Lithium Battery Reports & Tests' 9/08

[AndyH]

One of the key "issues" with this dual stud style of cell is the poor sealing of the studs, and electrolyte loss.
<snip>
Seriously much as I like the electrical performance, this construction issue is a deal breaker for me.

The Headway has a much beter design.

Anyone care to comment?

If the PSI cell has a good seal, then we have to compare the entire cell. (I think we can agree that a leaking cell should be replaced - whether it's an electrode seal, a punctured foil pack or a cracked SLA.) I've read papers that suggest any cell with a rolled seam will leak over time. This suggests that the laser-welded seams might be superior. This is also a point being used by A123 on some of their cells, so I don't think the benefit of welded seams is 'marketing' driven. I've talked with the folks at PSI and they say that publishing torque specs and mounting guidelines (I.E. don't mount by the studs - use the cell body) has eliminated leaks and broken studs.

I still haven't cut away the end of the Headway cell that's potted in what appears to be epoxy so I can't say what's happening there. I was somewhat surprised at all the rust under the metal caps, and the steel on aluminum. One thing in PSI's favor aside from the welded seams is that it doesn't appear that dissimilar metals corrosion will be an issue.

 

[BMI]

Since as a manufacturer's representative, many here won't believe what I say regarding discharge rates and over all performance so I think it is best if any test results published here are performed by an independant tester (calling Doctorbass).

Can you share anything about these cells Armin?

I think it would be very interesting to see a direct comparision performed between Headway, Ping and BMI.

Tests I would personally like to see results for would include-
1) Internal impedance measurement of each cell
2) Discharge curves at say 3C, 5C and 10C
3) The temperature of the cell recorded at the end of the discharge at the above rates (this will be very interesting)
4) Actual capacity measurement to see how close the cell is to the manufacturer's claimed capacity.

So is Doctorbass up to the task?

I want to evaluate a pair of cells as well - will the best representative cells come directly from you? Or my neighbor McStar? Or?

I am not sure exactly what you would like me to share about the cells other than they are very high quality which is shown in very consistent performance from one cell to the next.
There is no such thing as a "best representative cell" since every cell is manufactured to a high quality standard and if it doesn't pass QC after manufacture it doesn't leave the factory.

One cell which Doctorbass has came from mcstar in Texas, another came from my stock here in Oz. These cells were sent about two months ago now. I am about to send Bob Macree a cell for testing from my latest shipment from the factory which arrived only yesterday.
I don't think you could get three more varied cells than these.

 

[Ypedal]

And i shipped 2 PSI cells to Doc i got from Raymond King at psi back in august 08 as well. :wink:

 

[BMI]

One of the key "issues" with this dual stud style of cell is the poor sealing of the studs, and electrolyte loss.

this previously posted by bobmcree

I have read a number if reports where cell damage has resulted from electrolyte loss after less than 6 months use.

Headway have a completely different construction on there screwed cells, and so don't have this issue.

http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=8109&p=122950&hilit=+BMI+inside#p122950

Seriously much as I like the electrical performance, this construction issue is a deal breaker for me.

The Headway has a much beter design.

Anyone care to comment?

There seems to be quite a lack of information/eduction about 40138 cells which is the main reason they are leaking.
I can't see any lock washer under the flat washer in the pic of these green PSI cells? This is encouraging overtightening of the nut. I would guess that many people are way overtightening the nuts when joining cells together.
The most important thing to realise is that the terminal studs are an electrical connection and NOT a mechanical connection. After all would you support or lift a lead acid battery out of a car by its battery terminals (I think not!)
The cell body should be what supports the cells rather than the terminals. Therefore some type of cell holding frame should be used to support the cells such the the frames I supply for holding groups of four cells together or the PSI "lego blocks" or something similar.
As of about a month ago I decided to supply a cell instruction leaflet when ever I supply cells to a customer so they know the proper way to connect their cells when making up battery packs. I am pretty sure Lifebatt nor PSI supply any instructions with their cells.

