LifePO4 batteries for motorgliders - are we there yet?

Its time again to change batteries in my motorglider. There are 4 lead batteries with modified (vibration proof) terminals. A major pita.
I have been enviously following the threads for improved batteries for pure gliders. Lighter, more performance, holding their charge, longer life cycle yada yada...
I have more avionics than ever and want more capacity for improved safety but have no room to spare. I would also like to shed some of the weight and get better life. I am ready.
The question is however, how LIFEPO4 batteries will do with a mixed high amp crank demand of a self starter and deep cycle mode during long flights with enough umph to start at the end of the day when needed.
Does anybody have experience or words of (scientific - not regulatory) wisdom?

Responding to a request for more detail:

DG-808B Solo engine
Four 6v,12 Ah lead acid battery (150x50x110 mm)
Batteries are 'permanently' mounted in bays slightly larger than current battery size .
Batteries are connected parallel/series to create 12v system.

Hadn't seen DG80x installations, but sounds just like the DG400.
Last time at Schempp-Hirth, they were using LiFePO4 for avionics but not the engine.
If LIFePO4s are still not suggested for the engine, you could put in two of them for avionics and use two SLAs only for the engine. Plenty of gusto for either circuit.
This would require separate charging points for the two types, and keep the Phosphates off the engine's charging circuit.
Jim

On Monday, January 4, 2016 at 2:23:51 PM UTC-8, Chris wrote:
Responding to a request for more detail:

DG-808B Solo engine
Four 6v,12 Ah lead acid battery (150x50x110 mm)
Batteries are 'permanently' mounted in bays slightly larger than current battery size .
Batteries are connected parallel/series to create 12v system.

Assuming this is a DG800 I'd leave the (4) engine start
batteries well alone; my experience is that they last about 10
years. The batteries, bought from DG, are hardly cheap but as
you are probably not in Europe you can probably fit a set for a
fraction of the money the DG agent wants. Cheap and simple
known technology.
If you are in Europe it's not legal to change these batteries to
Lithium types; secondly it's expensive, thirdly it will require a
new "weight and balance" as the c. of g. will change.
Better to change the DG wiring so that all your hungry avionics
runs from one (or two) "soaring" batteries (NiMH or Lithium
type) on the luggage shelf. You can charge these from solar
cells on the engine doors.
I've run this system without any problems. The important point
to remember is that DG have wired up the aircraft so that
everything, except the electric vario, runs off the (4) engine
start batteries! Personally I think it's a daft way to arrange
things: if you run the radio, transponder, horizon etc then your
critical engine start batteries are depleted (even if you have
the optional solar panels on the fuselage). Don't be taken in by
that cute battery switch labelling, whatever its position most
everything is still depleting your main batteries.

On Monday, January 4, 2016 at 1:39:04 PM UTC-8, Chris wrote:
Its time again to change batteries in my motorglider. There are 4 lead batteries with modified (vibration proof) terminals. A major pita.
I have been enviously following the threads for improved batteries for pure gliders. Lighter, more performance, holding their charge, longer life cycle yada yada...
I have more avionics than ever and want more capacity for improved safety but have no room to spare. I would also like to shed some of the weight and get better life. I am ready.
The question is however, how LIFEPO4 batteries will do with a mixed high amp crank demand of a self starter and deep cycle mode during long flights with enough umph to start at the end of the day when needed.
Does anybody have experience or words of (scientific - not regulatory) wisdom?

Not a DG, but I have been using an LiFeP04 for the engine start battery in my ASH26E for a year now. While the engine start battery can power the avionics, I have a separate (LiFePo4) battery for that. You need to find a Li battery that fits in the same spot, has charge/discharge/current protections built in, and has a max discharge capacity sufficient to crank the starter reliably. I measured the ASH starter at 150 amps stall current and 100 or so while cranking. The battery I am using is a CTC LFP128198, rated at 19.8 AH and 160 amps discharge for 30 seconds.

Beware of LFP batteries advertised for motorcycle or auto start which will say something like "20 AH equivalent" as these generally will deliver the same high discharge current for a short time, but do not actually have the AH capacity to run instruments.

I have had no problem at all with the battery, and it cranks the engine much better than the LA battery that it replaced, holding the voltage about 3 volts higher during cranking.

Years ago I used to sail ocean going multihulls; I recall Tom
Follet saying something along the lines of: "In a multihull if you
ain't got speed you ain't got nothing".

Something similar applies to motor gliders: "If you can't start
the engine you ain't got nothing". You're just lugging around a
load of expensive complicated ballast that can't be dumped.

