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  #1  
Old 06-02-2018, 10:14 AM
Pilot1973 Pilot1973 is offline
 
Join Date: Feb 2015
Location: Rockville, MD
Posts: 6
Default 3A starter fuse blows repeatedly

I have a 2014 RV-12 S-LSA that has developed an issue where it is blowing 3A starter fuses. I originally thought it was a starter solenoid issue, but after replacing the solenoid, Iím still having the same issue. It sometimes blows when cold, sometimes when hot, and generally when the starter switch is released.

Iíd appreciate any guidance.

Darren
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  #2  
Old 06-02-2018, 11:06 AM
Tom Martin Tom Martin is online now
 
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Location: Ontario, Canada
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You should go with a stronger fuse, 5 to 7amps, if the wire size will accommodate that current. If not then replace the wire with a larger size and fuse. I am sure that someone will step in with the correct phrasing.
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  #3  
Old 06-02-2018, 11:45 AM
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Lenny Iszak Lenny Iszak is offline
 
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Location: Palm City, FL
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Starter solenoids pull around 5 amps. Use a 7.5A fuse instead. They are much stronger than a master solenoid, since they are switching hundreds of amps.

Besides going with a higher sized fuse make sure the wire you are protecting is sized accordingly.
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  #4  
Old 06-02-2018, 12:17 PM
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Piper J3 Piper J3 is offline
 
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Quote:
Originally Posted by Tom Martin View Post
You should go with a stronger fuse, 5 to 7amps, if the wire size will accommodate that current. If not then replace the wire with a larger size and fuse. I am sure that someone will step in with the correct phrasing.
.

His airplane is S-LSA, and as such, he can't deviate or make changes...
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Jim Stricker
Hinckley, Ohio
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PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC
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RV-12 E-LSA #120058 AWC Jul 2012 - Bought Flying Oct 2015 with 48TT - Hobbs now 406

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  #5  
Old 06-02-2018, 12:37 PM
Mich48041 Mich48041 is offline
 
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Location: Riley TWP MI
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Hundreds of RV-12s are flying with 3 amp start fuses. If I remember right, originally that fuse was 2 amp but was upped to 3 amp when the 2 amp occasionally blew.
Try disconnecting the small orange wire from the start contactor. Then cycle the start key switch several times to see if the fuse still blows. If not, then temporarily replace the 3 amp fuse with a 1 amp and cycle the key switch several more times. If the fuse still does not blow, then chances are that there is nothing wrong with the aircraft wiring.
Is there a diode connected to the start contactor coil? If not, I would install one to protect the start switch contacts from arcing. Connect banded end of diode to orange wire. Connect other end of diode to ground.
The ignition modules are on the same circuit. Follow that wire to the ignition module to make sure it is not shorting to ground.
If you can not find anything wrong, use a 5 amp fuse. I would not go higher than that.
EDIT:
I read Piper J3's post after posting the above.
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Last edited by Mich48041 : 06-02-2018 at 12:44 PM. Reason: Added last sentence
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  #6  
Old 06-02-2018, 08:04 PM
Pilot1973 Pilot1973 is offline
 
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Location: Rockville, MD
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Thanks Jim, Joe, and Mike.

Fuses are sized to prevent fires or damage to components. Replacing one with an oversized fuse is unwise at best.

Disconnecting the lead and checking the operation and looking for chafing or a short are good suggestions. Thanks! I considered adding a diode, but wanted to ask the audience for other suggestions first considering that itís been working fine without one for four years...

Darren
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  #7  
Old 06-02-2018, 08:26 PM
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Tony_T Tony_T is offline
 
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Quote:
Originally Posted by Pilot1973 View Post
Thanks Jim, Joe, and Mike.

Fuses are sized to prevent fires or damage to components. Replacing one with an oversized fuse is unwise at best.

Disconnecting the lead and checking the operation and looking for chafing or a short are good suggestions. Thanks! I considered adding a diode, but wanted to ask the audience for other suggestions first considering that it’s been working fine without one for four years...

Darren
The D-180 airplanes had a diode for the starter switch contacts but it is out of sight located in the control board. The SkyView airplanes are supposed to have a diode at the starter solenoid. See plans page 45A-08; the 45A section is available on Van's website if you don't have it. Since your plane is a SLSA it must have the SkyView avionics and there should be a diode installed on the starter solenoid and it will be plainly visible. It is in blue heat shrink and attached to the right hand mounting bolt of the starter solenoid.

You should be able to easily confirm if the diode is present. Like Joe Gores says above, the diode protects the starter switch from arcing and, if I understand how it works, it shunts the back current generated by the collapsing magnetic field in the solenoid to ground when the ignition switch is released. That correlates with your original post. A second possibility is the diode has failed.
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Last edited by Tony_T : 06-02-2018 at 10:25 PM.
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  #8  
Old 06-02-2018, 08:28 PM
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Mike S Mike S is offline
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Location: Dayton Airpark, NV A34
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Quote:
Originally Posted by Pilot1973 View Post
considering that it’s been working fine without one for four years...

Darren
OK, data here leads to questions -------were there any changes made to the plane just prior to the start of the problem?? Or component failures that required replacement ?? or anything else you can think of??

Something new going on after four good years of operation raises a red flag to me.........

Have you checked for corrosion or loose connections on both the hot side, and ground ?? Check for looseness in crimped connections and loose push on connectors. All of these can raise resistance, and that will eat fuses.
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Last edited by Mike S : 06-02-2018 at 08:32 PM.
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  #9  
Old 06-03-2018, 06:09 AM
blythet blythet is offline
 
Join Date: Sep 2011
Location: selma, NC
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Default Blowing Start Fuse

Had exactly the same issue several years age. Finally found one of the soft start wires had slipped out of it's connector at the ignition module and was grounding to adjacent bracket. It was well hidden and tough to see.
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  #10  
Old 06-03-2018, 07:24 AM
Mich48041 Mich48041 is offline
 
Join Date: Apr 2008
Location: Riley TWP MI
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Default Troubleshooting ideas

Short circuit tester:
Method 1.
Cut apart a blown fuse to get the two spade connectors. Solder a wire about one meter long to each spade. Plug the spades into the RV-12 fuse holder. Connect the other ends of the two wires to a test light. Disconnect the orange wire from the start contactor. Turn on master switch. Have a helper hold the key switch in the start position. (Make sure starter is disabled.)
Briefly touch the orange wire to ground to make sure that the test light works. Now while watching the test light, wiggle the full length of the orange wire and also the purple ignition wire. If the test light illuminates, there is a short circuit to ground.
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Method 2.
Leave master switch turned off. Disconnect orange wire from start contactor. Connect a test light between battery positive and the orange wire. Briefly touch orange wire to ground to make sure that test light works. Wiggle orange wire and purple ignition wire. If test light illuminates, there is a short circuit to ground.
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Method 2 is easier but does not test upstream of the start switch, but the problem is most likely firewall forward.
If purchasing a test light, make sure it does NOT have an internal battery. The test light will be powered by aircraft battery.
I have never used this testing method on the RV-12 start circuit. Depending on the resistance of the ignition start module, the test light might illuminate dimly all of the time, then get brighter if a wire shorts out.
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