quick sanity check of my lipo upgrade

[MrDude_1]

Can someone give me a quick sanity check to make sure this all makes sense?

This is the wiring plan for my lipo upgrade. Two 4s lipo bricks make up one 8s unit. I have 4 such units making a 8s4p pack. The stock controller has a 33v limitation, so I am keeping it at this voltage for now.
As you can see the balance leads should go to a DB37 connector, explained below.

The DB37 connector just leads all the balance leads to outside the battery compartment, without interconnecting anything. By not having them all in parallel, if one cell goes bad, it wont try to balance via the tiny balance wires, nor will it drag down all the other cells in parallel... or atleast thats the idea.
The only worry with a D-sub connector is the possibility of bending pins if you're not careful. that is why the batteries are on the female side. so if i wedge a pin in sideways, it will be on the male side... overall just have to be careful and never force the connector.



This is the male side. as you can see I plan to make at least 2 of them.
Plug 1 lets me use a cell-log on each battery and check or balance them individually.
Plug 2 lets me plug in all of them in parallel for balance charging the entire pack.





Anyone have any thoughts? sanity check? props for my mad MSpaint skillz? :lol:

 

[MrDude_1]

No thoughts?

 

[hodgie]

I am no expert by any means. But curious why the bulk charge plug is on the "other side" of the motor controller? Shouldn't battery charging be direct to the battery pack using a bms for safety/management?

 

[MrDude_1]

I am no expert by any means. But curious why the bulk charge plug is on the "other side" of the motor controller? Shouldn't battery charging be direct to the battery pack using a bms for safety/management?

In this case, the bulk charger goes to the large pads on the controller board where the 4 battery wires are. It's the only place where the left pack and right pack meet... also it has a connector there for it from the stock charger. It used to be lead acid powered. There is no BMS, I use a Lipo balance charger at home and a bulk charger at work. I need a portable charger eventually for the road....but this works for now.

 

[wesnewell]

You must have a lot of time on your hands. You've taken something that is so simple and made it look very complicated.
http://endless-sphere.com/forums/viewtopic.php?f=14&t=39666

 

[dogman dan]

When you connect plug 2, it will short since all the packs will still be connected in series at the main discharge wires.

Sounds like you are about to bury some cheaply made, well known to be volatile cells in a battery box with poor access to it. When some of those cells chafe, get punctured, or puff, your first indicator of that might be when you call the fire department to your house on fire.

I suggest building it so you can periodically remove and inspect your packs, check for balance at the original balance plugs, and take action if any cells appear to have puffing or physical damage. This way, you don't need to hook them to a central balance plug at all.

 

[MrDude_1]

You must have a lot of time on your hands. You've taken something that is so simple and made it look very complicated.
http://endless-sphere.com/forums/viewtopic.php?f=14&t=39666

lol.. yeah. Alot of time. I am a Programmer/Analyst/Engineer... If I do my job correctly the first time, nothing is broken for me to fix.. so I sit here and browse the internet, waiting for problems or the next project. Lots of free time, stuck infront of a PC.


That said... looks like I have exactly what is in that thread. I dont think the drawing looks complicated, but then again.... I am a Programmer/Analyst/Engineer... You should see what we end up with on the whiteboards lol.

Is there something wrong? Its the same 2 packs in series... four times, in parallel.

When you connect plug 2, it will short since all the packs will still be connected in series at the main discharge wires.

I dont think it will short anything. I am paralleling as 8 cell packs NOT all as 4 cells. Please look at it again and tell me if I am wrong, but I believe that since this is already a 8s4p pack from the main discharge wires, wiring all balance connectors in a 8s parallel will work.. As long as I keep the high-cell and low-cell correct for each one.
This lets me balance them all at half the amperage of a huge 4s pack, AND I get to keep the main power wires together. The plug just serves as a balance board.
Or am I missing something? I realize its critical to keep track of the "high" pack and the "low" pack when making the harness.

Sounds like you are about to bury some cheaply made, well known to be volatile cells in a battery box with poor access to it. When some of those cells chafe, get punctured, or puff, your first indicator of that might be when you call the fire department to your house on fire.
I suggest building it so you can periodically remove and inspect your packs, check for balance at the original balance plugs, and take action if any cells appear to have puffing or physical damage. This way, you don't need to hook them to a central balance plug at all.

On the contrary, everything is easily accessed. This is all in a scooter with a single top I can pull off in seconds. Much faster than alot of ebike setups. The cells themselves are hardpacks (so yes, I can not see puffing anyway) and each hardpack is spaced with room around it and held in place with gratuitous amounts of velcro. I can remove and inspect a pack very easily, just pry it up off the velcro and inspect.

