What John wrote below helps a lot to understand the relationship of
battery & generator. The problem I've had recently has not related
to running enough electrical items in flight, rather, it has been
battery capacity for cold starts: e.g. when my local A&P ran a bunch
of "test starts," such as when he was adjusting the pull-starter he
tried it out a bunch of times, or when he cleaned the spark plugs and
was testing whether that smoothed-out how the engine was running.
Then when I went to fly next, there was not enough power to start
up. Yesterday, he had to give it a "jump start," but after I flew
45 min. to my destination, did 3-4 starts & run-ups there for the
prop-balancing guy, and then it sat for 2-3 hrs. but still started
fine for me to fly home.
John (et al.), can you please address battery capacity for cold
starts? Is it correct that a Concorde 35 will be better for this
purpose than a 25? The A&P wants me to get a 35 (and, Hartmut: he
says a field approval is no problem, and he'll measure the box for
fit, before buying it.) Is a 35 better for my purposes than a 25?
Other than the few lbs. extra weight, am I asking for any kind of
additional problems if I get the 35? My 414-C has a C-85 and a
generator, not an alternator.
Linda
N3437H (Sky Sprite)
L.A.
1a. Re: batteries
Posted by: "John Cooper" [email protected]
Date: Wed Jun 16, 2010 6:16 am ((PDT))
On 6/14/2010 7:31 PM, Todd Fischer wrote:
> Reading the Univair memo it sounded like the older generators just
> couldn't handle charging the larger batteries and only approved the
> RG25 batteries.
>
>
This is a misconception. The larger battery has more capacity, so it
will take longer to discharge, as well as longer to recharge, but,
unless you continually discharge it, which means your constant
electrical load exceeds the generator capacity, it will remain charged
the same as a smaller battery. OTOH, if you are exceeding the capacity
of the generator on a regular basis, the smaller battery will go flat
faster.
If the RG-35 battery is in good shape, and you charge it up (once), and
you do not exceed the capacity of the generator with your electrical
load, then the battery will work fine.
As an aside, the constant load on the electrical system should not
exceed 80% of the generator capacity. Constant load includes comm
recievers, nav radios, transponders, nav lights, etc.; everything that
is not intermittent, e.g. landing lights, flap motors, gear motors, comm
transmitters, etc.
-- John Cooper
Skyport East
www.skyportservices.net
