SamRich
100 W
Yes it works. It logs stuff like when charging started and stopped etc...themelon said:
LTO Lithium Titanium Oxide (Titanate) Battery 30S (now 32S)- Seeking the Ultimate Commuter Battery
- Thread starter SamRich
- Start date
cal3thousand
10 MW
What bike/motor/controller are you using this on?
llile
1 kW
- Joined
- Dec 18, 2010
- Messages
- 457
Here are my Requirements:
72V Nominal
60 A Cont /100A peak.
> 10Ah for commute.
LTO:
For my energy requirement I need 11ah cells.
That's 30 1S 11ah pack @ $9 each = $270 (great deal on Ebay, also available on Aliexpress for $15 a cell)
Weight is 30 x 340g = 10Kg or 22 lbs
According to specs I should get 5000 cycles - but I'll assume 4000 since that would be 90% or 10 Ah.
That's 64000 miles per pack or $0.004 - $0.007 per day (depending on where you buy the LTO). <- Cheapest
And here is a comparison to the classic LiFePO4 that lots of us started out with:
Ping LiFePO4
(2) 36V 10AH LiFePO4 battery packs in series
$696 incl shipping from Singapore
Weight 3.4 KG X 2 = 6.8 kG or 14.96 Lb
~2000 cycles or more
25600 miles per pack or $.027 per mile
I've got 300-odd cycles on a larger LiFEPO4 pack and have almost 7000 miles on it. Definitely have lost some capacity though.
cwah
100 MW
SamRich said:macribs said:
The issue with building a pack with much more capacity than needed is that you end up with much more weight - of course - and that's the point here. In fact, I would say that you actually do need it, not for energy capacity but for power capacity.
That's what is great about LTO. What it lacks in specific energy it makes up in specific power
It all depends on your requirements.
So I thought I'd put down a detailed analysis for my application - and please tell me if I'm missed anything.
Here are my Requirements:
72V Nominal
60 A Cont /100A peak.
> 10Ah for commute.
Consider these 4 potentialy viable options that meet these requirements on paper.
Value LIPO: Multistar
For my power requirement I would need at least 30Ah (3C)
That's 3 x 5 x 4S 10 ah pack at ~$50 each = ~$750 (on sale now usually ~$65 or ~$1000 per pack)
Weight is 15x800g = 12kg or 26.4 lbs <- heaviest
In theory as you say, if I use it nicely I could get at least 1000 cycles (11Ah per cycle) before I get too much sag at 100A, although in practice it seems to be much less - see PS.
That's 16000 miles per pack or $0.0460 per day.
Quality LIPO: 65C Graphene
For my energy requirement I would need 10Ah (that would be cutting it close - I would probably go with 15Ah, but I'll use 10Ah)
That's 2 x 4 x 5S 5 ah pack at ~$100 each = ~$800
Weight is 8x750g = 6kg or 13 lbs <- lightest
(15Ah would be 20lb and $1200)
Rated for 600 cycle (probably inflated).
That's 10000 miles for the 10ah battery or $0.080 per day. <- Most expensive
Panasonic NCR18650PF 2900mAh 10A
For my power requirement I would need 20S10P
That's 200 cells at $4 each = $800
Weight is 200 x (45.3g ) = 9kg or 20 lbs
I'll be generous and estimate 1000 charges
That's 16000 miles per pack or $0.050 per day.
Did not include $200 welder (that I don't have) and additional considerable cost of holders and strip needed to build this type of pack.
LTO:
For my energy requirement I need 11ah cells.
That's 30 1S 11ah pack @ $9 each = $270 (great deal on Ebay, also available on Aliexpress for $15 a cell)
Weight is 30 x 340g = 10Kg or 22 lbs
According to specs I should get 5000 cycles - but I'll assume 4000 since that would be 90% or 10 Ah.
That's 64000 miles per pack or $0.004 - $0.007 per day (depending on where you buy the LTO). <- Cheapest
Conclusions:
For what I need LTO is in fact comparable weight and a lot cheaper by a factor of 10X.
Panasonic is clearly a close runner up, and probably the winner for most, which is why it is so popular. I would get 3X the range! It was tempting to go that route, but was deterred by having to spot weld the pack properly with 200 cells at 100A rating and the impact on it's long term mechanical and electrical durability. Could also have bought 2X 72V 11Ah packs from Luna Cycle for $1200 but that's a bit steep both short term and long term - wise.
