Shunt breakage

[Rhino]

Those are too expensive. I thought you meant not flying 'at that time'. In any case, I was just more curious about the allowable methods rather than trying to directly critique what you had. Wasn't sure if that policy carried over from my military days into civilian aviation.

 

[swatson999]

Or the pic could have been from the presumably flying Rocket, given the semantic ambiguity in the post.

 

[Carl_Froehlich]

Or, remove the process and eliminate the problem. Three RV builds and never found a need to have a shunt. Voltage is really the only indication needed for electrical system health. During testing I do measure current loads but that is a one time thing using a regulated power supply to verify component power draw. Once done the data is incorporated into the POH for Emergency Immediate Actions and such.

When was the last time you say an ammeter in a car?

Carl

 

[Marc_J._Zeitlin]

Voltage is really the only indication needed for electrical system health....

I will respectfully disagree. If one installs an ammeter shunt in the appropriate place (to measure current in and out of the battery), one can get a real-time measure of the battery health. There are three ways of installing the ammeter shunt:

• Alternator Output
• Bus Load
• Battery In/Out

I will agree that the first two are not important or useful _IF_ your system has been designed correctly and you never need/use more than 80% of your alternator output for continuous loads.

But measuring current in and out of the battery will give you a head's up as to your battery's health - while the voltage tells you that the alternator's working, seeing 0A - 1A into the battery (after the startup recharge bolus has passed) tells you that your battery is healthy. If you constantly see 3A - 5A or more into the battery, even when it's supposedly fully charged, you know it's on the way out, and it's time to get a new one. And if you see any current OUT of the battery while the voltage is high and the alternator's theoretically working, you know that your design was inadequate and it's possible to overload the alternator.

Cars have idiot lights, if you're lucky - just because they don't show folks information doesn't mean there's not useful information to be had.

 

[rjones560]

I don’t entirely agree. My amp meter (Dynon EMS) measures alternator output, either the main or the standby. I also have a voltmeter built into my Dynon EMS. Besides that my Vertical Power Pro shows me the load on every circuit in real time and amps in or out of the battery. I have an EarthX ETX900 (5.3 pounds) mounted on the firewall of my RV10 with a blast tube going into the front of a custom battery box for cooling. I live in Las Vegas and temperatures of 110+ are the norm in the summer. My Barrett 540-X has 9-1 pistons at 290hp and the EarthX EXT900 cranks it over quite smartly with my B&C starter. The EarthX battery will draw close to 60 amps right after startup.
Not everyones situation is the same. I personally like having both volts and amps available. Since neither take up much room on my 7” instrument screen it is easy to have both. Right after startup the volts will be lower than normal, but the reason why is obvious when you see the alternator is putting out 60 amps.

 

[Rhino]

You don't need the shunt for the Skyview if you have a VP-X, because the VP-X has a built-in shunt, and you don't use a shunt to measure voltage. Besides the obvious stuff, your EarthX battery is different from the norm because lithium-ion batteries accept a much higher charging current. So, what Marc stated was correct for a standard, traditional battery. You just don't have a standard, traditional battery.

 

[rjones560]

The VPX view covers my moving map so I don’t have it in front of me most of the time. The EarthX batteries are not lithium ion. They are lithium iron. I would not put a lithium ion battery in an aircraft. They catch on fire occasionally. The amp meter is not as important as the volt meter but I am happy to have it. The screen space it takes is minimal.

 

[Marc_J._Zeitlin]

Besides the obvious stuff, your EarthX battery is different from the norm because lithium-ion batteries accept a much higher charging current. So, what Marc stated was correct for a standard, traditional battery...

Marc has two EarthX lithium batteries in his plane, and what Marc stated was correct for those, as well . Right after starting, I'll see 30A - 50A of charge into each battery, but within a minute or two, it'll be down to 0A - 1A, as indicated is reasonable for a healthy battery. No difference in shunt/amperage information content - just a much higher after-start charging current shown for a short period of time .

 

[Bill Putney]

I have had the Dynon 60 amp shunt break around the mounting holes twice in 330 hours. It is attached to the fire wall high on the right of my RV10. I was especially careful about mounting it the second time to make sure there was no extra pressure on it. This time I got a friend with an end mill to make me a replacement part to mount the metal part on out of Delrin. It is a solid piece with holes in all the right places to mount the metal piece and properly countersunk. Hopefully this is the last time I have to fix it. It sure is mounted much more solidly than the hard plastic piece it used to be mounted on.

