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LiFe Battery

 
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hivanhaecker(at)gmail.com
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PostPosted: Tue Jun 28, 2022 9:23 pm    Post subject: LiFe Battery Reply with quote

Three years ago I decided to equip my little C-85 powered aircraft with a B&C starter and LiFe battery ( Shorai 18 Ah). No provision for charging onboard. It worked great and would easily start the engine a dozen times before I would charge it with an 800mA Battery Tender that was advertised as suitable for both lead acid and LiFe batteries. It was never discharged to the point that it failed to rapidly spin the engine. All went well until a few months ago when I noticed that the battery became sluggish after only a few starts. Now it’s only good for one start before it needs recharging. So the battery is now almost useless. I had (of course!) hoped for a longer useful life. The big question is: have I mismanaged the battery by recharging it only occasionally instead of more often, or did I use an inappropriate charger, or just bad luck of the draw on this particular battery? Thanks for any opinions.

Ivan Haecker


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stuart(at)stuarthutchison
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PostPosted: Tue Jun 28, 2022 9:50 pm    Post subject: LiFe Battery Reply with quote

There is much misleading information out there suggesting chargers suitable for Lead Acid are also suitable for Lithium. Do they work? Yes. Do they compromise Lithium longevity? Also yes, absolutely, unless they have a Lithium specific mode.

Kind regards, Stu

Sent from my iPhone

Quote:
On 29 Jun 2022, at 15:31, H. Ivan Haecker <hivanhaecker(at)gmail.com> wrote:

Three years ago I decided to equip my little C-85 powered aircraft with a B&C starter and LiFe battery ( Shorai 18 Ah). No provision for charging onboard. It worked great and would easily start the engine a dozen times before I would charge it with an 800mA Battery Tender that was advertised as suitable for both lead acid and LiFe batteries. It was never discharged to the point that it failed to rapidly spin the engine. All went well until a few months ago when I noticed that the battery became sluggish after only a few starts. Now it’s only good for one start before it needs recharging. So the battery is now almost useless. I had (of course!) hoped for a longer useful life. The big question is: have I mismanaged the battery by recharging it only occasionally instead of more often, or did I use an inappropriate charger, or just bad luck of the draw on this particular battery? Thanks for any opinions.

Ivan Haecker


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hivanhaecker(at)gmail.com
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PostPosted: Tue Jun 28, 2022 10:03 pm    Post subject: LiFe Battery Reply with quote

The charger has two modes. One for lead acid and one for LiFe . I assume the LiFe mode charges at a slightly higher voltage?
Ivan Haecker

On Wed, Jun 29, 2022 at 12:52 AM Stuart Hutchison <stuart(at)stuarthutchison.com.au (stuart(at)stuarthutchison.com.au)> wrote:

Quote:
--> AeroElectric-List message posted by: Stuart Hutchison <stuart(at)stuarthutchison.com.au (stuart(at)stuarthutchison.com.au)>

There is much misleading information out there suggesting chargers suitable for Lead Acid are also suitable for Lithium. Do they work? Yes. Do they compromise Lithium longevity? Also yes, absolutely, unless they have a Lithium specific mode.

Kind regards, Stu

Sent from my iPhone

> On 29 Jun 2022, at 15:31, H. Ivan Haecker <hivanhaecker(at)gmail.com (hivanhaecker(at)gmail.com)> wrote:
>
> Three years ago I decided to equip my little C-85 powered aircraft with a B&C starter and LiFe battery ( Shorai 18 Ah). No provision for charging onboard. It worked great and would easily start the engine a dozen times before I would charge it with an 800mA Battery Tender that was advertised as suitable for both lead acid and LiFe batteries. It was never discharged to the point that it failed to rapidly spin the engine. All went well until a few months ago when I noticed that the battery became sluggish after only a few starts. Now it’s only good for one start before it needs recharging. So the battery is now almost useless. I had (of course!) hoped for a longer useful life. The big question is: have I mismanaged the battery by recharging it only occasionally instead of more often, or did I use an inappropriate charger, or just bad luck of the draw on this particular battery? Thanks for any opinions.
>
> Ivan Haecker

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PostPosted: Wed Jun 29, 2022 5:58 am    Post subject: LiFe Battery Reply with quote

Hi Stu.
The Battery Tender (charger) you mentioned is intended for LiFeO3 batteries. I have one too. I have been through two Li FeO3 batteries. In my case it appeared they didn't like the charging system on board the aircraft, even though the charging current went to zero soon after starting the engine. I assumed it was not being overcharged, but don't really know what caused the problem. Now I have a much cheaper sealed lead acid battery, which I hope will be bombproof. Installed in the tail cone, rather than atop the firewall, it will also help with a slightly nose heavy condition. I have learned latterly that some LiFeO3 batteries will "turn themselves off," when they get down to a 20% charge. Not a good thing in an aircraft.
Cheers! Stu. Ashley

---


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kenryan



Joined: 20 Oct 2009
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PostPosted: Wed Jun 29, 2022 8:16 am    Post subject: LiFe Battery Reply with quote

I'm not sure the 20% cut off number is accurate; I suspect that it is not. But putting that aside, there is another way of looking at this--all batteries have a limited capacity. Lead acid batteries will happily discharge until they are dead or badly damaged Lithium batteries with a BMS will stop discharging before they are ruined. How can this be a bad thing? 

