news: BRCA Advice on Charging Li-Po Cells
Jan 2, 09:13 PM by Simon EversSafety Advice on Charging Li-Po Cells from the BRCA
Many have started to use Li-Po Cells now.
If you havent already read this article from January, it is a good idea.
Here is some useful info provided by the BRCA.
‘’Safety with Li-Po Batteries
A guide to safe use of Li-Po batteries, from the British Radio Car Association.
Any rechargeable battery that is currently on the market has a risk of explosion, fire, and smoke emission if not handled properly. Despite the stories that have made the press, Lithium (Li-Po) batteries are not fundamentally unsafe, but they need to be treated with a lot more care and respect than NiCd or NiMh. Just because a supplier of a Li-Po battery does not label or warn of the dangers of their product does not make that product safe.
The principal risk is fire, which can result from improper charging, crash damage, or shorting the batteries, and this can be difficult to extinguish. Fire occurs due to contact between lithium and oxygen in the air. It does not need any other source of ignition or fuel to start, and burns almost explosively. A lithium battery fire is very hot (several thousand degrees) and is very good at starting additional fires that can result in loss of models, cars and other property. Homes, garages and workshops have also burned.
These warnings can be a little scary, and they should be as these Li-Poly packs can be very dangerous if not handled correctly, but please try and keep this information in perspective. Kitchen knives and chip pans can also be very dangerous if not handled properly and there will probably be more injuries caused by scalpels or super glue in eyes than batteries. The following precautions should help you enjoy using Li-Po batteries without having a major incident.
General Precautions
Only charge Li-Po batteries on a charger specifically design for Li-Po batteries. Li-Po chargers are available at varying prices, depending upon the features, for the same price or, or lower than, NiMh chargers.
Always ensure you use the correct charging voltage for the cell count. This will be 7.4v (2S) for car packs.
The maximum charge rate should be 1C, e.g. 3.2A for a 3200 mAh pack. For best charging, low charge rates should be used where possible.
Double check the charge voltage (or cell count), mAh, and current before each charge.
Never leave charging Li-Po cells unattended (at any charge rate).
It is best to charge Li-Po cells in an open space on a non-flammable, non-conducting surface (such as a bare cement floor, brick or quarry tile) and away from flammable materials.
Check your charger for safety. After charging, check battery with a digital voltmeter, the voltage for a fully charged pack should be between 8.32V to 8.45V.
Do not charge the battery inside your model, inside your car, on home furniture or wood floor/carpet, or anywhere near flammable material.
The minimum safe discharge voltage is 5.0V (2.5V per cell) when under load, or 6.0V (3.0V) per cell when not on load.
A number of the electronic speed controllers have a Li-Po feature built into their software; make sure that this has been enabled. Otherwise consider fitting a Li-Po cut-off device. Failing that, stop driving when your motor loses power, remove the battery from the car, and recharge it.
If using a Li-Po receiver pack then you will need to use a 6V regulator with it that will supply enough current for to power your radio equipment.
Use connectors that can not be short circuited, or use silicon fuel tube to protect exposed connections. Under no circumstances should the ESC wires be soldered directly to your battery.
Do not short the battery as it may catch on fire. If you accidentally short a battery, place it in open space and observe the battery for 10 minutes. It may swell up and possibly even catch on fire.
Have a dry powder fire extinguisher or a bucket of dry sand within reach in case of a fire.
Cell balancing is a way of ensuring your Li-Po will deliver the maximum performance and capacity over a prolonged period of time, although some manufacturers claim that it is not required with their batteries.
Li-Po packs are designed for operating temperatures up to 40°C and under no circumstances must they become hotter than 60°C.
You may need to add weight to your car to balance it and/or reach the minimum legal weight.
If a pack is involved in a crash or is otherwise damaged, remove the pack from the model and inspect for damage to the pack and the wiring/connections.
Lithium polymer batteries do not have a hard steel case like a NiMh battery. Instead, a special aluminium foil encloses them. Therefore, they do not vent. If the integrity of the battery is compromised, swelling will occur. If the battery is damaged and the case begins to expand, discontinue use immediately. ‘’