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3A starter fuse blows repeatedly

Pilot1973

Member
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, I?m still having the same issue. It sometimes blows when cold, sometimes when hot, and generally when the starter switch is released.

I?d appreciate any guidance.

Darren
 
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.
 
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.
 
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...
 
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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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
 
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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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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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.
 
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.
-
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.
 
There was another thread here last week with a fuel pump fuse blowing during start on a RV12. Ended up being the battery. Seems about right time to check the battery on a 2014 A/C. Have you tried it?

Jay
 
Short circuit tester:
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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We have a winner! See video below. Now the tricky part: replacing the wire(s).

https://youtu.be/RJiA73p-Bdo
 
Starter lock nut loose

I've had a related problem - intermittently blowing starter fuses. Rewired the starter solenoid thinking maybe the 22awg wire chaffed somewhere. No dice. Pulled and tested the solenoid on the bench. 4.5 ohms, which seems fine.

So finally I pulled the PCB and found the retention nut on the starter switch had worked its way loose and was shorting the hot side of the flyback diode to ground via the pins on the spar pin relay switchs' relay.

https://youtu.be/hAfS0tJNPmA
 

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Hope you drop a note to the factory about that. I have the -iS with a different circuit board.. but the same button..

Next time I'm behind my instrument panel I'll give it a drop of Loc-tite and secure it. Easier to prevent that than to track down an electrical gremlin 10 years from now.
 
Yeah will do. Here was my solution: Threadlocker and a zip tie, so if the Threadlocker somehow lets go then the zip tie will keep it from contacting the board.
 

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Blowing starter fuses in Legacy RV-12

My Legacy RV-12 sn #1200105 that was completed in 2010. It has a standard Dynon 180 avionics set up. Recently I started blowing the 3 amp starter fuse. The symptoms have progressed to the point where the Spar Pin light flashes when the Ignition Key is engaged and the prop is turning. After several ignition engagements the 3 amp fuse blows. Have sent info to Van's Tech Support after talking talking to them yesterday.
 
My Legacy RV-12 sn #1200105 that was completed in 2010. It has a standard Dynon 180 avionics set up. Recently I started blowing the 3 amp starter fuse. The symptoms have progressed to the point where the Spar Pin light flashes when the Ignition Key is engaged and the prop is turning. After several ignition engagements the 3 amp fuse blows. Have sent info to Van's Tech Support after talking talking to them yesterday.

know nothing about Rotax or the 12. However, most starters use a contactor to move the large amperage required for starting. A contactor is a solenoid that uses electricity to create a magnetic field (done by sending current through a VERY long copper winding) that moves the two contact points together, allowing big amperage for the starter motor to use. If you are blowing fuses, it is likely that resistance has dropped in the solenoid activation circuit. The winding in the contactor are very thin copper and it can fray if not fully secured (manufacturing flaw). It could also be a loose wiring connection. When the resistance drops, the amount of current drawn also rises and eventually cause a fuse to blow. It could also be a minor shorting that is causing this.

Check wiring with an ohm meter and replace solenoid if it is in spec.
 
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Put a diode across the solenoid coil.

If the fuse is blowing when you release the key, then a diode may help.

(when the magnetic field in the coil collapses and sends a voltage spike in the opposite direction)..

Could be a simple short circuit somewhere between the ignition key and the solenoid -- turning the key sends power to the solenoid and somewhere along that wire, its touching ground and shorting out.. Maybe intermittent if vibration (perhaps from the prop starting to rotate) makes the wire contact ground.
 
The problem has NOT progressed. Coincidently there two unrelated problems.
The spar pin magnetic reed switches work a whole lot better when mounted parallel to the magnet. Many early builders had problems with those switches because they were mounted perpendicular to the magnets. Change the mounting orientation.
Bob Nuckolls drawings call for a 7 amp starter contactor fuse. It should be safe to replace your 3 amp fuse with a 5 amp fuse. Like others have suggested, make sure that there is a diode across the starter contactor coil. The banded end of the diode must be connected to positive.
 
If your battery is getting old that could be the cause.
If the battery voltage dips lower than normal while cranking it can cause a higher than normal amp draw on that circuit.
 
Blowing starter fuses in Legacy RV-12

The problem has progressed to the point where the Spar Pin Light does not light when the either or both of the spar pins are disengaged. The Start key now engages the the starter without pushing on the Spar Pin override. When the Start key is released there is in a flicker of the Red Light (but not every time). I have not blown a starter fuse since this new incarnation of the problem has appeared.
 
I was wrong about the two problems not being related. Relays don't fail often, but check for a defective
spar spin relay. Or maybe there is a foreign object causing a short circuit on the circuit board.
 
