72V LiFePo4 Question

I am assuming you are wanting larger amp hour batteries. The 100 AH cells are going for about $200 each now, and you will need about 21 or 22 cells. So with the charger & BMS, you are looking more in the $5000 to $5500 range.

These places can order you good quality large cell LiFEPO4 batteries, (I beleive the brand is "High Power") although they don't list them on their web sites:

http://www.texaselectricbikes.com/

http://www.thunderstruck-ev.com/contactus.htm

The fellow from EV tech has built some monster batteries out of these cells and they have performed really well

I was told to stay away form the Thundersky cells by an ex supplier. They had issues with quality controll, so a good percentage of the cells they shipped out were DOA, which is a real nightmare to have to sort out when building up packs.

This is basically the exact same thing i'm trying to accomplish for much less $$ with parallel pack balancing using cheaper cells (like ping batteries) Check out the cell balancing thread, its like 3 down from this thread.

Even if your spending less money on cheap cells, you can get nearly twice as many so that you don't even have to use a high discharge rate. If you don't have to use a high discharge rate, then you get extended range, it seems like a a very fair trade-off as you don't really end up losing anything.

We could probably assemble it for you and it wouldn't be that much, just shipping and such on-top of the original price (regardless of where you get your cells).

Yesa's website says they are develeoping 50Ah cells with 5C discharge rates. You might check with Sam to see if they are available. My two 36V 20Ah packs from Yesa cost less than $1.10 per Watt-hour, including shipping, BMS, and charger. So if the 50Ah cells are comparable in price, you would probably be able to get a 50Ah pack at 72V for less than $4000.

Jake

Sam is Yesa's sales rep.

Not exactly sure what you mean by 100AH cells (this would imply 100 amp hours as opposed to say...a max discharging current of 100 amps). At 72v this would be ALOT of money for Yesa batteries....

With my recent quote lets see what it would add out to.

"The price of LiFePo4 36V20Ah battery pack is USD 790 including the Battery Management System (BMS) and one 3A Charger."

Heres the picture http://www.yesa.com.cn/product_pack.asp?lb=2&id=0
12 cells....This adds up to 12 cells in in series, each producing approximately 3.2v and 20Ah. While i have my doubts about how such a small cell could possibly have a 20 AMP HOUR capacity...That is beyond the question being answered here. Ping similarly appears to mis-use the term as his batteries MUST discharge at 2C for the amperage draw to make any sense at all. However 2C is only a slight exaggeration, as oppose to like 5C. For instance, if i were to mis-use the same terminology with a123's i could say that one cell has a 230ah rating. This of course being calculated by multiplying the a123's MAXIMUM burst discharge current (100C) times the nominal amperage of 2.3A.

Anyhow...

onto the cost:
cost per cell in Yesa's pack: 790$ / 12 cells = 65.83$ per cell. Ok, maybe the amperage rating is accurate as these are VERY expensive per cell.... But... How much would 100Ah cost???

1 cell = 20Ah * 3.2V
if you want 100Ah and 72V thats 7.2kWh total. (means you can discharge 7200 watts for 1 hour straight or 1 amp for 100 hours...whatever)

so the amount of cells you would need is 7200 watts / (20Ah * 3.2 = 46watt/hours) = 156.5 cells total
at 65$ per cell * 156.5 cells thats 10173.9$

Only slightly higher then your original estimate ;)

Someone might want to check my math however, its been a long night. Anyway, hope this helps.

Do you need the very best highest discharge LiFePO4 system around well check out the LiFePO4 batteries from www.edealsbargains.com.au

see specs on ]the LiFePO4 below
Lithium Fe PO4 Batteries (LiFePO4)

Not all LiFePO4 batteries are the same as use a variety of different construction methods. Some give advantage of shape and using less space, others have the ability to discharge their stored charge over a shorter period (Maximum continuous discharge current or C-Rates).
The maximum continuous discharge current of a battery is important in high load settings such as an electric bicycle motor but less important to low prolonged current demanding settings such as lighting.
Battery manufactures indicate the “maximum continuous discharge current” by indicating its “C” value. A battery can continuously discharge a current calculated from its capacity (Amp hours) x “value” given from manufactures tests and unique to the battery and its design.