Why anyone would choose to run their avionics off their engine
start batteries is beyond me. A brief trawl through the motor
glider accident statistics should be enough to convince. The
wretched engines have quite enough failure modes without
adding battery issues.

At 00:40 05 January 2016, jfitch wrote:

Not a DG, but I have been using an LiFeP04 for the engine start battery
in
my ASH26E for a year now. While the engine start battery can power the
avionics, I have a separate (LiFePo4) battery for that. You need to find a
Li
battery that fits in the same spot, has charge/discharge/current
protections built in, and has a max discharge capacity sufficient to crank
the
starter reliably. I measured the ASH starter at 150 amps stall current and
100 or so while cranking. The battery I am using is a CTC LFP128198, rated
at
19.8 AH and 160 amps discharge for 30 seconds.
Beware of LFP batteries advertised for motorcycle or auto start which
will
say something like "20 AH equivalent" as these generally will deliver the
same high discharge current for a short time, but do not actually have
the
AH capacity to run instruments.=20

I have had no problem at all with the battery, and it cranks the engine
much better than the LA battery that it replaced, holding the voltage
about 3
volts higher during cranking.

Can you post a link to the factory approving data that authorizes the
switch from the SLA to LifePo4 batteries?

On Tuesday, January 5, 2016 at 11:00:07 AM UTC-8, soarin wrote:

Can you post a link to the factory approving data that authorizes the
switch from the SLA to LifePo4 batteries?

No. As with the hundreds of gliders using LFP batteries for instruments, it is a substitution made at the owner's discretion and rules interpretation. The SLA battery supplied by the factory is a hardware store battery, not TSO'd or otherwise qualified either. In the case of the ASH26E, the specific battery originally supplied is no longer available and has been already replaced several times.

I'm also using a LiFePo4 battery (illegally) for cranking the engine.
I found a type that is recommended for UL airplanes with the Rotac 912 engine. It has very high cranking max current, practically the same external size (very small mod needed to the battery box, reversible).

It has slightly higher standard voltage (13.9 V IIRC), and the voltage drop while cranking is much much lower than with Pb batteries. So the engine cranks faster and I believe starting has become faster too. For the same reason, the alternator and regulator only charge the battery to (let's say) 90% of full capacity. A few times per year I bring a programmable charger and the old Pb battery to the sailplane, rig it to the battery connector, feed Pb power to the charger, and fully charge the LifePo4 battery. There is practically no self-discharge, so provided I opened all circuit breakers after last flight, the battery is still fully dependable even after many months.

The overall energy stored is inferior to the spec of a new fully charged Pb.. So you have an inferior number of possible attempts to start. But as the voltage remains practically constant even when substantially depleted, I consider it a convenient exchange.

This is also the reason why, with Lifepo4, you should definitely not draw panel power from the engine battery.

Aldo Cernezzi

Aldo, I don't understand what you mean in the following statement:

"A few times per year I bring a programmable charger and the old Pb
battery to the sailplane, rig it to the battery connector, feed Pb power
to the charger, and fully charge the LifePo4 battery."

Please explain. Are the Pb and Li batteries connected in parallel at
this time? And why not simply use a LiFePO4 charger to charge up your
LI battery? Does your Li battery have a BMS installed? Your alternator
probably does not produce a high enough voltage to fully charge your Li
battery as you stated. What does the battery manufacturer say about
charging the battery to a lower level?

Curious,
Dan

On 1/7/2016 1:46 AM, wrote:
I'm also using a LiFePo4 battery (illegally) for cranking the engine.
I found a type that is recommended for UL airplanes with the Rotac 912 engine. It has very high cranking max current, practically the same external size (very small mod needed to the battery box, reversible).

It has slightly higher standard voltage (13.9 V IIRC), and the voltage drop while cranking is much much lower than with Pb batteries. So the engine cranks faster and I believe starting has become faster too. For the same reason, the alternator and regulator only charge the battery to (let's say) 90% of full capacity. A few times per year I bring a programmable charger and the old Pb battery to the sailplane, rig it to the battery connector, feed Pb power to the charger, and fully charge the LifePo4 battery. There is practically no self-discharge, so provided I opened all circuit breakers after last flight, the battery is still fully dependable even after many months.

The overall energy stored is inferior to the spec of a new fully charged Pb. So you have an inferior number of possible attempts to start. But as the voltage remains practically constant even when substantially depleted, I consider it a convenient exchange.

This is also the reason why, with Lifepo4, you should definitely not draw panel power from the engine battery.

Aldo Cernezzi

--
Dan, 5J