New Tech Batteries

[carusoam]

2 minutes ago, 65eTurbo said:

All true.  In my  case it is easy load aft of the CG envelope.  Hard to load ahead of it.  20 pounds out of the tailcone would let me move a 30 pound bag to the back seat and carry an extra 3.2 gallons of fuel in my 90 gallon tanks.

Looks like you may have adjusted weight locations when the turbo was added up front…

Did the battery move aft at the same time?

 

The M20K Rockets got a pair of batteries that are set far back in the tail cone….  There is a slider board for the hangar… to aid in the removal and installation of the batteries….. they are that far back…

 

It is great to have options!

Best regards,

-a-

[GeeBee]

I would agree that these new tech batteries require an integral battery management system. However, you have to think of your electrical system like a hydraulic system. Right now your battery is like a very robust accumulator. It absorbs surges, replenishes excessive demand. If you place a "management system" you are essentially placing an orifice to the accumulator.....which kind of defeats the accumulator. Without making the pump (aka the alternator) and the pressure regulator (aka the voltage regulator) much narrower in its operating range and more responsive to demand and decline, trouble will brew for the entire system. Alternatively you can upgrade the "pipes" (aka the wiring) to absorb more potential. IOW without a "holistic approach" to the electrical system, simply placing an "orifice" in front of the battery makes me very skeptical. 

 

[N201MKTurbo]

Lets say you did make a proper lithium battery system. One thing you will need to get used to is the different discharge behavior. A lead acid battery will gradually lose voltage almost down to zero, and if you charge it soon after that it will do little harm to the battery. If you let that happen to a lithium battery, it will likely catch fire. If I remember correctly you want to stop discharging the cell at about 3.5 volts or it will permanently damage the cell. The voltage will stay fairly constant until the cell is discharged and then you get a fairly steep reduction in voltage. In other words the battery will be just fine then nothing.

 

[A64Pilot]

The Lifepo4’s will not catch fire and really don’t need a BMS, but even on a lead acid battery a BMS is useful. There are  great many motorcycle and auto starter Lifepo4 batteries and have been for years, with no fires.

https://www.amazon.com/s?k=lifepo4+motorcycle+battery&crid=217HFRQ68GNFL&sprefix=lifepo4+motor%2Caps%2C209&ref=nb_sb_ss_ts-doa-p_1_13

You should have a three stage charger though, like is very common on boats. I had a Balmar 614 on my boat. We really should have one on our aircraft, but not likely worth the expense of Certification, They are really just sophisticated voltage regulators is all.

https://balmar.net/balmar-technology/multi-stage-regulation/

Unlike a lead acid battery, for max lifespan a Lithium battery should never be fully charged, much less overcharged, if you had a 12V Lithium battery and fed it 14V continuously. you will overcharge it, but that’s easily overcome.

For example the 2010 Toyota Prius cycles it’s battery pack between 40 and 80%, it never allows more than a 80% charge and in its service life may be cycled hundreds of thousands of times. Anyone with Hybrid experience knows battery cycling in city traffic is pretty rapid because the engine shuts off every time you lift the throttle and the AC etc keeps running on battery 

It can be done both easily and safely, question is as it’s such a niche market and FAA Certification is assumed to be hard and expensive, can you make money from it? What’s the return on investment?

Now if you want to go to actual (normal) Lithium batteries like for instance the NCA batteries Tesla uses, then yes it’s going to be hard because if they aren’t treated right, they will burn and do so with the ferocity of a Magnesium flare.

When charging model airplane Lipo packs. you do so in a fire proof container, because we abuse them with very rapid charges and discharges and occasionally one does burn. It’s rare but every now and again you crash a model and the battery gets damaged and lights off. Let me tell you, you really can’t put that fire out until after the battery is finished burning.

Intentional overcharge of a smallish model Lipo pack

 

[N201MKTurbo]

12 hours ago, A64Pilot said:

The Lifepo4’s will not catch fire and really don’t need a BMS,

https://www.amazon.com/s?k=lifepo4+motorcycle+battery&crid=217HFRQ68GNFL&sprefix=lifepo4+motor%2Caps%2C209&ref=nb_sb_ss_ts-doa-

If you read the fine print on all the batteries listed, they all have integral battery management systems.

