LiFePO4 A123 battery pack + BMS project!

[Rafaelrz]

Where can I buy a good but affordable BMS to build a a123 battery pack?
I have the a123 green cells, I just need a good BMS (not too expensive). I'll be running 6S9P LiFePO4. and my controller has a 40A max current.
Also, what else will I need to complete the pack? Nickel tabs, wires, connectors?

I'll be posting pics and specs as soon as I start building it. It's going to be a pack "made with care".

Cheers!

 

[999zip999]

Not to many 6s packs maybe you like a 8s as is more common. 24v battery and charge to 29.6v with a bms. This is for a 24v motor. What do you like this for ? 40 amp. needs a good and not cheap battery. So what parelle ? ect. Like say some thing. Is this for a boat ?

 

[Eascen]

Are the tabs already on the batteries? If not a spot welder isn't even something I've ventured down...

 

[agniusm]

Looks like RC build ?! As per my thread, you can find BMS here for your 6S: http://www.bestekpower.com/192v6spcmbmspcbforlifepo4batterypack/ many different discharge options to suit you.
I think most of them would around same reliability as all Chinese and you will not find exact answer to that, so might as well buy one and do some thorough testing/watching.
I would suggest to get someone to spot weld the tabs professionally.

 

[Rafaelrz]

Not to many 6s packs maybe you like a 8s as is more common. 24v charge and charge to 29.6v with a bms. This is for a 24v motor. What do you like this for ? 40 amp. needs a good and not cheap battery. So what parelle ? ect. Like say some thing. Is this for a boat ?

The reason I'm using a LiFePO4 a123 cells with 6S9P configuration (19.8V, 20.7Ah) is because I'm going to build a pack for a R/C electric motor, in this case its a Neumotor 1905/3Y (720KV).
At its peak efficiency of 91.5% it develops 248W (keeping me under the legal limit where I live) and the motor simulator on Castle Creation website is very good and complete with information.
That's why I didn't find a reason to go 24V, If I put 24V on that motor it will surpass the 250W limit, and I did some calculations considering Power needed in the overal to overcome wind resistance, grade and rolling ressistance.
Doing that I saw that I need roughly 190W to cruise at 25 km (15.5 mph) considering transmission losses and motor efficiency too. The math gets kind complex but I did everything in Matlab, so no hassle at all.
I could even use a motor that develop 200W at peak efficiency, gear it down correctly and use a derraileur or hub gear to optimize my cruising experience, but since the legal limit is 250W I decided to go for that, so I get a little bit more power and torque when needed, for example, hilly terrains of faster start ups.

 

[Rafaelrz]

Are the tabs already on the batteries? If not a spot welder isn't even something I've ventured down...

I'm buying the a123 cells (3.3V 2300mAh) from one of the guys here on the foruns. He sells to many users on E-S. I believe they are packs containing three a123 cells each, but no nickel tabs whatsoever. BTW, can someone be kind enough to tell me a simple list of materials so I can solder these cells together? I saw people on DIY battery pack use glue, thermoplastic, tabs, connectors, etc... What type of each one of these things?

I'll appreciate the help, as always..

 

[Rafaelrz]

Looks like RC build ?! As per my thread, you can find BMS here for your 6S: http://www.bestekpower.com/192v6spcmbmspcbforlifepo4batterypack/ many different discharge options to suit you.
I think most of them would around same reliability as all Chinese and you will not find exact answer to that, so might as well buy one and do some thorough testing/watching.
I would suggest to get someone to spot weld the tabs professionally.

You are right agniusm it's a RC build!
The 6S BMS you told me says on the website "6S (19.2V)" but my pack is LiFePO4 3.3V x 6S = 19.8V is there a problem with that?
I'll have to find a spot weld solution indeed, I didin't go after that yet.

 

[agniusm]

Only A123 cells have nominal of 3.3V all others are 3.2 which is 19.2V but that value is no use to you. Most important ones are LOW VOLTAGE CUT OFF AND HIGH VOLTAGE CUT OFF.
You can ask for HVC and LVC limit to be set for you in your case 3.65V HVC PER CELL = 21.9V cut off AS YOUR CHARGER. LVC could be set to whatever 2.0V, 2.5V (Look on each BMS where it says LVC/HVC - adjustable!

 

[Rafaelrz]

Only A123 cells have nominal of 3.3V all others are 3.2 which is 19.2V but that value is no use to you. Most important ones are LOW VOLTAGE CUT OFF AND HIGH VOLTAGE CUT OFF.
You can ask for HVC and LVC limit to be set for you in your case 3.65V HVC PER CELL = 21.9V cut off AS YOUR CHARGER. LVC could be set to whatever 2.0V, 2.5V (Look on each BMS where it says LVC/HVC - adjustable!