It's bad only if you are relying on the advertised capacity number to size your battery. Bob has taught us all that we cannot rely on the advertised capacity number, rather, we should do annual capacity checks to verify the actual capacity. It's just a matter of factoring in BMS behavior when you decide on the size battery you need. 
Would it be nice if there was a switch you could throw to disable the BMS low voltage protection in a real emergency? Sure! Is the lack of such a switch a good reason to write off LiFe technology? Not in my opinion.
On Wed, Jun 29, 2022 at 6:00 AM <ashleysc(at)broadstripe.net (ashleysc(at)broadstripe.net)> wrote:

[quote]--> AeroElectric-List message posted by: ashleysc(at)broadstripe.net (ashleysc(at)broadstripe.net)

Hi Stu.
The Battery Tender (charger) you mentioned is intended for LiFeO3 batteries. I have one too. I have been through two Li FeO3 batteries. In my case it appeared they didn't like the charging system on board the aircraft, even though the charging current went to zero soon after starting the engine. I assumed it was not being overcharged, but don't really know what caused the problem. Now I have a much cheaper sealed lead acid battery, which I hope will be bombproof. Installed in the tail cone, rather than atop the firewall, it will also help with a slightly nose heavy condition. I have learned latterly that some LiFeO3 batteries will "turn themselves off," when they get down to a 20% charge. Not a good thing in an aircraft.
Cheers!   Stu. Ashley

---


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Ceengland



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PostPosted: Wed Jun 29, 2022 10:55 am    Post subject: LiFe Battery Reply with quote

On Wed, Jun 29, 2022 at 12:25 AM H. Ivan Haecker <hivanhaecker(at)gmail.com (hivanhaecker(at)gmail.com)> wrote:

Quote:
Three years ago I decided to equip my little C-85 powered aircraft with a B&C starter and LiFe battery ( Shorai 18 Ah). No provision for charging onboard. It worked great and would easily start the engine a dozen times before I would charge it with an 800mA Battery Tender that was advertised as suitable for both lead acid and LiFe batteries. It was never discharged to the point that it failed to rapidly spin the engine. All went well until a few months ago when I noticed that the battery became sluggish after only a few starts. Now it’s only good for one start before it needs recharging. So the battery is now almost useless. I had (of course!) hoped for a longer useful life. The big question is: have I mismanaged the battery by recharging it only occasionally instead of more often, or did I use an inappropriate charger, or just bad luck of the draw on this particular battery? Thanks for any opinions.

Ivan Haecker
Could have been something as simple as a defective battery (atypical lifespan). But if you were going 10-12 starts before recharging, that could well have seriously stressed it. Most batteries like to be kept within a range of charge states. Lithium might have a slightly wider range while maintaining full output voltage, but repeatedly taking them to near full discharge isn't healthy for them, either.
My personal choice is for me to be 5-10 lbs lighter than average, be healthier, and keep the extra  $150 in my bank account. Wink
Charlie


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PostPosted: Wed Jun 29, 2022 8:52 pm    Post subject: LiFe Battery Reply with quote

Good that the battery tender had a Lithium profile … maybe the battery was ultimately a dud or less than expected quality. I assume by LiFe Ivan means LiFePO4 (Lithium Iron Phosphate).
Actually Ken, the same rated LiFePO4 battery will deliver 80% of its charge at a relatively flat Voltage profile before the BMS protects the battery, but the same rated Lead Acid can only be discharged to 50% before charge is necessary or permanent damage can result. No matter what tech, we often get what we pay for, hence Odyssey Lead Acids have a good reputation and some LiFePO4s (like Invicta) do as well. Unsure if LiFePO degrades in high-heat conditions the same way Li-Ion does … if so, firewall forward wouldn’t make much sense, but either way they have huge energy density and can’t be extinguished with a typical fire extinguisher (because the degrading cathode liberates oxygen inside the case), so there's safety issue to consider in that too.

Kind regards, Stu [quote] On 30 Jun 2022, at 2:15 am, Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote:
I'm not sure the 20% cut off number is accurate; I suspect that it is not. But putting that aside, there is another way of looking at this--all batteries have a limited capacity. Lead acid batteries will happily discharge until they are dead or badly damaged Lithium batteries with a BMS will stop discharging before they are ruined. How can this be a bad thing?
It's bad only if you are relying on the advertised capacity number to size your battery. Bob has taught us all that we cannot rely on the advertised capacity number, rather, we should do annual capacity checks to verify the actual capacity. It's just a matter of factoring in BMS behavior when you decide on the size battery you need.

Would it be nice if there was a switch you could throw to disable the BMS low voltage protection in a realemergency? Sure! Is the lack of such a switch a good reason to write off LiFe technology? Not in my opinion.

