Thundersky LFP sag at 5C

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Thundersky LFP sag at 5C

Post by coulomb » Sun, 15 Feb 2009, 04:18

Weber and I are running into some questions about ThunderSky LFP cells at high discharge rates. The "Thunder Sky Instruction Manual" says that the maximum discharge current (impulse) is 10C. But the graphs seem to suggest that there is about a 0.3v drop for 1C. So 10C could only be into a short circuit. Or maybe the 0.3v sag happens over a period of time, so for short high current demands like accelerating from a stop, the sag might not be so bad.

So can anyone give any real-world data points on this? Acmotor, do you ever draw 5C; if so, for how long, and what are the sags like? Does it depend on temperature? (There is some evidence that TS cells like to be at about 60 degrees C to "wake them up" and enable higher current draws.)

We're caught between TS LFP cells and LifeBatt cells at a quarter the capacity and hence a quarter the range for about the same money (but the LifeBatts have BMS built in). Both have about the same continuous current rating (3C vs 12C/4), and the LifeBatts can surge to 14C/4. But what the TS LFP do above 3C is a bit of a mystery. We'd obviously prefer the TS for the 4x range, assuming we can afford the weight (about 300kg).

Thanks in advance for all input.

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Post by antiscab » Sun, 15 Feb 2009, 05:57

in summer, when temperatures are up around 30 deg or more,
at 3C on my bike i see 2.8vpc

i do remember when we were playing around with zilla view in robs bmw,
that his 160AH cells could put out 750A at 2.66vpc (4.7C)

so 5C from TS cells is doable, you just wont be able to do better than 3C during winter.
perhaps if you really heat up the cells, the fabled 10C is possible

are the lifeBatts similarly affected by heat?

personnally, i went for TS for the greater range for the same $$

Matt
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Post by weber » Sun, 15 Feb 2009, 20:51

antiscab wrote: so 5C from TS cells is doable, you just wont be able to do better than 3C during winter.
perhaps if you really heat up the cells, the fabled 10C is possible

are the lifeBatts similarly affected by heat?


I can't find any info on that. I'd guess they would be similar since the chemistry is the same.

The other good thing about the BMI/Lifebatt modules is the 3 year warranty. But they cost more than 3 times as much per kilowatt-hour.

It's hard to decide what's worse, only having a 30 km range (10 Ah LiFeBatt), or only having a 1 year warranty, and having to carry an extra 200 kg (40 Ah ThunderSky).

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Post by antiscab » Sun, 15 Feb 2009, 20:56

yup, its a decision alright, and you get what you pay for.

on the upside, if you get LifeBatt, you would be the first in the association to be able to test and report back on how good their modules are (that i know of).

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Post by lithbattboss » Mon, 16 Feb 2009, 01:46

antiscab wrote: yup, its a decision alright, and you get what you pay for.

on the upside, if you get LifeBatt, you would be the first in the association to be able to test and report back on how good their modules are (that i know of).

Matt
Yep....exactly right....you only get what you pay for.
Sure a BMI or Lifebatt cell might cost considerably more (initially) than a TS cell. Its is a long term investment in quality. A BMI/Lifebatt pack which has 3000 cycles/3years minimum warranty I would of thought would give more peace of mind than a TS pack with only 12 months warranty. Its a lot of dollars down the drain if you have any cell failures in just over 12 months. Do the sums yourself. Not to mention the benefits of the much higher discharge rate capability of the BMI battery.
Shaun Williams has already killed two sets of lead acid batteries in a very short time due to the steep hill he must climb from the main road to get to his house in the Brisbane suburb of Upper Mount Gravatt. Apparently a single 144V 10Ah battery module can provide more than sufficient discharge capability to power his electric Toyota Echo up his steep hill several times with ease. And this is with a single battery only! Try doing the same experiment with a TS battery and see how long it lasts.
You don't have to believe what I say (even though I know I am speaking the truth). Contact Shaun directly and I am sure he will expain exactly the actual tests he has put the BMI battery through. If you are in Brisbane even go and have a look for yourself. After all seeing is believing.
http://www.electric-echo.com/lifepo4/index.shtml

By the way LiFePO4 batteries gain capacity when heated. Performance is improved as well. This is why the A123 batteries used in killacycle are warmed up in an oven before racing.
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Post by weber » Mon, 16 Feb 2009, 02:09

Thanks lithbattboss,

You are, of course, Armin Pauza, an Australian seller of BMI/LifeBatt products.

