Homemade Battery Packs

Batteries, Chargers, and Battery Management Systems.
User avatar
ridethelightning
1 MW
1 MW
Posts: 1784
Joined: Jul 21, 2013 9:48 pm

Re: Homemade Battery Packs

Post by ridethelightning » Nov 01, 2015 8:18 am

thanks for that.

its my understanding is that cells in a parallel group must naturally all be at the same voltage level if connected together to act as one single cell, or am I mistaken ?

This is the fundamental question I wanted to clarify here.

if it were the case I can see it would not make too much difference if the cells were slightly different voltage to begin with, as long as they are in roughly the same condition?

User avatar
DrkAngel
10 GW
10 GW
Posts: 4513
Joined: Dec 15, 2010 11:14 am
Location: Upstate-Western-Southern Tier NY. USA

Re: Homemade Battery Packs

Post by DrkAngel » Nov 01, 2015 8:39 am

Cells of slightly differing voltages are just fine to connect in parallel. (Your variance is very close and better than typical of same batch cells)

Preceding post updated-enlarged - check it again.

If you purchased same brand model cell from different suppliers ...
I would recommend building banks of cells with equal numbers of cells from each supplier.
While each batch should be nearly identical ...
batch
age
storage temperature
etc.
all result in differences in cell condition.

Good method if from reputable suppliers. (Nearly identical voltages is a good indicator!)
Unless you want to carefully test and rate every cell ... ?
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.

New & Improved - Acronym Definitions

Index - Homemade Battery Packs - Updated - November 2015

EBike Toolbox - Bargains! $

Endless Sphere Wiki

ASK1
10 mW
10 mW
Posts: 32
Joined: Apr 21, 2015 10:56 pm

Re: Homemade Battery Packs

Post by ASK1 » Nov 01, 2015 6:24 pm

flyingbeekeeper wrote:
ASK1 wrote:Hey guys. I posted about my proposed build back in May, and got very sidetracked and never started on it.


My question is: is there any simple way for me to test this parallel group before I go on, to make sure all batteries have good contact with the rails? I don't have the equipment to do any kind of capacity testing, unfortunately.

Not the best way to do it, but if you are forced too, well then, lets try to make it work. Get a bunch of rubber bands and rubber band every cell (once you tape them together) to force that braid to keep contact. This may be you best bet.

But really, go buy a $30 soldering iron kit. You will thank us later for this advice.
I would use solder in a heartbeat if I didn't think the heat would damage the cells. That would be a much better build. But how do I do it without frying my cells?

User avatar
DrkAngel
10 GW
10 GW
Posts: 4513
Joined: Dec 15, 2010 11:14 am
Location: Upstate-Western-Southern Tier NY. USA

Re: Homemade Battery Packs

Post by DrkAngel » Nov 01, 2015 7:28 pm

In thread write-up
Soldering 18650's
More recent
ESWiki Soldering 18650's
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.

New & Improved - Acronym Definitions

Index - Homemade Battery Packs - Updated - November 2015

EBike Toolbox - Bargains! $

Endless Sphere Wiki

User avatar
kje
100 W
100 W
Posts: 177
Joined: Apr 07, 2012 11:55 pm
Location: Oslo, Norway

Re: Homemade Battery Packs

Post by kje » Nov 02, 2015 8:09 am

What can I use to bulk charge 18650 batteries 60p at 4.2V? My imax charger can charge max 5a, but it would be great to charge these batteries at 30A in parallel... What charger is best for this job? Anything I can make myself?

User avatar
DrkAngel
10 GW
10 GW
Posts: 4513
Joined: Dec 15, 2010 11:14 am
Location: Upstate-Western-Southern Tier NY. USA

4.2V ≥30A Capable Chargers

Post by DrkAngel » Nov 02, 2015 12:00 pm

MeanWell S-150-5 works great.
Requires documented mod.
150w / 4.20V = 35A capable

Also just modded a MeanWell S-320-5 for 60A+ charging for 4.20V

Either will require multiple heavy duty leads attached at separated points to approach full capability!

