VR/battery connection blown fuse

[Darick]

Help needed from electrical gurus...the center post of my voltage regulator is connected to the battery positive pole as per AeroVee plans. Additionally I added a 20 amp fuse to this connection. This was done when I originally wired everything in 2016 or so and can't remember the reason at this time. It may have been from reading about alternator disconnects or runaway voltage regulators. Thinking about it now it doesn't make much sense to put a 20 amp fuse on a device that produces 20 amps. Ummmmm?

Up until this point of fifteen hours Hobbs time, I have had no problems but today I flew one hour, took a one hour break and continued flying. This flight ended when the fuse blew which drained the EarthX battery to an auto shutoff mode. A safe landing was made with engine power of course, since the primary ignition continues on without external power (thank you John Monnett).

I haven't given much info here but can someone offer a starting place to trouble shoot. Perhaps putting in a higher rate fuse to start and go fly?

B & C also now has the Bob Nukolls designed voltage regulator with crowbar protection which is sounding really nice.

[Rynoth]

I used a 25A fuse and haven't had an issue. I have the B&C crowbar setup. I ran 10AWG from the regulator to the master/battery. Keep in mind that the fuse is primarily there to protect the wire(s), if the wire can handle more amps then a larger fuse may be prudent.

[mike.smith]

I've had a 30A fuse for 6 years with no issues. It blew once when it was supposed to, when I had an electrical issue.

[sonex1374]

Darrick,

Two things come to mind about your AeroVee voltage regulator failure situation.

First, the fuse should have a margin over the current it typically sees. Fuses can "wear out" so to speak, sort of like bending a piece of metal back and forth until it cracks from fatigue. Loading the fuse to it's nominal rating thru many cycles can hammer away at it until it finally fails. Just like with many other things, it's good to have a cushion built in. Replace the fuse with a 25 or 30 amp and that will provide the cushion, while still protecting the wire from burning up in a dead-short situation.

Secondly, You need some sort of low voltage monitoring on your panel. I'd recommend using either a dedicated low-voltage light that activates or an alarm programed into your EFIS. If you use an alternator disconnect relay like in the AeroElectric Connection recommended diagrams (or also contained in the new B&C regulator) then you can really easily have an alternator-disconnect light to tell you the alternator is offline and warn you in advance that you'll be drawing down your battery from here on out.

Now for a few words about voltage regulators and EarthX batteries...

Voltage regulators can fail in two ways: fail to provide output at the correct voltage (e.g. to regulate); and fail to rectify the AC input into a DC output (e.g. to rectify the alternator signal). In practice, two failure modes are by far the most common: 1) output at excessive voltage, 2) no output at all. The crowbar over-voltage protection takes care of the excessive voltage failure mode by immediately disconnecting the runaway alternator from the instruments before any damage can occur. The alternator-offline light or the low-voltage light/EFIS warning will notify the pilot that the alternator is not outputting anything.

These two warning/notification approaches used together pretty much have you covered. If you skip one or the other, the pilot must monitor the state of the electrical system much more closely to detect either of those problems. In the case of the over-voltage situation, you might have anywhere from a couple seconds to perhaps a minute before excessive voltage does any damage, and if you're not looking at the volt meter you just might miss the window of opportunity to intervene and avoid damage.

If the alternator goes offline you'll have more time to notice as the battery slowly depletes itself and the voltage falls, but in the case of a lithium EarthX battery the voltage stays relatively the same until the battery is at like 10% of it's energy remaining (making it hard to see just how low on juice the battery really is). You'll have to make the connection the battery is going flat in a pretty narrow time frame before the battery's internal protection kicks in and shuts it off.



You can see in the graphic above that the voltage on an EarthX drops from about 13 volts to 12 volts at the 90% expended state, while a lead acid battery goes from about 12.8 volts to about 11 volts at the same 90% state. Not only is there less overall decrease in voltage on an EarthX, but you can't use the same numbers as a low-voltage warning point to signify the battery is getting low (EarthX needs to warn about 12.3 while a lead-acid should warn about 11.6). Just a few other considerations to understand when using different batteries.

Again, having some automation do this monitoring and warning for you allows more time flying for flying and less time monitoring.

Jeff

[Area 51%]

Darrick,

Two things come to mind about your AeroVee voltage regulator failure situation.

First, the fuse should have a margin over the current it typically sees. Fuses can "wear out" so to speak, sort of like bending a piece of metal back and forth until it cracks from fatigue. Loading the fuse to it's nominal rating thru many cycles can hammer away at it until it finally fails. Just like with many other things, it's good to have a cushion built in. Replace the fuse with a 25 or 30 amp and that will provide the cushion, while still protecting the wire from burning up in a dead-short situation.