It is my belief that high quality cells such as BMI and A123 which are fully lazer welded will have a much longer life than cells which have their end caps merely pressed into place or are spot welded in a couple of places. With lazer welded cells the cell is completely impervious to the ingress of humidity, moisture and other atmospheric contaminants.
For this reason I think the Chinese made cells will start failing much quicker in use than BMI or A123 cells.
Time will tell and we will see if my theory in correct in a year or two. If I am right it will mean that people think they are saving money by buying cheaper cells such as Headway etc. but long term it will turn out to be more costly and of false economy.

 

[dnmun]

gosh lapwing, right here too.

my favorite topic, end caps. i have previously expressed concern about the risk of damaging the connection between the end cap and the 'collector' disk where all the tabs of the individual electrodes are welded sequentially as they are wrapped up on the jelly roll machine. i do not know, but i presume that quality control is in the machine that does the continuity test on each new electrode as it is wrapped onto the ever increasing spiral. so they control the thickness of the cathode materials and separator by a feedback process loop driven by the continuity test in the jelly roll tab welder.

i don't think there is any doubt about the need to keep the electrolyte inside the cell, but i was most concerned that twisting of the stud or that top plate would cause discontinuities to develop between the top end cap plate and the underlying collector plate, especially if the weight of a huge pack like that huge 5P 16S Headway pack built with the copper plates for the connector plate with the first of the screw top blue cells came out. i think he had 3 separate events where the entire 5P followed the bad one over the cliff since they are tied together in the 5P.

headway has now built packs with a 2P four hole plate, but the entire pack moves together mostly and may not put too much stress on the studs. i asked them to go back to the large serial link, small parallel link for the 2P. just to reduce that risk, and it seems it is less money because less metal for the connectors.

also i worry that the retorque of aluminum studs will create a problem from stress fracturing of the aluminum and eventual stud failure. perhaps having a female thread on the endcap will help. but i am looking for just the perfect serrated washer to use there under the lug when i build this next pack, and use gel and prevent corrosion in the contact once the initial torquing of the lockwasher pushes through the aluminum oxide surface layer into the metal itself.

stainless screw is ok, but i think steel should do the trick too since the current path will be through the serrated washer into the lug mostly because that is where the lowest metal to metal resistance will be present. but soft multi stranded cable to the next cell to reduce torque on the end cap.

 

[Lapwing]

Making a battery is an expensive and complicated undertaking and if it wasn't I'd be rolling my own. :?


To clarify my point (and just to be clear - I am not promoting one cell brand over another)

Wouldn't it be nice if the designers would take care of the mechano-electric issues, that have been a problem, when "improving" cells.

I expect at $15-$30 per cell, for there to be no mechanical issues. Likewise basic galvanic corrosion, should be engineered out of battery.

The batteries we want are not "Eveready" disposables, and construction practices should not reflect that. They need to be mechanically and galvanically engineered to last 10 years from a mechanical perspective, this so we can use the touted "3000 cycles".

 

[bobmcree]

the cells in my photo did not leak because of over-tightening. they leaked because the vendor never passed on the information he had available regarding handling of the cells. i had no idea how critical it was not to put any torque on the studs. i attached stiff jumpers to the cells and strapped them together with duct tape for bench testing. the differential movement of the cells caused stress on the studs that made the cells leak. IMO a teflon washer secured by a nut and no pressure relief valve is not a good way to keep electrolyte in a cell. other cells however leaked seriously when the original vms discharged them to <1v while the pack was sitting on the shelf, destroying all 12 cells.

the cells that i built into a pack for the latest e-cruzbike using the new 'leggo block' holders should perform well, but i do not think i should have to go to one manufacturer for the cells and another to buy blocks that make up for the poor design of the cells.

i see the hollow threaded aluminum studs on these cells as an even bigger problem waiting to happen when the aluminum tube cracks from vibration. i believe this problem may have been solved on newer cells but i am not sure, will ask armin.

