Homemade Battery Packs

Batteries, Chargers, and Battery Management Systems.
calamity_walking   10 µW

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Re: Homemade Battery Packs

Post by calamity_walking » Jun 25 2015 9:18pm

It's amazing how much information is in this thread, it almost overwhelming. I just got my first ebike (ezip trailz 2013) and it came with 3 lead acid batteries, I would like to build my own lithium battery for it but I'm not sure where to start.
I think it would be good to use one of the original battery cases that holds the two 12 volt lead acid batteries, but I'm not sure what the best choice for the lithium battery would be. I would prefer to have a few large batteries rather than dozen of smaller ones, but I see that most of the batteries in this thread are of the second variety. Is it because of the cost?

I have some electrical experience (completed one year of a two year electrical tech program so far), this kind of project would be great for my schooling.
Any advice would be greatly appreciated.

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DrkAngel   10 GW

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Re: Homemade Battery Packs

Post by DrkAngel » Jun 25 2015 10:52pm

See "Index" for links to eZip specific threads.

Lithium packs are almost always built up in banks of several cells.
(7s12p >> 7 x 3.7V = 25.9V) & (12 x 2600mAh = 31.2Ah)
The exception being large, size and capacity, Headway type cells and relatively small RC Lipo type "batteries".
Even the 12V 10Ah LiFe = SLA replacement, is packed with a goodly number of cells inside. ("Bamboo", "Dakota" 2x 24V 10Ah = $356 delivered etc.)

FYI - Tesla Model S uses 7000 cells in its battery.

The term battery actually refers to a group of same type items working together in concert.
Thusly, the term Artillery battery refers to a series of artillery pieces acting together.
Similarly, a series of electrical cells acting together is a battery of cells >> battery.
Single AA, C, D cells are not, technically, "batteries". 6V and 9V are = several small cells inside battery casings.
Last edited by DrkAngel on Jun 27 2015 1:30am, edited 1 time in total.
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Re: Homemade Battery Packs

Post by calamity_walking » Jun 26 2015 10:31am

Thanks for the reply, I see where I was mistaken. Those Dakota batteries seem great, I wish they were cheaper though :D .
Are they much better than these lithium iron ones? http://www.amazon.com/Lithium-Battery-S ... -+12v+10ah

I see that the ampere hours rating is a bit less but other than that they seem just as good, and almost 30% cheaper. Any reason not to use these?

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DrkAngel   10 GW

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Re: Homemade Battery Packs

Post by DrkAngel » Jun 26 2015 12:27pm

Image
Looks interesting.
"Weight" makes me suspicious of "creative advertizing".
But, measure carefully for fit, pay with PayPal, measure actual capacity >> get money back if not as described.

Major consideration might be apparent lack of BMS?
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calamity_walking   10 µW

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Re: Homemade Battery Packs

Post by calamity_walking » Jun 26 2015 1:30pm

Found an even cheaper price with free shipping for prime (http://www.amazon.com/Battery-Tender-BT ... op?ie=UTF8)
Do lead acid batteries have BMS?
If i get the specified charger, what could the lack of a BMS cause?
I assume I can't use the old lead acid chargers with these anyway.

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DrkAngel   10 GW

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Re: Homemade Battery Packs

Post by DrkAngel » Jun 26 2015 2:34pm

Lead acid batteries are largely self regulating - excess charge burnt off as heat - no BMS necessary.
Lithium cells are very temperamental and a BMS (Battery Management System is highly recommended for cell voltage regulation leading to increased safety and prolonged life)

LiFePO4 (also a variant of Lithium) falls in between, being much more resilient than the more common Li-ion and LiPo.

SLA battery charger is supposed to work properly, but!... confirm charger voltage and compare to requirements.
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Re: Homemade Battery Packs

Post by riba2233 » Jun 26 2015 4:36pm

DrkAngel wrote: LiFePO4 (also a variant of Lithium) falls in between, being much more resilient than the more common Li-ion and LiPo.

I must strongly disagree about this one, lifepo4 can die much more easily, it has steep curve at the bottom and top of SOC, and thus can easily get out of balance very quickly. Liion and lipo don't have that kind of curve and will stay in balance better. This is especially true for modern 18650 cells, manufactured with high tolerance.