Examples:
- Battery with value “2C” 10Ah battery could provide a “max. continuous discharge current” of 2 x 10 ie 20 Amps.

- Battery with value “8C” 10Ah battery could provide a “max. continuous discharge current” of 8 x 10 ie 80 Amps

- Battery with value “2C” 40Ah battery could provide a “max. continuous discharge current” of 2 x 40 ie 80 Amps.
· Do not confused “max. continuous discharge current” with peak current of a battery. Peak current is very high but it is sustainable only for a few second and essentially represents shorting out the battery.
· Choose your battery carefully and spend your money wisely….. quality is remembered long after the cost is forgotten.
· If you have an application such as emergency lighting you do not need these high quality, high sustained current delivery batteries. The cheaper imports will be suitable.
· Because our batteries are high maximum continuous discharge current batteries – up to “13C” a 24v 10Ah battery could be used with up to a 3000W motor !!! (3000W motor draws 3000watts/24 volts current ie approximately 120 amps !!).
· If you research your LiFePO4 battery types we are confident you will be returning and choosing these batteries – not the cheapest – just the very best out there.

http://www.edealsbargains.com.au/page2.php for details on LiFePO4
or call dean on 0404977013 int. +614-0497-7013

180lbs of SLA Sheesh, what is it going into?

Well as far as total Watts your current pack is is 2952.

Probably going to need at least 100lbs or about 4.5-6kWh. Depending on what kind of cells you go with...If you go with expensive cells you can get less and keep the weight real low. Much more expensive though. Even given the high discharge rate of lithiums, unless you're going with like a123's or something, you still wanna discharge at less then 10C to make sure the batteries survive a long time, so you want a bit of wiggle room so to speak (so get at least 3.5kWh total).

If your going with cheap cells like Pings (although his seem a bit hard to come by these days) then you want to get more batteries just to make sure you have the same power as you did with the SLA. Of course you will also have a much improved range. (more total kWh the more range).

What kind of motor are you using? It will help as then I can look up when it is most efficient. For instance a motor running at 72v might be most efficient at 3500rpm and 6.4kW.

If you send me your Motor Specs with the Range and Top Speed you want to achieve I can spec. a LiFePO4 HPS System for you.
I think it could also be close to your budget and would include VMS & 3 Year warranty. Our Cells are rated @ Maximum Discharge Current (Continuous) of 120 Amps. Maximum Discharge @ 18 second pulse rate = 140 Amps.

Best Regards,

don [at] lifebatt.com

50lb motor? Ouch...but on the plus side...5500 rpm!!! Would love to have that.

Anyway, specing out a lifepo4 system would require that you know the efficiency of the motor, the weight of the vehicle with rider, the terrain, and the gearing. So that might be a bit hard. Knowing what the CURRENT amp draw is would eliminate the need for any calculations.

Doesn't seem to be a lot of details on that motor, or at least not in my quick google search.

The lithiums are a lot smaller then the SLA so it shouldn't really be an issue.

My advice is to keep your eyes open for a pack that doesn't look like a total scam and includes a bms that SUITS YOUR PURPOSE! Cell balancing and a nice charger would be good too. (actual balancing...not "auto-balancing with no apparent balancing circuitry") Or, bypass the bms and use something like a kelly pwm controller to manage the max amp draw. Personally I like the second option as then if its too weak you can always raise the ampdraw ceiling (potentially at the risk of lowering the life of the batteries, depending on their quality)

MOTOR SPECS IF YOU KNOW THEM:

Voltage
Nominal
Minimum
Maximum
Discharge Current

Discharge characteristic
Average
Peak
Minimum
Constant Pulsed Intermittent Random OTHER
mA Amps x C
mA Amps x C
mA Amps x C

Capacity
mAh Ah Wh kWh

Don Harmon

I checked your existing Optima batteries and they are rated @ 41Ah. So you now have a 72V /40 Ah System to be general.