 

[bobmcree]

soft multi stranded cable to the next cell to reduce torque on the end cap.

i believe this is critical to prevent the kind of intercell movement stress on the studs that caused my first cells to leak just from test handling. tinned copper or silver plated coax braid is a good material

 

[AndyH]

There seems to be quite a lack of information/eduction about 40138 cells which is the main reason they are leaking.
I can't see any lock washer under the flat washer in the pic of these green PSI cells? This is encouraging overtightening of the nut. I would guess that many people are way overtightening the nuts when joining cells together.

I agree, Armin, that there's been an information/education gap. With respect, Armin, I fail to understand how the presence or lack of a lock washer prevents overtightening. I know from personal experience that one can overtighten a joint or break a fastener with a lock washer in place - I've done it too many times! I keep a jar of "previous examples of what didn't work" on the bench to remind me to get the specs and a torque wrench before getting to work. We talked about it in an earlier thread and it's outlined here as well..

Bottom line - don't assume, get info from the manufacturer or supplier first, and RTFM. Mount cells by the case. Remember that the shrink wrap is thin and that the cell casing is 'LIVE' and can be shortedjust as well as either terminal. And use a torque wrench. There are work-arounds, but a torque wrench is still necessary for set-up. For example:

An estimate of torque can be had if one uses a spring-type lock washer (the same one every time) and has previously calibrated their technique with a torque wrench. For example - one can experiment and find that a particular spring washer compresses fully when the nut is tightened to X torque, and that it takes 1/4 turn additional to reach the the desired torque. This is an approximation, and is VOID if any changes are made to the connection - additional terminals, moving from pure copper to tin plated terminals, the addition of any lubricant, sealant, or other substance (such as loc-tite).

The most important thing to realise is that the terminal studs are an electrical connection and NOT a mechanical connection. After all would you support or lift a lead acid battery out of a car by its battery terminals (I think not!)
The cell body should be what supports the cells rather than the terminals. Therefore some type of cell holding frame should be used to support the cells such the the frames I supply for holding groups of four cells together or the PSI "lego blocks" or something similar.

As of about a month ago I decided to supply a cell instruction leaflet when ever I supply cells to a customer so they know the proper way to connect their cells when making up battery packs. I am pretty sure Lifebatt nor PSI supply any instructions with their cells.

Actually, Armin, you might be surprised to learn that PSI has supplied instructions since at least 3 Sep 2007. I've supplied instructions to my customers as well - last update was 24 Nov 08.

It is my belief that high quality cells such as BMI and A123 which are fully lazer welded will have a much longer life than cells which have their end caps merely pressed into place or are spot welded in a couple of places. With lazer welded cells the cell is completely impervious to the ingress of humidity, moisture and other atmospheric contaminants.
For this reason I think the Chinese made cells will start failing much quicker in use than BMI or A123 cells.
Time will tell and we will see if my theory in correct in a year or two. If I am right it will mean that people think they are saving money by buying cheaper cells such as Headway etc. but long term it will turn out to be more costly and of false economy.

100% agreement here, Armin. It appears that A123 moved from rolled seals to laser welded joints in their 26650 cells for just that reason:

This new design does not use crimp seals and instead opts for a more advanced “all laser welded” construction optimized for very low humidity penetration over the life of the battery as well as stronger, thicker dual plate headers.

Andy

 

[Jeff]

the cells in my photo did not leak because of over-tightening. they leaked because the vendor never passed on the information he had available regarding handling of the cells. i had no idea how critical it was not to put any torque on the studs. i attached stiff jumpers to the cells and strapped them together with duct tape for bench testing. the differential movement of the cells caused stress on the studs that made the cells leak. IMO a teflon washer secured by a nut and no pressure relief valve is not a good way to keep electrolyte in a cell.

