Need help on 18650 battery series/parallel plan

Batteries, Chargers, and Battery Management Systems.
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jimbo69ny
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Need help on 18650 battery series/parallel plan

Post by jimbo69ny » Feb 12, 2018 12:35 am

Hey Guys,

In a nutshell I am building an additional battery pack for my 2014 Rav 4 EV to extend the range. The OEM pack is a Tesla built 92s48p with 2600 mah 18650 cells.

I am building a 92s31p to run in parallel to the OEM pack. I have room for 9 vertical modules with 10 series blocks in each PLUS 2 series blocks on the right side of the box. That will give me the 92 series cells and the voltage to match the OEM pack.
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That out of the way, I am really hoping you guys can help me structure the layout of my modules. I know multiple connections is best so I suspect I know which option you guys will like better. But it gets confusing because I am also incorporating cell fuses just like Jehu and other youtubers. I'm sure you know what I am talking about.

Option 1 - Positive all on one side, negative all on the other. I would join each block in series at the top of the module. Each module will be run in series with the one next to it.
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Option 2 - Alternating cells - whole thing flows nice and easy.
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Option 3 - Alternating cells - the thicker black lines are buss bars to connect one block to the next. This option has larger blocks opposed to long chains. More interconnectivity between blocks. More confusing, to me at least.
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Don't like any of those options? Here is a blank slate, print it, write on it and tell me what I should do.
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Last edited by jimbo69ny on Feb 12, 2018 3:41 pm, edited 1 time in total.

jimbo69ny
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Re: Need help on 18650 battery series/parallel plan

Post by jimbo69ny » Feb 12, 2018 12:39 am

I would really appreciate your help!

Thank you!

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jonescg
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Re: Need help on 18650 battery series/parallel plan

Post by jonescg » Feb 12, 2018 2:37 am

My eyes are going blurry :D

I think any approach where the series current path is not limited is the best. So probably your first drawing. If there are 31 cells in parallel, try to ensure all 31 cells have a series connection to the next 31 cells. Sometimes that's not practical, but aim to get most of them doing that.

Neat work on the wooden box BTW. I suggest an inlet and outlet for air cooling, if nothing else.

jimbo69ny
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Re: Need help on 18650 battery series/parallel plan

Post by jimbo69ny » Feb 12, 2018 8:45 am

Really? Option 1? Even option 2 seemed better. I thought you guys would say option 3 is best because there are so many connections. I like option 1 because it’s probably the easiest with the least connections.

Yes I am adding holes on the left and right sides. I have 2 - 104 cfm cooling fans on the way. They are 120x120 cm. They look like computer cooling fans but are high flow.

Here are the fans I purchased.
https://www.ebay.com/itm/NMB120mm-FBA12 ... 2749.l2649

This is the temperature control switch
https://www.ebay.com/itm/W1209-12V-50-1 ... 2749.l2649

Joachim
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Re: Need help on 18650 battery series/parallel plan

Post by Joachim » Feb 12, 2018 1:59 pm

Nice wurk 8) these cellholders are the wurst thing i can see in the pack...

jimbo69ny
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Re: Need help on 18650 battery series/parallel plan

Post by jimbo69ny » Feb 12, 2018 2:18 pm

Oh yeah you dont like the cell holders? I think gluing them together is a pretty bad idea personally. No airflow and you cant replace a cell if it goes bad.

Joachim
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Re: Need help on 18650 battery series/parallel plan

Post by Joachim » Feb 12, 2018 3:23 pm

take a good look on a tesla module cell holders....these black china holders are to weak for a heavy pack :lol:

jimbo69ny
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Re: Need help on 18650 battery series/parallel plan

Post by jimbo69ny » Feb 12, 2018 3:40 pm

I appreciate the reply but I am satisfied with these holders. It may only be plastic but the entire structure of the module will become stronger once the cells and buss bars are added.

Can anyone please help me with my question in my original post? Pretty please?

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jonescg
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Re: Need help on 18650 battery series/parallel plan

Post by jonescg » Feb 12, 2018 6:22 pm

jimbo69ny wrote:
Feb 12, 2018 8:45 am
Really? Option 1? Even option 2 seemed better. I thought you guys would say option 3 is best because there are so many connections. I like option 1 because it’s probably the easiest with the least connections.
Well thats assuming I interpreted your drawing correctly. Is the solid line meant to be like a run of flex wire soldered to the nickel? And the series connections are loops at either end? In that case don't use that approach. Make the current flow like a broad river rather than a narrow rapid.

Punx0r
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Re: Need help on 18650 battery series/parallel plan

Post by Punx0r » Feb 16, 2018 4:08 am

This is potentially a complicated pack. The end of this thread shows the sort of thing that can be done to ensure the electrical connections are good to evenly balance the load on each cell: https://endless-sphere.com/forums/viewt ... &start=200

However with a pack this large you may need to consider cooling, else the cells in the middle of the pack could end up significantly warmer than those on the outside. As the capacity, internal resistance (hence current output capability) and ageing effects all vary with temperature this can lead to problems with balancing and reliability.

That you have cell spacers is good so air can flow between them, rather than packing them as a dense block. Having vents in the top and bottom of the box to allow a convection flow of air through the pack may be a good idea.

jimbo69ny
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Re: Need help on 18650 battery series/parallel plan

Post by jimbo69ny » Feb 16, 2018 8:43 am

Yup, I have already purchased the cooling fans. 2 - 104 CFM fans

https://www.ebay.com/itm/Panaflo-Case-C ... 1438.l2649

Here is my project
http://www.myrav4ev.com/forum/viewtopic.php?f=9&t=2191

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