Li Poly Batteries

That thing's rated for 2C, or 200mA current. That's not enough to fire an average E-match, much less estes igniter. Subject it to too much higher current and you're looking at those shorting problems mentioned earlier.

Reading the document on this is interesting.

Originally posted by cjl
That thing's rated for 2C, or 200mA current. That's not enough to fire an average E-match, much less estes igniter. Subject it to too much higher current and you're looking at those shorting problems mentioned earlier.

Click to expand...

But it did.

I don't use them for that. I use two in series (because the electronics want more than 3.7V) to fire flashbulbs. They have no problem burning through a Christmas bulb. I haven't tried an electric match.

Oh - it will do it. But, it is more than the rated current by quite a bit, so you can get into some permanent battery damage. That's one of those things you have to be really careful with on a lithium.

Originally posted by cjl
Oh - it will do it. But, it is more than the rated current by quite a bit, so you can get into some permanent battery damage. That's one of those things you have to be really careful with on a lithium.

Click to expand...

I have no intention of using them that way but I couldn't resist trying. I also hooked one up to a small electric motor and let it run for a few minutes. The battery got a little warm!

Originally posted by cjl
Oh - it will do it. But, it is more than the rated current by quite a bit, so you can get into some permanent battery damage. That's one of those things you have to be really careful with on a lithium.

Click to expand...

You will not get permanent damage for a Li-Po battery by firing an igniter with the referenced Li-Po battery.

The datasheet states the internal impedence is 0.025 ohms. The resistance of an Estes igniter is ~0.8 ohms. You need 2 amps to fire an Estes igniter so the minimum voltage requirement is V=ri=0.8*2=1.6 volts. A single Li-Po cell generates ~3.7 volt, so and if we consider a low resistance for the wiring the total pyro circuit resistance is in the range of 1-1.25 ohm. The current draw would be i=V/r=3.7/1 to 3.7/1.25 = 3 to 3.7 amps peak, and as you heat the igniter the resistance increases so the current draw decreases. A conventional igniter circuit operates for ~1 second. Triggered for a second, you would be consuming not more than 3.7*3.7=13.7 Joules of energy. The energy capacity of the battery is C =0.1 AH*3.7volts*3600 J/watt-hr=1332 joules. Firing the igniter consumes ~1% of the battery's capacity. The battery weighs 10 g. Assuming a heat capacity of ~1 J/g-K, the approximate temperature rise in the battery is 13.7J/(10g*1J/g-K)~1.4 C or ~2.5F so it doesn't overheat the battery either.

Even if you were to short out the battery, a complete short circuit of the battery would heat the battery to ~-1332J/(10g*1g-K) or ~140C or 250 F above it's starting temperature. It may get hotter internally and bulge the casing or melt the plastic and rupture it, but it won't get hot enough to catch fire. (but it will certaily burn your skin, anything over 50C can give you a burn.) Li-Po batteries have a solid conductive polymer electrolyte, so unlike the flamable liquid electrolyte in the Li-ion batteries in your laptop, Li-Po batteries don't throw out flaming liquid and are quite safe, and the stuff inside the battery is not more chemically dangerous than what's inside other batteries.

For those folks who still believe that Li-Po batteries are an unacceptable risk, please read the attached DOT regulations concerning the air shipment of lithium batteries on passenger aircraft. You should be able to do the math and assess for yourself what DOT and the FAA consider dangerous.

Bob

quote:

These aren't all that expensive:

https://www.sparkfun.com/commerce/pr...products_id=731

Click to expand...

Thanks for the link. These look almost identical to the ones I'm designing around, and they're cheaper!

The battery weighs 10 g. Assuming a heat capacity of ~1 J/g-K, the approximate temperature rise in the battery is 13.7J/(10g*1J/g-K)~1.4 C or ~2.5F so it doesn't overheat the battery either.

Click to expand...

The sparkfun site said its mass is under a gram, and a very similar battery I'm using weighs 1.2 g. The formatting on the spec sheet is kind of messed up so I think it obscured the decimal point.

