Dual battery setup for Leberg ignition

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skelly
Posts: 23
Joined: Tue Nov 27, 2018 9:15 pm
Location: Derbyshire

Dual battery setup for Leberg ignition

Post by skelly » Thu Jan 07, 2021 2:27 pm

Hi everyone,

I have a conundrum regarding batteries and could do with some inspiration if poss please.

I am rebuilding a kitfox mk2 and it has a KFM112M engine which utilises a Leberg dual ignition system.
Now..
In the Leberg info it says I need 2 batteries, one for each ignition A&B.
However, in the pursuit of weight saving, I am keen on looking into lightweight lithium batteries but split charging 2 lithium batteries is problematic.

I can get a mosfet regulator/rectifier to charge one lithium battery and have that as my main battery (including cranking) and then have a small 7AH lead acid battery which will a back up battery (not connected to the charging system).

This seems like the lightest and most sensible way of doing things but it does go slightly against the info in the Leberg blurb as I would be mostly running from one battery only although the chap from Skycraft says that this is acceptable.

Have any of you had experience with anything like this ?

Cheers,
Skelly.
Jon Skelson
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JimCrawford
Posts: 59
Joined: Tue Apr 20, 2010 2:23 pm

Re: Dual battery setup for Leberg ignition

Post by JimCrawford » Wed Jan 20, 2021 6:04 pm

Hi Ian,

I am installing a dual Leburg system on my Nipper and have a few comments that might prove useful:

My original intention was to use a pair of LiFePO4 batteries but I have fallen back on gel cells for several reasons. The main driver is that a gel cell system (including alternator) is very nearly weight neutral compared with the twin mags removed from the aircraft. However the batteries' location can be altered to fine tune the CofG of the aircraft and it just so happens that a pair of gel cells mounted in the first bay behind the seat is just right. Also I'm not weight critical in the Nipper so I don't have a necessity to save every gram. If I used Lithium cells then they would have to be rather further aft, deep in the fuselage, which would require going in through the fabric which is in good condition and I'm loath to do that. If the opportunity arises in the future then I wouldn't have any problem with a LiFePO4 installation.

However I've found that there are a few issues which need resolution before that happens;

1. The current LAA document SM 14337 issue 4 ( Standard Mod: Lithium iron phosphate batteries ) excludes aircraft types that are electrically dependent and specifically references Leburg ignitions.
You will need a separate mod application for your aircraft and probably some negotiation with engineering before you can proceed with a LiFePO4 installation.
2. It is my opinion that the battery should have an internal battery management system (BMS). Otherwise they can be tricky to charge correctly without risking damage. I enquired about the Varley types, approved by the LAA for occupied areas, and I only discovered by phoning that they don't have a BMS and the charging voltage, quoted as 14.4 volts, was required to be +- 0.2 volts (IIRC). A tight spec that is unlikely to be met by any regulator not designed specifically for this purpose. Similarly the Shorai data sheet has dire warnings about charging. There are many alternative batteries available and it should be possible to find one with a BMS that will satisfy the LAA.
3. A side issue with some standard regulators is that their mode of operation may require the battery to act as an electronic flywheel analogue to maintain stability. If a battery goes off line then the associated bus driven directly from the regulator may damage connected kit.
4. I'm not a fan of the Leburg schematic layout. In particular feeding the backup battery from the main bus via a diode will result in partial charge on a backup which is already undersized for the claimed 7hr run time. My modified installation has two completely separate busses, more comprehensive fusing and two 'full size' batteries.


Jim
Jim Crawford
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skelly
Posts: 23
Joined: Tue Nov 27, 2018 9:15 pm
Location: Derbyshire

Re: Dual battery setup for Leberg ignition

Post by skelly » Thu Jan 21, 2021 10:02 pm

Hi Jim,

Thanks for that, very informative.
I think I will go for 2 x 7AH gel batteries to take care of the ignitions and a split charger.
I may then use a non charged lipo4 battery just for engine cranking with short wires but I am not 100% decided yet.

I'll keep you posted on how things pan out.

Cheers,
Skelly.
Jon Skelson
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Neil Spooner
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Joined: Wed Jan 07, 2009 5:22 pm
Location: Colchester, Essex

Re: Dual battery setup for Leberg ignition

Post by Neil Spooner » Mon May 03, 2021 8:13 am

For the Leburg a 7ah & 4 ah are fine if they are being charged in flight.
If you are not going to charge the batteries in flight be aware that you will damage the Leburg controller if the voltage drops too low.
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JimCrawford
Posts: 59
Joined: Tue Apr 20, 2010 2:23 pm

Re: Dual battery setup for Leberg ignition

Post by JimCrawford » Tue May 04, 2021 12:13 pm

Neil,

When I initially attempted to get my conversion approved without the alternator by engineering I was pointed at the EASA construction standards which require an engine driven power source to charge the battery (ies). I'm sure that the LAA doesn't have to rigidly follow the CS requirements as long as they can be convinced that a particular change can be shown to be safe. However I was also advised at the time by a 'source' that it would be quicker to modify the engine to take the alternator than to get a total loss battery system approved.

I don't like the published scheme of charging the backup battery by a diode feed from the primary bus. It won't get anywhere near its capacity.
My scheme uses two identical and separate systems.

Jim
Jim Crawford
002559

skelly
Posts: 23
Joined: Tue Nov 27, 2018 9:15 pm
Location: Derbyshire

Re: Dual battery setup for Leberg ignition

Post by skelly » Tue May 11, 2021 10:42 am

Interesting stuff,

My KFM engine has a single phase generator which is exactly the same as some Ducati motorcycles.
To be honest I don't think it has the sufficient output to successfully charge a lithium battery so that sorts that out.

So now I just have to decide on which gel batteries to use with a split charging system.

And what sort of split charging system.

Cheers,
Skelly.
Jon Skelson
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MikeM
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Re: Dual battery setup for Leberg ignition

Post by MikeM » Sat Jun 05, 2021 8:29 am

Skelly, when I had my Jodel D9 with a Leburg system on a 1600 VW, I used two Yuasa batteries, one being 7Ahr (NP7-12) and the backup a 2Ahr (NP2-12). The latter was narrow and didn't take up much space. Worked fine.
Mike Mold (007106)
Jodel D117A G-BFEH, Watchford Farm, Devon

skelly
Posts: 23
Joined: Tue Nov 27, 2018 9:15 pm
Location: Derbyshire

Re: Dual battery setup for Leberg ignition

Post by skelly » Tue Jun 15, 2021 7:06 pm

Thanks Mike,

That sounds exactly as the instructions in the Leberg manual.

That setup would work fine but I also need a battery with enough oomph to crank the engine.

I'm seriously looking at a LiFePo4 main battery with mosfet reg-rec and a back up battery that isn't connected to the charging system which will be a smaller LiFePo4 battery.
I think that if I choose the components and battery's carefully I'll be fine.

I just hope that my single phase generator can provide a decent steady output to keep the battery happy.
The generator is the same as an early Ducati Monster.

Cheers,

Skelly.
Jon Skelson
043254

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