LiFeYPo4 questions

[PNjunction]

Then I stumbled across Thundersky 700ah cells (same yellow cells as Winston??). I can pick up these cells for $560/cell with 700ah from several different suppliers. Seems like one hell of a deal. Any thoughts on these?

Thundersky's pre-date the Winston/Sinopoly/Balquon split. Since that time of Thundersky, it is reputed that the more modern Winstons have higher manufacturing tolerances, improved chemical and build quality. Also the addition of Yttrium (The "Y" if LiFeYp04) is supposed to improve extreme cold weather performance.

IMPORTANT - some very old ancient documentation on Thunderskys show them as having / needing an initial charge to 4.2v per cell. DO NOT DO THIS. Likewise, 2.5v per cell as a discharge limitation is not something to use as an LVD. This is akin to setting a lead-acid LVD to 10.7v - too low, don't go there. Unfortunately, you may see these ancient specs in some modern commercial "drop in" lifepo4 replacements. I guess they didn't get the memo 4 years ago.

My inclination is to leave the old Thundersky's in the hands of experienced practitioners, not a first timer. Again, I have no personal experience with anything but GBS, but would be cautious about old stock Thunderskys - I'd have to verify the storage voltages myself to make sure that no cell is dead from improper high-heat storage or mishandling over the years.

Here is an example of a 12v / 400ah bank of Winstons undergoing testing for marine use. Note that this test goes WAAAY too far in discharge, something we should never experience:

https://www.youtube.com/watch?v=oJ8AfJsOhsM

While he took this down to nearly 100% DOD discharge, there is no indication that he limited current during the recharge at that low DOD!! If you go under 80% DOD, you should not apply any more than about 0.01C until the cells reach 3.2v again - whereupon you can apply normal charge current. So don't go below 80% DOD in the first place, and of course never leave a lifepo4 in a badly discharged condition for very long. Get to it asap.

Note that for my land-locked system, I'll be having none of that rat's nest, but simple pack-level maintenance as described here:

http://www.solarpaneltalk.com/showthread.php?17609-Simplified-lifepo4-charging-and-care

I don't think I will have a problem assembling the individual cells with my friend who is in the solar industry.

Cool. Just make sure he knows what he is doing, ie using a torque wrench set to the proper specs for the terminal connections, and also making sure that the terminals and links are clean before assembly. Last thing you need is a high-resistance terminal here, and having the bms mask the issue with incessant balancing, or melting the case around the terminals. Basic battery care really.

Do all battery cell banks need to be strapped to prevent expansion?

Yes. This prevents any side or top-torque breaking or twisting the cell terminals if the cells were just loosely assembled and sat down. Any significant movement without banding/strapping and game over. Tall cells operating under high-heat environments have been reported to slightly buckle or sag, and this is also bad, since you don't want any expansion within the case itself separating the anodes/cathodes away from each other. Under abusive over or undercharge practices, the cells can expand, but having them strapped and banded is not a cure for improper charging! Don't do that in the first place.

[Sunking]

PNJunction,
Thanks for the help. I will look into those companies that you mentioned. Being new to all this, I agree that EVers seem to have a lot more on their plate when it comes to the whole system setup and potential problems.

How so?

Most DIY's use a Warp 9 and 13 electric motors. Both are 72 volt motors, and they use a single battery string of Calb 100 AH batteries with a BMS. Those with Deeper pockets just step up in voltage to 144 volts using the same Calb 100 AH battery. Even th ebig boys working in R&D use the same Calb 100 AH cell up around 400 to 600 volts using AC induction motors with VFD. Not much difference between 48 and 72 volts.

[PNjunction]

Here I am breaking my own rule about EV, but in the spirit of KISS, here's how to "bottom balance". Some might do this because it is not uncommon to drive the battery down to dangerously low levels, and with the application of high-current, one of the cells can easily go reverse polarity right under your nose. They want the cells to reach the LVD all at the same time.