I have already emailed Shaun Williams and asked him to respond here.

It would be useful to know if you have you offered to reward Shaun in any way for any sales he might assist you with.

Regards,
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Post by antiscab » Mon, 16 Feb 2009, 02:25

ah yes, i forgot about shaun williams

140A from smallest TS cell (40AH) isnt a problem, of course comparing a 40AH cell to a 10AH cell would be cheating (on my part :p, unless of course we are talking for the same upfront cost)

LithBattboss - how do you work out how many cycles the pack has done? does the BMS keep a record?
also, what is the definition of a failed pack under the warranty?
your website appears to just link to the US one.

Matt
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Post by Electrocycle » Mon, 16 Feb 2009, 02:29

without taking longer life span into consideration (which hasn't been real world proven yet anyway), for the same money you can get enough extra capacity in TS cells that you're only running them at ~3C to match the BMIs output at 10C, but will have much greater range (minus some extra weight penalty).

A 144v 10Ah battery is very small for an EV, but for specific short range use it makes sense.
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Post by acmotor » Mon, 16 Feb 2009, 03:07

Just pushing some numbers around here...

10Ah battery pack in BMI/Lifebatt, 3yr warr, BMS built in, 3000? cycles
At 120A this would be 12C. Considering ESR, the cell voltage would be 3.2-(120x.006)=2.48V (or higher if warm)

similar cost to but less than half the weight of..

40Ah battery pack in TS LiFePO4, 1yr warr, no BMS, 2000-3000? cycles
At 120A this would be 3C. Considering ESR, the cell voltage 3.2-(120x.004)= 2.72V (or higher if warm)

with me so far ?

The range on TS is at least 4 times as far as BMI given these Ah sizes.

The DOD on 40Ah TS is 25% for same range as DOD of 100% on 10Ah BMI
Even if the BMI gave 3000 cycles, the TS would be likely to give 5000+ cycles at that shallow DOD and in fact could deteriorate to 25% of original capacity and still do the range if 10Ah was enough in the proposed EV in the first place.

Downside... TS is heavier, a bit over twice the weight.

TS or not TS is hardly an obvious choice as some would suggest !

Follow my thinking ?
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Post by lithbattboss » Mon, 16 Feb 2009, 03:47

weber wrote: Thanks lithbattboss,

You are, of course, Armin Pauza, an Australian seller of BMI/LifeBatt products.

I have already emailed Shaun Williams and asked him to respond here.

It would be useful to know if you have you offered to reward Shaun in any way for any sales he might assist you with.

Regards,
-- Dave Keenan


Dave to answer your question, Shaun is no different to any other valued BMI customer in his reaction to the performance of the BMI battery. Many people from all over the world tell me it puts a smile on their face when they try a battery out and compare it to the performance of previous batteries they have used.
Shaun says what he wants to say entirely independantly of me. I don't pay him to say "nice things" or give him any special favours in any way. Shaun thoroughly researched the LiFePO4 battery industry before deciding to purchase his first BMI battery back in July 08.
He purchased one 144V block to start with to perform his own tests to see if all the performance claims were true. The idea was to try one battery out so he could see the exact size and see how many blocks he could fit in his car (bearing in mind the battery can be fitted in any orientation since there is no spillable liquid in the batteries).
I have no idea if in the end Shaun will buy two, three, four or more batteries for his Echo. You will need to ask him yourself.

The one thing I do know is that Shaun bought his battery at the best time possible back in July last year since the Aussie dollar was almost on a par with the US dollar at that time. The echange rate now is appalling so most people can't affort to buy good batteries here in Australia (which is a shame)due to the current state of the Aussie rupee. Thats not to say that Shaun is the only happy BMI customer. You could talk to any of the other BMI battery owners in Germany, Austria, USA, and several other countries around the world who are equally happy as Shaun is with the performance of their batteries for their various applications. Do you really think I pay all these people to "say nice things"? Quality speaks for itself and is why it costs more. After all there is a reason why a BMW or Mercedes motorcar costs more than a Holden or a Ford. Batteries are no different.

