Lithium ion batteries

[Richard Mole]

I'm trying to get up to speed with the new battery technology that has become well established in motor sport for example.Batteries using the LiFePO4 technology are also being marketed by Aircraft Spruce for example.

Among the brand leaders are Earthx who produce three different sizes specifically for aircraft - that Rotax now endorse, for example - which apparently have integral Battery Management Systems (BMS) to reduce the operating hazards to a minimum.

But there are other Earthx products without this protective BMS technology that are also sold by Aircraft Spruce. Indeed Spruce also sell not a few competing brands with LiFePO4 technology but no BMS. This raises the obvious question of whether these simpler batteries are already 'safe enough'.

I need a small and very light battery for a Vee twin B&S engine of about 2/3 L.
The Earthx batteries with their BMS are too big and too heavy.

The Red Top 8 Ah (lead acid AGM) battery at 2.7 kg in my Jodel spins the 2.4L engine with no trouble at all and I find that a battery change every 5 years or so works out well. Although 8 Ah sounds ridiculously inadequate the critical thing is the cranking current, as my avionics and electric horizon have fairly meager requirements. More modern avionics use even less power (why can't we buy them with a USB port to run off the battery re-chargers for ipads?). The battery is recharged in flight from a system that was originally designed for motor bikes and adapted by the engine manufacturer several decades ago. It works well.

In fact, the tiny Varley Li 3 battery of 2.5 Ah produces a similar cranking current to the Red Top 8.
I know folk who are using the bigger brother Li 5 to start their 0-200.
Putting all this together the Li 3 seems a perfectly reasonable choice for my small Vee twin B&S.

The Li 3 weighs about 0.5 kg against the 2.7 kg of the Red Top 8 which is a useful saving
see http://www.varleyredtop.com/pdf/Li3_2015.pdf
And Wessex Light Aeroplane Company offer a 10% LAA member discount on all Varley batteries.

I think on-board re-charging of the Li battery is likely to be the most hazardous aspect in routine operation (a dead short would be considerably worse and potentially very nasty indeed). The voltage regulation of many engine driven alternator charging systems is very crude and it may be unwise to assume they will never exceed the safe upper limit (around 14.4V or so I believe).

But there must be many LAA members out there already using this new battery technology. Please tell us your field experience and any special precautions you adopt as I haven't been able to find a TIL on the topic.

For example,
Can anyone recommend a suitable small BMS to sit between the charging output designed for a Lead/acid battery and the new Li batteries (or is that a pipe-dream)?
Does anyone rely upon an over-voltage warning light and a manual or automatic isolating switch if it comes on?
I have heard of folk who install an Li battery purely for starting. They re-charge after a couple of dozen flights either from a safe mains or other battery unit (taking the adaptor along in their pocket so as not to get stuck away from base).
Are there any knowledgeable LAA electrical engineers out there who have other ways of improving the safety of their on-board charging systems.
Or is it time to take a more relaxed approach - I almost said fit and forget!

[tnowak]

Richard,

I am not an expert in this field but believe Battery Management Systems (BMS) have to be integral to the battery in order to monitor individual cells. I think they monitor temperature as well as voltage and current drawn and include some kind of battery isolation device. These parameters can't be monitored externally.

Also, it is unlikely your usual GA generator/alternator (wind or engine driven) is unlikely to be suitable for charging these new technology batteries.

I suggest you contact the battery manufacturers directly for technical advice as I have found them very helpful.

Tony Nowak

[tnowak]

Richard,

Must proof read before posting !

I am not an expert in this field but believe Battery Management Systems (BMS) have to be integral to the battery in order to monitor individual cells. I think they monitor temperature as well as voltage and current drawn and include some kind of battery isolation device. These parameters can't be monitored externally.

Also, it is unlikely your usual GA generator/alternator (wind or engine driven) will be suitable for charging these new technology batteries.

I suggest you contact the battery manufacturers directly for technical advice as I have found them very helpful.

Tony Nowak

[Richard Mole]

Hi Tony,

I did write to Varley seeking technical advice and they have been very helpful.
‘I have just bought one of your LI-3 batteries (Invoice 136019) through the Wessex light aeroplane Co and was intending to use it on a microlight with a small 670cc engine. But I was taken aback by the warning ‘The battery is not suitable for continuous charge applications’ as I was intending to re-charge during flight from a small engine-driven alternator through a regulator designed for a lead acid battery. Please tell me whether or not that constitutes ‘continuous charge’ because if so I cannot use the battery.’
Varley replied 'The application that you are intending to use it on is what it is designed for, the Li-3 is an engine start battery and being charged from the alternator wont cause any issues.'

I asked a supplementary question 'Good, just what I was hoping for. I have a DMS 3 step charger type 9640 with 14.7/2.7A output I bought it for the Odyssey 8Ah lead acid AGM battery some years ago. Is this charger also suitable for the Li 3 or must I buy another charger (perhaps the max voltage is too high)? '
Varley told me 'Although you could use the current charger that you have I would suggest our lithium charger. If you charge the Li-3 off the current charger that you have you would need to ensure that it is turned off as soon as it is charged as leaving it on trickle charge would cause the battery to fail as the lithium battery doesn’t self discharge like a lead acid battery does. Our lithium chargers can be left on the Li-3 as once its charged the charger then goes open circuit so nothing is being put back into the battery as nothing is being drained.'

