The issues surrounding lithium batteries.

[Downunder]

An interesting video about alternators and lithium batteries and some potential problems.

Although automotive based, it shows a what can go wrong. The complexities of lithium not only relate to voltage, but the internal resistance as well. It shows the importance of a dedicated battery management system (BMS) for Lithium.

[David Isaac]

Interesting watch.

Some of this stuff not well known about the LIPOs.

 

It beggers belief that anyone would just automatically think that a whole new battery technology can simply be bolted up to a standard Alternator for charging. Most should know by now that LiPOs can take a full charge voltage right up to fully charged and the current stays up there. This will result in alternator over heat unless you over size your alternators ro, as Victron suggest install a temp monimtoring management system to reduce the charge current as the alt temp rises.

 

Victron are one of the best in this field of research, I run some of their gear and about to run a whole more in off grid systems.

[onetrack]

The speeds they are running the alternator at in the tests are very low, in comparison to actual alternator speeds in engine operation.

Most alternators run between 5 and 6 times engine speed. So, with an engine idling at, say 500 RPM, the alternator is already doing 2,500 to 3,000 RPM.

 

Alternators need to run at around 2,000 (alternator) RPM to start producing charge, they produce maximum charge rate at around 6,000 RPM, and they can often run to 30,000 or 35,000 RPM.

 

The tests above were done at 1,500 and 3,000 alternator RPM. I'm surprised the alternator even produced charge current at 1,500 RPM. At 3,000 RPM, the alternator speed is only a little above engine idle.

The tests would have been more indicative of real conditions if the alternator was tested at 6,000 to 10,000 RPM - at which speeds the fan is producing a vast amount more cooling air, than it is at 1500 RPM.

[facthunter]

The advantage of an alternator Generally is it's ability to produce a good charge at fairly low rotational speeds. It's limit output is a function of RPM and rotor magnetism (Current in rotor windings.). I think RPM's are a little lower than they might have been once. Park the car with lights on against a white surface and the brightness comes as soon as the regulator cuts in at a fast idle. Nev

[Bruce Tuncks]

I only use my lithium ferrous battery to start the engine. As soon as the battery is back to voltage, the charging is switched off and the "battery" is now just a couple of big capacitors which the alternator thinks is the battery. This is how the radio etc has power while the battery is disconnected.

I need to make the disconnection automatic, another project on the list... In the meantime, I just switch it off when the voltage returns to 14.2 volts. This is usually well before takeoff.

The battery I use is from hobbyking and it has no BMS.

[facthunter]

Batteries take the little bumps out of the voltage reading. I'm still an AGM person. which is really lead acid. I have run setups where the regulator holds a steady voltage but often without a battery you will blow small bulbs etc Some of the fancy gadgets won't like spikes. Nev.

[Flightrite]

I like my LiPo's......in my toy planes nowhere else thanks??

[Old Koreelah]

Flyers had used LiFePO4 batteries for several years before I fitted mine a couple of years ago.

I'm interested in hearing of actual problems experienced.

Most seem to have a BMS and be sold as drop-in replacements, so the batteries themselves seem to last okey. Until this discussion, I'd not heard about their impact on the charging system.

[Bernie]

Interesting watch.

Some of this stuff not well known about the LIPOs.

 

It beggers belief that anyone would just automatically think that a whole new battery technology can simply be bolted up to a standard Alternator for charging. Most should know by now that LiPOs can take a full charge voltage right up to fully charged and the current stays up there. This will result in alternator over heat unless you over size your alternators ro, as Victron suggest install a temp monimtoring management system to reduce the charge current as the alt temp rises.

 

Victron are one of the best in this field of research, I run some of their gear and about to run a whole more in off grid systems.

X2 on Victron

[Bruce Tuncks]

Electric vehicles, including planes, now use lithium batteries ( not Li-po's though ). Lead acid is soon to be obsolete.

[spacesailor]

I only use my lithium ferrous battery to start the engine. As soon as the battery is back to voltage, the charging is switched off and the "battery" is now just a couple of big capacitors which the alternator thinks is the battery. This is how the radio etc has power while the battery is disconnected.

I need to make the disconnection automatic, another project on the list... In the meantime, I just switch it off when the voltage returns to 14.2 volts. "

Can you show us a pic of your setup.

And most of my lipo model batteries Die after a while, just wont charge. Posibly too much heat in my shed.

spacesailor

[Kyle Communications]

I still dont trust Lithium batteries to go in a aircraft with the std rotax regulator even if the battery does have a BMS. There are so many large voltage spikes coming from the rotax generator its not funny and I really wonder how the BMS will handle them over time in these batteries

 

We have been working on a new regulator for the rotax which will do most all batteries. The regulator in a std rotax the ducati one there are about 3 different designs but the stupid part is they are using a std bridge rectifier ..well they are good for 50 hz the diodes dont like it when you start hitting it with 400 and 500 hz..they get hot and distort the waveform. We have come up with a modified regulator and also a voltage and current foldback limit also a charge cutout limit and you can set what type of battery as of course there are different charge voltage limits between the std type wet/matt battery and Lithium batteries.