But note this other item in the spec sheet:

7.3 Short-circuit
At 20±5
, connect batteries’ anode and cathode by wire
which impedance less than 50m, keep 6h. N
No explosion or fire

Click to expand...

I was pointed to some rc links which kind of goes in the direction of if LiPolys are damaged be careful. The first link is -

https://www.rcgroups.com/forums/showthread.php?t=209187

This section from the above link caught my eye -

[If you crash in ANY way carefully remove the battery pack from the aircraft and watch it carefully for at least the next 20 min. Several fires have been caused by damaged cells being thrown in the car and then the cells catch fire later and destroys the car completely."]

Further down there is another post I found interesting :

--------------------------------------------------------
CAUSE UNDETERMINED:
Multi cell pack catches fire in flight (5)
Lipo pack catches fire in car (60)
2s pack starts house fire (84)
In flight F3A fire reported (92)
New pack partially burns sitting on desk (96)
Pack ignites with no known cause (97)
Pack catches fire in pick up truck (105)
In Air ignition – (125)
Pack ignites in pocket (132) - AWKWARD IN PUBLIC
Pack ignites in car at 3AM (134)
--------------------------------------------------------

Another link warning that damaged LiPoly batteries are a fire hazzard -

https://www.3dhobbyshop.com/LiPoly_Safety.aspx .

The part that is interesting seems to be in all the RC links I have been sent -

[DO NOT immediately put a crashed Li-Poly battery into your automobile without the protection of a fireproof container.]

It seemsthe arguements for or against using LiPoly packs in rockets is similar to the seat belt debate. Until it happens you do not think there is going to be a problem, but if it does happen, and you don't have the seat belt on, you are seriously screwed.

Originally posted by bobkrech
For those folks who still believe that Li-Po batteries are an unacceptable risk, please read the attached DOT regulations concerning the air shipment of lithium batteries on passenger aircraft. You should be able to do the math and assess for yourself what DOT and the FAA consider dangerous.

Click to expand...

DOT is concerned with risk AS SHIPPED, not AS USED. For example, the DOT regulations for rocket motors does not infer the risk of using a rocket a rocket motor (or misusing one).

-John

bobkrech said:

You will not get permanent damage for a Li-Po battery by firing an igniter with the referenced Li-Po battery.

The datasheet states the internal impedence is 0.025 ohms. The resistance of an Estes igniter is ~0.8 ohms. You need 2 amps to fire an Estes igniter so the minimum voltage requirement is V=ri=0.8*2=1.6 volts. A single Li-Po cell generates ~3.7 volt, so and if we consider a low resistance for the wiring the total pyro circuit resistance is in the range of 1-1.25 ohm. The current draw would be i=V/r=3.7/1 to 3.7/1.25 = 3 to 3.7 amps peak, and as you heat the igniter the resistance increases so the current draw decreases. A conventional igniter circuit operates for ~1 second. Triggered for a second, you would be consuming not more than 3.7*3.7=13.7 Joules of energy. The energy capacity of the battery is C =0.1 AH*3.7volts*3600 J/watt-hr=1332 joules. Firing the igniter consumes ~1% of the battery's capacity. The battery weighs 10 g. Assuming a heat capacity of ~1 J/g-K, the approximate temperature rise in the battery is 13.7J/(10g*1J/g-K)~1.4 C or ~2.5F so it doesn't overheat the battery either.

Even if you were to short out the battery, a complete short circuit of the battery would heat the battery to ~-1332J/(10g*1g-K) or ~140C or 250 F above it's starting temperature. It may get hotter internally and bulge the casing or melt the plastic and rupture it, but it won't get hot enough to catch fire. (but it will certaily burn your skin, anything over 50C can give you a burn.) Li-Po batteries have a solid conductive polymer electrolyte, so unlike the flamable liquid electrolyte in the Li-ion batteries in your laptop, Li-Po batteries don't throw out flaming liquid and are quite safe, and the stuff inside the battery is not more chemically dangerous than what's inside other batteries.