EDIT: Additional item of probable compatibility 5V 30A <$15 delivered
If not oem adjustable is very likely modable using same method as with MeanWells
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.

New & Improved - Acronym Definitions

Index - Homemade Battery Packs - Updated - November 2015

EBike Toolbox - Bargains! $

Endless Sphere Wiki

User avatar
kje
100 W
100 W
Posts: 177
Joined: Apr 07, 2012 11:55 pm
Location: Oslo, Norway

Re: 4.2V ≥30A Capable Chargers

Post by kje » Nov 04, 2015 4:49 am

DrkAngel wrote:MeanWell S-150-5 works great.
Requires documented mod.
150w / 4.20V = 35A capable
Will this speed up the charging process on my 60p 4.2V bank? Or will it slow down at the end of charge like my Imax? If I set my Imax to 5A the amp is going down to 0.5 towards the end. Will this happen with MeanWell S-150-5 as well?

User avatar
DrkAngel
10 GW
10 GW
Posts: 4513
Joined: Dec 15, 2010 11:14 am
Location: Upstate-Western-Southern Tier NY. USA

Re: Homemade Battery Packs

Post by DrkAngel » Nov 04, 2015 5:56 am

Standard CC\CV charging.
Constant Current = much faster
Constant Voltage = initially faster but slows similar to iMax as 4.20V neared.
For quicker charge and longer battery life ...
Charge at 4.20V but stop charge when actual battery charge reaches ≤4.10V.
Volt-amp meter would allow gauging-approximating actual charged voltage by amp input.
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.

New & Improved - Acronym Definitions

Index - Homemade Battery Packs - Updated - November 2015

EBike Toolbox - Bargains! $

Endless Sphere Wiki

User avatar
kje
100 W
100 W
Posts: 177
Joined: Apr 07, 2012 11:55 pm
Location: Oslo, Norway

Re: Homemade Battery Packs

Post by kje » Nov 04, 2015 6:15 pm

Thank you!

I'm going to make my own battery pack for this motor:
48V  750W BBS02 Bafang Central Motor, Current limit: 25A 

How big battery pack do I need to make and how many cells do I need?

User avatar
flyingbeekeeper
10 W
10 W
Posts: 70
Joined: Jan 31, 2015 11:59 pm
Location: Austin Texas

Re: Homemade Battery Packs

Post by flyingbeekeeper » Nov 04, 2015 6:35 pm

kje wrote:Thank you!

I'm going to make my own battery pack for this motor:
48V  750W BBS02 Bafang Central Motor, Current limit: 25A 

How big battery pack do I need to make and how many cells do I need?
I have the exact same voltage need and motor and I have built 2 packs. Thus, I can soundly help advise you.

First, the motor is wonderfully efficient. On a 15% grade 1 mile hill in Austin, I used to use 30a on a hub motor and still had to get off and push. With the BBS02, I can ride up the hill at 9mph in bottom gear using only 16amps. Chainring 44T, and lowest gear. So your need for amperage is quite different with a mid drive.

I built a 13s5p pack initially that worked, but pushed the specs of 2-3C a little too much and the batteries got warm (150F). Finally, I settled on a 13s9p pack. While some batteries were 2600mah and others 2200mah, I realized they had degraded by cycles in the laptops and were now on average 2000mah. This means 9x2ah ~ 18ah pack at 13s9p. Therefore 1C discharge is 18amps which will be well inside 98% of my riding and I'm in a steep hilly area. When I cap out at 25a that will be 25/18 = 1.4 C and I'll only hit 25a for a few seconds at most. If you go above 16amps, you are in too high a gear with the BBS02.

My theory is that a 13s9p pack will have a likely life of 500 cycles, which is a good trade off for weight. If I want longer life, I'd go 13s12p and the pack would be happy at a 0.5C discharge for 99% of its life.