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DrkAngel   10 GW

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Re: Homemade Battery Packs

Post by DrkAngel » Jun 26 2015 6:30pm

A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring:
There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

I enjoy enlightening ... and enlivening the spirit of the innovators.

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veloman   1 GW

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Re: Homemade Battery Packs

Post by veloman » Jun 26 2015 7:42pm

calamity_walking wrote:Found an even cheaper price with free shipping for prime (http://www.amazon.com/Battery-Tender-BT ... op?ie=UTF8)
Do lead acid batteries have BMS?
If i get the specified charger, what could the lack of a BMS cause?
I assume I can't use the old lead acid chargers with these anyway.

Did you notice the battery label in your link says 25.6 watt hours? For $66? :shock:
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Re: Homemade Battery Packs

Post by calamity_walking » Jun 26 2015 10:11pm

veloman wrote: Did you notice the battery label in your link says 25.6 watt hours? For $66? :shock:
Yeah I did, I was gonna do some research on that. It seems kind of low, i cannot find much info on how that compares to similar batteries (like the dakota).
Will search around some more tonight.

Edit: I'm not sure this is a good choice anymore, it seems most people only use these to to start their motorcycles.

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Re: Homemade Battery Packs

Post by DrkAngel » Jun 27 2015 1:21am

calamity_walking wrote:
veloman wrote: Did you notice the battery label in your link says 25.6 watt hours? For $66? :shock:
Yeah I did, I was gonna do some research on that. It seems kind of low, i cannot find much info on how that compares to similar batteries (like the dakota).
Will search around some more tonight.

Edit: I'm not sure this is a good choice anymore, it seems most people only use these to to start their motorcycles.
As I said "based on weight, labeled capacity seems creative" ...
25.6wh ÷ 12V = 2.13Ah!
SLA "equivalent" indicates some "creative" conversion reasoning.
A little learning is a dangerous thing;
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There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

I enjoy enlightening ... and enlivening the spirit of the innovators.

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veloman   1 GW

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Re: Homemade Battery Packs

Post by veloman » Jun 27 2015 9:23am

When you pull 100amps from an 8ah SLA, you probably only get 2.13ah or 25.6wh.

I'm not sure why anyone is looking at these starter batteries for ebikes.....
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calamity_walking   10 µW

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Re: Homemade Battery Packs

Post by calamity_walking » Jun 27 2015 12:17pm

DrkAngel wrote: As I said "based on weight, labeled capacity seems creative" ...
25.6wh ÷ 12V = 2.13Ah!
SLA "equivalent" indicates some "creative" conversion reasoning.
So, for comparison, what would the wh be for the dakota? 120?

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DrkAngel   10 GW

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Re: Homemade Battery Packs

Post by DrkAngel » Jun 27 2015 3:50pm

calamity_walking wrote:
DrkAngel wrote: As I said "based on weight, labeled capacity seems creative" ...
25.6wh ÷ 12V = 2.13Ah!
SLA "equivalent" indicates some "creative" conversion reasoning.
So, for comparison, what would the wh be for the dakota? 120?
Volts x Amps = Watts
Volts x Amp Hours = Watt Hours

Wh on the Dakota should be a true 120wh.

Oem eZip 24V SLA = 240wh (@ 20 hour discharge) 120-150wh in normal use (@ <1 hour discharge)
Dakota 24V should be nearly 240wh actual

Compare to my eZip battery builds
(rated at new capacity)
7s12p 2160mAh LiPo build = 671.328wh
7s12p 2600mAh 18650 build = 808.08wh ...
9s12p 2600mAh 18650 build = 1038.96wh ...
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Re: Homemade Battery Packs

Post by Skalabala » Jun 28 2015 1:20pm

DrkAngel, bud does your old cells actually still have 100% OEM capacity??
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calamity_walking   10 µW

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Re: Homemade Battery Packs

Post by calamity_walking » Jun 28 2015 1:22pm

DrkAngel wrote: Compare to my eZip battery builds
(rated at new capacity)
7s12p 2160mAh LiPo build = 671.328wh
7s12p 2600mAh 18650 build = 808.08wh ...
9s12p 2600mAh 18650 build = 1038.96wh ...
Wow, thats pretty amazing. How much does it cost for you to build those? Do you by any chance sell them?
I'd like to try to build one myself at some point but judging from the pictures it seems like i'd have to get a lot of tools and meters that I don't currently have.