I have a large electric boat project coming up next month in Australia. This will really showcase the difference between BMI and TS batteries.
BMI are the world leaders in LiFePO4 battery technology and the battery monitoring and diagnostics area is where we really shine since we are approx. two years ahead of our closest competition in this area.

After all does a TS battery have the capability to perform an automatic test of every battery every 12 hours and if any cell in any battery pack is determined to be out of specification (or to have some other fault) an SMS is sent to the customer's phone or the customer is sent an email to inform them to check their battery?

It is this leading edge technology combined with the superior performance from a battery which uses genuine Phostech Lithium in its construction which makes it more expensive initially but a better long term investment. That doesn't just go for BMI, but any of the other LiFePO4 battery manufacturer's who also use Phostech Lithium from Canada/Germany.

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Post by lithbattboss » Mon, 16 Feb 2009, 05:11

antiscab wrote: ah yes, i forgot about shaun williams

140A from smallest TS cell (40AH) isnt a problem, of course comparing a 40AH cell to a 10AH cell would be cheating (on my part :p, unless of course we are talking for the same upfront cost)

LithBattboss - how do you work out how many cycles the pack has done? does the BMS keep a record?
also, what is the definition of a failed pack under the warranty?
your website appears to just link to the US one.

Matt


Matt, the BMI batteries contain a VMS or Voltage Management System (as distinct from a BMS)which provides the cell balancing function, error recording/logging of total number of over-charges, number of over-discharges, number of times the battery is over-temperature and it records the total number of full charge cycles. It also provides output signals to the DB9 data connectors on the front of the battery which are used to interface with external control devices. It also performs warning functions depending on voltage thresholds and provides both audible warnings (via a buzzer built in to the battery) as well as a visual warning with indicator LED's when approaching over charge (OHV)and over discharge (OLV) conditions. It also performs other functions related to battery warning via the worldwide electric vechicle alerting system known as GlobeTRAC and allows communication between up to 255 separate battery packs via an RS232 network.

Only full/deep charge cycles are recorded so no partial/shallow cycles are recorded in the VMS. Therefore the warranty in most (if not all) EV applications would be based on time rather than cycles (3 years rather than 3000 cycles). For certain approved applications this warranty is extended to 5 years.

Yes my Australian website has been disabled since there will be a new up to date LBA/BMI website which is expected to be online in the next two weeks. This will have the most current information and will go a long way to answering many questions people have regarding the batteries, how they work and other areas where I find many people are very confused (such as the meaning of cell bar code numbers, difference between green 40138 cells compared to grey 40138 cells as well as a host of other information.

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Post by weber » Mon, 16 Feb 2009, 05:27

lithbattboss wrote:
Shaun says what he wants to say entirely independantly of me. I don't pay him to say "nice things" or give him any special favours in any way.


My apologies Armin,

I didn't mean to offend either you or Shaun. I'm sure you sell the product because you believe in it, not the other way 'round. And it's great to talk to an engineer rather than just a saleman. However I feel that readers should know about any related commercial interest on the part of the advice giver, so they can make up their own mind.

You declared your commercial interest with your very first post back in August 2008. But I was concerned newer readers might not be aware.

If this time next year the new 14 Ah BMI/Lifebatt cells are no more expensive than the 10 Ah are now, and they can provide the same continuous current (which would only be 8.5C), and if they come with a 5 year warranty for EV use (why not, since the built-in BMS can verify any warranty conditions?), then I think they may be in with a chance.

