Charging methods for LiFePo batteries

[John Johnson]

In my previous glider, I had a removable LiFePo battery that really worked out well (15Ah battery, ~0.95A typical panel draw). I typically flew 9-10hrs between charging it and would see a ~10Ah charge go back into it using a cheap Ah meter. I liked being able to bring it home and keep it in the recommended semi-discharged storage state until the next time I flew. The night before flying I would put it on the charger (in a large ceramic fire-safe flower pot) and it was ready the next morning to go back in the glider for a day (or 2 or 3) of flying.

My new glider’s avionic battery is a 20Ah sealed lead acid type. It’s difficult to access under a cockpit floor panel and is not meant to be removed routinely so I have to charge it in-situ. My club’s gliderport doesn’t have power so I had to install a solar panel tied directly to a charge controller at my shade hangar spot. When I park the glider, I plug it into the solar charger and leave it charging until my next flight. This is working ok because the battery is a sealed lead acid type and the charge controller maintains it in the proper state for that battery type.

I’d like to go back to a higher capacity LiFePo battery but I’m not sure how to manage the charging process. Assuming I have a proper solar charge controller setup that won’t confuse the battery’s built-in battery management system, I still have the issue of proper storage charge level. I don’t want a LiFePo battery sitting at full charge all the time (right?). My gliderport is 90mi from home and I usually arrive ~2hrs before flying. If I added an external battery bank on my solar setup, I wouldn’t have to rely on the marginal morning sunshine to provide a full charge – but would still need a 4-5A charge rate to get there in time (closer to 1.6A panel draw on the new glider).

So, I currently have a simple charging setup with a SLA battery that is working but probably only has an effective 10Ah capacity. So far, this is seems adequate in conjunction with the glider’s small solar panels (they supply about 1A). And, to be fair, I could switch over to the motor battery (another 20Ah SLA) late in a flight and maybe not eat much into its starting capability if I needed a save. I'm planning for 8+hr flights next season and would like more margin.

Going to LiFePo is going to make battery charging a lot more complicated – or is it? Am I being too concerned about having a LiFePo battery kept in a fully charged state? Any advice on how you or others are dealing with in-situ LiFePo charging? (yes, I’m worried about fires too)

Thx, JJ

[Stuart Venters]

My K2's have spent most of their life (since 2017) on the charger and
so far no issues. I've heard LiIon is best stored between 30 and 70%
charge, but for LiFe, the only story I've heard is that with age, they
sometimes loose capacity and to fix it you need to leave them on the
charger for a week or so.

[R]

Thinking you have a 31, do you have a third position forward of the spar?

R

[John Johnson]

On Friday, December 9, 2022 at 1:34:38 PM UTC-7, R wrote:
> Thinking you have a 31, do you have a third position forward of the spar?
>
> R

Yes, a 31. I don't currently have a 3rd position setup but it would be fairly easy to add one. It's certainly a worthwhile thought.
JJ

[jfitch]

I find the typical battery arrangement in the 26/31 inadequate for my needs for the reasons you state. I use a 12 AH LFP sitting on the baggage shelf, easily removed to home and charged however you think best. AS used to install the wiring for this in every glider, I think.

Regarding keeping an LFP at full charge, some manufacturers as well as some independent testers have published some data, suggesting that while there is a reduction in life, it is modest, in the 10% range. It is perhaps more important to cycle the battery through a complete cycle (like down to <10% and back up to full) at least once every six months, or maybe 3 months depending on who is doing the recommending. A full charge for several hours is often needed to have the top balancing BMS do the right thing. I would leave a properly set up LFP charger on the under-the-knees battery without much concern. Properly set up meaning CV charge at correct voltage followed by disconnect (no float).

[John Johnson]

On Friday, December 9, 2022 at 12:57:13 PM UTC-7, Stuart Venters wrote:

> My K2's have spent most of their life (since 2017) on the charger and
> so far no issues. I've heard LiIon is best stored between 30 and 70%
> charge, but for LiFe, the only story I've heard is that with age, they
> sometimes loose capacity and to fix it you need to leave them on the
> charger for a week or so.

A friend just told me something similar. I was assuming Lixx = Liyy for recommended storage state. His method is to put the charger on a 5hr timer and leave the battery sitting under a full charge until his next flight. I'll do some reading and look closer at manufacturer's recommendations.
thx, JJ

[John Johnson]

On Friday, December 9, 2022 at 1:59:36 PM UTC-7, jfitch wrote:
>
> .... I would leave a properly set up LFP charger on the under-the-knees battery without much concern. Properly set up meaning CV charge at correct voltage followed by disconnect (no float).

