Homemade Battery Packs

C rates are off to the right side of the graph, at least on my image.
otherDoc

DrkAngel said:

liveforphysics said:

DarkAngel- Just for fun, where would you place the maximum usable C-rate for this LG 18650?

Click to expand...

You forgot to list the C rate usage, for each different colored line!

Which is the entire purpose of the graph!

Click to expand...

Get a wider monitor. lol

Or right click, save picture as, and then you can view the whole thing.

Or right click, find image source, and view there.

"Maximum Usable" is almost directly in apposition to "recommended usable".

Although I tested my new pack as 2 "C" capable, I feel it to be very comfortable at my .3 -.5 "C" "continuous usage" rate.

I prefer to cruise, ... for hours! ... Not race, or climb hills at 6C for <10 minutes!

For my purposes, my 10lb 31.2ah Li-ion pack is ideal.

Oh! ... and total cost, including 25.9v Li-ion charger, was about $50.
No, not a balancing charger, but charged my pack, with all cells, well within safety range. (4.17v - 4.2v)

Tenergy Intelligent 2A Charger for 25.9V 7S Li-ion / Li-Polymer Battery Pack - $23.63

The Tenergy "Intelligent" Li-ion seems to be designed to not require a PCB (BMS).
"# Patented 4 Stage charge algorithm guarantee 100% Protection ...
# Automatic change 7S 25.9V Li-Po/Li-ion battery from any status."

View attachment Tenergy Li-ion.pdf

I would thing that, with 2 amps, into an 31ah pack, it is possible that any possible overvoltage might be safely dissipated, as moderate heat?

"Homemade" 25.9v 31.2ah Li-ion pack.
Just finished my first trial run. Took 2 days. Cruised at an average 18 mph. Of course I was "forced" to take a few "runs" at 22+mph.
Cruised for about 30 miles, then spent today riding around town, checking out the local "Community Yard Sales Weekend" ... another 11 miles. Finally decided to recharge, after red battery level led flickered under moderate throttle, red led indicates 24v level.

Residual voltage was measured at 25.8v, down from 29.4v. Using a, very safe, 24.5v as empty, (3.5v per cell).
Wow! That figures to 55.8miles per "full charge" ... without pedaling!!!
edit: "Empty" recalibrated as 3.6V (25.2V pack voltage).
"Motor only" range 45-50 miles!

Less than 14.4Wh/mile is pretty good. (actually probably a lot less, as that would assume 100% DoD of 808Wh (25.9 x 31.2), and you probably didn't really run it down that far, right?)



On my very heavy CrazyBike2, with speeds about like yours, my aged, needs-rebuilding ~11Ah 48V LiFePO4 Vpower pack (~600Wh capacity left in it) gets about 20 miles at around 27-29Wh/mile.

The pack is made of cylindrical 18650 cells. I think the BMS is setup to cut off at about 80% DoD, IIRC, but I'm not certain of that. There are a couple bad strings in it that need repair, that drop a lot faster than the others, or I'd get more range out of it.

I can push range to ~27 miles or more if I keep it down to 12-15MPH, but all the starts and stops in traffic combined with the heavy bike are pretty hard on the pack.


I still have about 300 LiCo cells that I'd like to sort and build another pack from, but I keep having to put that on the back burner. I'm sure there are a significant amount of bad cells, so I figure by now I'd get about 200 good ones out of that, at ~1.5-2Ah each, for a minimum theoretical ~1KWh of power (though I don't expect I'd actually end up with that much).

So I'm watching this thread among others for potentially helpful info once I get around to doing this.

DrkAngel said:

I would thing that, with 2 amps, into an 31ah pack, it is possible that any possible overvoltage might be safely dissipated, as moderate heat?

Click to expand...

Well, that depends on the chemistry. LiCo doesn't work that way, AFAICR, though there are versions of Li chemistries that do (LiMn? whatever the "Konion" cells are made of, IIRC).

liveforphysics said:

DarkAngel- Just for fun, where would you place the maximum usable C-rate for this LG 18650?
It has 3.05watt-hours usable energy at 3C (and can only deliver that much energy if you're hitting it continuously so the cell stays hot from the initial voltage drop heating it).