Once again, balance does not mean trying to obtain the same capacity out of the cells, they merely want the VOLTAGES to be the same to help prevent a nasty reverse-polarity situation.

As solar users, you *could* do this, but then you leave your balance ragged at the top. You choose one method or the other, you don't do both.

1) If you have a decent charge in your bank already, you do a bulk discharge until each cell is roughly near 3v.

2) Using some sort of automation (hobby charger, programmable dc power supply that can deal with batteries etc), you take each cell down to about 2.6 to 2.75v depending on who you talk to. Some may place all the cells in parallel and do it that way, or others might do each cell individually still connected in series. It is just tedious, but in the wrong hands, if you aren't on the ball, you are in the DANGER zone of taking your cell too far.

3) You are looking for a "resting" voltage which implies that you may need to do this multiple times after the cells have rested for 15 minutes to several hours since they tend to recover voltage after a rest. Once they are fnally stable rested at 2.6 - 2.75 (stick to one value only), you can then begin a charge.

4) NOTE NOTE - I have often NOT seen the common procedure of using NO MORE than 0.01C to initially bring these low cells back out of the deep discharge knee to 3.2v before using the normal full current! I wonder how many EV'ers do a nice bottom balance, and then hammer their cells with too much current initially.

5) Once the VERY FIRST CELL hits about 3.5V - STOP. Take note of your charger voltage, and use this as your HVD. Again, to do this right takes cell level monitoring and you may not have an exacting top-balance. Just use the very first cell to reach 3.5v as your guide.

6) VERIFY your charger's voltage with a FLUKE! I can personally attest to my West Mountain Radio voltage being off a little bit. If you want precision, you'll verify that your charging gear is actually up to spec! With thousands of dollars at stake, there is no reason to use some cheap-o voltmeter.

Man, I did it now. Hope I didn't open the floodgates. But some solar guys ask me about this. I tell them not to under-design their banks in the first place!

[SunEagle]

6) VERIFY your charger's voltage with a FLUKE!

Does that mean I shouldn't use my Extech EX530 meter?

[PNjunction]

I own an Extech 470 myself for general purpose stuff, but won't use anything but a Fluke for li-ion battery management.

I'm not a multimeter snob, but here goes the why for Fluke ...

I can trust a Fluke out of the box, without having to verify the accuracy. When I do, the specs are exceeded, and not a sloppy window. With li-ion, the difference between 3.697v on a Fluke, and 3.600v on the Extech can be a big deal. This is especially so for guys using chemistries other than lifepo4, where the difference between 4.2 and 4.3v is even more dramatic.

One thing you can do if you haven't already, is measure a typical 3v watch or other consumer battery, take that battery to someone with a Fluke or even better accuracy stuff, measure and compare. Now you can compensate on the Extech if you have to.

Because voltages change so quickly in the deep discharge and steep charge knees, I need both speed of the display, along with no overshoot or undershoot when I put the probes on the batteries. While an 87V was fine for doing this, it was overkill for just voltage measurements, and the lowest end of the line, the 11X series has proven to be very adequate with lifepo4. I can't wait around for the Extech to settle.

Flukes tend to fail gracefully when I make a mistake and blow the HRC fuse with a tiny snap. I don't want a cheaper meter blowing out through the seams and into my hands when I do this. Internal blast-shields and so forth are a big deal when I make a mistake with a 400ah battery. Ordinarily this kind of internal protection is designed to help prevent arc-flashes in huge industial panels, but I feel safer with a Fluke even at relatively low voltages - but possible 100's of amps going through temporarily when I goof.

It just freaks me out when I see videos of guys with kilo-buck lifepo4 banks using 10$ dimestore voltmeters to measure their infrastructure. The 530 is obviously better than that, but it still doesn't meet my needs around lifepo4 batteries.

Know that these are just my personal opinions - if one wants to use something else, go for it. Other meters (well, ok maybe Agilent excepted) just remind me of Dirty-Harry: "Do you feel lucky, punk?"