Thanks, this is good to hear. My friend's shut-off timer method sounds well-aligned.

Thinking about it, I would prefer to not add a 3rd battery. It's just one more system to maintain, test, pre-flight, etc. My strong preference is a primary avionic battery with a good manufacturer reputation and significantly more capacity than I need. I'd like to think the motor battery can serve the backup role in the very rare event that actually becomes necessary.

I guess that means my shade hangar solar system needs to get more complicated - but at least it stays on the ground.

thx, JJ

[Stuart Venters]

Some chargers discharge the battery when the AC is unplugged. Depending
on where you put the timer, you may want to verify the charger you have
is well behaved without AC.

[John Johnson]

On Friday, December 9, 2022 at 3:49:22 PM UTC-7, Stuart Venters wrote:
> Some chargers discharge the battery when the AC is unplugged. Depending
> on where you put the timer, you may want to verify the charger you have
> is well behaved without AC.

Good point. Maybe set the timer up with with a relay so it both opens the connection to the battery and drops power to the charger.

I usually leave a power meter attached between the battery and charger. This lets me monitor and log the charging Ah's needed vs flight time. If I put it on the battery side of the relay, I'd be able to continue with that health monitoring method. But I'd also need to be sure the meter load was very low or it would also become a discharge problem.

It's a good thing I mostly enjoy solving these types of problems.
thx, JJ

[R]

Tecmate Optimate DC-DC Charger
Dakota Lithium 54 ah as power supply
Dakota Lithium 10ah bat. #3

You most likely have PS-12200 as your mains.
You do not want lithium under your seat.

R

[2G]

On Friday, December 9, 2022 at 11:36:07 AM UTC-8, John Johnson wrote:

I have the following setup for charging sans AC connection:

HiTec X2 AC/DC multi-chemistry charger
PowerSonic LFP 50 AHr donor battery
LFP solar charge controller
50W solar panels (2)

This setup guarantees that the donor battery will not go flat while charging (which you won't find out about until you get to the field, depriving you of adequate time to charge your avionics battery in time). Using PbS batteries as the donor isn't a good idea because the X2 is VERY sensitive to input DC voltage and will prematurely terminate charging, again too late for you to do anything about it. The solar panels will replenish your donor battery while flying, so you will have plenty of energy to recharge overnight.

Granted, this won't leave much change out of a $1k bill, but it won't leave you high and dry on a beautiful flying day.

Tom

[2G]

BTW, here are the links to these parts:
https://www.amazon.com/Hitec-RCD-Black-Multi-Function-Charger/dp/B075MFD6H3/ref=asc_df_B075MFD6H3/?tag=hyprod-20&linkCode=df0&hvadid=312184153387&hvpos=&hvnetw=g&hvrand=2345915175429565278&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9033822&hvtargid=pla-645189894226&psc=1
https://www.hawkusa.com/manufacturers/power-sonic/batteries/lithium-iron-lifepo4/psl-btp-12500-m8?gclid=Cj0KCQiA1sucBhDgARIsAFoytUtSDsqrgPFqa7K2kbg8M5-Naw9iZBg1ryRIagRVFopLfjPiqeN2KGAaAivREALw_wcB
https://www.amazon.com/gp/product/B01MRWTAB5/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
https://www.amazon.com/gp/product/B00DCDQKII/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Tom

[Eric Greenwell]

On 12/9/2022 7:00 PM, 2G wrote:
> On Friday, December 9, 2022 at 11:36:07 AM UTC-8, John Johnson wrote:

...

>>
>> Going to LiFePo is going to make battery charging a lot more complicated – or is it? Am I being too concerned about having a LiFePo battery kept in a fully charged state? Any advice on how you or others are dealing with in-situ LiFePo charging? (yes, I’m worried about fires too)
>>
>> Thx, JJ
>
> I have the following setup for charging sans AC connection:
>
> HiTec X2 AC/DC multi-chemistry charger
> PowerSonic LFP 50 AHr donor battery
> LFP solar charge controller
> 50W solar panels (2)
>
> This setup guarantees that the donor battery will not go flat while charging (which you won't find out about until you get to the field, depriving you of adequate time to charge your avionics battery in time). Using PbS batteries as the donor isn't a good idea because the X2 is VERY sensitive to input DC voltage and will prematurely terminate charging, again too late for you to do anything about it. The solar panels will replenish your donor battery while flying, so you will have plenty of energy to recharge overnight.
>
> Granted, this won't leave much change out of a $1k bill, but it won't leave you high and dry on a beautiful flying day.
>
> Tom

I use the same system as Tom, but a different selection of components leaves most of a $1k
bill (prices from Amazon), and has been sufficient for years with a panel drawing 1.5A
from a 20AH LiFePO4 battery. I typically fly about 6 hours, never more than 8.

