# Experienced Very-High Headway Self-Discharge?



## coryrc (Aug 5, 2008)

Hi all,

I have many Headway cells which arrived ~2 months ago and nearly all measured 3.3V (the bad ones were thrown away). Shortly thereafter, all the good ones were charged to 3.65V in parallel. Never exceeded 3.65V. Then they were stuck in a box with foam insulating each cell.

I just checked today and many range from .7V to 3.20V.

They are fairly evenly spread in three groups:
3.32-3.33V (expected)
3.26-3.30V
0.70-3.20V

My only hypothesis is high self-discharge. I am going to do some cycle tests on the ones above 1.1V to see if they meet their Ah rating.

Anybody else notice Headway cells with this problem?

Thanks,
Cory


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## steven4601 (Nov 11, 2010)

Do you have a histogram of the voltage levels?
or how many of total are bad?


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## rwaudio (May 22, 2008)

steven4601 said:


> Do you have a histogram of the voltage levels?
> or how many of total are bad?


I have a small batch that have never dropped a measurable amount in 2 months. They drop to 3.3xV after a day then stay there.


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## cbliss (Jun 28, 2010)

Can't speak of Headway, but have experience with Thundersky and A123. 3.3x would be normal for a reasonably charged battery that has been sitting. I have seen good batteries from 2.28 to 3.32 with 3.30 and 3.31 being the average. When you charged to 3.65, did you allow adequate time for all to attain a full charge? A problem with parallel charging is some of the batteries may be pretty full while others are still low. 

I have just under a hundred cells that have been in crates for months with the factory charge and I measure them periodically. The lowest is 3.29 and the highest 3.31 They have remained unchanged. I have yet to put a full charge on them. When I do charge them, it will be under BMS control and I will know which ones are doing what.

The ones with .7 volts sound pretty bad. Did you really chuck them, or send them back under warranty. When taking delivery of new batteries, you should immediately check the voltage and notify the vendor of any low cells at the time of delivery.


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## coryrc (Aug 5, 2008)

steven4601 said:


> Do you have a histogram of the voltage levels?
> or how many of total are bad?


I guess it is still pretty bad, but now that I've seen them myself, not quite as bad as I relayed before:

After ~2 months:
Out of 80, any not below are 3.32-3.33V (i.e. good, expected)
8 are between 3.28-3.30V
19 are between 3.20-3.28
5 are between 3.00-3.20
3 are between 2-3
2 are < 1

Previous batches are just fine. Just wondering if anyone who has bought in the last couple months and hasn't used their cells yet has noticed a self-discharge issue.


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## coryrc (Aug 5, 2008)

cbliss said:


> When you charged to 3.65, did you allow adequate time for all to attain a full charge?


Yes, they were left on a charge of 3.65V until the current was below 2.6mA per cell.



cbliss said:


> The ones with .7 volts sound pretty bad. Did you really chuck them, or send them back under warranty. When taking delivery of new batteries, you should immediately check the voltage and notify the vendor of any low cells at the time of delivery.


Hmm, this batch actually didn't have any bad ones fresh off the boat (previous orders had only a couple and it wasn't worth shipping). Sorry for the bad information.


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## Tesseract (Sep 27, 2008)

Hi coryrc... we have seen this with Headway cells, too. It seems to be a factory defect type of problem - a contaminant in the electrolyte and/or solvent that causes the batteries to self-discharge in short order. A properly built LFP cell has essentially no self-discharge at all. I have an old school TS 200Ah cell that I have checked every week or so over the last 18 months and the voltage hasn't budged a bit.

Unfortunately, these cells need to be tested for capacity, internal resistance and, apparently, self-discharge rate at incoming inspection. Needless to say, once you've done all of that - as a business, anyway - you then need to charge A123 prices to recover your labor expenses.


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## frodus (Apr 12, 2008)

I had some self discharge, but that was after a year of sitting without any charge. they came back, and apear to have acceptable discharge capacities.