When you say 3.65 HVC it means the BMS will let my cells charge up to that value? It means going beyond 3.3V in the case of a123 cells. I presume there will be no problems then.
What should be the HVC and LVC for a a123 cell like the ANR26650M1A?

 

[agniusm]

Only A123 cells have nominal of 3.3V all others are 3.2 which is 19.2V but that value is no use to you. Most important ones are LOW VOLTAGE CUT OFF AND HIGH VOLTAGE CUT OFF.
You can ask for HVC and LVC limit to be set for you in your case 3.65V HVC PER CELL = 21.9V cut off AS YOUR CHARGER. LVC could be set to whatever 2.0V, 2.5V (Look on each BMS where it says LVC/HVC - adjustable!

When you say 3.65 HVC it means the BMS will let my cells charge up to that value? It means going beyond 3.3V in the case of a123 cells. I presume there will be no problems then.
What should be the HVC and LVC for a a123 cell like the ANR26650M1A?

Oh mate, you need to do some reading
3,65V for these cells = fully charged
2,0V = fully discharged
3.3 = storage

 

[999zip999]

Building a battery is not as easy or cheap as you think. A lot of hidden cost of building a battery and the time and hard to get parts. It's better to start with a premade battery with BMS as it could be cheaper in the long run with all the down time. Yes a good battery is a little expense but a good battery if cared for will last a long time. You pay up front as a charge is only 10-15 cents.

 

[Rafaelrz]

I've looked carefully through the http://www.bestekpower.com/ but I can't decide between two models (and I don't know what's their differences).
The comparisson is between these two BMS: http://www.bestekpower.com/192v6spcmbmspcbforlifepo4batterypack/PCM-D120.html and http://www.bestekpower.com/192v6spcmbmspcbforlifepo4batterypack/PCM-D149.html
Since my motor uses aprox. 15A continous and 24A max current, which one should I choose?
The differences are that the red BMS says its current is ajustable 20-25A and has a balance/equilibrium of 4.2V +- 0.025V I don't know what that means. The green one has a fixed current of 30A and has a balance/equilibrium of 3.6V +- 0.025V
Everything else is almost the same. I can't decide. Who knows a bit about BMS around?

 

[migueralliart]

Let me also clarify that A123 cells (at least the 26650) format may charge up to 3.65V but they go down and stay at normally 3.3v. Even a short throttle blip will bring them down to 3.3 or 3.4v.

 

[agniusm]

My thoughts are on the green one. You probably could reduce current by desoldering a shunt. If its 30A then each shunt would be for 7.5A. This is just my blind guess.

 

[Rafaelrz]

http://www.bestekpower.com/192v6spcmbmspcbforlifepo4batterypack/PCM-D149.html - The green one.

If I take one shunt out, that would bring down the current to a maximum 22.5A. Where are the shunts in that image? I suspect you're talking about that 4 parallel bars in the bottom left corner. That's it?
But what's the ideia behind lowering the BMS max current? It will permit a maximum of 30A but my motor will only drain aprox. 15A continuous and 24A max current. Also we have to consider the ESC.

 

[agniusm]

RC motors are for models as are ESC. It is complicated to run them correctly without overheating and with your knowledge it could be long and expensive learning curve. I am confused why you did not choose hub motor for this. I myself was considering to build a scooter but did not find enough confidence. You need to do a lot of studying before you even begin with parts, will save yourself a bunch of money,

 

[Rafaelrz]

I am aware of that...
I've been reading lots of stuff since I began with this idea of building my own ebike, which was last month. I didn't buy anything yet, didn't spend a single buck.
Just reading and trying to expose my doubts, but hey, I've also been making good progresses with my project. I've already decided many key aspects of it.
The reason I decided going the hard way is mainly because I was unhappy with hub motors. I think they are heavy, inefficient and not stylish at all.
As a mechanical engineer, I don't mind to design and build something even if that means hardship and lots of time spent.
I'll do it slowly day by day, take my time and end up with something I can call my own creation, but ultimately, something efficient, beautiful and something that I can look at and be happy with (and that doesn't include the hub motor)

Cheers!