$35 ISDT Q6 Nano Lipo Battery DC-DC Charger/Discharger,
$70 Miady 12V 16Ah Deep Cycle LiFePO4 Battery
$21 ExpertPower 10A 12/24V Intelligent PWM Solar Charge Controller
$58 HQST 50W 12V Polycrystalline Solar Panel

$184 Total

I have an older DC-DC charger that works but is annoying, and an AC Li charger that came
with the glider battery, that serve as backup.

--
Eric Greenwell - USA
- "A Guide to Self-launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications

[John Johnson]

> > I have the following setup for charging sans AC connection:
> >
> > HiTec X2 AC/DC multi-chemistry charger
> > PowerSonic LFP 50 AHr donor battery
> > LFP solar charge controller
> > 50W solar panels (2)

>. Tom

> I use the same system as Tom, but a different selection of components leaves most of a $1k
> bill (prices from Amazon), and has been sufficient for years with a panel drawing 1.5A
> from a 20AH LiFePO4 battery. I typically fly about 6 hours, never more than 8.
>
> $35 ISDT Q6 Nano Lipo Battery DC-DC Charger/Discharger,
> $70 Miady 12V 16Ah Deep Cycle LiFePO4 Battery
> $21 ExpertPower 10A 12/24V Intelligent PWM Solar Charge Controller
> $58 HQST 50W 12V Polycrystalline Solar Panel
>
> $184 Total

Tom, Eric, thanks for providing your examples. I currently have a 150W panel and charge controller that I'm directly connecting, in turn, to each of my -VRLA- batteries for charging (find the engine battery is always close to being fully charged already). I'll research a LFP donor battery and decide if I'm sticking with a DC-DC setup or adding an inverter. Since the solution will be bundled for going with me on Safaris, I'm leaning toward the extra capability an inverter setup will provide. I'll also need another 'traveling' panel to take on the road.

Great information from everyone - appreciate it. I feel confident now to proceed with a LFP avionic battery while keeping my engine battery as-is (VRLA).

thanks, JJ

[2G]

Eric's solution has one major problem: he is using a 16AH battery to recharge a 20AH battery. This, simply, DOES NOT WORK! Believe me, I have tried that option and it FAILED! If you want a fool-proof solution the donor battery needs to be roughly double the size of the charging battery. On the other hand, if you don't care if the system works and you are left high and dry when it's time to go fly, then go cheap on the donor battery.

Tom

[2G]

I will add that the same goes for under sizing the wattage of the solar panels. Solar panels NEVER deliver the nameplate wattage since that is only possible at noon at the equator with the panels pointed DIRECTLY at the Sun. My two 50W panels SHOULD deliver 8.3A; I have NEVER seen 8.3A and am satisfied if they deliver HALF of that (and you get nothing if the Sun is blocked). And that is at the best time of day, dropping off before and after noon. By over-sizing the panels I know that I can recharge my donor battery WITHOUT QUESTION. My approach, contrary to Eric's, is to guarantee the system will deliver the results in even the most extreme conditions.

Tom

[Eric Greenwell]

My situation is not as dire as Tom suggests, for several reasons
* my longest flights (8 hours) only require the 16AH donor battery to replace 12 AH
* I put the donor battery on charge by 8am, so it has almost 12 hours to recover
* I can also charge the glider from my tow vehicle battery using the same DC-DC charger

Generally, if there is enough sun to make the thermals we need, there is enough sun to
fully charge the donor battery. I've only had to use the vehicle once in the 10 or so
years I've been doing this. It can easily charge the glider at 4A (max glider battery
charge rate) and still be ready to fly as usual. Also, there is an option to solar
charging: put the donor battery on charge at some place on the field that has AC power.
That's an option everywhere I fly, or use your tow vehicle battery to power the DC-DC charger.

I'm a minimalist, Tom's a maximalist: pick a point on the spectrum between us that
satisfies your requirements.