FYI - In my hilly terrain I get 17wh/mi, 2.5-2.9 ah/mi.
I charge to 4.1v/cell = 53.3v and discharge till 3.3 when the BBS03 shuts off (43v cutout)
Range is 52 miles

User avatar
flyingbeekeeper
10 W
10 W
Posts: 70
Joined: Jan 31, 2015 11:59 pm
Location: Austin Texas

Re: Homemade Battery Packs

Post by flyingbeekeeper » Nov 04, 2015 6:48 pm

Here's one for DrkAngel -

I'm on my 3rd battery build, and the more I've built, the more I realize how little I know.

My question is this - after I charge up the cell initially to do the self-discharge test and wait a week, what gradient levels do you set for the results?

for example - I charged to 4.20v
After a week or two, I grade them into these gradients:
4.18-4.20 : excellent, goes in pack if has capacity > 75%
4.16-4.17 : good, permissible in pack if has capacity > 75%
=<4.15 : not trusted in pack, only for other projects

Essentially cutting off any cells that fall more than 0.05v. Am I being too strict here?

Before you chastise me for charging to 4.20 and not 4.15 or 4.10, I didn't see the wisdom in lowering my target voltage until this last batch. From here on, I'll charge to 4.10 to better see the self-discharge. I just didn't trust cells that wouldn't charge up to 4.20 and come off the charger at 4.19 or higher.

User avatar
flyingbeekeeper
10 W
10 W
Posts: 70
Joined: Jan 31, 2015 11:59 pm
Location: Austin Texas

Re: Homemade Battery Packs

Post by flyingbeekeeper » Nov 04, 2015 7:02 pm

riba2233 wrote:Did you put extra insulation between series rows, in between cells? If not, this screams fiiireee :lol:

These cells are usually so wrecked that 0.5 C should really be peak rate.
That does bring up another question. Should there be a layer of insulator between each bank? Perhaps duck tape or clear packing tape? I didn't see any on Drkangels, is it there?
Also, is there a reason to build packs tightly and stack batteries in diamond fits to get the most batteries in or to stack them square to leave an airgap on the edges?

User avatar
DrkAngel
10 GW
10 GW
Posts: 4513
Joined: Dec 15, 2010 11:14 am
Location: Upstate-Western-Southern Tier NY. USA

Re: Homemade Battery Packs

Post by DrkAngel » Nov 04, 2015 7:32 pm

I tend towards using only the best 4.18V and up ...
But I am a bit flexible, dependent on quantity available.

Testing up a few hundred Sanyo presently, may keep the best 108 for a 9s12p 33.3V eZip rebuild, 4.18Vand up.
But, capacity mapping shows these Sanyo cells optimal at a 4.06V charge point, so will let the remainder set till self-discharge determined and use the acceptable in one of the large inverter packs I pulled 2 x 18Ah SLA out of.

My Black iMax B8 balance charges to 4.07V at LiIn setting.
Last edited by DrkAngel on Nov 07, 2015 9:04 am, edited 1 time 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.

New & Improved - Acronym Definitions

Index - Homemade Battery Packs - Updated - November 2015

EBike Toolbox - Bargains! $

Endless Sphere Wiki

User avatar
DrkAngel
10 GW
10 GW
Posts: 4513
Joined: Dec 15, 2010 11:14 am
Location: Upstate-Western-Southern Tier NY. USA

Re: Homemade Battery Packs

Post by DrkAngel » Nov 04, 2015 10:57 pm

flyingbeekeeper wrote:
riba2233 wrote:Did you put extra insulation between series rows, in between cells? If not, this screams fiiireee :lol:

These cells are usually so wrecked that 0.5 C should really be peak rate.
That does bring up another question. Should there be a layer of insulator between each bank? Perhaps duck tape or clear packing tape? I didn't see any on Drkangels, is it there?
Also, is there a reason to build packs tightly and stack batteries in diamond fits to get the most batteries in or to stack them square to leave an airgap on the edges?
Usually, I stacked cells squarely ... not for ventilation.
To stabilize, I wrapped entire pack in clear boxing tape, so no airflow.
Of course at my recommended .5C discharge w 1C surge, there is no notable heat production.
When wrapped tightly cells don't move >> no movement >> no rubbing - no wear through.