For those folks who still believe that Li-Po batteries are an unacceptable risk, please read the attached DOT regulations concerning the air shipment of lithium batteries on passenger aircraft. You should be able to do the math and assess for yourself what DOT and the FAA consider dangerous.

Bob

Click to expand...

I am not trying to be rude, but it doesn't seem to me that you have been to very many rocket launches. At the launches I go to, about 1 out of 10 big rockets crash. Most of those crashes are going to damage a LiPo battery, because they have a flimsy foil case. Air transport regulations are a whole different thing, because if the plane crashes, the damage is already done. Who cares if the battery catches on fire after the plane crashes? However, with a rocket, our main risk is starting a fire. Have you seen the videos of the battery that is punctured with a nail and catches on fire? How does your math explain that?

I don't know what your level of risk is, but I think that if there is a 1 in 100 or 1 in 500 chance of starting a fire, then that is too high. Over the course of a year, we would easily have that many crashes, and start at least 1 forest fire. In the southeast, there is a drought, and we usually launch in remote areas, so the forest fire could be devastating.

David

If 1 in 10 big rockets crash, then there are other problems to start with. Also, if you read what he actually wrote, he stated that they will not catch fire, regardless of what happens to them.

palomar said:

Most of those crashes are going to damage a LiPo battery, because they have a flimsy foil case.

Click to expand...

I disagree. It's a matter of packaging. I put two cells together, encased them in heat shrink tubing and fastened them with velcro to the piece of plywood that held the electronics. The rocket was a reasonably heavy hybrid going for a nice low flight to 800'. I forgot to arm the electronics so the rocket went straight up and straight down. The batteries got knocked off the velco and bounced around a little but there was no damage to them. The rocket wasn't as fortunate. Years ago I had a rocket that had an altimeter that used a 9V battery make a sudden stop from a much lower altitude. That's when I learned what's inside a 9V battery because it broke open on impact.

cjl said:

If 1 in 10 big rockets crash, then there are other problems to start with. Also, if you read what he actually wrote, he stated that they will not catch fire, regardless of what happens to them.

Click to expand...

But what he said is not true. There are all kinds of videos on youtube of LiPo batteries catching on fire. And even if you discount those as fake, I know 2 people who fly RC planes who have had RC batteries catch on fire after a plane crash. One of them had his car burn up, because he put the plane in the trunk after a crash and it caught on fire 20 minutes later. He showed a lot of math, but real world experience says that they do catch on fire. And I do agree that 1 in 10 rockets crashing indicates a problem, but that is a fact as well. These are experienced Level 3 fliers, and occasionally a parachute gets stuck or a charge fails to go off. Often the crashes are enough to smash everything in the altimter bay. I have many first hand pictures - i've even seen a 9v battery get smashed.

So I think the question comes back to - what odds of a forest fire are acceptable?

David

I disagree that LiPoly batteries are safe. The discharge rate of some lithium's are rated at 20C. If there is an internal or external short a 1 amp battery can pump out 20 amps long enough to do damage. Another danger comes from the hydrogen released as the battery heats up. The explosion that results when the hydrogen goes up is impressive. I KNOW! My wireless mouse blew up. The explosion wiped out the mouse, damaged my flat screen and spewed crap over half my the room. If I had been in the room, I would have been blinded in at least one eye. If the gas cannot escape fast enough, but not fast enough to explode, the gas can fuel a serious fire.

Will it happen in a rocket? Who knows, but, I think the possibility is definitely there.

There are new Lithium batteries out that are based on different designs and chemistries that reduce the possibility of over heating and/or releasing hydrogen - https://www.batteryspace.com/prod-specs/HLCF18650PLi-ion.ppt .

palomar said:

But what he said is not true. There are all kinds of videos on youtube of LiPo batteries catching on fire. And even if you discount those as fake, I know 2 people who fly RC planes who have had RC batteries catch on fire after a plane crash. One of them had his car burn up, because he put the plane in the trunk after a crash and it caught on fire 20 minutes later. He showed a lot of math, but real world experience says that they do catch on fire. And I do agree that 1 in 10 rockets crashing indicates a problem, but that is a fact as well. These are experienced Level 3 fliers, and occasionally a parachute gets stuck or a charge fails to go off. Often the crashes are enough to smash everything in the altimter bay. I have many first hand pictures - i've even seen a 9v battery get smashed.

