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G3X Shunt Signal Fuse

tgmillso

Well Known Member
Sponsor
Hi All,

From the G3X shunt you are supposed to have the signal wires running back to the GEA24 fused to 1A. I tried this using a typical glass bussmann fuse in a screw together inline fuse holder, but I seem to be getting erratic sensor readings. I took it apart and put some tefgel on the terminals, and this only made things worse. Is there a better way of fusing these wires? I was thinking a fusible link soldered in place, but this wire would be so **** small it would be ridiculous. I'm guessing I'd just have to peel a few wires out of an existing wire to make the link out of:
https://www.powerstream.com/wire-fusing-currents.htm
Alternatively I was thinking a mini blade fuse holder with a 1A fuse, but I just didn't want to encounter the same problems I am seeing with the glass bussmann fuses.

Cheers,

Tom.
RV-7
 
Littelfuse Pico Fuse 1A

This is what I am installing in my G3X system. You should be able to get these 1A Littelfuse Pico Fuses from any good electrical supplier, or from Amazon, Amazon Link
 
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Excellent. Thanks Tony. This is exactly what I was looking for. I presume I just connect them to the respective ends of the 22 awg wires, then throw a bit of heat shrink around it and call it good.

Tom.
 
I tried those little pico fuses and the lead wire is very thin and fragile, I broke several just from normal moving wires around during assembly. I ended up changing for a small blade fuse assembly and have had no issues since. If you can find a way to support the pico so the leads have no stress they should work fine.
 
Just crimp some 1/4" female fast-ons to your wires, and slide them directly onto the blade fuse. Use heat shrink to insulate the fast-ons and a large piece over the whole thing.
 
I have Dynon but same style shunt. Originally I had installed the smallest wire I had, figured chances are it would never consume more than 1 amp, but if it did I was protected.

Well good news is the small wire did burn up and work, bad news is because all of it was small, I had to run all new wires. Aside from wires nothing hurt and wasn't a horrible job. I now have the larger blade style fuses mounted inches from the shunt.
 
Thanks Chris. Do you have a source on quality blade fuse holders and fuses? I'm thinking the individual inline waterproof types probably make sense, as my fuses will need to be in the engine compartment. I don't want to get burnt a second time around with dodgy fuse holders again if I can help it, and if I'm going to be shipping these from the US I may as well get both the blade fuse and pico types and see which works best.

Tom.
 
I used small fuses that look like resistors (forget what they are called) and solder them in line with the wiring, then cover with shrink wrap. This is not something that I would expect to change often. I solder them in at the end by the shunt, so they can be replaced.

Larry
 
Thanks Chris. Do you have a source on quality blade fuse holders and fuses? I'm thinking the individual inline waterproof types probably make sense, as my fuses will need to be in the engine compartment. I don't want to get burnt a second time around with dodgy fuse holders again if I can help it, and if I'm going to be shipping these from the US I may as well get both the blade fuse and pico types and see which works best.

Tom.

I got mine from Amazon, just search waterproof mini blade fuse holder and get the smallest gauge wire ones, I think it's 16ga. The auto parts store had some but the wire was much heavier gauge and not needed for a 1 amp circuit. The Pico fuses will work also just find a way to support the tiny leads so they don't fatigue easily and break.
 
Another option to consider is just not installing a shunt, to keep things simple. You can use voltage to determine if the alternator is working. The bus voltage is at about 12v when the alternator is off, and 14v when the alternator is on and engine running. If you turn on the alternator and don't see a rise to 14v then something is wrong.

Additionally, if you plan your electrical loads ahead of time you have a good idea that the alternator can power all the devices on the aircraft. Then during flight test you can turn everything on and validate that the system can maintain 14v over time.

Another option to think about...
 
Another option to consider is just not installing a shunt, to keep things simple. You can use voltage to determine if the alternator is working. The bus voltage is at about 12v when the alternator is off, and 14v when the alternator is on and engine running. If you turn on the alternator and don't see a rise to 14v then something is wrong. SNIP

+1. Three RVs and none have a shunt.