Diamond stacking makes a more rigid build.
Also let me fit 1kWh+ in an eZip pack!
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.

New & Improved - Acronym Definitions

Index - Homemade Battery Packs - Updated - November 2015

EBike Toolbox - Bargains! $

Endless Sphere Wiki

ASK1
10 mW
10 mW
Posts: 32
Joined: Apr 21, 2015 10:56 pm

Re: Homemade Battery Packs

Post by ASK1 » Nov 05, 2015 1:23 am

DrkAngel wrote:In thread write-up
Soldering 18650's
More recent
ESWiki Soldering 18650's
Hey DrkAngel,

After attempting this, I realized I have questions about the process:
  • Are both the solder bead on the cell and the solder bead on the braid facing up? Meaning that they do not touch?
  • And you are pressing the solder iron onto the solder pre-applied to the braid, which then in turn pushes the braid into the solder bead pre-applied to the cell, and the whole thing melts together?
  • And to be clear, no additional solder is being applied in the soldering step, it's just the solder that was pre-applied?
That is how I did it just now on a test cell. The bond strength is quite good, but I wonder if I applied too much heat...

Also I don't know how you guys do this without a fixture. My cell spacing and alignment is going to by all wonky without one.
Last edited by ASK1 on Nov 05, 2015 3:17 am, edited 1 time in total.

ASK1
10 mW
10 mW
Posts: 32
Joined: Apr 21, 2015 10:56 pm

Re: Homemade Battery Packs

Post by ASK1 » Nov 05, 2015 3:10 am

This is how I'm going to lay the pack out, if I proceed with soldering. Both series tabs and parallel rails will be tinned copper braid.

Image

User avatar
DrkAngel
10 GW
10 GW
Posts: 4513
Joined: Dec 15, 2010 11:14 am
Location: Upstate-Western-Southern Tier NY. USA

Re: Homemade Battery Packs

Post by DrkAngel » Nov 05, 2015 5:52 am

1. Make sure that solder points are clean, abrasion, with emery cloth, or dremel tool, works great. Typically, there is a "glaze" or plating present, scraping with a sharp knife works, also.
2. Use soldering paste - flux, a slight dab is plenty. (I use a Q-tip)
3. Apply small bit of solder to soldering iron, (25w minimum, higher recommended - 50 watt+), allow to attain full temp.
4. Apply to abraded fluxed point for 2-3 seconds, remove iron and confirm solder bead applied. If failed, allow to cool, then reflux and retry with slightly longer application, or higher temperature.
5. Connect cells. I just began using a pre-tinned copper braid, (Tinned Copper Braid). It works wonderfully. Pre-flux and apply small bead of solder to braid, or wire, at the connection point.
6. Apply braid to cell, apply solder to iron, pause for temp raise, push iron on top of braid till it collapses onto cell.
7. Remove iron, braid must cool for several second, before setting.

Tip: Use probe to position and hold soldered wire etc. It is important to not have movement while solder solidifies or solder joint will be very weak! Small cheap chrome plated screwdriver works nicely.

Method should be adjusted for variations, quality and wattage of soldering iron is the major variable. A more powerful iron spends less contact time on battery and actually transfers less heat.

Soldering is partially an art, with experience you can develop a "feel" for the "art".

Practice can be done on "dead" cells. "Practice makes perfect."
  • " 6. Apply braid to cell, apply solder to iron, pause for temp raise, push iron on top of braid till it collapses onto cell." More solder on tip and allowed to regain heat allows a faster-safer heat transfer.
  • Solder bead against solder bead is preferable for quicker (less heat transfer) soldering
  • Additional solder on iron pressed into braid at contact point and all solder blends, recommend SS plated small screwdriver, or similar to stabilize "joint while solder solidifies
Test method on tested poor cells, if available, and confirm same condition after.
lighter braid on everything except power rails is acceptable.
I ... use no "spacing" ... cells tight together - no heat production at recommended charge-discharge rates.
Cells standing on end between 2 blocks of 2 x 4 could keep nice and straight, but tinned copper braid keeps pack flexible until pack is wrapped tightly with clear boxing tape. Only after pack has been "tried and true" would I better wrap with duct tape. Clear boxing tape allows visual and mutimeter leads poked through tape inspection.