And I have to admit to lusting after the capabilities of that built-in BMS. :-)

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Post by mjcrow » Mon, 16 Feb 2009, 06:15

OK, I'm not trying to step on anyones toes here, but there is another alternative to TS or Lifebatt or PSI, they are called Headway, a lot of e-bikers are using them with good results, and they are priced pretty much between TS and Lifebatt, so a possible compromise. They do packs of various sizes, and loose cells, the packs can be ordered with BMS installed, and they have a variety of BMS types to suit different applications. If you want more info, discharge rates, etc, there is heaps of info over on Endless Sphere forums. The direct contact at Headway is Victoria (her English is quite good) email: market@headway-cn.com or chcj55@gmail.com they also give discount for large orders (over 1000 cells or equivalent) remembering most of their cells are 38120s 10ah 5c LiFePO4. Approx pricing (from one of the threads on ES is 72v 20Ah (48 cells) pack $910USD FOB China including BMS.

These are the ones I would be buying if I was ready to buy, I have researched quite a bit and these seem to be the best bang for the buck that are reputable (there are some cheap and nasty batteries out there) and come with BMS and Charger. It is also good to see independant testing comfirming the quality of the products (see the Discharge Curve Thread linked below). Headway don't use Phostech, although I think they will if you request it with a large quantity order and pay a premium. I am yet to see any hard research done showing what improvement is made by using Phostech, so if anyone has that info please post it.

Some related Headway cell threads Discharge Curve Thread, Inside the Cells, Pics of the factory, Comparison of some premade packs

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Post by lithbattboss » Mon, 16 Feb 2009, 06:47


My apologies Armin,

I didn't mean to offend either you or Shaun. I'm sure you sell the product because you believe in it, not the other way 'round. And it's great to talk to an engineer rather than just a saleman. However I feel that readers should know about any related commercial interest on the part of the advice giver, so they can make up their own mind.

No apology required Dave.
Thats what these forums are good for. To answer peoples questions and to learn from the experiences of others. As an electrical engineer and a licenced electrical contractor with considerable experience in industrial electronics including variable AC and DC motor drives in industry I learn a great deal from others in this and similar forums.

Whether you agree with me or disagree it doesn't really matter because we are generating some healthy debate which is good for everyone.

All I can speak about is my own experiences and since I have over the course of my time in recent years as an engineer in the critical power industry having installed literally thousands of batteries of various chemical composition for companies such as IBM, Apple Computer, BHP, GE, Esso-Exxon Oil, McDonalds and many others too numerous to name here I consider myself quite fortunate to have an undertanding of the battery industry and the pros and cons of most of the battery types and companies concerned.
I always provide accurate, factual and truthful information so if there is anything I say which you disagree with please let me know so I can clarify the situation in more detail.

There are many new suppliers of LiFePO4 batteries popping up daily and jumping on the EV battery bandwagon. Many of these companies are just sales companies with very little technical knowledge regarding the products they sell. At least as an engineer I can explain in detail about the products I supply and you have the comfort of knowing you are dealing with someone locally here in Australia rather than trying to communicate with someone in China or some other foreign country.

Everyone can decide for themselves and form their own opinion about different brands of batteries, motors, motor controllers, etc.
The only question I would ask is if ThunderSky wants to enhanse its reputation by showing it sells a reliable product why doesn't it offer 3 years (or longer) warranty also?

If a company won't back its own product with a lengthy warranty then why should a customer of that company have more faith in the product they provide than the manufacturer themselves?


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Post by antiscab » Mon, 16 Feb 2009, 06:54

yeh, ive seen the headways aswell (especially the ones with the bolt on terminals, similar to the PSI cells)

the K2 cells seem to be even more powerful (20C+), except they need tab welding.
Ian Hoopper's playing with those in his mx5 i think

lotsa different cells to play with.

If you need high power and pre-made packs, then LifeBatt would be the way to go.
if you dont need high power, then id be more inclined to go TS

it just depends on your project and goals

Matt
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Post by weber » Mon, 16 Feb 2009, 08:20

lithbattboss wrote: If a company won't back its own product with a lengthy warranty then why should a customer of that company have more faith in the product they provide than the manufacturer themselves?


I totally agree. Take the price, divide by the warranty period and divide by the amp-hours. Which has the lowest dollars per amp hour per warranty year?

