I proposed this idea in the discussion on BMS design techniques, but I think it deserves its own thread. My idea, essentially, is to make a module consisting of cells in series to produce perhaps 1.6 kWh at 160V (10 Ah), so they may be connected in series and/or parallel for up to 640 VDC and any Ah rating needed.
Each module would be self-contained, with an integral BMS and protection against short circuits, overloads, overcharging, and critical low cell voltage. It would have the ability to disconnect itself, if needed, but it would also allow connection to an external charger or controller to take appropriate action.
It may also have a built-in charger, which simply plugs into a standard 120 or 240 VAC receptacle, with either fast (1 hour 1C) charging at 1.5 kW (120V 13A), or overnight charging at 1/10 C. This may be constructed using a capacitor/rectifier voltage multiplier circuit, which is inexpensive, lightweight, and inherently current limited. Its disadvantage is lack of line isolation, but each battery pack would have an internal disconnect which isolates the pack from its external terminals, so it would be completely isolated during charging, as well as when the vehicle is shut down, or upon a crash or other emergency event.
Here are the details (which are suject to discussion and modification):
These are ballpark figures, of course. Costs would be lower in high volume or for DIY kits. Using Li-Ion or NiMH would cut the battery cost in half. I think this may be a viable option, and I plan to pursue it with my tractor project in mind. What think ye?
Each module would be self-contained, with an integral BMS and protection against short circuits, overloads, overcharging, and critical low cell voltage. It would have the ability to disconnect itself, if needed, but it would also allow connection to an external charger or controller to take appropriate action.
It may also have a built-in charger, which simply plugs into a standard 120 or 240 VAC receptacle, with either fast (1 hour 1C) charging at 1.5 kW (120V 13A), or overnight charging at 1/10 C. This may be constructed using a capacitor/rectifier voltage multiplier circuit, which is inexpensive, lightweight, and inherently current limited. Its disadvantage is lack of line isolation, but each battery pack would have an internal disconnect which isolates the pack from its external terminals, so it would be completely isolated during charging, as well as when the vehicle is shut down, or upon a crash or other emergency event.
Here are the details (which are suject to discussion and modification):
- DC rated fuse (20A 300-1000VDC) for ultimate protection. About $10. Like this: http://www.mouser.com/ds/2/358/typ_ASO_10.3x38-23452.pdf http://www.mouser.com/ProductDetail...GAEpiMZZMseCiJT91fwIq0NOZ6gHtyDpL/9WZzvR%2bA=
- 20-50A, 600-1200V IGBTs for pack disconnect. 2 x $3.00 = $6: http://www.mouser.com/ds/2/149/HGTP10N120BN-189785.pdf http://www.mouser.com/ProductDetail...=sGAEpiMZZMv5VNPK0aSx5Jb6s2BFhZpvQ2PkS2O77mI=
- Electromechanical relay for pack isolation (not for DC switching under load), 20A contacts, 12 VDC coil, 2 x $3 = $6: http://www.mouser.com/ds/2/378/027_832-1480.pdf http://www.mouser.com/ProductDetail...=sGAEpiMZZMtSzCF3XBhmWz8euXj//HNaBFn2e4/cLUQ=
- BMS master board, with USB or CAN interface, about $50.
- Cell BMS units, 50 x $3 each = $150.
- LiFePO4 cells, 3.2V, 10Ah, 50 x $16 (at $0.40/Wh) = $800
- 1.5 kW charger: $100
- Enclosure, terminals, connections, and hardware: $100
These are ballpark figures, of course. Costs would be lower in high volume or for DIY kits. Using Li-Ion or NiMH would cut the battery cost in half. I think this may be a viable option, and I plan to pursue it with my tractor project in mind. What think ye?