Edge, rather than center, of larger, flattened, tinned copper braid might be an easier solder point for you?
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.

New & Improved - Acronym Definitions

Index - Homemade Battery Packs - Updated - November 2015

EBike Toolbox - Bargains! $

Endless Sphere Wiki

User avatar
DrkAngel
10 GW
10 GW
Posts: 4513
Joined: Dec 15, 2010 11:14 am
Location: Upstate-Western-Southern Tier NY. USA

Re: C Rate Damage

Post by DrkAngel » Nov 06, 2015 5:29 am

DrkAngel wrote:As proposed-championed earlier,
It seems C rate is more directly related to actual capacity vs original rated capacity.

C rate is a major and progressive factor in battery deterioration!

Image
Deterioration to 80% of original capacity:
3C produces < 50 cycles
2C produces ~ 250 cycles
1C produces ~ 500 cycles
High C rate discharges (and charges) are progressively damaging and as actual capacity declines, deterioration accelerates rapidly!

My recommendation of limiting charges and discharges to ≤ .5C (1C surges) based on actual Capacity, is designed to extend battery toward optimal lifespan with reasonable battery size.
I decided to graph up better and quantify the capacity loss as indicated by the above graph.
Profile seems very similar to the typical Laptop LiCo cell formulation.
Discharge Rate vs Capacity Loss.jpg
Discharge Rate vs Capacity Loss.jpg (103.98 KiB) Viewed 2398 times
Deterioration to 80% of original capacity:
3C produces < 70 cycles
2C produces ~ 325 cycles
1C produces ~ 700 cycles
High C rate discharges (and charges) are progressively damaging and as actual capacity declines, deterioration accelerates rapidly!

Very noticeable is that capacity loss is progressive.
Likely, the capacity loss creates an increased "relative" C rate.
On the 2C discharge line, at the 66.7% point, actual discharge is at 3C of the actual present capacity and degradation reflects that accelerated capacity loss.

Noting the 3C discharge line, capacity degradation seems to stabilize similar to the 2C line after an initial plummet.
This is likely attributable to some inherent discharge limitation.
Last edited by DrkAngel on Jan 13, 2016 8:01 am, edited 1 time 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.

New & Improved - Acronym Definitions

Index - Homemade Battery Packs - Updated - November 2015

EBike Toolbox - Bargains! $

Endless Sphere Wiki

User avatar
flyingbeekeeper
10 W
10 W
Posts: 70
Joined: Jan 31, 2015 11:59 pm
Location: Austin Texas

Re: C Rate Damage

Post by flyingbeekeeper » Nov 06, 2015 9:22 pm

DrkAngel wrote:
DrkAngel wrote:As proposed-championed earlier,
It seems C rate is more directly related to actual capacity vs original rated capacity.

C rate is a major and progressive factor in battery deterioration!
Very interesting! Good science and effort! I noticed you changed 2 variables and not just one. It would be quite interesting to find out if it is the discharge or the charge rate that has the most influence on lifespan.

User avatar
kje
100 W
100 W
Posts: 177
Joined: Apr 07, 2012 11:55 pm
Location: Oslo, Norway

Re: Homemade Battery Packs

Post by kje » Nov 07, 2015 11:33 am

flyingbeekeeper wrote:
kje wrote:Thank you!

I'm going to make my own battery pack for this motor:
48V  750W BBS02 Bafang Central Motor, Current limit: 25A 

How big battery pack do I need to make and how many cells do I need?
I have the exact same voltage need and motor and I have built 2 packs. Thus, I can soundly help advise you.

