h.letchworth said:
So having a charger that you can set the voltage is really the life saver here? When charging the lipo you'd set the voltage to charge at then wait for it to get to full capacity? I'd assume the charger would have a volt meter so you could see, or do you set up your own volt meter to monitor the cells?
I recommend a proper pre-built Lifepo4 or Li-ion battery for a first time ebiker. You can always build your self a lipo battery pack in the future and have two batteries.
Most Lipo fires happen when people 'bulk charge' or I prefer 'blind charge' lipo backs which means they charge up the pack via the main discharge leads, just like a positive and negative terminal on a car battery. Just like inside a car battery there is no BMS inside the battery, or in other words nothing in the pack but raw battery cells hooked in series to build up the voltage.
A 48volt battery pack has 12 lipo cells (each cell can handle max 4.2volts) so 12 x 4.2 = 50.2volts (still called a 48v battery). Charging up a whole back of cells in series and just hoping they all charge in balance volts is considered dodgey because some cells may take x2 as long to charge and some cells might charge twice as fast. What happens is some cells might actually reach 4.8volts while some are still as low as 3.8volts.
When a lipo cell hits 4.8volts it will often burst into a spectacular fire and ignite the rest of the battery cells next to it.
Another way I like to imagine it is as if instead of cells you had a bunch of balloons stuck on the same multi-holed pipe, as you blow air (like charge) into the pipe some balloons will get bigger faster then others and one balloon is likely to pop before you reach your desired air pressure (or total charge voltage).
I sometimes ride my bike and watch all the voltages on individual cells if I think I have a bad cell. These are called cell-logs.
http://1drv.ms/S7ZorV
When you buy a battery pack on ebay or via many websites they use Lifepo4 or Li-ion cells that have built in BMS circuitry in the battery pack that monitors every individual cell and cuts out an external chargers charge when the voltage gets as high as it can and also disconnects the discharge leads when the cells get to low to protect them from over discharge. Also Lifepo4 or Li-ion cells are considerably different in nature and wont burst into flames anywhere nearly as easily or as intensely as lipo.
A lot of people that build a lipo pack buy an advanced charger to charge them up properly instead of building a BMS circuit into the battery pack (or bulk charging) . Charger looks like this http://www.hobbypartz.com/75p-1220-charger.html , this charger has 12 balance points so it can charge and monitor 12 cells at the same time.
If you buy a battery with a BMS built in (standard on ebike battery packs) you don't need the charger like above or a 12volt power supply to feed it.
All you need is a basic 48volt charger that plugs in by simple input leads of positive and negative (like a car battery charger). You almost always receive one free with a 48volt ebike battery purchase, there also quite light in weight compared to an RC charger like the Thunder 1220 above so you can take it to work on the bike.
Buying a prebuilt pack you don't have to think about what your doing when you charge it you just plug in the single cable and it does the rest. And you won't get what a lot on this forum call KFF (Kentucky Fried Fingers)
And like I said at the start of this post, you don't have to have the same battery forever, you can always build a lipo pack later down the track if you want and have two batteries.
As for the kit, if your getting to some everyday 26inch local mountain bike then I think the first kit wesnewell suggested would work well, all the kits / sellers suggested offer good value for money, just depends on how good of a kit you want to buy.