The shunt mounting fasteners should be slightly smaller than the mounting holes in the shunt allow, so that any flexing of the airframe its attached to isn't trying to snap off the shunt mounting ears. Next size down screws with some heat shrink tubing to center the screws and nylon washers above and below the mounting ears so the shunt can float a little. There's no mass there, so you don't need a pair of 1/4" bolts to hold it down. Maybe a better solution than changing the shunt base to Delrin would be to attach a new shunt to an aluminum plate (rigid block). That would transfer the physical loads to the plate and keep the mounting screws from trying to snap the mounting holes out.

The concern I would have with changing the base material of the shunt is that the original base was very rigid (brittle) by design. This held the terminal posts and the shunt element in a very rigid physical position with relation to each other. The whole shunt moves as one piece. This keeps the shunt components isolated from twisting or pulling against each other regardless of what the material the base is attached to does. There are lots of insulator material choices for manufacturers to choose from. Invariably they choose Bakelite or some other very stiff material, I don't think that's an accident.

Changing the base to Delrin, which is more flexible, solves one problem and I suspect will ultimately create another. The shunt element is rigidly attached to the terminal posts which are now attached to the vibrating airframe by a flexible material. As a consequence the vibration is now flexing the shunt element (probably concentrated at the points where the thin element attaches to the terminal posts). I think at some time in the future the point where that flexing is happening is going to work harden enough and fracture. As the fracture progresses, the resistance of the shunt will change and the ammeter reading will become inaccurate (read higher than the current passing through it actually is). The remaining material will also heat up by resistance heating as more current passes through a smaller cross sectional area. That heating will accelerate the hardening and the rate the fracture it moving. Depending on how the meter is in the circuit, as a "Load Meter" or "Charge Meter", a failure of the charging system or complete failure of the electrical system will happen (probably on short final at night in IMC).

 

[Rhino]

The VPX view covers my moving map so I don’t have it in front of me most of the time. The EarthX batteries are not lithium ion. They are lithium iron....

Yeah, I knew that. Typing without the brain in gear again.

 

[Carl_Froehlich]

I will respectfully disagree. If one installs an ammeter shunt in the appropriate place (to measure current in and out of the battery), one can get a real-time measure of the battery health. SNIP.

Nope - any battery only cares about buss voltage. Buss voltage above terminal voltage and the battery charges. Buss voltage below terminal voltage and the battery discharges.

I simply do not consider adding two big cable terminals on the firewall a great idea - so I don’t use a shunt. If you really must have real time current information recommend a Hall Effect current sensor. The Dynon EMS section discusses using the sensor from Grand Rapids.

Never used a VPX box so cannot comment on it.

Carl

 

[Marc_J._Zeitlin]

Nope - any battery only cares about buss voltage. Buss voltage above terminal voltage and the battery charges. Buss voltage below terminal voltage and the battery discharges.

I simply do not consider adding two big cable terminals on the firewall a great idea - so I don’t use a shunt. If you really must have real time current information recommend a Hall Effect current sensor. The Dynon EMS section discusses using the sensor from Grand Rapids.

My comment was not about knowing whether the battery is charging or not charging. It was about knowing the battery health. I know what makes a battery charge (or discharge). But with my batteries fully charged to 13.2V, a bus voltage of 14.4V will still result in a current draw into the battery of 0A - 1A. This means the battery is fully charged and healthy. But if I see a 5A charging current into the battery after 20 minutes of flight, when the battery should long since have been fully re-charged, I know that the battery is not healthy and is drawing current when it should not.

Feel free to operate with less information if you like - that's obviously your prerogative. I choose to have more information, not just about the alternator, but about the battery as well, and was explaining to those interested why having that information might be useful. For the minuscule weight of either the shunt or the GRT coil sensor (I have both - one for the bus 1 and one for bus 2), since the wiring comes with the EMS-220 module harness and I didn't cut all the wires off at the connector, I recommend having more information, not less.

And you can mount the shunt anywhere - it doesn't have to be on the firewall, if you have some objection to putting it there. Pretty much anywhere works, physically. Having worked on over 140 different "N" numbered E-AB aircraft, most of which have had ammeter shunts or coils on them, about 1/3 of those wired the way I recommend, I've never seen a failure of a shunt (but have seen coil failures, if the wires and coil itself aren't strain relieved properly).

 

[airguy]

Throw in an electrical issue in the air, with a little load-shedding activity and troubleshooting to see where the loose amps are getting out of the fence, and you might find that shunt to be more useful than before.