[Orv Neisingh]

There have been several of my clients who have installed lithium batteries into their Rotorway helicopters recently. I new very little about lithium batteries until one ship that I was instructing in recently suddenly had a complete electrical failure and engine out at altitude. I was able to perform a successful autorotation into a small field with no damage to us or the helicopter other than a slight bend in one skid. When the engine quit so did all of the electronic instruments and I had no airspeed or rotor rpm displays so it made performing a successful auto pretty intense. 

On examination we found both of the 30 amp fuses near the alternator blown shutting all power from the alternator. The ship was running only on the lithium battery and showing 12.7 volts in flight. After about 45 minutes of flight the battery was depleted to the point that the internal circuitry shut off all power to the electrical system even though it had been displaying 12.7 volts up until the time of the electrical shut off. We researched the issue and there is a complete and reliable fix to the electrical system that we can discuss if anyone is interested. Don't let this happen to you.

[Tim Morris]

So, it was running on battery the whole time?  Seams like a warning light was needed that shows if the alternator is running or not.  I don’t have a lithium battery but I installed a warning light.  Not perfect, but good enough to show if the alternator is working or not.

[Lyle Swallows]

Tim, the real issue with misuse of Lithium batterys is not building the system to the application of Lithium battery. Lithium discharges at a much flatter voltage curve when compared to Lead Acid,

so most Low Voltage warning lights come on at 12.7 showing the Alternator is not charging. Lead acid natural resting voltage is about 12.4-12.6
Lithium resting voltage is 12.8-13.2 roughly. i could be off slightly.

a lithium resting at 100% voltage will show 13.2 and lead acid will show 12.6
a lithium at 20% will show 12.8 and lead acid will show about 8-9volts.

many people use an external voltage regulator such as the B&C LR3E which can be adjusted by the B&C guys to show a Low Voltage warning at 13.5 indicating the Lithium Battery is not being charged. otherwise they come on at 12.7 for normal applications.

[Orv Neisingh]

Our not being familiar with lithium batteries, we could see a constant 12.7-12.8 volts during that flight which was a great voltage for a standard battery but not a lithium battery. On that particular flight we had two failed start attempts before finally getting the engine started. Those failed attempts drew the battery down and when the alternator was turned on after engine start the lithium battery drew all of the available amperage to recharge, drawing more than the 30 amps the fuses were rated for so they failed. We were then running on only the power remaining in the batteries. 

After researching the proper solution we installed an external voltage regulator designed for the lithium battery, it comes with a warning light that we installed on the instrument panel. We also installed an amperage sensor that the alternator leads pass through and it's associated amp gauge that is mounted in clear view to monitor during flight to insure that the alternator is providing power to the charging system. We also installed a 30 amp breaker for the overhead panel and a 60 amp breaker with #6 wiring next to the alternator to provide the lithium battery with ample amperage when required. 

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The top photo shows the amp gauge on top of the fuel tech computer, the middle photo is how I wired my own alternator with amp coil and 30 amp breakers, the bottom photo shows the wiring we did on the lithium battery with voltage regulator, 60 amp breaker for the battery with #6 wiring to the battery.

[Tim Morris]

Yep.  Good stuff.  All that extra stuff to support this new battery.  I think I will keep mine.

[Lyle Swallows]

Yep.  Good stuff.  All that extra stuff to support this new battery.  I think I will keep mine.

definitely pro's and con's every builder must weigh.

i've opted for the lithium and supporting equipment/monitoring devices. weight savings ends up Nil in my mind but battery capacity is larger incase of alternator failure/shutdown.

[Orv Neisingh]

That is true Tim but always being able to monitor the output of the alternator via an amp gauge is critical in your instrument scan. I have installed the amp probe coil and display on my own non lithium system and it is a real comfort to see that all is well with the alternator output. I also like the breakers because if one trips on a previous flight you can easily see the red flag on the breaker indicating a trip during your pre-flight walk-around. The two stock 30 amp fuses must be physically removed and inspected on each pre-flight and I don't know of many who do that.