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Re: Homemade Battery Packs

Post by 999zip999 » Jun 28 2015 1:49pm

You can buy new cells spot welded in parallel strips 5p or 6p. What will fit your case and solder them in a series (7 ) or ? then wire a bms a good learning experience for a electric student. Lot's of build threads. There are many old izip's on the road with replacement batteries. I bet Dr.Angle has many Battery options for you. I would go with 12ah or more. Lead is dead unless you only want to go 8mi. and then charge as soon as they cool down and keep them in a full state of charge so they last longer. Just like your car battery is always fully charged, it makes them last longer. Always at full charge. But Lead is dead. You should go with a good li-ion battery. Don't to cheap. As it will cost you double.

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DrkAngel   10 GW

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Re: Homemade Battery Packs

Post by DrkAngel » Jun 28 2015 4:23pm

Skalabala wrote:DrkAngel, bud does your old cells actually still have 100% OEM capacity??
"(rated at new capacity)"
Just to show potential ... from new cells.
NOS Dell LiPo and 18650s have been as good as 90% + of "rated".
I capacity test all recycled cells and tend to build packs with >80% of new rated capacity.

Stiil running a 33.3V 31.2Ah with less than 50% but all banks have stayed balanced!
A little learning is a dangerous thing;
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There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

I enjoy enlightening ... and enlivening the spirit of the innovators.

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DrkAngel   10 GW

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Re: Homemade Battery Packs

Post by DrkAngel » Jun 28 2015 5:58pm

calamity_walking wrote: Wow, thats pretty amazing. How much does it cost for you to build those? Do you by any chance sell them?
I'd like to try to build one myself at some point but judging from the pictures it seems like i'd have to get a lot of tools and meters that I don't currently have.
With hunting and patience ... I've gotten reasonable good cells at < 50¢ each.
You take your chances though, on percentage of good cells and remaining capacity..

As to building and selling batteries ...
I feel it important to monitor and be able to repair or tune pack as needed.
The only way I can be assured of that is if the person knowledgeably builds his own pack.
I have built packs recently ... but only for local eBikers that monitor and bring to me for scheduled inspections.

Half way into the process of evaluating a large batch of LiPo cells ... the deal for my chosen motorcycle, for electric conversion ... fell through.
So, might have some tested and rated cells available ... ?

Self-discharge testing about 1000 2.16Ah cells.
(3.7V x 2.16Ah x 1000 = 7.992 kWh)
A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring:
There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

I enjoy enlightening ... and enlivening the spirit of the innovators.

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eMotorcycle Battery Build - delayed?

Post by DrkAngel » Jun 28 2015 7:10pm

DrkAngel wrote: Half way into the process of evaluating a large batch of LiPo cells ... the deal for my chosen motorcycle, for electric conversion ... fell through.
So, might have some tested and rated cells available ... ?

Self-discharge testing about 1000 2.16Ah cells.
(3.7V x 2.16Ah x 1000 = 7.992 kWh)
All cells in each stack precisely equalized to within 2/1000th V.
Image
Wove tinned copper braid in parallel of closely voltaged cells ... to precisely equalize
Image
Discharged 1st batch as 30s2p using 2 60w light bulbs for a 1 Ah per hour capacity test.
Image
Nearly 1000 cells running self-discharge test
Image
Finally started evaluating the Dell packs that used the Sony cells
Image

Will eliminate any self-discharging cells;
test all cells for a comparative IR;
confirm all banks in each pack of same IR;
run 30s discharge evaluations (discharge capacity test).
Attachments
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Last edited by DrkAngel on Jun 29 2015 7:02am, edited 2 times in total.
A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring:
There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

I enjoy enlightening ... and enlivening the spirit of the innovators.

