The place for technical discussions about GA and flying.
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By Dino
#1820426
I suspect my battery is dying and I've been toying with a LiPo replacement.
Any thoughts from those that have done the same?

It's for an LAA aircraft with an 0-320.
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By Rob P
#1820509
I too am intrigued.

What was it about your conventional battery that you are hoping a LiPo will improve on?

I use conventional batteries, I replaced one in the 4, as far as I know that still lives on in G-DUDE, the 6 is still on the battery it came with in 2014.

I turn the key, it swings the prop. I really don't need anything further from a battery.

Rob P
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By RichJordan
#1820513
I liked the idea of Lithium for lighter weight and better CCAs and put a Varley Li5 into my CTSW (Rotax 912ULS).

I had 3 fail in less than two years. One went open circuit while I was in the air.

My aircraft has the recommended capacitor etc. Friends with different brands of lithium battery have not had the same issues, but unfortunately the Li5 is the only one that fits in my battery holder without hacking it up.

Gone back to AGM now (Odyssey), very little weight penalty and much better reliability. Plane had 12 weeks inactivity October/December and fired straight up.
By Shoestring Flyer
#1820518
I have had an EarthX ETX36C Lithium battery installed in my Rotax engined LAA Permit aircraft for the past 5years without any problems at all and would definitely buy another for the weight gain alone.
Its a very small unit and only weighs 1.5kg.
It does what it says on the tin and just works fine!

You will need LAA approval for the change to a lithium battery and also a proper Lithium battery charger for the occasions when you run it low when messing with avionics in the hangar etc and can't run the engine.
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By Peter Kelly
#1820570
I can't say if changing to a Lithium battery is the right thing for you to do but I can give my personal experience based on my own aircraft and having fitted them to a number of customer's aircraft.

But before that, you say you have had a number of batteries fail in a relatively short time. On this basis alone, I can say with about 95% certainty that this is nothing to do with the batteries and everything to do with the charging system. The biggest killer of batteries is over-charging (closely followed by under charging).

The other 5% of my bet would be on some kind of leakage current when the aircraft is in the hangar resulting in long periods at low charge and subsequent sulphation of the battery.

Before you do anything with the battery, get the charging system checked- out. A couple of years ago I was asked to replace the battery in a Cub as it would not hold charge. The owner had changed the battery every couple of years since he'd owned the aircraft... I put a voltmeter on the battery terminals with the aircraft on the ground and it was charging at about 15.8 volts with the electrolyte bubbling away... Not so slow battery death... We changed the regulator and the battery and as far as I know it's been fine ever since.

If that doesn't reveal an issue, pull the earth lead off with everything switched off and put a sensitive ammeter in the circuit to see if there is any leakage.

A modern high quality AGM/VLRA battery (Odyssey or similar) should last at least five years, probably seven or eight. We have just replaced the batteries in our boat after 13 years...

Looking at Lithium batteries specifically, any of the makes/models approved by the LAA will be excellent. I would recommend them unreservedly. EarthX are a bit more sophisticated as they have a rudimentary warning light to let you know if they are unhappy, but their actual performance will be very similar between brands.

The advantages are many.

• Significantly increased cranking current for similar sized batteries
• Flatter discharge curve so you get a useable voltage all the way down to fully discharged unlike lead acid. (Useful if you rely on the battery in case of an alternator failure in IFR.)
• Very significantly lighter than lead acid for the same capacity and cranking current
• Can be fully discharged without any damage or reduction in cycle-life
• Significantly longer life (years and cycles) than lead acid
• Very low self-discharge rate.
• Lower total-life cost than lead-acid

The only real disadvantage is the initial purchase cost.

If you operate a weight-critical aircraft, the weight savings are magnificent. Changing from Lead-acid to Lithium in my Continental O-200 powered permit-aircraft saved a total of just over 10Kg which equates to around 30 minutes extra endurance.

PM me if you want specific details.

P
By MikeW
FLYER Club Member  FLYER Club Member
#1820583
Peter Kelly wrote:The biggest killer of batteries is over-charging (closely followed by under charging).
.
charging at about 15.8 volts with the electrolyte bubbling away... Not so slow battery death...


P


I think a bit of care over terminology is needed here.
I worked for a major L/A battery manufacturer (both automotive and industrial, flooded and SLA) for some years and we always saw more problems from undercharging than overcharging, in the sense of the amount of time on charge at the correct voltage or slightly over, up to maybe 14.2V for a modern battery, a bit less for older types. Lots of people think a couple of hours charge occasionally is enough and it isn't!
Overcharging in terms of too high a voltage such as the 15.8 mentioned above is indeed quite a quick killer but we didn't often see that.
By Dino
#1820586
Thank you everyone for your replies so far, especially Peter for your extensive comments.
BTW It wasn't me that had killed a number of batteries, that was Rich.
(I do have a small continous draw if I leave the battery connected - the clock, but I'm aware of that.)
Weight is indeed the main reason for considering the change: the current Concorde battery is 22lbs, Something like an Earthx 680 is 4lbs.
I'm not sure how to decide on capacity and am wondering if i could get away with something even smaller like a Varley Li5 @ 2.5lbs.
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By Peter Kelly
#1820590
Mike W.