Where did you get them? It's possible they sat around.


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## coryrc (Aug 5, 2008)

Tesseract said:


> Hi coryrc... we have seen this with Headway cells, too. It seems to be a factory defect type of problem - a contaminant in the electrolyte and/or solvent that causes the batteries to self-discharge in short order.


Bummer. In our latest batch, even the "good" cells averaged 10% loss per month (measured by charging until 3.65V -- took 2 hours at 0.1C).


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## coryrc (Aug 5, 2008)

frodus said:


> I had some self discharge, but that was after a year of sitting without any charge. they came back, and apear to have acceptable discharge capacities.


We have some bought a year ago (from EV Components FWIW); of four that were never used, two are still >3.3 and the other two are above 3.0V.



frodus said:


> Where did you get them? It's possible they sat around.


They came straight from Headway via boat. Hmm, in our original batch from EVC, about 5% were bad (<3.25V). But this time *none* were. If they sat around at EVC for even a short time, perhaps that was a decent-enough self-discharge test. This time, about 10% were terrible after a couple months -- not too far off from the original.


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## jackbauer (Jan 12, 2008)

What build code is on the cells? Is it the same across them all?


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## frodus (Apr 12, 2008)

coryrc said:


> We have some bought a year ago (from EV Components FWIW); of four that were never used, two are still >3.3 and the other two are above 3.0V.
> 
> 
> 
> They came straight from Headway via boat. Hmm, in our original batch from EVC, about 5% were bad (<3.25V). But this time *none* were. If they sat around at EVC for even a short time, perhaps that was a decent-enough self-discharge test. This time, about 10% were terrible after a couple months -- not too far off from the original.


 
Mine were from a year ago, and AFAIK, that was the last batch we imported. If you let them sit, they will discharge over the course of a year. Mine did and I had like 4-5 out of 200 that were lower than 2V, the rest were just fine. I'm almost done charging them. They do NOT ship the cells fully charged, so you need to charge/cycle them when you get them.

Bad is not <3.25V, bad is more like below 2.0V, which is the LVC of a cell. So anything past that is overdischarged. The knee is pretty sharp though, so I'd say anything below like 2.5V. But it all depends on if you charged the cells to begin with, they're not fully charged to start.


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## coryrc (Aug 5, 2008)

Tesseract said:


> Hi coryrc... we have seen this with Headway cells, too.


Oh, and did/do they replace the bad ones for you?


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## coryrc (Aug 5, 2008)

jackbauer said:


> What build code is on the cells? Is it the same across them all?


Hmmm, good thought. I assume the middle 4-character thing is the date code? Is the last number a serial number?

The "perfect" ones (3.32V two months after charge) were a mix of JK19 and JK18. No JK19-series were less than perfect.

All the other categories were a mix of JK17 and JK18.

The two worst cells (under 1V) were JK17.

Hmmm. I guess we'll demand replacements of all the JK17 at least. Hopefully the JK18 as well.


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## coryrc (Aug 5, 2008)

frodus said:


> Mine were from a year ago, and AFAIK, that was the last batch we imported. If you let them sit, they will discharge over the course of a year. Mine did and I had like 4-5 out of 200 that were lower than 2V, the rest were just fine. I'm almost done charging them. They do NOT ship the cells fully charged, so you need to charge/cycle them when you get them.


They were all fully-charged within two weeks of receipt at the most.



frodus said:


> Bad is not <3.25V, bad is more like below 2.0V, which is the LVC of a cell. So anything past that is overdischarged. The knee is pretty sharp though, so I'd say anything below like 2.5V. But it all depends on if you charged the cells to begin with, they're not fully charged to start.


Anything with that much self-discharge after only two months is unacceptable in my book. 3.28V at no current is almost empty! Well, I think. Time to do some capacity tests.


