Lithium batteries v/s NiMH batteries the Debate! Battery technologies

In view of the intensity of the debate between Mik and John, relating to different battery technologies. I thought it may be of interest to have a wider range of views about battery technology. After all the heart of any EV is the performance of the battery, so this should be a subject for some really creative contributions and ideas!

Gentlemen???......

Well, the only person that I know who seems to rate NiMH as a "better battery for BEV's" than LiFePO4 is Mik. The majority sees LiFePO4 (and other Lithium chemistries) as superior.

LiFePO4 advantages:
- they have better energy density
- they have better power density
- they have better cycle life for deep cycles
- the base materials are far less expensive and more abundant

NiMh advantages:
- more robust to low voltage abuse
- proven to last hundreds of thousands of cycles in real world "low stress" applications (parallel hybrids like Toyota Prius and Ford Escape)

And on the downside:

LiFePO4 - not much in the way of real world history
NiMH - shown in a real world application to need a good BMS and charging regimen otherwise shortened life should be expected.

Both LiFePO4 and NiMH need a good BMS and need to be operated within their operating parameters.

Any argument Mik puts forth about the BMS for a LiFePO4 system would, IMO, appear to apply equally well to a NiMH system. Look at the Vectrix and the Vectux as real life examples.

But, I suppose NiMH is better if you decide to run a pack without even the most basic low voltage cutoff protection. However, that seems like a pretty weak reason to invest time, effort and/or money in NiMH development - unless your bike already has a NiMH charger...

Mik - you're barking up the wrong tree with this one. Turn your unquestionable talents to somewhere you can get a bigger bang for your buck...

I suggest reading through the electric_vehicles_for_sale group on groups.yahoo.com for an alternate view of NiMH .vs. Li-ION. That mailing list is dominated by Doug Korthoff whom you may remember from Who Killed the Electric Car (he had a couple scenes one of which was to give chase in his RAV4-EV to a truck full of EV's headed to a ship at the Port of LA). He leased an EV1 and owns a RAV4-EV. WARNING that mailing list is a hotbed of conspiracy style thinking.

I gather his claims are

- NiMH is the only chemistry proved in real use in real vehicles to have 100,000+ mile range
- LiION cannot make that kind of total life range
- NiMH has been prevented by Cobasys from being used in vehicles for some unknown reason (he points to oil company ownership of Cobasys)
- Li-ION is expensive

Uh.. he may have more than that, it's all I can come up with this early in the morning. He does have a tendency to rant so maybe the flood of words hides a small set of points.

Anyway - The NiMH used in the RAV4-EV is different than the NiMH we usually use on bicycles etc. These are large format cells (95 AH) and of course Toyota put in a good BMS. There are several hundred RAV4-EV's still on the road some of whom have gone past 100,000 miles. I've had the opportunity to ride in two RAV4-EV's one time on the highway (BTW immediately after meeting Chris Paine) and it seemed like a very competent SUV. It was a very normal ride and easy to forget we were being driven by electrons rather than gasoline.

It is true that for some reason Cobasys didn't allow vehicular use of NiMH chemistry. I used to own shares of Energy Conversion Devices (one of the parents of Cobasys) and every time they mentioned NiMH licensing the agreement included "no vehicular use". That did lead to a lawsuit against some companies who used small cell NiMH in hybrid cars. The lawsuit led to the creation of Cobasys. ECD and Cobasys has long had partial ownership from oil companies. There are many claiming the oil company involvement is behind the "no vehicular use" clause in NiMH licensing. Cobasys recently sold the NiMH patents to a Chinese company.

In one electric_vehicles_for_sale message Doug did say something about Gold Peak (the supplier to Vectrix) having an early NiMH licensing agreement which did not preclude them from using NiMH in vehicles.

To put my own opinion into the pot..

I've tried NiMH for bicycles and been left with a bad bad experience. Woefully underpowered and never got it to work well. That is the D cell NiMH have a 10A discharge rate but my bicycle had a 35A controller and this taught me the importance of looking at the spec's more carefully than I had. Later I tried a set of parallel SubC cell packs that had the correct discharge rate but still didn't provide enough power for the bike and were tricky to get charged properly. Also my experience with NiMH AA cells in portable electronics is bad because they have a high self discharge rate and most of those batteries I have don't hold a charge.

Of course this is without BMS. Maybe with a BMS it would have been a better experience. But who sells small scale NiMH packs with BMS? I never heard of BMS's until lithium packs came along.

