Big Headway pack design

[CroDriver]

Hi guys.

I'm replacing my ThunderSky cells in the BMW with Headway P 8Ah cells.

I ordered 900 cells that should arrive next week. I'm planing a 112s8p configuration.

Here is how the cells will be assembled:

Top view

Side view:

It's also very likely that I'll split the pack in a bigger and a smaller sub pack since I have limited space in my car.

The frame will be very strong since the cells are bolted directly to each other and any instability and twisting could be a problem.

I would appreciate design suggestions. Is someone seeing a mistake in the design?

Thaks

 

[lifepo4ever]

why so many volt and less ah capacity?

 

[CroDriver]

why so many volt and less ah capacity?

Because power is I*U. Less "I" (current) and more "U" (voltage) means better efficiency and better performance at high RPMs

 

[dnmun]

order spares at the same time.

 

[kadir]

Hi guys.

I'm replacing my ThunderSky cells in the BMW with Headway P 8Ah cells.

I ordered 900 cells that should arrive next week. I'm planing a 112s8p configuration.

Here is how the cells will be assembled:

Thaks

Hi Cro, I thought you were going with cell_man's 15Ah cells.. why did you switch to headways?

 

[ahambone]

Why the 8 AHr cells and not the 10 ahr screw-tab cells? What are you planning on using to interconnect the cells with? I'm using a 120 cell (24s x 5p) pack right now and am curious why you went with the tabbed cells. Maybe you have assembly machinery that I didn't have access to. (BTW, size regardless, these are great cells).

Cheers,
--Adam

 

[voicecoils]

Why the 8 AHr cells and not the 10 ahr screw-tab cells? What are you planning on using to interconnect the cells with? I'm using a 120 cell (24s x 5p) pack right now and am curious why you went with the tabbed cells. Maybe you have assembly machinery that I didn't have access to. (BTW, size regardless, these are great cells).

Cheers,
--Adam

The 8Ah cells have higher discharge rates.

The tabbed cells allow for higher energy and power density on a volumetric basis. Slight weight advantage too.

For a massive pack, paying to to have it tab welded locally should be a small part of overall cost.

 

[CroDriver]

Why the 8 AHr cells and not the 10 ahr screw-tab cells? What are you planning on using to interconnect the cells with? I'm using a 120 cell (24s x 5p) pack right now and am curious why you went with the tabbed cells. Maybe you have assembly machinery that I didn't have access to. (BTW, size regardless, these are great cells).

Cheers,
--Adam

They do have screw terminals. They look exactly the same like 10Ah cells.

Does someone know how much they would sag at 20C and 30C?

Hi guys.

I'm replacing my ThunderSky cells in the BMW with Headway P 8Ah cells.

I ordered 900 cells that should arrive next week. I'm planing a 112s8p configuration.

Here is how the cells will be assembled:

Thaks

Hi Cro, I thought you were going with cell_man's 15Ah cells.. why did you switch to headways?

I'm using his cells for another project, not the BMW.

 

[frodus]

Looks like it sags to about 2.4V at 200A (25C) and is run for 11 seconds, which would be 1600A for your pack.... and I doubt it'l see that for very long. 5C (40A) it sags to 3.05V and is run for 12.5minutes.

 

[CroDriver]

email me at tgintz@evcomponents.com and I can send you a discharge of 25C on the 8Ah cells.

Looks like it sags to about 2.4V at 200A (25C) and is run for 11 seconds, which would be 1600A for your pack.... and I doubt it'l see that for very long. 5C (40A) it sags to 3.05V and is run for 12.5minutes.

Hi,

Seems like the mail isn't working... HAL tested 6 sample cells for me. They sagged to 2.0V at 200Amp but some cells sag to 1,5V at the same current.

 

[frodus]

oops, too many email addresses

travis@evcomponents.com

 

[CroDriver]

oops, too many email addresses

travis@evcomponents.com

Again not working.

Isn't your mail tt@evcomponents.com?

Btw. You know me. The Croatian guy that buys lots of Zillas

 

[frodus]

wrong travis, I'm travis gintz, that's travis travelstead.

travis@evcomponents.com is the correct address.

 

[olaf-lampe]

Hmmm, seems my earlier post is gone?

I recommended to use plastic sheets between the cell rows to manage evenly airflow.
And I wondered how you'll balance the cells? I see tons of cables and fuseholders that hinder airflow.
Unfortunately there is no BMS that fits between this inline cell pack.
-Olaf

 

[CroDriver]

Hi Olaf. Since power is my goal and not cycle life I won't cool the pack. They perform better when hot.