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Nomadic_greasemonkey   1 µW

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Re: Homemade Battery Packs

Post by Nomadic_greasemonkey » Jun 28 2015 10:40pm

Hi all, my first post here. :)

I plan on making a 3s10p 18650 li ion pack for my 1 meter long homemade rc fishing boat. I want the pack to be long and flat for the sake of roll-stability, but I'm unsure of which configuration would be the easiest to make ?

Like this : IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII (~30 cells lying flat ) or : 2 x 15, or multiple sticks -------- ?


Any advice or help is appreciated,

N_g

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Re: Homemade Battery Packs

Post by Skalabala » Jun 29 2015 2:01am

Nomadic_greasemonkey wrote:Hi all, my first post here. :)

I plan on making a 3s10p 18650 li ion pack for my 1 meter long homemade rc fishing boat. I want the pack to be long and flat for the sake of roll-stability, but I'm unsure of which configuration would be the easiest to make ?

Like this : IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII (~30 cells lying flat ) or : 2 x 15, or multiple sticks -------- ?


Any advice or help is appreciated,

N_g
Hey bud :)

The IIIIII will be the easiest. But this will look good and will be sturdy but some careful building will be needed.
http://www.batterysupports.com/images/1 ... 20pack.jpg
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Comparative IR as Capacity Estimate

Post by DrkAngel » Jun 29 2015 7:53am

Using Comparative IR as Capacity Estimate

With the large quantity of cells that I am testing, it seems proven out that ...

With cells of same manufacture, (age, batch etc.), and same starting voltage, the degree of voltage sag under a specific load-discharge indicates a reasonable comparative estimate of capacity.

With the large quantity of cells in my project I was able to separate cells by "Ver: #" and when indicated, group by actual date of manufacture.

Image
(several dozen more 6 packs not in picture)

After self-discharge test, and removal of defective packs ...
Next test will be a 1 minute discharge using a 12V 3.33A 3D printer heating element, in cup of water.
(4.32Ah battery with 3.33A discharge = .77C discharge rate)
At a timed 1 minute, I will meter and mark pack by voltage sag, EG. .58V.
Then I will quickly confirm individual banks of nearly identical sag. (any notable divergence will be segregated for cell level testing and use.)

Capacity test banks of 30s2p will be grouped by similar Comparative IR and starting voltage.
Most stacks were charged precisely within a couple thousandths of 4.100V/cell.
With 4320mAh (2p), I will likely discharge for 3 hours = 3000mAh, then label with resultant voltage for direct battery capacity comparison.
Might meter samples further for more accurate capacity rating - (3.75V -3.6V = 850mAh + 3000mAh for 3850mAh capacity )
or
Will use my capacity map of these cells to estimate full capacity:

Image
A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring:
There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

I enjoy enlightening ... and enlivening the spirit of the innovators.

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Re: Homemade Battery Packs

Post by Nomadic_greasemonkey » Jun 29 2015 1:59pm

Skalabala wrote:
Hey bud :)

The IIIIII will be the easiest. But this will look good and will be sturdy but some careful building will be needed.
http://www.batterysupports.com/images/1 ... 20pack.jpg


Thanks for that Skalabala, but unfortunately there's not enough space for 3x10 sticks/triangle shape. Battery compartment is around 60 cms long, so I guess the IIIIIII config is the best for me.

Are there any diagrams available showing how a pack like that are best soldered into parallell & series ? ( I did search, btw) :)

Thanks, N_g :)

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Re: Homemade Battery Packs

Post by Skalabala » Jun 29 2015 2:34pm

Nomadic_greasemonkey wrote:
Skalabala wrote:
Hey bud :)

The IIIIII will be the easiest. But this will look good and will be sturdy but some careful building will be needed.
http://www.batterysupports.com/images/1 ... 20pack.jpg


Thanks for that Skalabala, but unfortunately there's not enough space for 3x10 sticks/triangle shape. Battery compartment is around 60 cms long, so I guess the IIIIIII config is the best for me.

Are there any diagrams available showing how a pack like that are best soldered into parallell & series ? ( I did search, btw) :)

Thanks, N_g :)

Cool bud.
Just make three parallel packs of 10 each and series them then :) +IIIIIIIIII-+IIIIIIIII-+IIIIIIIII- perfect :lol:
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