RV-8 aft battery box for 2 EarthX900-VNT

[dmn056]

I've modified my F-877A-1 battery tray to accept two EarthX 900-VNT batteries, side by side, with a contactor for each. I checked the loads, and it's well over-strength and quite stiff.



The extra pieces are cut from the spare angles in the fuselage kit, plus a floor of 0.032" 2024-T3. Was able to cut the F-877C battery hold down in half, with just enough length to span the EarthX batteries.



Structure is assembled with MS20426AD4 solid rivets. For securing the hold-down bolts, had to use MS21051L4 single lug plate nuts on underside of battery box and trim the corners of the adjacent angles for clearance.



The assembly installs to the baggage ribs using the same fastener locations as for the standard battery tray. The centre two holes use AN509-10R9 screws, and the four forward and aft fasteners are replaced with MS27039-1-11 pan head screws. The spanwise angle flanges are a bit light on edge distance for the pan head screws, but all screw loads except tension will be carried by the original F-877A-1 battery tray.

 

[bmellis11]

Nice work. I need something like this for my -8. This is very helpful. Thanks for posting.

 

[Dougnabbit]

Really nice job!

 

[Bob Redman]

Good one Dan.

Bob Redman

 

[Jonnyb]

To ask a dumb question, why the 2 batteries?

 

[dmn056]

To ask a dumb question, why the 2 batteries?

No such thing as a dumb question.

Because I'm installing a SDS EFI/EI system for my engine, and I want a very high degree of redundancy. I want to be sure that battery storage capacity is not the limiting factor on keeping the engine operating. Using two ETX900 batteries gives better than 25Ah of usable capacity.

 

[2theskyy]

No such thing as a dumb question.

Because I'm installing a SDS EFI/EI system for my engine, and I want a very high degree of redundancy. I want to be sure that battery storage capacity is not the limiting factor on keeping the engine operating. Using two ETX900 batteries gives better than 25Ah of usable capacity.

What’s your Ah usage for the SDS only, the SDS with your avionics?
Since the 2 batteries will be on separate busses for redundancy. You’ll have two 2awg cables running the length or relay/switch near batteries?
I’d like to run the SDS someday. I’d planned on it originally but ran into snags.

 

[Carl Froehlich]

No such thing as a dumb question.

Because I'm installing a SDS EFI/EI system for my engine, and I want a very high degree of redundancy. I want to be sure that battery storage capacity is not the limiting factor on keeping the engine operating. Using two ETX900 batteries gives better than 25Ah of usable capacity.

Dan,

Good approach.

For your electrically dependent engine I suggest you get power to it outside the master solenoids. Here adding two to four 30 amp relays provides for redundate backup modes. The relays would be mounted at the batteries, between each battery and your engine buss(s). Several options on how to design for operation. The main point however is when you have smoke in the cabin you retain your immediate action of opening both master solenoids - this mitigates the more severe risks. The secondary point is that you create modes of operation if a master solenoid fails (the solenoid itself, the master switch or any associated wiring).

Once you make the leap to a two battery ship you open many doors to design in options to reduce the risk of engine loss and/or a dark panel in IFR.

Carl

 

[dmn056]

What’s your Ah usage for the SDS only, the SDS with your avionics?
Since the 2 batteries will be on separate busses for redundancy. You’ll have two 2awg cables running the length or relay/switch near batteries?
I’d like to run the SDS someday. I’d planned on it originally but ran into snags.

The SDS system in minimum power cruise mode will use about 7A. The SDS system plus VFR avionics in minimum power cruise mode will use about 18A.

I have two contactors located beside the batteries, using the standard mount points on the Van's F-877A-1 battery tray. This means I only run one 2AWG cable forward from the battery location.

However, as Carl suggested above, I'm powering the SDS EFI/EI system outside the contactors, running two 10AWG wires through 20A ANL fuses forward to the EFI/EI bus, allowing me to power off the entire aircraft electrical system while keeping the engine running.

 

[2theskyy]

The SDS system in minimum power cruise mode will use about 7A. The SDS system plus VFR avionics in minimum power cruise mode will use about 18A.

I have two contactors located beside the batteries, using the standard mount points on the Van's F-877A-1 battery tray. This means I only run one 2AWG cable forward from the battery location.

However, as Carl suggested above, I'm powering the SDS EFI/EI system outside the contactors, running two 10AWG wires through 20A ANL fuses forward to the EFI/EI bus, allowing me to power off the entire aircraft electrical system while keeping the engine running.

I had just began designing the electrical and had used the cirrus system to get thinking. That’s as far as I got before going a different route until later.

Thank you