In non-vehicular use ( I include aeroplanes as vehicles), you are 100% correct. Undercharging and sulphation is the main cause of death - especially leaving the battery at a low state of charge for long periods.

In vehicles and especially aeroplanes with ancient nasty voltage regulators, overcharging results in a quick death.

OP. The Varley LI-5 works well with O-200 sized engines. I’ve never tried it with an O-320. Most of the O-320s I’m familiar with use Odyssey PC680s. I’ll check the specifications in the morning but from memory the LI-5 may well crank as well as the apparently larger Odyssey.

The key to success will in having a good starter motor and the correct impulse coupling on the mags. And a well set up carb/fuel injection.

It also goes without saying that properly sized battery cables and clean terminals all along the way make a huge difference

But look at the charging first...
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By Paul_Sengupta
FLYER Club Member  FLYER Club Member
#1820599
Shoestring Flyer wrote:and also a proper Lithium battery charger for the occasions when you run it low when messing with avionics in the hangar etc and can't run the engine.


Don't the lithium batteries you buy for aeroplanes and such have built in chargers? I'd have thought they would just take in whatever the alternator or battery charger supplies and then regulates it for the lithium cells contained within. Is this not the case?
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By Charles Hunt
#1820602
You know my expertise with anything electrical, but surely that might be a built in regulator, but surely not a charger?
By MikeW
FLYER Club Member  FLYER Club Member
#1820707
Peter Kelly wrote:Mike W.

In non-vehicular use ( I include aeroplanes as vehicles), you are 100% correct. Undercharging and sulphation is the main cause of death - especially leaving the battery at a low state of charge for long periods.

In vehicles and especially aeroplanes with ancient nasty voltage regulators, overcharging results in a quick death.
.


@Peter Kelly
Our principal aircraft fitments were Hawk, BAe 146, F16 and Puma - we didn't tend to see charging problems with those!
We didn't do GA batteries but when I put one block of the 4 used in the Hawk (20Ah SLA) in my Jodel the problem was undercharge, the poor old Delco dynamo struggled to get over 13.8V. (The reg was OK.)
Old cars in some overseas locations did the same but modern vehicles either worked correctly or produced nothing.
I take your general point though. GA aircraft other than very recent have to run on old junk that would have been dumped from cars long ago, and if you get serious overvoltage from an alternator, it's a quick killer especially with SLA.
By Peter Kelly
#1820726
To those asking about 'charging' lithium batteries, a bit more detail...

All the batteries available to to GA market are Lithium-Iron-Phosphate chemistry (LiFePo for short). These are the best (only) satisfactory compromise for aviation use as they are thermally stable and do not exhibit 'thermal-runaway' events in the same way as other lithium battery technologies (as used in mobile phones for example). The small downside of LiFePo technology is that it does not provide the highest possible energy density offered by other technologies.

LiFePo batteries are very safe and with suitable qualification may be shipped by air as non-hazardous cargo.

You might be surprised to learn that inside your typical LiFePo battery, there are a multitude of small cylindrical cells (shorter and fatter than a typical AA battery). The cells are essentially a commodity item manufactured in huge volumes. These cells are fabricated into a battery using spot-welded links. The cells are arranged in a series-parallel configuration to provide the required voltage and amp rating.

In a lead acid battery, the 'chemistry' is essentially connected directly to the battery leads. Not so in a lithium battery. This has electronics between the individual cells and the battery terminals. Both the charging and discharging are managed by a Battery Management System (BMS). The quality of the BMS is what sets the different battery manufacturers apart. The best BMS monitor individual cell voltages and control the charging and discharging to balance loads and state of charge. Cheap one are, as might be expected, less sophisticated (but still safe). They all use a small computer to run the process and some clever high-power silicon to do the switching.

To a very great extent, the BMS does protect the battery against overcharging and discharging. Typical BMS monitor cells temperature, current etc. and limit the current when critical parameters are exceeded. But, the BMS can only do so much. If you try and charge a (nominal) 12V battery at 24 V, the BMS will probably just shut down. Maximum efficiency is obtained with a balanced system. Typical charging voltages for LiFePO are a tiny bit higher than for single-stage lead-acid charging. 14.5-14.6V for LiFePo as against an optimum of around 14.4 for Lead-acid. Your standard aircraft alternator set at 14.4 v will do just fine.

Hope that is helpful...

P