So I bought a toolbox intending to pack it with a 14s20px2 18650 with a double row configuration making the two packs in series with each other, but it turns out the box isn't wide enough for 14s so now it is a 13s20p x2 in parallel in single row configuration. My BMS is a 14s but I think it can be configured to handle 13s just fine. The question is can I just jumper each row of cells from the bottom pack to the top pack to create in essence a 13s40p but wire the two packs in parallel and be ok?I am trying to figure out how to make the BMS happy. I can post pictures once I finish testing the cells.
14s20p vs 13s40p Pack configuration
- Thread starter Radiyox
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daromer
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No you cant paralell and series a pack att same time. Instant Short..
Most cheap bms systems cant be changed but you need to look at the products sheet for the One you have.
Often 14s fits better om 48v systems. But check your Charger and load that they can handle custom voltage range.
Most cheap bms systems cant be changed but you need to look at the products sheet for the One you have.
Often 14s fits better om 48v systems. But check your Charger and load that they can handle custom voltage range.
Korishan
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Radiyox said:
I think this is what you are asking.
In the image, both options are available. The one on the left uses 1 BMS whereas the one on the right uses 2.
The biggest difference here is that the left one needs to be able handle the higher cell count. To the BMS, electrically, you have only 1 battery pack connected. It also needs to be able to handle the higher amps required during charge/discharge.
The one on the right can handle smaller loads and smaller balancing.
Both options have their pros/cons.
daromer
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What you do is basically just creating 1 pack out of 2 with wires. => 1 BMS. Note that the interconnect need to be thick enough. If you have the slightest ir difference between the packs internally (2nd hand cells have that...) you can have a higher rush between those balance wires and they will burn up.
Ie dont make them to thin.
Ie dont make them to thin.
Korishan
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Yes, when connecting the packs up with the left option, the overall string voltage needs to be <0.1-0.2 voltage difference, and the interconnected packs that are connected parallel needs to be <0.05-0.1V difference when connecting. Otherwise, depending on how may cells are parallel in a group, it could end up be huge amps rushing through between them.
"balance" leads don't normally need to be very big as they will generally only carry mA of current. However, initial connecting they will need to not burn up. Which is why the voltages need to be almost identical before connecting.
The other option is to have limiting resistors in place. This adds complexity, but can add a level of safety.
If you need to pull a pack down, just connect a vehicle light bulb (not headlight) to that pack to lower it's voltage a little. They are low wattage and can lower the pack voltage at a controlled level.
"balance" leads don't normally need to be very big as they will generally only carry mA of current. However, initial connecting they will need to not burn up. Which is why the voltages need to be almost identical before connecting.
The other option is to have limiting resistors in place. This adds complexity, but can add a level of safety.
If you need to pull a pack down, just connect a vehicle light bulb (not headlight) to that pack to lower it's voltage a little. They are low wattage and can lower the pack voltage at a controlled level.
daromer
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Balance leads dont have to be thick at all but interconnecting leads need to be able to handle the current transferred between packs during normal usage. On 2nd hand cells and depending on how its built that can be alot. Especially if you happen to have 1 pack with newer cells compare to 1 with older.....
Thank you for all your help so far. I am learning a lot. This is the BMS I have: https://www.lithiumbatterypcb.com/p...cle-and-e-scooter-protection-2-2-3-2-2-2-2-2/
I have the 14s 60A version. I don't see anywhere that it limits the number of cells in a string. I chose this one for the bluetooth capability. Also, I am not certain about whether it can be made to work with 13s. I read somewhere that just sticking wires 13 and 14 together to the last string will do it but I am curious what your opinions are on this approach.
I have the 14s 60A version. I don't see anywhere that it limits the number of cells in a string. I chose this one for the bluetooth capability. Also, I am not certain about whether it can be made to work with 13s. I read somewhere that just sticking wires 13 and 14 together to the last string will do it but I am curious what your opinions are on this approach.
So I went ahead and purchased this 100A 13s BMS. As I re-crunched the numbers, I realized I needed something beefier since this will hook up to this 3500W inverter. By my calculations that will mean a max draw of ~75 A divided by the two packs means around 38 A each. I have the packs assembled but now I need to know how best to connect terminal wires to them. I was watching this video and wondering if that is sufficient if I use two 10 AWG wires in a similar configuration, but mine would have to extend to the end of the pack instead of sticking out the sides as he has them due the container they will be in. I would then have to make them different lengths or loop one of the leads back on itself.
Keeping in mind that I am going with the configuration like this:
I was planning on tacking the two leads on each positive and negative and routing those into separate positive and negative bus bars to plug into the BMS and charge controller. Will that tax the nickel strip too much?
Here is one of the assembled packs:
Thanks for all the help.
Keeping in mind that I am going with the configuration like this:
I was planning on tacking the two leads on each positive and negative and routing those into separate positive and negative bus bars to plug into the BMS and charge controller. Will that tax the nickel strip too much?
Here is one of the assembled packs:
Thanks for all the help.
I found this chart which looks like I have about 7.5 A capacity on the 8 mm 0.2 mm thick 100% nickel strip I have. With 38 A per pack that means about 1.875 A per cell. So by doubling the zinc strip from about the 4th cell in on each side, and placing the power leads in the middle of cells 8 and 9 from each side, I should not exceed 7.5 A for any stretch of single thickness strip.
ajw22
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While that should work for the strips, all the cells at/near position #8/#9 (red circle, left pic) would be exposed to higher charge/discharge currents and will degrade prematurely. The usual way around this issue is to attach the pos/neg leads on opposing corners of the battery (right pic), so that the current has equal path length through all cells. Of course, this necessitates having a thicker strip that can handle 38A for the first & last rows.