We make an HPS-7210 LiFeBATT pack. The specs. for this is 72V / 10Ah. Size of this pack is 7.17" L. x 7.17" W. x 6.36" H.
Weight: 27.7 lbs ea. Price: $ 1,500.00 ea.

You can use (2) of these to get a 72V / 20Ah LiFePO4 system which would be the close equivalent to what you have now with your
Lead Acid system. With LiFePO4 you can acheive roughly the same performance using half the Amp hours that you use for Lead Acid.

Each Pack has it's own VMS (Voltage Management System) and you need to have a controller on your bike that can handle high & low
voltage cut-off. We currently do not make a 72V Charger, so you will have to supply one or you can use (2) of the LiFeBATT 36V
Chargers. Warranty is 3 Years.

Regular Charger 36V / 8A: $ 175.00 - Charges Pack in 2 Hours.
Speed Charger: 36V / 15A: $ 350.00 - Charges Pack in 30 Minutes.

Delivery direct from the Factory in Taiwan - Add $200 Shipping or wait until July of this year when we have stock here in the U.S.
Receive product two weeks from time of order now. This will change to 3-5 Days in July.

Best,

Don Harmon

Let me clarify - Warranty on Packs is 3 Years. Warranty on Charges is 1 Year.

Don

I checked your existing Optima batteries and they are rated @ 41Ah. So you now have a 72V /40 Ah System to be general.

We make an HPS-7210 LiFeBATT pack. The specs. for this is 72V / 10Ah. Size of this pack is 7.17" L. x 7.17" W. x 6.36" H.
Weight: 27.7 lbs ea. Price: $ 1,500.00 ea.

You can use (2) of these to get a 72V / 20Ah LiFePO4 system which would be the close equivalent to what you have now with your
Lead Acid system. With LiFePO4 you can acheive roughly the same performance using half the Amp hours that you use for Lead Acid.

Each Pack has it's own VMS (Voltage Management System) and you need to have a controller on your bike that can handle high & low
voltage cut-off. We currently do not make a 72V Charger, so you will have to supply one or you can use (2) of the LiFeBATT 36V
Chargers. Warranty is 3 Years.

Regular Charger 36V / 8A: $ 175.00 - Charges Pack in 2 Hours.
Speed Charger: 36V / 15A: $ 350.00 - Charges Pack in 30 Minutes.

Delivery direct from the Factory in Taiwan - Add $200 Shipping or wait until July of this year when we have stock here in the U.S.
Receive product two weeks from time of order now. This will change to 3-5 Days in July.

Best,

Don Harmon

Okay.. so you're saying we have to think of the bigger picture when buying LiFePO batteries .. just like one has to think of the bigger picture when buying a compact flourescent bulb. I first found CFL's in 1990 and while the price per bulb was eye popping I could do the math of the same number of lumens, requiring less electricity, and a longer lasting bulb, and see that over time a CFL will pay for itself even with the higher up-front price. I only buy CFL's, despite the higher up-front price, and have done so for nearly 20 years now. You could probably make a similar argument with the higher up-front price of LiFePO packs...?

$3000 + $350 + $200 = $3550 for 72v20ah + 2 8ah chargers + shipping ...???

Yes, his original question was if he could purchase a complete system for $4,000.00 per his needs? If you add it all up it's $3,900.00 including the Speed Chargers and warranty of 3 Years on his packs. Remember - All LiFePO4 are NOT created equal! This all works if you have cell specs close to what LiFeBATT offers: http://www.lifebatt.com/cellspecs.html We can't make claims on other LiFePO4 packs that are out there.

Don Harmon

With LiFePO4 you can achieve roughly the same performance using half the Amp hours that you use for Lead Acid.

