Lurkin
100 kW
I'm in the process of designing mine at the moment, which ideally will be a modular pack to fit in a Q76R frame.
This will be the first battery I have built from scratch and progress is slow. I going to try and detail how I've gone about this in this thread, for positive criticism from others and also to show people who haven't done this before, hopefully where to correctly start and go about it.
I've decided to use 18650s, 3500mah cells in 48v configuration (or higher if they come out by the time I get round to fully deciding on design and quantity) in similar fashion to Offroader. It seems this would be 13S, based on 48/3.7v = 12.97v nominal and a max of 54.6v (4.2v x 13 = 54.6v). I'm assuming this is the correct SP configuration as 12S would mean 44.4v nominal and only 50.4v max. Thus the battery is going to be at 48v less of the time than 13S.
Power: max 1300w
V: 48v
I: 27.08333a
AH:I x T(Hrs)
I: 27.08333a
T: 1.5
Ah: 41Ah
Gross up to only use 80%
Ahg:Ah/0.8
Ah:41Ah
Ahg:51Ah
Cell capacity:3.5Ah
Total cells required in parallel: 15P
Cells in Series:
V: 48v
Nominal V:3.7v
Cells in Series:13S
Source: http://www.powerstream.com/battery-capacity-calculations.htm
Total cells required: 13S x 15P = 195 cells
Individual cell spacers required = 2 x 195 = 390 cell spacers.
I will use a combination of square clip together style battery holders and pre made sections which do not clip together to provide the structure. This is to provide air between the cells as I have another plan if they are getting a bit warm for comfort 8) I have found some premade spacer arrays which use less cell spacing (thickness of plastic between the cells is smaller), allowing more cells to be stuffed into the same space yet retaining the 'easy to construct' structure. I am debating as to whether to pressure pack them, snath style, or spot weld them, or a combination of both. The advantage being of a pressure pack will be that it allows the higher usage cells to be replaced in approx. 1 - 2 years. It would be nice to whip out the old and sneak in the new. Also, Snaths design includes a nice plastic structure around the battery, protecting it in use and during insertion/removal from the frame.
There will be a pack of cells which are to be be removed and used on another bike in some instances (will still be 13S, just the capacity to be decided. Likely to be as close to half as I can get). Rodney64 had an excellent plastic/acrylic Lipo design which make them into protected bricks - which is sort of what I have in mind, yet made for a removable 18650 pack. The frame will probably also need an internal steel structure to separate the removable brick from those that aren't. Some will not be removable/in a easily useful shape due to the difference in design of the Q76R frame to the Flux Alpha.
Pack building question: I have seen discussion about current bottlenecks - how likely is this with spot welded nickel designs? Supposedly the max current I will draw will be 32a.
I am now up the key battery charging choice: BMS or balance charger. I would prefer BMS to avoid complex battery harnesses being played with when exhausted, but I've never wired one before and it's a little daunting. Given there appears to be a new thread almost daily on endless with BMS wiring questions, I take it I'm not the only one a little bamboozled. To complicate things further, there are discussions of PCB or 'not real BMS's'.
BMS requirements:
I: 27.08333a (as above). I think it would be prudent to get a BMS capable of matching the current requirements, if not exceed them. Therefore I will look to a continuous discharge/charge of 35a. I've summarised the main tech sheets for all 13S BMS from Bestech and attached them, but I'm still not really any wiser as to which is the best for me :lol:
Some posts reference Bestech, but I've never dealt with them. Bestech have loads of choices, even at the same voltage and current levels. I'm not sure which to pick or what benefits to be looking for. Others have purchased from ebay or aliexpress, then discover that they don't know how to wire them or get any form of provided diagram. I would rather figure out how this works before buying anything more.
I understand that 'real' BMSs typically bulk charge to a certain voltage, then bleed the other parallel packs to match (top down).
BMS questions:
Is 35a continuous rating for the BMS enough?
Is there a reliable BMS vendor which has diagrams and clear distinction of which BMS to pick?
Is there attributes I should be looking for?
Is it likely the BMS will be smart enough to charge a reduced pack size when a module has been removed vs full pack? (I.e. if I want to unplug half the 'P's so the remaining pack is still 13S, just reduced in capacity)
Is it possible to get a BMS which just takes the bulk charge and distributes it, turn off the charge to parallel packs are they are complete? I.e. constant balance charge rather than bleed format?