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## frodus (Apr 12, 2008)

coryrc said:


> They were all fully-charged within two weeks of receipt at the most.


hmm, then if the ones below 2V are that low, they may be bad. Did this batch you're talking about come from Headway direct? Let me know how the warranty replacement works out.





coryrc said:


> Anything with that much self-discharge after only two months is unacceptable in my book. 3.28V at no current is almost empty! Well, I think. Time to do some capacity tests.


not really, but you should match cells in parallel if you can. Voltage is not an indication of State of charge with lithium. Do a discharge test/capacity test and see how they perform.


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## steven4601 (Nov 11, 2010)

Almost true!
Lithium Polymer does tell its SOC by its voltage though. 

Odd fact is that they refer to them as 3.7V cells, but in reallity they are 4.2V when full and empty at 3.6..3.7V. The voltage slope is linear in between between the two states.


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## frodus (Apr 12, 2008)

steven4601 said:


> Almost true!
> Lithium Polymer does tell its SOC by its voltage though.
> 
> Odd fact is that they refer to them as 3.7V cells, but in reallity they are 4.2V when full and empty at 3.6..3.7V. The voltage slope is linear in between between the two states.


Not really correct.... RC people use Voltage because they're pulling such high C at a constant rate that it apears to be less of an S curve, with the middle part being more linear. With EV people using them under varying discharge rates, with stops and goes, SOC is not indicated by voltage. All batteries have an S curve. If it was linear, they'd be more like capacitors. I've never seen a battery that had a linear discharge curve.

A test I did:
Kokam (lipo) 7.5Ah test at 5C (I've got higher discharge rates, I think up to ~15C which was the limit of my setup)

Ran at ~37.5A for ~12.5minutes (I ran some before and some after for reference).
Got to ~113degrees F
Started at 4.21V and ended at ~2.7V


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## steven4601 (Nov 11, 2010)

Well the big flat spot in the middle with LiFe is not present with LiPo's.Perhaps due to the large voltage difference between full and empty.

Back on topic,
I am interested in how this Headway battery self-discharge issue turns out. Just ordered 400+ 38140S cells and this post is making me a bit worried


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## frodus (Apr 12, 2008)

steven4601 said:


> Well the big flat spot in the middle with LiFe is not present with LiPo's.Perhaps due to the large voltage difference between full and empty.


_Actually,_ that big flat spot _is_ present in lipo, and other chemistries of batteries that I've seen, but it all depends on your rate of discharge on how flat it is. At 1C I could see a very flat part in the middle. True that it does act differently than Lifepo4, but it's still an S-curve, and it's not linear. The higher discharge rates, the _closer_ to linear falling curve it gets, but for how we use these cells, voltage is not an indication of SOC, and your assumptions only work for cells under constant load. As soon as you let off the load, your voltage comes back up. 



steven4601 said:


> Back on topic,
> I am interested in how this Headway battery self-discharge issue turns out. Just ordered 400+ 38140S cells and this post is making me a bit worried


I wouldn't worry too much, but I would get some sort of discharger or some sort of IR measuring device so you can match cells. If you match cells in parallel you should be just fine. Weed out the few cells that might not meet your spec. That's what I've done, albeit slowly.


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## coryrc (Aug 5, 2008)

frodus said:


> hmm, then if the ones below 2V are that low, they may be bad. Did this batch you're talking about come from Headway direct? Let me know how the warranty replacement works out.


 Yes and will do!



frodus said:


> not really, but you should match cells in parallel if you can. Voltage is not an indication of State of charge with lithium. Do a discharge test/capacity test and see how they perform.


Not entirely true. At rest voltage does show SoC even with LiFePO4, it's just 20-30mV from 80%-20% (or somewhere around there... I don't have a copy of this spec). But even if it weren't, if the cell should be anything but empty at 3.32V, then less must be empty or very near!

This application requires low self-discharge, which is why any change over 2 months is unacceptable.