I concur with Bob on this point.
Although the stud type cell connections may provide an easier means of integration by novice users, the fact that no clear declaration existed until recently that the large protruding studs could not be used for mechanical support is lousy engineering at best.
And the lack of a welded seam ensures a relatively short chemistry life, certainly less than the 10yr/~2000 cycle life the purchasers have been advised when staying inside the SOA parameters.


Regards, Jeff

 

[AndyH]

I am not sure exactly what you would like me to share about the cells other than they are very high quality which is shown in very consistent performance from one cell to the next.

Armin, Don and others on this forum learned the hard way that anyone can 'say' anything about anything and get away with it for at least a little while. As I see it, testing performed by the Doc is only necessary because too many vendors and manufacturers rely on unscientific 'test results' - which are little more than biased testimonials - to provide 'proof of performance'. Real test results are standardized and repeatable.

Here's an example from another industry. A small Houston oil company created a new auto engine oil. They did all the 'important' steps: got a trademark on the color of the bottle, trademarked the color of the dye used in the oil, gave it away to people in exchange for testimonials, and got some small-time racers to use it. They made outlandish claims for their 'premium' 'high-performance' product and vehemently argued with anyone that suggested it was less than a gift from the gods. Unfortunately for them, all oil companies test each other's products. Some companies started to raise the 'BS' flag when independent testing they contracted showed the subject's 'synthetic' products were often beaten by other's petroleum products. One company filed a complaint with the National Advertising Division of the Council of Better Business Bureaus - the U.S. advertising industry's watchdog group. The company has been found to have been misleading customers and is now forbidden to use any of it's previous claims in an attempt to sell its products.

Anecdotal evidence based solely on the experiences of individual consumers is insufficient to support product efficacy claims...While the advertiser may quote from published articles if it provides clear and conspicuous attribution to the publisher, it may not rely on such articles to support efficacy claims for which it has no reliable independent validation.

Back to your question - I may be way off target here, but would expect it to be very easy for you to provide the info requested by the thread, or details similar to that provided by PSI for their zero-percent Phostech cells.



View attachment 40138chargeprofile[1].jpg
View attachment 40138chargetime[1].jpg
View attachment 40138cyclelife[1].jpg


link

 

[BMI]

I am not sure exactly what you would like me to share about the cells other than they are very high quality which is shown in very consistent performance from one cell to the next.

Armin, Don and others on this forum learned the hard way that anyone can 'say' anything about anything and get away with it for at least a little while. As I see it, testing performed by the Doc is only necessary because too many vendors and manufacturers rely on unscientific 'test results' - which are little more than biased testimonials - to provide 'proof of performance'. Real test results are standardized and repeatable.

Andy, I feel very sorry for you. It sounds like in your experience everyone is out to deceive you and tell you lies.
That is a very sad way to see the world because believe it or not, there really are some ethical and decent people left in this world who do tell the truth.
Please don't lump me in the same boat as Don Harmon since I don't just "say" anything unless it is the truth.

Often (believe it or not) customer testimonials are extremely important since there is nothing more valuable than a customer who has actually used a product in real life (no matter what it is) and they are extremely satisfied with its performance. Especially so when the customer has previously used other similar products which they find were far less satisfactory. This is especially true of LiFePO4 batteries.
Sometimes customer satisfaction is gained as a result of buying a product after listening to others own personal experiences and this can be a far more valuable thing than purely seeing a load of graghs, charts and figures.
Maybe you think that people like mcstar, micro13car and numerous other people in more than a dozen different countries who are very happy with not only the quality and performance of the BMI products I supply but the additional technical support and help I also provide, were paid by me to say all those nice things. Well the fact fact is I don't and haven't paid anyone to say any "nice things" ever. They make these positiive comments because they really are happy and are not as disillusioned with the world as you seem to be.

Andy please don't take these above comments personally. It is just the way you come across to me.

 

[TylerDurden]

Let's get back to basics.

Re:
BMI
PSI
Lifebatt

Where do the cells originate?
What companies sell which cells?
Which cells are the same/different?
Who works for or with whom?