Or, 7.7 watt-hours usable energy at 1C.

Or, 9.4 watt-hours usable energy at 0.2C

Also, would you continue to call it maximum C-rate if the cell sagged below 1/2 resting voltage at that C-rate (normally these little feces cells just saturate the current collector and fall on their face before this happens), so that as current output increases, the amount of power you're getting from the cell is decreasing?

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Wow, that is horrible. 1C is stressing it out. And that's a *new* cell.

I cannot argue with the price, then again i would never want to solder together all those cells.

neptronix said:

Wow, that is horrible. 1C is stressing it out. And that's a *new* cell.

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What are you talking about?
Your graph states that, at 1C, the 18650 Li-ion cell provides 92% of rated!

Brushless motors are typically 85-90% efficient whereas brushed DC motors are around 75-80% efficient.

The best controllers can, typically, attain 95% efficiency ... but only at full throttle!
Partial throttle provides worse efficiency, than the Li-ion at 1C.

Logical conclusion?
Li-ion cells, even at 1C, would be, the strongest, (most efficient), component, of a typical eBike propulsion system!

neptronix said:

I cannot argue with the price, then again i would never want to solder together all those cells.

Click to expand...

My pack took about 10 minutes to solder the cells, and another 15 min to add the balancing wires. ?

P.S. With my 450w+ motor, my homemade 10lb, 25.9v, 31.2ah pack only approaches 1C draw at full throttle, from a dead stop, which I never do. (Best way to produce damaging heat, and waste power. Ranks right along with low speed full throttle hill climbing.)

Wow!
I hadn't expected it, but at my typical usage of .33C, It would appear, it is possible, to be getting, close to 100%, (of battery rated), efficiency from Li-ion 18650 cells!(97-98% of rated!)

Based on graph.


And! ... my maximum surge usage is still better than 92% efficient!

As performed by my 450w EZip Trailz
w/homemade
10lb.
Li-ion 18650 cell,
25.9v,
31.2ah battery pack,
average speed of 18mph.
40-50 mile range - without pedal assist!

Alright, I am a total newbie and want to replace the old, heavy LA pack on my ezip trails.

I got ~45 batteries from two local computer service shops. about half is free, another half is $1 a piece. Not bad!
View attachment 2
Now I take them apart and ready to do test and build a battery pack for my ezip trailz from walmart.


However, I'd like to ask a few questions before I make mistakes and burn down the house.

if I want to build a 25.9V 12Ah pack from, say 2000mAh Lipo cells, I need to put 6 cells in parallel and 7 in series, right? I'd also like to add PCB (with equilibrium function http://www.batteryspace.com/PCM-wit...r-Only-CU-J185-Battery-Pack-at-10A-limit.aspx) to the pack. From what I heard, I should wire them like the following picture:


So my questions are:

is it the right way?

If one cell in the parallel went bad, wouldn't it affect / destroy all other cells in the parallel? or the PCB will prevent bad cell affect other cells?

I am not sure how equilibrium works here. I mean, those 6 cells are in parallel, how the PCB determine each individual cell is at the same voltage? or I understand it wrong?

How do I charge this? is a smart charger all I need (http://www.batteryspace.com/smartcharger28afor259vli-ionpolymerrechargeablebatterypackstandardfemaletamiyaplug.aspx)?

I have heard balance chargers. Aren't they redundant to the PCB here (regarding charging only)? I imagine they like smart charger with build in PCB?

I know there are a lot questions. I have read some literature. but I am far from understand all this stuff. a pointer or two would be very appreciated!

Thanks a lot!

18wheeler said:

Alright, I am a total newbie and want to replace the old, heavy LA pack on my ezip trails.

I got ~45 batteries from two local computer service shops. about half is free, another half is $1 a piece. Not bad!