On Wed, Jun 29, 2022 at 6:00 AM <ashleysc(at)broadstripe.net (ashleysc(at)broadstripe.net)> wrote:
[quote] --> AeroElectric-List message posted by: ashleysc(at)broadstripe.net (ashleysc(at)broadstripe.net) Hi Stu. The Battery Tender (charger) you mentioned is intended for LiFeO3 batteries. I have one too. I have been through two Li FeO3 batteries. In my case it appeared they didn't like the charging system on board the aircraft, even though the charging current went to zero soon after starting the engine. I assumed it was not being overcharged, but don't really know what caused the problem. Now I have a much cheaper sealed lead acid battery, which I hope will be bombproof. Installed in the tail cone, rather than atop the firewall, it will also help with a slightly nose heavy condition. I have learned latterly that some LiFeO3 batteries will "turn themselves off," when they get down to a 20% charge. Not a good thing in an aircraft. Cheers! Stu. Ashley ---


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PostPosted: Wed Jun 29, 2022 9:30 pm    Post subject: LiFe Battery Reply with quote

Yes, I did mean to write LliFePO4. And I do have it mounted on the engine
side of the firewall. I have seen others mounted in that position and
assumed (dangerous word) that the environment would be acceptable. When I
buy a replacement, I’ll consider an Odyssey. But my gut feeling is that I
was just unlucky and got a “Friday afternoon” battery. Too many examples of
others having better luck with theirs.
Ivan Haecker

On Wed, Jun 29, 2022 at 11:55 PM Stuart Hutchison <
stuart(at)stuarthutchison.com.au> wrote:

[quote] Good that the battery tender had a Lithium profile … maybe the battery was
ultimately a dud or less than expected quality. I assume by LiFe Ivan
means LiFePO4 (Lithium Iron Phosphate).

Actually Ken, the same rated LiFePO4 battery will deliver 80% of its
charge at a relatively flat Voltage profile before the BMS protects the
battery, but the same rated Lead Acid can only be discharged to 50% before
charge is necessary or permanent damage can result. No matter what tech,
we often get what we pay for, hence Odyssey Lead Acids have a good
reputation and some LiFePO4s (like Invicta) do as well. Unsure if LiFePO
degrades in high-heat conditions the same way Li-Ion does … if so, firewall
forward wouldn’t make much sense, but either way they have huge energy
density and can’t be extinguished with a typical fire extinguisher (because
the degrading cathode liberates oxygen inside the case), so there's safety
issue to consider in that too.

Kind regards, Stu
On 30 Jun 2022, at 2:15 am, Ken Ryan <keninalaska(at)gmail.com> wrote:

I'm not sure the 20% cut off number is accurate; I suspect that it is not


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kenryan



Joined: 20 Oct 2009
Posts: 424

PostPosted: Thu Jun 30, 2022 5:28 am    Post subject: LiFe Battery Reply with quote

Ivan, you are correct. There are a lot of examples of LiFe batteries being used without incident. Millions and millions of examples in everything from motorcycles to jetskis to bicycles to, yes, airplanes. Everyone I know with an experimental airplane is now using a LiFe battery (admittedly that's not a large sample). 

On Wed, Jun 29, 2022 at 9:33 PM H. Ivan Haecker <hivanhaecker(at)gmail.com (hivanhaecker(at)gmail.com)> wrote:

[quote]Yes, I did mean to write LliFePO4. And I do have it mounted on the engine side of the firewall. I have seen others mounted in that position and assumed (dangerous word) that the environment would be acceptable. When I buy a replacement, I’ll consider an Odyssey. But my gut feeling is that I was just unlucky and got a “Friday afternoon” battery. Too many examples of others having better luck with theirs.
Ivan Haecker

On Wed, Jun 29, 2022 at 11:55 PM Stuart Hutchison <stuart(at)stuarthutchison.com.au (stuart(at)stuarthutchison.com.au)> wrote:

[quote] Good that the battery tender had a Lithium profile … maybe the battery was ultimately a dud or less than expected quality.  I assume by LiFe Ivan means LiFePO4 (Lithium Iron Phosphate).

Actually Ken, the same rated LiFePO4 battery will deliver 80% of its charge at a relatively flat Voltage profile before the BMS protects the battery, but the same rated Lead Acid can only be discharged to 50% before charge is necessary or permanent damage can result.  No matter what tech, we often get what we pay for, hence Odyssey Lead Acids have a good reputation and some LiFePO4s (like Invicta) do as well.  Unsure if LiFePO degrades in high-heat conditions the same way Li-Ion does … if so, firewall forward wouldn’t make much sense, but either way they have huge energy density and can’t be extinguished with a typical fire extinguisher (because the degrading cathode liberates oxygen inside the case), so there's safety issue to consider in that too.


Kind regards, Stu


[quote] On 30 Jun 2022, at 2:15 am, Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote:

I'm not sure the 20% cut off number is accurate; I suspect that it is not. But putting that aside, there is another way of looking at this--all batteries have a limited capacity. Lead acid batteries will happily discharge until they are dead or badly damaged Lithium batteries with a BMS will stop discharging before they are ruined. How can this be a bad thing? 

It's bad only if you are relying on the advertised capacity number to size your battery. Bob has taught us all that we cannot rely on the advertised capacity number, rather, we should do annual capacity checks to verify the actual capacity. It's just a matter of factoring in BMS behavior when you decide on the size battery you need. 


Would it be nice if there was a switch you could throw to disable the BMS low voltage protection in a real emergency? Sure! Is the lack of such a switch a good reason to write off LiFe technology? Not in my opinion.


