nuckolls.bob(at)aeroelect
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 Posted: Mon Jul 28, 2014 7:57 am Post subject: Lithium Battery Experience - Sept. Kitplanes Article |
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At 05:00 PM 7/27/2014, you wrote:
--> AeroElectric-List message posted by: "jaustinmd" <john(at)jaustinmd.com>
Bob requested in his recent article that those experimenting with Lithium batteries relate their experiences. I built a Zenith STOL CH750 with a Jabiru 3300 engine - a day/VFR, non-electrically dependent aircraft - perfect for experimentation! Thank you for taking the time to share . . . I purchased a Ballistic 12-cell. Initially, things were fine - it spun the 3300 as good or better than the PC680 (and saved about 12-13 lbs doing it!).
However, I began to get erratic tach readings and looked at the alternator leads where the tach picks up and the Jabiru OEM female spade leads appeared burned! After consulting Jabiru USA, I replaced the rather flimsy leads with quality AMP female spade connectors.
According to the Jabiru wiring diagram for this engine http://tinyurl.com/mpsmquh the tachometer drives from a variable reluctance pickup that looks at features on the flywheel . . . gear teeth, bolt heads, etc.
This is a TINY signal that is unlikely to burn anything. What you may have observed in terms of discoloration is corrosion. But in any case, if you have spade terminal females getting loose or corroded, be aware of the potential for similar problems every other place you used this same terminal . . . this particular failure would not have been related to your battery change-out. THEN, my 20 amp alternator breaker began to trip! Where was this breaker installed? At this point, I did a lot of research and found that since the Jab 3300 doesn't output charging current 'til about 1800-1900 rpm, . . . typical of ALL brands and sizes of permanent magnet 'dynamos' . . . . . . my theory was that the connectors were frying due to the surge of charging current after take off and low internal resistance of the battery, and once the connectors were corrected, the little Ballistic battery was getting hit with a surge of charging current in excess of 20 amps and tripping the breaker. Those connectors were not associated with any part of the battery recharging current. I did two things - I reviewed my wiring and found I was good for up to a 35 amp breaker to protect it, so I replaced the breaker with a 35A, and switched to an EarthX ETX36D which supposedly has close to the capacity of the PC680. Why the battery change? When I'm informed as to the location of 20/35A breakers, we can begin to figure out root cause of the tripping phenomenon you observed.
It's not clear that the trip is related to the differences in batteries. The alternator is rated for 200W continuous which is 200/14 or about 14A. It MIGHT be that the lithium battery's willingness to accept charge at 14v is greater than the Lead-Acid . . . I'll need to explore that with some lithium cells on the bench. If that's true, then substitution of lithium for lead in your particular installation may be putting your rectifier/regulator/ alternator at risk. These systems are generally not current limited like wound-field alternators. So while up-sizing the breaker may have fixed a symptom, it doesn't answer the question as to why the 20A breaker was popping. Do you have an alternator loadmeter . . . if not, would you be willing to install one temporarily to sort out the questions? Time will tell as to durability and performance of the EarthX, but for now I'm a happy camper! It's not clear that the AeroVoltz would not be performing as well as the EarthX . . . But the EarthX does feature a full-up battery management system not unlike that installed in the TrueBlue products presently finding their way onto TC aircraft.
Bob . . . [quote][b]
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