Now I take them apart and ready to do test and build a battery pack for my ezip trailz from walmart.


However, I'd like to ask a few questions before I make mistakes and burn down the house.

if I want to build a 25.9V 12Ah pack from, say 2000mAh Lipo cells, I need to put 6 cells in parallel and 7 in series, right? I'd also like to add PCB (with equilibrium function http://www.batteryspace.com/PCM-wit...r-Only-CU-J185-Battery-Pack-at-10A-limit.aspx) to the pack. From what I heard, I should wire them like the following picture:


So my questions are:

is it the right way?

Click to expand...

First off, I would highly recommend, same model-brand capacity cells, most importantly, of the same ah rating. ex. 2600mah cells.
20ah is the minimum capacity that I can recommend, 30ah preferable!

Please! Try to find a better - matched collection of battery packs. It looks like you are primed for an extremely complex endeavor, with the expectation of a very disappointing out come.

Wiring diagram looks reasonable, but PCB should come with proper instructions.

18wheeler said:

If one cell in the parallel went bad, wouldn't it affect / destroy all other cells in the parallel? or the PCB will prevent bad cell affect other cells?

I am not sure how equilibrium works here. I mean, those 6 cells are in parallel, how the PCB determine each individual cell is at the same voltage? or I understand it wrong?

Click to expand...

Cells in parallel will equalize eachother. 1 Cell of parallel going bad, will drag down that bank of cells, leading to premature failure and reducing capacity of entire pack.

18wheeler said:

How do I charge this? is a smart charger all I need (http://www.batteryspace.com/smartcharger28afor259vli-ionpolymerrechargeablebatterypackstandardfemaletamiyaplug.aspx)?

I have heard balance chargers. Aren't they redundant to the PCB here (regarding charging only)? I imagine they like smart charger with build in PCB?

I know there are a lot questions. I have read some literature. but I am far from understand all this stuff. a pointer or two would be very appreciated!

Thanks a lot!

Click to expand...

Li-ion charger of appropriate voltage is necessary. I previously posted a link to one, for less than $24.
Yes, PCB & balance charger are an unnecessary redundancy.

I recommend you start at the beginning of this thread and read all posts by DrkAngel, I tried to provide, a fairly complete, blueprint for success.

Other than that I can offer ... Good Luck!

Start from the beginning and macth like cells them test. You will have a lot of bad cells or cells that don't match to be recycled.

DrkAngel said:

"Homemade" 25.9v 31.2ah Li-ion pack.
Just finished my first trial run. Took 2 days. Cruised at an average 18 mph. Of course I was "forced" to take a few "runs" at 22+mph.
Cruised for about 30 miles, then spent today riding around town, checking out the local "Community Yard Sales Weekend" ... another 11 miles - 41 miles - total. Finally decided to recharge, after red battery level led flickered under moderate throttle, red led indicates 24v level.

Residual voltage was measured at 25.8v, down from 29.4v. Using a, very safe, 24.5v as empty, (3.5v per cell).
Wow! That figures to 55.8miles per "full charge" ... without pedaling!!!
edit: "Empty" recalibrated as 3.6V (25.2V pack voltage).
"Motor only" range 45-50 miles!

Click to expand...

Range testing completed! Typically, I do pedal constantly. Partly to avoid attracting unwanted attention, NYS hasn't legalized eBikes, secondly for the exercise and thirdly, to extend range, (hardly seems relevant, with my exteeeeendeded! range.)
I bought my first eBike 3 years ago, my heart and health were in a pitiful state of neglect-suffering, (50 year old with sedentary lifestyle). I felt it necessary to exercise, with the safety of a way home, when I became "spent".
As my health rejuvenated, I continued to increase the bikes capability, as a manner to continually challenge myself.

