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  #1  
Old 01-22-2021, 12:47 PM
dwaynebob dwaynebob is offline
 
Join Date: Jan 2005
Posts: 40
Default Earthx Battery Placement

Alcon,

I realize opinions on Earthx are all over the place, but I was going to see if there is a consensus of where to place the battery. It's nearly impossible for me to mount my 680c on the engine side of the firewall. The only way I could make it work is if I use a remote oil filter location (not a fan). After talking to the factory about their note "if a battery is located inside the cabin it should be in a protective enclosure that vents to the outside." It turns out that that is a requirement for certified aircraft as ordered by the FAA and doesn't apply to experimental. Here is what would have to happen for an earthx battery to have a thermal runaway (very unlikely with LiPo4 chemistry I'm told by various resources).

1) My alternator would have to fail and produce an overvoltage situation.
2) My Regulator with overvoltage protection would have to fail.
3) The BMS overvoltage circutry in the battery would have to fail.
4) My cockpit battery fail annunciator light (bought with the battery) would have to fail.
5) My other to volt meter warning systems would have to fail or me not notice the warning indicators.

Seems to me, the risk is very low. I don't have a lot of build experience, but I have owned RV-4's since 2004 (with an accidental purchase of an F1 Rocket for 3 of those years) and have never had an electrical issue except for replacing a solenoid and battery.

I wanted to keep this to the RV-3 community because there might be a way to mount it ouside the firewall that I may be overlooking. I did have plenty of room in either of the cheeks, seems like an odd place to put it, but it certainly fits. Wasn't sure if that would be a problem for the structure as it ways about 3.5 pounds.

Advice appreciated, unsolicited or otherwise.

Dwayne
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  #2  
Old 01-22-2021, 12:58 PM
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rv8ch rv8ch is offline
 
Join Date: Feb 2005
Location: LSGY
Posts: 3,570
Default

Hi Dwayne, why not just put it in a protective enclosure that vents to the outside? Are there some constraints to that suggestion?
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  #3  
Old 01-22-2021, 05:55 PM
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TnMike TnMike is offline
 
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Location: Lewisburg,Tn
Posts: 305
Default

I have an EarthX VNT900 and Shorai backup battery in my RV3B.
The EarthX is vented out the right gear leg fairing.
Both are in the tunnel between the rudders against the firewall.
No issues for 3 years.
Mike Kellems
RV3B N931M
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  #4  
Old 01-22-2021, 07:47 PM
David Paule David Paule is offline
 
Join Date: Dec 2009
Location: Boulder, CO
Posts: 4,664
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Which model battery fits the cheek? I think that's a good place for it, frankly.

If it were mine, I'd cut a piece of .020 titanium (I have some on hand anyway) to nest on the side skin adjacent to the battery, just in case. Perhaps a couple of keeper rivets to hold it in place. It might act as a firewall in the unlikely event that were needed. Some 1/16" Fiberfrax as a sandwich filling would be optional. A piece of stainless firewall material would work, too.

If your cheeks are aluminum, riveted per plans, they should to be adequately strong. Of course you'd need a hatch big enough to replace the battery. I'd find some way to distribute the battery weight on the cheek, something like foam. And then drill a vent hole somewhere in a low-pressure region on the cheek, if there is such a thing, just in case it does vent.

The propwash swirls and the canopy is downwind of that, so maybe the right cheek would be better than the left.

Dave
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  #5  
Old 01-22-2021, 08:02 PM
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Larry DeCamp Larry DeCamp is offline
 
Join Date: Apr 2010
Location: Clinton, Indiana
Posts: 1,051
Default Are there facts for this dilemma ?

There is a history of opinions about this topic. Earthx understandably leans toward (lawyer speak) and offers a vented system. The OP rationale follows my current practice:
* Voltage regulator has OV protection
* The battery has over current / voltage protection
But, if problems progressed beyond the failure of these two safeguards, what ?
* Will the fuse floor melt and drop the battery out hanging by the cables ? What does a vent do to eliminate this event ?
* Will the acrid fumes be so debilitating a cracked canopy will not facilitate a landing ?
I don't know , so I join the OP inviting knowledgeable input.
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  #6  
Old 01-22-2021, 11:52 PM
dwaynebob dwaynebob is offline
 
Join Date: Jan 2005
Posts: 40
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The 680c fits nicely in the aluminum cheek, and according to the instruction manual, the earthx can be mounted in any orientation. If I mount it sideways, I can easily service it when I remove the cowling. The battery would mount to the fuselage, I was thinking a doubler would work but a piece of stainless may be a better option.

Last edited by dwaynebob : 01-22-2021 at 11:55 PM.
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  #7  
Old 01-23-2021, 12:04 AM
dwaynebob dwaynebob is offline
 
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Posts: 40
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Mickey and Larry,

Sounds obsessive compulsive but the reason I didn't want to build a stainless battery box was because it adds 4 pounds....this plane is going to be very light, so I'm being as lean as I can.

With regard to Larry's comment, having 2 failsafe systems for my battery seems more than adequate...i.e. regulator and BMS on the battery itself. Also, keeping my charging system in good working condition will help. My research on Earthx problems has, as far as I can tell, involved builders (or current owners who bought the plane) who didn't follow recommendations by the manufacturer, specifically, they didn't install the warning light that shows a potential battery problem. I bought the light and will have it in a high vis location. My buddy who is helping me get this bird back in the air suggested a .30 cal ammo box...weighs 4 pounds but it would protect in case of a thermal runaway. He uses them for a lithium solar battery system for his cabin.
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  #8  
Old 01-23-2021, 11:42 AM
blaplante blaplante is offline
 
Join Date: Jan 2010
Location: Southern California
Posts: 169
Default Another Fail Mode or Two

Having put together some off-grid lithium battery packs, there is another failure mode that hasn't been considered, and the BMS might not protect: Internal short between the cells of the pack. Each lifepo4 cell is approx 3.2 volts, so similar to lead-acid cells you need to connect several in series to produce a "12 volt" battery. While rather unlikely in a commercially constructed battery (vs. DIY), a short of a cell to another cell will cause the alternator to over voltage the remaining cells. In my off grid batteries, the final fail-safe is a battery fuse (oversized) to just disconnect the battery if something gets beyond the BMS. [Let me be clear - I'm not advocating a battery fuse in an airplane!]

More likely is a cell to develop an internal short, which is why Telsa (and my) packs have fuse wires on every cell connection. Otherwise with (in my case) 13 cells in parallel, when one cell shorts there are 12 cells dumping full amperage into the failed cell. Does EarthX have individual cell fuses? No idea.

I suspect a box could be made lighter than 4 pounds if something was fabbed out of firewall thickness stainless. I mean, off the shelf there's https://www.amazon.com/Fortress-Meta.../dp/B07F3CHWLR at 3.7 pounds. Probably lose a few ounces taking the handle off. And it appears to be way bigger than needed.
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  #9  
Old 01-23-2021, 03:10 PM
dwaynebob dwaynebob is offline
 
Join Date: Jan 2005
Posts: 40
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Stole an idea from an RV-4, since my oil cooler is the old style on top of the engine, there is lots of room behind the left baffle....just a mock-up for now but I think it will work and no worries about smoke in the cockpit.
https://drive.google.com/file/d/1aOh...ew?usp=sharing
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  #10  
Old 01-23-2021, 05:59 PM
David Paule David Paule is offline
 
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Location: Boulder, CO
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It might be worth checking the temperature there especially after shut-down on a hot day. The max storage temperature is 70 C or 158 F and I'd bet that will be exceeded.

I like the cheek idea....

Dave
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