First, the motor is wonderfully efficient. On a 15% grade 1 mile hill in Austin, I used to use 30a on a hub motor and still had to get off and push. With the BBS02, I can ride up the hill at 9mph in bottom gear using only 16amps. Chainring 44T, and lowest gear. So your need for amperage is quite different with a mid drive.

I built a 13s5p pack initially that worked, but pushed the specs of 2-3C a little too much and the batteries got warm (150F). Finally, I settled on a 13s9p pack. While some batteries were 2600mah and others 2200mah, I realized they had degraded by cycles in the laptops and were now on average 2000mah. This means 9x2ah ~ 18ah pack at 13s9p. Therefore 1C discharge is 18amps which will be well inside 98% of my riding and I'm in a steep hilly area. When I cap out at 25a that will be 25/18 = 1.4 C and I'll only hit 25a for a few seconds at most. If you go above 16amps, you are in too high a gear with the BBS02.

My theory is that a 13s9p pack will have a likely life of 500 cycles, which is a good trade off for weight. If I want longer life, I'd go 13s12p and the pack would be happy at a 0.5C discharge for 99% of its life.

FYI - In my hilly terrain I get 17wh/mi, 2.5-2.9 ah/mi.
I charge to 4.1v/cell = 53.3v and discharge till 3.3 when the BBS03 shuts off (43v cutout)
Range is 52 miles
Nice ☺ Maybe I'm going for 13s12p. Is that 156 cells if each cell is about 2A?

Is it smart to have a power out wire for each parallel bank so I can charge them individually? (13 banks with power out).

User avatar
DrkAngel
10 GW
10 GW
Posts: 4513
Joined: Dec 15, 2010 11:14 am
Location: Upstate-Western-Southern Tier NY. USA

Re: Homemade Battery Packs

Post by DrkAngel » Nov 08, 2015 11:54 am

flyingbeekeeper wrote: However, I have found a few packs with red Sanyo UR18650fm m46a batteries. WHen charging these, I've had two doubles get 180F+ hot when charging.
Hot Sanyos
Decided to test up the last few hundred red Sanyos I had laying around. (Unable to find any definitive markings of specific models "3.6V 2600mAh" from original pack)
Was able to find about a dozen pairs that got similarly warm-hot.
I pre-evaluated resting voltage and all but 2 had been setting below 2.5V.
Similarly, all cells maintained ~room temperature until exceeding ~4.15V.

Although I don't intend on exceeding 4.10V with these Sanyos, I determined to test every one with a 4.22V initial charge.
Decided to weed out any potential problems - Hopefully!

I will separate and retest heating pairs to hopefully determine if some treatment induced similar behavior in both of pair or if some fault created the malfunction in single cell. (heat conducted to 2nd cell by tabs?)

Additional note:
After testing and placing hundreds and hundreds of similar Sanyo cells in various builds, I have never experienced a similar overheat "in service".

Good IR
Did find a few red Sanyo with excellent IR, green safety ring on top compared to the typical aqua. (Built Craftsman 12V drill battery packs with same in pre-2009, use daily - still great)
Will be comparing my IR evaluation to actual capacity from discharge test.
Pack build banks will be capacity and IR balanced.
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.

New & Improved - Acronym Definitions

Index - Homemade Battery Packs - Updated - November 2015

EBike Toolbox - Bargains! $

Endless Sphere Wiki

Hummina Shadeeba
1 MW
1 MW
Posts: 1604
Joined: Apr 25, 2014 10:26 pm

Re: Homemade Battery Packs

Post by Hummina Shadeeba » Nov 09, 2015 10:45 pm

Has anyone made a flexible battery pack by potting battereis in polyurethane? It seems ideal as the rubber is cheap and comes in varying durometer, lighter than aluminum, waterproof, bang resistant, and flexible for the bottom of a skateboard or something. Could be safer to as all the cells could be somewhat isolated. Then the polyurethane can be mounted by gluing it with more polyurethane to the polyurethane coating on the skate deck surface

(Add a thin layer of soft silicone before potting cells for expansion)
Is there a reason I shouldn't try this?
Would there be a better flexible connection than simply spot welded wires to cells?