Thanks Tony for your observation that the BMS must be integral with the battery as it ‘manages’ individual cells.

I see that Aliant LiFePO4 batteries, with some sort of integral BMS, produce a small battery Aliant X1P with similar dimensions to the Li3, good CCA and it is perhaps just a little lighter. It is sold by Aircraft Spruce and the blurb states ‘Aliant batteries are the preferred choice for major manufacturers like Tecnam , JMB Aviation , BRM Aero , Alpi Aviation , ICP , Trixy Aviation and Aero Tomark'.

It is made in Italy and can also be sourced via European motorsport retailers. The maker’s website http://www.go-aliant.com states:
'This family of batteries is indicated for the replacement of all types of lead batteries currently in use without making any changes to the electrical system on board the vehicle. '
And under the ultralight aircraft tab
‘Thanks to technology and the product certifications carried on ALIANT series X and XP, these models are suitable for use as starter batteries for ROTAX engines, JABIRU, SIMONINI, Polini and other, without requiring changes to the electrical system of the airplane’.

That is about as far as I have got at the moment. Perhaps it’s too soon to expect feedback from users. A null return in this case is actually good news because a battery incident is likely to be pretty serious - and we would likely hear about it through the usual channels.

[Christopher Rose]

New Eurostar Ev-97 SL microlights have Aliant X3 batteries you can read the dealers advice at http://lightsportaviation.org.uk/aliant.html.
Very small light battery for all on board electrical needs including starting Rotax 912. Used a lot on racing motorbikes.

[Richard Mole]

Thanks for the post Christopher.
Its becoming a convincing option.

[JimCrawford]

I’m submitting a mod for my Tipsy Nipper to utilise Leburg ignition with LiFePo batteries. This is outside the remit of SM 14337 (installation of LiFePo batteries) which excludes ‘electrically dependent systems’ such as electronic ignition. Consequently this must be a new mod with comprehensive analysis and testing to prove serviceability and safety.
I tried to get information regarding the Varley Li-5 as it seems a likely candidate for this application and is specifically mentioned in SM 14337 but the only contact on the Varley site is [email protected] and I didn’t get a reply to my email. A phone call revealed some numbers and a promise of more by email, but that hasn’t happened, most disappointing. Brian Hope’s article in the mag has as much data as I’ve managed.
The most significant information is the tight voltage requirement for charging the battery, 14.2 to 14.4 volts (by phone but 14.2 to 14.6 in the article). I believe this is typical of batteries that have no internal management system. the UN 38.3.4.7.2 test requirement is 22 volts for 24 hours “Rechargeable batteries meet this requirement if there is no disassembly and no fire during the test and within seven days after the test.” Disassembly as defined here is essentially an explosive rupture.
I was told that the charging bus should never exceed 16 volts to avoid damage, I didn’t get a time limit on that overvoltage.
The Leburg wiring scheme as distributed in the manual isn’t satisfactory and I have reworked it to resolve the problems. The standard motorcycle type regulators are also unlikely to be compatible with the LiFePo batteries so I have completed the schematic design of a regulator specifically to interface between the Honda CB600 alternator as suggested in the Leburg documentation, and a LiFePo system. It is also suitable for a lead acid gel cell system. The design matches all the requirements in CS23.1351 to CS23.1367.
Once LAA engineering have cast the Runes over my mod application I will re-edit it for the magazine so that anybody going this route can take advantage of my workings.

Jim

[Seanjd]

Hi Jim
Have you got any updates on this?

I am thinking of installing a battery on my Champ, purely to use as an on-board power source for a radio & transponder. Having checked the approved MODS I cannot find one listed for my aircraft type but am sure it has been done before and I do have some info from USA on this having been done before.

I will speak to the LAA team and get some advice and guidance also before opening my wallet, but a quick search on here showed your post, hence my question.

Sean

[JimCrawford]

Hi Sean,

I'm pushing on with this project, I have a set of three crankshaft adapters on the lathe and, when they are finished, I'll be rigging up my alternator test set.
As I've mentioned in a previous post, plan A is to write up this whole exercise as a series of articles for the LAA mag and I've just made contact with Brian Hope in order to get some editorial guidance. I don't know how much this will be of interest to you because I guess that you aren't interested in the electronic ignition or the dual battery system. I think you are probably more interested in the subset of the mechanical fit of a battery to your aircraft and adding suitable wiring. I'm sure that this would come under the LAA mod scheme as a simple mod for your aircraft as there is unlikely to be a standard mod to copy. I would imagine you would end up with something rather similar to that in my glider where a battery pack is removed from the aircraft to charge overnight.
I hope to cover all this sort of info in my articles. There is much to do so I must push on; "I must just check the garage" gives a couple of hours on the lathe & mill, welcome peaceful relief from the chaos of the visiting extended family plus grandchildren over Christmas!

Seasons Greetings

Jim

[Seanjd]

I think you are probably more interested in the subset of the mechanical fit of a battery to your aircraft and adding suitable wiring. I'm sure that this would come under the LAA mod scheme as a simple mod for your aircraft as there is unlikely to be a standard mod to copy. I would imagine you would end up with something rather similar to that in my glider where a battery pack is removed from the aircraft to charge overnight.

Spot on Jim and many thanks for the reply
Merry Christmas

Sean