Battery Pack Design

Csecrist3

10 mW
Joined
Feb 25, 2021
Messages
32
I am currently ramping up to start my motorcycle conversion. I am using a '96 Kawasaki ZX600 roller chassis along with some bits from an electric car I picked up.

I am going to start with the battery as all of my other components are tailored to this and the controller. I've been discussed with a fellow member on here about these items and what my charger can hold and produce.

I am using A123 26650 LiFePo4 batteries I picked up on a trade. A deal I couldn't pass up. I configured the system to be a 32S 15P set up and to fit it in the area, I am doing the serious connection as a folded set. The photo below shows along with the battery diagram.

My question is, what parallel connections am I needing as far as the length of the battery pack? I have 2 photos. Both the same battery packs. One is blank for anyone to drawer on it and help with some feed back and the other is what I am thinking for the parallel set up.

Also, for the BMS, I am using the ZEVA EVS modules. I have 3 units (Each able to have 12 series connections) so the last unit will only have 8 connections and room to grow the pack if needed. Where and how do I connect those wires for the BMS.

Any thoughts would help greatly.
 

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If you've never build a battery pack before, I suggest you start with something smaller than a 32s15p since a failure in that pack will mean certain destruction of the pack and probably whole bike. Parallel carry capacity is generally done using nickel sheet or copper sheet and series connections completed using silicone insulated copper wire, anywhere that may bend / flex -> silicone wire, anything that won't move -> nickel/copper sheet and spot welding. You'll need insulated P-groups (barley/fishpaper) insulated positive battery terminals (although I think on the A123 LifePo4s they're negative) using fish paper/ barley rings. Balance wires start at B- or B0 (which is pack negative generally, check BMS wiring though) and connect to every positive terminal for every series connection, so using a mulitimeter probing the balance wires you should see consecutive voltage increase ie: 1S=3.5V, 2S=7V, 3S=10.5V, 4s=14V, 17.5V etc.

Seriously though, batteries are not something to mess with unless you're really comfortable with the risks that come with them. You're dealing with 120V DC and thats no joke.
 
itsrow, thanks for the reply and thanks for reminding me of the dangers of messing with batteries. I've had my fair share of dismantling some batteries and slipping and causing quite the scare, but nothing major as of yet.

I like your idea of using the coper insulated silcone wire where things bend and that's a smart idea. What size wire would that be and how would I connect that to the battery itself? Spot weld a small nickel strip to the top and sandwich the wire in between or another way possible?

I am using the fishpaper/barley insulators for the tops and bottoms for extra precautions along with using the structured battery holds to keeps things a bit rigid. I'll take the safety precautions as needed.

What advice would you have for the BMS balance wires? I have attached photos showing the balance wires attaching to the positive side.

Also, what parallel connections should I have in my pack? I have a photo of what I think should be the parallel connection with the red strips along the ends. Thoughts? Could you possibly draw on the photo to show a bit more?

Again, I am still new to the EV world, but I've done a bit of fabrication as well.
 

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I have attached the unfolded version where the red strips are the parallel connections on the negative sides of the battery cells. Is this more accurate of what is needed? Then I can add the BMS wires to the parallel red strips for balancing. So the very top of the photo is the battery pack positive and the very bottom is the battery pack negative. Obviously the connections between cells are + to -, + to -, so on and so on.
 

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I believe that when using LiFePO4, a nominal 48V pack is 16S? This suggests you are shooting for 96V / 32S?

A 48V pack can run an inverter to provide 120V AC in an emergency, so I recommend two 16S packs in series. Also, if you have a BMS failure, then you might only lose one 16S pack from permanent damage.

Motorcycles are capable of pulling very high amps. A pure nickel strip is perfect for the parallel connections, but very poor for the series connections.

Go to the battery stickey index, and find the copper/nickel sandwich thread.
 
I appreciate the feedback, spinningmagnets. How would you conduct a pack this size for the motorcycle use? You mentioned 2 16S packs, how would that look between the 2? Have a connector? I believe my controller limits a 500 amp current limit. This is from the Kelly controller 1231 I have.
 

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Since I have 32S15P, at 10A per cell based on the P-count, I would be pushing 150 Amps, is this correct? Or would it be pulling the 500 amps as my controller limits it? Also, I was reading the sandwich thread and you mentioned simply having copper bus bars on the ends to connect them rather than having the copper thin sheets between the cells and the nickel strips?

Where would you get the thick copper bus bars? Any ebay sellers that are reputable or?
 
Yes 16S LFP is standard for 48V

Also 8S (24V) is very common for inexpensive hobby balancing chargers and testing gear.