Maybe oh maybe if Cobasys had allowed vehicle use we'd have a different opinion going on. As it stands the only NiMH packs we can build are from cells meant for portable electronics, not for vehicular use.

In the Li-ION world I've got pingping packs that are still going great after a year. On the other hand I have a pack of Headway 10AH cells that have never been used because cells keep going bad. The fault there seems to be whenever the BMS wire to one of the cells gets loose then that cell goes bad, so something about the BMS is killing cells if the BMS wire gets disconnected. The point is that Li-ION cells will quickly go bad when over-discharged. Hence you must have good protection against both over-discharge and over-charge.

I don't know enough to know whether a full BMS is required (e.g. with balancing functions) or whether simply LV and HV protection is required.

Alternate view of NiMH .vs. Li-ION.

Please note I am talking of Lithium Iron Phosphate = LiFePO4. Not any other Lithium based chemistry. Just as Mik is speaking of NiMH not NiCad.

It's an important distinction.

You make a good point bringing up the RAV4-EV. That would seem to be flying in the face of the current auto makers concerns that NiMH isn't the right choice for BEVs. I wish I'd have raised that question at the SAE meeting. Darn!!!

However, I still contend LiFePO4 is the better choice when compared with NiMH.

I'll read the rest of your posts in more detail but I wanted to point out that LI-ION is not the same as LiFePO4 and in this discussion the specifics are important.

LI-ION is not the same as LiFePO4

I'm aware that LiFePO4 is a specific chemistry but I've always been using "Li-ION" to refer generically to all lithium battery chemistries. Maybe that was wrong..?

LI-ION is not the same as LiFePO4

I'm aware that LiFePO4 is a specific chemistry but I've always been using "Li-ION" to refer generically to all lithium battery chemistries. Maybe that was wrong..?

I think you are correct that Li-ION can be used to cover all chemistries. However, I've often heard people use it when referring to LiPo (which stands for Lithium Polymer NOT one molecule of Lithium and one molecule of Polonium).

However, in this "debate" my commentary is only directed towards LiFePO4 and there are enough fundamental differences between say, LiFePO4 and LiPo that I think any argument that attempts to lump all Lithium chemistries together is likely to be somewhat flawed. Just as I wouldn't try and lump the characteristics of NiCad and NiMH together.

Can I claim a KO in round one if Mik fails to show? ;-)

How about from the perspective of upside potential? Which technology shows the most potential for developing into something more powerful? Or will both technologies wind up being passed over for a superior technology in the next few years?

How about from the perspective of upside potential? Which technology shows the most potential for developing into something more powerful? Or will both technologies wind up being passed over for a superior technology in the next few years?

From: http://www.batteryuniversity.com/partone-5A.htm

Lithium-ion has not yet reached full maturity and the technology is continually improving. The anode in today's cells is made up of a graphite mixture and the cathode is a combination of lithium and other choice metals. It should be noted that all materials in a battery have a theoretical energy density. With lithium-ion, the anode is well optimized and little improvements can be gained in terms of design changes. The cathode, however, shows promise for further enhancements. Battery research is therefore focusing on the cathode material. Another part that has potential is the electrolyte. The electrolyte serves as a reaction medium between the anode and the cathode.

The battery industry is making incremental capacity gains of 8-10% per year. This trend is expected to continue. This, however, is a far cry from Moore's Law that specifies a doubling of transistors on a chip every 18 to 24 months. Translating this increase to a battery would mean a doubling of capacity every two years. Instead of two years, lithium-ion has doubled its energy capacity in 10 years.

from: http://www.nsti.org/Nanotech2009/abs.html?i=1317 - speaks of a 10 fold increase in capacity over today. However, expect it to be 5 or 10 years from coming out of the lab.

The theoretical specific energy of lithium metal/aqueous couples is greater than 10,000 Wh/kg and commercial batteries are expected to exceed 1000 Wh/l and Wh/kg.

In the nearer term these guys: http://www.seeo.com/index.html are apparently claiming 300 Wh/kg.

At the SAE conference the two companies who talked about advanced battery research the most were Ford and Toyota. If I remember Ford was looking in advances of solid state batteries (which I believe uses a ceramic instead of electrolyte) and Toyota was pushing forward with Lithium/Air batteries.

Exciting times!

p.s. no one was pushing forward with Nickle.