I'll have a BMS board on the top of every 8 cell parallel row. I don't need a BMS board for every cell, just for the 112 series rows.

Hmmm, seems my earlier post is gone?

I recommended to use plastic sheets between the cell rows to manage evenly airflow.
And I wondered how you'll balance the cells? I see tons of cables and fuseholders that hinder airflow.
Unfortunately there is no BMS that fits between this inline cell pack.
-Olaf

 

[pm_dawn]

Hi CroDriver!

Are you planning to have busbars between every parallell pack in the series ?
I would think that the design of the busbars would be crucial in these hi-amp solutions.
Personally I would probably go for half the height for each parallell pack to possibly get a better distribution of current in the busbars.
So the eight cells would be stacked as four cells in heigth and two cells wide, then have two layers to create the right number of packs in series.

Anyway it looks like lots of fun. !!!


Regards
/Per

 

[CroDriver]

Hi Per.

Yes, bus bars will be installed between every parallel pack. The bus bars of two series cell rows at the end of the pack will be connected with a small bus bar on every cell. Your idea sounds good but I already started machining the housing for the cells A pity you didn't mention it before but I hope that the current distribution will be OK this way

Hi CroDriver!

Are you planning to have busbars between every parallell pack in the series ?
I would think that the design of the busbars would be crucial in these hi-amp solutions.
Personally I would probably go for half the height for each parallell pack to possibly get a better distribution of current in the busbars.
So the eight cells would be stacked as four cells in heigth and two cells wide, then have two layers to create the right number of packs in series.

Anyway it looks like lots of fun. !!!


Regards
/Per

 

[pm_dawn]

Hi !

There is no need to change the housing. It was more a question about the busbars. U can still have the cells placed the same way but just connect them differently. I was thinking something like this.




Where the busbar furthest away connects the top and bottom parts.

I'm not sure that it would be any better than your original design.
I have seen something on the forum here before about busbars. I think it was some thread by DocBass.

Regards
/Per

 

[7circle]

QUOTE : ...112S...

Is your Cell Matrix Drawing Corrrect?

The Pic show 8p x (19 x 6) OR 8p x 114S
Not 112S which would be 8P x (8 x 14)S

Wow 64AH x 360V for 23kWh

QUOTE: 2.4V at 200A (25C)
25C power 112 x 2.4 x 200A = 56 KW

Nice grunt for 0 - 100ks

Be interseted in cost to complete battery frame.

Thinking of idea to keep BMS on top for all 8P groups...

Top stuff

 

[7circle]

Sorry, PM_Dawn's suggestion of regrouping put me off tangent.

The string of 8 in line would work well for current distribution for all except the end cable take offs.

>Cro-drive ... your initial drawing suggests 8 cells on a busbar to the top with link to next row which could be more restrictive to current flow.

If the +ve to -ve of two columns of 8 are side by side a larger/wider buss bar with 8+8=16 holes would work.

Then you have to link the one Slab layers with the 8P on their own to the next.

If your design did go with 19 columns of 8P the series connections will be on the far side of the slab which will be a shorter linkage solution.

Maybe a pair of mating right-angle tabs could link the layers. They could attach to cells 4 and 5 in the middle of the 8P column.

Some people have mentioned not to stress the cell posts as the are intergral to pressure valves and not strength supports.
It's intersting stuff
Cheers 7cmilies

Edit: Oh, Sorry Crodriver, I didn't notice your connection between slab layers using STUD LINKS. See my post below.

 

[ebikes-sf]

Some people have mentioned not to stress the cell posts as the are intergral to pressure valves and not strength supports.
It's intersting stuff
Cheers 7cmilies

I like these interlocking cell holders available for 10Ah cells (probably for 12 and 16ah as well), they allow flexible pack configurations:

 

[7circle]

... lost my half edited reply ...

[if the pack is 8P x (6 x19)S]

Using studs fastening each cell into sticks of 6 cells in series, the momentum transfer when cells are shaking/vibrating along this axis will stress the studs. Imagine a 3g vibration!
Best case is only the mass of 5 cells in the stick transfering the stresses through the stud link.
But i can imagine it would be worse when the cells bloat and jam in the support holes the whole pack could be linked together with no expansion alowance.

As has been mention in other posts the headway terminals are crimped insto place with plastic insulating ring and also have limited strength.

So how much stress/strain can they cope with?
Or do you just accept very little and attach flexable bus links for all interconnections.

Since power is my goal and not cycle life I won't cool the pack. They perform better when hot.

How many cycles do you expect from the cells?