[Craig Reinholt]

> Eric's solution has one major problem: he is using a 16AH battery to recharge a 20AH battery. This, simply, DOES NOT WORK! Believe me, I have tried that option and it FAILED! If you want a fool-proof solution the donor battery needs to be roughly double the size of the charging battery. On the other hand, if you don't care if the system works and you are left high and dry when it's time to go fly, then go cheap on the donor battery.
>
> Tom

This opinion is incorrect.
I've been using 12v 20ah SLA batteries (old glider batteries) with a B6AC AC/DC -DC charger to charge my 12v 20ah avionics and engine battery since I've owned my. Never an issue getting the job done.
Craig

[R]

I don’t see the need to lug around solar panels unless you’re camping out and eating squirrels.
Must be a ‘out west’ thing…brownouts and rolling power interruptions.
We have plenty of A/C power in the east.
One battery, two chargers. I picked a Lithium as my power supply (donor) because of its light weight and life span.
Since I race, I have a 3rd 10ah for redundancy.
I have a hard time understanding how a lower ah battery can charge a higher one to full capacity. Isn’t that in the ‘perpetual motion’ ‘fusion’ ‘I want everything free’ line of thinking?
Then again, ‘out west’.

R

[John Johnson]

R, thanks for getting me to re-think the safari charging situation. Was thinking I would need to plug the donor into a charger right after disconnecting from the glider in the morning (solar panel mounted to the trailer). Depending on the field, it may not be easy to find/beg/borrow an AC outlet near the tarmac. But with something like a 100Ah LFP donor, I could get 4-5 glider charges out of it before taking it off-field for recharging overnight before a rest day.
thx, JJ

[Dan Marotta]

Instead of all of these complex systems, panels, controllers, etc., I
just bough an inverter at Amazon and can charge my batteries in the
evening/morning in the car or simply leave it plugged in and forget it
until the next flight. Considerably less expensive, too...

https://smile.amazon.com/gp/product/B004MDXS0U/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Dan
5J

[Eric Greenwell]

On 12/12/2022 10:49 AM, John Johnsonrote:

If you are driving your tow vehicle every day or two, you can use it's battery to charge
your donor battery without running down the tow car battery. If you do have a 40W-50W
solar panel on the trailer, you can easily get by with 30AH a Life battery for 5-10 days.
It'd be significantly smaller, lighter, and cheaper than a 100AH Life.

[Eric Greenwell]

On 12/12/2022 9:34 AM, R wrote:
> I have a hard time understanding how a lower ah battery can charge a higher one to full capacity. Isn’t that in the ‘perpetual motion’ ‘fusion’ ‘I want everything free’ line of thinking?

It works for me because a flight does not completely discharge my 20AH avionics battery;
instead, a typical flight discharges it only 9 to 10 AH. My 16AH donor battery can easily
replace that smaller amount.

But you can think of me as a Wizard without getting an argument!

[Eric Greenwell]

The people most attracted to these methods can not easily remove their batteries from the
glider, which includes every Schleicher self-launcher, and perhaps all the DG
self-launchers, too. If the battery can be removed, most pilots just take it home with
them. I wish I could do that, but removing and replacing the avionics battery is a 40
minute process. The typical engine run is enough for the alternator to keep the starter
battery charged, so it rarely needs external charging (Schleicher gliders, anyway)

[Dave Nadler]

On 12/12/2022 12:34 PM, R wrote:
> Isn’t that in the ‘perpetual motion’ ‘fusion’ ‘I want everything free’ line of thinking?

Any day now Henry!
https://www.reuters.com/business/energy/us-announce-scientific-breakthrough-fusion-energy-sources-2022-12-12/

[Moshe Braner]

"Fusion is the energy source of the future, and always will be!"

[2G]

You have seriously degraded you whole system by not using an MPPT (maximum power point tracking) solar charger. A PWM charger will deliver less than half the energy than an MPPT charger. Charging energy varies like a half sine wave, so there is very little in the morning and late afternoon. My panel draws typically 2 A, so an 8 hour flight needs 16 AHr. The entire system may be 60 to 70% efficient given all of the power conversions (I have not actually measured this as my solution is over-kill), so I will need a raw 23 to 27 AHr. This will take ALL of the output my solar panels can deliver. Note that if the panels don't deliver the necessary energy I have plenty of reserve in my donor battery.

This is also why it is MANDATORY that you actually measure the power consumption of your panel, preferably in flight. The largest consumer is my flight computer, the LX9070, which draws around 0.75 A (depends on display brightness). I also have a backup glide computer/vario, the S100, which draws around 0.3 A. Now add a radio, transponder with ADSB/Out, S10 vario, and a Garmin G5 primary flight display and you are up to 2 A.

Pilots that have less energy needs, current and/or time, can size their charging systems accordingly.

I went to this after having flights cut short because the battery wasn't fully charged prior to flight, a real PITA. I guess that fits perfectly into Eric's minimalist outlook.

