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2 or more bms in series, charging in paralel
#1
i want to build an e-bike using a 36v 1000W motor but i face a problem that im not sure about the solution i want charge my battery pack with a 12v power supply so i will be using 3*3s bms that have to output in total 36v but im not sure about my wiring or if its possible
https://image.noelshack.com/fichiers/201...232230.jpg
edit: i already saw that i have 3 direct short circuits
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#2
(03-10-2019, 10:25 PM)edyxrp Wrote: i already saw that i have 3 direct short circuits

Yeah that's the problem.  
Here's some ideas:
- have the batteries in 3 separate modules, you could charge each separately when disconnected from the system.
- have 3x separate chargers (isolated, not grounded outputs, etc) you could charge the pack in circuit.
- step up the existing 12V charger (depending on type) to 36V with a boost switching supply device.

If you tried having the batteries in tree separate "equal" packs & disconnected from bike & motor but then attempted to parallel them to use one charger, you would likely have issues with imbalanced voltages causing uncontrolled current flow until they equalized.
Running off solar, DIY & electronics fan :-)
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#3
(03-10-2019, 10:25 PM)edyxrp Wrote: i want to build an e-bike using a 36v 1000W motor but i face a problem that im not sure about the solution i want charge my battery pack with a 12v power supply so i will be using 3*3s bms that have to output in total 36v but im not sure about my wiring or if its possible
https://image.noelshack.com/fichiers/201...232230.jpg
edit: i already saw that i have 3 direct short circuits
Additionally, you face the problem that the BMS usually are not designed to cut-off 3 times the voltage.
1 kWp in Test
4 kWh battery target - plus Mobile Home battery
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Electronics ? No clue. Am machinery engineer.
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#4
10s bms and use stepup Converter.
Cherry67 likes this post
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#5
Agree… 10s BMS is ideal with a step up converter to use with your 12v supply.

Alternately, easy to find a 36v charging supply from all those hoverboards, I would just get that and simplify the setup.
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#6
(03-11-2019, 04:53 PM)Crimp Daddy Wrote: Agree… 10s BMS is ideal with a step up converter to use with your 12v supply.

Alternately, easy to find a 36v charging supply from all those hoverboards, I would just get that and simplify the setup.

Absolutely.
1 kWp in Test
4 kWh battery target - plus Mobile Home battery
Ultra low cost
Electronics ? No clue. Am machinery engineer.
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#7
thx i will use a 48v battery because i already ordered th bms for one and will vary the speed using pwm to activate a mosfet but my motor is 36v and 1000W.Do you think the motor can handle that tension or should i figure something out to lower the tension?
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#8
Get your self a DC/DC buck converter for the motor that can do 1kW. that one can also if variable vary the motor speed. Easier and you get correct max voltage directly
The Ultimate DIY Solar and build place
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
Upcoming: 14S 18650~30kWh | Automatic trip breakers, and alot more
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#9
(03-11-2019, 06:29 PM)daromer Wrote: Get your self a DC/DC buck converter for the motor that can do 1kW. that one can also if variable vary the motor speed. Easier and you get correct max voltage directly
not sure about this one first its rlly expensive and i cant find any powerfull buck converters
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#10
(03-11-2019, 04:53 PM)Crimp Daddy Wrote: Agree… 10s BMS is ideal with a step up converter to use with your 12v supply.

Alternately, easy to find a 36v charging supply from all those hoverboards, I would just get that and simplify the setup.

that'd be a '42V' [lithium! CC/CV] charger.

10s is the key.  (3*3s != 36V nominal).

is your motor brushed, or unbrushed?  if its two-wire (brushed) this is all somewhat easier.  I prefer unbrushed myself, as they are 'waterproof' and the work is done / onus is on the controller, much more than the motor.
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