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Post by weber » Mon, 16 Feb 2009, 10:02

Another thread on the Headway cells. Seems the odd dud cell gets shipped.
http://www.endless-sphere.com/forums/vi ... &start=195
Last edited by weber on Wed, 18 Feb 2009, 04:46, edited 1 time in total.

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Post by lithbattboss » Mon, 16 Feb 2009, 19:11

The Headway cells are not too bad for a "mid-performance" Chinese cell (I actually know the North American Distributor for Headway).
My only main concern is the quality control (lack of). This is why sometimes people receive bad cells.
Also the measured cell impedances are all over the place as you can see here (half way down the page)-

http://endless-sphere.com/forums/viewto ... &start=285

The results from the second lot of testing are much better than those of the first tests but how can you be sure you will be sent all good cells. Maybe they have resolved the QC issues?

If you are using a pack made from Headway cells make sure you use a very good BMS because if you don't you risk damaging cells due to imbalance occuring due to the varying cell impedances.
I have heard of instances in the US where some Headway e-bike packs have failed afer only a short period of use. I think this is not so much a problem with the actual cells but more to do with the BMS which is used.


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Post by weber » Wed, 18 Feb 2009, 16:03

Here's what I emailed to Shaun Williams (Electric Echo)
weber wrote: Hi Shaun,

A friend and I, in Brisbane, are planning to do an AC electric conversion of a 1990's Mazda MX-5 (2 seater sports car). We have benefited greatly from your website and seeing the car and hearing your talk at the Albion Peace Centre some years ago. Thank you.

Our battery pack would need to be in the range of 300 to 600 volts, preferably the latter. We have a tough choice to make between two sets with approximately the same cost, (about $14,000) and the same current capabilities (120 A continuous):

BMI/LifeBatt 10 Ah (from Armin Pauza)
Pros:
    Only 100 kg pack
    Less space required
    3 year warranty
    Built-in BMS
Cons:
    Only 30 km range

ThunderSky 40 Ah    (from Ross Blade)
Pros:
    120 km range
Cons:
    300 kg pack
    More space required
    Only 1 year warranty
    Have to build own BMS

Ideally we'd like something in between. e.g. 200 kg with a 60 km range and 2 year warranty would be fine. But there is no such option.

As the only person in Australia with any EV experience of BMI/LiFeBatts, would you be so kind as to give your opinion on this vexed question. And so others can benefit, could you please do it in this thread in the AEVA forum?

viewtopic.php?t=956&p=9136#p9136

Many thanks.
-- Dave Keenan
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And here is Shaun's reply (with permission):
Shaun Williams wrote: Hi Dave,

Cool ride! That reminds me...I wonder how Ian Hooper's (ZEVA) MX-5
conversion is going? Not much on his website recently.

Anyhoo excuse me for not posting this on the forum because I'm too lazy to
register but feel free to cut and paste if you consider anything worthwhile
in this reply... :-)

Arrghh! I remember that talk at Albion I think I upset a few Prius owners
and Solar Panel resellers that night! I had one serious case of
foot-in-mouth that night.

600V's, that's a mighty high voltage! Whose AC are you using MetricMind?

Nice to see some sensible (read: realistic) range figures, you've obviously
been doing your homework.

Ok, I don't have much BMI experience yet as I've only cycled my test battery
a couple of times but here's my thoughts so far;

The BMI "BMS" still requires some external electrickery to stop the battery
going over/under voltage when the VMS detects and signals an out-of-limits
sample. This can be relays to o/c the charger/controller or a big fat
solenoid contactor.

If you are going to have a single string of around 200 cells you need to be
sure that the battery balancing circuitry works really well because if 1
(ONE) of those cells gets badly out of balance then the whole pack is at the
mercy of that one weak cell. For me the jury is still out on the BMI battery
balancing circuitry as it uses tiny little SMD resistors covered in heat
sinking compound to dissipate the shunted current of the fully charged
cells. This may work fine but I'll have to do at least 30 cycles before I
can be more confident.

Of course, when you win Lotto you can drop another 100kg of BMI Lithium in
parallel with the existing pack but this adds another complication... If a
cell fails in one string then the other buddy string will dump as much
current as it can into it until the voltages equalize. This has the
potential (albeit remote) to damage the crippled string even more, although
isolation contactors on each string should fix this problem.

