A Lipo lesson

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thobin

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I have been putting the final touches on all my AV bays switching all my power to Lipo batteies. So far as far as I can tell they have a pretty impressive charge life especially for the low power suck that most altimeter draw. Never the less I recently ran into one slight problem with one of my lipos.

They may not be all that new to rechargeable world they are new to me and I learned a valuable lesson with one of my batts, I inadvertently left it connected to one of my altimeters when I put it away till the next launch. (2 months away) Oops!:bang:

Normally I never leave any batt hooked up when not in use for a long period of time, anyway the lipo was drained dead to 0 volts. Now some of you may ask why this is a problem and with a quick Google search as I did you will find that a lipo charger will not charge a 0 volt lipo, because it has dropped below the minimum voltage that lipos are meant to be kept at.

Now I didn't read further to find out why they must be kept at certain voltage (I could care less, now that I know I just wont let it happen again.) :facepalm: What I did want to know was could it be saved?... What I have found that you can bring a completely drained Lipo back up to a voltage that your charger will recognize and start charging. Do do this you need to charge it for a few minuets as a nicad battery, depending on the voltage of the lipo, a 3.4 might only take minute or less.

Now this is risky and you need to watch the lipo make sure it doesn't heat up or swell up. (Never leave it unattended no matter how you are charging it!)
Once you have done that you can hook it up as a lipo and your charge should pick it up and let you charge the batt normally.

Now that said I doubt I would every trust it to run an altimeter again at least never by it's self with out a backup. but at least it can be used to power up a non essential item you may have.

SO remember unplug you batteries it will save you some headache!


TA
 
It is worse than that.

Any lipo battery pack will include a battery protection circuit intended to protect it from various faults. But one thing it will not do is protect from the small but constant current drawn by the battery protection circuit. A single lipo cell without a protection circuit will maintain a charge for a very long time. A battery will be completely discharged by the battery protection circuit given enough time.
 
I am just getting into Lipos myself, so far I have had amazing results but how you maintain them is very different from other battery chemistry that I am used to. I am using Thunderpower and invested in a decent charger, which I believe is well worth it. Here is a link on the charger I have which in itself is insightful on Lipo batteries in general, especially storage.

https://www.youtube.com/watch?v=YNTL8-y0hYs
 
It is worse than that.

Any lipo battery pack will include a battery protection circuit intended to protect it from various faults. But one thing it will not do is protect from the small but constant current drawn by the battery protection circuit. A single lipo cell without a protection circuit will maintain a charge for a very long time. A battery will be completely discharged by the battery protection circuit given enough time.

Lithium batteries used for model aircraft and cars have no such protection circuit.

I am just getting into Lipos myself, so far I have had amazing results but how you maintain them is very different from other battery chemistry that I am used to. I am using Thunderpower and invested in a decent charger, which I believe is well worth it. Here is a link on the charger I have which in itself is insightful on Lipo batteries in general, especially storage.

https://www.youtube.com/watch?v=YNTL8-y0hYs

Good choice. A good charger will last quite a while and will prevent damage. Why trust $100's of batteries to a $40 charger?
 
I fly rc as well... sometime ago I converted from fuel to electric and had to learn a lot when it comes to lipo batteries.
What I found is that they are really good if handled properly and can be VERY bad if not.

My suggestion for those that are using lipos is to browse over on this link below where you will find a wealth of info on lipos, chargers, etc.

https://www.rcgroups.com/batteries-and-chargers-129/

Hope this is helpful.
Ed
 
Get a lipo bag as well. Saved me loads of times. Converted a 50cc gas plane to electric and runs dual 12s Lipos, haved 1 go pop on me and very glad for the bag
 
One fact about lipos that is still missing from the rocketry conventional wisdom is that bigger is not safer when it comes to rockets. A tiny, 110mAhr cell is all that you need to run most altimeters for over an hour on the pad and still have plenty of juice to fire charges. Cells larger than 160 mAhrs can put out short circuit currents that exceed most altimeter max current ratings. Shorts do happen, especially during prep or ground testing (LEDs used to test altimeter outputs, without current limiting resistors, are a prime culprit here). If an altimeter deployment channel switch gets fried from over-current, the usual result is that is will be stuck on all the time. That can make an unsafe situation the next time it gets armed at the pad, or worse yet, in the prep area. So pay attention to manufacturer's recommendations about how much current the deployment channel switches can handle.
 
