PINNED - Lithium battery conversion/info

[wilsonintexas]

ok, I am getting there. But that means I ask really dumb questions. I did re-read this thread and did not see his topic discussed. I understand no monoblock, the c is to low. I also saw some other headways that were rated at 3c, not the 10c. So I know I need to be careful and be sure I am looking at apples to apples.

As I was looking for a local supplier, and came across some batteries rated at 40. 50, and even 100c. That seems like they are gilding the lily.

But, for a starting point, these are 7.4 volts, and rated at 60 amps, for $47 each. I could put 5 in series, for 37 volts, and a 4 in parrell, for 240 ah for about $950.

some go as high as 100c..... If we are after high C ratings, when do they become unbelievable?

I know hat connecting them gets to be a challenge, but they have gold plated terminals available, which should be decent.

Just one example.

I am still leaning toward the headway, the screw terminals and connection plates make assembling them more reliable. But since I do not have a space limitation, it looks like I can get the voltage and current ratings a little cheaper. ... but just asking.


code 98P-60C-4200-2S2P-Hardcase-Shorty

Weight (g) 206
capacity (mAh) 4200
max cont discharge rate (C) 60
max burst discharge rate (C) 120
max cont current (Amp) 252
max burst current (Amp)? 504
Series (S)? Parallel (P) 2S2P
Length(mm) 95.55
width (mm) 46.64
Thickness(mm) 25.16
Wire Gauge 12
code 98P-60C-4200-2S2P-Hardcase-Shorty

is it even worth looking into these

[Williamclark77]

No. Those are lipo, which are lithium polymer. Not Lifepo4, which are lithium iron phosphate. Very different chemistry. Lipo are amazingly powerful batteries, but very unsafe for this use and can only be discharged a few dozen times. Lipo batteries are for hobby type stuff like remote control cars and planes. Most are recommended to be charged in a kevlar fireproof bag outdoors. These batteries do not play. Lifepo are what you want. Quite safe with a long life.

The US dealer for Headway is Headway-headquarters.com. I've bought many lithium cells from them. Go browse their site and keep asking questions no matter how dumb you think they are.

[Burgerman]

> I also saw some other headways that were rated at 3c, not the 10c.

Certain suppliers (not the manufacturer) downrate them to 3C and 5C for some reason. Probably because 10C seems too much and in reality they are maybe 7C or 8C, as the manufacturer claims are unrealistic. So suppliers downrate them so as to not get as many returns due to abuse. They do the same with the prismatics and say they are .3C cont etc on some sites.

The BLUE headways are all really 10C and regularly used at 10C by the eBike community. There are some hard to find red headway cells that are higher C albeit at a slightly lower capacity (only 8Ah). So ignore that 3C spec and just buy. Don't let these suppliers talk you into a BMS either. That's a sure way to get lots of problems...

http://www.wheelchairdriver.com/BMS.htm

[wilsonintexas]

I have see the red 8ah ones available, they seem to be 10c as well. I saw them for about $15.0 each.

What is the real C rating on them? on evassemble, they list the max continuous current at 80, so that would be 10c. If t is higher, it might be a good buy.

[Burgerman]

There were 10Ah 10C cells.
And red 8Ah 15 - 20C cells.

Same physical size. For our purposes its best to go with the blue ones. And to fit as many as you can in the space we have available. Even the prismatic will work. I would personally go with prismatics like CALB in a car where there a lot of space for a big pack (which lowers the load per cell) as they are cheaper and less cells required. But on an ebike or motorcycle/powerchair the blue headways. Might use the red ones on a drag bike!

[wilsonintexas]

Got it, blue ones it is..... for the last time


I just found the list of electronics in the thread of were to get things. So I will start adding them to the spreadsheet.

[Burgerman]

You will need to think about chargers if you plan on more than 24v as the 14S charger that I use is out of production. There are 8 cell chargers, (24v) easy enough. But you will need two and split the batteries electrically to charge 13 series.

[wilsonintexas]

I was looking at the

HYPERION EOS 720i Super Duo
7S 16N Charger-Dual 20A/500W 14S

It sounds like it is two 720 chargers packaged together. It is about $279 here in the states.

I still need to figure out the best way to break down the battery build to be able to charge it on duo charger. I do not know if I can do one large cell and just hook up the tap leads to each of the sides.

Or
do I need to basically make 2 packs, and then with Anderson connectors join them when running.

[Burgerman]

No because both the black charge leads are at the same 0Volts.

You will need to split it into a 7 cell and a 6 cell pack. And charge separately. Or find another 13 or 14 or more charger.

