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  #1  
Old 12-29-2013, 03:50 PM
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ChiefPilot ChiefPilot is offline
 
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Location: Twin Cities, MN
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Default How I installed a LiFePo battery and saved 11lbs!

This past December saw the first condition inspection on my -6A. Aside from the inspection, I had decided to use this time to install some upgrades. One of the upgrades was to replace the 15.7lb PC-680 battery with a 2.7lb Shorai LFX18L1-BS12 LiFePo battery.

Much has been written here and elsewhere about the merits of Lithium-Iron-Phosphate batteries (see this thread for a great discussion). Rather than re-hash the discussion around the tech, I wanted to share how I installed this battery in my RV without making any changes to the airframe, wiring, or battery box. I hope someone finds this helpful!

Operation
Since the first question I'm sure many will ask is "How well does it work?", I'll start with that. In short, I can tell no difference in normal operation between this battery and the PC-680. I have an IO-360-B1B w/8.5:1 pistons and dual P-mags and this battery spins the Hartzell BA prop with the same gusto as the PC-680, if not more. I've had it in weather down to -1ºF and it has performed as expected. I'm continuing to watch this carefully, as I have only about five hours of running time so far but I don't expect any surprises. I do like the weight savings however!

The Installation
The first step was, of course, to obtain said battery. I ordered the battery directly from Shorai and received it a few days later.


I had previously removed the PC-680 from the aircraft and compared the two side by side. Clearly, the Shorai battery is significantly smaller - but the weight difference is even more dramatic. Not wanting to count on published specs, I measured both batteries myself. The Shorai matched the published specifications in all respects, and indeed weighed only 2.3lbs. Interestingly, the only discrepancy with published specs I found was with the PC-680 - the Odyssey site claims the PC-680 weights 15.4lbs but mine measured 14.0lbs.



One of the goals for this upgrade was to be able to preserve the ability to do a "drop-in" upgrade. This preserves the possibility of going back to the PC-680 at some point in the future, and also eliminates changes to the airframe/FWF configuration. Since the Shorai battery is significantly smaller than the PC-680, that means that an adapter is needed to secure the batter within the larger space of the PC-680 battery box.

Enter a large chunk of UHMW plastic. I love working with this stuff - it's relatively cheap, it's easy to mill, and it's reasonably lightweight. Certainly other materials could be used - aluminum, or perhaps even wood - but I had envisioned starting with UHMW and so that is the path I went down. The original chunk looked like this:


I used this material to make two "end caps" that positioned the battery in the correct location with the PC-680 box in all three axis (fore/aft, left/right, and vertically). This allows the battery to be secured in the box by the same aluminum bar and AN bolts as the PC-680. This approach also means that the battery cables reach the terminals without modifications.


The actual installation took just a couple of minutes: place the blocks into the battery box, place the Shorai battery into the blocks, install the battery straps, and then finally attach the battery cables.


The last part of the process was updating the logbook along with weight and balance information. Overall weight savings was exactly 11lbs; I'm sure this would be a bit more for folks who have a heavier PC-680. Since my RV has the training wheel up front along with a constant speed prop, saving 11lbs on the firewall was a welcome change.
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Last edited by ChiefPilot : 12-29-2013 at 04:12 PM.
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  #2  
Old 12-29-2013, 04:02 PM
Bevan Bevan is offline
 
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Excellent report. Can you tell us more about the engine that this battery has no trouble starting? Please include size, compression ratio, mags or EI etc.

I have been considering the Shorai as well. I'm not flying yet so there's no immediate plan to order the battery yet. But I thought I would need the biggest battery Shorai makes which does not fit in the battery box designed for the PC680.

Bevan
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  #3  
Old 12-29-2013, 04:14 PM
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ChiefPilot ChiefPilot is offline
 
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Quote:
Originally Posted by Bevan View Post
Excellent report. Can you tell us more about the engine that this battery has no trouble starting? Please include size, compression ratio, mags or EI etc.
Sure - it's an Aerosport Power IO-360-B1B w/dual P-mags and 8.5:1 pistons. It typically starts on the second or third blade when cold, or much later if warm and I ham fist the throttle/mixture during a hot start. The new battery hasn't helped my hot-start skills, unfortunately, and instead behaves just like the PC-680 it replaced .
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  #4  
Old 12-29-2013, 05:36 PM
rv7charlie rv7charlie is offline
 
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Location: Pocahontas MS
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Default Questions...

Is your plane 'electrically dependent' (meaning the your avionics)?
If so,
How does the actual total energy in the battery compare to the SLA you removed?

The reason I ask is: I keep reading that almost all the various lithium tech batteries being sold for starting duties use 'equivalent capacity' ratings. If I've read correctly, this means they have the same starting capacity (high current drain) but often have significantly lower total energy (loose interpretation: they won't power avionics as long).

I hope it can handle the lower drain duties; I'd like to save that weight, too.

Charlie

Last edited by rv7charlie : 12-29-2013 at 05:38 PM. Reason: clarity
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  #5  
Old 12-29-2013, 08:10 PM
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ChiefPilot ChiefPilot is offline
 
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Quote:
Originally Posted by rv7charlie View Post
Is your plane 'electrically dependent' (meaning the your avionics)?
If so,
How does the actual total energy in the battery compare to the SLA you removed?