BTW, re the TS option; will 300kg push your vehicle over GVM which might
complicate registration?

Hope this has been at least a little helpful. Anyways, I guess your next
question will be "When do you expect to have done 30 cycles on the BMI?".
:-)

Cheers,

Shaun Williams.
Last edited by weber on Wed, 18 Feb 2009, 05:06, edited 1 time in total.

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Post by Electrocycle » Wed, 18 Feb 2009, 17:45

yeah I thought the BMI BMS's 100ma shunt capacity could be a bit low, but since the cells should be very well matched it *shouldn't* cause a problem.
If a cell gets even slightly out of whack you won't be able to charge at any decent rate without getting an over voltage on a cell before the rest are fully charged.
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Post by antiscab » Wed, 18 Feb 2009, 19:42

100ma on a 10AH cell is more than sufficient.
the 700ma balancer that i have on my 40AH cells are also used on the bigger 200AH cells.

LiFePO4 doesnt fall out of balance that quickly, you need some way to balance it every so often. if you balance on every full charge with a BMS, then you can get away with low balancing current.

Matt
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Post by acmotor » Wed, 18 Feb 2009, 20:10

Jury is still out on that one.

A new pack of cells nicely balanced is OK but as they age it could take a day to re-balance 10% battery Ah and the need for a charger with 100mA trickle mode.

As you know, battery life is stated as the number of cycles/years for the effective capacity to reduce to around 60% of original. That also means there is likely to be some spread of cell capacity as the pack ages. True, the capacity of the pack is always limited by the weakest cell, but what tends to happen is the stronger cells never get fully charged and end up failing.

The other issue is the ability to use regen.
As the shunt balance Amps reduce, the near full battery (or unbalanced pack) regen becomes more difficult.

Limited shunt balance also limits the charge rate.

I am using around 5% shunt balance on my TS cells.
iMiEV MY12     110,230km in pure Electric and loving it !

antiscab
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Real Name: Matthew Lacey
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Thundersky LFP sag at 5C

Post by antiscab » Wed, 18 Feb 2009, 21:47

thats true.

I would expect Rob would encounter balance problems in his mustang first since hes using Rods 0.7A balancers on 200AH cells.

If not, then i would, since i have the most heavily cycled cells (i think? im at 16'000km with a 40km range to 80% dod, so say 400 80%dod cycles equivalent. can anyone top that?).
but then again im using the same 0.7A balancers on my 40AH cells

the float mode on most SLA chargers would be sufficient for balancing, as long as it works out to more than 3.6vpc (assuming using Rods BMS).
that pretty much works out to 15cells to each 48v charger.

anyway, if being left balancing overnight every night doesnt keep your pack balanced.... IMHO, i would say your pack is at the end of its life

regen does indeed make things more complicated.
ACmotor - have you tried no current limit constant voltage charging on a string of 90-95% charged cells?

Matt
Matt
2017 Renault zoe - 25'000km
2007 vectrix - 156'000km
1998 prius - needs Batt
1999 Prius - needs batt
2000 prius - has 200 x headway 38120 cells

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acmotor
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Thundersky LFP sag at 5C

Post by acmotor » Thu, 19 Feb 2009, 03:08

More info ?
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antiscab
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Thundersky LFP sag at 5C

Post by antiscab » Tue, 24 Feb 2009, 08:25

by no current limit constant voltage charging,
i was refering to testing to see how a pack would behave when you are doing regen, and the controller is using a dump load to hold the pack at the programmed max voltage.
In this case, the pack would be operating with a voltage limit, and a current limit well above what the pack can absorb.
would some cells shoot ahead of 4.2vpc?
at what SOC would they shoot ahead?

i was wondering if you had tested for similar charge acceptance rates across a pack.

Matt
Matt
2017 Renault zoe - 25'000km
2007 vectrix - 156'000km
1998 prius - needs Batt
1999 Prius - needs batt
2000 prius - has 200 x headway 38120 cells

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