[SunEagle]

I own an Extech 470 myself for general purpose stuff, but won't use anything but a Fluke for li-ion battery management.

I'm not a multimeter snob, but here goes the why for Fluke ...

I can trust a Fluke out of the box, without having to verify the accuracy. When I do, the specs are exceeded, and not a sloppy window. With li-ion, the difference between 3.697v on a Fluke, and 3.600v on the Extech can be a big deal. This is especially so for guys using chemistries other than lifepo4, where the difference between 4.2 and 4.3v is even more dramatic.

One thing you can do if you haven't already, is measure a typical 3v watch or other consumer battery, take that battery to someone with a Fluke or even better accuracy stuff, measure and compare. Now you can compensate on the Extech if you have to.

Because voltages change so quickly in the deep discharge and steep charge knees, I need both speed of the display, along with no overshoot or undershoot when I put the probes on the batteries. While an 87V was fine for doing this, it was overkill for just voltage measurements, and the lowest end of the line, the 11X series has proven to be very adequate with lifepo4. I can't wait around for the Extech to settle.

Flukes tend to fail gracefully when I make a mistake and blow the HRC fuse with a tiny snap. I don't want a cheaper meter blowing out through the seams and into my hands when I do this. Internal blast-shields and so forth are a big deal when I make a mistake with a 400ah battery. Ordinarily this kind of internal protection is designed to help prevent arc-flashes in huge industial panels, but I feel safer with a Fluke even at relatively low voltages - but possible 100's of amps going through temporarily when I goof.

It just freaks me out when I see videos of guys with kilo-buck lifepo4 banks using 10$ dimestore voltmeters to measure their infrastructure. The 530 is obviously better than that, but it still doesn't meet my needs around lifepo4 batteries.

Know that these are just my personal opinions - if one wants to use something else, go for it. Other meters (well, ok maybe Agilent excepted) just remind me of Dirty-Harry: "Do you feel lucky, punk?"

I understand you preference to Fluke. They make really quality meters.

Before I use any meter on AC circuits I try to make sure they have a CAT IV @ 600v rating. Most of those cheap meters either don't show the rating or have a CAT II @ 600v. I never feel lucky when it comes to electricity. I just stay cautious.

[PNjunction]

I've learned to slow down around batteries. At $11 a pop for an HRC fuse, I'm learning quickly.

The reason I don't want any major drama if a multimeter fuse blows, cat rated or not, is also to protect myself from involuntary jerk-reflex injury from the sound!

If I'm really on the ball, I try to take a second look around where my elbow, forehead or whatever might go when I do this and think about another approach when things are tight or pointy obstacles are nearby. And of course not driving my hands into another live circuit.

I have to watch myself from becoming complacent around a "simple" 4S battery and wiring.

[SunEagle]

I've learned to slow down around batteries. At $11 a pop for an HRC fuse, I'm learning quickly.

The reason I don't want any major drama if a multimeter fuse blows, cat rated or not, is also to protect myself from involuntary jerk-reflex injury from the sound!

If I'm really on the ball, I try to take a second look around where my elbow, forehead or whatever might go when I do this and think about another approach when things are tight or pointy obstacles are nearby. And of course not driving my hands into another live circuit.

I have to watch myself from becoming complacent around a "simple" 4S battery and wiring.

Complacency is the number one reason for Utility line men deaths. You can never get too comfortable when handling energized cables and equipment because then you get careless.

[PNjunction]

It may seem oversimplistic, but safety is one reason I use GBS cells. They are the only ones that include removable purple top-terminal covers over each cell, which can save your you-know-what provided one actually uses them.

There are other high-quality cells like CALB, Winston, etc of course, so I'm not trying to sound like a salesman. But if it ever came to dropped-wrench time, at least with the GBS you'll have a fighting chance right off the bat when they show up at your door.