[A64Pilot]

1 hour ago, N201MKTurbo said:

If you read the fine print on all the batteries listed, they all have integral battery management systems.

A Lifepo4 bank will live longer if there is a rudimentary BMS, and there isn’t much to one, so why not?

Originally they were all A123 cells and that was it, no BMS

BMS is another undefined word, for a Lipo or Li-ion battery they individually monitor each cell and charge each cell independently as well as monitor temp and disconnect the battery when full, something that is not friendly to alternator systems. We have to have that huge capacitor in the system, in mechanical terms think of it as an hydraulic accumulator. An alternator output isn’t really DC, it’s AC rectified to DC so therefore it’s pulsed DC, we need that battery to maintain voltage at low RPM and to supply pure DC, smooth surges etc.

For a Lifepo4 bank usually all they do is regulate voltage to prevent an overcharge

However Lithium technology is growing like computers did in the 80’s, pushed largely I’m sure by the desire for electric cars, but whether we see them in GA aircraft is really more desire, than capability in my opinion

Most of us don’t really “need” one, lead works fine for us, and many Lithium chemistries don’t like real cold and often have to be heated, which further complicates things.

Add that into that I can’t see Concorde or Gill terminating the constant income from replacements, I’m not sure it will happen.

I think it’s like electronic mags, we could have had self generating electronic drop in ignition 50 years ago, but didn’t, perhaps Lithium batteries will be the same?

 

[N201MKTurbo]

Lithium batteries do not charge their cells equally. The cells are greatly affected by temperature and it is impossible to keep all the cells the same temperature, either through self heating or external temperature. They must be equalized. the minimum BMS will equalize the cells. They do this by operating a charge pump that takes charge from the highest voltage cells and transfers it to the lowest voltage cells. These circuits operate from battery power continuously until a equalization threshold is reached. 

The problem is that the cells are charged in series with a single charge current. If one cell is at say 4.1 volts, another cell is at 3.7 volts and the third is at 3.9 volts for a total battery voltage of 11.7 volts, if this battery is charged further the first cell will go into an overcharge condition before the the lowest charge cell is fully charged.

I haven't studied the new chemistries. All my experience is with Lion batteries. I suspect the new chemistries raise the full charge voltage so the overcharge voltage was raised so there is less chance of overcharging an individual cell. This also means the batteries are never fully charged.

[N201MKTurbo]

Here is some interesting info on different lithium battery chemistries.

It shows the lithium iron phosphate batteries are more robust then the other chemistries. They also have one of the lowest energy densities, but still three times higher than lead acid.

https://batteryuniversity.com/article/bu-205-types-of-lithium-ion

 

[A64Pilot]

The “trick” to making a Lifepo4 battery last in a automotive or aircraft application is ideally a three stage alternator regulator or at least turn the voltage down to 13V or so if a single stage regulator

”Legacy” aircraft in the Army used Nimh batteries and on them we adjusted the voltage regulator twice a year due to temperature changes.

Of course a modern voltage regulator adjusts voltage automatically based on battery temperature, but our aircraft voltage regulators are certainly not modern.

Cell balancing is absolutely essential on other Lithium chemistries, especially when you get to large batteries like used in electric cars with hundreds or even thousands of cells, but for a 4 cell Lifepo4 12V battery, not so much. 

From memory LFP AKA Lifepo4 has about half the energy density of many other Lithium chemistries, but is gotten much better, hence starting this year all “normal” range Tesla’s will have the Chinese manufactured CATL Lifepo4 packs, all long range Tesla’s will keep the NCA Lithium packs due to higher power density.

Supposedly the CATL packs are million mile packs, but I suspect they will die from calendar aging prior to cycling out, who drives a million miles in say 20 years? I doubt the pack will last 20 years?

https://www.bbc.com/news/technology-52966178

Edited January 28, 2022 by A64Pilot