Hi,
I'm new to this forum, and new to electronics in general. However I own an electric bike and I'd like to extend its range by plugging a second Li-ion battery pack (called extender) in parallel with the original one. Basically my goal here is to build a small electronic device that allows connecting the two packs in parallel but with some refinements, that is using diodes and a MOSFET. I'd need some help to understand and design the circuit as well as how to build it in practice.
First the context:
My ebike has a 350W Bosch engine with a 36V 400Wh (11Ah) LiMn Bosch battery pack. I'd like to supplement it with a 36V 15Ah Sony LiMn battery pack so as to bring the total capacity to >25Ah. Both battery pack would be used in parallel but the system always needs at least the Bosch battery to run as there is some communication between the Bosch pack and the engine and it is not possible to use the bike with another battery alone. Note that the engine can draw 15A in some situation (the nominal rating of the engine is 350W but it can reach up to 500W).
What I'd like to do*:
I want to build a small connecting device that allows plugging the two battery pack in parallel. However I need the following:
a) I need to use diodes to to allow the two battery packs to be used at different charging levels and thus at different voltages. The diodes would prevent current from flowing from the battery with the highest voltage to the other and bursting everything into flames. Although some people have already done such parallel conection on similar bikes as mine I'm really not wanting to do it without diodes. I already bought 2 of these ideal diodes for this purpose http://re-voltage.eu/electronicsID80V2.html
b) The bike should be able to run on the Bosch battery alone (stock setup) or with both the Bosch and the extender pack. However the extender should be automatically disconnected from the motor once the Bosch battery gets disconnected, otherwise the controller on the bike would fire an error code. Originally I thought about using a relais to achieve this but a MOSFET seems more appropriate.
c) I would stay on the safe size and design the circuit for a load of max 30A. Moreover although the system is 36V, a fully charged battery pack is usually around 42V so I guess that components should whistand minimum 60V.
What I've been proposed so far:
On a german forum on ebikes I've found the following diagram (courtesy of Gringolito on pedelecforum.de) to achieve a similar thing. However as I do not understand much in german, I did not understand much as well.
The engine would be connected to the right of this diagram.
Note that D1 and D2 are 2 ideal diodes. The N-MOSFET is IRFP4368. R1=470K, R2=22K, R3=15K and the capacitor C1=~0,1µF. Akku1=Bosch pack, Akku2=extender pack. As far as I understood on this diagram, wires are connected when there is a dot where they cross. If there is no dot then two crossing wires are not connected.
Now the questions:
1) Do you think this circuit is suitable for what I intend to achieve*? I understand that when akku1 is connected, the capacitor gets charged and the MOSFET gate is triggered, which then allows to use the extender pack. However when akku1 gets disconnected, wouldn't the capacitor keep its charge for a while so that the MOSFET gate would remain triggered*? That would allow the extender to remain connected after akku1 is disconnected, which is not wanted here! Or is the capacitor drained through R3??
2) What could be the purpose of R1 here?
3) The IRFP4368 has a source-to-drain voltage of 75V which is OK for my application. However the gate-to-source voltage is 2-5V only. Since the gate should be triggered from akku1 (which can be up to 42V), how can I connect akku1 to the gate and have a voltage in the right range (2-5V)? Is that the purpose of R2?
4) Do you think the resistor and capacitor rating are appropriate here*? The max current is currently 15A but I'd like to design the system so that the motor can draw up to 30A (either 30A from akku1 only or 15A from both pack).
5) On what support would you build this circuit? 30A seems quite high for PCB tracks (it seems they should be several centimeters wide to support that current). Would a perforated board work (with eletronic components joined using 2.5mm squared wire = AWG13)?
Thanks a lot for any input, suggestion or comments!
I'm new to this forum, and new to electronics in general. However I own an electric bike and I'd like to extend its range by plugging a second Li-ion battery pack (called extender) in parallel with the original one. Basically my goal here is to build a small electronic device that allows connecting the two packs in parallel but with some refinements, that is using diodes and a MOSFET. I'd need some help to understand and design the circuit as well as how to build it in practice.
First the context:
My ebike has a 350W Bosch engine with a 36V 400Wh (11Ah) LiMn Bosch battery pack. I'd like to supplement it with a 36V 15Ah Sony LiMn battery pack so as to bring the total capacity to >25Ah. Both battery pack would be used in parallel but the system always needs at least the Bosch battery to run as there is some communication between the Bosch pack and the engine and it is not possible to use the bike with another battery alone. Note that the engine can draw 15A in some situation (the nominal rating of the engine is 350W but it can reach up to 500W).
What I'd like to do*:
I want to build a small connecting device that allows plugging the two battery pack in parallel. However I need the following:
a) I need to use diodes to to allow the two battery packs to be used at different charging levels and thus at different voltages. The diodes would prevent current from flowing from the battery with the highest voltage to the other and bursting everything into flames. Although some people have already done such parallel conection on similar bikes as mine I'm really not wanting to do it without diodes. I already bought 2 of these ideal diodes for this purpose http://re-voltage.eu/electronicsID80V2.html
b) The bike should be able to run on the Bosch battery alone (stock setup) or with both the Bosch and the extender pack. However the extender should be automatically disconnected from the motor once the Bosch battery gets disconnected, otherwise the controller on the bike would fire an error code. Originally I thought about using a relais to achieve this but a MOSFET seems more appropriate.
c) I would stay on the safe size and design the circuit for a load of max 30A. Moreover although the system is 36V, a fully charged battery pack is usually around 42V so I guess that components should whistand minimum 60V.
What I've been proposed so far:
On a german forum on ebikes I've found the following diagram (courtesy of Gringolito on pedelecforum.de) to achieve a similar thing. However as I do not understand much in german, I did not understand much as well.
The engine would be connected to the right of this diagram.
Note that D1 and D2 are 2 ideal diodes. The N-MOSFET is IRFP4368. R1=470K, R2=22K, R3=15K and the capacitor C1=~0,1µF. Akku1=Bosch pack, Akku2=extender pack. As far as I understood on this diagram, wires are connected when there is a dot where they cross. If there is no dot then two crossing wires are not connected.
Now the questions:
1) Do you think this circuit is suitable for what I intend to achieve*? I understand that when akku1 is connected, the capacitor gets charged and the MOSFET gate is triggered, which then allows to use the extender pack. However when akku1 gets disconnected, wouldn't the capacitor keep its charge for a while so that the MOSFET gate would remain triggered*? That would allow the extender to remain connected after akku1 is disconnected, which is not wanted here! Or is the capacitor drained through R3??
2) What could be the purpose of R1 here?
3) The IRFP4368 has a source-to-drain voltage of 75V which is OK for my application. However the gate-to-source voltage is 2-5V only. Since the gate should be triggered from akku1 (which can be up to 42V), how can I connect akku1 to the gate and have a voltage in the right range (2-5V)? Is that the purpose of R2?
4) Do you think the resistor and capacitor rating are appropriate here*? The max current is currently 15A but I'd like to design the system so that the motor can draw up to 30A (either 30A from akku1 only or 15A from both pack).
5) On what support would you build this circuit? 30A seems quite high for PCB tracks (it seems they should be several centimeters wide to support that current). Would a perforated board work (with eletronic components joined using 2.5mm squared wire = AWG13)?
Thanks a lot for any input, suggestion or comments!
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