Tom

PS I use the display of the X2 to show me the AHr delivered and double-check that with an inline battery charging monitor (if the X2 has a fault at any time like due to low input DC voltage, the AHr delivered display is gone and you don't know what your charging deficit is).

[Dan Marotta]

I was curious about the by-products of fusion reactions and came across
the following discussion. Pretty interesting.

https://www.quora.com/What-would-be-the-by-products-of-Nuclear-Fusion?share=1

Dan
5J

[R]

Yeh….I remember ‘Fusion’ from the ‘60s. It’s right up there with Quantum Computing, Cryptocurrency, sending humans to Mars, and Carbon Credits.
Chernobyl
LALA Land
FTX
Cancer
Liberal Europeans smoking weed.

R

[youngbl...@gmail.com]

Better be careful R, with these kind of comments you may be ban from Twitter and Facebook. OBTP

[Eric Greenwell]

This looks a like a better description than Quora:

https://www.pppl.gov/news/2021/10-facts-you-should-know-about-fusion-energy

Fusion will be a great way to charge LiFePO batteries! Don't sell your solar panels just
yet...

Eric

[Dan Marotta]

I saw a bunch of whoop-te-do with all of the climate change BS. No
numbers as stated on Quora. Give me numbers, not politics.

Dan
5J

[Mark Mocho]

Give me numbers, not politics.

And please explain your plan for fusion containment. We've had practical fusion power since 1952 when the US detonated the first hydrogen bomb. However, because there was no containment, the only "practical" use was to blow the hell out of an atoll in the Pacific. Making excess power from a fusion reaction for something like a billionth of a second isn't what I consider enough reason for the mainstream media to wet their pants and predict how "soon" we will have super clean, free, and politically correct "climate change" electricity.

And Martin's quote is the best I've seen:

[Eric Greenwell]

The big news is, for the first time in any fusion experiment, the reaction produced more
energy than the lasers delivered to the chamber. To make an aeronautic analogy, I'd say
fusion has reached the same stage the Wright brothers reached on December 17, 1903, with
their 59 second, 852 foot flight.

[youngbl...@gmail.com]

Eric, don't get too excited about this breakthrough in Fusion Energy. The primary concept of making Fusion Power is through heat developed by lasers, maintaining that heat requires power and a huge amount at that. Just recently the Liverpool lab produced 10 quadrillion units of power from this concept, yet they did tell us the real story.
I work with lasers more often than you think, they are impressive and dangerous as well, Fusion has a long way to go, yet breakthroughs are advancing, just not as rapidly as FTX and Enron. Old Bob, The Purist

[Martin Gregorie]

On Tue, 13 Dec 2022 11:16:46 -0700, Dan Marotta wrote:

> I was curious about the by-products of fusion reactions and came across
> the following discussion. Pretty interesting.
>
> https://www.quora.com/What-would-be-the-by-products-of-Nuclear-Fusion?
share=1
>

Thanks for posting that: its about the best short discussion of the fusion
power problem I've seen.

The common factor of all fusion reactor designs (and probably including
Bussard ramjets too) seems to be the sheer destructiveness of the fusion
byproducts given the energy they carry.


--

Martin | martin at
Gregorie | gregorie dot org

[Eric Greenwell]

The lab (Lawrence Livermore National Laboratory) that produced the "10 quadrillion units
of power from this concept" a year ago is the same lab that just had the breakthrough.
They are making good progress, but I don't expect to live long enough to see one operating
continuously.

[Mark Mocho]

"Fusion is the energy source of the future, and always will be!"

Sorry. Quote from Moshe, not Martin

[Martin Gregorie]

Nice quote!

Here's another good write up in the recent fusion test shot@ worth a read,
I think.

https://arstechnica.com/science/2022/12/what-enabled-the-big-boost-in-
fusion-energy-announced-this-week/

[kinsell]

Gosh, with all those hardware and energy management issues to deal with,
maybe you should take a flight engineer with you? Give you more time to
look outside.

I'm a big fan of just using a properly sized battery, making sure it's
charged, and then go fly. I'll look at the panel voltage occasionally,
sometimes look at the voltage drop when transmitting on the radio, but
don't really obsess about it. In 14 years of flying, never lost power
to the panel, or had a battery related failure to start the engine.
I've done 8 hr flights, but frankly don't enjoy that anymore.

My situation is very similar to the OP, a Schleicher motorglider with
the two large 20 AH batteries. He says 1.6 amp panel draw, with an amp
supplied by the solar panels. So eight hour flights times .6 amp is 4.8
AH according to my calculations. He has a 20 AH battery, and could
easily tap into another 20 AH, and has decided he needs "more margin".
Really? He has seen no problems with the current setup, and the math
doesn't begin to show a potential problem, but he has to "upgrade" from
20 AH to a 15 AH lithium basttery. Why? Because LITHIUM!!!