So I think the question comes back to - what odds of a forest fire are acceptable?

David

Click to expand...

Those are much higher energy, much larger cells than what you would use for rocketry - not really comparable.

palomar said:

I am not trying to be rude, but it doesn't seem to me that you have been to very many rocket launches. At the launches I go to, about 1 out of 10 big rockets crash. Most of those crashes are going to damage a LiPo battery, because they have a flimsy foil case. Air transport regulations are a whole different thing, because if the plane crashes, the damage is already done. Who cares if the battery catches on fire after the plane crashes? However, with a rocket, our main risk is starting a fire. Have you seen the videos of the battery that is punctured with a nail and catches on fire? How does your math explain that?

I don't know what your level of risk is, but I think that if there is a 1 in 100 or 1 in 500 chance of starting a fire, then that is too high. Over the course of a year, we would easily have that many crashes, and start at least 1 forest fire. In the southeast, there is a drought, and we usually launch in remote areas, so the forest fire could be devastating.

David

Click to expand...

David

I don't know your level of expertise in Hazmat Shipping, Safety and Risk Evaluation, Battery Chemistry, and the design and construction of electronic systems for military and aerospace related systems. I have 36 years of professional experience in these areas so I have a fair bit of knowledge in these matters.

I was specifically refering to a 10 g Li-Po battery. All Li-Po batteries sold must meet certain minimum safety test standards. These tests are required internationally for all Li-Po cells before they be sold and shipped, let alone use. The purpose of transportation regulations are not to prevent fires after a crash, but rather to prevent a fire or other situation cause by a hazardous material that will cause a crash.

Safety Test

Test conditions：The following tests must be measured at flowing air and safety protection conditions. All batteries must standard charge and lay 24h.

Item Test Methods Performance

7.1 Over charge - At 20±5℃, charging batteries with constant current 3C5A to voltage5V, then with constant voltage5V till current decline to 0. Stop test till batteries’ temperature 10℃ lower than max temperature. ==> No explosion or fire

7.2 Over discharge - At 20 ± 5 ℃ , discharge battery with 0.2C5A
continuously 12.5h. ==> No explosion or fire

7.3 - Short-circuit - At 20±5℃, connect batteries’ anode and cathode by wire which impedance less than 50mΩ, keep 6h. ==> No explosion or fire

7.4 Extrusion - At 20±5℃, put the battery in two parallel steal broad, add pressure 13kN. ==> No explosion or fire

7.5 Thermal shock - Put the battery in the oven. The temperature of the oven is to be raised at 5±1℃ per minute to a temperature of 130±2℃ and remains 60 minutes. ==> No explosion or fire

The bottom line is that there is nothing that can happen in a rocket crash to a 10 grams Li-Po battery that will cause a battery fire.

Bob

bobkrech said:

David

I don't know your level of expertise in Hazmat Shipping, Safety and Risk Evaluation, Battery Chemistry, and the design and construction of electronic systems for military and aerospace related systems. I have 36 years of professional experience in these areas so I have a fair bit of knowledge in these matters.

I was specifically refering to a 10 g Li-Po battery. All Li-Po batteries sold must meet certain minimum safety test standards. These tests are required internationally for all Li-Po cells before they be sold and shipped, let alone use. The purpose of transportation regulations are not to prevent fires after a crash, but rather to prevent a fire or other situation cause by a hazardous material that will cause a crash.

Safety Test

Test conditions：The following tests must be measured at flowing air and safety protection conditions. All batteries must standard charge and lay 24h.

