lipoly v. lifepo4

[gunthn]

Forgive my ignorance here, but can someone clue me in as to the weight vs. power comparison on the two.

Let's start with a ping 48v 20ah Wgt. 9.5kg power 58v x 20ah = 1160 kw

Lipoly (somebody fill in the blank here for wgt. v. pwr. comparison)

Thanks

 

[recumpence]

Actually, your Ping would be under 1kwh. It is 48 volt not 58 volt.

A typical Lipo 48 volt, 20ah Lipo pack would weigh around 14 pounds. You can get that down to 10 pounds if you really search for high density cells. But, for High C rating (20C or better), you are looking at 14 pounds weight with wires and connectors.

Your Ping will not have any where near the power output of the Lipo pack. That 20AH pack I mentioned is good for 400 amps burst or 200 amps continuous with very little voltage drop under load!

Lipo is the shining star for output as well as weight (they are normally half the weight of Life Po4). They are not without their hazards, though. You need a proper charger and you also need to adhere to some specific handling cautions to use them safely.

Matt

 

[gunthn]

here is a specific battery for comparison

HYPERION G3 VX 6s 5000 MAH 22.2V 35C 812g.

22.2 x 3 = 66.6v

5000ah x 4 = 20 ah

4 sets at 20ah x 3 to exceed the voltage of the ping by 8 v (pings actually charge to 58v not the nominal 48v)

12 sets x 812g. = 9.744 kg. 20ah x 66.6v = 1.332 kw

ping 9.5 kg 20ah x 58v = 1.16kw

they would seem rather equivalent according to this rough (if perhaps flawed analysis

please do correct my errors here. C rating aside there seems no comparison there but 200amps is way more than I need..

as for cost the lipos would seem to exceed the ping by a factor of three but again clue me in here I have no experience with lipos(or pings for that matter), and I would try if I thought the cost/benefit was there.

 

[Russell]

I don't have a PING but I do have a 16 cell "48V" LiFePO4 battery and while the charger goes up to 59.3V the battery voltage falls quickly after the charger is removed. On the bike the surface charge burns off rapidly until the voltage is around 52-53V. The average voltage the battery puts out, which I derive by dividing the total Watt-hours consumed by the total Amp-hours used is usually 50-51V. I suspect a Ping is similar to my battery so I would use 50V and not 58V when determining capacity and making comparisons.

-R

 

[Miles]

Ok, Power density isn't important, for you. How about energy density?

Ping = 97 Wh/kg

Cheapo 20C Turnigy Li Po = 138 Wh/kg

Comparison done using nominal voltage ratings........

 

[Ypedal]

You also have to consider volume, the Ping will be bigger in size vs lipo by a significant amount ( have to google the specifics actually.. brb)


edit :

Ping type:
http://en.wikipedia.org/wiki/Lithium_iron_phosphate_battery

Volumetric Energy density = 220 Wh/L

Lipo type :
http://en.wikipedia.org/wiki/Lithium-ion_battery
Volumetric energy density: 250 to 530 Wh/l

 

[TPA]

here is a specific battery for comparison

HYPERION G3 VX 6s 5000 MAH 22.2V 35C 812g.

22.2 x 3 = 66.6v

I think that is nominal voltage. If you want to compare hot off the charger, as you are doing with the ping, it should be about 4.1V/cell for the lipo

4.1V X 6 = 24.6V

24.6V X 3 = 73.8V

73.8V X 20Ah = 1476 Wh.

some folks charge to 4.15V with lipo

 

[Russell]

If you want to compare hot off the charger, as you are doing with the ping, it should be about 4.1V/cell for the lipo

No one should compare a LiFePO4's voltage hot off the charger to LiPo or LiMn because that voltage for a LiFePO4 battery is meaningless. The surface charge on a LiFePO4 can be several volts which is burned off in seconds once under way.

-R

 

[gunthn]

If I measure mine after say a ten mile ride it is still registering 55+ volts and I imagine that a lipo would register high as well if charged to say 4.1v per cell.

But this has been enlightening and show in more concrete terms the advantage of lipos over lifepo4

Ok. how about cost?

What are people paying and what is a 'good deal'?

 

[TPA]

If you want to compare hot off the charger, as you are doing with the ping, it should be about 4.1V/cell for the lipo

No one should compare a LiFePO4's voltage hot off the charger to LiPo or LiMn because that voltage for a LiFePO4 battery is meaningless. The surface charge on a LiFePO4 can be several volts which is burned off in seconds once under way.

-R

Well, TBH, one should not use the "hot off the charger" value to get Wh capacity anyway. It should be nominal voltage for all batts when making comparisons between chemistries, correct?

