Battery Care and Maintenance
Safety
BPS batteries are intended for use only with the S-CAB Battery Power Supply (BPS). They use one or more lithium-polymer (LiPo) cells, singly, or connected in parallel, and are protected by a fuse within the battery package.
Warning: LiPo cells store a lot of energy in a small volume and come with a warning to use responsibly. By deciding to purchase these batteries, the user accepts all liability for any consequences resulting from opening, puncturing, or misuse of the battery package. A blown fuse cannot be replaced by a user and the battery must be returned for repair or replaced with a new battery.
Warning: LiPo cells store a lot of energy in a small volume and come with a warning to use responsibly. By deciding to purchase these batteries, the user accepts all liability for any consequences resulting from opening, puncturing, or misuse of the battery package. A blown fuse cannot be replaced by a user and the battery must be returned for repair or replaced with a new battery.
Battery Protection
The BPS includes battery protection that would otherwise be included in a PCM (Protective Circuit Module) integrated into the battery package. Specifically, the BPS prevents over-charging and over-voltage, as well as protection from under-voltage and battery overload. When combined with short-circuit protection provided by the battery fuse, BPS design provides a very safe battery power source.
Battery Fuse
The fuse is either 6 amps or 8 amps, depending on battery's intended use. Maximum battery current occurs when battery is at minimum voltage (about 3 volts) and BPS output is greatest; 1 amp or more. With these conditions, the ratio between battery current and BPS output current is approximately 4 to 1. BPS output of 1 amp consumes 4 amps battery current.
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A common cause of a blown fuse is an attempt to measure battery voltage at the battery socket. There is high risk that multi-meter probes will momentarily short-circuit battery output and blow the fuse, which clears the short instantaneously (there won't even be a spark).
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Care and Maintenance
UnpluggingBattery plug and socket are tight by design and not intended for frequent disconnection. It is important to avoid unplugging by pulling the leads. Eventually, a wire will pull out of the connector. An IC Extraction Tool is one simple way to avoid this problem.
Discharged BatteryThe following behavior by a loco that was operating normally indicates its battery must be recharged.
ShutdownConclude a battery powered operating session by either parking the loco for battery charging or be sure to turn the battery off and prevent slow discharge while a loco is not in use.
Momentarily shorting BPS shutdown wires ("SDN") opens an electronic switch which prevents battery discharge. This can be done irrespective of whether a battery is charging (BPS input on) or is not charging (BPS input off).
Shorting can be as simple as touching the 2 BPS brown wires together (during testing, for example), or connecting a normally-open push-button, or a magnetic reed switch. It can also be done with a decoder command.
To confirm turn-off, have a light on, or sounds audible and watch/listen for shut down.
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LiPo Battery chargingAlways use a compatible battery charger for lithium polymer (LiPo) batteries. For good battery life, charging current should be within battery specifications, should be constant and decrease to zero as cell voltage approaches maximum (4.2 volts). Exceeding maximum voltage is dangerous.
BPS Battery ChargingBattery charging occurs whenever a BPS has power input (its gray wires) from a connector or powered track. Depending on track voltage, a loco operating on powered track can draw all or part of its power from the rails.
Charging occurs whether a loco is moving or stationary and charge rate is approx. 450 mA until the battery approaches full voltage, at which point, charging current drops to a value no greater than is needed to hold battery voltage at 4.2 volts. (Zero if there is no battery load.)
If a loco is stationary, a decoder continues to require some current (typically between 20 and 80 mA, depending on type of decoder). which implies something less than 450 mA is available to charge the battery. This drain can be eliminated by turning off battery discharge. A similar result is automatic when BPS input voltage exceeds 12.5 volts since, in either case, rectified input provides output power with no contribution from the battery.
Over-dischargeOver-discharge is not safety related, but can be frustrating. BPS under-voltage protection turns off a battery when its voltage drops below 2.7 volts, which provides sufficient margin to prevent over-discharge. With load removed, battery voltage typically recovers to approx. 3 volts and can be recharged without difficulty.
Avoid repeated attempts to use a discharged battery: A battery discharged below 3 volts can be turned on (and may operate LED lights) but BPS will shut down when motor load is applied. This drains more energy from an already depleted battery and repetition eventually leads to over-discharge. In extreme cases, the battery cannot be recharged.
How to recover: In most cases, BPS can recharge an over-discharged battery by removing all load while charging. Use the following procedure:
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Questions, questions
When to charge? |
Where to charge? |
For planned/scheduled operating sessions, charge batteries immediately before the session. For impromptu operation, charge batteries at the end of a long session. For long periods without use, it's best to leave a battery partly discharged.
Since LiPo batteries have no "memory effect", recharging a partly discharged battery is okay. How much track should be wired?This is a trade-off between battery size and layout design. When using locos that can only accommodate small batteries, more powered track extends a loco's operating time before requiring a full recharge. So far as powered track is concerned, the most important objective is avoid the task of wiring inaccessible and/or complicated sections (lots of switches) of the layout. There's no need to wire track in locations that are difficult to clean.
What is the life of a LiPo cell?LiPo cells slowly loose their ability to store full charge. Manufacturers' typically specify life as 500 full charge/discharge cycles. This could imply 10 years for a model loco that has heavy use once a week.
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Reliable electrical contact between wheels and track is important if using rails for battery charging. The good news, track cleaning is only necessary at track locations used for charging. For full recharge, choose a location where a loco can be parked for several hours.
For large layouts and longer operating sessions, power a few "refueling" areas that are easily wired and where locos are likely to spend extra time.
How long will a LiPo stay charged?LiPo batteries have a very long shelf life (measured in years). When a BPS is turned off there is a tiny, unavoidable, leakage current. Typically, a battery will hold adequate charge for 3 to 6 months. Best practice is to charge a battery briefly before operating a loco that has not been used for a month or more.
Long-term storageFor storage of a year or more, it's advisable (though not essential) to remove and store each battery separately in its own plastic envelop or wrapper. The battery should remain good for a number of years.
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