Hello LML gang,

We want to thank everyone who provided their experience and advice regarding the placement of batteries on the engine side of firewalls.  Based on feedback received on and off the list, we decided to go forward with two PC680s on the hot side of the firewall.  The PC680s will have metal jackets and we’ll cover the battery holders with Zetex fire blanket.  If that proves too warm we’ll duct cool air to them.  This helps our c.g. ,gets us nice short lines to the starter (6”), and looks a bit safer than in the cabin (eg. battery short, fire, smoke etc.).

We also appreciate the advice from some to move our hydraulic pump behind our seats where it’s much easier to work on.  We’ve already taken up that space, however, with a removable air conditioning unit  -- a high priority when it looked like we were going to be sentenced to life in Houston to the end…   Just one of the tradeoffs.  Fortunately, we have the removable cargo compartment windows which help enormously with maintenance in the back – though Allyson will continue to specialize in maintenance of systems in the tail.

Thanks again,

Valin & Allyson Thorn

Legacy Project

Boulder, Colorado

Hey LML gang,

We’re planning on installing our two Odyssey PC680 AGM 12V batteries (connected in series for 28 V system) on our Legacy’s firewall for airplane center of gravity control.  This will help our cg because we have a light weight MT prop, a removable electric air conditioner behind the seats, and our hydraulic pump in the original design location behind the bulkhead in the tail.

We’ve seen quite a few airplanes at Oshkosh with batteries on their firewall.  But, as we finalize our firewall layout we couldn’t help but wonder if there are any issues with the thermal environment on the firewall – especially when we’re looking at one of the batteries being downstream of the airflow going through the oil cooler.

Has anyone measured the temperatures around the firewall in flight?  Has anyone had any issues with their batteries installed on the firewall?

Odyssey’s stated operating temperature range for their PC680 batteries , without a metal jacket, is -40°F (-40°C) to 113°F (45°C)and with a metal jacket is -40°F (-40°C) to 176°F (80°C).

Mounting them up high on the firewall is likely the coolest.  And avoiding the oil cooler air flow on the left side would be cooler.  We can get them both on the right side away from the oil cooler but would like to avoid getting the airplane’s Y/lateral cg too far from the middle with other heavy things already on the right side.  We’d also prefer to not install them at the top of the firewall (more like middle) so we don’t have to have a remote oil filter setup and to free that top space for other components.  Installing a battery up high on the left side requires a remote oil filter setup because of interference for replacement of the oil filter.

Without data and only intuition it seems that the metal jacket PC680’s with max op temps of 176 deg F should be okay.  Would appreciate hearing of people’s flight experiences, firewall temperatures, and comments/advice related to a battery installations on firewalls.

Thanks,

Valin & Allyson Thorn

Legacy Project

Boulder, Colorado