Sounds like he's going way out of his way, complicating his charging
requirements, in order to justify that change. Golly gee, we've never
seen that before, have we? Certainly not on R.A.S.!!!

Dave

[Eric Greenwell]

On 12/9/2022 11:36 AM, John Johnson wrote:
> Am I being too concerned about having a LiFePo battery kept in a fully charged state? Any advice on how you or others are dealing with in-situ LiFePo charging? (yes, I’m worried about fires too)

I had my 20AH Bioenno Life battery for several years before I learned Li batteries lasted
longer when stored at about 50% capacity. It lost about 3% capacity per year, a big
improvement over my former 20AH SLA batteries which lost closer to 10% a year. Now, I
still charge it fully during the flying season, but store it at 50% charge during the six
month winter off-season, so I expect it will lose even less capacity per year than the
already small 3%.

LiFePO4 batteries have an excellent safety record. Even 2G is willing to use them in his
glider. Follow the charging requirements and temperature limits, and you'll be fine.

[jfitch]

Eric, not "every Schleicher self launcher". I have a 12AH LFP on the baggage shelf, removing it is a 5 second exercise. It will power the panel as long as any day lasts and is easily removed for recharging where every you'd like. Much more convenient than the avionics battery under the seat. The OP said he didn't want a third system - but in my glider it is not a third system. I have no avionics battery under the seat, so, same number of systems, just more accessible. In the event of a problem with the shelf avionics battery I can switch the power bus to the engine start and continue the flight (it will power the panel for several days and still start the engine). The number of times this has happened in my 22 years of ownership? Zero. There is consistent whinging about the Schleicher under the seat battery, and various solutions some of which amount to a small electric substation like Tom's. Completely unnecessary.

[2G]

I have never seen anyone report the energy delivered by glider-mounted solar panels. It wouldn't be hard to do using this battery analyzer:
https://www.amazon.com/gp/product/B00C1BZSYO/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
I think the claim of 1.0 A is merely a WAG unsupported by actual measurements. Remember, while thermaling under the clouds you are getting zero. I have estimated that you will average less than 0.5 A, and that isn't reliable, so I chose not to have the solar panels installed. I do have a total of 32 AHr using a 2nd 12 AHr LFP battery in the baggage compartment. Note to Jon: while this battery can be removed easily (not in 5 sec, though), it is in parallel with the glider-mounted 20 AHr avionics battery so they have to be charged together.

Tom

[2G]

I wouldn't get too excited about fusion yet: the experiment produced enough energy to power a Tesla for about one mile (305 WHr). And if you compare the cost to produce that energy vs what it costs off of the grid you would be massively disappointed. The main point was that they were able to have a net power output, a first for fusion research.

Tom

[Eric Greenwell]

On 12/14/2022 8:29 AM, jfitch wrote:
> On Monday, December 12, 2022 at 12:47:16 PM UTC-8, Eric Greenwell wrote:

...

>>>>> R
>>>> R, thanks for getting me to re-think the safari charging situation. Was thinking I
>>>> would need to plug the donor into a charger right after disconnecting from the glider in
>>>> the morning (solar panel mounted to the trailer). Depending on the field, it may not be
>>>> easy to find/beg/borrow an AC outlet near the tarmac. But with something like a 100Ah
>>>> LFP donor, I could get 4-5 glider charges out of it before taking it off-field for
>>>> recharging overnight before a rest day.
>>>> thx, JJ
>> --
>> Eric Greenwell - USA
>> - "A Guide to Self-launching Sailplane Operation"
>> https://sites.google.com/site/motorgliders/publications
> Eric, not "every Schleicher self launcher". I have a 12AH LFP on the baggage shelf, removing it is a 5 second exercise. It will power the panel as long as any day lasts and is easily removed for recharging where every you'd like. Much more convenient than the avionics battery under the seat. The OP said he didn't want a third system - but in my glider it is not a third system. I have no avionics battery under the seat, so, same number of systems, just more accessible. In the event of a problem with the shelf avionics battery I can switch the power bus to the engine start and continue the flight (it will power the panel for several days and still start the engine). The number of times this has happened in my 22 years of ownership? Zero. There is consistent whinging about the Schleicher under the seat battery, and various solutions some of which amount to a small electric substation like Tom's. Completely unnecessary.