[reed cundiff]

Thread devoted to LFP users

There is a lot of interest in LFP usage in solar/off grid applications; however, there are seemingly very few folks that have experience with them I noted on the Northern Arizona Wind and Solar forum that it might be a good idea to have a thread devoted to folks with actual hands on experience with LFP battery banks for such usage. Should like to know if folks are interested in such a thread getting started. Should like it on actual experience or valid questions: should hope naysayers would got to other thread.

Have not found a thread/forum yet that does discuss actuall usage.
Reed

[Sunking]

Have not found a thread/forum yet that does discuss actuall usage.

Just the way the market works. As of yet Lithium chemistry is not an economical alternative. Until LFP or any of the other forms will have to be able to compete long term, and as of now it cannot. The only market that can justify the use is EV's, and not every EV went lithium because of expense.

Its just plain ole economics 101.

[reed cundiff]

It would be far more helpful to answer the question(s) posed, then to go off on one's own thought line.
Reed
erstwhile senior physicist at Army Research Laboratory

[PNjunction]

Have not found a thread/forum yet that does discuss actuall usage.

About the closest you'll get to sanity using lifepo4 nearly the way we use them is here:

http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069.html

At this time however, in most other forums, all the discussion turns into an endless bench-racing of specs and pricing, where financial gurus and those from outside our application with no hands-on whatsoever jump into the fray. It is usually a thankless job for moderators to keep things under control.

Of course nobody counts the learner-banks, or ones destroyed by sulfation from insufficient charging, improper EQ, exposed plates and all the plethora of lead-acid maintenance that *should* be done.

Sunking is an exception, although I will take exception to his financial outlook from a long-term standpoint. Problem is, we haven't achieved even a decade of use to back things up, despite manufacturer predictions. HOWEVER, one must understand that these are shark-filled waters and he is trying to protect the neophyte from falling into things hook, line, and sinker, so I understand the gist. Uh oh, here it comes!

I think most of us using lifepo4 just go underground to avoid the surface drama, and smile approvingly - as long as we weren't taken in by the sharks to start out with. We'll probably have to wait at least 5 more years to satisfy the decade of use argument, but by then the focus may have changed that they haven't been used for 100+ years like lead.

Lead and LFP can coexist peacefully - each of which needs to be properly engineered and maintained. Problem is, when discussing LFP, one is always on the defensive, and that becomes very tiring to participate in rather quickly.

[Sunking]

Lead and LFP can coexist peacefully - each of which needs to be properly engineered and maintained. Problem is, when discussing LFP, one is always on the defensive, and that becomes very tiring to participate in rather quickly.

Well I am speaking from direct experience with EV's where LFP has already been put to to real life use. Currently One of the least expensive, not the cheapest is Calb CA series an dis very popular in the DIY EV field with a track record. Current pricing is in the neighborhood of $0.40/wh compared to $0.20 for high end FLA. The LFP has roughly 1000 cycles compared to 2000 cycles of FLA. It is just simple economics at this point in time.

GBS is another popular brand of LFP and one of the more expensive brands. They just came out with another upgrade because the line of yesterday performed poorly. Even their new line appears to fall short of less expensive brands like Calb. He asked why not many threads or no forums, and he got his answer because there is not enough commercial interest until the economics change. It is really that simple and don't forget I am a huge supporter of Lithium batteries, but I will not lie about them or make hay where there is none. As of now the cost is justified for EV use because weight and density is #1 priority in a vehicle. Weight is not an issue for RE systems.

Bu tif you want to know how to size them and technical aspects have at it and I will help, but to say they are ready for prime time in RE they are not. To go one step further they are not ready for EV's, and they wil be ready for EV's before Solar RE applications because there is where all the money in R&D is going. RE is just going on the ride benefiting from another application as a side show. .

[Mike90250]

I want to be in the info sharing business, so SolarPanelTalk DOES have a
Forum/Off grid solar/Batteries : energy storage/ Lithium-ion section which you have found.