On Wed, Jun 29, 2022 at 6:00 AM <ashleysc(at)broadstripe.net (ashleysc(at)broadstripe.net)> wrote:

[quote] --> AeroElectric-List message posted by: ashleysc(at)broadstripe.net (ashleysc(at)broadstripe.net)

Hi Stu.
The Battery Tender (charger) you mentioned is intended for LiFeO3 batteries. I have one too. I have been through two Li FeO3 batteries. In my case it appeared they didn't like the charging system on board the aircraft, even though the charging current went to zero soon after starting the engine. I assumed it was not being overcharged, but don't really know what caused the problem. Now I have a much cheaper sealed lead acid battery, which I hope will be bombproof. Installed in the tail cone, rather than atop the firewall, it will also help with a slightly nose heavy condition. I have learned latterly that some LiFeO3 batteries will "turn themselves off," when they get down to a 20% charge. Not a good thing in an aircraft.
Cheers!   Stu. Ashley

---


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Ceengland



Joined: 11 Oct 2020
Posts: 378
Location: MS

PostPosted: Thu Jun 30, 2022 6:04 am    Post subject: LiFe Battery Reply with quote

Quote:
"I'm not sure the 20% cut off number is accurate; I suspect that it is not. But putting that aside, there is another way of looking at this--all batteries have a limited capacity. Lead acid batteries will happily discharge until they are dead or badly damaged Lithium batteries with a BMS will stop discharging before they are ruined. How can this be a bad thing? "
It can be a bad thing in a couple of ways. 1st, if you lose the alternator. You may need that last few watts to keep the engine turning or the panel lit to make it safely to the ground. I'd happily trade a battery for the airframe (or my life). Would you accept an engine controller that went into 'limp mode' or completely shut down the engine with low oil pressure?
2nd, The existence of a disconnect device means that a malfunction in the device itself can cause a 'false positive' and *create* an emergency.
FWIW...

On Thu, Jun 30, 2022 at 8:31 AM Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote:

[quote]Ivan, you are correct. There are a lot of examples of LiFe batteries being used without incident. Millions and millions of examples in everything from motorcycles to jetskis to bicycles to, yes, airplanes. Everyone I know with an experimental airplane is now using a LiFe battery (admittedly that's not a large sample). 

On Wed, Jun 29, 2022 at 9:33 PM H. Ivan Haecker <hivanhaecker(at)gmail.com (hivanhaecker(at)gmail.com)> wrote:

[quote]Yes, I did mean to write LliFePO4. And I do have it mounted on the engine side of the firewall. I have seen others mounted in that position and assumed (dangerous word) that the environment would be acceptable. When I buy a replacement, I’ll consider an Odyssey. But my gut feeling is that I was just unlucky and got a “Friday afternoon” battery. Too many examples of others having better luck with theirs.
Ivan Haecker

On Wed, Jun 29, 2022 at 11:55 PM Stuart Hutchison <stuart(at)stuarthutchison.com.au (stuart(at)stuarthutchison.com.au)> wrote:

[quote] Good that the battery tender had a Lithium profile … maybe the battery was ultimately a dud or less than expected quality.  I assume by LiFe Ivan means LiFePO4 (Lithium Iron Phosphate).

Actually Ken, the same rated LiFePO4 battery will deliver 80% of its charge at a relatively flat Voltage profile before the BMS protects the battery, but the same rated Lead Acid can only be discharged to 50% before charge is necessary or permanent damage can result.  No matter what tech, we often get what we pay for, hence Odyssey Lead Acids have a good reputation and some LiFePO4s (like Invicta) do as well.  Unsure if LiFePO degrades in high-heat conditions the same way Li-Ion does … if so, firewall forward wouldn’t make much sense, but either way they have huge energy density and can’t be extinguished with a typical fire extinguisher (because the degrading cathode liberates oxygen inside the case), so there's safety issue to consider in that too.


Kind regards, Stu


[quote] On 30 Jun 2022, at 2:15 am, Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote:

I'm not sure the 20% cut off number is accurate; I suspect that it is not. But putting that aside, there is another way of looking at this--all batteries have a limited capacity. Lead acid batteries will happily discharge until they are dead or badly damaged Lithium batteries with a BMS will stop discharging before they are ruined. How can this be a bad thing? 

It's bad only if you are relying on the advertised capacity number to size your battery. Bob has taught us all that we cannot rely on the advertised capacity number, rather, we should do annual capacity checks to verify the actual capacity. It's just a matter of factoring in BMS behavior when you decide on the size battery you need. 


Would it be nice if there was a switch you could throw to disable the BMS low voltage protection in a real emergency? Sure! Is the lack of such a switch a good reason to write off LiFe technology? Not in my opinion.


On Wed, Jun 29, 2022 at 6:00 AM <ashleysc(at)broadstripe.net (ashleysc(at)broadstripe.net)> wrote:

[quote] --> AeroElectric-List message posted by: ashleysc(at)broadstripe.net (ashleysc(at)broadstripe.net)

Hi Stu.
The Battery Tender (charger) you mentioned is intended for LiFeO3 batteries. I have one too. I have been through two Li FeO3 batteries. In my case it appeared they didn't like the charging system on board the aircraft, even though the charging current went to zero soon after starting the engine. I assumed it was not being overcharged, but don't really know what caused the problem. Now I have a much cheaper sealed lead acid battery, which I hope will be bombproof. Installed in the tail cone, rather than atop the firewall, it will also help with a slightly nose heavy condition. I have learned latterly that some LiFeO3 batteries will "turn themselves off," when they get down to a 20% charge. Not a good thing in an aircraft.
Cheers!   Stu. Ashley

---


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kenryan



Joined: 20 Oct 2009
Posts: 424

PostPosted: Thu Jun 30, 2022 7:16 am    Post subject: LiFe Battery Reply with quote

I agree with your comment regarding a BMS override switch. Just thought I would throw it against the wall. I'm glad it's not sticking because I see no need for such a switch.

