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  #11  
Old 05-20-2018, 05:06 AM
DickB DickB is offline
 
Join Date: Nov 2015
Location: Williamsburg, VA
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We had the same problem .. first fuse blew immediately after takeoff although cranking seemed to be fine. Everything we checked seemed to be ok including the battery voltage with the pump on. After a few blown fuses, we finally discovered it was actually the Odyssey battery which was delivered with the kit and only about 6 months old. Replaced the battery and have not had a recurrence for the past 2 years. Not sure what the battery problem was unless it was an intermittent internal short causing the voltage to drop.
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  #12  
Old 05-20-2018, 09:14 AM
hthaman hthaman is offline
 
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You are right Dick, tested battery by advanced auto store and CCA value came out for 33 ( rated 170). New battery is same PC680 ? I heared there is a lighter battery available now ??
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  #13  
Old 05-20-2018, 01:36 PM
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Phantom30 Phantom30 is online now
 
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Quote:
Originally Posted by hthaman View Post
You are right Dick, tested battery by advanced auto store and CCA value came out for 33 ( rated 170). New battery is same PC680 ? I heared there is a lighter battery available now ??
EarthX LiPi battery (pretty much a drop in replacement. Save somewhere around 10 lbs. Your engine will crank faster/better. They advertise here on this site.
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  #14  
Old 05-20-2018, 02:08 PM
Mich48041 Mich48041 is offline
 
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Location: Riley TWP MI
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Electrical loads that have a switching power supply will draw less current as the voltage goes up and will draw more current as the voltage goes down. Examples are modern avionics that are designed to operate on 10 to 30 volts. I have read about a strobe switch that got hot, even though the strobe kept on working. Evidently that strobe has a switching power supply. When the defective switch dropped voltage, the strobe compensated by drawing more current, which made the switch even hotter.
It seems unlikely that a fuel pump would have a switching power supply. I conducted an experiment with a spare Facet 40105 fuel pump. I ran it with a 12 volt battery and measured the current at about 3/4 of an amp. Then I switched to a 6 volt battery. The pump still made noise but it quit pumping. The current dropped to about 1/2 amp. The 3 amp fuse in series with the pump never blew. I know the experiment did not duplicate the conditions in an aircraft. But it seems to me that the fuel pump does not draw more current when the voltage drops. Maybe the avionics cooling fans, that are on the same circuit, caused the fuse to blow. This is a good example of why each electrical load should have its own fuse. A discrete fuse for each item would make troubleshooting much easier. An even more important reason to have a separate fuse for each load is to prevent a bad component that blows a fuse from disabling an unrelated component.
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  #15  
Old 05-20-2018, 02:15 PM
Dave12 Dave12 is offline
 
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Good thought food Joe.
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  #16  
Old 05-20-2018, 05:09 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by Mich48041 View Post
I know the experiment did not duplicate the conditions in an aircraft. But it seems to me that the fuel pump does not draw more current when the voltage drops.
Testing a pump with no fluid load or back pressure?.... your right, it is no where close to a valid test.

The little cooling fans draw just about nothing for power. They would have a very insignificant influence on current draw with a dip in voltage.

If you want to do a real test, disconnect the fans and try starting your engine with an under charged battery and let us know what happens.
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  #17  
Old 05-20-2018, 05:52 PM
Mich48041 Mich48041 is offline
 
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The pump was pumping gasoline, albeit out of a can and right back in. You are right, simulating the conditions with a weak battery would be a better test.
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  #18  
Old 05-22-2018, 07:01 AM
Mich48041 Mich48041 is offline
 
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hthaman, did a new battery cure the fuel pump fuse blowing problem?
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  #19  
Old 05-22-2018, 05:23 PM
hthaman hthaman is offline
 
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Quote:
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hthaman, did a new battery cure the fuel pump fuse blowing problem?

I come to know tomorrow.
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  #20  
Old 05-23-2018, 07:07 PM
Mich48041 Mich48041 is offline
 
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I conducted an experiment today on my RV-12. Not wanting to ruin the PC680 aircraft battery, I disconnected it. In its place, I used the riding lawn mower battery connected with jumper cables. I thought that the lawn mower battery might have trouble cranking the Rotax 912ULS, but it cranked just fine. I left the ignition switches turned off so that the engine would not actually start. I turned on all electrical loads, including landing light, to run the battery down. I periodically cranked the engine as the battery slowly ran down. It took an hour and a half for that cheap $35 lawn mower battery to drop its voltage down to 11.5 volts. The engine still cranked, albeit noticeably slower. The fuel pump fuse never did blow. I was not able to duplicate the symptoms reported by others. Perhaps there is some magic voltage that causes the fuse to blow and I never happened to crank the engine at that particular voltage. In my airplane, the fuel pump is the only load on that 5 amp fuse.
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