Secondly, You need some sort of low voltage monitoring on your panel. I'd recommend using either a dedicated low-voltage light that activates or an alarm programed into your EFIS. If you use an alternator disconnect relay like in the AeroElectric Connection recommended diagrams (or also contained in the new B&C regulator) then you can really easily have an alternator-disconnect light to tell you the alternator is offline and warn you in advance that you'll be drawing down your battery from here on out.

Now for a few words about voltage regulators and EarthX batteries...

Voltage regulators can fail in two ways: fail to provide output at the correct voltage (e.g. to regulate); and fail to rectify the AC input into a DC output (e.g. to rectify the alternator signal). In practice, two failure modes are by far the most common: 1) output at excessive voltage, 2) no output at all. The crowbar over-voltage protection takes care of the excessive voltage failure mode by immediately disconnecting the runaway alternator from the instruments before any damage can occur. The alternator-offline light or the low-voltage light/EFIS warning will notify the pilot that the alternator is not outputting anything.

These two warning/notification approaches used together pretty much have you covered. If you skip one or the other, the pilot must monitor the state of the electrical system much more closely to detect either of those problems. In the case of the over-voltage situation, you might have anywhere from a couple seconds to perhaps a minute before excessive voltage does any damage, and if you're not looking at the volt meter you just might miss the window of opportunity to intervene and avoid damage.

If the alternator goes offline you'll have more time to notice as the battery slowly depletes itself and the voltage falls, but in the case of a lithium EarthX battery the voltage stays relatively the same until the battery is at like 10% of it's energy remaining (making it hard to see just how low on juice the battery really is). You'll have to make the connection the battery is going flat in a pretty narrow time frame before the battery's internal protection kicks in and shuts it off.



You can see in the graphic above that the voltage on an EarthX drops from about 13 volts to 12 volts at the 90% expended state, while a lead acid battery goes from about 12.8 volts to about 11 volts at the same 90% state. Not only is there less overall decrease in voltage on an EarthX, but you can't use the same numbers as a low-voltage warning point to signify the battery is getting low (EarthX needs to warn about 12.3 while a lead-acid should warn about 11.6). Just a few other considerations to understand when using different batteries.

Again, having some automation do this monitoring and warning for you allows more time flying for flying and less time monitoring.

Jeff

Jeff...I just installed an EarthX 680C. In the brochure it promised both low AND high voltage protection with a fault light that would indicate either failure.

Did I read it wrong, or did I get duped (yet again) by a smooth talking salesperson?

I'm keeping the battery either way, just need to know if further steps should be taken.

[sonex1374]

...[snip] I just installed an EarthX 680C. In the brochure it promised both low AND high voltage protection with a fault light that would indicate either failure.

I don't think you got duped or there's any problem. The EarthX BMS does protect the battery from most threats, but just remember that the function of this bit of kit isn't to protect you or the airplane....it's to protect the battery from abuse, which can lead to shorter life and/or a battery fire. The warning indicators will tell you after-the-fact why the battery isn't acting normally (over/under volts), but it doesn't really monitor any trends as they are happening, and it can't give you an advance warning that it's gonna kick in soon.

I think the only thing you need to do is have some sort of active voltage monitoring that will alert you with an EFIS message or panel light indicating the voltage is out of bounds. If the voltage is too high the BMS should prevent damage to itself, but you'll still want to remove the source of the too-high voltage, and that's what an alternator control does (using a relay, switch, etc). On the topic of alternator control methods, the best approach is to ensure the alternator goes stone-cold dead, rather than simply disconnecting the output of the regulator to the electrical system. An alternator that continues to feed a failed voltage regulator could, under the worst of cases, melt the poor thing literately to slag.

Lastly, set your lower voltage limit appropriately - I recommend 12.3 - 12.4 volts. You can nudge this down a bit with experience, but remember at 12.0 volts it's pretty well depleted.

Lithium batteries have their advantages, but they have just a few things that we should keep in mind that are a bit different than old-style lead acid batteries. It's easy enough to do things correctly, while enjoying the superior performance of lithium.

Jeff

[Darick]

Jeff thanks for all of your explanations. The time you take helping us fly safer is really appreciated.

Ever since Bob Nukolls was on the podcast talking about his regulator, I've wanted one. What happened to me last week has made that desire become a top priority.