With regards to the capacity issue, I cannot make the case more plainly than this: If you are comparing a LiFe battery that provides x watt-hours of energy (regardless of what is left after the BMS shuts it down) or a lead acid battery that provides 0.9x watt-hours of energy before things quit working, obviously the LiFe battery will keep things running longer. I was only addressing the previous post (and now your post) that indicated that because the LiFe batteries still have energy left when the BMS shuts them down, that is justification for rejecting the technology. I disagree, based on the above logic. FWIW


On Thu, Jun 30, 2022 at 6:13 AM Charlie England <ceengland7(at)gmail.com (ceengland7(at)gmail.com)> wrote:

[quote]
Quote:
"I'm not sure the 20% cut off number is accurate; I suspect that it is not. But putting that aside, there is another way of looking at this--all batteries have a limited capacity. Lead acid batteries will happily discharge until they are dead or badly damaged Lithium batteries with a BMS will stop discharging before they are ruined. How can this be a bad thing? "
It can be a bad thing in a couple of ways. 1st, if you lose the alternator. You may need that last few watts to keep the engine turning or the panel lit to make it safely to the ground. I'd happily trade a battery for the airframe (or my life). Would you accept an engine controller that went into 'limp mode' or completely shut down the engine with low oil pressure?
2nd, The existence of a disconnect device means that a malfunction in the device itself can cause a 'false positive' and *create* an emergency.
FWIW...

On Thu, Jun 30, 2022 at 8:31 AM Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote:

[quote]Ivan, you are correct. There are a lot of examples of LiFe batteries being used without incident. Millions and millions of examples in everything from motorcycles to jetskis to bicycles to, yes, airplanes. Everyone I know with an experimental airplane is now using a LiFe battery (admittedly that's not a large sample). 

On Wed, Jun 29, 2022 at 9:33 PM H. Ivan Haecker <hivanhaecker(at)gmail.com (hivanhaecker(at)gmail.com)> wrote:

[quote]Yes, I did mean to write LliFePO4. And I do have it mounted on the engine side of the firewall. I have seen others mounted in that position and assumed (dangerous word) that the environment would be acceptable. When I buy a replacement, I’ll consider an Odyssey. But my gut feeling is that I was just unlucky and got a “Friday afternoon” battery. Too many examples of others having better luck with theirs.
Ivan Haecker

On Wed, Jun 29, 2022 at 11:55 PM Stuart Hutchison <stuart(at)stuarthutchison.com.au (stuart(at)stuarthutchison.com.au)> wrote:

[quote] Good that the battery tender had a Lithium profile … maybe the battery was ultimately a dud or less than expected quality.  I assume by LiFe Ivan means LiFePO4 (Lithium Iron Phosphate).

Actually Ken, the same rated LiFePO4 battery will deliver 80% of its charge at a relatively flat Voltage profile before the BMS protects the battery, but the same rated Lead Acid can only be discharged to 50% before charge is necessary or permanent damage can result.  No matter what tech, we often get what we pay for, hence Odyssey Lead Acids have a good reputation and some LiFePO4s (like Invicta) do as well.  Unsure if LiFePO degrades in high-heat conditions the same way Li-Ion does … if so, firewall forward wouldn’t make much sense, but either way they have huge energy density and can’t be extinguished with a typical fire extinguisher (because the degrading cathode liberates oxygen inside the case), so there's safety issue to consider in that too.


Kind regards, Stu


[quote] On 30 Jun 2022, at 2:15 am, Ken Ryan <keninalaska(at)gmail.com (keninalaska(at)gmail.com)> wrote:

I'm not sure the 20% cut off number is accurate; I suspect that it is not. But putting that aside, there is another way of looking at this--all batteries have a limited capacity. Lead acid batteries will happily discharge until they are dead or badly damaged Lithium batteries with a BMS will stop discharging before they are ruined. How can this be a bad thing? 

It's bad only if you are relying on the advertised capacity number to size your battery. Bob has taught us all that we cannot rely on the advertised capacity number, rather, we should do annual capacity checks to verify the actual capacity. It's just a matter of factoring in BMS behavior when you decide on the size battery you need. 


Would it be nice if there was a switch you could throw to disable the BMS low voltage protection in a real emergency? Sure! Is the lack of such a switch a good reason to write off LiFe technology? Not in my opinion.