Can I claim a KO in round one if Mik fails to show? ;-)

You can claim a KO once you can show me a few Lithium battery EV's that have passed the 10,000km, 20,000km, 50,000km, 80,000km, 100,000km mark etc!
Of course, by then the existing NiMH EV's might still be ahead, because they seem to keep going and going and going...

Apart from Antiscabs correction

reversing a {LiFePO4} cell will kill it straight away, but just overdischarging it won't.

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In a nutshell:

NiMH batteries are abuse tolerant.

Lithium batteries are abuse intolerant.

A BMS for a Lithium battery needs to be much more complex and much more redundant and fail safe than a NiMH BMS.

The BMS for a Lithium battery needs to be fail safe, with multiple safety shutdown mechanisms. Just sending an error signal if there is trouble is not good enough, because cells will then end up getting reverse charged or overcharged before long. Each of the multiple parts of the Li-BMS needs to check and send "OK' signals at specified, frequent intervals.
Whenever just one of the BMS components malfunctions, the battery is at immediate severe risk. Either the system goes into shutdown (or some other reduced power emergency mode), or risk cell destruction. Depending on the details of the BMS, it might be very complex and expensive to diagnose and repair such "false positive" error messages (that is when the BMS reports an error when there is no error).
False negative errors will very likely cause severe and sometimes dangerous battery damage ( = when there is a fault but it goes undetected).

Due to the high component number it is very likely that BMS malfunctions will plague Li-EV's for quite some time before a rock-solid, very reliable and relatively cheap system is available!

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Regarding the lack of progress in NiMH battery development: I do not know how much improvement might be possible or not, but it seems logical to me that no further development is occurring because of the patent problems. If you know you will get sued if you produce large format NiMH batteries, why sink millions into further development?

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In any case, John, you are already doing what needs to be done: Produce EV's and get them out on the road so that we can eventually know, not just assume, if they work reliably!

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Has anyone got any information about the Tesla Roadster's LiFePO4 batteries behavior in the real world?
How are they holding up so far?

Can I claim a KO in round one if Mik fails to show? ;-)

You can claim a KO once you can show me a few Lithium battery EV's that have passed the 10,000km, 20,000km, 50,000km, 80,000km, 100,000km mark etc!
Of course, by then the existing NiMH EV's might still be ahead, because they seem to keep going and going and going...

Apart from Antiscabs correction

reversing a cell will kill it straight away, but just overdischarging it won't.

my concerns about Lithium (and any other battery chemistry for that matter) remain unaddressed and unchanged!

Hi, I knew you'd turn up sooner or later! ;-) Good to see you :-)

Let the games begin...

In a nutshell:

NiMH batteries are abuse tolerant.

Lithium batteries are abuse intolerant.

A BMS for a Lithium battery needs to be much more complex and much more redundant and fail safe than a NiMH BMS.

And you base this claim on your experience with the stellar BMS that is in the Vectrix?????

The BMS for a Lithium battery needs to be fail safe, with multiple safety shutdown mechanisms. Just sending an error signal if there is trouble is not good enough, because cells will then end up getting reverse charged or overcharged before long. Each of the multiple parts of the Li-BMS needs to check and send "OK' signals at specified, frequent intervals.

Nonsense. Yes your suggested design may be more robust but there's absolutely no data backing up why this is required for Li not Ni. Our BMS is actually relatively simple - but it is still superior to the VX-1 BMS. That's because it's a per-cell BMS and it actually balances the pack during charging.

Whenever just one of the BMS components malfunctions, the battery is at immediate severe risk. Either the system goes into shutdown (or some other reduced power emergency mode), or risk cell destruction. Depending on the details of the BMS, it might be very complex and expensive to diagnose and repair such "false positive" error messages (that is when the BMS reports an error when there is no error).
False negative errors will very likely cause severe and sometimes dangerous battery damage ( = when there is a fault but it goes undetected).

More hyperbole. More nonsense. Chemistry plays no role in the situation you described. The battery is NOT "at immediate severe risk".

Due to the high component number it is very likely that BMS malfunctions will plague Li-EV's for quite some time before a rock-solid, very reliable and relatively cheap system is available!

Completely untrue. I present the Goodrum/Fechter BMS as a simple, elegant design. We worked with Gary and Richard over the summer and made some changes and improvements for our requirements.

Regarding the lack of progress in NiMH battery development: I do not know how much improvement might be possible or not, but it seems logical to me that no further development is occurring because of the patent problems. If you know you will get sued if you produce large format NiMH batteries, why sink millions into further development?

