Another EV bike :)
Posted: Fri Jul 12, 2013 8:45 pm
Hello, just sharing my project details, for comment as much as for amusement.
The bike is a derilict FZR1000 frame and wheels, with most of the plastics and fuel tank. I've sold thew engine/exhaust/electrics which all paid for the bike itself
The batteries were going to be lipo. I'ld collected a lot of 10Ah lipo packs consisting of 4 x 2500mAh packs in a parallel which werte designed as a travel battery gizmo, but they just couldn't be trusted to provide more than 1C discharge without getting too hot and the pouches swelling.
I've sold the lipo's and over about 8 months I've been buying odd ebay sales for used laptop battery packs. I've spent much of the past week consolidating what I have and reckon I have 700 useable 18650 cells, of between 1800 - 2600mAh capacity.
The pack is where the work is going to be. I've categorised the batteries - 700 have a voltage of 2.9V or above - 140 have a voltage of 2.5 - 2.9V (many of these seem to recover following a slow charge - and lots more below 2.5V (some recover some just get hot !
Next job is to charge and discharge every cell to measure it's capacity. Although I have a cell analyser which can accurately analyse an individual cell, I obviously need something capable of bulk opperations ! For this, I've built a discharger which can discharge 8 cells through a fixed resistor at a time. The gauge value I'll probably end up using is simply time taken to reach 2.9V from a fully charged state. The dishcarger is pic based, has a simple 16 x 2 lcd display and costs about £15 to make, which is just as well because I'm going to build another one or two when more 18650 cell holders arrive.
To charge them up I've bought 22 single cell chargers which can pass 1 Amp during bulk charging. The charger's are cheap and seem to be reliable and quite intelligent, even slowly charging a cell from 2.3V with 90mA until the voltage reaches about 2.97V, when it goes into bulk charge mode with a CC/CV method.
I'm also buddying the lithium pack with a small lead acid pack. I've read a few articles about this mixed chemistry method, and there seems to be a few benefits. The lead batteries I have are 5Ah 12V good quality batteries from UPS supplies, capable of 40Amp each. I have 15 of them, so 25Ah at 36V seems right.
Unfortunately, my motor is from a golf cart and 24V-36V is about it's limit before it gets too hot. The controller is an old GE10 SCR controller. I'll build the battery pack to allow it to be reconfigured at a later date for higher voltages.
I'ld like to hear from anyone else who has built a 'massively parallel' laptop/18650 cell battery pack. BMS issues seem to be less important with such a large parallel pack but I'm still thinking I could build my own BMS based on a design I came up witha couple of years ago, should it be required.
Thats it for now !
Chris
The bike is a derilict FZR1000 frame and wheels, with most of the plastics and fuel tank. I've sold thew engine/exhaust/electrics which all paid for the bike itself
The batteries were going to be lipo. I'ld collected a lot of 10Ah lipo packs consisting of 4 x 2500mAh packs in a parallel which werte designed as a travel battery gizmo, but they just couldn't be trusted to provide more than 1C discharge without getting too hot and the pouches swelling.
I've sold the lipo's and over about 8 months I've been buying odd ebay sales for used laptop battery packs. I've spent much of the past week consolidating what I have and reckon I have 700 useable 18650 cells, of between 1800 - 2600mAh capacity.
The pack is where the work is going to be. I've categorised the batteries - 700 have a voltage of 2.9V or above - 140 have a voltage of 2.5 - 2.9V (many of these seem to recover following a slow charge - and lots more below 2.5V (some recover some just get hot !
Next job is to charge and discharge every cell to measure it's capacity. Although I have a cell analyser which can accurately analyse an individual cell, I obviously need something capable of bulk opperations ! For this, I've built a discharger which can discharge 8 cells through a fixed resistor at a time. The gauge value I'll probably end up using is simply time taken to reach 2.9V from a fully charged state. The dishcarger is pic based, has a simple 16 x 2 lcd display and costs about £15 to make, which is just as well because I'm going to build another one or two when more 18650 cell holders arrive.
To charge them up I've bought 22 single cell chargers which can pass 1 Amp during bulk charging. The charger's are cheap and seem to be reliable and quite intelligent, even slowly charging a cell from 2.3V with 90mA until the voltage reaches about 2.97V, when it goes into bulk charge mode with a CC/CV method.
I'm also buddying the lithium pack with a small lead acid pack. I've read a few articles about this mixed chemistry method, and there seems to be a few benefits. The lead batteries I have are 5Ah 12V good quality batteries from UPS supplies, capable of 40Amp each. I have 15 of them, so 25Ah at 36V seems right.
Unfortunately, my motor is from a golf cart and 24V-36V is about it's limit before it gets too hot. The controller is an old GE10 SCR controller. I'll build the battery pack to allow it to be reconfigured at a later date for higher voltages.
I'ld like to hear from anyone else who has built a 'massively parallel' laptop/18650 cell battery pack. BMS issues seem to be less important with such a large parallel pack but I'm still thinking I could build my own BMS based on a design I came up witha couple of years ago, should it be required.
Thats it for now !
Chris