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## frodus (Apr 12, 2008)

Haven't heard that before, if you've got more info on SOC related to the resting voltage of a cell for lifepo4, I'd love to read up more on it.

Well, get with headway. Most of mine that have been sitting for a year, without any initial charging, were above 3.3V each. I only had maybe 4 out of 200 that weren't. Maybe they can give you replacement cells.

Good luck, let us know.


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## coryrc (Aug 5, 2008)

frodus said:


> ... Let me know how the warranty replacement works out.


*blink*

*blink*

They agreed they had some bad batches (JK15 and JK17 seem to be terrible, some in JK18) and to replace all the bad cells, which ended up being 2/3 of them.

Wow. I'm very impressed with Headway.


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## frodus (Apr 12, 2008)

WOW, good on them!

are you shipping the bad ones back?


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## Beemer (Jun 2, 2011)

coryrc said:


> Hi all,
> 
> I have many Headway cells which arrived ~2 months ago and nearly all measured 3.3V (the bad ones were thrown away). Shortly thereafter, all the good ones were charged to 3.65V in parallel. Never exceeded 3.65V. Then they were stuck in a box with foam insulating each cell.
> 
> ...


Cory, the $64,000 question:
What did you use to charge these cells to reduce some perfectly good Headways into poorer cells than received?


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## coryrc (Aug 5, 2008)

Beemer said:


> Cory, the $64,000 question:
> What did you use to charge these cells to reduce some perfectly good Headways into poorer cells than received?


Huh? The factory acknowledged they sent us a bad batch of batteries and has already sent the replacements. As well, others have chimed in acknowledging this as a problem.

So, to answer your loaded question, an earlier model of this rack-mount, super-expensive 0-8V power supply set to 3.65V and not compensating for voltage drop (so they never exceeded 3.65V):
http://www.sorensen.com/products/xg1500/XG1500_Overview.htm


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## coryrc (Aug 5, 2008)

frodus said:


> Bad is not <3.25V, bad is more like below 2.0V, which is the LVC of a cell.


The context of this post is the OC voltage after resting two months. I promised a follow-up and here it is.

We charged a group of 10 cells from the bad date code with an approximate resting voltage of 3.28V +/- 10mV. They took nearly 100Ah of charge, so they had self-discharged nearly 100% in two months, which is way too high for our application.


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## Beemer (Jun 2, 2011)

100% self discharge in two months is worthy of total prostration, a written apology and personally checked cells, hand delivered.

Will you let us know how the replacement cells perform?

Worrisome, I was considering buying a case of 10, 60V 50AH headway packs for my trike project.


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## jackbauer (Jan 12, 2008)

Very odd. I've been running a 48s4p pack of 16ah cells in my car for the past 3 months. No bms. No balancing. If they drifted even a small percentage i'd have had my own personal fouth of July by now.


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## frodus (Apr 12, 2008)

I've had only a couple cells that ended up self discharging that much out of 230 or so cells. 

Realize also, they don't ship them fully charged. 

I think it was a bad batch, I know many many customers that have had no problems like this high self discharge.


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## coryrc (Aug 5, 2008)

Beemer said:


> 100% self discharge in two months is worthy of total prostration, a written apology and personally checked cells, hand delivered.
> 
> Will you let us know how the replacement cells perform?
> 
> Worrisome, I was considering buying a case of 10, 60V 50AH headway packs for my trike project.


We have many Headway cells of various ages doing just fine. It was just a bad batch. But as Travis mentioned, there are occasionally a few "bad" cells in every group.


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## frodus (Apr 12, 2008)

that was from a group over a year ago, and I left them sitting, in a garage, and hadn't touched them the entire time. Only a couple below 2V, and they came back just fine. Slow self-discharge didn't seem to hurt. I'm not putting it in my pack, but I'll be using it for my 12V aux battery.

Just make sure you buy from a company that has a warranty.


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