[wilsonintexas]

I found this one for $229. L little cheaper than a hyper dual.

this is from the manual:
The TP1430C is capable of charging/discharging 1S (3.7V) to 14S (51.8V) LiPo, LiIon and LiFe (A123) batteries, as well as 1-40 cell NiCd and NiMH along with 3S (6V) to 24S (48V) Pb (lead-acid) batteries

so far that is the only one I have found that can do more than 12s.

but still looking.

[wilsonintexas]

nix that charger, no PC interface. I will split the battery pack and go with 2 chargers in sync or a duel charger.

[Burgerman]

Buy a large high power iCharger.

[wilsonintexas]

looking into them, I found this comparison chart on the icharger site. Looks like they are limited to 10s.

That site has a nice write-up on lipo batteres.
http://www.icharger.co.nz/articles/Arti ... eries.aspx

Here is a comparison table.

[Burgerman]

12Ah 10C continuous cells that I am using. http://www.headway-cn.com/en/showproducts.php?id=1561
Headway actual manufacturer site.
There are 20C too, same size as 10Ah, but just 8Ah instead but higher C rate.

[Burgerman]

http://www.chargery.com/doc/Chargery%20 ... 20V3.1.pdf

Battery level, alarm, state of charge meter that works and is for up to 16 cells or 48v systems.

And small simple cheap.

[wilsonintexas]

It looks like they have two new cells out, a 50ah and a 100ah cells. They look pretty lzrge, the 100ah cell weighs in at 3kg. I am checking the cost. it will be interesting o see the cost.

50 ah
Specification
Nominal Voltage 3.2V
Nominal Capacity(0.5C,25℃) 50Ah
Weight(Approximate) 1.6kg
Dimension(Diameter*Height) Φ63*219mm (ABOUT 2.5 IN BY 8.6 IN)
Standard Discharge(25℃)
Max. Continuous Discharge Current 100A
Discharge Cut-off Voltage 2.5V
Standard Charge
Max. Charge Voltage 3.65V
Max. Charge Current 100A


100ah

pecification
Nominal Voltage 3.2V
Nominal Capacity(0.5C,25℃) 100Ah
Weight(Approximate) 3kg
Dimension(Diameter*Height) Φ76*306mm (ALMOIST 3IN BY 12IN)
Standard Discharge (25℃)
Max. Continuous Discharge Current 100A
Discharge Cut-off Voltage 2.5V
Standard Charge
Max. Charge Voltage 3.65V
Max. Charge Current 200A


12ah
Items Specification
Nominal capacity 12000mAh (0.5c)
Nominal voltage 3.2V
Battery internal resistance ≤6mΩ
Maximum charge current 5C（60A）
Maximum charge voltage 3.65±0.05V
Maximum discharge current 10C（120A）
Cut-off discharge voltage 2.0V
Maximum dimensions Diameter 38±1mm (ABOUT 1.5 IN BY 6.6)
Height 142±1mm
Weight About 400g

[Burgerman]

Look at the C rate.

The large cells are 2c and 1c only at maximum allowable rate (much shorter life if you go near that maximum).

The smaller cells I use are 10C so much higher current rated. 5 and 10x greater. So its easy to keep away from the limit, and gain greater service life and long term reliability. Bigger cells work fine too, especially in say a car where there is room for a very large pack - meaning the cells don't get worked as hard.

In any lithium system you need to aim for high C rate, large capacity, if you want good longevity and take advantage of the opportunity and advantages of lithium.

Alternatively, you CAN fit a small capacity and not particularly high rate lithium battery. And get non of the long service life, longer range, or better performance advantages offered. This is what the manufacturers will do. It cheap, and easy to do and good for marketing...

[JoJo7]

I am just beginning to plan converting my wheelchair to lithium batteries. I have been reading this thread but still have some fundamental questions I could use help with:
1) am I correct in understanding that if, for example, you wanted to make something to substitute for a 12 V lead battery you would wire 4 lithium cells in series? For example, if you are using 20 cells altogether they would be wired up as a series of 4 groups of 5 parallel wired cells and that, after the initial cell-by-cell balancing you described in one of your early messages, you re-charge using the Hyperion as if you had 4 cells to balance during charging?
2) I thought that lithium cells required balancing during discharge also. I can't find where you describe whether/how you do this in your lithium powered chairs.
Regards,
Joe

[Burgerman]

1. Yes.

2. They don't need balancing and should NEVER be balanced at any point other than when full while charging.

[JoJo7]

Thanks for the verification of my understanding of item 1.
I'm still unclear about the 2nd question:
There are many sites on the Internet that describe balancing lithium cells while DISCHARGING. For example the following paragraphs from Wikipedia:

http://en.wikipedia.org/wiki/Battery_balancing
/*------------------------------
"Typically, the individual cells in a battery have somewhat different capacities and may be at different levels of state of charge (SOC). Without redistribution, discharging must stop when the cell with the lowest capacity is empty (even though other cells are still not empty); this limits the energy that can be taken from and returned to the battery.