Well, that's possible - but not what the battery chemists says. Whichever is true it shows that NiMH is headed the way of the dodo (with respect to powering BEVs). Heck even if it were a Betamax vs. VHS type of war - face it, you're on the side of the Betamax. I encourage you to put your time and effort into a sunrise technology not a sunset one.

In any case, John, you are already doing what needs to be done: Produce EV's and get them out on the road so that we can eventually know, not just assume, if they work reliably!

But, this is the strange thing. There's a track record of VX-1 battery problems and you yourself have been very critical of the BMS set up in the VX-1. Yet, you still feel that NiMH is superior and spread FUD and doomsday scenarios about Li technology. This seems strange to me.

Has anyone got any information about the Tesla Roadster's LiFePO4 batteries behavior in the real world?
How are they holding up so far?

The Tesla doesn't use LiFePO4 batteries...

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Now, lest my strong words be taken as a sign of rudeness or aggressiveness - please don't worry. I'm enjoying this debate and pushing buttons as furiously as Mik is pushing them in return. I have great respect for Mik - he's done an immense amount of work on the Vectux.

Now, if only I could shift him away from 90's battery technology...

John, I did not mention your BMS or the Vectrix BMS.

I don't base my assessment on that alone, either.

I base it on a fair bit of reading, on several different EV forums and other sites, about the subject.

You got to read what I write and answer to those points if you want to have a meaningful debate. You think I am writing about your bike and the Vectrix, you may be forgiven for that, but you are wrong.

And I am not spreading doomsday scenarios - I just don't like the blind faith that so many seem to be putting into "Lithium Batteries", as if that was a guarantee to solve problems!

And if you think you can drag me into "games" in which you know that the masses are behind you, but you keep ignoring the few points I make, then think again!

Seeing that we cannot agree on the most basic facts about batteries, and you seem to have more knowledge than me and more interest and time to research and write it all up in detail, why don't you just answer this first question with some references:

Are NiMH batteries abuse tolerant?

Fair enough commentary. Sorry if I got carried away - just having fun. So here goes...

Are NiMH batteries abuse tolerant?

Yes NiMH are abuse tolerant. In fact NiMH are more abuse tolerant than LiFePO4 (BTW, I've never claimed otherwise). However, they are not abuse tolerant enough for BEV usage - in other words NiMH still needs a sophisticated BMS to prevent premature loss of capacity.

I don't have references for this, but seeing as there is alot of Vectrix information on these forums I put forth the Vectrix as an example of real world proof of the need for a BMS on an NiMH powered vehicle. I would also refer folks to your postings on these boards.

Note, for those who feel I'm already taking the debate in a direction not explicitly asked by Mik - I'm only interested in the use of cells for a BEV of motorcycle/maxi-scooter or larger format.

Ooh, what fun. Now, one for you, perhaps you would also answer:

For practical, real world usage in a BEV does NiMH need a BMS?

You can claim a KO once you can show me a few Lithium battery EV's that have passed the 10,000km, 20,000km, 50,000km, 80,000km, 100,000km mark etc!

Mik, this particular complaint seems to be a little misleading. You are claiming that lithium batteries aren't robust because they haven't yet racked up high mileage. However, that's not necessarily a reflection of the robustness of the battery technology. It seems to me that the more likely conclusion is that lithium battery technology is simply newer, and thus hasn't had time to experience long term testing yet. It might be far lest robust than NiMH, or far more robust, but using vehicle longevity as evidence of this is simply flawed logic, given the disparity in starting points.

If you want to make that conclusion, you need to control for manufacture date of the vehicle and quantity produced. So, for vehicles built in 2008, what fraction has passed the 100,000km mark, by battery chemistry? I'd bet the sample is too small to draw any type of statistical conclusion. :)

(quietly knocking on door hoping the masters will allow entrance...) :-)

I have some LiFePO4 experience, but no hands-on NiMh. I'll see if I can add fuel, I mean, provide useful info for at least one 'side' of this debate.

As a retired analyst, I'm not at all surprised that NiMh users like the battery. But frankly, what else have they used? It's possible that 'you never forget you first' also applies to the 'religion-like' characteristics of other experiences we have as humans. ;-)

Yes - NiMh has been around longer, and has been in EVs and HEVs longer. It's difficult to argue with real world experience. But if we're to be bound by Mr. Mik and Mr. Korthoff's logic that we should use the product with the longest experience tail, then gasoline wins hands-down. It's been moving billions of vehicles for more than 100 years, afterall. ;-)

According to Wikipedia, the first commercial NiMh cell hit the streets in 1989 after more than 22 years of development. The first LiFePO4 patent goes back to 1996. Look how far and how fast LiFePO4 has come in its short life!

