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Kellym
Joined: 10 Jan 2006
Posts: 1705
Location: Sun Lakes AZ
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 Posted: Sun Sep 04, 2011 2:05 pm Post subject: Initial experience with dual Odyssey PC680s powering RV-10 |
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The one factor you haven't mentioned is which starter you chose. Some
light weight starters require a MUCH larger current draw than
others(over 300 amps vs less than 200). If they don't get the full
current the starter wants, it won't have the torque to move the piston
past TDC.
On 9/4/2011 2:27 PM, Dave Saylor wrote:
| Quote: |
Bill,
You might try moving one of the 680s closer to the firewall and tie
into the large no. 2 cable up there. Also, triple check all the
connections to make sure they're really solid.
Are you using a ground cable or strap back from the engine case to the airframe?
FWIW, I grounded my aft-mounted 925 to the vertical edge of the
baggage floor that supports the tailcone closeout. I used a braided
grounding strap. Works great.
Dave Saylor
AirCrafters
140 Aviation Way
Watsonville, CA 95076
831-722-9141 Shop
831-750-0284 Cell
On Sun, Sep 4, 2011 at 12:58 PM, Bill Watson<Mauledriver(at)nc.rr.com> wrote:
>
>
> 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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_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD |
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Mauledriver(at)nc.rr.com
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| Posted: Tue Sep 06, 2011 8:08 am Post subject: Initial experience with dual Odyssey PC680s powering RV-10 |
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I seem to be overlooking the obvious, or as a old Spanish saying goes, "looking for the burro while sitting on the burro".
It seems that I have a bad battery. It's amazing how easy it is to talk one's self into overlooking the obvious. It helps to have the right tools but you actually have to use them and believe them.
Anyway, after fully charging my starter battery I was unable to get any better readings than 8.5 volts with a 200amp load at the starter, 9.0 volts at the battery.
Going back to a battery I had pulled, I get 9 volts with a 200 amp load at the starter, 10 volts at the battery. And it had not been topped off.
That seems like some pretty straght forward findings and yet I'm still doubting it. Will have to try a couple of starts and check everything again.
In any case, that HF "carbon pile" battery tester is looking like a very useful piece of equipment in maintaining an all electric, 2 battery aircraft.
Bill "remaining high up on the learning curve" Watson
On 9/6/2011 9:54 AM, Bill Watson wrote: [quote] (my original post seems to have been blank - pardon if this is a re-post with some additional info)
Some data:
Using the HF Battery Load Tester with a 200amps load applied at the disconnected starter lead, I got 7.5 volts on one battery, 8 volts with both batteries. That is short of the 9 volts you suggested I should get,
I used a 6" 8awg lead for the ground attached to one of the starter's mounting bolts.
I saw a similar results when I went to a ground block directly on the firewall (I think this block has a 8awg line running back to the batteries in addition to it's airframe connection).
My plan is to repeat this test tomorrow after re-charging the batteries. I'll also test the battery directly. Assuming I get the same result, and the battery is good, it appears that I have some deficiency in either the ground or power circut for the starter.
I'll try to use the tester to work my way from the starter back thru the power circuit and the ground connections.
Some more data:
After charging overnight and working my way back towards the battery, I hooked up the tester to the battery side of the starter solenoid and the ground stud on the firewall. I got 8.5 volts going to 8.0 volts after 15 seconds with a 200 amp load.
Then I took the tester directly to the battery - 8.5 volts with a 200amp load (??!!). Bad Battery? I think not, so...
Yesterday, I went out an bought Schumacher charger at Walmart. I had been using another 'maintainer' type charger (I'll get the brand and specs later). With all this electrical work, I felt like I needed something with more options like fast/slow charge. I charged up some older batteries including my old 680s. One battery was clearly bad per the tester and wouldn't take a charge. The other one seemed good. And after a full charge, it tested 10 volts (at) 200amps for 15 seconds. That's more than I was getting with my 'fully charged' new battery.
I think I have some charging issues. I suspect at this point that the 'maintainer' type charger is not fully charging my 2 batteries for some reason. That combined with the fact that almost every flight is followed by much battery draining panel work followed by charging.
So, right now I'm using the new charger on the batteries in the aircraft. I suspect when finished, I'll be getting 10 volts (at)200 amps at the terminals, and close to that at the starter.
Will report later.
Bill "transitioning from building to operating mode" Watson
On 9/4/2011 5:53 PM, Robert L. Nuckolls, III wrote: | Quote: | At 03:28 PM 9/4/2011, you wrote:
| Quote: | --> AeroElectric-List message posted by: "Richard E. Tasker" <retasker(at)optonline.net> (retasker(at)optonline.net)
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 |
Absolutely. These batteries have a DEMONSTRATED ability
to do the job for which you've installed them. You need
DATA on where energy from the batteries is being lost
before it reaches the starter motor.
Unfortunately, the current draw of a starter motor
is so wiggly, it's difficult to get meaningful measurements
on a starter while standing behind a swinging prop. Suggest
you acquire the use of a battery load tester like this
Harbor Freight product
--
Unhook the starter feed wire at the starter and put
a bolt through the lug end with a nut to get a good
grip. Clip the red test lead to the bolt (you don't
want an imperfect connection to burn your lug).
Similarly, fabricate a short piece of 4AWG with
a lug-bolt assembly on one end and a lug on the
other suitable for grounding to your engine . . .
preferably the same bolt that attaches the starter.
The voltmeter on this tester reads voltage
right at the test clips . . . so you don't need
to worry about votlage drop in the long fat-wires.
Simulate an engine cranking event while cranking
the load tester up to 200A . . . you should have
9V+
Use the same tester to load each battery until
the voltage drops to 9V. Each battery should
be capable of delivering 9V at 400 amps or more.
Bob . . .
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