time to judge the effectiveness of various voltage and current tests with lifepo4.

Example tests of charging (>.05C current, .1C or more typical) and later evaluation of rested voltages:

1) Charge to 3.5v and stop.
2) Charge to 3.6v and stop.
3) Charge to 3.5v and allow absorb current to drop to .05C.
4) Charge to 3.6v and allow absorb current to drop to .05C.

It was easy to find that options 3 and 4 both result in a "fully" charged cell, but option 3 merely takes longer.

PNjunction, the display is handy. One of my questions with it, and the likes of, is how accurate is it? Or is it accurate enough for basic needs thus making it useful.
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You did list a few charging scenarios above and this pic lines up with #4. The 12 volt pack was charged to 13.6 and then held there until the end amps setting (.05c, 10 amps in this case) was reached. At that point, the pack entered the "float" stage at 13.5volts. Once at float, a small current of 1.9amps(charging) is reflected on the screen. Upon initial install, the pack/brain/ needs to be charged to 14.2v to start at the full 100%.
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The only thing I noticed was the lcd screen's viewing angle didn't jive with my (aging) eyesight. I did notice when viewing it from just below the horizon it was better. No menu settings helped, but turning the lcd upside down did - and there's a menu adjustment to make the visual right-side-up.
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This system has a secondary screen that shows the individual cell voltage and temperature. Haven't gotten that far to check the accuracy but it's on the list.
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Thanks for the charge scenarios. You and others have mentioned these over the many posts. I'll pan on going through them just to observe but am slightly biased to #3. That may be some of the residual from 11 years of lead... Have a good day!
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~CrazyJerry