So paralleling 15 cells into groups at 1S, then building "sub pack" modules out of those into an 8S string would be IMO a good long term strategy.

4S of those modules getting you to 32S for 96V nominal.

I am curious to know whether / how well the Zeva BMS can handle that architecture.

10A per single cell is a lot even for A123, hopefully those are not so worn, have you done per-cell QA cap testing on them yet?

If you are welding the parallel connections it will be very difficult to do so once the modules are assembled.

But say 10A is doable, that is indeed a top limit of 150A for the whole pack, so the 500A becomes irrelevant, you need to protect the pack by programming the controller or otherwise limiting it from pulling over 150A.

That is Battery Current of course

Phase amps / Motor Current will be much higher at high torque / low speed operations, where wiring / motor overtemp will set your operational limits.
 
john61ct, thanks for the feedback and makes sense with what you're saying. Break them out into smaller pack and connect them in a sense. I like that idea and then I can "fold" them accordingly to the pack dimensions I am needing.

To note, I am using the individual cell holders for some rigidity and air movement amongst the cells as well as building a battery box. It would be ideal to make a box that can be broken down. Let's say I only need 48V for a completely different build, I can simply remove 2 sets of the pack and use it else where.

As far as connecting the smaller packs, what connectors and bus bars in a sense and other hardware would be necessary for this build?

I would be programming the controller to be lower than the 10A/P-count since they are used cells, but moderately used. I have not done much QA as of yet. I am working on that as we speak to get better numbers on internal resistance and see how they are functioning.
 
I'd just use capacity as my go/no-go test, afaic 80% is EoL if building a "new" pack from secondhand.

That is 80% of new as actually measured, not nameplate rating. Order a few brand new ones as your benchmark.

Measure ESIR as well for giggles, but so many variables there, not good for "state of health" without a pro-level testing setup and long-term track records established for comparison.
 
I have built 10p34s pack of these A123 green cells. And I'm doing +600A in burst and average ~200A in 10 minutes times.

My build thread: https://endless-sphere.com/forums/viewtopic.php?f=14&t=85912
And one of the last video riding with that pack: https://www.youtube.com/watch?v=DPWSidVa2Vw
And I'm using also Zeva BMS units, 3 of them.

If you want I can give you excel file also. I have 6 temp sensors (4 located on the cells and 2 in output positive and negative connection)
Right now about 30 cycles in use and have not noticed any degredation :)
 
nuxland,

Great Build and I didn't come across it in my search. I will definitely go through it thoroughly and see what you have done as a guidance!

As far as my construction with the 4 packs of 8S15P resulting in 32S15P overall, what connections between the bus bar and the nickel strips would be recommended? Could I sandwich them between 2 bus bars and have the nickel strips in between with some hardware as far as nuts and bolts or?

As far as connecting the packs + and - ends, what connectors are recommended as well? I bought some 8mm x 0.2mm pure nickel strips for my connections. Would this be enough for the series and parallel connections or?
 
I built my pack so that series connection between cellgroups are at least the same 35mm2 as my cables between battery and controller.
So in my case, i used 0,5mm thick copper and 10mm wide (5mm2 per cell) and as I have 10P it is 50mm2 copper between cells.
But I was also aiming for 600A current :)

But if you want welded pack then 0,2 copper is max you can weld with kweld I have read, but not tested myself.
Just today I tested 0,25 nickel to A123 positive side and I could only weld splitted (two piece) nickel with my kweld at 150J and 98ms and 1742A :) If it was not splitted then even with 250J weld was weak.
But 0,25 nickel (10mm wide) is the same as 0,0625 copper, so 0,625mm2 per cell and 6,25mm2 per 10 cell. Thats around 10AWG so the same as regular lipo pack with X90 connector.

PS! You need big connections in series, not parallel, So in your last picture grey connection is used to push current and red just to parallel cells.
 
So the series connections just have to be able to handle the 150A I am wanting to achieve is that correct? Your 600A burst is a lot of amps and I wouldn't nearly touch that with the pack I am building unfortunately!

Could I double up the Nickel strips I have purchased to help with the amps or?

So between each pack, you used the x90 connectors as well? Are those wires soldered to the nickel strips? Sorry for the dumb questions, just want to be as clear as I can be.
 
Csecrist3 said:
So between each pack, you used the x90 connectors as well? Are those wires soldered to the nickel strips? Sorry for the dumb questions, just want to be as clear as I can be.
No, I did not use XT90 in A123 pack. You should read my build thread, there is written in detail how I did it.

