Here's a good read that I stumble upon one of the forum with regards to LIPO Batteries.
First of all, LiPo cells are no more dangerous than any other kind of cell (NiCD, NiMH etc). All cells will fail if mistreated or misused.
LiPo packs come in two flavors, hard case and soft case. Hardcased have a tough plastic box around the pack internals, and they are resistant to most impacts. They are usually more expensive than soft case packs, but they are vastly safer to use. Hardcased will have connectors either sunk into the pack itself or on the wire. Bear this in mind for what car you'll be fitting it into. Hardcase packs can be modified slightly, though, to aid fitment.
C-Rating is something else to consider. When looking at packs, you'll see a couple of numbers, such as '5000mah 30C'. This is the amount of current the pack can supply under load. You'll need to do a bit of maths to work it out.
3.8 x 30 = 114A
4.8 x 15 = 72A
The resulting number is an indicator for how ''punchy'' the pack will feel when driven hard - the higher the number, the better. Do the maths and work out which will be better for you, as a lower capacity/high C pack is better for racing than a high capacity/lower C pack, but will be the other way around for bashing.
C-ratings aren't the only thing to look at when buying a pack, though. Some people will say ''A 30C pack is all you need''. This statement is very misleading and potentially dangerous. For example, say you have a car with a brushless system which is rated at 120A. That means you need a pack which will supply 120A when asked. So, you should try a look for a pack which exceeds this requirement. This can be done with a combo of higher capacity/lower C-rating, or lower capacity/higher C-rating. However, don't automatically think that a high-C-rated pack will always be enough. For example...
If someone said you'd need a 30C pack to power the 120A system, it may sound like any 30C pack would do. Is a 1500mMAh is OK because of its 30C? It definitely isn't OK.
5000MAh (5.0A) x 20C = 100A
5000MAh (5.0A) x 30C = 150A
4000MAh (4.0A) x 45C = 180A
1500MAh (1.5A) x 30C = 45A
As with most stuff, the more you spend, the better the pack. Beware of packs with soft cases, and packs with suspiciously good numbers from the Far East through eBay (a lot are just made-up numbers). If you use a pack that can't supply enough current, then the pack will overheat and fail with spectacular consequences.
The method most LiPo chargers use is the CC/CV method. This means that the user inputs the charge rate, cell count and/or capacity, and the charger will then charge the pack in the following way:
- Charge to peak voltage (3.7v per cell) at max charge current (1C normally)
- Holds the voltage at 3.7v per cell until the pack is approx 80%, lowering the amperage constantly
- ''Fills up'' the remaining capacity while keeping the voltage the same
For all packs and applications, charge at the rate of 1C. This means that 100mah = 0.1A.
3600mah = 3.6A
4000mah = 4.0A
5400mah = 5.4A
Expect the charging times in the 20 to 75min region.
Some packs can be charged at 2C, 3C or even higher, but the overall useable life of the pack is drastically cut (from 500+ cycles to 100ish cycles), and there isn't any performance benefit to charging higher (just decreased charging times), so it's not worth it
You can balance charge packs too, where each individual cell in the pack is charged on its own. This requires a dedicated balance charger or a separate balancer. You don't need to balance charge on every charge, but depending on the manufacturer, you should do so every 50 or so charges.
Double and triple check all charger settings (cell type, capacity, and voltage) before starting the charge.
LiPo cells do not need manually discharging as they don't suffer from the memory effect that NiMH or NiCD's used to. They should never be allowed to drop below 3v per cell. When this happens, there is an irreversible chemical reaction inside the cell itself, the cell expands. The cell will now be fit for the bin. For general driving/bashing, you should use a Low Voltage Cutoff (if your ESC doesn't have one built-in). This is a device that is wired in line with the ESC and receiver and alerts you to when you approach the 3v threshold (by LED or buzzer). If you are using LiPo cells for 5-minute races, you don't need an LVC.
As the design of LiPo packs has such a flat discharge curve, it's easy to see when the pack is low on capacity. If you are driving and the car starts to slow down, then stop immediately, and remove the pack from the car.
If you are storing LiPo packs for up to a year, its best idea not to store them fully charged, but neither at 3v/per cell. Just charge them like normal, then have a quick 3-5min drive, then put into storage. When you come to use them again, check the pack voltage on a multimeter before charging.
When a pack comes to the end of its useable life (or the pack fails and puffs up), there is a simple method to make the pack safe for disposal. This is tried and tested but both car and aero LiPo users.
- Attach the pack to a low drain across the main terminals (like a fan, lighting kit etc), in an open area. This is to discharge the pack to 0.0v.
- Fill a plastic container with tap water, then add salt to it. Lots of salt, around half a cup per gallon. Then, submerge the pack. This is to neutralize the chemicals as much as possible and to dissolve the aluminum tabs that connect the cells in the pack.
- Leave for 7 days to completely discharge, then wrap in newspaper, and throw away in the household rubbish bin.