Tesla is pushing things forward with 'old skool' lithium ion - the same as used in laptop computers. Other automakers are geeking-out with LiFePO4, in spite of its current expense, because of the reasons already listed by John. While NiMh has more 'inertia' behind it, LiFePO4 is coming on strong.

LiFePO4 battery managament isn't nearly as involved as some might suggest. Cell level low voltage protection is required. This is easily accomplished with three very inexpensive components per cell. For longest life, balance the cells once in a while and don't routinely over charge them. While most manufacturers recommend 3.65V per cell or so, damage doesn't appear to be a problem until we get above 4.3V. And if charged to 10V per cell they won't ignite.

So...for real-world LiFePo4 pack management, set the controller for an appropriate 'pack average' low voltage point. Set the charger for an appropriate 'pack average' high voltage point. Add a cell-level low voltage detector. Add a shunt or other method of keeping an individual cell from overcharging. Anything beyond this is geek stuff to interface with vehicle computers or draw pretty pictures. The cells don't care as long as they're not over charged or over discharged. (This ignores charge and discharge current as keeping this in check applies to all battery choices.)

A number of LiFePO4 manufacturers submitted cells to Sandia Labs for testing. The focus of the tests was hybrid electric vehicles and power grid load leveling. These place low demands on cells - lower than PHEV or pure EV use. Here's a link to results of Sandia's analysis of Phoenix Silicon International (PSI) cells. Note - at the time of the report, PSI made LiFeBatt cells. This is no longer the case. LiFeBatt appears to be contracting with Headway for cells - and the 'knowledge transfer' should improve their product quality. http://www.rechargeablelithiumpower.com/media/SANDIA2008-5583_PSI.pdf PSI's current cells are better than those tested, and they're in late development of the next generation now that should increase capacity while also bringing prices down.

I predict that NiMh will disappear entirely once large scale LiFePO4 production is on-line and prices come down. I also predict NiHm supporters will be pining for their lost love long after NiMh plants are gone. That's not technical superiority - that's life.

Andy

AndyH, Thanks, I think we're on the same page but I think your post puts it better than mine.

AndyH, Thanks, I think we're on the same page but I think your post puts it better than mine.

I agree!

RE: unfairness of asking for 10000 / 20000 / 50000 / 100000km examples : Of course you need to take vehicle age into consideration. I'm not saying they need to match the RAV4 EV before the data can be used as preliminary evidence, or strong indicators that the LiFEPO4 batteries will have a long lifespan.

So lets just start with 10000km vehicles: Which ones are out there, how many are out there and how many have so far made it to 10000km?
Or even just to 1000km if they have only been around for a few months. (I see AndyH has just gotten there, congratulations!)
As a reliable main vehicle EV they should be doing at least 5000 to 10000km per year.

If they exist and the majority of them has no battery or BMS problems, then why not mention a few examples?

You may call it what you want, but I call it realistic to want to see real world results to back up claims.

There is much more that can go wrong with batteries in real world EV's driven by real customers than what gets tested in the lab! Life has that habit of throwing surprised at you when you test your shiny new theories in practice! You may also be blown away by the sheer stupidity of many people and the ways of destroying equipment that they come up with which you never ever dreamed of!

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Yes, it's easy to ask for real world proof of performance claims. And it is sensible! And it is fair!

And I am not telling people not to use Lithium batteries! (Not that anyone listens, anyway...)

The "We just need Lithium batteries and the problems will be solved" brigade seems more religious to me than than my cautious approach!

You may also have a look at http://visforvoltage.org/forum/6751-elusive-holy-grail-batteries if you got the impression that I am on some religious crusade for NiMH - I'm not!

...
Ooh, what fun.
...

How about this for a laugh:

I have managed to do what the manufactures claim is impossible, that is to set fire to a Lifepo4 pack resulting in the complete destruction of my little Fiat 126. The heat was so intense, even the gearbox casing near to the batteries melted into a puddle under the car. The glass in the doors actually melted and ran down the inside of the doors! This happened early this month (Feb 2009) during the middle of the night. No one saw it go up or even reported the fire. By the morning it had completely burnt itself out. One of the battery boxes was still slightly warm when the car was discoved at 7:30am.

http://www.batteryvehiclesociety.org.uk/forums/viewtopic.php?t=1825

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That one triggered some of the BMS debates I vaguely recall, and what fail-safe mechanisms are needed or not.