On Wed, Jun 29, 2022 at 6:00 AM <ashleysc(at)broadstripe.net (ashleysc(at)broadstripe.net)> wrote:

[quote] --> AeroElectric-List message posted by: ashleysc(at)broadstripe.net (ashleysc(at)broadstripe.net)

Hi Stu.
The Battery Tender (charger) you mentioned is intended for LiFeO3 batteries. I have one too. I have been through two Li FeO3 batteries. In my case it appeared they didn't like the charging system on board the aircraft, even though the charging current went to zero soon after starting the engine. I assumed it was not being overcharged, but don't really know what caused the problem. Now I have a much cheaper sealed lead acid battery, which I hope will be bombproof. Installed in the tail cone, rather than atop the firewall, it will also help with a slightly nose heavy condition. I have learned latterly that some LiFeO3 batteries will "turn themselves off," when they get down to a 20% charge. Not a good thing in an aircraft.
Cheers!   Stu. Ashley

---


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PostPosted: Thu Jun 30, 2022 8:42 am    Post subject: LiFe Battery Reply with quote

At 12:49 AM 6/29/2022, you wrote:
Quote:
--> AeroElectric-List message posted by: Stuart Hutchison <stuart(at)stuarthutchison.com.au>

There is much misleading information out there suggesting chargers suitable for Lead Acid are also suitable for Lithium. Do they work? Yes. Do they compromise Lithium longevity? Also yes, absolutely, unless they have a Lithium specific mode.

Excellent question!

For over ten years now I've watched the lithium
based dialog and market . . . and participated
to a small degree.

I've had several maintainers/chargers
with 'mode' switches that claimed to accommodate
various battery chemistries. Even plotted the
charge profiles on a couple to see if different
mode settings produced a significant difference
in performance.

At the same time, virtually all lithium battery
products are advertised as plug-n-play
into applications previously served by
wet or sealed lead-acid.

I've not encountered an alternator voltage
regulator with a lithium/wet/svla selector
switch.

Yes, lithium is not as forgiving as slva . . .
this is why the 'uptown' lithium products
include battery management electronics:
Some combination of O.V. protection, over-discharge
protection, over-heat protection, high discharge
rate protection and perhaps individual cell charge-
balancing.

One assumes that all this 'protection' is to
secure the advertised plug-n-play performance
for replacing lead-acid while standing off
risk of catastrophic, externally induced failures.

If interchangeability of lead-acid and lithium
specific chargers is potentially 'misleading'
then one should refer to the engineering
and marketing literature for the lithium product
under consideration. If the thing is intended
to replace lead-acid without modification to
the vehicle's power system, then it follows
that the same interchangeability would apply
to chargers.

I've had several lithium products run through
my shop over the past ten years . . . still
have an EarthX sample that has been happily
existing tied to the same family of lead-acid
maintainers now pushing 20 or more years old.

Bob . . .

Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"


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PostPosted: Thu Jun 30, 2022 12:52 pm    Post subject: LiFe Battery Reply with quote

At 10:14 AM 6/30/2022, you wrote:
Quote:
I agree with your comment regarding a BMS override switch. Just thought I would throw it against the wall. I'm glad it's not sticking because I see no need for such a switch.

Agreed. The BMS 'should' be configured to disconnect
the cell array when voltage per cell drops below the highest
discharge voltage allowed to prevent permanent damage
to the cell(s).

For LiFePO4 this is generally on the order of

The capacity rating of any battery should be stated
in some energy defining units like Watt-Seconds, Joules,
Watt-Hours, etc. The Ampere-Hour is an arcane
unit of measure . . . it works too if that's the
best you've got.

Every manufacturer of a lithium cell will prescribe
a discharge cutoff voltage. Here's one example calling
out 2.5 Volts:

http://aeroelectric.com/Mfgr_Data/Batteries/LithiumCells/Samsung/INR21700-50E.pdf

A typical LiFePO4 discharge profile will look something
like the attached plot. This is a plot published by
A123. Their cutoff for the plots was at 2.0 Volts.

In either case, note the slope of the plots just below
2.5 volts . . . nearly gone and fading fast. The
BMS cuttoff Voltage may or may not be specified by
the manufacturer of your particular battery . . . but
if not, you should ask 'em.

If they have a 4-cell stack, then a battery cutoff
of 10 Volts would not be out of line . . . this is
below the point where any accessory designed for
aviation applications is expected to function . . .
and even if it were still providing service down to
8.0 Volts . . . it would not enjoy that condition
for long.

So yes, unless your battery has an unrealistic
cuttoff voltage, a BMS bypass switch would add
no value. By the time a cell drops below 2.5
Volts, it's time to go to plan-C.





Bob . . .

Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"


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PostPosted: Thu Jun 30, 2022 1:11 pm    Post subject: LiFe Battery Reply with quote

At 08:58 AM 6/30/2022, you wrote:
Quote:
Quote:
"I'm not sure the 20% cut off number is accurate; I suspect that it is not.

It depends on the battery manufacturer's selected
cutoff voltage but it behooves them to set it as
low as practical . . . which is generally below
a voltage where the battery still possesses useable
energy. I think that 20%/80% meme is a spillover
from some of the electric vehicle battery protocols.
I think I read years ago that some EV energy management
systems work to operate the battery at no less than
20, no more than 80 percent for improved cycle
life. Hence improved service life.

This had nothing to do with the chemistry's
best energy performance.

Quote:
Quote:
. . . batteries with BMS will stop discharging before they are ruined. How can this be a bad thing? "
It can be a bad thing in a couple of ways. 1st, if you lose the alternator. You may need that last few watts to keep the engine turning or the panel lit to make it safely to the ground. I'd happily trade a battery for the airframe (or my life). Would you accept an engine controller that went into 'limp mode' or completely shut down the engine with low oil pressure?