I didn't realize you were using the 12Ah battery instead of the OEM battery - thought it
was "in addition to". I do have the OEM installed wiring, so I could use a battery like
you do. It'd have to bigger, say 16AH, because 12AH would be marginal with my 1.5 amp
panel draw.

[Martin Gregorie]

I'm not excited at all, so far, about any form of fusion device. They are
a nice idea in theory, but so far that's all they are, and have been since
1957's Zeta machine.

I'd love the Bussard ramjet to be a real thing, but AFAIK nobody has ever
had even the faintest idea how to make its exhaust (and hence thrust) come
out the back.

[jfitch]

My panel draws about 1.5A as well. With the LFP you can use most of it, so it would run low at around 7 hours (I have tested that). But I have the solar panels, these contribute about half of that draw in the sun and a quarter of that under clouds (by actual measurement). After a long flight, for me about 6.5 hours, I'm down typically 5 or 6 AH. It does actually take 5 seconds or a bit less to remove the battery, without rushing. Maybe as much as 10 seconds to install, I have to align and plug in the PowerPole connector. Without the solar a really long flight might use up a 12 AH, but 16 would be safe, unless your glider has lights and is legal for night flight.

[2G]

The connector is not the issue: it is the battery tie-downs that take the time. I decided that the $2,800 solar panel equals a $100 battery - if it is working.

[Ludovic]

> Going to LiFePo is going to make battery charging a lot more complicated – or is it? Am I being too concerned about having a LiFePo battery kept in a fully charged state?

I've had 2x LiFePo4 15Ah batteries for 6 years now.
I always keep them on the charger during the flying season. I keep them off the charger during winter, except for a charge every month or so...
I test their capacity every year. This year, after 6 years they are both still at 92% of their nominal capacity.

So Id' say...don't worry too much, it's fine to keep the batteries on the charger !
If I had to change batteries now, I'd go for NMC batteries though: https://www.gliderpilotshop.com/nmc-12-20-14-4v-20ah.html

Regards
Ludovic

[Eric Greenwell]

I don't have solar panels, so the 16 AH would be my choice, and I already have one (the
current donor battery). I might also be able to mount the present 20AH avionics battery
instead in the baggage shelf - have to make some measurements. A 1kg lead disk on the
front peg would compensate for the removal of the 20AH battery from the under-knees
location, I think.

Shelf mounting is much more attractive than previously, now that we have lightweight Li
batteries. In the olden days, mounting a 12-15 lb SLA battery behind my head was not
appealing.

[Eric Greenwell]

The only advantage over the equivalent LFP (like the Power-Sonic PSL-BTP-12200) appears to
be lighter weight. The disadvantages are lower fire safety, no Bluetooth, and higher cost.
What makes NMC appealing to you?

[jfitch]

I'd certainly agree that the panels sourced from AS are not cost effective. I got mine essentially free, and they do provide some useful charge. It takes very little to hold a 12 or even 16AH LFP in place. A simple tray with a strap over the top is all that is necessary.

[2G]

So, have you measured the outrush current caused by connecting the fully charged 12 AH battery in parallel with the partially discharged 20 AH battery (which I presume you still use)?

Tom

[jfitch]

Not sure what battery you are referring to. I don't have the 20 AH instrument battery under the knees, not installed. There is no way to parallel the batteries in my glider. Instruments stay on the 12 AH all day every day. If I ever have to switch instruments to the engine battery it is a rotary switch, break before make. In practice the only time I ever run the instruments off of the engine start battery is to do some quick chore like download logs with the instrument battery not installed. But in any case, the inrush current really should not be much of a concern: the high battery voltage sags a bit under load and the low battery rises quickly, limiting the current. I have heard this concern from others, I think I will measure it with the current probe on an oscilloscope to see just what it looks like. Since both sides are fused (and BMS'ed), you can't damage anything, but might end up with blown fuses and no power to the instrument bus.

[2G]

The current could be quite high, as I found with my transfer capacitor, but quite brief, as it was with the capacitor. Why didn't you use the avionics battery under the seat pan, just so you could remove the battery easily for charging? 12 AH, BTW, wouldn't be enough for me for a single decent flight.

Tom

[jfitch]

How did you test the current spike?

When I bought my glider it did not have the avionics battery under the seat pan. It had a 12 AH battery on the shelf just as it has now. I've never missed the missing battery, and never missed having to complain about charging it. The 12 AH battery is usually around half discharged after about a 6 - 7 hours flight. That is with the solar panels. But for 17 years I flew without the solar panels, and even with an AGM battery never ran out of power from the 12 AH. That is with a pretty full panel: COM, transponder, two electric varios w/gps nav, tactical computer, FLARM, ADSB out. Maybe you have a higher power budget, but I'm not sure what I would add.

