Cascade hybrid batteries

[cycleops612]

Unless u r good at skimming, i am not suggesting u read

http://ntnu.diva-portal.org/smash/get/diva2:174476/FULLTEXT01.pdf

Its a v hi brow thesis, but it has moments of concise clarity to we mortals.
~
" “Cascade multilevel converter in hybrid electric vehicles,”"

sadly i cant paste pertinent bits.

He puts the problem/point i am sorta on about, far better than i can. We agree it seems, that "cascade" is a good term for it. Its what i searched on~.

my simple version is:

Storage is clearly THE issue for EVs, and huge R&D resources are dedicated to eking improvements from the various deeply flawed options.

But little thought is given to cleverly combining strengths and weaknesses of various power sources to average out into a nice, usable power source for an ev. The paradigm is predominantly one storage technology onboard.

A Prius is an apt hybrid. But why stop there? Why not a plugin with a tiny ICE motor generator or fuel cell (little more than on onboard charger/~minimal base load - say 20-30% of full throttle power capability) AND; 10% lipo, 5% supercap, 40% limn, 45% lifepo4 (easily customised for users needs).

Bulk up on the good enough for normal power batterys, and hang the expense for a little turbo power in the mix.

Unlimited range for non extreme use (like hour after hour of full throttle on the freeway w/ no fast charging points) and similar squirt to a motor car.

more to the point, a pure EV needs variously; range, peak power (a c-rate of 2-3 seems right), affordable, light,...

All qualities which vary greatly with different storage types. A clever controller would allow use of several types, each rubbish if used alone, to combine into a cost effective ~ideal battery.

One thing all chemistries hate, is being taxed at their limits - its a chemical reaction, not a switch. This hybrid cascade approach would help.

I understand being clever with big levels of power is fraught, but at lower levels such as modest ebikes and EVs, i get the impression all sorts of power massaging is possible efficiently~ these days?. ~historically recent advent of mosfets?

Perhaps multiple controllers is a simplifying DIY paradigm, one cheap mainstream controller feeds into another, to even out power incompatibilities - say to combine some lipo with some li-mn (seems a good hybrid to me for burst c-rates as well as affordable range and longevity from the main storage investment).

another combo is limn & lifepo4. One is light & the other no voltage sag - you can get usable power when 80% empty, by supplementing it from another source before feeding it to the motor.

I gather combining wind and solar power requires this?

Clearly I am an E-noob.

Where am i wrong?

Discuss.

 

[Okami]

Can you do a follow up on this one? Document is quite a long read.. I really would like to know how to safely ''cascade'' high discharge li ion batteries and low discharge (laptop grade) ones..

 

[Hillhater]

Firstly, in terms of technology, that is a dated document. Published in 2009, based on prior research, so most of the information will be 10 years old. ...in which time cell development has advanced significantly.
For "general" EV use...say a typical car like the Leaf, there is little or no advantage in combining various cell chemistrys.
Lifepo4 offeres no advantage over LMc and the potential "power" capeability of Ultracaps is not needed since the LMc cells can provide sufficient given the Ahr capacity required for practical range.
Some might see an advantage in having a small on board ICE generator, but that is purely a personal preference based on intended use. A PHEV would be the better choice in those situations.
There may well be significant advantages for hybrid cells/ultracaps/ generators etc but only for extreme or unique applications such as aircraft, drag racers, and more relavently the current F1 drive trains which already use this type of installation.

 

[redilast]

Can you do a follow up on this one? Document is quite a long read.. I really would like to know how to safely ''cascade'' high discharge li ion batteries and low discharge (laptop grade) ones..

There is no safe, reliable, robust way for you to DIY pair cells of low and high discharge capabilities. To do it properly you need the different cell types in their own cell groups controlled by circuitry that interacts with the other circuitry of the other pack of the other cell chemistry. The good news is though that there is generally no need to hybrid cells, as manufacturers for years now have been making hybrid cells which offer a good balance between high capacity and high discharge current. Several years ago when this article was written there were few if any hybrid cells. There was High discharge low capacity cells like LiMn (IMR) cells around 1500mAh max, and then there was 2600-2900mAh laptop grade cells. Now we have 10A rated GA's and 20A rated LG HG2's etc.

 

[Sunder]

People have been paralleling cells of different discharge rates for ages. When googling around, I saw some very old threads about using the then expensivr Lirhium cells to boost cheaper Nickle and Lead batteries.

I am about to use a tiny LTO battery to boost a sagging LFP battery.

If you think about it even using unmatched cells of the same type, or parallelling packs of different capacity is doing exactly this.

But really, I can't see many useful applications at the current market. Between LFP and LiPo variants cover most needs between longevity, power density and energy density.

 

[cycleops612]

Firstly, in terms of technology, that is a dated document. Published in 2009, based on prior research, so most of the information will be 10 years old. ...in which time cell development has advanced significantly.
For "general" EV use...say a typical car like the Leaf, there is little or no advantage in combining various cell chemistrys.
Lifepo4 offeres no advantage over LMc and the potential "power" capeability of Ultracaps is not needed since the LMc cells can provide sufficient given the Ahr capacity required for practical range.
Some might see an advantage in having a small on board ICE generator, but that is purely a personal preference based on intended use. A PHEV would be the better choice in those situations.
There may well be significant advantages for hybrid cells/ultracaps/ generators etc but only for extreme or unique applications such as aircraft, drag racers, and more relavently the current F1 drive trains which already use this type of installation.

re point 1. I think i covered that.