Who did your FMEA for you? What are your battery-only
endurance requirements? What are your plans for periodic
maintenance checks to assure that your endurance goals
are maintained?

Quote:
Quote:
2nd, The existence of a disconnect device means that a malfunction
in the device itself can cause a 'false positive' and *create* an
emergency.

Not sure what that would be. The BMS has what you would
consider to be a solid state battery contactor that is
controlled by software and sensors in the management
sytem. It would be no big deal to add a 'low volts
disconnect override' feature to the BMS controller.

Activating such a feature would not be a situational
risk as it cannot inadvertently create a hazard to
ship's electro-whizzies . . . only hazard to the battery's
internal chemistry as a consequence of an over discharge
where one attempted to squeeze a few more percent
of total capacity from the device.

This would be the operational equivalent of adding
a special suction line to unusable fuel sumps
with a control enabling one to truly suck the
tank dry. But what would be the value?


Bob . . .

Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"


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PostPosted: Thu Jun 30, 2022 1:49 pm    Post subject: LiFe Battery Reply with quote

Quote:
but the same rated Lead Acid can only be discharged to 50% before charge is
necessary or permanent damage can result . . .

Actually . . . not so. SVLA is rather tolerant of
total discharge as long as you can live with
a reduced service life. The CycleLife profile
attached shows the expected reduction in cycle life
for discharge depths of 30 to 100%

It only takes about 10% of total battery capacity
for pre-flight checks and cranking a Beechjet's engine.
So as long as the generator comes on line to support
cranking the second engine, it's no unreasonable to expect
a rather long cycle life.

The DischargeCurves plots show expected energy
delivered for a discharge to essentially zero
percent on each cycle. This is called 'deep cycle'
service and is not something the battery cannot
routinely handle.

When one cap-checks an SVLA battery, a known
load is applied until terminal voltage drops
to 10.5V. For a LiFePO4 with or without BMS,
I would still terminate the test at 10.5 volts
or BMS trip out . . . which ever occurs first

For BOTH technologies, remaining energy in the
battery will be very low on the order of 5%
or less.


Bob . . .

Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"


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wsimpso1



Joined: 04 Nov 2018
Posts: 26
Location: Saline MI

PostPosted: Fri Jul 01, 2022 5:08 am    Post subject: Re: LiFe Battery Reply with quote

The concerns I have with LiFe batteries - and these are not disqualifies - are:

Our baseline is SVLA battery and its connections, and they do have low but real chance of failing and dropping the battery out of the power loop, and we design our systems knowing this can happen. We live with the set of risk (severity times frequency) that this gives us, and we seem comfortable with it too…

Go to LiFe batteries, and we probably have similar low levels of likelihood of a mechanical failure causing us to lose the battery, but now we have added to that there is a set of gadgets internal to the battery that is designed to remove the battery from the power loop. At some level, it too can have failures that cause us to lose the battery, even if nothing is wrong. This is adding failure modes to our system.

In most industries, when we add failure modes, we have to be able to show that aggregate risk is actually made smaller by doing so. In order to make up for adding some risk (sum of severity times frequency for new failure modes) to the already present risk from the battery, well, the new risk has to be really small AND the existing risk has to be made smaller.

Maybe the LiFe batteries do pose small enough risk compared to SVLA batteries and our failure tolerant design covers battery failure adequately. I will remain skeptical until there is a lot more data indicating LiFe are in total of lower risk to us.

Bill


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PostPosted: Fri Jul 01, 2022 3:24 pm    Post subject: LiFe Battery Reply with quote

Quote:
Our baseline is SVLA battery and its connections,
and they do have low but real chance of failing and
dropping the battery out of the power loop,
and we design our systems knowing this can happen.

I've never had occasion to consider this as
a 'factor' in either OBAM or TC aircraft
designs. What is your evidence for frequency
of the event . . . and what are the design
rules for mitigating effects of such an event?

Quote:
Go to LiFe batteries, and we probably have similar low
levels of likelihood of a mechanical failure . . .
<snip
. . . is adding failure modes to our system.

Okay, are you aware of any such incident and what
was the outcome of that incident?

Quote:
Maybe the LiFe batteries do pose small enough risk
compared to SVLA batteries and our failure tolerant
design covers battery failure adequately. I will
remain skeptical until there is a lot more data
indicating LiFe are in total of lower risk to us.

Okay, BOTH technologies will no doubt be controlled
with a battery contactor and master switch. Artful
FMEA says account for risk of loss for those
components.

Now, what difference does it make if your add
more electro-whizzies into the analysis? Accommodating
failure of the battery contactor, by extension, covers
all other failures that manifest as a battery-disconnect
event.

So how does failure of the BMS to convey energy
out of the battery become more than a maintenance
event?


Bob . . .

Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"


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wsimpso1



Joined: 04 Nov 2018
Posts: 26
Location: Saline MI

PostPosted: Sat Jul 02, 2022 7:24 pm    Post subject: Re: LiFe Battery Reply with quote

All things can break. The question of this experienced product engineer is then how often does this occur and how severe is the result of a failure. Some might take the perspective that the risk of completely losing the battery is vanishingly small. Others might say we already have that failure mode covered, so it is no big deal. OK for you guys.

