retasker(at)optonline.net
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 Posted: Sun Sep 04, 2011 12:34 pm Post subject: Initial experience with dual Odyssey PC680s powering RV-10 |
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Have you measured the voltage at the starter and an adjacent ground point and compared it to the same measurement at the battery terminals, both while cranking?
Possibly you have a bad or loose connection somewhere that is contributing to your hard cranking.
Certainly worth a try (if you haven't already done this) to avoid replacing the battery and battery holder.
Dick Tasker
Bill Watson wrote:
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I've just flown the first dozen hours with my new RV-10 and am a bit disappointed with one design decision, that is, the use of dual PC680s. When starting with a single new PC680, I don't seem to
have the cranking power I'd like to have.
Unless the battery is fully charged, it just barely turns over the first compression stroke on a cold engine (IO-540). If it does turn over, it cranks fine but sometimes it takes several tries to
get over the first compression stroke.
At the same time, my EAA Tech Counselor has been working on a rear battery for a Citabria. He used the certified version of the 680 but found the same situation. Now he is in the process of
changing it out for the same reason.
If I crossfeed the 2 batteries, I get better cranking performance but again, unless both batteries are fully charged, I'm likely to cause a re-boot of the 3 GRT HX screens powered by the 2nd battery.
At this point, I'm thinking I need to change my battery configuration to include 1 PC925 for cranking. But doing so will lose the periodic interchange capability I was after.
I'd be interested in comments or suggestions. If you are planning something similar, I'd say "beware" at this point. Here's some more background....
My RV-10 has the batteries installed behind the cargo area with (1) 2AWG cable feeding the starter from 1 or both batteries. A 2nd 8AWG cable carries the rest of the power forward. The batteries
are both grounded close to where they are located and no separate ground cable is used. I followed Bob's grounding advice pretty closely.
What I was after with the Z-14 was the ability to run most of the panel on one battery without the engine running. And then to have a second battery capable of most engine starts. Linking the
batteries together providing an option for tough starts or partially discharged batteries.
Why run the panel? I've been in a couple of situations where I've had to compromise between running the avionics for extended periods or conserving power for a start.
What I also envisioned was a panel with as few switches as possible (Z-14 req'd switches not withstanding) and as few breakers as possible. So it is a fuse-centric design, with 4 breakers and no
avionics master or separate on/off switches for any of the panel stuff. I really like the result. However, I've already found myself having to crossfeed the batteries for a start which caused me
to lose my engine instrumentation on the GRT HX display while it re-booted.
So, I really like the design except for not having enough cranking juice on a single battery. I'm thinking the next size Odyssey on the starter will fix it but cost me 10.5 lbs (in a good W&B
spot), interchangeability, and the need to design a new battery mount.
Bill "really loving the new '10" Watson
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