Without balancing, the cell of smallest capacity is a "weak point", it can be easily overcharged or over-discharged while cells with higher capacity undergo only partial cycle. For the higher capacity cells to undergo full charge/discharge cycle of the largest amplitude, balancer should “protect” the weaker cells; so that in a balanced battery, the cell with the largest capacity can be filled without overcharging any other (i. e. weaker, smaller) cell, and it can be emptied without over-discharging any other cell. Battery balancing is done by transferring energy from or to individual cells, until the SOC of the cell with the lowest capacity is equal to the battery's SOC.

Battery redistribution is sometimes distinguished from battery balancing by saying the latter stops at matching the cell's state of charge (SOC) only at one point (usually 100% SOC), so that the battery's capacity is only limited by the capacity of its weakest cell."
/*------------------------------

What am I missing?

[shirley_hkg]

That's why only cells with same capacity are put together to form a battery pack.

Dynamic balancing is good but very complicated and expensive. We don't need that either. Essential is to avoid any cell being discharged below 2.5V.

What I do is to watch the overall voltage not below 25V during use ; for 8S 24V setup. We control the discharge manually.

[JoJo7]

I still don't get it. 8S, 25V-> 3.1V each cell?

[shirley_hkg]

Assuming the worst scenario, only 1 cell gets bad and all the other 7 are full.

3.3 X 7 + 2.5 = 25.6 V.

[Burgerman]

Regardless of cost balancing while less than 100 percent is bad.

You cannot balance them at 95% down because the voltages do not drop. And may even rise on some cells depending on temperature etc. Different cells may be a few mV different even at the exact same state of charge. SO "BALANCING" based on accurate voltage actually may spend all day UNBALANCING by capacity.

Balance at the top above 3.45v only. Preferably above 3.50v Never lower.

When battery is empty, all cells will drop roughly the same time. Monitor these, once. Whichever group becomes empty first, is the only one you need watch in the future. But by the time this one drops from 3v down to 2.5, the rest will also have started falling significantly.

Then because you have not messed about with them, they will all still be perfectly balanced on recharge, taking just a few seconds to complete the charge. Each one needing the exact same Ah replacing to fill to 100%.

[steves1977uk]

http://www.rcgroups.com/forums/showthread.php?t=2319645

Trying to get a proper preset made for the Headway cells on the PL8.

Steve

[Burgerman]

Why would you need one? Charge as A123 or LiFe cells. Or if they insist on charging while balancing too low then make a custom setting.

[steves1977uk]

That's the problem... the presets for A123 setups which doesn't allow the balance voltage to be set any higher than 3.30v, even if you customise it. There isn't any presets for LiFe and the only presets that allows the balance voltage to be set at 3.50v are the LiPo generic ones which uses a slighty different charging algorithm I take it?

So that's why I'm seeing if the guys who make the charger can provide the proper charging algorithm for A123/LiFe cells.

Steve

[Burgerman]

It will still work as you charge it at a sensible rate. It will just unbalance it to begin with a little and then fix it later on...

[Burgerman]

If you take a 3.60v per cell fully charged pack and remove .5 of an Ah from it the voltage is then approx. 3.35v per cell. But not exactly the same across every cell. There may be a .010 variation across them. This 3.5v per cell may stay the same (or even rise slightly as temp increases), as you take the next 20Ah or so out...

So lets say you have 7 cells at 3.310v and 1 cell at 3.390v. (Even though they are all in EXACTLY the same full minus .5Ah state). Sometimes this difference is the charger or BMS inaccuracy, sometimes its a real difference.

If you then try to make that ONE cell fall by 0.080v to match the others, you (or the BMS / Charger?) will need to remove possible 20 Ah to do so. Now you have a battery where 1 set of the 8 is 20Ah OUT of balance! But the voltages match...

Only LiFePO4 do this, and only some types. So it makes no sense to try and determine state of charge or to balance them at any other time other than FULL based on terminal voltage. This is one reason BMS ruin them...

[steves1977uk]

Thanks for the explaination BM

One question I do want to ask, is it normal for a pack to take about 10 hours to charge after 7-8 days usage indoors? The charger cuts off after 8 hours and I have to start it again to finish off the balancing part.

Cell rows 1 and 2 charges to about 3.450 volts and then drop away in the range of 3.363-3.370 volts and slowly recharges at 1 amp until they are within 0.04 volts of cell rows 3, 4 and 5 which hover around 3.471 volts.

Cell rows 6 and 7 are in the 3.530-3.540 range and cell row 8 charges to 3.600 volts and waits for the others to catch up.

Once the pack is charged, the cells are within 0.04 volts of each other after a few minutes of use (3.30-3.34 volts).

Steve