If you build 4 packs of 8s and intend to connect them via some connector then mounting BMS is difficult.
Do you have some central unit also that is talking via canbus to these BMS units (zeva BMS units themself only monitor and balance a little) and stop charging or etc when temps or cell voltages out of range?
 
I am currently reading your build as we speak. Very impressive build and intuitive to the nonwelding portion.

As far as my fabrication abilities and the sources around myself, I won't be able to go to that extent hence the reason for welding the nickel strips.

This is my purchase of the ZEVA system. ZEVA BMS Product List.JPG

Not sure if that's all I need as I'm doing more of a budget build to say the least.
 
Csecrist3 said:
What temp sensors did you have as well?
I bought also temp sensors from him (you can attach 2pcs per BMS unit).
https://www.zeva.com.au/index.php?product=116

With Electric Vehicle Management System V3 and EVMS Monitor V3 these BMS units work like a charm :)
And you can then also buy some elcon/tc charger with canbus. Zeva management system can then control that also.
 
The charger that came with the package deal is a Delta QuiQ 1000. I am going to have another individual I met online to download the algorithm for this battery pack. He was actually insisting going with this configuration to meet the algorithm perfectly.

I saw you have 4AWG wire for the ends of the battery packs. How did those do? I was intrigued on how you curled the ends of the copper around the wire and most likely crimped those or? I would like this pack to be able to be removed for other projects if need be or even if I wanted to do maintenance on the battery itself. What end connectors should I consider along with the wiring for those?

What about the sizing on the nickel strips for my series connections?
 
nuxland said:
stop charging or etc when temps or cell voltages out of range

aka HVC functionality, that does not necessarily need to be provided by a full-time connected BMS, since it is only needed while charging

Zeva can however control charge regulation via CAN, Elcon for example

> zeva BMS units themself only monitor and balance a little

Are you saying they cannot provide LVC to protect against over discharging while in use?

 
john61ct said:
nuxland said:
stop charging or etc when temps or cell voltages out of range

aka HVC functionality, that does not necessarily need to be provided by a full-time connected BMS, since it is only needed while charging

Zeva can however control charge regulation via CAN, Elcon for example

> zeva BMS units themself only monitor and balance a little

Are you saying they cannot provide LVC to protect against over discharging while in use?
Yes they can but you need to have another unit (in my case olimex) in his case zeva own "Electric Vehicle Management System V3" that will act then. Zeva BMS12 unit itself only report information (it does not control other equipment) and does a very little balance 120mA.
 
nuxland,

I saw you have 4AWG wire for the ends of the battery packs. How did those do? I was intrigued on how you curled the ends of the copper around the wire and most likely crimped those or? I would like this pack to be able to be removed for other projects if need be or even if I wanted to do maintenance on the battery itself. What end connectors should I consider along with the wiring for those?

What about the sizing on the nickel strips for my series connections?
 
Csecrist3 said:
nuxland,

I saw you have 4AWG wire for the ends of the battery packs. How did those do? I was intrigued on how you curled the ends of the copper around the wire and most likely crimped those or? I would like this pack to be able to be removed for other projects if need be or even if I wanted to do maintenance on the battery itself. What end connectors should I consider along with the wiring for those?
Manual work with the pilers. In one of the pictures at beginning you can see that these end coppers are one piece. But it was hard to bend/curle these so I cut these in 10mm wide. So curled with pilers striped the wire and used pilers to crimp a little. Then used a very big soldering iron to solder wire to copper.

Csecrist3 said:
What about the sizing on the nickel strips for my series connections?
I'm right now starting to build 18p20s pack from 18650 cells (target 150A and 200A peak) and considering using 6AWG wire for output together with QS8-S connector. Your 8mmx0.2mm nickel will be 24mm2 nickel if used in each 15p series connection and is the same as 6mm2 copper. And that has 50A continous rating. But 15x2,5Ah=37,5Ah (usable ~32Ah) and with 150A continious it is empty in 13 minutes. I'm using 35mm2 that has 150A continious raiting. So my opinion is that you nickel 8mmx0.2mm is fine if you do not go over 150A.
 
Another individual on here mentioned the 10A per P-Count would be to the absolute max for the used cells I have so I would keep a bit below that resulting in the 150 A continuous rating. Not looking for huge speeds or anything, more or less a commuter and the ability to actually achieve a conversion like this.

Thanks for the help and I'll be using those connectors as well for the main connection point to the rest of the bike. I will also use the 4awg wire to connect the connectors as well. Would it be advisable to use the 4awg wire throughout the rest of the build for the HV wires or should I use something larger? When I mean the rest of the build, I'm meaning for the wiring to the contactors and the motor?
 
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