 

[gunthn]

i did ask forbearance for my ignorance

 

[Doctorbass]

Hot of the charger mean nothing because it's only 5% of the discharge voltage level.
You really need to know what is: NOMINAL VOLTAGE OF A CELL

The real reference state that:

EXPLANATION OF LITHIUM ION NOMINAL CELL VOLTAGE

The nominal voltage of a cell is the AVERAGE voltage this cell will have when discharged at 0.5C between the fully charged voltage down to the lower voltage cut.

So it's average voltage during discharge from these voltages:

LiFePO4 are 3.6V to 2.0V

LiMNO2 and LIPO are 4.2V to 3.0V

Doc

 

[swbluto]

I wish that's what "nominal voltage" was. Nominal anything basically means "by name" or whatever someone describes it as. The name of something does not have to adhere to a standard such as the 50% SOC level OC voltage, but that would be nice.

Example, ping's "48 volt" battery is nominally 48 volts. That's the nominal voltage that ping has given it / named it as. That entails that the nominal cell voltage is 3 volts, however, the open circuit voltage of a lifepo4 cell is definitely not 3 volts at 50% SOC. It's 3 volts at 50% SOC only at some given current level, that dependent on its internal resistance which is again dependent on age, temperature and other minutiae.

I think what we're looking for is the average output voltage when comparing the two chemistries.

 

[Ypedal]

LFP has a very flat voltage profile, roughly 3.1 to 2.8v under load for most of them.

Lipo/cobalt/manganese have a slope profile that goes from 4.2 down to 3.0, state of charge can be determined by voltage under load pretty accurately, something you can't really tell with LiFePo4

 

[Russell]

Well, TBH, one should not use the "hot off the charger" value to get Wh capacity anyway. It should be nominal voltage for all batts when making comparisons between chemistries, correct?

Yes that's true if you don't want to get into the nitty-gritty details which can get pretty...uh, gritty. There are differences in cell counts and discharge characteristics that affect the working voltage, for example there are 10 cell LiPo/LiMn and 12 cell LiFePO4 '36V' packs and 14 cell LiPo/LiMn and 16 cell LiFePO4 '48V' packs and each has a different nominal voltage but for convenience we label them the same. Ebikes.ca is even offering a 15 cell '48V' LiFePO4 pack!

Here’s a couple of curves that illustrate how different the discharge characteristics of LiMn and LiFePO4:





At first glance you may say LiFePO4 is better because it's flatter but you can see it came way down from the initial charger voltage whereas the LiMn curve decends from a higher starting point. With LiMn (and I'm guessing LiPo) where you charge it is where it stays and then it slowly declines from there as you use it.

I was kinda disappointed that my 48V LiFePO4 didn't have a higher average voltage output but that's my fault I guess for not studying the curves more closely. For maximum speed from a '48V' pack I'd probably want a 14 cell LiMn or LiPo pack because it would have a genuine starting voltage of up to 58.8V (assuming 4.2V/cell) compared to about 54V for LiFePO4 (once the useless surface charge is removed). For '36V' packs it makes less of a difference and a 12 cell LiFePO4 would probably have a small advantage over a 10 cell LiMn/LiPo pack. My little 36V/6Ah LiMn pack delivered on average a 37.0V output but could vary from 36.3V to 38.1V depending on the depth of discharge and how hard it was run. If that were a 14 cell pack I therefore would expect an average of 51.8V compared to my present 48V LiFePO4 pack which has delivered a real-world average of 50.4V over 11 cycles. Of course with any chemistry the stouter the cells the higher the average voltage will be under the same load.


-R

 

[Doctorbass]

I wish that's what "nominal voltage" was. Nominal anything basically means "by name" or whatever someone describes it as. The name of something does not have to adhere to a standard such as the 50% SOC level OC voltage, but that would be nice.

Example, ping's "48 volt" battery is nominally 48 volts. That's the nominal voltage that ping has given it / named it as. That entails that the nominal cell voltage is 3 volts, however, the open circuit voltage of a lifepo4 cell is definitely not 3 volts at 50% SOC. It's 3 volts at 50% SOC only at some given current level, that dependent on its internal resistance which is again dependent on age, temperature and other minutiae.

I think what we're looking for is the average output voltage when comparing the two chemistries.

Well I did a mistake!.. I had a bad information, sorry for that guys.

The Battery university website state that Nominal voltage of a Lithium ion cell is determined like this:

The nominal voltage of a lithium-ion battery is calculated by taking a fully charged battery of about 4.20V, fully discharging it to about 3.00V at a rate of 0.5C while measuring the average voltage.

