What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Considering the EarthX EXT900-VNT

Status
Not open for further replies.

Hartstoc

Well Known Member
I posted this as a reply within another thread but, considering how many owners are thinking about switching to lithium, thought it worthy of its own in general discussion. The EXT900-VNT is something of a game-changer that stands alone even among the other EarthX batteries designed for experimental aircraft, but several EarthX vendors do not even list it as available.

A little more expensive and a bit heavier than the unvented version, but unique among all lifepo batteries available now in that it features a containment vessel and a pair of vents intended to overboard noxious gasses that would be generated in a thermal runaway scenario. It is really the only lithium battery out there designed to be safely mounted inside the passenger cabin, a far more battery-friendly environment than any firewall-forward location. I hope that other battery manufacturers will come forward with less expensive batteries sporting these features, but as far as I know this is the only one for now.

https://earthxbatteries.com/shop/etx900-vnt

I have a pair of these around which I’m designing a fully redundant twin battery system with enough ampacity to allow not only dual lightspeeds, but a fully redundant twin-electric fuel pump system that will allow me to completely eliminate the engine driven fuel pump from my Airflow Performance FI system. The two together weigh about 5# less than the single PC680 they will replace.
 
Last edited:
Interesting. I have dual 900s that I was planning on mounting under the seats of my rag and tube airplane. I didn't realize they had a special version for in-cabin installations.

"Two 3-foot vent tubes"

What is the risk of Lithium Iron Phosphate venting in the cabin? I thought they were a sealed unit.
 
Deleted, mishap cause had nothing to do with EarthX. Contact DR.
 
Last edited by a moderator:
I do wish that EarthX and other manufacturers would be more open about the technical aspects of the BMS systems built into their batteries so users could be more knowledgable about this still-new technology.- Otis

Actually,
EarthX has been extremely open. I urge you to call Kathy and ask her anything. I?ll keep flying my ETX900 as long as it?ll last and will get another.
 
Actually,
EarthX has been extremely open. I urge you to call Kathy and ask her anything. I’ll keep flying my ETX900 as long as it’ll last and will get another.

Sorry- I did not mean to imply that EarthX is not generally very open. My own exchanges with them have been delightful and reassuring. This led to my purchase of two new EXT900-VNT’s.

I was just expressing a little frustration trying to find Detailed BMS info, and I cannot claim to have put a great deal of effort into it. I do appreciate that much of this info is propriatary, but it is an interesting topic. The BMS(battery management system) is working at somewhat cross purposes. On the one hand, it is there to protect the battery from abuse, shutting it down when there is danger of damage or thermal runaway. On the other hand, especially with airplanes, it has the important job of insuring that every single electron possible is made available to the user before it goes into shutdown mode.

I’d love to learn more about the design philosophy that is being brought to these systems. My early experiences with lithium battery powered tool was so frustrating that I went back to cadmium for my many power tools. The lithuims would shut down without warning in the middle of a taskeven though they seemed to have lots of power remaining, whereas thecads juskeep on giving until they cannot.- Otis
 
?Proprietary ?... I think that?s the magic word here. They gotta preserve their product, but I for one love their product.
 
Might want to read this one too, since you're going all-electric on pumps and ignitions. Sounds like an OV event, followed by a battery disconnect, followed by (unknown). It would be great if someone got the full story from the owner, as there is bound to be a lesson or two.

https://app.ntsb.gov/pdfgenerator/R...D=20171031X10251&AKey=1&RType=Prelim&IType=LA

Yes, this is exactly the type of scenario that requires really good, truly redundant design. First line of defence is OV protection like that provided by B&C regulators that completely shuts down the alternator in a few milliseconds. You need at least one battery in the system at all times that will not directly experience the OV event, and a BMS on the one that does experience it that will not shut down its battery too quickly, so as to give the OV protection on the alternator time to work. The EarthX BMS is such a system. Finally, once the alternator is shut down, you need the ability to directly connect each ignition, fuel pump, or other critical devices directly to either battery via well designed critical loads busses on each battery. All very doable, but with great care. - Otis
 
I fly a two EarthX ETX900 setup. Two separate circuits which can be paralleled.
I start engine with both batteries on line and then fly with only one, alternating batteries occasionally to keep both charged.
I figure that if one battery BMS shuts down it’s no big deal, switch to the other.

