This design decision is to save weight, but the weight savings is at the expense of battery capacity, resulting in critical cranking voltage and very little excess capacity. (It is even more problematic if the battery is cold.) This can be problematic if: 1) The engine does not start in the first 5 seconds when cranking; or 2) If the battery has been drained by having the electrical accessories running for some time before cranking the engine; or 3) If the alternator fails in flight, you have less than an hour of time (probably only 30 minutes) to use radios, transponders, etc. before the battery runs out.
If the battery runs out before starting the engine, getting to the battery to jump start it would normally require lifting the pilot seat for access. (Or getting out of the plane to hand prop!)
If the battery runs out before starting the engine, getting to the battery to jump start it would normally require lifting the pilot seat for access. (Or getting out of the plane to hand prop!)
One solution is to carry an EarthX Jump Start battery. This small Lithium Iron battery is quite powerful and relatively safe. By installing the EarthX connector harness using E-Flite EC-5 connectors, you can connect the jump battery while sitting in the pilot's seat. The same harness provides an SAE connection for the Battery Tender without lifting the seat. (The EarthX Jump Start is also a great backup for charging an iPad and smartphone, but is probably not a good solution for the task of adding battery capacity for use in the case of alternator failure.)
Another solution is to carry a "JumpPac" system using a 12v lead acid battery similar to the one offered by StartPac.
Adapting this unit with the large Cessna style receptacle to the wiring on the Cub would have required some work, so I chose to build my own custom unit using the same model YTZ10-S Yuasa AGM battery and EC-5 connectors installed in the Cub. This offered one major advantage in that, when connecting batteries in parallel, it is best if they are the same type and size. So, by using the same battery, it would be acceptable to leave the "JumpPac" connected for a period of time--with or without the engine running. Another issue was that the FAA rules for carrying a AGM battery "in the cabin" limits the battery to 100 watt hour capacity--the Yuasa YTX10-S meets that rule.
I simply repurposed an old polypropylene Dewalt tool case to hold the battery. I protected the wiring with a 100 Amp "slow blow" circuit breaker. This device will allow 200 amps for 10 seconds or 250 amps for 5 seconds and can also serve as an "off/on" switch. I fabricated a harness with E-Flite EC-5 connectors (same as the EarthX harness installed on the Cub's battery.) using 8 gauge high temp silicone insulated wire. (The max wire size for the EC-5 connectors is 8 gauge and it requires careful and precise solder work. 8 gauge is desireable because it limits voltage drop in the harness.)
In addition, I wired in a cigar lighter receptable, fused at 15A, to allow for the "JumpPac" to be used to power a portable air compressor or other "accessory" like a heater or 110V inverter when stopped over during a cross country flight or a camping trip. The receptable also allows a digital voltmeter to be used to determine battery state of charge. Finally, I also installed another fused harness to allow for the Jump Pac battery to be charged using the same Battery Tender SAE connector that I use for the Cub battery.
So the JumpPac can be carried behind the rear seat during a cross country trip. (Fits snug fore/aft between the storage container and seat, and the tiedowns restrain it from vertical and side movement.) If it is needed to jump start the Cub, or connected for additional reserve capacity for a long flight, then it can remain connected during flight, essentially increasing the plane's capacity from 8 Amp Hours to 16. It can also be stored in a heated area with the pilot, so that it is at full capacity when starting a plane that has sat out in the cold.
When tested, with the JumpPac connected during starting, starter voltage was nearly 10 volts as compared to 9 volts with the single battery. Cranking speed was comparable to an automobile and as good or better than most certified GA planes with big and heavy batteries. The JumpPac weighs 10.8 pounds.
Another solution is to carry a "JumpPac" system using a 12v lead acid battery similar to the one offered by StartPac.
Adapting this unit with the large Cessna style receptacle to the wiring on the Cub would have required some work, so I chose to build my own custom unit using the same model YTZ10-S Yuasa AGM battery and EC-5 connectors installed in the Cub. This offered one major advantage in that, when connecting batteries in parallel, it is best if they are the same type and size. So, by using the same battery, it would be acceptable to leave the "JumpPac" connected for a period of time--with or without the engine running. Another issue was that the FAA rules for carrying a AGM battery "in the cabin" limits the battery to 100 watt hour capacity--the Yuasa YTX10-S meets that rule.
I simply repurposed an old polypropylene Dewalt tool case to hold the battery. I protected the wiring with a 100 Amp "slow blow" circuit breaker. This device will allow 200 amps for 10 seconds or 250 amps for 5 seconds and can also serve as an "off/on" switch. I fabricated a harness with E-Flite EC-5 connectors (same as the EarthX harness installed on the Cub's battery.) using 8 gauge high temp silicone insulated wire. (The max wire size for the EC-5 connectors is 8 gauge and it requires careful and precise solder work. 8 gauge is desireable because it limits voltage drop in the harness.)
So the JumpPac can be carried behind the rear seat during a cross country trip. (Fits snug fore/aft between the storage container and seat, and the tiedowns restrain it from vertical and side movement.) If it is needed to jump start the Cub, or connected for additional reserve capacity for a long flight, then it can remain connected during flight, essentially increasing the plane's capacity from 8 Amp Hours to 16. It can also be stored in a heated area with the pilot, so that it is at full capacity when starting a plane that has sat out in the cold.
When tested, with the JumpPac connected during starting, starter voltage was nearly 10 volts as compared to 9 volts with the single battery. Cranking speed was comparable to an automobile and as good or better than most certified GA planes with big and heavy batteries. The JumpPac weighs 10.8 pounds.
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