Adrian,
I realize this is an Ohm's law thing, however for the math challenged and the uneducated of us, would you please explain further, with a couple of examples.
ThanksInquiringing minds want to lean!":confused:
 
I saw the tittle of this thread and thought it might be about a botched plastic surgery. Thankfully, it's not. Carry on.
 
Adrian,
I realize this is an Ohm's law thing, however for the math challenged and the uneducated of us, would you please explain further, with a couple of examples.
ThanksInquiringing minds want to lean!":confused:

I just wrote a lengthy reply with examples, but it took too long, so I got automatically logged out and it got lost. :facepalm:
 
Here is a little tidbit on altimeters like an Egg Timer that has two battery sources. One for the altimeter, one for the pyro circuit. The 3.7V power for the altimeter is turned on and off at the switch. If one has ematches or charges attached to the pyro circuit and the 9V or whatever pyro battery isn't switched too, the pyro battery will drain out over time.

How do I know?:eyeroll: When bench testing, I used LED's in the 9V pyro circuit so I could get continuity and the Egg Timer would go through the powerup cycle completely.

I found with the 3.7V altimeter power turned off, the LED's in the 9V pyro circuit glowed just a "little bit".:jaw: It probably has something to do with the continuity circuit. I believe it is recommended in the instructions to use a switch on the pyro battery.

This can be a PITA in some situations like loading everything in advance before a launch. Yeah, some may be aghast at pre-preparation but my opportunities to fly don't come often and I like to have as many rockets ready to fly so's not have to mess with installing and packing the rockets onsite.

Besides having to install an extra switch (for the pyro battery), the only workaround is not to install the charges on the terminals for deployment until at the launch site and nearly ready to launch.

I believe the OOP Parrot was in the same situation but it had two screw switches on the board. The "on/off" and the "arming" for the pyro battery. Adrian, correct me if I'm wrong that the Parrot could drain the pyro battery with charges on the terminals with the "arming" switch
"on".

Sooooooooooooooo.........................to avoid draining the pyro battery in dual power source electronics best to follow the makers instructions to a "T".

Featherweight Altimeters magnetic switch is great but it does draw a tiny bit of current in the off position. If one loads the rocket and lets it sit
a few months, might run into trouble with a partially drained battery. A fully drained battery is no problem, just an "aw shoot" moment to change it out.
I work around this by connecting the wire to the magnetic switch the night before the launch and have flown happily for a half a dozen launches. (Disconnect if I expect to get a second flight out of the battery later.)

The single battery units (MAWD, SL100, Adept and others) that go on/off with a single switch are suited better for pre-preparation unless one has gone through the trouble of using 2 switches on a dual powered deployment altimeter. (Could be a pain on some smaller projects) Kurt
 
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I just wrote a lengthy reply with examples, but it took too long, so I got automatically logged out and it got lost. :facepalm:

A Post Saving Lesson (PSL) for A Lipo Lesson (ALL) :)

I've had that happen a time or two myself, Adrian - heartbreaking at times. I started grabbing what I was writing periodically and saving in a text file --- but recently discovered that you can just 'page back' in your browser and you should find your post still there. Can't speak with absolute authority on that - but I has seemed to work. (I'm using FireFox).

-- john.
 
One fact about lipos that is still missing from the rocketry conventional wisdom is that bigger is not safer when it comes to rockets. A tiny, 110mAhr cell is all that you need to run most altimeters for over an hour on the pad and still have plenty of juice to fire charges. Cells larger than 160 mAhrs can put out short circuit currents that exceed most altimeter max current ratings. Shorts do happen, especially during prep or ground testing (LEDs used to test altimeter outputs, without current limiting resistors, are a prime culprit here). If an altimeter deployment channel switch gets fried from over-current, the usual result is that is will be stuck on all the time. That can make an unsafe situation the next time it gets armed at the pad, or worse yet, in the prep area. So pay attention to manufacturer's recommendations about how much current the deployment channel switches can handle.