Both batteries and mounts/solenoids together weigh less than the Odyssey they replace.

Edit: I have a 20amp lightweight alternator and over voltage protection through my VPX
 
Last edited:
I fly a two EarthX ETX900 setup. Two separate circuits which can be paralleled.
I start engine with both batteries on line and then fly with only one, alternating batteries occasionally to keep both charged.
I figure that if one battery BMS shuts down it’s no big deal, switch to the other.

Both batteries and mounts/solenoids together weigh less than the Odyssey they replace.

Edit: I have a 20amp lightweight alternator and over voltage protection through my VPX

You’ve got the right idea! I think the very best forms of redundancy are designed such that you are using the “emergency backup system” as part of routine, everyday flight, so good for you! I worry over those little backup batteries that are held in reserve for emergencies- if you do not test them very regularly, including shutting down the main and actually flying on the backup, you may get a nasty surprise when you really need them. You also have a massive 800 cold-cranking amps for starting, which not only makes the starter very happy, but means that each of those batteries barely notices the discharge from a single start, so they are happy campers. My system will be very similar.

One question, is yours “idiot proof” in the sense that it is impossible to accidentally leave both batteries connected to the main bus simultaneously other than when starting? I have a simple solution for that if not.- Otis
 
Otis,
No, not idiot proof, but it really isn’t a problem if I accidentally leave both on. I normally leave both on until after t/o, and the alternator charging has filled both batteries, then switch one off.
It’s part of my checks to swap batteries and fuel tanks, so unlikely I’d miss it for too long.

BTW both batteries turn the engine (Superior XIO360 with 10:1 compression) over so fast that I reckon I could taxi with it!!
 
Otis,
No, not idiot proof, but it really isn?t a problem if I accidentally leave both on. I normally leave both on until after t/o, and the alternator charging has filled both batteries, then switch one off.
It?s part of my checks to swap batteries and fuel tanks, so unlikely I?d miss it for too long.

BTW both batteries turn the engine (Superior XIO360 with 10:1 compression) over so fast that I reckon I could taxi with it!!

Given the huge combined Ampacity of the EXT900?s, it may not be a problem as you say. The one concern there(if your airplane is ?electron dependent?) would be that it might be possible to drain both batteries before discovering that your alternator had suffered some sort of stealth failure.

My system will address this by having an on-off-on master switch. Each EXT900-VNT will have its own contactor to the main bus, so in normal operation only one battery can be ?hard connected? to the bus at a time. The non-connected battery WILL be charged but at a slightly lower voltage through a Shotky diode. I?ll adopt your medthod of switching back and forth periodically to ?top-off? the opposite battery at full voltage.

For starting with both batteries, I?ve come up with a little trick I?m kind of proud of. The start button will be covered by a spring-loaded access cover. When you hold the cover open with one finger, a hidden momentary switch is activated that energizes the contactor for the second battery, so both are engaged while you push the start button with another finger of the same hand. When you let go after engine start, the second battery is disengaged from the bus.- Otis
 
SNIP...

My system will address this by having an on-off-on master switch. Each EXT900-VNT will have its own contactor to the main bus, so in normal operation only one battery can be ?hard connected? to the bus at a time. The non-connected battery WILL be charged but at a slightly lower voltage through a Shotky diode. I?ll adopt your medthod of switching back and forth periodically to ?top-off? the opposite battery at full voltage.

For starting with both batteries, I?ve come up with a little trick I?m kind of proud of. The start button will be covered by a spring-loaded access cover. When you hold the cover open with one finger, a hidden momentary switch is activated that energizes the contactor for the second battery, so both are engaged while you push the start button with another finger of the same hand. When you let go after engine start, the second battery is disengaged from the bus.- Otis

I offer that having both batteries always on the alternator output (for normal operations) has advantage over any ?one battery on, one battery off? setup. The batteries are perfectly happy running in parallel. Thus in normal mode both batteries are availble for engine start as well as fault isolation backup modes.

I use two PC-625 batteries but there is no reason not to do the same with an EarthX battery. I replace one battery every three years so neither is more than six years old. This provides some assurance on battery capacity.