 

[agniusm]

Hey, sounds good. I like when people do it hard way, best learning way, at least for me. There is a thread here on 29" carbon bike, stealth, low power, nice build.
I cant help you with RC build, have no experience at all. I dont know why nobody jumps in with knowledge.
I think the weak point will be ESC

 

[Rafaelrz]

Hey, sounds good. I like when people do it hard way, best learning way, at least for me. There is a thread here on 29" carbon bike, stealth, low power, nice build.
I cant help you with RC build, have no experience at all. I dont know why nobody jumps in with knowledge.
I think the weak point will be ESC

This ebike build thread is just starting, don't worry, as things get more interesting I'm sure people will jump in and each one will contribute with a bit of knowledge. 8)
As for the ESC my friend, I don't think it's going to be the only weak point, this "weak spots" appear all the time during these kinds of projects, its the price to pay for trying to figure out and build things from your own instead of just buying them straight.

No worries at all, we are here for the challange. Many people will help during this process, I'm sure of it and in the end we will have a better knowledge about how all this works.
Battery will be A123 ANR26650 M1A green cells, 3.3V and 2300mAh. I'm planing on doing a pack with 6S9P, which translates to 19.8V and 20.7Ah. The BMS will probably be the green one we discussed above, its likely to be the best shot for this project.

Regarding the motor, I'm still trying to decide between these two:
An inrunner NeuMotor 1905/3Y that at peak efficiency of 89.7% develops 248W of power, voltage is 19V, continous current is 14.5A and max current is 24A. It has 720KV and using 19.8V battery we achieve aprox. 14256 RPM
An outrunner AxiMotors 5320/34 that at peak efficiency of 90% develops 250W of power, voltage is 20V, continous current is 15A and max current (the manufacturer didn't specified that: I still need to look for that info). It has 207KV and using 19.8V we achieve aprox. 4098 RPM (much lower than the inrunner).

My thoughts are: If their prices aren't too different (I didn't source their prices yet) I believe I would go for the outrunner, because having almost the same efficiency, there is no reason choosing a motor that spins faster if I can use the outrunner with 4098 RPM and get a much simple reduction drive. BTW, I intend to reduce that RPMs to mid-90 RPM, which is an average cyclist cadence, and connect the motor to the crankset. This way, if everything is geared down correctly, the cyclist will be pedaling at an average cadence while the motor will supply assistance at its most efficiency range. :wink: The rear wheel will have a Shimano Nexus Inter 8 so I can get the beneficts of shifting gears.

How about that? Come one people, jump in, give me your thoughts.
Cheers.

 

[Rafaelrz]

I finally received the information from the manufacturer of the AXI outruinner (modelmotors.cz) about its last unknown specs. Continous current: 15A, maximum current: 50A (short time). This is good.
Also, the manufacturer suggested a controller called Jeti Spin Pro 77 Opto which supports up to 77A of maximum current. I'm suspecting its too much and I won't be needing that.
In the same page it can be seen other Spin controller versions, what do you think? Since I will need a controller capable of reading the output of a torque sensor, I believe these controllers won't do.

Here it is some pictures of the two motors in the "brawl":
NeuMotor inrunner 1905/3Y - http://www.rcgroups.com/forums/showthread.php?t=1387784 (Price: 189.00 USD)
AXI outrunner 5320/34 - http://www.rcgroups.com/forums/showthread.php?t=1117292 (Price: 249.00 USD)

And here it is the controller that the manufacturer recommended - https://www.electricwingman.com/jeti/spin-77-opto.aspx
Regarding the controller, I think I'm not getting that one as I said before, I'm more inclined for the Greentime controllers, since I've heard they can be custom made with torque sensing input.

Give me your thoughts! :wink:

 

[Rafaelrz]

Can someone tell me the basic differences between these two BMS? What's the difference of a PCB and a PCM?
http://www.bestekpower.com/16v5spcmbmspcbforlifepo4batterypack/PCM-D123.html
http://www.bestekpower.com/16v5spcmbmspcbforlifepo4batterypack/PCB-D132.html

Which one do you suggest for a A123 battery pack?

 

[agniusm]

Different wording?! board and module meaning the same.

 

[Rafaelrz]

Different wording?! board and module meaning the same.

Oh, thanks! That simplify thing a lot. I thought they were different in some way.
BTW, which one do you think will work better for the 5S10P a123 cells? Their features are almost the SAME! I believe one can charge faster than the other? It says "max charge current 10/20A"

Coments please.

 

[999zip999]

It's best to spot weld your battery and place a gasket between the neg. case and the pos. tit on top, to help as not to short. No worries on the neg. side as the whole case is neg.

 

[Rafaelrz]

If the cells that I'm going to use, the A123 ANR26650 M1A (3.3V and 2300mAh), says that the maximum charging current is 10A for that cell.
When I build a pack with 5S12P can I choose a BMS that says maximum charge current of 20A or must I respect the maximum charging current at 10A??