 

Another big issue is the regulator from Carmo that everyone is pushing do what a lot of motorbikes do and that is as your battery gets charged the regulator shorts the coils on the generator. This heats up the coils in the generator. Our unit disconnects the coils from the regulator which unloads the generator coil and switches off the charge/short cycle on the generator. There is a bit more in it but thats a simple explanation for it. Proto version is going on the aircraft now to see how it goes. The over voltage and current regulator and limiter will be a separate box that will mount under the std ducati regulator but we will also have our own regulator as a replacement that is also a separate unit but the 2 will bolt together.

 

The std old generator on the rotax and the regulator can not handle these new chemistry batteries. it was not designed for it. It was designed for the old wet style lead acid battery these new batteries are way different in what they require

[Kyle Communications]

If you havent seen the output of a Rotax generator this is what it looks like

I can drive my test rig from 0 to 5000 rpm

 

Here is the waveform of one of the first itterations of the new regulator.

As you start to add load to the generator each cycle gets switched to supply the load required. you will see the frequency at the bottom of the display it is decreasing . This is a fixed load on the generator and this is how it switches more of the waveform as the speed of the engine is reduced to be able to supply the load

 

[Kyle Communications]

This is the second test rig I made...it is currently being used for the regulator development but will be modified to do my CDI unit testing as well to add to the one I already have for timing checks. This rig is driven by a AC servo motor to be able to get enough grunt to drive the generator to full rpm at full current load

 

.

[onetrack]

Lead acid is soon to be obsolete.

 

Bruce, don't bank on that. The Lead-Acid Battery Manufacturers have formed a consortium or association to ramp up a fightback against Lithium batteries.

There's a range of new L-A batteries that offer superior performance to the standard L-A batteries.

 

https://batterycouncil.org/

 

BiPolar L-A batteries - Advanced Battery Concepts – Better Batteries, Better World (see "technology")

 

Carbon Foam cell L-A batteries - Firefly International Energy

 

Firefly batteries have been in full production for a couple of years now, and are popular with marine and RV users. However, Firefly are struggling to keep up production to meet demand, and they're only available in Nth America.

 

Both of the above new designs offer lighter weight (as compared to traditional L-A batteries), longer life, improved charging ability, and cheap manufacturing, making for a much cheaper battery than lithium.

The above batteries are also easily and fully recyclable, utilising current L-A recycling systems.

 

However, the bottom line is, Lithium still wins hands-down when it comes to sheer weight-saving overall.

[Old Koreelah]

...We have been working on a new regulator for the rotax which will do most all batteries...

Mark I recall you telling me about that project a couple of years back. There is certainly a market for it.

I ended up fitting a PowerMate and I'm happy with it, but have only done a few long trips so far.

[Kyle Communications]

Yes the project has had a hiatus for a little while with other stuff taking priority. It took a while to get the new Rotax high speed rig made and running properly so we can actually test and load test them on a real generator. Getting the unit running smoothly at 5000 rpm took a bit of effort in line up with bearings and flywheel balancing etc. My other test rig I use for the CDI is only driven by a normal electric motor and hasnt got enough grunt to drive the reduction to get it to spin at 5000 rpm so thats why its around 2000 rpm. I have another electronic test box to test the CDI at 5000 rpm but that is to make sure the current f the CDI in run and shutdown are within limits. The slower test rig tests for start rpm firing also kill and softstart function and also timing when the modules shift from retard to advance. This high speed one will be setup to do both the regulators and CDI in all modes. Just want to use it for the moment to finish the regulators then I will turn it into the full house version and I will convert the old one to the same so I have a spare...The AC sevo motor isnt cheap though..about 1400 bucks by itself..but superb torque and speed control

[RFguy]

I am a industry user (non aviation) of batteries. Comms, remote sites, high temp environments.

The biggest industry problem is people confusing LiFePO4 (3.25 terminal voltage, 3.65 max) with "lithium poly and lithium ion' (3.7V terminal, 4.1 / 4.2V max) .

They have very different behaviours, they are very different batteries.

I would have a LiFePO4 battery in my plane any day. They are essentially unconditionally stable and safe. I would rather not have a Lead Acid because of the rather nasty failure modes. I would NOT permit a 'Lithium ion' in my plane. No way. Not ever.

pronounced - LiFePO4 "Life - poh" and Lithium Ion often referred as " lie-po" or "lie poly"

[Old Koreelah]

...I would have a LiFePO4 battery in my plane any day. They are essentially unconditionally stable and safe. I would rather not have a Lead Acid because of the rather nasty failure modes. I would NOT permit a 'Lithium ion' in my plane. No way. Not ever...

From my own reading, I agree, RF. Trouble is, our planes also carry iPads, phones, etc which seem to be built around the nasty sort of lithium. They rarely fail, but I have an iPhone and a Li battery pack which both suddenly swelled up, rupturing their cases.

If they fail at 8,500' we have a problem.