How do you explain that one?

RE: unfairness of asking for 10000 / 20000 / 50000 / 100000km examples : Of course you need to take vehicle age into consideration. I'm not saying they need to match the RAV4 EV before the data can be used as preliminary evidence, or strong indicators that the LiFEPO4 batteries will have a long lifespan.

So lets just start with 10000km vehicles: Which ones are out there, how many are out there and how many have so far made it to 10000km?
Or even just to 1000km if they have only been around for a few months. (I see AndyH has just gotten there, congratulations!)
As a reliable main vehicle EV they should be doing at least 5000 to 10000km per year.

If they exist and the majority of them has no battery or BMS problems, then why not mention a few examples?

You may call it what you want, but I call it realistic to want to see real world results to back up claims.

Mik, with great respect, I agree 100% that real world results speak volumes. But I think your 'gentle demands' are unreasonable. One might expect there to be more automakers using NiMh if it really was the best on the market. NiMh as a battery chemistry has been around for 42 years and has been a commercial product for 37. The RAV4 EV hit the road in 1997 according to wikipedia. This suggests that Toyota were learning how to manage a box of NiMh well before LiFePO4 was developed as a chemistry. Put another way - it took a whopping 30 years to get today's reliable NiMh pack on the road but only 13 for LiFePo4.

Manufacturers don't gamble - they go for sure things. They tend to be very conservative. In spite of the history, experience, and inertia behind NiMh, no new automakers are designing around NiMh - they're working with the new technology with only a 13 year track record - and they're moving toward a chemistry that is more expensive today. Why?

My 1050 miles on LiFePo4 is without an installed BMS. I plug shunts in during charge for balancing. Here's a guy in California with more than 5000 miles on a LiFePO4-filled Honda S2000. DIY Electric Car has plenty of other LiFePo4 conversions that are racking up the miles.

Here's a 2000km 2009 EFun bike. Here's 4100km on an XM3500Li. Here are some 1000km reports from late 2008.

In the PHEV world, you've got A123-Systems Hymotion LiFePo4 pack as well as the boxes sold and installed by Plug In Supply and their dealers, including AutoBeYours. I know that Plug In Supply has about 2 years' experience with LiFePo4 PHEV packs.

There is much more that can go wrong with batteries in real world EV's driven by real customers than what gets tested in the lab! Life has that habit of throwing surprised at you when you test your shiny new theories in practice! You may also be blown away by the sheer stupidity of many people and the ways of destroying equipment that they come up with which you never ever dreamed of!

Folks have been killing batteries since well before gasoline became a fuel of choice and that's not likely to change anytime soon. But that has absolutely nothing to do with chemistry.

Yes, it's easy to ask for real world proof of performance claims. And it is sensible! And it is fair!

There are many, many real world users racking up Lithium miles every day. All one needs is eyes to see and ears to hear...

How do you explain that one?

Now your trolling. That car was a home conversion and was plugged into a charger and left alone. Even the owner doesn't know what happened.

I guess something like that could never happen with NiMh, though, could it? Except that it might have. Prius caught fire sitting in the owner's driveway - not plugged into anything...

How do you explain that one?

Looks like it's already been addressed by AndyH.

However, I have no intention of answering any of your questions until you do me the courtesy of following your own "rules". You asked a straightforward question I answered it. I asked you a straightforward question. You completely ignored it and introduced a picture of a burnt out wreck.

Hardly seems like you're walking the walk that you set out.

Off topic: Oh yes, I particularly love when someone offers some self-deprecating graciousness and someone else piles on. I refer to the opening of your last time you quote me. What's the smiley face for sticking my tongue out at you? ;-) (that wink is because for crissake don't take yourself too seriously, I try not to)

So, to save you the effort of looking for the question (slightly re-worded - feel free to answer either one, they're intended to be the same):

Does an NiMH powered BEV require a BMS?

And, because I'm feeling like you owe me a follow on question (hey, I'm in the US we're supposed to feel entitled!)

Does an NiMH powered BEV require a sophisticated BMS? (To me sophisticated would imply: Temperature compensation, per cell LVC, per cell over-voltage, per cell charge balancing. Feel free to provide your own definition of sophisticated)

Alternatively, just accept that you're swimming upstream on this one. Don't take my word for it. Do some open-minded research and I think you'll draw the same conclusions from numerous sources. I've supplied a few (see above).