I do know of two pilots I have reason to trust who have described their own experiences with a total failure of a battery (not wiring, but an internal failure that isolated the battery electrically from the airplane) while in flight. While anecdotal, I suspect that gives us some reason to believe that such a failure has some real frequency in our airplanes. I have no idea how small this frequency is and admit that I know nothing of the rest of the maintenance state of these batteries.

The two events occurred in flight. One was detected by an oscillating ammeter reading then the alternator field breaker tripped (or a reset was attempted), resulting in a total electrical failure. In the other case the alternator stayed online until shut off on the ground, and was found that the battery was off line. In both cases the airplanes were simple magneto fired engines being flown in VMC, and were flown to airports for safe landings, which only reinforces our training here that adequate backup really should be present for the failures we think are real.

Adding failure modes to a system does increase total risk from the system (risk = severity * frequency) unless other parts of the system have been made more reliable in the same process. I suspect that internal battery connections are not much different in SVLA and in LiFe batteries, but I could be wrong.

As we are trained on AEC, the concerned designer can examine the failure modes and see to it that any failure mode does not result in a severe outcome nor unnecessarily raise total risk by checking for and perhaps adding suitable redundancy. That issue does not change, but I do suspect that batteries with added internal gadgets may well have higher likelihood of total failure. Be forewarned and design accordingly.

Bill Simpson


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PostPosted: Mon Jul 04, 2022 8:49 am    Post subject: LiFe Battery Reply with quote

Quote:
Others might say we already have that failure mode
covered, so it is no big deal. OK for you guys.

How does one arrive at a conclusion of
'no big deal'? There are no suppositions
allowed in the conduct of an FMEA. Some things
are known by simple deduction . . . if that
wire becomes unhooked, some electro-whizzy
ceases to function.

But what about that battery disconnect
thing? There are a number of variables that
drive the system's ability to function.
Regulator design, alternator dynamics,
nature of operating loads. FEMA credit
for any particular failure cannot be
claimed without CONFIRMATION of a
condition for which there is no obvious
or first-hand knowledge.


Quote:
I do know of two pilots I have reason to trust who have described their own experiences with a total failure of a battery (not wiring, but an internal failure that isolated the battery electrically from the airplane) while in flight. While anecdotal, I suspect that gives us some reason to believe that such a failure has some real frequency in our airplanes. I have no idea how small this frequency is and admit that I know nothing of the rest of the maintenance state of these batteries.


It would have been interesting to do a
failure analysis on the subject batteries.

Exactly. Yes, there are cases where batteries
have gone open-circuit. Skip Koss (Concorde
battery guru) related several events to
me . . . post event teardown revealed
manufacturing defects. In his tenure with
Concorde, he could count those events
the fingers of one hand.


All cases occurred in aircraft that would
function alternator-only. The famous
(or infamous) split-rocker switch was
birthed out of a concern for alternator-
only operations. Generators would run
happily sans-battery but those alternators
were a new thing. I was a lowly tech-writer
back then an not privy to any testing
or perceptions of risk experienced by the
engineers. Nonetheless, whether or not it
was really necessary in all cases, the split
rocker became firmly embedded in aviation
zeitgeist for about 60 years.

A few years later, I was tasked to craft a
new regulator design for the Bonanzas and
Barons. I was astonished to read that Beech
expected an alternator to start up cold and
run sans-battery. Cold start? No battery?
Seems that these airplanes had independent
alternator and battery switches. There was
no prohibition in the POH for alternator-only
operations. Further, the alternators being
used at the time had residual field flux that
would permit start-up sans battery. That's
a long story!

Quote:
The two events occurred in flight. One was detected by an oscillating ammeter reading then the alternator field breaker tripped (or a reset was attempted), resulting in a total electrical failure. In the other case the alternator stayed online until shut off on the ground, and was found that the battery was off line. In both cases the airplanes were simple magneto fired engines being flown in VMC, and were flown to airports for safe landings, which only reinforces our training here that adequate backup really should be present for the failures we think are real.

To be sure, artful FMEA discovers and mitigates
real risks. Suppositions requiring verification
need to be tested. While doing the obligatory
test-area-flyoff with a new or recently modified
airplane, one is well advised to do the good
test pilot things and confirm/refine your
plan-A/plan-B operations.


Quote:
Adding failure modes to a system does increase total risk from the system (risk = severity * frequency) unless other parts of the system have been made more reliable in the same process. I suspect that internal battery connections are not much different in SVLA and in LiFe batteries, but I could be wrong.

The unfortunate thing about the dark-n-stormy-night
stories is that they very seldom achieve resolution
of root causes. The instances you've cited
cannot rise above anecdotal status without
investigation and discovery of root cause.
But they certainly contribute to builder/pilots
who have 'worries' but lack tools for mitigation.

This is the beauty of FMEA . . . we don't wrestle
with failure rates we only study outcome of flight
assuming that the failure will occur. It matters
not if MTBF on the thing is 1000 or 100 hours.


Quote:
As we are trained on AEC, the concerned designer can examine the failure modes and see to it that any failure mode does not result in a severe outcome nor unnecessarily raise total risk by checking for and perhaps adding suitable redundancy. That issue does not change, but I do suspect that batteries with added internal gadgets may well have higher likelihood of total failure. Be forewarned and design accordingly.

True . . . but artful design is limited by
a lack of information. The 'scientific method'
demands that every supposition be questioned.
The more folks participating in the conversation
the better.


Bob . . .

Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"


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