I do agree with each battery having it?s own master solenoid to connect to the common buss. I offer however that by adding a four 30 amp relays to feed two avionics busses (these are not connected to the common buss) you can gain significant redundancy and have process to isolate most common failure risks. My POH immediate action for an electrical fault is to open both master solenoids, putting half the panel on it?s own battery - backup cross connect available if needed. This is the most robust configuration. After the immediate action the pilot can then look to see what happened while flying for at least 2 hours (fuel dependent, EFII engines less time) to land if not able to correct.

Carl
 
The EarthX does not disconnect for OV, it blocks the excess current

EarthX has mentioned this in many different threads here in VANS but as the over voltage protection the BMS provides is such an important feature and misrepresented or misunderstood feature, I believe it is important to post again. Copied directly from the manual:

? In the event of a charging system failure where the voltage increases to above 15.5V, the resistance to charging current increases, and above 16V the charging current is completely blocked. The time delay for this feature is 2 second to allow the aircraft alternator?s over voltage protection (crowbar circuit) to activate first. This design offers charge voltage protection greater than 40V. The discharge current (current out of battery) is unaffected in this situation. EarthX requires having automatic over-voltage protection (crowbar) for alternator type charging systems (not required for <20 Amp pad mount standby alternators).?

This is why we require over voltage protection on your plane if you have an alternator that is greater than 20 amps as the BMS protects the battery, not the rest of the equipment in your plane and in a scenario where the regulator has failed, the EarthX BMS will block the excess current coming into the battery but the current will have to go somewhere, which will be your equipment, and having over voltage protection ensures all your expensive equipment inside your plane is protected. An alternator that is less than 20 amps does not have the ability to produce more than the 40V which is why this alternator does not require OV protection. So again, note they do not cut off for an over voltage situation for this exact type situation but instead block the excess current coming in but still allows current out.
 
Last edited by a moderator:
EarthX has mentioned this in many different threads here in VANS but as the over voltage protection the BMS provides is such an important feature and misrepresented or misunderstood feature, I believe it is important to post again. Copied directly from the manual:

? In the event of a charging system failure where the voltage increases to above 15.5V, the resistance to charging current increases, and above 16V the charging current is completely blocked. The time delay for this feature is 2 second to allow the aircraft alternator?s over voltage protection (crowbar circuit) to activate first. This design offers charge voltage protection greater than 40V. The discharge current (current out of battery) is unaffected in this situation. EarthX requires having automatic over-voltage protection (crowbar) for alternator type charging systems (not required for <20 Amp pad mount standby alternators).?.

Thank you Kathy. You're right, there does seem to be some confusion about BMS function.

EarthX nominal full charge voltage is 13.3V, correct? There is one positive post for connecting the battery to the system. With the alternator holding bus voltage at any level more than 13.3V, current flow from the battery is impossible.

So, check me please. Is this an accurate scenario?

Master ON, engine not running, no alternator output. The battery has an outflow, supplying 13.3V to the main bus.

Engine running at cruise RPM. Bus voltage is normal at 14~14.5V. Battery is charging or fully charged. There is no outflow from the battery.

The alternator's voltage regulator begins to fail. Bus voltage rises to 15.5V. The BMS begins limiting the voltage applied to the cells, thus limiting current inflow. There is no outflow.

Bus voltage rises to 17V. The BMS limits applied cell voltage to a maximum of 16V. There is no outflow.

A few moments later, the alternator's over-voltage protection takes it offline.
The alternator output becomes zero. Bus voltage immediately drops to 13.3V, as the battery resumes supplying electrons to the bus.

If correct, I will have some follow up questions.
 
The "crowbar" overvoltage module should blow the field breaker in milliseconds once the threshold voltage has been exceeded, nominally 15v.

Ed Holyoke
 
The "crowbar" overvoltage module should blow the field breaker in milliseconds once the threshold voltage has been exceeded, nominally 15v.

Ed, the nominal trip points are 16.5V for Plane Power, and 16V for B&C. I called 'em.

I used 17V in the above example so we can learn how the EarthX BMS really works.
 
I offer that having both batteries always on the alternator output (for normal operations) has advantage over any “one battery on, one battery off” setup. The batteries are perfectly happy running in parallel. Thus in normal mode both batteries are availble for engine start as well as fault isolation backup modes.

I use two PC-625 batteries but there is no reason not to do the same with an EarthX battery. I replace one battery every three years so neither is more than six years old. This provides some assurance on battery capacity.