"Unless u r good at skimming, i am not suggesting u read

http://ntnu.diva-portal.org/smash/get/d ... TEXT01.pdf

Its a v hi brow thesis, but it has moments of concise clarity to we mortals."

the rest i dont agree with, but thats ok.

 

[Hillhater]

.......
another combo is limn & lifepo4. One is light & the other no voltage sag - .......
Where am i wrong?
Discuss.

Which one do you believe has no sag ?
All batteries have voltage sag,..some more than others,
the amount of sag depends on various factors, such as,..the applied discharge load, the capacity, SOC, IR , etc .

 

[cycleops612]

Well yes redilast. circuitry is the crux of it i agree.

i am more on about theory. its less complicated & hence obscure.

Controllers are already pretty smart, even cheap ones, but they dont have multiple power source inputs (perhaps regenmakes it two sources?) - so as to intelligently pick & choose from the strengths of various types of power sources for different conditions.

of course there is a need, and of course there is a need for onboard ice or fuel cells, just as there is a need for the prius hybrid concept.

we know storage is the most limiting factor in EVs, yet we all settle for a single, compromise type of battery chemistry.

Ideally; durable, hi dis/charge, cheap, compact, steady voltage... But you can only pick the ~two which matter most to you.

We need lipo for that big hill & its ability to charge fast, we want lfp say for longevity and cost effective charge/discharge up to 3c.

Even flywheels can be a poor mans huge super cap. An intelligently managed combo of storage types adds up to more than the sum of the parts. no compromises yet longevity from the frugally used hi performance/short life lipo e.g.

It bears stressing that they work as a team. In low power draw times, the lfp could prime the lipo/supercap cells, or the ICE could add charge fast rate w/o stressing any of the team. This cannot be done by an ice car. A very small engine can have great effect in a hybrid in random traffic. It can store its power output as a fast acting reserve.

The starting point for engineers on an ev is, "how many kilos of batteries can we get away with, because we need all we can get to make it sorta like a real car"

i think the suggested hybrid approach can help a lot. a 20kw car with a 4kw 100cc ICE as charger/assist, 4 kwh lipo & 50kwh (~40kg) lfp say, would make a fine city ev. Most days, no petrol engine needed for the commute - just battery charge. On busy or hot a/c days, the motor charges and assists to the max to maintain max charge & extend range. Waste ice heat is a car heater too BTW.

The chinese and others are busy doing a related thing i like a lot. The concept is like the trolley cars of yore, but without the hassle, hazards and expense of continuous wiring above. In a town which has trams now, they use buses with fast charge batteries, and after a brief spell running on a bit of wired route (even better if the bus gains altitude on the grid), it is charged to go 20km independently of the grid. Other cities just have electric contacts at some scheduled bus stops for a fast charge top up. The advantages of trolley buses w/o the wires.

 

[cycleops612]

.......
another combo is limn & lifepo4. One is light & the other no voltage sag - .......
Where am i wrong?
Discuss.

Which one do you believe has no sag ?
All batteries have voltage sag,..some more than others,
the amount of sag depends on various factors, such as,..the applied discharge load, the capacity, SOC, IR , etc .

LFP/lifepo4 is a clear winner for a flat volt discharge curve, longevity. ...

but its beside the point and unconstructive to argue on this.

Suffice to say they all have strengths and weaknesses, and it helps to intelligently pick and choose between them, given driving conditions.

 

[Hillhater]

A flat discharge curve is no indicator of voltage sag.
Not an argument, just a clarification of terminology.
Also, battery voltage is not necessarily related to voltage applied to the motor, as the inverter/controller will control the motor voltage, so a flat discharge curve may not be benificial.

 

[cycleops612]

A flat discharge curve is no indicator of voltage sag.
Not an argument, just a clarification of terminology.
Also, battery voltage is not necessarily related to voltage applied to the motor, as the inverter/controller will control the motor voltage, so a flat discharge curve may not be benificial.

well the charts I see have volts on the y axis and capacity on the x axis. As the voltage is ~constant for lfp, the chart line is flattish vs limn/lipo eg. til~97% empty (at 1c rate).

lfp:

https://www.google.com.au/search?q=discharge+chart+lifepo4&espv=2&biw=1408&bih=662&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjqu-CmgP_PAhUEKZQKHTShBnoQsAQIGQ#imgrc=kZacqXL4CsB0BM%3A

both limn & lfp are shown here: (- recommended folks. The specifics are always distractingly arguable, the pattern/shape of the curve is not)

http://budgetlightforum.com/node/16699

or more briefly, a typical limn etc 18650 cell discharge chart:

http://lygte-info.dk/pic/Batteries2012/NCR18650A%20protected%20%28Green%29/NCR18650A%20protected%20%28Green%29-Capacity.png

Controllers that are inverters (how efficient?) are new to me. They sound; new, dear, hi end - rare in the wild.

I do very much like the sound of the latest (sine wave?) controllers which have a limited kinda simulated CVT effect (by playing with existing? voltage).

If it is as u say, odd then, that the seemingly ~universal solution to sag around the forums is overkill c-rates or battery capacity. Which is a nonsense argument by other chemistry/cell format supporters in an apples with apples debate. (also makes nonsense of the extent of respective weight advantages, and space to a lesser extent).

I regrettably digress. The topic is not what the differences are. Only that there are differences which can be exploited toward better storage device via mixing intelligently for projected usage. Just as a prius combines the strong suites of ICE and batteries.