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jan_de_jong(at)casema.nl
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plevyakh
Joined: 10 Jan 2011
Posts: 39
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 Posted: Sun Nov 01, 2015 6:29 am Post subject: Re: LiFePO4 endurance battery? |
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Jan,
I installed an EarthX ETX680 in my GlaStar about two months ago. I have roughly 40 flight hours on the battery. I'm very pleased with my installation so far. Engine starting is much improved over my Odyssey PC680. Engine start improvements are a result of 1) moving the battery forward from an AFT tail cone location to on the Firewall (gained 4.5V of starter voltage), and 2) the increased cranking amps of the ETX680.
I'm using Bob's Z13-8 architecture as my base but with some differences (e.g., Dual Lightspeed Ignition system).
I have a Main Bus, Endurance Bus, and Battery Bus. After the installation I did a Endurance Bus "load test"...by simulating failed primary alternator (B&C Specialty 60 amp), and failed backup alternator (B&C SD-8 (8amp)) and running on only the ETX680 battery.
I had a voltmeter on the battery bus with battery bus voltage at 13.2V at beginning of test, and 12.87V at the end of test...End of Test established when my Instrument Panel "Blue LED Battery Warning light" came on my panel.
My endurance bus load was 7.4amps. Outside Air Temp was 75deg F.
The ETX680 battery ran for 63 minutes until the LED Battery light came on. The LED battery warning light is run by the EarthX Battery Management System (BMS). One function of the BMS is that a flashing LED light indicates that one or more of the cells are discharged greater than 80%. More on the BMS can be found in the EarthX manual.
Since I have the SD-8 backup alternator...I won't need to push the ETX680 battery this hard...but it's good to know I have roughly an hour of flight time before my warning light comes on (Battery Ops Alone). I plan to re-run this test at each Annual inspection to maintain awareness of it's capacity as I use up life cycles.
I did reset my B&C Specialty Voltage regulator trip point for recharge to 14.5V as recommended by Bob K. in a previous thread of Lithium batteries. I'm also running cooling hoses to the battery to keep it cool since it's installed FWF in the engine compartment.
I highly recommend Bob Knuckoll's battery series in KitPlanes magazine...these articles are worth the price of annual subscription alone!
Howard (GlaStar N19HL approaching 100 hrs flight time).
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Howard Plevyak
GlaStar / Cincinnati, Ohio |
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nuckolls.bob(at)aeroelect
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| Posted: Sun Nov 01, 2015 8:37 am Post subject: LiFePO4 endurance battery? |
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Since I have the SD-8 backup alternator...I won't need to push the ETX680 battery this hard...but it's good to know I have roughly an hour of flight time before my warning light comes on (Battery Ops Alone). I plan to re-run this test at each Annual inspection to maintain awareness of it's capacity as I use up life cycles.
I did reset my B&C Specialty Voltage regulator trip point for recharge to 14.5V as recommended by Bob K. in a previous thread of Lithium batteries. I'm also running cooling hoses to the battery to keep it cool since it's installed FWF in the engine compartment.
I highly recommend Bob Knuckoll's battery series in KitPlanes magazine...these articles are worth the price of annual subscription alone! |
Good work sir . . . thanks for sharing. I trust
you'll write down the results of your findings.
I've taken a hiatus on the KP articles . . .
got a couple in process on the hard drive, one of
which is a wrap-up piece on COMPARATIVE performance
of a stock lead-acid, an EarthX LiPO and I'm
thinking of running an 18 a.h. SLVA to round
out the data package.
It's going to be a while . . . in the mean time,
cogent studies such as yours will assisting in
expanding the body of knowledge.
Bob . . . [quote][b] [quote][b]
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peter(at)sportingaero.com
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| Posted: Sun Nov 01, 2015 8:43 am Post subject: LiFePO4 endurance battery? |
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The way these batteries are going there is the potential for a different
battery bus architecture.
An aircraft battery is usually performing 2 different requirements,
firstly stored energy to start the engine and secondly as a back-up
power supply should the engine driven system fail, or to fill in for
short term loads. Starting requires a large current for a few seconds
(if everything works properly), back-up power requires more modest
currents for much longer. The two requirements are quite different and
require different batteries. For many years we have used lead-acid
batteries for both tasks as the minimum battery required for reliable
starting was adequate for the back-up task, but those typically
available;e are relatively heavy - say 17lb for a PC680 common in
Lycoming engined aircraft. There is a strong argument, advocated by Bob
and others, to use two cheaper batteries of the same type - one for
starting and one for back-up - and to replace one each year (there is
more to this argument - read The Connection).
With the progress in Lithium battery technology this may no longer be
the optimum strategy - as long as the promises of Li battery makers are
true... Lithium batteries are significantly lighter than lead-acids for
the same task (not always the same stored energy). Also batteries
optimised for starting probably don't store sufficient energy to meet
the back-up requirement. Also a Lithium battery capable of providing
starting currents and storing sufficient energy for the back-up case can
be 5x more expensive than a pure back-up battery. As any Li battery
suitable for aviation use will have an on-board battery management
system, and can cope with being depleted to a point where the BMS shuts
off without a life penalty, it is likely that Lithium batteries will
last much longer than lead-acids. Li batteries are also attractive are
they don't lose much charge over time.
An Li battery designed to crank a Lycoming can be relatively small and
light. With a companion back-up battery the combined weight will be less
than one 15Ah lead-acid. The cost will be 2 or 3 times that of a PC680,
but the lithiums should last a lot longer. Clearly there is little data
available beyond battery manufacturers' claims as these batteries are
only just becoming available in any significant numbers and the
technology is still maturing.
I have been talking to a Lithium battery company in the UK about a
sailplane application. To provide some numbers, a 20Ah battery, which
will provide a maximum of 20A, weighs 2.8kg (6.2lb) and has a life of
3000 cycles (probably 10x an equivalent lead acid) and would retail at
(around) $200. A Li battery to start a Lycoming (nominally a 5Ah
battery) weighs around 2.5lb, has a similar 3000 cycle life expectancy,
but might cost around $300. Overall this pair would weigh around half a
PC680, but would be at least 3x more expensive and will require a more
complex electrical system.
Once these batteries have proven their reliability any aircraft that
doesn't require any significant back-up capability may be able to
realise a 12lb+ weight saving at a relatively modest $/lb rate.
Who knows where this will go in the next year or two, and which
particular Li technology will become favoured.
Peter
On 01/11/2015 13:13, Jan de Jong wrote:
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