Added bonus 1 of LTO: I don't have to build as many pack and balance as many cells, which I know for some of us is most of the fun
Added bonus 2 of LTO: LTO can be charged outdoors in freezing weather - kinda nice not to have to carry in a 25lbs battery everyday 4 months out of the year.
Added bonus 3 of LTO: I could charge it in 20 min @ 30A - BMS limited, but will probably look at 18A (35 mins) since that's about all I can get from a 120V outlet.
PS I have tried the 30Ah Multistar Lipo combo. At first I was using 20Ah with my 50A/60A contoller and that worked pretty well for a year until I would get sometimes LVC on the way home @8Ah. But then got a new 60A/100A controller so thought I would build a fresh 30Ah pack. Right off the bat, after 5Ah I would hit LVC on hard acceleration which is about 3C. Either need 40Ah (no way!) or probably got a bad pack although I measured each 10Ah pack and IR was 10mOhm per cell on average (compared to my one year old pack that had 20mOhm IR)... anyway I'd have to figure which specific cell was bad and that's a pain... hence why I'm looking for a sustainable/reliable solution...
To compare apple to Apple you need to use WH as indicator of capacity.....
A LTO cell according to the manufacturer is about 25.3wh when discharged at 1C.
30s gives you a capacity at 759wh max.
Now consider the ncr18650pf is about 10wh, 200 cells gives you 2000wh. You'd have 3 times more capacity than LTO.
Now, if you use your ncr18650pf very conservatively, and only charge them up to 3.9v. they'll certainly last as long or longer than your LTO cells and still have the 750wh needed to achieve your commute
I have a pack with 210 ncr18650 for 3 years. I use it almost daily and charge to 4v/series, and it's still going strong.
I had however to change some series maybe twice in 2 years (the series went to 0v), but that happen to any cell. I'd say cell failure and mechanical damage are a much bigger risk than lifecycle!
SamRich
100 W
cwah said:
As you know, there's energy density (specific energy) and power density (specific power).Generally speaking, Lipo has better energy density (Wh/kg) while LTO has better power density (W/kg) so it depends what you need - engineering is all about tradeoffs. For my application I was looking at the smallest size battery capable of delivering 100A irrespective of Wh, but as you state (and I also mentioned) Lipo would give you more energy for the same power.
However, I disagree that only charging to 3.9V would still allow you to achieve 10000 cycle with ncr18650pf due the chemistry's nominal cycle rating and shelf life.
Here a charts from http://batteryuniversity.com/learn/article/types_of_lithium_ion illustrating the various tradeoffs.
Proper building design should mitigate the risk of cell failure and mechanical damage for any chemistry.
cwah
100 MW
Again, use power to compare Apple to apples...
Average voltage of LTO cell is 2.3v. with 31s you have 71v.
If you need 100A it means you need 7100w of power.
If you were to get ncr18650pf, max discharge is 10A. So if you get a slightly larger battery with 230 cells you can also get 7000W discharge.
It would be about the same weight, but you could have considerably larger range available.
I've been using them for over 3 years now and no evident sign of significant capacity loss so far. I think I only balanced them once in 3 years and voltage is still very close between series.
I've probably cycled the pack over 500 times, although with a 2100wh pack, I mostly do shallow cycles...
Average voltage of LTO cell is 2.3v. with 31s you have 71v.
If you need 100A it means you need 7100w of power.
If you were to get ncr18650pf, max discharge is 10A. So if you get a slightly larger battery with 230 cells you can also get 7000W discharge.
It would be about the same weight, but you could have considerably larger range available.
I've been using them for over 3 years now and no evident sign of significant capacity loss so far. I think I only balanced them once in 3 years and voltage is still very close between series.
I've probably cycled the pack over 500 times, although with a 2100wh pack, I mostly do shallow cycles...
regardless whether it's power or energy or doughnutz;
by definition density is always by volume.
the term 'specific' is a modifier to specify mass.
density by volume or by mass are distinctly different properties & not parenthetic.
that implies it's just different terms for the same property, which it's not.
by definition density is always by volume.
the term 'specific' is a modifier to specify mass.
density by volume or by mass are distinctly different properties & not parenthetic.
that implies it's just different terms for the same property, which it's not.
SamRich said:
SamRich
100 W
Toorbough ULL-Zeveigh said:
Thanks for the clarification you are correct. I guess I was assuming that most lithium based cells have similar densities - so specific and density are pretty much interchangeable for the purpose of this conversation.
Mmmm doughnuts
ElectricGod said:
Probably the best place for our tangent is here for sure.