With my 31.2ah Li-ion and my 26ah Lipo, I now have a trip range of 100mile, at about 20mph.
Of course, with pedal assist, that should stretch into 150, possibly 200 miles, at 20mph.
Yes, the EZip is designed to carry 2 battery packs

DrkAngel said:

Wow!
I hadn't expected it, but at my typical usage of .33C, It would appear, it is possible, to be getting, close to 100%, (of battery rated), efficiency from Li-ion 18650 cells! (97-98%+ of rated!)

Based on graph.


And! ... my maximum surge usage is still at, better than 92% efficient!

As performed by my 450w EZip Trailz
w/homemade
10lb.
Li-ion 18650 cell,
25.9v,
31.2ah battery pack,
average speed of 18mph.
40-50 mile range - without pedal assist!

Click to expand...

All my eBike project are done with the EZip Trailz model, Trailz & Mountain Trailz.
Enhancement include:
36v conversion
regearing the motor, for 25% additional speed
regearing from the oem 14-28T chainring 7spd freewheel to an 11-32T - for higher pedaling speed
better "roadworthy" tires
25.9v battery upgrade Li-ion - Lipo
Lights tail & turn signal

One of my EZips is regeared & 37volted to make it 30mph capable, of course, this does require heavy pedal assist, (450w motor@37v = 675w)

I think I have taken the EZips as far as possible.

Future Projects:

My next "real" EBike will be an AmpedBikes hub kit build. 26" kit is 23mph capable @36v, but 48v rated (30mph?). They just upgraded to a 36-60v controller, with, presumably, motor comparable.

Would love to get a 700C front hub kit, and put it on my Haro Express Deluxe, but the wonderful suspension fork has alloy dropouts, which, supposedly wont hold up to a hub motor.

Oh, Might just take one of my spare EZip gear motors and drop it into the triangle of a bike and drop a chain around an inner front ring, producing a 7spd ebike!
Either I could add a 14T freewheel to the motor, or remove legs-pedals from crank, plus add footpegs ... somewhere.

Of course, still in the offing is an etrike conversion. Schwinn Meredian with eZip motor added. Nice cargo space and hanging big SLA batteries below the rear axle will greatly increase stability.
"Schwinn Meridian Adult Tricycle"Front hub motor would work, but In prefer the re-gearing ability of the EZip gear motor.
Rear freewheel:
16T=20mph
20T=16mph
22T=14mph
etc.
I've had many requests as mobility devices for nearby Senior housing project.

Also, I have been recycling 35ah SLA batteries, from the same seniors, using the BatteryMinder rejuvenation process, fairly good success rate of restoring battery capacity-capability.
BatterMinder DeSulphation

DrkAngel said:

Of course, still in the offing is an etrike conversion. Schwinn Meredian with eZip motor added. Nice cargo space and hanging big SLA batteries below the axle will greatly increase stability.

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Stability? Why can't you achieve the same thing with LiCobalt? There is no upside, not even cost given that you are able to get laptop batteries at close to nothing.

SamTexas said:

DrkAngel said:

Of course, still in the offing is an etrike conversion. Schwinn Meredian with eZip motor added. Nice cargo space and hanging big SLA batteries below the axle will greatly increase stability.

Click to expand...

Stability? Why can't you achieve the same thing with LiCobalt? There is no upside, not even cost given that you are able to get laptop batteries at close to nothing.

Click to expand...

Ballast!
The main complaint on these bikes is the risk of tipping.
10lbs of li-ion helps very little, compared to the 60lb, of comparable SLA.
And ... I get the SLA for, nearly, free.

Also, without the "need" for pedaling, a big comfy seat can be dropped down, further lowering the center of gravity, thus, enhancing stability.
Foot platforms w/outrigger skid pads, or "training wheels", could be added, for additional turning safety, in "Mobility Device" application.
Beats paying $2000-$3000, or more, for other "mobility devices".
Plus the bonus of higher speed, and a cargo basket, for runs to the grocery store, etc.

DrkAngel said:

Ballast!
The main complaint on these bikes is the risk of tipping.
10lbs of li-ion helps very little, compared to the 60lb, of comparable SLA.

Click to expand...

I know what you mean. But why not 60lbs of Li-ion? What's the harm of have 6x range?

