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Battery cranking power

 
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dreel(at)cox.net
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PostPosted: Sun Mar 05, 2006 12:27 pm    Post subject: Battery cranking power Reply with quote

Here's a data point on cranking power available from the Panasonic LC-RD1217P battery. OAT 43 degrees, no pre heat. Oil 50 wt break-in oil. Installation: O360A1A, Sky Tec model 149-12LS starter with battery mounted aft of rear baggage compartment in an RV8A. Standard three contactor installation of battery, starter, and contactor on starter. The fully charged battery has had little use & measured 12.8V. What happened was the engine turned over two revolutions and stopped. Subsequently I could just get one revolution at a time just as though it was being hand proped. After 5 or 6 of these, a cylinder fired and I did get the engine started

Initially I thought I needed to redo my installation or switch batteries. Later, I realized that the heavy oil was probably the culprit & once I went to 20W50, performance would likely be more satisfactory. Have others found temperature limits where the cranking power of this battery is barely adequate?

Dave Reel - RV8A


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jeffpoint



Joined: 10 Jan 2006
Posts: 72
Location: MKE

PostPosted: Sun Mar 05, 2006 4:15 pm    Post subject: Battery cranking power Reply with quote

One important data point you're missing- what kind of prop do you have?
The combination of a small battery (like the Panasonic) and a permanent
magnet motor-type starter (like the Skytec) along with a light prop will
cause problems. It sure did for me. The problem is that permanent
magnet starters have a very high current draw (compared to more
expensive, wound field starters) and that a small battery like the
Panasonic may not be able to keep up. Combine that with the low inertia
of a lightweight prop, and you've got problems. Not to mention, this
scenario has been demonstrated to lead to kickbacks, which will damage
the starter.

I went through similar problems with my setup. Same battery and starter
as you, wood prop, O-360 A1A on my RV-6. Starting performance was
always pretty anemic. At about 80 hours it gave up all together, and
inspection revealed that the starter housing was cracked (kickback.) I
solved the problem by upgrading to a permanent magnet starter, which is
expensive and slightly heavier, but draws much less peak current. Now I
can almost get the tail up on starter power alone.

The heavy straight weight oil and cold temps certainly aren't helping,
but the real problem is the starter/battery combination.

There's plenty of discussion about this issue in the archives.

Jeff Point
RV-6
Milwaukee
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Jeff Point
RV-6
Milwaukee WI
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bicyclop(at)pacbell.net
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PostPosted: Sun Mar 05, 2006 7:27 pm    Post subject: Battery cranking power Reply with quote

Another missing data point is size of the battery cables running from
aft of the baggage compartment. If they're undersized, they'll drag the
available voltage at the starter down.

Pax,

Ed Holyoke

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dreel(at)cox.net
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PostPosted: Mon Mar 06, 2006 7:54 am    Post subject: Battery cranking power Reply with quote

Thanks for the pointers Jeff. I'll look into the permanent magnet issue. The prop is a Hartzell constant speed.

The wire is 2awg Ed.

Do not archive

Dave Reel - RV8A


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martin(at)gbonline.com
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PostPosted: Mon Mar 06, 2006 5:29 pm    Post subject: Battery cranking power Reply with quote

ED and listers,
I experienced a similar problem on my RV8 5 years ago when I finished my
RV8. I finally realized that I had grounded the battery to the airframe in
the back of the fuselage. This does not work. First their is to much
resistance and second, grounding to the rear fuselage creates and electronic
"Ground Loop" which creates all kinds of electrical and electronic problems.
The proper way is to route both the power cable and a similar size ground
cable parallel to each other (not twisted) ground cable to a central point
at the firewall and the power cable to the central power buss.
Hope this helps , it sure worked wonders for me.
Dick Martin
RV8 N233M
the fast one
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bicyclop(at)pacbell.net
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PostPosted: Mon Mar 06, 2006 9:29 pm    Post subject: Battery cranking power Reply with quote

Sounds big enough to me.

Ed

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jeffpoint



Joined: 10 Jan 2006
Posts: 72
Location: MKE

PostPosted: Tue Mar 07, 2006 5:02 am    Post subject: Battery cranking power Reply with quote

As an experiement, try swapping out your starter some time with a
different one, like an old Prestolite or the like. I think you'll find
that, while it's heavy and slower turning, that it turns the engine over
with your current battery with no problems.

Jeff Point
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Jeff Point
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Milwaukee WI
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skylor4(at)yahoo.com
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PostPosted: Tue Mar 07, 2006 7:38 am    Post subject: Battery cranking power Reply with quote

One thing that I haven't seen mentioned yet is the
fact that the Panasonic LC-RD1217P has a higher
internal resistance than the Odyssey batteries do.
Panasonic literature states 12 miliohms at 77 degrees,
while the Odyssey PC680 is 7 miliohms. This may not
sound like much, but during high current draw when
cranking the engine, this can make a considerable
difference in voltage drop at the battery.

Skylor
RV-8 Under Construction
Firewall Forward...


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