This will be the first battery I have built from scratch and progress is slow. I going to try and detail how I've gone about this in this thread, for positive criticism from others and also to show people who haven't done this before, hopefully where to correctly start and go about it.
I've decided to use 18650s, 3500mah cells in 48v configuration (or higher if they come out by the time I get round to fully deciding on design and quantity) in similar fashion to Offroader. It seems this would be 13S, based on 48/3.7v = 12.97v nominal and a max of 54.6v (4.2v x 13 = 54.6v). I'm assuming this is the correct SP configuration as 12S would mean 44.4v nominal and only 50.4v max. Thus the battery is going to be at 48v less of the time than 13S.
Power: max 1300w
V: 48v
I: 27.08333a
AH:I x T(Hrs)
I: 27.08333a
T: 1.5
Ah: 41Ah
Gross up to only use 80%
Ahg:Ah/0.8
Ah:41Ah
Ahg:51Ah
Cell capacity:3.5Ah
Total cells required in parallel: 15P
Cells in Series:
V: 48v
Nominal V:3.7v
Cells in Series:13S
Source: http://www.powerstream.com/battery-capacity-calculations.htm
Total cells required: 13S x 15P = 195 cells
Individual cell spacers required = 2 x 195 = 390 cell spacers.
I will use a combination of square clip together style battery holders and pre made sections which do not clip together to provide the structure. This is to provide air between the cells as I have another plan if they are getting a bit warm for comfort 8) I have found some premade spacer arrays which use less cell spacing (thickness of plastic between the cells is smaller), allowing more cells to be stuffed into the same space yet retaining the 'easy to construct' structure. I am debating as to whether to pressure pack them, snath style, or spot weld them, or a combination of both. The advantage being of a pressure pack will be that it allows the higher usage cells to be replaced in approx. 1 - 2 years. It would be nice to whip out the old and sneak in the new. Also, Snaths design includes a nice plastic structure around the battery, protecting it in use and during insertion/removal from the frame.
There will be a pack of cells which are to be be removed and used on another bike in some instances (will still be 13S, just the capacity to be decided. Likely to be as close to half as I can get). Rodney64 had an excellent plastic/acrylic Lipo design which make them into protected bricks - which is sort of what I have in mind, yet made for a removable 18650 pack. The frame will probably also need an internal steel structure to separate the removable brick from those that aren't. Some will not be removable/in a easily useful shape due to the difference in design of the Q76R frame to the Flux Alpha.
Pack building question: I have seen discussion about current bottlenecks - how likely is this with spot welded nickel designs? Supposedly the max current I will draw will be 32a.
I am now up the key battery charging choice: BMS or balance charger. I would prefer BMS to avoid complex battery harnesses being played with when exhausted, but I've never wired one before and it's a little daunting. Given there appears to be a new thread almost daily on endless with BMS wiring questions, I take it I'm not the only one a little bamboozled. To complicate things further, there are discussions of PCB or 'not real BMS's'.
BMS requirements:
I: 27.08333a (as above). I think it would be prudent to get a BMS capable of matching the current requirements, if not exceed them. Therefore I will look to a continuous discharge/charge of 35a. I've summarised the main tech sheets for all 13S BMS from Bestech and attached them, but I'm still not really any wiser as to which is the best for me :lol:
Some posts reference Bestech, but I've never dealt with them. Bestech have loads of choices, even at the same voltage and current levels. I'm not sure which to pick or what benefits to be looking for. Others have purchased from ebay or aliexpress, then discover that they don't know how to wire them or get any form of provided diagram. I would rather figure out how this works before buying anything more.
I understand that 'real' BMSs typically bulk charge to a certain voltage, then bleed the other parallel packs to match (top down).
BMS questions:
Is 35a continuous rating for the BMS enough?
Is there a reliable BMS vendor which has diagrams and clear distinction of which BMS to pick?
Is there attributes I should be looking for?
Is it likely the BMS will be smart enough to charge a reduced pack size when a module has been removed vs full pack? (I.e. if I want to unplug half the 'P's so the remaining pack is still 13S, just reduced in capacity)
Is it possible to get a BMS which just takes the bulk charge and distributes it, turn off the charge to parallel packs are they are complete? I.e. constant balance charge rather than bleed format?
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