After reading several threads on TRF about LIPOs burning out altimeters, I found some LiFe packs that were low discharge - rated 1C.
(LiFe cells are similar to LIPOs, slightly less voltage and much safer when charging - less likely to start a fire ). I thought this would be perfect to protect my altimeters. Turns out the output really is limited and I tested a 1500mah pack and the voltage dropped too much when firing the ematch and reset the altimeter.
So just a warning. This seemed like the perfect solution but don't go this route.
 
One fact about lipos that is still missing from the rocketry conventional wisdom is that bigger is not safer when it comes to rockets. A tiny, 110mAhr cell is all that you need to run most altimeters for over an hour on the pad and still have plenty of juice to fire charges. Cells larger than 160 mAhrs can put out short circuit currents that exceed most altimeter max current ratings. Shorts do happen, especially during prep or ground testing (LEDs used to test altimeter outputs, without current limiting resistors, are a prime culprit here). If an altimeter deployment channel switch gets fried from over-current, the usual result is that is will be stuck on all the time. That can make an unsafe situation the next time it gets armed at the pad, or worse yet, in the prep area. So pay attention to manufacturer's recommendations about how much current the deployment channel switches can handle.

Is it really a function of capacity in mAh or is it the product of the capacity and the discharge ('C') rating that is more critical?

And for the Raven, what is the maximum? I have a very compact 125mAh 25C LiPo from Thunder Power, is this one safe?


Sent from my iPhone using Rocketry Forum
 
...... If one has ematches or charges attached to the pyro circuit and the 9V or whatever pyro battery isn't switched too, the pyro battery will drain out over time.

There is no problem if you use a switch ( in my case Shurter rotary selector ) to open the pyro circuit and at the same time short the igniter, so not only the drain will be fix but it's a standard safety approach we like to use around here.
 
Lithium batteries used for model aircraft and cars have no such protection circuit.



Good choice. A good charger will last quite a while and will prevent damage. Why trust $100's of batteries to a $40 charger?

Yes so true, buy a good charger save your money and don't waste your batts. There are a ton of great chargers that will charge all your battery types. In my quest to maintain my Lipos I have been looking for a small field voltage checker that I can use at the launch, solving two issues, one I can check before I launch to make sure I have the power. Two in my search for a voltage checker I have learned that you don't want the Lipo pack to drop below 20% max charge, so I can keep tabs on that.

This is the one I'm looking at getting, any one have any other suggestion?
https://media.hyperion.hk/dn/sentry/


TA
 
Here is a little tidbit on altimeters like an Egg Timer that has two battery sources. One for the altimeter, one for the pyro circuit. The 3.7V power for the altimeter is turned on and off at the switch. If one has ematches or charges attached to the pyro circuit and the 9V or whatever pyro battery isn't switched too, the pyro battery will drain out over time.

How do I know?:eyeroll: When bench testing, I used LED's in the 9V pyro circuit so I could get continuity and the Egg Timer would go through the powerup cycle completely.

I found with the 3.7V altimeter power turned off, the LED's in the 9V pyro circuit glowed just a "little bit".:jaw: It probably has something to do with the continuity circuit. I believe it is recommended in the instructions to use a switch on the pyro battery.

This can be a PITA in some situations like loading everything in advance before a launch. Yeah, some may be aghast at pre-preparation but my opportunities to fly don't come often and I like to have as many rockets ready to fly so's not have to mess with installing and packing the rockets onsite.

Besides having to install an extra switch (for the pyro battery), the only workaround is not to install the charges on the terminals for deployment until at the launch site and nearly ready to launch.

I believe the OOP Parrot was in the same situation but it had two screw switches on the board. The "on/off" and the "arming" for the pyro battery. Adrian, correct me if I'm wrong that the Parrot could drain the pyro battery with charges on the terminals with the "arming" switch
"on".

Sooooooooooooooo.........................to avoid draining the pyro battery in dual power source electronics best to follow the makers instructions to a "T".