Blowing starter fuses in Legacy RV-12

Is there any way to check the DPDT 5A Relay without having to remove the circuit board? I see where the circuit board was removed for a loose retaining nut grounding problem but that looks like a big deal to me. Then assuming the DPDT 5A Relay is the problem then replacing the relay looks like another big deal. I need some encouragement and hand holding to proceed further. Building the Airplane was a great experience and a lot of fun. SB's and fixing things sucks! Bob Kibby N712BK
 
Is there any way to check the DPDT 5A Relay without having to remove the circuit board? I see where the circuit board was removed for a loose retaining nut grounding problem but that looks like a big deal to me. Then assuming the DPDT 5A Relay is the problem then replacing the relay looks like another big deal. I need some encouragement and hand holding to proceed further. Building the Airplane was a great experience and a lot of fun. SB's and fixing things sucks! Bob Kibby N712BK

Unfortunately, on the D-180 version RV-12 there is no easy access to the fwd side of the panel like there is with the later versions (by just removing the pilot side screen) so I would suggest you remove the fwd upper skin so that you can take a good look and see what is going on.

With the way your symptoms have changed, I think a loose anchor nut causing a short is a good possibility.
 
A defective relay is unlikely. It's internals would have to fall apart. More likely is a foreign object like Scott suggested. The relay can be checked with an ohmmeter IF you can get at the terminals. The problem is that the control circuit board has two layers. I can't remember if the relay terminals are easily accessible or not. A foreign object doesn't necessarily have to be big to cause a problem. Even a very short piece of a single strand of wire can cause problems.
 
SAME PROBLEM

I've had a related problem - intermittently blowing starter fuses. Rewired the starter solenoid thinking maybe the 22awg wire chaffed somewhere. No dice. Pulled and tested the solenoid on the bench. 4.5 ohms, which seems fine.

So finally I pulled the PCB and found the retention nut on the starter switch had worked its way loose and was shorting the hot side of the flyback diode to ground via the pins on the spar pin relay switchs' relay.

https://youtu.be/hAfS0tJNPmA

I had the same problem where the nut came off of the key switch and shorted the board. The spar pin warning light flashed and eventually blew the fuse. The problem is that the lock washer was left out during manufacture. The nut backs off and eventually makes its way down, shorting out the PCB. I called Vans support and was told that the switch modules were vender built and to just use a thread sealant. I think this is a bigger problem than Vans is ready to admit. I tightened mine with a wrench then used a sealant on the threads. You would have to unsolder the key switch to install a lock washer. And yes, you must remove the avionics cover to remove the switch module. PITA but I’m back in the air. A new switch module is $360 and you still don’t get a lock washer. My advice: Fix it and be done.
 
I had the same problem where the nut came off of the key switch and shorted the board. The spar pin warning light flashed and eventually blew the fuse. The problem is that the lock washer was left out during manufacture. The nut backs off and eventually makes its way down, shorting out the PCB. I called Vans support and was told that the switch modules were vender built and to just use a thread sealant. I think this is a bigger problem than Vans is ready to admit. I tightened mine with a wrench then used a sealant on the threads. You would have to unsolder the key switch to install a lock washer. And yes, you must remove the avionics cover to remove the switch module. PITA but I’m back in the air. A new switch module is $360 and you still don’t get a lock washer. My advice: Fix it and be done.

The key switch has never had a lock washer. Only the over ride switch has ever had a lock washer.
After a couple of reports of the nut coming loose the assembly process was updated to include the use of thread locker on the key switch nut.
 
Thanks Scott. At least those of us reporting this now know we are not alone here and that others have experienced this same loose key switch nut problem. Somehow I missed the recommendation to add the thread locker and as a result wound up being stranded with a no start issue at a remote location. Not a fun fix for sure.
 
Thanks Scott. At least those of us reporting this now know we are not alone here and that others have experienced this same loose key switch nut problem. Somehow I missed the recommendation to add the thread locker and as a result wound up being stranded with a no start issue at a remote location. Not a fun fix for sure.

Sorry, I guess I wasn’t clear.
The build process that the vendor uses when building the modules was updated to include the use of thread locker.
 
Blowing starter fuses in Legacy RV-12

Scott, don't know what "loose anchor nut" means. Also having trouble understanding the electrical schematic. On the Ignition and Start Module diagram the wiring lines each end with a box,#3, and are colored red or green. There are 4 #3 boxes with no wiring. What is the meaning of the #3 and their color?
 
Blowing starter fuses in Legacy RV-12

Scott, is there a replacement board available if I find that the relay is bad? Is there a vendor for circuit board repaired?
 
Scott, don't know what "loose anchor nut" means. Also having trouble understanding the electrical schematic. On the Ignition and Start Module diagram the wiring lines each end with a box,#3, and are colored red or green. There are 4 #3 boxes with no wiring. What is the meaning of the #3 and their color?

Bob, I think you are looking at the wrong diagram.