 

[AndyH]

edit: I found some tech info on a BMI site. Is this yours, Armin? http://lithbattoz.com.au/index.php?page=battery-cells. You could have answered most of my question with a single link! /edit

<snipped>

You'll not be surprised to hear that your assessment of 'where I'm coming from' is not what I said or intended. Please note that I didn't say anything about paid testimonials.

Conversation example 1: "How many rocks are in my hand?" (one, two, three, four, five, six) Looks like six. "Thank you."
Conversation example 2: "How many rocks are in my hand?" My customers are happy and I didn't have to buy their comments. "Ummm, I was looking for six, but thanks anyway."

I'm actually trying to help you sell your products. Why? The more cells PSI makes the more prices can come down - and that helps us all. The world needs more EVs and less arguing.

Testimonials are sales tools. Accurate data is the foundation that keeps the sales floor out of the swamp. How many testimonials will you personally use when searching for an appropriate circuit breaker for your electric boat project? How many houses will you buy without an inspection? How many cars will you buy with no window-sticker that outlines what's under the bonnet? I suspect you understand what I'm saying - one doesn't graduate from university with a 'hard science' degree and have a career in the 'real world' without some combination of knowledge and common sense, so I'll assume you understand and leave it at that.

[removed comments about data - BMI data is referenced above.]

Let's get back to basics...

Where do the cells originate: Taiwan

What companies sell which cells: PSI's cells are sold by PSI, Cyclone Taiwan, Rechargeable Lithium Power, and possibly Dreifels in Switzerland. I've also purchased them from Sam at Yesa and have been happy with the sale and service. There are others.

Which cells are the same/different? If the cell is a 40138-format LiFePo4 cell, it's made by PSI. It's my understanding that PSI holds the patents for this size and their construction methods. The pictures of the 40138 cells being manufactured and tested (including the drum of Phostech material) posted on various websites (including the Electric Echo site) are the production floor at PSI, and the people seen in the pictures are PSI employees (look for the telltale green cells). Phostech material is an option for cell construction at PSI. I've been told that the addition of Phostech material during cell construction doesn't make a meaningful difference in cell performance. The performance data provided by PSI are from cells with no Phostech material.

Who works for/with whom: Mr. Raymond King was my first rep at PSI. He left the company to build his own business (EVSI). I have heard others report that he also works for LiFeBatt, but have no ability to either confirm or deny that.

When searching for personal-use cells I bought from Yesa. Later, while looking for cells to stock, I looked at PSI, LiFeBatt and BMI - each claimed to be a manufacturer. LiFeBatt had tech info but too much drama. I found one person affiliated with the BMI factory but could not get tech or performance info. PSI provided information, access to engineering staff, test parameters and results, and insight into their QA/QC system. I chose them. Each shipment of cells comes with an inspection sheet for those cells. I've never received a cell that has shown any deviation from their reported testing. I come from a military career and worked in aerospace parts QA - this is the behavior I expect from an ISO9001 registered factory that's been in the lithium cell business since 1996.

edited to update links...10max...had to rework some of the info.

 

[recumbent]

Thanks Andy for answering the questions we all wanted to here.

I bought 48 volts of rectagular LIFEPO4 cells and they only lasted me one season before they dropped to almost half the amp hrs. Perhaps it was because i drained them to LVC a few too many times, or the poor BMS, or the way they are packed into the box and not filled with the organic, iso alcohol smelling substance, like this one i took apart.

Beware of this boxy form factor is the only thing i can figure out so far, but i'm no expert, just leary about the life expectancy.
I could have bought lithium Polymere batteries with 4 Lbs less weight, smaller size, and more power for the same price. Okay, maybe more risk also.
But we are the eager test pilots, and that's how we learn.

 

[swbluto]

Thanks Andy for answering the questions we all wanted to here.

I bought 48 volts of rectagular LIFEPO4 cells and they only lasted me one season before they dropped to almost half the amp hrs. Perhaps it was because i drained them to LVC a few too many times, or the poor BMS, or the way they are packed into the box and not filled with the organic, iso alcohol smelling substance, like this one i took apart.