SamTexas said:

DrkAngel said:

Ballast!
The main complaint on these bikes is the risk of tipping.
10lbs of li-ion helps very little, compared to the 60lb, of comparable SLA.

Click to expand...

I know what you mean. But why not 60lbs of Li-ion? What's the harm of have 6x range?

Click to expand...

First one would go to my mother. ...
She might call me up from 300 miles away and say she can't get back home.
She forgot to take the charger, to recharge, for the return trip.

eTrike discussion, given it's own thread!

eTrike Conversion - as Mobility device! ... ?

Tenergy Li-ion charger is doing remarkably well!
Latest charge "balanced" all cells fairly well.
All cells were either 4.19v or 4.18v or 4.17v.

If safe charging can be maintained with this cheap charger, then price of a Li-ion battery system just dropped ... further!

Thanks for keeping us updated.

I've started to assemble the individual 6s1p packs (double celled so 12 cells total) but after i'm done that i'm kinda stuck as i'm waiting for parts.

waiting for ballance leads and charger....i have no way to charge these mofos!

finding out the shape of the cells is the most frustrating prospect without a balancing charger. With those balancing chargers its pretty easy...deplete the cells to a known voltage and then charge them and see how many Ah's it takes...that will give u your capacity.

i did a much cruder way...ran the batteries on the same draw for same amount of time and looked at voltage drop. the ones with the average or above got chosen the bottom ones got seperated.

I had a failure with my iMax B8 balance charger.
Charging S712P pack at 5amps, when there was a pop, then input voltage error message.
Would not charge, in any mode.
Disassembled and found 1 cracked Mosfet, replacement, with spares, ordered and shipped.
Will try again at 5amps after repair. Hopefully damage limited to Mosfet.

Possibly a faulty component. Will retest at 5 amps, if OK, will push to the full rating of 7amps.

Friends finding out the same issue....his got something like the Imax 6. Anywho, using the built in ac/dc transformer he cant go past 3.5Amps even though its rated at 5Amps...gets voltage input....hes going to try finding a DC input and bypass the transformer as that sucker gets HOT!

iMax B8:
I, previously, received the input voltage error, using a variety of power inputs, 20amp computer PS, 18ah SLA w/charger attached, 15amp computer PS.
This error occurred as iMax approached 5amp output.
Possibly higher amp capable at lower cell count?
Possibly higher amp capable at higher Volt input? 11-18v input accepted, only used 12v.

Notes:
Charge is set timed at 2 hours.
Single cell charging pushes somewhat above 4.2v.

Haven't tried program modes yet, should be able to modify, to cure "quirks".

Tenergy 25.9v 2A charger
No major complaints.
No cells charged above 4.2v.
Cells remain nicely equalized, within a couple 1/100ths of eachother.
Seems to charge to about 4.15v, charging light turns green but continues slowly charge-equalize? till all cells attained 4.17v - 4.19v.

minor problems:
Charger gets very warm, could use fan. I disassembled, but failed to find 12v, or 5v, power point, might gang a resister & 12v fan to 29.4v output.
Fully discharged 30ah pack might take a full day to reach highest equalized voltage. Due to its pulse mode of charging, trying to gang 2 chargers together would not be recommended. Best solution - build 2nd pack, fully charged pack always available and trip mileage doubled.

DrkAngel said:

Tenergy 25.9v 2A charger
No major complaints.
No cells charged above 4.2v.
Cells remain nicely equalized, within a couple 1/100ths of eachother.
Seems to charge to about 4.15v, charging light turns green but continues slowly charge-equalize till all cells attained 4.17v - 4.19v.

Click to expand...

That's VERY VERY interesting. If it does work the way you observed, then why would anyone bother with a balance charger or with a BMS? And based on your observation, one could also claim that LiCobalt cell also self-balance, just like LiMn.

No need to reply here. I have started a new thread for this discussion
http://endless-sphere.com/forums/viewtopic.php?f=14&t=28496