:wink: 7circles

 

[scoot]

This has been my experience thus far with attaching the Headway cells end to end:

Even with just a single junction of 2 cells attached end to end with a set screw or stud, it is very important to stabilize the cells from any movement sideways at that junction to avoid torsion forces that will inevitably result in popping out the epoxy joints on the negative pole. While easily repairable it is a PITA and a good thing to avoid . Using bus bars (or plates) sandwiched between the cell ends that are connected likelwise to adjacent cell rows is highly effective provided both the x & Y axes of potential movement are restricted... the connectors on the ends seem to be plenty strong enough to handle the side to side forces provided they are not subjected to torsional forces IMO. Another approach is to tape or tie wrap the cells on either side of the stud connections when the cell rows are staggerd stacked where each cell row helps support its neigbor row(s), or to have a rigid battery case with zero clearance that serves as a splint, if you will. Bottom line is whatever it takes the cell junctures need to be effectively supported or flexible connections will be needed.

 

[CroDriver]

QUOTE : ...112S...

Is your Cell Matrix Drawing Corrrect?

The Pic show 8p x (19 x 6) OR 8p x 114S
Not 112S which would be 8P x (8 x 14)S

Wow 64AH x 360V for 23kWh

QUOTE: 2.4V at 200A (25C)
25C power 112 x 2.4 x 200A = 56 KW

Nice grunt for 0 - 100ks

Be interseted in cost to complete battery frame.

Thinking of idea to keep BMS on top for all 8P groups...

Top stuff

It's not 200A, it's more like 2000 Amps (8 ah X 8 X 30 = 1920 Amp)

It's a 112s pack, the 3D model is just for illustration

... lost my half edited reply ...

[if the pack is 8P x (6 x19)S]

Using studs fastening each cell into sticks of 6 cells in series, the momentum transfer when cells are shaking/vibrating along this axis will stress the studs. Imagine a 3g vibration!
Best case is only the mass of 5 cells in the stick transfering the stresses through the stud link.
But i can imagine it would be worse when the cells bloat and jam in the support holes the whole pack could be linked together with no expansion alowance.

As has been mention in other posts the headway terminals are crimped insto place with plastic insulating ring and also have limited strength.

So how much stress/strain can they cope with?
Or do you just accept very little and attach flexable bus links for all interconnections.

Since power is my goal and not cycle life I won't cool the pack. They perform better when hot.

How many cycles do you expect from the cells?

:wink: 7circles

I think that my design will keep the cells in place quite good

I expect 500 cycles or less. More would be nice but I don't hold my breath for it

Sorry, PM_Dawn's suggestion of regrouping put me off tangent.

The string of 8 in line would work well for current distribution for all except the end cable take offs.

>Cro-drive ... your initial drawing suggests 8 cells on a busbar to the top with link to next row which could be more restrictive to current flow.

If the +ve to -ve of two columns of 8 are side by side a larger/wider buss bar with 8+8=16 holes would work.

Then you have to link the one Slab layers with the 8P on their own to the next.

If your design did go with 19 columns of 8P the series connections will be on the far side of the slab which will be a shorter linkage solution.

Maybe a pair of mating right-angle tabs could link the layers. They could attach to cells 4 and 5 in the middle of the 8P column.

Some people have mentioned not to stress the cell posts as the are intergral to pressure valves and not strength supports.
It's intersting stuff
Cheers 7cmilies

Edit: Oh, Sorry Crodriver, I didn't notice your connection between slab layers using STUD LINKS. See my post below.

This has been my experience thus far with attaching the Headway cells end to end:

Even with just a single junction of 2 cells attached end to end with a set screw or stud, it is very important to stabilize the cells from any movement sideways at that junction to avoid torsion forces that will inevitably result in popping out the epoxy joints on the negative pole. While easily repairable it is a PITA and a good thing to avoid . Using bus bars (or plates) sandwiched between the cell ends that are connected likelwise to adjacent cell rows is highly effective provided both the x & Y axes of potential movement are restricted... the connectors on the ends seem to be plenty strong enough to handle the side to side forces provided they are not subjected to torsional forces IMO. Another approach is to tape or tie wrap the cells on either side of the stud connections when the cell rows are staggerd stacked where each cell row helps support its neigbor row(s), or to have a rigid battery case with zero clearance that serves as a splint, if you will. Bottom line is whatever it takes the cell junctures need to be effectively supported or flexible connections will be needed.

Thanks for the advice, I'll try to support the cells with plastic mounts to avoid any cell movement.

 

[CroDriver]