So why install an ampmeter? If you are old enough you may recall that all cars had an ampmeter but none had a voltmeter. The reason is ampmeters at the time where easy and cheap to make. Voltmeters were expensive. Now you never find a car with an ampmeter. A voltmeter tells me everything I must know - even if running a standby alternator.

Some thoughts:
- If I ever really wanted to install and ampmeter I would use a hall effect sensor, not a clunky shunt.
- Anyone that really wants to use a shunt should never us "fusible links". Use a fuse. Why would you want to design in a wire melting your protection?
- If you want to take data, run the plane on your regulated power supply (never a battery charger) and see what the current draw is during various load conditions. One time test.

Carl
 
That's funny!

"...Anyone that really wants to use a shunt should never us "fusible links". Use a fuse. Why would you want to design in a wire melting your protection?..."

That is EXACTLY what a fuse is; a wire that melts to break the circuit.:D

I know what you mean though, at least the fuse is contained and replaceable.

I am still curious as to WHY a previous poster had his wires burn up; there should be very little current in the wires going from the shunt to the GEA24...
 
"...I am still curious as to WHY a previous poster had his wires burn up; there should be very little current in the wires going from the shunt to the GEA24...

While there is very little current going to the GEA 24, if one of those wires were to come into contact with ground (e.g. insulation were rubbed off with vibration, cut, etc.) you would then have a direct short from the alternator or battery to ground! The current flow in that case could be a couple hundred amps.:eek:
 
Here's a picture of the simple blade fuse/faston in-line fuse that I described in an earlier post:

St6LeZZNfL7UiUYxatCFP-hBNHHpQ3pY05k6Txme4ViRZav25EjsJvPT71W0l_NtOstOcxN2qjYx_o3iXhQXTSjliS9UmnoC0MNCd8uf3ZC6_aBMHpypN66OU4fXhxG-YATCAhphxYY7yV5lsAHY7zJj0Mjod_yoxp5zgDnmjE39PxHUXKCObJeSGzcuVGghmLD1zujdkSq7Du0K37LtMqJYSUvUbImG8YQiHo1RIJ2AOmUieEOzQ9mCyXWyKmMt0icPU-8lA0AakxjCOsbxOXWXaqdiL72Qx0qAEzuL-GEkKfxFFJU_qatjeQZhMc4ChW8l2yqQ5bz23FOaDaw7RjGUB9jWTr4I2zgmRj7Xaab_7ty9ksiURSZibTvSWR3rbqN8xfNiEbTCNBJ0cAejckWZd6FhMw2hFq7yNjYQkFFIpQHNlnVq4xHwynyetLNFyT88KF5NxEXS_4qNjrNHpDzVMuFp4G1dk1R8zrSBFaSvXJ8NDb2JJDrQOSEe_HFFbDhyxmVO45reXxk6hPdM4feZa1BmuEtlJc1LABIpynTcoA-9Q7jU1gxjjW9ENzajCzmR64PGbrH97XCYbhRYXt6yHBuujVAGDJMxYwEXhciIur5WwrFPg3PrgstLhvuoG1rsbAFMStvidW-fHrLPPIhseX2RfPCyHa5HSVtLr1Zm6Z97MABaoSMH8O1BhbyIPYo2RfKjK6JZk81KTKet7sFlMDh_lqDIGkKinXr-507o_kzH=w400-no


Behind the silicone tape are two blade fuses and four fast-on connectors. Can't get any simpler than this. Here you can see the fuses peeking out:

xl9T4ipTucy4AAga_Ddo32F-pvrSawqKmR6jo2fvucdxjvC6ubl51Dt4GewBenOSLtXAnt0NpeL4Q_32NmWjL6QlT7GJqDGhq3f-Ih0eb6T1nAhMXUZOf8MPyUfPK0hP9Ffrxkc_ZjDIWEutAH0RNVzOeDvS7XKnmiOO3pSGHSweeg1803QVBVgBPgYu5LkoNBrp_6WRoDWN-2ZxZOeIF2lXbsWCPhKQ1hgVR_-Tb7uS26WT-u9SPIQ3hH6UjIlwt96ixh2OX9T04ABVWlrp17HEYsNBsYBI7uFHxpU4_hJvA20mSp65nNcRo9ud-wp-Bj6K3v3B9xaF5IBKKcrRKqfyjWZE-IOHrgDjD0wFwV2k33nE80hJtKhDV4Yt2sZ7IUJtWQTkptycMISflc9ULNePYvOauhaLKW9FbVEBStTcFT42yaCVe9g4s7cJsDMsRrAyufLcDisFFxUtl6h5d0PowIzCXpTkGiK5rT7T606h7GxT9rnyeR7hSBoetNU67oP1Zn5J8j5q3qavtL3FicvD3l6TUqQ0S4fJxUmPlDVv88fIlCJdUN3H0cY9nMmcOW6vgvXT0g-pp-jdUvsQsSbs3oBwKp-B4wrdBFG4FBOrIe9r7lXwzRTGpWzRmLyjEqtmHCVxeG9O55Eh4XT7mpV58AKhAgw-Dp1L8KkELiz2R5VJbBCQWbbtvO2e4-y_ioabbT1tMTc7PBihEVEHtI7OhR5eozZHgmhM4iLzU4IkIiZ-=w400-no
 
Shunt or GEA24 or Wires?

Hi, I need help, My electrical data is not being displayed correctly.

Shunt is inline between the main battery contractor and the VPX. All has been working fine for 2 1/2 years. Now I'm seeing reading of 0 or 1 amp on the G3X screen, instead of the normal 8 to 10 amps draw I'm used to seeing.

When I look at the engine data for the flight, I see many minutes of 0 amps then a 13 amp spike then 1 amp for a number of minutes then back to 0 amps then another spike of 15 to 10 amp a few minutes later, then back to 1 amp then 0 amps again.

Batteries are charging at 13.8 to 14.1 all the time, VPX amp readings for various components are showing normal amp draw per circuit.

So I thought wire frayed or chaffing, tested continuity from the GEA24 plug J243 to the shunt... no shorts, no issues obvious. The wire is a shielded twisted pair as specified in the G3X install manual. Wired to pins 36 and 37 in J243 plug.

Don't really know how a shunt does it works, but it doesn't seem to have any visible issues. No loose connectors or screws. The shunt looks just like it did when I installed it.

No other issues showing up in the G3X coming from data supplied by the GEA24.

Any thoughts would be most appreciated. Would like to figure it out short of swapping out the GEA24 and or the Shunt.

Shunt was purchased and is the one listed in the Stein catalog for the G3X installation.
 
I used a fusible link a-la Bob Knuckles way back when I built the RV7. Still going strong with no issues.
 
Hi Steve,
I?m not sure if this will solve your issue, but today I finally test flew my aircraft with new fuses, and my current fluctuation issues went away. Even though the glass fuses looked fine, they had a fracture at one end internally that would cause trouble only when affected by a certain frequency vibration. Replaced with new fuses the problem has gone. I will soon be changing out the glass fuse holders to waterproof inline blade fuse holders which look to be more robust.
Tom.
 
Crazy Ammeter Readings

Hi guys,
I installed standard glass fuses on in-line holders on my RV8 ammeter shunt.
I just flew it after few years of construction and during the following flights, I got crazy ammeter warnings with readings like -300 amps or so, coming back to normal few seconds later... and repeating again a minute after.
And after few repetitions of such warnings, the ammeter went inop (crossed)
Powered everything off and landed, checked the airplane and everything looked ok. The garmin logs showed values of -700 amps!! kinda crazy...
After reading this thread, I cleaned the contacts on the fuse holders and has been working ok for the last couple flight hours...
I plan to replace the holders for blade type anyway...
Was that the kind of erratic readings you were having?
Cheers, Alex
 
Hi Alex,
My readings were similar to yours with the glass fuses. Even with a new set of fuses, it didn't take long before they would start throwing erratic readings. I have since replaced them with blade style holders and 1A blade fuses, and since then everything has been fine. Definitely worth upgrading.

Cheers,

Tom.
 
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