I really like this idea as everyone uses hard li-ion packs and on a skateboard it ruins the feel of the deck

I want to make a battery pack using 18650s (12s and roughly 5 amp hour)

So.. I'd only need 12 of these :
http://m.miniinthebox.com/en/power-3-7v ... fgodE9YLkg

Sounds great to me. Looking for naysayers. Id likely set it up as packs of 6s for the balance leads.

User avatar
DrkAngel
10 GW
10 GW
Posts: 4513
Joined: Dec 15, 2010 11:14 am
Location: Upstate-Western-Southern Tier NY. USA

Re: Homemade Battery Packs

Post by DrkAngel » Nov 10, 2015 1:54 am

Hummina Shadeeba wrote:I want to make a battery pack using 18650s (12s and roughly 5 amp hour)

So.. I'd only need 12 of these :
http://m.miniinthebox.com/en/power-3-7v ... fgodE9YLkg

Sounds great to me. Looking for naysayers. Id likely set it up as packs of 6s for the balance leads.
1. Cells are bogus!
No such thing as 5000mAh 18650s!
and
Anything listed next to UltraFire cells is likely just as bogus as UltraFires.
2. Spot welding wires to cells is problematic. Best to spot weld tabs to cells and solder wires to tabs.
3. 3" duct tape on both sides of spaced cells (~½") is a great start for safe flexible builds. Push cells closer to each other till duct tape bonds to duct tape. Seal together, pencil, or alternative, on each side pressing together.
Heavy 2" duct tape over each end to add protection.
Seal all in large shrink tubing?
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.

New & Improved - Acronym Definitions

Index - Homemade Battery Packs - Updated - November 2015

EBike Toolbox - Bargains! $

Endless Sphere Wiki

User avatar
DrkAngel
10 GW
10 GW
Posts: 4513
Joined: Dec 15, 2010 11:14 am
Location: Upstate-Western-Southern Tier NY. USA

Embedded Cell Feasibility?

Post by DrkAngel » Nov 11, 2015 10:14 am

Hummina Shadeeba wrote:Has anyone made a flexible battery pack by potting battereis in polyurethane? It seems ideal as the rubber is cheap and comes in varying durometer, lighter than aluminum, waterproof, bang resistant, and flexible for the bottom of a skateboard or something. Could be safer to as all the cells could be somewhat isolated. Then the polyurethane can be mounted by gluing it with more polyurethane to the polyurethane coating on the skate deck surface

(Add a thin layer of soft silicone before potting cells for expansion)
Is there a reason I shouldn't try this?

Sounds great to me. Looking for naysayers. Id likely set it up as packs of 6s for the balance leads.
The major difficulty is the possibility-probability of needing to repair.
Disassembly-repair-reassembly being extremely difficult.
Also problematic - the direct test-monitor of individual cells.
Balance leads are a reasonable solution but are susceptible to possible damage and corrosion.
Last edited by DrkAngel on Nov 13, 2015 7:53 am, edited 3 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.

New & Improved - Acronym Definitions

Index - Homemade Battery Packs - Updated - November 2015

EBike Toolbox - Bargains! $

Endless Sphere Wiki

Hummina Shadeeba
1 MW
1 MW
Posts: 1604
Joined: Apr 25, 2014 10:26 pm

Re: Homemade Battery Packs

Post by Hummina Shadeeba » Nov 11, 2015 12:01 pm

Duct tape, while it could make a great practical pack, potting in a soft rubber is a world away in producing something that's likely to impress your friends and woo possible sex partners.
Good to know about those cells. I don't know much about batteries but enough to check at least. But lipo packs are much easier to build and with just Velcroing them to the board I'm still feeling safe enough and it's worked really well so far

Post Reply