If anyone in this thread is interested, several of us managed to wander off topic from Bluetooth BMS's onto LTO in this thread:
https://endless-sphere.com/forums/viewtopic.php?f=14&t=88676
ElectricGod
10 MW
I'll be building an LTO pack soon. I intend to go to 131 volts or 48S. I currently have 24 LTO cells and have worked out how to connect together the tabs as cheaply and reliably as possible. My solution is to bolt together the tabs with brass M6 screws, washers and nuts. I can solder directly to the brass if needed for balance leads. Also the cell tabs will get folded over so that there is more aluminum to aluminum contact before they are screwed together. Brass isn't the best conductor so the folded over tabs will overcome any brass losses. Balance wires will attach via a screw lug. I intend to NOT use a BMS at all and use super cap boards for any balancing.
This is a copper strip I added, but I I'm abandoning that for brass washers instead. The cost difference for the copper strip vs 4 brass washers is pretty significant. I think these predrilled copper strips were $2 each and 4 brass washers costs me 15 cents. At the ends of the pack where I will connect power leads, that's where I will possibly use these copper buss strips for bonding power wires to the aluminum tabs. I found solid copper hanger strip in a coil for far less money than these copper buss strips cost. The spool has something like 100 feet on it and cost me $25. I may reinforce every tab connection with some solid copper hanger strip, but I doubt it is really needed. With 2 tabs bonded together like this, I am at 10mm thick which easily fits between the tops of the individual cells.
This is a copper strip I added, but I I'm abandoning that for brass washers instead. The cost difference for the copper strip vs 4 brass washers is pretty significant. I think these predrilled copper strips were $2 each and 4 brass washers costs me 15 cents. At the ends of the pack where I will connect power leads, that's where I will possibly use these copper buss strips for bonding power wires to the aluminum tabs. I found solid copper hanger strip in a coil for far less money than these copper buss strips cost. The spool has something like 100 feet on it and cost me $25. I may reinforce every tab connection with some solid copper hanger strip, but I doubt it is really needed. With 2 tabs bonded together like this, I am at 10mm thick which easily fits between the tops of the individual cells.
I like it!...as long as the battery tabs are aluminum-to-aluminum, the metal on the outside that is clamping them together is free to be steel, brass, etc...
cal3thousand
10 MW
spinningmagnets said:
Some ideas and links littered throughout this PriusChat thread:
https://priuschat.com/threads/connecting-a123-20ah-lithium-prismatic-cells.111001/
Inwo
10 kW
Inwo
10 kW
Don't forget that pouches need to be contained with pressure plates.
ElectricGod
10 MW
Inwo said:
Did you do that? They look seriously over charged to get the cells to swell up like that.
Inwo
10 kW
Not I.
They were installed in an engine compartment for a two month test.
Wasn't driven over an hour.
After return from a short vacation they were dead and swollen.
Must have been enough draw to kill 22ah.
After that, I don't know the story. Whether swollen during charge or what.
Doubt if it was balance issue, as all are the same.
Over charging for hours is the only way I could damage them.
They were installed in an engine compartment for a two month test.
Wasn't driven over an hour.
After return from a short vacation they were dead and swollen.
Must have been enough draw to kill 22ah.
After that, I don't know the story. Whether swollen during charge or what.
Doubt if it was balance issue, as all are the same.
Over charging for hours is the only way I could damage them.
Inwo said:Not I.
They were installed in an engine compartment for a two month test.
Wasn't driven over an hour.
After return from a short vacation they were dead and swollen.
Must have been enough draw to kill 22ah.
After that, I don't know the story. Whether swollen during charge or what.
Doubt if it was balance issue, as all are the same.
Over charging for hours is the only way I could damage them.
Ok, so they will need a BMS, of sorts at least, in my truck. I thought that was to good to be true.
ElectricGod
10 MW
themelon said:Inwo said:Not I.
They were installed in an engine compartment for a two month test.
Wasn't driven over an hour.
After return from a short vacation they were dead and swollen.
Must have been enough draw to kill 22ah.
After that, I don't know the story. Whether swollen during charge or what.
Doubt if it was balance issue, as all are the same.
Over charging for hours is the only way I could damage them.
Ok, so they will need a BMS, of sorts at least, in my truck. I thought that was to good to be true.