How do you explain that one?

Now your trolling. That car was a home conversion and was plugged into a charger and left alone. Even the owner doesn't know what happened.

I guess something like that could never happen with NiMh, though, could it? Except that it might have. Prius caught fire sitting in the owner's driveway - not plugged into anything...

Thanks for the link, very interesting! But it is not trolling! The home conversion car with the LiFePO4 got so hot that the windows melted. It had no fuel tank, nothing much other than the Li battery to fuel the fire.

In the Prius fire pictures it looks like the window got sooted a bit instead of melting! The fire was not anywhere near as hot. And that's despite the Prius having a petrol tank which could have added fuel.

I don't have time to search around for discussion of this Prius event, but would be grateful if you have any links!

Now to your main misconception in this thread, AndyH:

One might expect there to be more automakers using NiMh if it really was the best on the market.
...
But if we're to be bound by Mr. Mik and Mr. Korthoff's logic that we should use the product with the longest experience tail, then gasoline wins hands-down.

It seems to me (from this line and from the other things you wrote) that you have fallen for John misrepresentation of what I am saying / writing.
See, I never said that NiMH is superior to another battery type, or that it should be used instead.

John starts his first line in this thread with the words:

Well, the only person that I know who seems to rate NiMH as a "better battery for BEV's" than LiFePO4 is Mik. ...

The problems is that I never said such a thing! Maybe I should have pointed that out earlier, but I don't have time to re-write and explain repeatedly to people who cannot engage in discussion without getting carried away and making assumptions, rather than addressing the points they so fervently criticize me for!
...
What I actually wrote, and what got John started, was this: (Over in another thread, as you know):

Reading all these credos for Lithium battery technology, again and again, I have to agree that they would not be able to sell many vehicles with NiMH technology.
But I do believe this is based more in consumer prejudices, than in limitations of the NiMH battery chemistry.
Until there are vehicles that have gone further with Lithium than with NiMH, the fact remains that the newer batteries might be worse.
The design principles needed for NiMH longevity are well known, and they were not followed in the VX-1 battery!

And then this:

...
You're absolutely right about the need for a high quality BMS solution with Lithium - it may even be more necessary than with NiMH.

It is definitely much more necessary than with NiMH! Lithium batteries will be destroyed within a few (or even just one) charge-discharge cycle without a BMS!

http://visforvoltage.org/forum/7585-vectrix-enters-asset-purchase-agreement#comment-43612
Well, that was not entirely correct for all Li type batteries, but I did not specify which ones, or for which vehicle types!

I don't claim that they are better or worse, but John and others claim that they are clearly better and safe.

The burden of proof lies with those people who make the claims that the newer, untested (in the real world) product is better and safer.

John, I'm not swimming upstream! It's you who claimed that I jumped in and started paddling! I merely stated the obvious: That we don't know where the river leads! There might be rapids, droughts, waterfall, or suddenly the tide comes back in and it starts flowing backwards!
Read my stuff and then tell me at what point I jumped into that river on which you are sailing!
As far as I am concerned, I'm standing on the shore, pondering where it may lead and what difficulties and dangers may lie ahead. You have set sails on that river, heading downstream! So have the vast majority of the other players involved.

I give up.

Sounds like an argument of 110 years ago! Horsedrawn carriages, versus the gasoline engine powered vehicles. The similar arguments could be made, as to miles driven, fire hazards, availability of feed or fuel, and complexity of control systems!-Guess which was the winner?-Bob

This had the potential to be such an interesting thread. I agree, marylandbob.

Sounds like an argument of 110 years ago! Horsedrawn carriages, versus the gasoline engine powered vehicles. The similar arguments could be made, as to miles driven, fire hazards, availability of feed or fuel, and complexity of control systems!-Guess which was the winner?-Bob

I think it is more akin to a debate about which breed of horse is better to draw the cart!
Or what to feed the horses...

Thanks for the link, very interesting! But it is not trolling! The home conversion car with the LiFePO4 got so hot that the windows melted. It had no fuel tank, nothing much other than the Li battery to fuel the fire.

In the Prius fire pictures it looks like the window got sooted a bit instead of melting! The fire was not anywhere near as hot. And that's despite the Prius having a petrol tank which could have added fuel.

I don't have time to search around for discussion of this Prius event, but would be grateful if you have any links!