I've seen this idea quoted elsewhere - that you can get twice the performance out of the same Ah comparing SLAs with LiFes. I'm not necessarily disputing it - but I am confused (and hence a little skeptical) and would like to understand the theory behind the claim a little better. I think it is to do with how the voltage remains higher for longer and then "drops off a cliff" with the LiFe batteries rather than the steady decline of voltage levels with SLAs, right?

However, what I don't get is why the LiFe batteries Ah rating wouldn't incorporate this fact into the stated capacity figure?

Can someone explain this to me or point me to a good resource?

Thanks.

:? :)

John , I Think that is because Amp hours is the mesure for TOTAL energy in the cell or battery Pb lead batterys start distructing and resistance goes up fast after the battery is about half full , as resistance goes up more energy is wasted in heeting up the battery Lifepo4 maintains it's low resistance till about 20-30% left . The two effects create the added range you experiance LaTer

Comparing Amp-hour ratings between PbA and LiFePO4 is tough. Peukert’s exponent explains the capacity expected from a PbA cell at given discharge currents. The equation is

I^x * t = Ah

I = current discharged

x = exponent

t = time

Ah = total Ah's

Most PbA cells have a Peukert’s exponent rating between 1.3 and 1.6. Good PbA cells have an exponent the gets closer to 1.15. We can’t assign this exponent to LiFePO4 because of chemistry differences, but an approximation of the Peukert’s exponent for comparison would be 1.05 for LiFePO4. As an example, a 20Ah LiFePO4 cell will produce approximately as much or more power as a 50Ah PbA cell at the same rated voltage.

Hope it helps ? For more info about LiFePO4 try this link: http://www.lifebatt.com/asksparky.html

Don Harmon

I'm obviously not understanding the math of that equation ..and it's been a long time since I last took a math class.. but the way I read that equation, a larger exponent results in more Ah.

The behavior I observe in lead acid batteries is the number of Ah's you get out depend on a) the quality of the battery, and b) the discharge rate. At a high discharge rate you tend to get fewer Ah's out than you get at a low discharge rate. Most SLA manufacturers quote capacity at a 20 hour discharge rate meaning a battery claimed to be 20Ah would be measured at a 1A discharge rate and if you discharged at 50A you might only get 10Ah out of the battery.

Don is surely right about lifepo4's not all being equal. even within the duct tape type, there are real differences between vendors. Less scientifically, I found the ping battery has a little less extra capacity than I was expecting, but I suspect I was on track for about 20 cycles of lifespan the way I was using the lead at the time. Despite the damagage I was doing, I was getting all the ah out of the lead, but only by continuing to ride a good 1/2 hour after they were dead. I know I'll want the best battery I can get for a bigger, faster scooter or motorcycle in my future. But right now the best lifepo4 battery is the one you can get your hands on, at a price you have the money to pay. I'm so glad I got my ping battery before the olympics messed with buisness in china. Don, I'm sure you will have no probem selling your superior product once it gets easier for us to buy it. Ping was very smart to put em on ebay.

Or according to the wiki..."For a lead-acid battery, the value of k is typically between 1.1 and 1.3 however."

Either way, it's definitely not fair to compare the ah discharge rating of the optimas with the continuous output of the lithium as most of these home-made EV's generally discharge the batteries at far above their nominal capacity...thus leading to a much shorter life, probably why they are being replaced in the first place.

Point being, its important to be able to handle the peak load and not just the "cruising draw".

Also, is it just me? Or are lifebatt's the most expensive non nano-phosphate batteries on the market. Granted, i suppose they have a long warranty and bms (no cms though).

Also...they are huge! http://i7.ebayimg.com/01/i/000/f0/c1/46be_1.JPG

pardon me if these aren't the same type, but it would make sense considering how heavy each of the lifebatt cells are. 359grams!

Anyway...simply comparing price, these are 72v 20ah (ah rounded im assuming) for $3000
whereas...for nano iron-phosphates from a123, 24 cells * 8 = 192 cells @ 18.3$ per cell = $3520, $500 more.
and of course the advantages of nano are pretty obvious.

A123 and LiFeBATT are both "nanophosphate" for your information.