Safety is the reason for making a central balance plug point.. there are two voltages of batteries in this system.. a high set and a low set.. if I was to plug in with balance leads to parallel balance charge, there is the risk I could mix them up.
I am trying to minimize that risk by using 8s balance leads. Then they're all on one connector.
If I left the balance leads on it, and a cell went bad, that cell on the other 4 packs would try to bring it up via the balance lead.... under load. This can push enough amperage to burn up the tiny balance wire.
Sooo.. I am trying to eliminate that risk.

On top of all this, I only charge it under supervision in its own "fire hole" area of the garage.... or next to me at work. The pack its self is in an aluminum box, on wheels, with a 4ft long handle. In a thermal event, I should be able to push it out the door...I have a 10ft straight shot toward the firedoors outside. once out there, I'll just let it burn.
That said, it hopefully never comes to that as I keep track of my cells, balance/check every other charge (because it only takes an extra 5 seconds to do it... ) and I do pop the board off to inspect/mod frequently. The scooter itself is like a firebox on wheels. it will suck if it burns but Im taking all the steps I can to both prevent it and minimize the risk if it does.

 

[dnmun]

why would you make it so complicated and then worry about charging it when you could just use a BMS and bulk charge it without the hassle of all the plugs which will inevitably fail.

 

[MrDude_1]

why would you make it so complicated and then worry about charging it when you could just use a BMS and bulk charge it without the hassle of all the plugs which will inevitably fail.

Mostly because of the cost of the BMS and the complication of finding lipo BMS thats compatible with this kind of lipo cell.

After its assembled there are two plugs. a power and a balance. I am confused on what will fail? If there's a opportunity to simplify it further, I am all ears. My mind isnt closed, I am open to options...

At some point after I have this working awhile, and after I convert to a brushless motor, I will add 8 more packs and revisit this... I will probably wire up a BMS of some sort then, but thats in the future.. atleast a year from now... I may even have other cells by then, and that would require a different BMS anyway.




as far as being complicated.. I thought this was just a standard 2 packs in series.... 4 times over. same thing as the ebike guys do, except I am using 4s instead of 6s.

 

[dogman dan]

Ok, 4s packs, will be permanently connected as 8s packs. That's fine. Each 8s section then can be paralleled with another, as apparently they already are, at the controller. So you can parallel the balance wires too, whenever you want.

I missed that in the text, and thought you were running 16s I thought you had another series connection at the controller.

looks all good.

 

[IdleMind]

I must have a lot of time too, because I did just about what you are showing including making a diagram.

There are 12 bricks making an 8s6p pack. Here's the completed pack. This is how it is configured in use.

The bricks are stacked in pairs. In the photo you can see each pair has a short harness that brings the two 4s plugs into an 8s plug. I can plug my cell log into each of the 8s connectors and quickly check all 48 cells. I always balance charge at about 350 watts using a removeable harness combines the six groups into one.

I don't use a bms because every time I charge I get see that the batteries are in balance and I am careful not to overcharge or over discharge.

 

[MrDude_1]

I must have a lot of time too, because I did just about what you are showing including making a diagram.

There are 12 bricks making an 8s6p pack. Here's the completed pack. This is how it is configured in use.

The bricks are stacked in pairs. In the photo you can see each pair has a short harness that brings the two 4s plugs into an 8s plug. I can plug my cell log into each of the 8s connectors and quickly check all 48 cells. I always balance charge at about 350 watts using a removeable harness combines the six groups into one.

I don't use a bms because every time I charge I get see that the batteries are in balance and I am careful not to overcharge or over discharge.

Thanks! that exactly what Im doing!

the only reason for the additional plug/harness is to monitor cells at will, even when bulk charging. I like being able to see them on my PC, while it charges next to me at work.

 

[chilledoutuk]

The simplest way to do this would be to run a few cycles on each pack weed out the duds.

Then build 2 4s4p banks by just wiring 4 packs in parallel.

This would keep the packs more in balance than if you wired them in series and then paralleled afterwards.

You could permanently connect these packs balance cables in parallel but i would either fuse these parallel connections or use a resistor to restrict the current so that should there be an imbalance in the cells you don't get 30 amps flowing though a 28 awg cable.

But to keep complexity down you could just leave the balance cables unconnected until you want to balance charge but I would again be careful to not allow large currents to flow through those balance cables when you make these parallel connections.

Every unfused cable you connect to you battery is a potential point of failure especially in a high vibration environment such as ebikes for this reason especially with highly volatile battery chemistry it is even more important to keep your cabling a simple and clean as possible.

 

[cal3thousand]

This isn't the exact way I would do it, but it would work. You just have to make sure you don't plug the wrong black and red together when series connecting (for example Battery 1 and Battery 2).

Are you planning on charging through the shunt on the controller? If you do, you get the added benefit of being able to monitor the charge on the CA.

 

[MrDude_1]

Well... I guess it was sane.
Did it all this weekend, and it works great.