Come on, Mik - you're smarter than this! Which has more energy - a pint of petrol or a gallon? I know that you're not actually suggesting that a small NiMh pack that't kept between 40 and 80% charged somehow made a 'safer fire' than an EV with a large LiFePO4 pack that's fully charged and still plugged into mains?! Please be giving to me a break!

Sorry - I have to agree with John. I enjoy a debate but this isn't one.

Come on, Mik - you're smarter than this! Which has more energy - a pint of petrol or a gallon? I know that you're not actually suggesting that a small NiMh pack that't kept between 40 and 80% charged somehow made a 'safer fire' than an EV with a large LiFePO4 pack that's fully charged and still plugged into mains?! Please be giving to me a break!

Sorry - I have to agree with John. I enjoy a debate but this isn't one.

You can find many details about the LiFePO4 battery fire in the link I provided. I can find you some more if you like.

Have you got a link to some discussion of the Prius fire? I'd like to read about it, I find it important to be informed about such events. But I don't have time to hunt it down myself right now.

Anyway, at least you agree that the energy source for the fire melting the gearbox casing and the windows in the Fiat must have been the LiFePO4 battery!

Lets stage a test: Use similar energy size/power capability propulsion packs, and heat them to the point of ignition, then see which one makes the worst fire, most heat, etc? Based on performance in my Vectrix scooter, I think that using 1 gallon of gasoline, and 40 ampere-hour batteries, at a nominal 125 volts (5.0 KWH Battery) would be a reasonable comparison, as similar range, at 50-60 mph, could be expected in a similar vehicle powered by either of these sources. I would think that burning a Ni-Mh battery would cause release of the HYDROGEN stored inside, and as we know, hydrogen is a good fuel, readily combustible in air. Lithium also will burn, the question is which battery, if both store identical electrical energy, will burn more violently, releasing the most THERMAL energy? How will the thermal energy released by battery destruction compare to the thermal energy released by burning 1 gallon of gasoline? How toxic are the fumes and byproducts? How difficult would it be to EXTINGUISH the respective fires? How much heat is required to START the respective fires? These are issues that seem most relevant to usage hazards. (Testing the respective batteries at a continuous 10 C discharge, and noting battery temperature rise/or other effects, under this abusive, rapid discharge, should also be noted)--Bob Curry

Lets stage a test: Use similar energy size/power capability propulsion packs, and heat them to the point of ignition, then see which one makes the worst fire, most heat, etc? Based on performance in my Vectrix scooter, I think that using 1 gallon of gasoline, and 40 ampere-hour batteries, at a nominal 125 volts (5.0 KWH Battery) would be a reasonable comparison, as similar range, at 50-60 mph, could be expected in a similar vehicle powered by either of these sources. I would think that burning a Ni-Mh battery would cause release of the HYDROGEN stored inside, and as we know, hydrogen is a good fuel, readily combustible in air. Lithium also will burn, the question is which battery, if both store identical electrical energy, will burn more violently, releasing the most THERMAL energy? How will the thermal energy released by battery destruction compare to the thermal energy released by burning 1 gallon of gasoline? How toxic are the fumes and byproducts? How difficult would it be to EXTINGUISH the respective fires? How much heat is required to START the respective fires? These are issues that seem most relevant to usage hazards. (Testing the respective batteries at a continuous 10 C discharge, and noting battery temperature rise/or other effects, under this abusive, rapid discharge, should also be noted)--Bob Curry

Bob - those are good points and worthwhile tests - once the point of a fire is reached. However, the goal of a robust BMS (and I'm going to use BMS in the broadest sense here) is to avoid such catastrophe.

If I remember correctly the hypothesis of the above battery BBQ shown by Mik was the cold temperatures changing the dynamics of charging and the system being unable to cope with that change. I don't remember the details - I do remember that we discussed this at CuMoCo around the time that thread was started (or maybe it was a couple of months later when we discovered it - point being we're aware of it). The CuMoCo BMS uses two pack temperature sensors and will disable the charging process well before the batteries reach the point of combustion (and also before they reach the point of damage - for comparison something which the VX-1 appears to suffer from is charging in hot ambient temperatures).

Note that I don't think the above paragraph plays into the debate of NiMH vs. LiFePO4 (thus I didn't introduce it before) - it's more of a debate on "what makes a good BMS?". However, Bob's response to the fire question is a worthwhile look at NiMH vs. LiFePO4 in the broadest sense. I wonder if Fire Departments out there have answers to these sorts of questions?

Here's hoping that none of us ever see our own battery BBQ!