I do agree with each battery having it’s own master solenoid to connect to the common buss. I offer however that by adding a four 30 amp relays to feed two avionics busses (these are not connected to the common buss) you can gain significant redundancy and have process to isolate most common failure risks. My POH immediate action for an electrical fault is to open both master solenoids, putting half the panel on it’s own battery - backup cross connect available if needed. This is the most robust configuration. After the immediate action the pilot can then look to see what happened while flying for at least 2 hours (fuel dependent, EFII engines less time) to land if not able to correct.

Carl

I agree that running batteries parallel is perfectly OK, and that they do not even need to be a matched set(that’s classic Bob Nuckolls), but embarassingly personal experience suggests that when a pilot goes into “idiot mode”, it can be profound. Coming up with redundant ststems that make it impossible for the pilot to inadvertantly run down both batteries is good!
 
Last edited:
Additional note

I offer that having both batteries always on the alternator output (for normal operations) has advantage over any “one battery on, one battery off” setup. The batteries are perfectly happy running in parallel. Thus in normal mode both batteries are availble for engine start as well as fault isolation backup modes.

I use two PC-625 batteries but there is no reason not to do the same with an EarthX battery. I replace one battery every three years so neither is more than six years old. This provides some assurance on battery capacity.

I do agree with each battery having it’s own master solenoid to connect to the common buss. I offer however that by adding a four 30 amp relays to feed two avionics busses (these are not connected to the common buss) you can gain significant redundancy and have process to isolate most common failure risks. My POH immediate action for an electrical fault is to open both master solenoids, putting half the panel on it’s own battery - backup cross connect available if needed. This is the most robust configuration. After the immediate action the pilot can then look to see what happened while flying for at least 2 hours (fuel dependent, EFII engines less time) to land if not able to correct.

Carl

I am not envisioning a one battery on/one battery off strategy. Instead, the on-off-on master switch allows one soft-connected battery and one hard-connected battery. The system will have absolute symmetry, in that it will not matter which battery you have hard-connected to the main bus at a given moment in time. The soft-connected battery does receive a charge through diodes, and it will be operating one of the electronic ignitions during normal operation by way of it’s always-on essential loads bus. It is, however, isolated from the draw down of a panel full of avionics, lights, etc that it would be exposed to if it were hard-connected to the main bus. Each essential device on the aircraft will have full-time access to EITHER of the two always-on essential loads busses, and so have access to any available power from either battery at all times. Everthing else on the aircraft gets only what the main buss has to offer. On my aircraft there are just four essential devices, two ignitions and two fuel pumps.-Otis
 
Last edited:
Thank you Kathy. You're right, there does seem to be some confusion about BMS function.

EarthX nominal full charge voltage is 13.3V, correct? There is one positive post for connecting the battery to the system. With the alternator holding bus voltage at any level more than 13.3V, current flow from the battery is impossible.

So, check me please. Is this an accurate scenario?

Master ON, engine not running, no alternator output. The battery has an outflow, supplying 13.3V to the main bus.

Engine running at cruise RPM. Bus voltage is normal at 14~14.5V. Battery is charging or fully charged. There is no outflow from the battery.

The alternator's voltage regulator begins to fail. Bus voltage rises to 15.5V. The BMS begins limiting the voltage applied to the cells, thus limiting current inflow. There is no outflow.

Bus voltage rises to 17V. The BMS limits applied cell voltage to a maximum of 16V. There is no outflow.

A few moments later, the alternator's over-voltage protection takes it offline.
The alternator output becomes zero. Bus voltage immediately drops to 13.3V, as the battery resumes supplying electrons to the bus.

If correct, I will have some follow up questions.


Hi Dan, I have answered your questions in red below:

Master ON, engine not running, no alternator output. The battery has an outflow, supplying 13.3V to the main bus. Yes, the battery has an outflow and the voltage will vary depending on the load.

Engine running at cruise RPM. Bus voltage is normal at 14~14.5V. Battery is charging or fully charged. There is no outflow from the battery. Correct, just acts as a large capacitor to reduce AC ripple from the alternator. No continuous outflow.