Item Test Methods Performance

7.1 Over charge - At 20±5℃, charging batteries with constant current 3C5A to voltage5V, then with constant voltage5V till current decline to 0. Stop test till batteries’ temperature 10℃ lower than max temperature. ==> No explosion or fire

7.2 Over discharge - At 20 ± 5 ℃ , discharge battery with 0.2C5A
continuously 12.5h. ==> No explosion or fire

7.3 - Short-circuit - At 20±5℃, connect batteries’ anode and cathode by wire which impedance less than 50mΩ, keep 6h. ==> No explosion or fire

7.4 Extrusion - At 20±5℃, put the battery in two parallel steal broad, add pressure 13kN. ==> No explosion or fire

7.5 Thermal shock - Put the battery in the oven. The temperature of the oven is to be raised at 5±1℃ per minute to a temperature of 130±2℃ and remains 60 minutes. ==> No explosion or fire

The bottom line is that there is nothing that can happen in a rocket crash to a 10 grams Li-Po battery that will cause a battery fire.

Bob

Click to expand...

I received a reply some time back from a person who tested batteries for a living. He descriped some seriously nasty experiments with batteries. From what I understood from his email was that Lithiums can hurt and burn no matter what the size.

The batteries that blew up my wireless mouse were two AA lithium primary batteries.Primary Lithiums cannot do 20C,yet they exploded. It is not pressure that causes LiPoly to burst into flames, it is heat and hydrogen from a external or internal short circuit. If you check online there are several people have had some very bad experience with Lithium batteries catching fire in small flashlights. Again, the probability is low, but one should be aware of the possibility and plan accordingly. Hight probability - no, but if it happens nasty things happen.

bobkrech said:

7.3 - Short-circuit - At 20±5℃, connect batteries’ anode and cathode by wire which impedance less than 50mΩ, keep 6h. ==> No explosion or fire

Click to expand...

This means the battery itself, right? I don't plan to try it with my Li-Poly batteries but I've stupidly put a 9V ni-cad in a pocket full of change and I'm pretty sure the coins were getting hot enough to light my pants on fire when I figured out what was happening. Actually, I'm not sure it wasn't the battery that was getting hot too. But the point I'm trying to make is, that once you rule out the battery chemistry, any power source has the potential to start a fire by heating up whatever is shorting it.

Arnold Roquerre said:

The batteries that blew up my wireless mouse were two AA lithium primary batteries.

Click to expand...

Are we all talking about the same thing? From what I've read, lithium ion and lithium ion polymer aren't the same thing. According to Wikipedia:

Cells sold today as polymer batteries have a different design from the older lithium-ion cells. Unlike lithium-ion cylindrical, or prismatic cells, which have a rigid metal case, polymer cells have a flexible, foil-type (polymer laminate) case, but they still contain organic solvent. The main difference between commercial polymer and lithium-ion cells is that in the latter the rigid case presses the electrodes and the separator onto each other, whereas in polymer cells this external pressure is not required because the electrode sheets and the separator sheets are laminated onto each other.

Your batteries that blew up aren't the same type of batteries that I've been using.

Arnold Roquerre said:

I received a reply some time back from a person who tested batteries for a living. He descriped some seriously nasty experiments with batteries. From what I understood from his email was that Lithiums can hurt and burn no matter what the size.

The batteries that blew up my wireless mouse were two AA lithium primary batteries. Primary Lithiums cannot do 20C,yet they exploded. It is not pressure that causes LiPoly to burst into flames, it is heat and hydrogen from a external or internal short circuit. If you check online there are several people have had some very bad experience with Lithium batteries catching fire in small flashlights. Again, the probability is low, but one should be aware of the possibility and plan accordingly. Hight probability - no, but if it happens nasty things happen.

Click to expand...

