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custom battery pack for Airwheel X8


ironfox

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Hello fellow eWheel enthusiasts,

 

I am planning to upgrade my battery capacity for the Airwheel X8 which is currently equipped with a 170 Wh battery pack.

I hope there are some electric experts who can help me B)

 

As far as i know, the original Airwheel battery has 16 Li-Ion-cells with a nominal voltage of 3,7V x 16=59,2V

The maximum capacity of a 18560 cell ist around 3400 mAh at the moment. So 16 cells provide around 200 Wh.

What type of BMS should be used? A centralized module with 16 balancer connections or cells with individual BMS? Does such a battery pack even work safely with decentralized individual BMS on top of the battery?

 

How should two or more battery packs be connected in parallel? Do you have to use a Hot-Carrier-/Schottky-Rectifier or something similar in order to  discharge the pack with the higher actual voltage ?

 

Does anyone have experience with an additional battery pack connected to the charging port? The "charging voltage" of this additional battery pack should be lower than that of the Airwheel battery charger. So how much of the capacity of that external battery pack can be discharged in reality?

 

I am looking forward to your answers! :D

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It's 3.7v to 4.2v.  A normal 16 cell BMS is what most packs have.  In general, you'll want to use the BMS in a match set of batteries.  Making your pack at home is not recommended since you won't have the same number of balanced cells to choose from.  Why not just buy a 2nd pack and hook it in parallel?  You could also buy a 170wh pack from another manufacturer if the mah specs of each cell is similiar. 

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just a purely experimental point of view: I connected an external 156wh 60V battery to my unicycle charging port (internal battery 132wh 60V). When I charge the system I connect ac plug to external battery only and wait until charger LED green for an hr.

Observations:

1. while discharging, the 2 connected batteries behave like communicating vessels, balance each other. Before adding external battery, from full 4 LEDs to 1 LED it would take a t time; now it's about 2xt.

2. at last stage of charging, the charger LED goes from solid red to alternating red/green with the green phase bexoming longer and longer until solid green.

3. before, on steep hills with only 1 LED left the unicycle would quickly drop voltage and give up. Now it seems able to maintain voltage much better when showing the same 1 LED left.

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@adi,

Paralleling batteries is common in the RC world. Just be carefull when doing so.

1. If the states of charge are very different, you risk an inrush current from the most charged to the less charged, grill the cables & connector and stress the battery (it would be equivalent to charging at very high intensity, not really battery friendly).

2. The charge cables going from the GX16 connector to the batterie are of small diameter, they are not really intended to be used for high motor currents, only for 2A charge currents. And they pass through an overcharge-protection mosfet on the Battery Management System board, which is not intended to handle high currents either.

If you have a not too powerfull motor (say 350W), the currents are around 5A, meaning about 2.5A for the auxiliary battery, it's ok.

But with a 1000W motor  or even 1500W motor (Firewheel, Solowheel...), currents may reach 20A, then you'll have sooner or later overcurrent problems on the cabling and the BMS.

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@adi,

Paralleling batteries is common in the RC world. Just be carefull when doing so.

1. If the states of charge are very different, you risk an inrush current from the most charged to the less charged, grill the cables & connector and stress the battery (it would be equivalent to charging at very high intensity, not really battery friendly).

2. The charge cables going from the GX16 connector to the batterie are of small diameter, they are not really intended to be used for high motor currents, only for 2A charge currents. And they pass through an overcharge-protection mosfet on the Battery Management System board, which is not intended to handle high currents either.

If you have a not too powerfull motor (say 350W), the currents are around 5A, meaning about 2.5A for the auxiliary battery, it's ok.

But with a 1000W motor  or even 1500W motor (Firewheel, Solowheel...), currents may reach 20A, then you'll have sooner or later overcurrent problems on the cabling and the BMS.

The DC resistance of an 18560 cell is somewhere around 2...20 mOhm. So lets assume the resistance of the 16cells-pack is around 0,160 Ohm. So if all other voltage drops in the wiring is neglected, a delta of only 0,32 V between the two batteries already causes a current of 2A. In reality, the wiring etc. will cause a higher resistance. Nevertheless i must admit that hobby16 is right saying that the thin wires of the charging port are easily overstressed.

The blinking of the charging LED on the charger is most likely caused by the triggering of the MOSFETs on the two BMS modules of the battery packs. I would not recommend to charge them in line, but disconnect them and charge separately.

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So lets assume the resistance of the 16cells-pack is around 0,160 Ohm. So if all other voltage drops in the wiring is neglected, a delta of only 0,32 V between the two batteries already causes a current of 2A. In reality, the wiring etc. will cause a higher resistance.

I agree a 0,32V delta will cause 2A current. But you can have up to 10V of delta between a discharged and fully charged 16S battery.

Even with 5V delta, something that may happen easily if you are not scrupulously organized (who is ?), the current at connection would be 30A, a level that would grill everything in its path (wires, connector, BMS mosfet, cells).

 

 

The blinking of the charging LED on the charger is most likely caused by the triggering of the MOSFETs on the two BMS modules of the battery packs.

No. It's just an intensity threshold ON the charger. On my chargers, it's around 150mA (i>150mA => red, i<150mA => green).

Here is an example of charge profile on my Firewheel battery, green curve for intensity. At the end of charge, the intensity decrease is rather flat, hence the charger's led flashing when intensity crosses the threshold.

When the led is green, there is less than 10% capacity you can cram into the battery, so it's better to stop the charge to reduce stress to the battery.

BUT sometimes, you must complete the charge to trigger the cells-balancing by the BMS.

 

charge_FW_20150412.jpg

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Thank you very much hobby16, your knowledge is really amazing! Tu peux être fier de toi. J'ai jamais rencontré qqn détenant des connaisances techniques si approfondies en ce qui concerne les EU. Je voudrais utiliser quelques de tes contributions pour notre groupe de google si tu me permets.

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  • 4 weeks later...

how bout a scooter battery can you place one of those?

In short, very unlikely. If you mean a petrol scooter the batteries have a low voltage in comparison to wheels (12V vs 55.5V), different chemistry (lead-acid vs lithium ion), and pretty poor capacity (7Ah pack is 84Wh but weighs 2 kilograms! You can get laptops that weigh less but have more battery capacity).

 

Best option for more range is more packs of 16 x 18650 cells in series (the cells not the packs, we don't need 200V in our wheels). Firewheel 779 uses 4 of them to increase range to supposedly 100km.

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