[Bruce Tuncks]

I have had 2 fires from Li-Po batteries with model planes and I agree that I don't want one in my Jabiru. But I have had a Li-Fe in my plane for years now and it is not only better at starting the motor, it is 5kg lighter than the Odyssey it replaced.

As regards the alternator, what Kyle Comms has been saying about Rotax alternators sure applies to Jabiru ones too. I have been only using the LiFe battery to start the motor, it is then disconnected as soon as the voltage "used" during the start is replaced.

A better alternator and a proper BMS ( battery management system ) is required if you want a "fit and forget" solution. What I am doing at the moment is designing a buzzer-warning setup so that if I have left the alternator connected to the battery for too long and it goes over the set voltage, I will be reminded.

I dunno about Li-ion batteries. These are used in Tesla cars etc and I have not personally experienced any fires, but I have read about them smoking... I think an airliner experienced smoke in the cockpit once. And where there is smoke...

[facthunter]

The smoke in the cockpit of an airliner is unlikely to be from the batteries which are located further away usually. That doesn't mean they not of concern.. Nev

[Downunder]

I am a industry user (non aviation) of batteries. Comms, remote sites, high temp environments.

The biggest industry problem is people confusing LiFePO4 (3.25 terminal voltage, 3.65 max) with "lithium poly and lithium ion' (3.7V terminal, 4.1 / 4.2V max) .

They have very different behaviours, they are very different batteries.

I would have a LiFePO4 battery in my plane any day. They are essentially unconditionally stable and safe. I would rather not have a Lead Acid because of the rather nasty failure modes. I would NOT permit a 'Lithium ion' in my plane. No way. Not ever.

pronounced - LiFePO4 "Life - poh" and Lithium Ion often referred as " lie-po" or "lie poly"

It's not about the batteries themselves, it's about aircraft charging systems designed for lead acid/agm batteries.

Different aircraft obviously have different charging and battery management systems too.

Aviation has very risk adverse culture (as it should be).

As you are new to aviation, making blanket statements that some readers may take at face value could be dangerous.

[RFguy]

Biggest problem with the world and lead acid batteries- LACK OF TEMPERATURE COMPENSATION

When a lead acid battery gets hot, the terminal voltage goes down.

and so the (non compensated) charging system thinks the battery is not fully charged,

so it charges a full battery even harder.

and then the battery in an overcharge state gets hotter

and you get a runaway. Ever seen bulging lead acid batteries ? And I have NEVER seen ANY temperature compensation on any aviation alternator charging system (or vehicle) .

 

With LiFePO4, no temperature compensation is required.

 

I am pleased you have had good results with the LiFePO4. They have a nice flat discharge curve, also.

 

If you do flatten them, just go really easy on the charge rate until they are back up to 2.7V/cell.

And, if there is not a cell balanced board built in, keep an eye on the individual cell voltage.

If they are old, or absued, or been flattend the cells will vary a little. During charging to full, you'll find maybe you have 3 out of 4 cells at 3.65 and 1/4 dragging its feet at 3.3 etc. in this case, apply current and voltage limited charge across the slack cell until it comes up to full like the others. if you only have a 12V charger, not a cell charger, just put a resistor in series with the 12V charger (to limited the current) and watch the cell voltage regularly... (since the 12V supply is capable of overcharging it given time)

 

Active battery balances in LiFePO4 have a 3.6V zener diode and a transistor. The idea is as soon as the voltage on the cell gets over 3.6V, charge is shunted into a load.

 

one quarter the weight and half the volume for the same capacity as a lead acid !

 

and lead acid batteries are garbage. they are useless below 33% state of charge., when I say 'useless' I mean you should not rely on them delivering that last 33% once they are in a low state of charge (as viewed by terminal voltage, not specific gravity of the electrolyte in the case of a wet cell.)

 

glen

Edited August 9, 2020 by RFguy

[RFguy]

and " As you are new to aviation, making blanket statements that some readers may take at face value could be dangerous. "

 

yes, I need to qualify everything and not make rash statements I guess, (like "Lead acid batteries are garbage") since there is a bunch of reasons for everything....

[RFguy]

Bruce, you said " As soon as the battery is back to voltage, the charging is switched off and the "battery" is now just a couple of big capacitors which the alternator thinks is the battery. "

 

I would be a bit careful about that- it depends what the time constant is in the alternator voltage regulator.

If there is insufficient capacity in the accumulator (battery, capacitor) the alternator output voltage will go through the roof potentially damaging all the electronics on board ! This happens because the alternator voltage regulator might have a 1 second time constant , and if the load is removed, or there is insufficient place for the charge to go, the voltage will shoot up before the regulator has time to reduce the field current. The better and modern regulators are generally fast enough , although the idea with the long time constant is that the alternator doesn't try and follow a rapidly varying load

 

Interesting about the comment about over-heating alternators. The diode rectifier packs in alternators are about the most robust electronics in the whole aircraft. They can be damaged by over voltage (if the load is disconnected and the regulator ramps up the effort) . Good design I would think would shield the diode pack from 'seeing' a hot surface. My Volvo had a sheet shield between the back of the alternator and the exhaust man, even though it was 6" away.

 

-glen