Arnold

You are comparing apples and oranges. There are dozens of Lithium battery chemistries, and not all of them are unfriendly. The older primary Lithium Thionyl Chloride batteries are nasty and are typically only found in certain military systems. They are nasty because they contain free lithium metal which is highy reactive, and in larger sizes tend to be touchy when used in a pack configuration under high discharge conditions. The UltraLife 9 volt primary batteries utilize an entirely different chemisty as do the Lithium polymer batteries which also use a different construction, and both have no free lithium, so this failure mode doesn't happen.

China is the world's largest producer of batteries of all types, and are the largest consumers of LiPo batteries, and the quality is excellent. (Their largest cell phone company has over 300,000,000 subscribers, more than the population of the US.) Unlike other battery chemistries, there is not such thing as a lower quality Li-Po battery simply because a low quality battery won't work satisfactory. Period.

There have been some issues with counterfit Li-Po cell Phone batteries which are much larger than the 10 gm Li-Po cell I specifically mentioned. The issue here was a manufacturing issue unrelated to battery chemistry, and none of these counterfit batteries underwent the internationally required QC testing to detect defective batteries before they leave the maufacturing facility.

The rash of "brand name" Li-ion computer battery failures that made lots of press earlier this year were due to a manufacturing process error, not battery chemistry. The same mnufacturing errors would have caused similar NiMH or NiCad failures as well. Li-Po batteries employ similar chemistry, however legitimate Li-Po batteries have significantly different internal construction and are not subject to the failure mode that those cylindrical Li-ion batteries experienced.

Any large multi-cell battery can be dangerous. The ubiquitious car battery is really dangerous when shorted. In my younger day when I drove junker, I had the battery hold-down clamp fail and short the battery out while I was driving on a bumpy road in Hartford. The 1/8" steel rod went white hot and burned through after setting the engine wiring and underhood insulation on fire. Battery chemisty was not an issue here, battery capacity and size was.

The biggest danger with large battery packs of any type is heating due a rapid discharge of the battery by shorting the terminals which is the problem with electric and hybrid vehicles that have crashed. Large current capability and high voltage from a battery pack represent an electrocution hazard and a fire hazard due to a wire shorting out. It has nothing to do with chemistry as most of the electric/hybrid cars use NiMH, NiCad or Pb battery packs.

Bob

bobkrech said:

David

I don't know your level of expertise in Hazmat Shipping, Safety and Risk Evaluation, Battery Chemistry, and the design and construction of electronic systems for military and aerospace related systems. I have 36 years of professional experience in these areas so I have a fair bit of knowledge in these matters.

I was specifically refering to a 10 g Li-Po battery. All Li-Po batteries sold must meet certain minimum safety test standards. These tests are required internationally for all Li-Po cells before they be sold and shipped, let alone use. The purpose of transportation regulations are not to prevent fires after a crash, but rather to prevent a fire or other situation cause by a hazardous material that will cause a crash.

Safety Test

Test conditions：The following tests must be measured at flowing air and safety protection conditions. All batteries must standard charge and lay 24h.

Item Test Methods Performance

7.1 Over charge - At 20±5℃, charging batteries with constant current 3C5A to voltage5V, then with constant voltage5V till current decline to 0. Stop test till batteries’ temperature 10℃ lower than max temperature. ==> No explosion or fire

7.2 Over discharge - At 20 ± 5 ℃ , discharge battery with 0.2C5A
continuously 12.5h. ==> No explosion or fire

7.3 - Short-circuit - At 20±5℃, connect batteries’ anode and cathode by wire which impedance less than 50mΩ, keep 6h. ==> No explosion or fire

7.4 Extrusion - At 20±5℃, put the battery in two parallel steal broad, add pressure 13kN. ==> No explosion or fire

7.5 Thermal shock - Put the battery in the oven. The temperature of the oven is to be raised at 5±1℃ per minute to a temperature of 130±2℃ and remains 60 minutes. ==> No explosion or fire

The bottom line is that there is nothing that can happen in a rocket crash to a 10 grams Li-Po battery that will cause a battery fire.

Bob

Click to expand...