Since you said you have a D-180 equipped airplane you would need to use this diagram - https://www.vansaircraft.com/wp-content/uploads/2019/01/D-180-Avionics_03-22-17.pdf

I have attached the relevant portion of the diagram below. Note that the two double dashed lines I circled in red are identifying the two different pcb portions of the switch module (I.E., everything within the boundary of those lines is on or directly connected to that pcb portion of the entire assembly). Don't use this for reference because it will be difficult to read because of the low resolution. Download the diagram using the link I provided.

The anchor nut that has been mentioned is the thin nut that threads onto the key switch to mount the key switch into the panel face of the AV-12 switch module. So when viewing the face of the instrument panel from the pilots seat it is on the back side of the switch module face plate, so it can only be seen by removing the top fwd top skin of the fuselage.
 

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There is no need for a schematic diagram or any electrical knowledge.
Just remove the control board from the plane and take it apart and inspect for any foreign objects like loose nuts or standoffs.
The control board has to be removed anyway if you think that it needs to be repaired.
I did mention a defective relay in a previous post, but that is HIGHLY unlikely.
 
Blowing starter fuses in Legacy RV-12

I removed the control board and found a loose Key Switch nut. The nut had been loose for so long that it had sawed a grove that eliminated the top of the third thread from the panel. Apparently the nut was recently dislodged from this location by Texas turbulence and migrated to the circuit board thereby causing my intermittent problem. Doesn't appear to be any collateral damage. Will reinstall the control board and check it out later this week. Thanks to all for your helpful inputs and encouragement to get on with removal of the control board. Bob Kibby N712BK
 
Blowing starter fuses in Legacy RV-12

Put the Ignition Switch Retaining Nut back in place with lock tite and a Cable Tie backup. Put the Control board in place and hooked up the Fire Wall Forward, Fuselage, and Power Connectors. Turned on Master Switch, Rotated the Spar Pin out of the retainer and did not get a Spar Pin Red Light. Turned Key and the starter engaged and spun the prop. Disappointing, was hoping that getting the retaining nut off the control circuit board would correct my problem. Bob Kibby N712BK
 
As long as the problem is not intermittent, we should be able to figure out what is wrong. Below is a schematic of the spar pin relay circuit. Notice that diode D2 connects to Dynon D-180 EMS pin 9. The D-180 monitors the status of the magnetic reed switches and should alarm if either switch is open. Does the D-180 give an alarm if either or both of the magnetic pins are out of position?
 

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Only opened the left spar pin. Will also try left and both tomorrow. Thanks for the schematic. I really have trouble with figuring anything out from the Van's schematic. Bob Kibby
 
Just re-read your last post and reviewed your schematic. I don't have the Dynon-180 installed! I'll install the D-180 this morning and retry. Bob Kibby
 
Installed D-180 and have all electrical connectors connected.

Both spar pins in: Spar Pin light flashes when Master is turned on or off. Starter engages when key is turned on.

Left spar pin out: Spar Pin light flashes when Master is turned on or off. Starter engages when key is turned on.

Right spar pin out: Spar Pin light flashes when Master is turned on or off. Starter engages when key is turned on.

Both spar pins out: Spar Pin Light is on and bright red when Master is on and red light goes out when Master is off. Starter does not engage when Master is on and key is turned on

Was hoping that everything would be OK when I installed the D-180. At least I did a proper response with both spar pins out which should isolate the problem for those that can understand electronics.

Bob Kibby
 
Your results appear as if the spar pin microswitches are wired in parallel instead of in series with each other. With the master switch off, if you can remove both spar pins and clip an ohm meter or continuity tester across the terminals of one of the microswitches, then manually actuate each microswitch individually. If the meter or tester shows continuity when you activate each switch, they’re wired in parallel instead of in series.
 
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Good catch Bob Y. I had assumed that the spar pin switches were wired
correctly because the plane has been flying for many years.
If the switches are wired in parallel instead of series, all of the test results make sense.
So Bob Kibby, all you have to do is wire the magnetic reed switches in series per the diagram in post
#41 above and your problem should be solved. And thank Bob Y.
To satisfy my curiosity, after correcting the wiring, watch the D-180 for
any indication when the spar pins are moved out of position.
 
I have been flying my RV-12 for 12 years and have checked the Spar Pin operation at every Condition Inspection and demonstrated the spar pin safety feature to many pilots that have looked at my airplane over the years. I really believe that the wiring is correct. Is there any other way with shorted wires, ect that could explain what is going on. Bob Kibby
 
I'll do the test that Bob Y suggested tomorrow. Remember that all this started when I started blowing starter fuses. How could I have started the engine for the last 12 years if the wiring was wrong? Puzzle me this Batman?
 
Bob, you are correct in that even if the switches were wired in parallel that would not cause any problem short of not getting an indication if only one of the spar pins was not fully seated. Your reported test results just pointed to that as being how they were wired. I’m having difficulty developing an alternate scenario where they could act that way.
 
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