Don Harmon

YUP

Whats with the huge (apparent) differences in performance then?
If there aren't any, how about posting more comparison info. I don't have any questions about a123's, they list everything about them in an easy to understand/navigate way on their site.

Really what I want to see is the discharge rate vs retained capacity as can be seen on the a132 site. If that information proves
to be of similar qualities to the a123's then i may have a customer or two for you.

I of course do not want to come across as overly critical, just skeptical as I like to make well-informed decisions.

Whats with the huge (apparent) differences in performance then?

WHAT HUGE DIFFERENCES IN PERFORMANCE ?

If there aren't any, how about posting more comparison info. I don't have any questions about a123's, they list everything about them in an easy to understand/navigate way on their site.

DO YOU FIND LIFEBATT'S WEBSITE HARD TO NAVIGATE? IT POSTS FAR MORE TECHNICAL INFORMATION THAN IS AVAILABLE ON A123'S WEBSITE !

Really what I want to see is the discharge rate vs retained capacity as can be seen on the a132 site. If that information proves
to be of similar qualities to the a123's then i may have a customer or two for you.

HAVE YOU TRIED THIS LINK ?: http://www.lifebatt.com/cellspecs.html

I of course do not want to come across as overly critical, just skeptical as I like to make well-informed decisions.

CERTAINLY, WE HOPE EVERYONE WOULD TAKE THE TIME TO CAREFULLY COMPARE CELL SPECS. BEFORE JUST BUYING ON PRICE ALONE. IT'S DIFFICULT WHEN COMPANIES DON'T PUBLISH THEIR SPECS ON THEIR WEBSITES.

On a seperate note since you mention A123, what can you actually purchase other than their "Developer's Cells? ? These would be the 26650M1 cells. Do they offer any complete packs with BMS and Chargers ? Do they really offer the public anything OTHER than small packs of "Developer's Cells ?

Where are the A123 Total Solutions products ? Oh I know you can crack open DeWalt power packs and go it on your own and make a decent system if you have the skill and patience and do not care about warranties. I am not trying to come across as overly defensive, just curious as I have tried to put out the best product line in the LiFePO4 marketplace targeted to Electric Vehicles.

Best,

Don Harmon

You sound pretty overly-defensive to me, and especially when i was right on the verge of changing my mind about lifebatt. =] Honestly i don't have any "loyalties" one way or the other, i'm going to be building a full-scale e-motorcycle in a few months and I want to be absolutely as well informed as I can possibly be, which is why i'm doing all this r&d beforehand. As a mech-engineer student, this is the hard part for me (learning about electronics), the building and such is the easy part. So I'm not really trying to argue one way or the other, i would just like to figure out why there inconsistencies in my understanding of whats going on (as opposed to assuming that these inconsistencies are an indication that one manufacturer is being misleading).

However, in the spirit of argument, to which I will always enjoy, here are my "quirks"
For starters, the lab tests page om the lifebatt site is not up. If its not up, there really shouldn't be a tab, just add the tab later.
Second...is there a place where it says nano? I hate to categorize, but other then checking out the website of the place you say is the supplier, theres no way to know.

I did find a bunch of new info by digging through the pdf. 60% of capacity at 10C The a123 graph shows about 99%+ retained capacity at 10C and above.
The 7C graph appears OK, but it only goes up to 250 cycles.

The "Burst" capacity on the a123 site is "over 100C" however they don't specify the length of the time where as yours is listed at 40C but the time IS listed..18s.

The maximum continuous current for one 72gram a123 cell is 70A
the maximum continuous current for one 359g lifebatt cell is 120A

so relative to eachother...359g of a123's is 359/72 = 4.98 * 70A = 350A
So while by weight, a123's can deliver 350 continuous, lifebatt can only deliver 120A

Anyway, for similar pricing, it would be nice to know how big these differences in performance really are. Not that I would actually buy a123's now anyway because of the high price and lack of bms/charging ability, but it could be useful in the future. I already have someone designing a pack balancer, i may extend that to a bms or cms for future models.