That is all fine, but what about a 50g or 100g battery that could be used for multiple staged airstarts? I'm sure you are very proud of your chemistry knowledge and experience, but here is a post showing 153 documented cases of LiPo batteries catching fire:

https://www.rcgroups.com/forums/showpost.php?p=1936758&postcount=5

palomar said:

That is all fine, but what about a 50g or 100g battery that could be used for multiple staged airstarts? I'm sure you are very proud of your chemistry knowledge and experience, but here is a post showing 153 documented cases of LiPo batteries catching fire:

https://www.rcgroups.com/forums/showpost.php?p=1936758&postcount=5

Click to expand...

Palomar

Did you read these threads? Virtually all of these incidents involved damaged, shorted. overcharged and overdischarged batteries. Many stories I read involved batteries that had been abused, damaged in crashes and by penetrations, and then were knowingly recharged after they had been observed to be damaged and none of these packs had the electronic protection circuitry that is supposed to be part of a LiPo pack.

I'm sorry but LiPo batteries are safe when used properly, it's the users that are careless and cavalier, and some instances down right dangerous. Does this callous attitude mean we should we ban a certain type of battery because a large number of users think they know far more than the manufacturer and blantantly refuse to follow the recommendations of the manufacturer and the battery industry? I think not. Does it mean the the CPSC should ban most currently marked LiPo battery packs? Probably.

Large batteries contain a large amount of stored chemical energy. The impedence of LiPo flatpacks is low and they are capable of delivering high currents for long periods of time. If you drive a screw or knife through such a pack you can easily delivery a kilowatt or more of power into whatever does the penetration and it gets hot. While the battery will not explode, the plastic casing can burn and certainly anything nearby can catch fire: your pants (yes someone threw a damaged battery in the pants pocket, their BMW (yes someone put a damaged battery on the rear seat of their car), the field box (yes someone threw loose LiPo batteries in their field box without protection), their kitchen (yes, someone charged a series/parallel pack without electronic protection unattended in their kitchen), etc., etc., etc.

The electronic battery pack circuitry I am talking about is expensive, probably about $80 for a high power pack, and from what I have seen, hobby R/C LiPo packs don't apparently contain them. Ok, well then please tell me how you can prevent a single cell in a pack from discharge to less than 2.5 volts or charging to more than 4.2 volts, and in the case of a series parallel pack, how you can prevent a highly charged battery from discharging into a discharged battery. The short and simple answer is that you can't.

Hobby R/C flyiers and some rocket folks routinely abuse LiPo batteries and then when they overheat and cause a fire, they cry foul. It's time for them to grow up, take some responsibility, spend the time to read and understand how to properly use LiPo batteries, and stop being so cheap and pay the bucks to make safe battery packs. Doing so isn't rocket science, it's plain old common sense.

Bob

I agree with you Bob. People just need to follow the recommended safety procedures for these packs and use common sense.

I just have one question for you Bob, how long does it take for a lipo pack to discharge to below the 3V minimum if left alone and not connected to anything?

Thanks,
Mike

sailmike said:

I just have one question for you Bob, how long does it take for a lipo pack to discharge to below the 3V minimum if left alone and not connected to anything?

Thanks,
Mike

Click to expand...

Mike

A stored LiPo battery is considered to be pretty much finished at 85% discharge level regardless of the terminal voltage, which under no load might still be as high as 3.75 V. It certainly can be discharged to even lower voltages, but it's recommended to occasionally charge batteries in storage to at least 3.9 volts and not let them drop below 3.6 volts to prevent degradation.

A LiPo cell self-discharges at a rate of 5% to 10% of capacity per month which implies a shelf-life of 36 to 18 months to the 85% discharged state. From what I can gather from several data sheets, LiPo batteries are typically shipped charged to 50% -> 10% of capacity.

Bob

bobkrech said:

Palomar

Did you read these threads? Virtually all of these incidents involved damaged, shorted. overcharged and overdischarged batteries. Many stories I read involved batteries that had been abused, damaged in crashes and by penetrations, and then were knowingly recharged after they had been observed to be damaged and none of these packs had the electronic protection circuitry that is supposed to be part of a LiPo pack.

