rocketbob
Well Known Member
Having done some work around testing Shorai batteries and studying how and why these batteries can fail and in some cases potentially catch fire, I've decided to make some changes to the electrical system to mitigate any potential failures that may result in a fire.
The biggest potential cause for a fire seems to be a dead short across the battery. The first place is at the battery so its mounted in such a way that there's no possibility of the terminals coming into contact with the airframe. That is easy to handle in this case because the batteries are so light they don't need much structure to hold them unlike heavy traditional lead aircraft batteries.
The other consideration is a short in one of the fat wires to the starter or alternator. I don't much worry about fixed wiring like to the fuse holders since its very unlikely to short by following known safe wiring practices. However, the starter and alternator are different. They shake, and the wires to them shake, so even though one can make the wiring safe I can't control something internally in the starter or alternator that could short.
I don't use external starter solenoids because of the noticeable degradation in performance from the small chance that the hot wire or starter could fail. External starter solenoids can and do fail as has been documented in other threads here.
Potentially with a LiFePO4 battery a massive short could cause a battery fire.
The solution is to put a larger 350A ANL current limiter in the starter wire as close to the battery as possible, and a smaller ANL to protect the alternator wire, which is done routinely.
Normally one doesn't see ANL fuses on starter wires but I do think it has merit with this type of battery and there really isn't any drawback to not putting one in, and is safer and more reliable than a starter solenoid.
The biggest potential cause for a fire seems to be a dead short across the battery. The first place is at the battery so its mounted in such a way that there's no possibility of the terminals coming into contact with the airframe. That is easy to handle in this case because the batteries are so light they don't need much structure to hold them unlike heavy traditional lead aircraft batteries.
The other consideration is a short in one of the fat wires to the starter or alternator. I don't much worry about fixed wiring like to the fuse holders since its very unlikely to short by following known safe wiring practices. However, the starter and alternator are different. They shake, and the wires to them shake, so even though one can make the wiring safe I can't control something internally in the starter or alternator that could short.
I don't use external starter solenoids because of the noticeable degradation in performance from the small chance that the hot wire or starter could fail. External starter solenoids can and do fail as has been documented in other threads here.
Potentially with a LiFePO4 battery a massive short could cause a battery fire.
The solution is to put a larger 350A ANL current limiter in the starter wire as close to the battery as possible, and a smaller ANL to protect the alternator wire, which is done routinely.
Normally one doesn't see ANL fuses on starter wires but I do think it has merit with this type of battery and there really isn't any drawback to not putting one in, and is safer and more reliable than a starter solenoid.
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