The reason I ask is: I keep reading that almost all the various lithium tech batteries being sold for starting duties use 'equivalent capacity' ratings. If I've read correctly, this means they have the same starting capacity (high current drain) but often have significantly lower total energy (loose interpretation: they won't power avionics as long).

I hope it can handle the lower drain duties; I'd like to save that weight, too.

Charlie
I have a Dynon D10A EFIS + D10 EMS; the EFIS has an internal battery pack which will run the unit for several hours. The Pmags provide their own power, so the engine isn't dependent on the battery to continue.

The LiFePO batteries have a very different discharge curve than lead acid batteries and so a direct comparison is difficult. A lead acid battery drops the voltage throughout it's discharge voltage whereas a LiFePo battery does not. If your GPS/COM requires 11.0 volts to function, an "equivalent capacity" LiFePo battery will likely power it longer than a lead acid battery since it will provide more time above 11.0 volts than will the lead acid version.
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  #6  
Old 12-29-2013, 08:32 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by rv7charlie View Post
The reason I ask is: I keep reading that almost all the various lithium tech batteries being sold for starting duties use 'equivalent capacity' ratings. If I've read correctly, this means they have the same starting capacity (high current drain) but often have significantly lower total energy (loose interpretation: they won't power avionics as long).
The ratings you are are speaking of are -

Cold cranking amps - the amount of amps the battery can supply in a maximum current draw condition (starter motor).

Amp / Hr rating - The number of hrs a fully charged batter can supply a current flow of 1 amp. I.E, the aviation standard Concord CB-25 battery is rated at 25 amp / hrs. A fully charged one should be able to supply 5 amps for 5 hrs (amps X time). In reality it is usually a bit less than rated because of losses with age, etc.

The cranking amps rating of the PC-680 is very close to the CB-25 but the amp / hr rating is lower (about 17 if I remember right). I don't know what the Shorai cranking amps rating is, but it sounds like it is also very close to the others if the engine cranks well. I would imagine that the amp hr rating might be even lower tough (is it listed in the supplied documentation?)

One caution comment to adopters of this type of battery...
I also am interested in experimenting with some of the new battery technologys for the weight and space savings potential now that the technology has matured quite a bit, but there are serious fire dangers with this type of battery. I would not install one without building a fully sealed fire proof case to contain it. Even then, I would at least consider adding a temperature probe to monitor what is going on inside that box.
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  #7  
Old 12-29-2013, 09:09 PM
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ChiefPilot ChiefPilot is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
One caution comment to adopters of this type of battery...
I also am interested in experimenting with some of the new battery technologys for the weight and space savings potential now that the technology has matured quite a bit, but there are serious fire dangers with this type of battery. I would not install one without building a fully sealed fire proof case to contain it. Even then, I would at least consider adding a temperature probe to monitor what is going on inside that box.
While that is certainly true of Lithium-Ion batteries, lithium iron phosphate batteries do not have the same thermal runaway failure mode. I avoided the lithium ion batteries precisely because of that reason.

More info: http://www.batterystuff.com/kb/artic...-overview.html
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  #8  
Old 12-29-2013, 09:28 PM
rockwoodrv9 rockwoodrv9 is offline
 
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Good answer!
Thanks for the info and pictures. Nice work.

I am on the other end of the weight problem. I have a O-320 (9A)and will have a FP Catto prop. I have the box built for the P-680 which makes the nose lighter yet. I like the idea of reducing weight - 11 lbs is a big savings, but maybe I won't be able to carry any baggage! I haven't done CG calculations yet, but if I keep reducing weight on the front, I can get aft heavy quickly. I also converted from a tail wheel and did not remove the wheel sleeve from the tail section.

Quote:
Originally Posted by ChiefPilot View Post
While that is certainly true of Lithium-Ion batteries, lithium iron phosphate batteries do not have the same thermal runaway failure mode. I avoided the lithium ion batteries precisely because of that reason.

More info: http://www.batterystuff.com/kb/artic...-overview.html
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  #9  
Old 12-30-2013, 07:16 AM
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flightlogic flightlogic is offline
 
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Rock wood, like you, my 9A needs weight in front, rather than rear. All my sample W/B calcs show problems when I fill fuel and take a guy rather than my wife. Adding the Antiaerosplat steel bar helps. I like this low weight battery technology especially if the thermal dangers are not there.
I am thinking of mounting one somewhere near CG mid point for backup.
I used to hand prop regularly in my Luscombes. Don't think I would try it on the Catto hanging on the RV
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  #10  
Old 12-30-2013, 11:36 AM
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ArVeeNiner ArVeeNiner is offline
 
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Sorry to go off topic a bit but I just ran my numbers for my 9A and with one gallon of fuel, a couple of 250 pounders, and 75 pounds of luggage, I'm still within the aft CG limit. I have a Catto and an O-320. It's pretty tough for my airplane to exceed the aft CG limit.

I now return you to your regularly scheduled programming.
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