Beware of this boxy form factor is the only thing i can figure out so far, but i'm no expert, just leary about the life expectancy.
I could have bought lithium Polymere batteries with 4 Lbs less weight, smaller size, and more power for the same price. Okay, maybe more risk also.
But we are the eager test pilots, and that's how we learn.

Have you put any of that in water? If not, will you and post a video?

 

[recumbent]

Have you put any of that in water? If not, will you and post a video?

No I haven't, but sounds like it might be a fun experiment.

Tell me the best way to get the most spectacular effect, should it be a shallow pan so the sparks are more visible? or just in a bucket full of water?

I have a camera handy, but only one opened battery case, so it has to be done right the first time.

 

[swbluto]

If anything happens, I would think a shallow black pan would provide the greatest spark visibility, if there are going to be any sparks. I don't really know if it's pure lithium as liveforphysics believes these things are made from pure lithium sheet metal so it would react violently with water but I would think it's actually LiFePO4 metal (Lithium+iron metal with some phosphate) so I don't think it would react with water. I was under the impression that that open cell was garbage, so try to with small cut-up quantities of the sheet if you prefer for safety. Or possibly just place a drop of water on the metal and see what happens.

I would think the lithium sheet would be reflective silver. I think I see some, but I'm not sure if my eyes are tricking me - Is that some kind of brown metal surrounding a silvery metal sheet?

 

[recumbent]

I would think the lithium sheet would be reflective silver. I think I see some, but I'm not sure if my eyes are tricking me - Is that some kind of brown metal surrounding a silvery metal sheet?

The layers are: plastic, then copper, coated with black powdery paint, another layer plastic then a layer of shiny aluminum colored metal coated with black powdery paint, then plastic, layered over and over.

And it does not react with water, although it did sizzle for few minutes when i first opened it up because of the shorting plates.

 

[BMI]

Let's get back to basics.

Re:
BMI
PSI
Lifebatt

Where do the cells originate?
What companies sell which cells?
Which cells are the same/different?
Who works for or with whom?

Ok now for the answers to the above questions-
PSI manufacture and sell the original/first generation 40138 cell (the old green ones)
BMI and Lifebatt sell the latest generation grey and red cells which are an improvement on the PSI cells. The BMI and Lifebatt cells use patented Phostech LiFePO4 powder which is manufactured in Germany and shipped to Taiwan for manufacture into 40138 cells.
So to put it simply once and for all BMI and Lifebatt cells are the same and come off the same production line while PSI cells are a different cell and use non Phostech LiFePO4 powder in their manufacture.

 

[TylerDurden]

Thank you Andy and Armin...
Your information adds validity to the conjecture that PSI manufactured the cells supplied for the Sandia testing. Current BMI/LB cells (if now actually manufactured in another plant) should not be regarded as the same or better until similar third-party reports are issued.

Armin:
Phostech lithium content will be regarded as marketing fluff, until comparative analysis shows definitive relationship of concentration-to-performance improvement in 40138 cells. Furthermore, concentration levels may be altered at the discretion of the cell manufacturer and cannot be verified until a certification standard is adopted. Case in point: LB claimed their green cells had Phostech content at a time that they didn't. Don Harmon declared on this BBS that the Phostech concentration levels will remain proprietary information. No potential buyer will take a claim of "special ingredients" seriously, until testing can prove there are effective levels of concentration and certification ensures effective levels are maintained. Even further, Sud-Chemie would not likely enter into an exclusive agreement with a startup enterprise; so Phostech lithium content (if ever proven effective) might be used in any manufacturer's cells.

All:
It is common for segments of a large enterprise to break-away and form a smaller enterprise using knowledge developed in situ (often using information withheld from upper levels of management). The perceived competitive advantage may be short-lived: the older, more established enterprise can compete using reputation and economies of scale, plus legal challenges of intellectual property rights, plus outright bribery of workers to reclaim pirated process information. It should not be long before PSI offers a direct performance match to the LB red-cell, with better prices and transparent operations.

