MPBA GUIDELINES ON USE OF LIPO BATTERIES
Lipo batteries are now used by a very significant number of model boaters and they must be treated differently to more conventional rechargeable batteries.
The most useful aspects of their operation is the very low self-discharge rate, which can be as low as one or two percent per month. This gives them the extremely useful property of being able to be charged when you come home from boating and still be fresh and ready to use even several weeks later.
Anyone who has forgotten to put their batteries on charge the night before a boating session will appreciate that.
However, they are different to conventional cells and probably the most important aspect of these batteries from a safety point of view are the consequences of overcharging, over discharging and crash damage.
The individual Li-Po cells are nominally 3.7 volts with a maximum fully charged rating of 4.23 volts and a minimum safe discharged rating of 3 volts.
If you over discharge the battery too much below 3 volts per cell you will almost certainly damage it permanently and it will not then accept a re-charge. NEVER leave a Li-Po battery connected to something that will allow even the slightest discharge, as the battery will be effectively destroyed in a few hours.
If you charge your battery beyond the 4.23 volt per cell limit, you risk damaging the battery and also have the possibility of a thermal runaway, resulting in a battery fire. You MUST use a dedicated Li-Po charger and, if your charger is not automatic, you MUST make sure that the voltage control on the charger is set correctly for the number of cells in the battery you are charging.
Most Li-Po cells and chargers have a cell balancing facility and the use of this will help keep the cells working efficiently and safely. In fact, we would not recommend the purchase of a Li-Po charger that didn’t have this facility available.
You must also use a speed controller (ESC) that is designed for use with Li-Pos and will not allow them to over-discharge.
Other precautions should also be taken when charging.
- Do not charge at more than 1C unless specifically authorized by the pack vender.
- Never charge batteries in a model, always remove them from the model.
- Charge on a safe surface in a position where a battery flare cannot ignite other items. A Li-Po burn only lasts a few seconds so it is not a long-term fire source but it is extremely hot and will easily ignite other flammable items that are in close proximity. Dedicated ‘charging bags’ are also available that will contain any Li-Po flare if used correctly.
- Damaged cells are usually very easy to spot as they ‘balloon’ out.
- The cells are generally ‘softer’ than the traditional Ni-Cd types and are much more susceptible to crash damage. Any visible damage to the cell should be treated with suspicion.
- Any cell that is ‘ballooned’ by charge/discharge problems or by crash damage should be discarded.
- Any cells you wish to discard must be made safe. The commonest recommended method of doing this with a damaged cell is to discharge the cell electrically and then submerge it in strong salt water for at least 12 hours. After this the cell is inert and may be disposed of at your local recycling site. For more guidance on the subject you should consult the Internet for the latest information on cell disposal.
- Always read the manufacturer’s information on the cells you are using, as this will give you the information on maximum charge and discharge rates.
Checking lipo volts in cells
4.23v = 100%
4.03v = 76%
3.86v = 52%
3.83v = 42% = typically used as a storage charge Recommended
3.80v = 30%
3.75v = 11%
3.70v = 0 %
(These are resting voltages not under load voltages)
All models must have a kill switch for the radio control equipment(excluding scale craft) this is operated from the outside of the model (loop system is recommend) in case of emergency the competitor, start assistant, recovery boat or any other person can interrupt the power supply between the motor and batteries.
Recommended for the race platform or pits area
A first aid kit, fire extinguisher, fire blanket and a bucket of dry sand has to be present.
It is up to the officer of the day to see where these are allocated on the day.
Lithium Metal fires
Lithium Metal fires must be tackled with a specialist lithium extinguisher, commonly sold as a L2 extinguisher. A sodium chloride extinguisher is not suitable for use on a lithium metal fire. Cells/batteries not containing Lithium as a pure metal do not require a L2 extinguisher.
DO NOT USE A WATER EXTINGUISHER
If any fire gets out of hand call 999
MPBA members are expected to operate lipo cells in a safe and responsible manner.
Batteries shall be securely fixed in the boat.
Do not mix batteries from different manufacturers.
The following changes are allowed across the board for all classes of competition i.e. : Fast electric, Scale, Round the Pole Hydroplanes and Straight running, whether it be for physical problems of getting cells into a boat or for class weight restrictions.
1. Removal of the plastic covering to enable batteries to comply with the required weight limits or physical problems of getting cells into a boat is permitted.
2. Competitors are able to change the connectors if they wish.
3. The wires can be changed as long as they are capable of taking the expected current load.
4. Please make sure that all other terminals apart from the one you are working on are covered with an insulating material to avoid the possibility of a short circuit. On completion of alterations please ensure that all connectors are insulated and that all bare cell terminals are covered with polyimide tape or another suitable heatproof material ( fibre glass tape is also suitable) this will ensure that there will not be a short circuit from any wires including balance leads.
5. NEVER ALTER THE GREY/SILVER PLASTIC CELL SACKS IN ANY WAY
These measures should only be carried out by competent people. If in any doubt as to your own ability you should take advice from someone that has the required experience.
Sometimes balance leads break away from a cell tag due to fatigue. The cell connection therefore has to be repaired or the battery thrown away. The latter is not an economic solution so it will be necessary to take the above precautions to re-solder the wire.
Review in 12 months