Because of the lower internal resistance, the average voltage of a spinel system will be higher than that of the cobalt-based equivalent. Pure spinel has the lowest internal resistance and the nominal cell voltage is 3.80V. The exception again is the phosphate-based lithium-ion. This system deviates the furthest from the conventional lithium-ion system

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

So it's with 0.5C and using the average.. Swbluto, you are right about the average

Doc

 

[swbluto]

http://endless-sphere.com/forums/viewtopic.php?f=14&t=12382

Here's a thread where I, Doctorbass and a few others quantatively compared the energy density differences between archetypal products of lifepo4 and lipo. It was found that lipo had about 1.5-1.6 times the gravimetric energy density (when you care about weight) and nearly 2x the volumetric energy density as ping's lifepo4 (What you care about when you have little space).

The C rates of the best of the best are pretty comparable between the two, so that'd suggest the power densities would mirror the corresponding energy densities of each chemistry.

 

[recumpence]

http://endless-sphere.com/forums/viewtopic.php?f=14&t=12382


The C rates of the best of the best are pretty comparable between the two, so that'd suggest the power densities would mirror the corresponding energy densities of each chemistry.

Really? So, you can get 30 to 40C Lifepo4? I thought Lifepo4 were limitted to 10C or so. 30C is not uncommon for Lipo. Heck, I have seen 60C Lipo.

Matt

 

[nsasch]

It's rare to see more than 2C out of LiFePo4, besides A123, even among the high-priced American-made batteries.

We can all just wait for EEStor's super-capacitor to come out. That will solve all of our problems. :lol:

 

[gunthn]

One more question.

How the hell do you charge 12 lipo packs at the same time.

 

[Doctorbass]

http://endless-sphere.com/forums/viewtopic.php?f=14&t=12382


The C rates of the best of the best are pretty comparable between the two, so that'd suggest the power densities would mirror the corresponding energy densities of each chemistry.

Really? So, you can get 30 to 40C Lifepo4? I thought Lifepo4 were limitted to 10C or so. 30C is not uncommon for Lipo. Heck, I have seen 60C Lipo.

Matt

A123 can do 60C and 30C CONTINUOUS

but one IMPORTANT thing is that A123 can be charged at 4.3C and still have 1000cycles

LiPo can't be charged that fast without compromizing cycles life

this is Why Electric Drag Racer love them.. fast charging... and ther high power per kg

Doc


Doc

 

[swbluto]

http://endless-sphere.com/forums/viewtopic.php?f=14&t=12382


The C rates of the best of the best are pretty comparable between the two, so that'd suggest the power densities would mirror the corresponding energy densities of each chemistry.

Really? So, you can get 30 to 40C Lifepo4?

Top-level insider connections to A123 can. :wink: Their newest products can put out twice the C-rate of their older generation due to new anode design (New anode design is also the main reason behind most of the recent lipoly advantages).

It's interesting, though, how "common" lipo providers can seemingly develop high C rate lipoly so "easily" whereas it seems high-C development with lifepo4 is limited to a123. I wonder what's the cause of the difference? Is lifepo4 development inherently more capital and research intensive?

 

[amberwolf]

Maybe a123 is just better at foiling industrial espionage.

 

[recumpence]

http://endless-sphere.com/forums/viewtopic.php?f=14&t=12382


The C rates of the best of the best are pretty comparable between the two, so that'd suggest the power densities would mirror the corresponding energy densities of each chemistry.

Really? So, you can get 30 to 40C Lifepo4? I thought Lifepo4 were limitted to 10C or so. 30C is not uncommon for Lipo. Heck, I have seen 60C Lipo.

Matt

A123 can do 60C and 30C CONTINUOUS


but one IMPORTANT thing is that A123 can be charged at 4.3C and still have 1000cycles

LiPo can't be charged that fast without compromizing cycles life

this is Why Electric Drag Racer love them.. fast charging... and ther high power per kg

Doc


Doc

The big problem with high C discharge on A123 cells is voltage drop. Yes they can support huge C rate, but they drop huge voltage in exchange.

On my 12S 3ah Lipo pack, I only see a 4 volt drop at 400 amps! Correct me if I am wrong, but A123 will not do that. Also, A123 are heavier than Lipo.

The big difference is safety. Lipo are less stable than A123.

Matt

 

[nsasch]

One more question.
How the hell do you charge 12 lipo packs at the same time.

I second that. Most LiPo cells can charge at 1 or 2C, but I have yet to find a charger that can supply that sort of current for high voltage packs (24-48V). I would switch to LiPo in a second, if I could find a charger that can charge 2kW-h in an hour.

Long trip? Put your batteries in a backpack, plug in your charger at Starbucks, pray that the lights don't dim, and start to use your laptop. An hour later, you've got 2kW-h.

I'm sure chargers do exist, but nothing I could find for consumers. Something can be done about it, but is there a solution now?

LiFePo4 chargers are a lot simpler and can be designed for 2000W or more, easily.