 

[BMI]

Armin:
Phostech lithium content will be regarded as marketing fluff, until comparative analysis shows definitive relationship of concentration-to-performance improvement in 40138 cells. Furthermore, concentration levels may be altered at the discretion of the cell manufacturer and cannot be verified until a certification standard is adopted. Case in point: LB claimed their green cells had Phostech content at a time that they didn't. Don Harmon declared on this BBS that the Phostech concentration levels will remain proprietary information. No potential buyer will take a claim of "special ingredients" seriously, until testing can prove there are effective levels of concentration and certification ensures effective levels are maintained.

Point 1) He who believes sales/marketing hype from Don Harmon is a fool (I am sure most people have learned this already the hard way as I have).
Point 2) Let the performance of the cells speak for themselves through an independant tester. This is why Doctorbass is testing BMI/PSI/Headway and Ping cells. There seems little point in specifications, curves, graphs, etc, being provided by any manufacturer's representatives whether myself or anyone else. There are too many skeptics out there. Let the independant results /answers come from Doctorbass since he is the only one who people believe.

 

[TylerDurden]

He who believes sales/marketing hype from Don Harmon is a fool (I am sure most people have learned this already the hard way as I have).

Marketing claims from *any* source are to be regarded with all due skepticism; Harmon merely has the distinction of being hoisted higher on his own petard-of-lies than others (so far).

There is a very good reason for suppliers providing reliable information: consumers can assess if the offerings are a match for their needs. More importantly, the suppliers that provide reliable information will be rewarded with profits that result from maintaining a reputation for delivering value.

 

[GGoodrum]

What Armin says tracks with the info I've gleaned from various sources, mainly that BMI now has their own production facility. That said, I totally agree with TD that the Phostech "hype" is just that, until we see independent proof that it makes a difference. To me it just sounds like one entity trying to get its "cut", so they imply a difference. I don't know, we'll see. Doc's tests will be very interesting indeed.

I still have two 12-cell packs from the early days when PSI and BMI were one in the same. I assume these are the same as what PSI continues to sell. I've got several hundred cycles on these packs, which normally go on the 72V/5304 setup on my wife's Townie. Sometimes I use them in conjunction with the 24s5p a123 setup I use on my Townie, for extra range. Recently I took the shrink off these packs to check the cells. They had no signs of leakage and all the cells are still very close in capacity. All are still a bit over 10Ah with a 2C load. I think one positive trait both the PSI and BMI cells have is consistancy during the manufacturing process. Most of these cells were from about 4-5 different production lots, but they were very close from day one, and they remain that way.

Here's my guess at what Doc will find. I think he will see that the BMI and PSI cells are virtually the same, but that neither are really what I'd consider 10C cells, if compared to 10C RC-type LiPos. For use in an ebike, forget the continuous and max C ratings. For everything I've tried, whatever the cell's continuous rating is, that is the max you can pull without too much voltage sag. In that context, I think a123s are good for about 25C, and my PSIs I'd rate at about 7-8C. I tried the 24s 10Ah PSI setup alone once, without the a123s, in my Townie which was capable of around 100A, at the time, and the most I could get was about 75A. I suspect that the BMIs will not be that different.

What will be really interesting is to see how the 10Ah "blue" Headways stack up. I'm guessing pretty well, maybe 4-5C. We'll see.

-- Gary

 

[Deepkimchi]

Wish Doc would take time off from drag racing to testing again. I need to buy another set of 40138 cells (and Lego mounts) before I move to Israel about 5 July. Don't think the mail room screener down there would like a bunch of cylinders showing up with terminals.

As Ypedal and I are finding, the rectangular green cells are fizzing out.

I have another older set of green Lifebatt 10ah cells which are doing fine.

Wonder who is providing what at which price?

DK