Mike Wills used the 2 motor cycle battery trick for the RV4.

 The situation is you use both batteries for starting
 and then, after a short while for charging purposes, you switch
 one off for flying.

 The other is kept in reserve in case of alternator or battery
 failures. This probably puts a glitch on the main power bus when the
 back up battery is switch in or out.

 I will add a choke and large capacitor on the main bus to smooth
 the glitch.

 Paul


 Just a suggestion,

 Look into Aeroelectric Connection ---Robert Nucholls. Google for his
 website. He is an aircraft electric Maven, involved with electronic
 design for major manufacturers.

 He has a constantly updated and updatable book which goes into most of
 the concepts and problems of aircraft electrical systems. It includes a
 multitude of schematics (circuit diagrams) ranging from the ridiculous
 to the sublime, depending on what your desires are. His website also has
 a plethora of references as well as blogs, bulletin boards etc.... easy
 to get lost in.

 A definitely recommended and perhaps required book.

 Using an engine that is totally electrically dependent behooves us to be
 more sophisticated in our electrical approach---- unless we have some
 glider training.

 Rich

 Does he talk about chokes on the main avionics buss?

 Two of these fit Mike's battery box. I am still not sure these
 are the one's he used as the batteries where missing when I picked
 up the airplane.

 There are a bunch of equivalents out there yet to be researched.


 Paul Lamar


More ideas from Nuckolls:

If you don't use a flooded acid battery, you don't need a battery box per se. Look for AGM, VRLA, or starved lead acid..  They are pretty common in motorcycle sizes.  Internal fiberglass mats keep the lead plates separated and wet with electrolyte, but there isn't enough acid to make a spill.  So, you just need a rack or strapping system to hold te battery to the structure. Good for 10 g's - crash standard.

There are good strategies for managing two batteries in a system. The first thing is you need active warning of a charging system failure. That way you can avoid nasty surprises.


Matt-

Thanks for the reminder Matt. A good old ammeter will supply that.
I have an Audio Flight Avionics AV8. I think it monitors voltage
with an alarm but I am not sure as I don't have the manual yet.

Here is some info on Yuasa batteries. These will fit or can be made to fit
the current battery mounting bracket. They seem to have a better power
to weight ratio than the half dozen other brands on the market.
I have not figured out the cost situation yet.

The Westco fits the battery mount best but it is too high and
heavy for 2 battery use.

Paul Lamar