I'm sorry but LiPo batteries are safe when used properly, it's the users that are careless and cavalier, and some instances down right dangerous. Does this callous attitude mean we should we ban a certain type of battery because a large number of users think they know far more than the manufacturer and blantantly refuse to follow the recommendations of the manufacturer and the battery industry? I think not. Does it mean the the CPSC should ban most currently marked LiPo battery packs? Probably.

Large batteries contain a large amount of stored chemical energy. The impedence of LiPo flatpacks is low and they are capable of delivering high currents for long periods of time. If you drive a screw or knife through such a pack you can easily delivery a kilowatt or more of power into whatever does the penetration and it gets hot. While the battery will not explode, the plastic casing can burn and certainly anything nearby can catch fire: your pants (yes someone threw a damaged battery in the pants pocket, their BMW (yes someone put a damaged battery on the rear seat of their car), the field box (yes someone threw loose LiPo batteries in their field box without protection), their kitchen (yes, someone charged a series/parallel pack without electronic protection unattended in their kitchen), etc., etc., etc.

The electronic battery pack circuitry I am talking about is expensive, probably about $80 for a high power pack, and from what I have seen, hobby R/C LiPo packs don't apparently contain them. Ok, well then please tell me how you can prevent a single cell in a pack from discharge to less than 2.5 volts or charging to more than 4.2 volts, and in the case of a series parallel pack, how you can prevent a highly charged battery from discharging into a discharged battery. The short and simple answer is that you can't.

Hobby R/C flyiers and some rocket folks routinely abuse LiPo batteries and then when they overheat and cause a fire, they cry foul. It's time for them to grow up, take some responsibility, spend the time to read and understand how to properly use LiPo batteries, and stop being so cheap and pay the bucks to make safe battery packs. Doing so isn't rocket science, it's plain old common sense.

Bob

Click to expand...

Bob, I am not trying to say that we shold ban LiPo battery packs. I agree that if used correctly, LiPo batteries are very unlikely to cause problems. You keep getting defensive and ignoring the question I originally asked. Have you ever seen a rocket crash? Don't you think a rocket crash would create the potential for a situation where a battery is damaged or shorted, and therefore could cause a fire? Don't you think these pictures show electronics bays that could have damaged the battery? Haven't you seen a rocket come in ballistic and it takes a long time to find the rocket, plenty of time for a fire to start and spread, especially in dry conditions?

https://www.fototime.com/{60EE34B0-4052-4327-A613-81F5F5C90DCB}/picture.JPG
https://www.fototime.com/{B0B89BD6-2321-4457-A7A0-F1B75783920E}/picture.JPG
https://www.nomatech.com/rockets/P4130050.JPG

You can of course respond along the lines of "if rockets were designed and flown correctly, they would not crash" but I do not believe that is valid either, because many of the rocket crashes I have seen are very experienced L3 and TAP members.

David

Don't you think these pictures show electronics bays that could have damaged the battery?

David

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Sorry, my previous post was missing the best picture ever of a rocket crash. See the altimeter all broken up? Can you at least admit that this could have damaged a LiPo battery?

https://www.nomatech.com/rockets/P6300014.JPG

David

palomar said:

Sorry, my previous post was missing the best picture ever of a rocket crash. See the altimeter all broken up? Can you at least admit that this could have damaged a LiPo battery?

https://www.nomatech.com/rockets/P6300014.JPG

David

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That's about what happened when my Tomahawk crashed. The altimeter snapped in half, 1,4" aluminum hardware was bend and sheared off, and the top 2/3 of the airframe (glassed) shattered into pieces less than 1" square.

Here's the stuff I saved:
https://www.micronetsoftware.com/gallery2/v/rockets/tomahawk/parts.jpg.html

The nose cone only went in a few inches the ground was extremely hard:
https://www.micronetsoftware.com/gallery2/v/rockets/tomahawk/nose.jpg.html

I can't remember what happened to the 9V battery.