No...not too good to be true, BUT you need to get the cell count high enough to handle the voltage swings of the cars electrical system. I have 2 cars. The VW does a great job of staying pretty much dead on at 13.8 volts all the time. My Ford truck however runs pretty hot at 15.6 volt peaks. I've tried a replacement regulator, but it still runs hot randomly. It kills batteries fairly quickly as a result. I've been buying the cheapest walmart battery every couple of years. You may have an issue like this. I'd do something like putting a capacitor bank in the car to level out power, but that's NOT going to fix the high voltage trends that I see in my truck. If you use LTO's as a replacement for your car battery and I'm seriously going to this in the VW soon, then add an extra cell to the pack so that cell voltages can't ever get close to over voltage levels.
Let's assume your electrical system is stable at 13.8 volts, then ideally at 2.7 volts per cell that works out to 5 cells. At 6 cells that gets you down to 2.3 volts per cell which is still well inside the power band for LTO's and gives you a safe margin for error if your car does what my Expedition does from time to time.
ElectricGod said:themelon said:Inwo said:Not I.
They were installed in an engine compartment for a two month test.
Wasn't driven over an hour.
After return from a short vacation they were dead and swollen.
Must have been enough draw to kill 22ah.
After that, I don't know the story. Whether swollen during charge or what.
Doubt if it was balance issue, as all are the same.
Over charging for hours is the only way I could damage them.
Ok, so they will need a BMS, of sorts at least, in my truck. I thought that was to good to be true.
No...not too good to be true, BUT you need to get the cell count high enough to handle the voltage swings of the cars electrical system. I have 2 cars. The VW does a great job of staying pretty much dead on at 13.8 volts all the time. My Ford truck however runs pretty hot at 15.6 volt peaks. I've tried a replacement regulator, but it still runs hot randomly. It kills batteries fairly quickly as a result. I just buy the cheapest walmart battery every couple of years. You may have an issue like this. I'd do something like putting a capacitor bank in the car to level out power, but that's NOT going to fix the high voltage trends that I see in my truck. If you use LTO's as a replacement for your car battery and I'm seriously going to this in the VW soon, then add an extra cell to the pack so that cell voltages can't ever get close to over voltage levels.
What I was worried about was continuous charging from the alternator. The voltage issue isn't really an issue as my truck is pretty much dead on 14.4-14.5 all the time so 6s should cover it nicely with margin.
There is probably something else in the circuit that makes it not an issue that I'm not thinking about though.
ElectricGod
10 MW
themelon said:
Current into the battery is a function of voltage difference between the source (alternator) and the destination (battery). If the battery is charged to 13.8 volts and the alternator is delivering 13.8 volts, then there is zero current flow into the battery. BUT, if the battery is at a lower voltage than the alternator, then you will have current flow into the battery. The voltage difference between A and B is why there is current flow. IE: you won't have continuous charging if the battery is at the voltage of the alternator.
ElectricGod said:
Thank you for that explanation. I had a feeling that it was something like that but not being anywhere near as educated in this area as you are I just couldn't quite put it together.
I always had it in my mind for some reason that it was equivalent to trickle charging. But that would really only make sense like you say if the voltage of the battery is actually lower than the source.
ElectricGod
10 MW
themelon said:
Educated...LOL...no not really. I did go to school for an EE in the late 80's, but otherwise any "education" I have is becasue I read about subjects that I want to know about. Anyone can do what I have done...if they stick to it. I remember not so long ago having no idea how mosfets work or how to use them, but then I read a lot and started messing with them and learned a lot in the process. Not rocket science at all.
If you don't have a watt meter on your charger, then I suggest you add one. This little fact about voltage difference and current flow is directly observable on a watt meter. You will see that the battery voltage is say 60 volts and your charger is at 82 volts. This large voltage difference equates to lots of current flow from the charger. AS you watch the battery voltage rise closer to 82 volts, you will see current draw drop off. The battery at 82 volts will no longer present a voltage drop for current flow from the charger and you will see the watt meter shows the same thing or 0 amps. I knew this conceptually, but to see the exact same behavior on my watt meter as I charged a battery was great confirmation. An alternator in a car charging a battery works identically.
ElectricGod said:
That's the kind of education I'm talking about, learn by doing and asking questions. It is the best way for me to learn, break, break, perhaps fix, repeat...
It's how I am where I am in IT with no formal secondary education. I just don't learn in a theoretical venue. I have to do it and that's why I am here and participating in the discussions. So I appreciate comments like yours that are actually constructive and corrective of my own ignorance. Being where I am in IT also makes it so I can afford to learn by breaking in this hobby
(just as long as I can avoid burning the house down)I have acquired all kinds of measuring tools in the last year or so. I even picked up an oscilloscope recently and a somewhat decent Fluke DMM. Now to figure out how and when to use the 'scope...