[2G]

I used a shunt resistor and a scope.

As I have already posted, my total drain is 2 A, so a 12 AH battery wouldn't last 6 hr IF it were fully charged. One must figure that about 1 hr of that is on the ground, so that would last me less than 5 hr flight time. I over-engineer the situation by having 32 AH total onboard, enough for at least two long flights w/o recharging.

Since you really can't determine charge state from a lithium battery's voltage, I measure the amount of AHr delivered to the battery to confirm that it is fully charged. However, if I turn everything on and the voltage is less than 12.9 V (with a 2 A load) I know the battery is NOT fully charged.

Tom

[william feiges]

Remember some of us need the weight of a lead acid battery to keep us in proper cg

[Eric Greenwell]

A 12-16AH Life battery added to the baggage shelf to power the avionics (as Jon does)
would allow you to disconnect the SLA in front, but leave it place to maintain balance.

The lead disk peg in my glider can hold 3 more disks, so I could add a disk, then remove
the disconnected battery to reduce the glider empty weight by about 10 pounds, while
maintaining the W&B. What a deal: reduce weight and complexity at the same time!

Eric

On 12/16/2022 8:38 AM, william feiges wrote:
> Remember some of us need the weight of a lead acid battery to keep us in proper cg

...

>> I used a shunt resistor and a scope.
>>
>> As I have already posted, my total drain is 2 A, so a 12 AH battery wouldn't last 6 hr IF it were fully charged. One must figure that about 1 hr of that is on the ground, so that would last me less than 5 hr flight time. I over-engineer the situation by having 32 AH total onboard, enough for at least two long flights w/o recharging.
>>
>> Since you really can't determine charge state from a lithium battery's voltage, I measure the amount of AHr delivered to the battery to confirm that it is fully charged. However, if I turn everything on and the voltage is less than 12.9 V (with a 2 A load) I know the battery is NOT fully charged.
>>
>> Tom

[2G]

The SLA is 3.5 kg heavier than the LFP. On my glider there is a foam spacer above the battery that is about 1 cm thick; a lead spacer (with appropriate insulation) would weigh about 1.5 kg, leaving 2 kg (1.5 kg if it were in the nose) to compensate for the lighter weight of the LFP.

Tom

[jfitch]

I measured the current spike shorting two batteries together. I used a CTS 20 AH LFP fully charged, and a Stark Power 12 AH LFP close to fully discharged. This would be the situation in my glider if there were a way to parallel the start and avionics battery. To measure, I used a Fluke 200 Gs scope with a Fluke hall effect current probe, with 100 KHz bandwidth. Unfortunately we are living in the 19th century here and I can't post the pictures. The result was a current spike of 8 A decaying to 6 A within < 200 microseconds, and to about 3 A in 20 milliseconds. While this might sound like a lot to you, it is about the same 8 A magnitude as the current spike when you turn on a Becker COM radio, though the Becker spike is of considerably longer duration (2+ ms above 6 A). Since I turn on my radio every time I fly, shorting the two batteries will not be anything I'd loose sleep over. It also isn't anything I ever do, or am likely to have reason to do.

[John Johnson]

On Friday, December 16, 2022 at 6:24:24 PM UTC-7, jfitch wrote:
> I measured the current spike shorting two batteries together. I used a CTS 20 AH LFP fully charged, and a Stark Power 12 AH LFP close to fully discharged. This would be the situation in my glider if there were a way to parallel the start and avionics battery. To measure, I used a Fluke 200 Gs scope with a Fluke hall effect current probe, with 100 KHz bandwidth. Unfortunately we are living in the 19th century here and I can't post the pictures. The result was a current spike of 8 A decaying to 6 A within < 200 microseconds, and to about 3 A in 20 milliseconds. While this might sound like a lot to you, it is about the same 8 A magnitude as the current spike when you turn on a Becker COM radio, though the Becker spike is of considerably longer duration (2+ ms above 6 A). Since I turn on my radio every time I fly, shorting the two batteries will not be anything I'd loose sleep over. It also isn't anything I ever do, or am likely to have reason to do.

Nice! thanks Jon, I really appreciate seeing data from a definitive experiment. Interesting how limited the spike was and how quickly it decayed. (I've always had problems trying to picture the simple RCL model attributes of a battery)
JJ

[2G]

That's about what I would have guessed given a 1 V difference and 0.1 ohm total resistance (battery internal resistance x 2 and wiring).

Tom