The alternator's voltage regulator begins to fail. Bus voltage rises to 15.5V. The BMS begins limiting the voltage applied to the cells, thus limiting current inflow. There is no outflow. The BMS does nothing yet. Generally, when regulators fail they do so within microseconds. In some cases, high temperature affects the regulator and the voltage regulation setpoint drifts up and down but rarely over 15.5V.

Bus voltage rises to 17V. The BMS limits applied cell voltage to a maximum of 16V. There is no outflow. These are complete regulator failures that cause voltage to jump to above 16 volts within microseconds, and the peak voltage is a function of the type charging system and the charging system RPM. For a 60amp alternator spinning at 10,000 RPM that could be 100 volts. And yes the inflow (charge) current is blocked, but this action is delayed for 2 seconds so the alternator?s over-voltage protection can activate first.

A few moments later, the alternator's over-voltage protection takes it offline.
The alternator output becomes zero. Bus voltage immediately drops to 13.3V, as the battery resumes supplying electrons to the bus. This is not exactly accurate; the alternator?s over-voltage protection should activate first. Per aircraft standard DO-160 the charging system over-voltage device should operate in less than 100milli-seconds at 40volt level, and less than .5 second at 20volt level and less 1 second at 16 volt.
 
Hi Dan, I have answered your questions in red below:

Thank you! Unfortunately, it seems you too were sidetracked into regulators and OV protection by my very poor choice of example. Sorry, my bad.

Let's try again. Forget alternators, regulators, and over-voltage protection. Focus on the battery management system. For our purposes, assume the charging power source is merely something which allows us to apply any desired voltage to the bus.

Ok, bus voltage at 14~14.5V simply charges the battery, or maintains full charge.

Bus voltage at 15.5V. The BMS begins limiting the voltage applied to the cells, thus limiting current inflow. True?

Bus voltage rises to 16.5. The BMS limits the voltage applied to the cells to a maximum of 16V. True? Please note the word "limits", as you generally state that charge current is "blocked".

To be specific, I am asking this question: If the bus voltage remains at 16.5V indefinitely, the cells will be (a) held at 16V indefinitely, or (b) held at some lesser voltage based on individual cell state, or (c) isolated from the bus?
 
Thank you! Unfortunately, it seems you too were sidetracked into regulators and OV protection by my very poor choice of example. Sorry, my bad.

Let's try again. Forget alternators, regulators, and over-voltage protection. Focus on the battery management system. For our purposes, assume the charging power source is merely something which allows us to apply any desired voltage to the bus.

Ok, bus voltage at 14~14.5V simply charges the battery, or maintains full charge.

Bus voltage at 15.5V. The BMS begins limiting the voltage applied to the cells, thus limiting current inflow. True?

Bus voltage rises to 16.5. The BMS limits the voltage applied to the cells to a maximum of 16V. True? Please note the word "limits", as you generally state that charge current is "blocked".

To be specific, I am asking this question: If the bus voltage remains at 16.5V indefinitely, the cells will be (a) held at 16V indefinitely, or (b) held at some lesser voltage based on individual cell state, or (c) isolated from the bus?

It is important here on this forum to stay focused on discussing/educating pilots and builders about aircraft situations, and your scenario of a sustained voltage of 16.5V is not plausible in an aircraft charging system. Either your regulator is working, which would be a voltage of 14.6V or less, or it is faulty, and will rise ?unregulated? and not sustain a constant voltage. But in very general terms, at 16V the BMS will block current going into the battery but it is not limitless protection, nor is it designed to protect your electronics. Bus voltage above 40V, your electronic equipment could be damaged, for any quality aircraft manufacturer will design their equipment to meet FAA standard DO-160. If you do not have over voltage protection or you do not manually take your alternator off line when you have a regulator failure, and your voltage climbs above 40V, you will damage your electronics in your plane whether you have a lithium battery or a lead acid battery.

If your questions are for a different type application, please email us at [email protected] with your questions as we do have many different markets, such as the Department of Defense, (DOD) that we work with and we can assist you in the design/application of a lithium battery in a particular system.
 
Deleted for rules violations. Contact DR.
 
Last edited by a moderator:
Deleted for rules violations. Contact DR.
 
Last edited by a moderator:
Deleted for rules violations. Contact DR.
 
Last edited by a moderator:
Deleted for rules violations. Contact DR.
 
Last edited by a moderator:
Status
Not open for further replies.
Back
Top