Featherweight Altimeters magnetic switch is great but it does draw a tiny bit of current in the off position. If one loads the rocket and lets it sit
a few months, might run into trouble with a partially drained battery. A fully drained battery is no problem, just an "aw shoot" moment to change it out.
I work around this by connecting the wire to the magnetic switch the night before the launch and have flown happily for a half a dozen launches. (Disconnect if I expect to get a second flight out of the battery later.)

The single battery units (MAWD, SL100, Adept and others) that go on/off with a single switch are suited better for pre-preparation unless one has gone through the trouble of using 2 switches on a dual powered deployment altimeter. (Could be a pain on some smaller projects) Kurt


My new process is just unplugging everything not in use. My AV bays are modular and easily removable with one bolt, so its simple to get them out, unplug or recharge what ever the case may be, without having to remove the lipos from the altimeter sled.


TA
 
One fact about lipos that is still missing from the rocketry conventional wisdom is that bigger is not safer when it comes to rockets. A tiny, 110mAhr cell is all that you need to run most altimeters for over an hour on the pad and still have plenty of juice to fire charges. Cells larger than 160 mAhrs can put out short circuit currents that exceed most altimeter max current ratings. Shorts do happen, especially during prep or ground testing (LEDs used to test altimeter outputs, without current limiting resistors, are a prime culprit here). If an altimeter deployment channel switch gets fried from over-current, the usual result is that is will be stuck on all the time. That can make an unsafe situation the next time it gets armed at the pad, or worse yet, in the prep area. So pay attention to manufacturer's recommendations about how much current the deployment channel switches can handle.

With the above noted would a 2s 120mAh 25C keep me in the safe zone in general? I have 4 different altimeters in mind that this battery may work with. Raven, Stratologger, Aim Usb, Marsa54L. Thinking of switching from 9v to lipo on all my dual deploy rockets.
 
With the above noted would a 2s 120mAh 25C keep me in the safe zone in general? I have 4 different altimeters in mind that this battery may work with. Raven, Stratologger, Aim Usb, Marsa54L. Thinking of switching from 9v to lipo on all my dual deploy rockets.

Choosing one battery for all your altimeters may be the simplest but might not be optimum. For instance some of your altimeters would be best with a 1s and others need a 2S. The more featured and populated (Aim and Marsa54L) probably would like more mah for comfortable pad time.

For the Marsa54L I use 2S 300mah lipos. Gives plenty of time between charges and peace of mind at a launch. The FETs are current limited so you do not have to rely on your battery to limit safe current.
 
Yes so true, buy a good charger save your money and don't waste your batts. There are a ton of great chargers that will charge all your battery types. In my quest to maintain my Lipos I have been looking for a small field voltage checker that I can use at the launch, solving two issues, one I can check before I launch to make sure I have the power. Two in my search for a voltage checker I have learned that you don't want the Lipo pack to drop below 20% max charge, so I can keep tabs on that.

This is the one I'm looking at getting, any one have any other suggestion?
https://media.hyperion.hk/dn/sentry/


TA
Lots of inexpensive checkers available from this source in their warehouses in the US, the EU, and HK. Choose by the reviews and cost:

https://www.hobbyking.com/hobbyking/store/RC_PRODUCT_SEARCH.asp?strSearch=lipo+checker

My inexpensive charger which I like. This one is very popular with RC folks and it's also available from multiple Hobbyking warehouse locations:

https://www.hobbyking.com/hobbyking...ncer_Charger_w_Accessories_US_Warehouse_.html
 
With the above noted would a 2s 120mAh 25C keep me in the safe zone in general? I have 4 different altimeters in mind that this battery may work with. Raven, Stratologger, Aim Usb, Marsa54L. Thinking of switching from 9v to lipo on all my dual deploy rockets.

Well, that battery will have a rated discharge rate of 3 Amps (0.120 Ah * 25C). Meaning it will happily put out 3 Amps till it is flat lined.

However it's short circuit output is usually quite a bit higher, most batteries have a burst (short duration) discharge rating as well as the constant output. In most 25C batteries I've seen it is anywhere from 30 - 45 C. So it can output 3.6 - 5.4 Amps for a few minutes before the battery will overheat.

The short circuit output is usually a bit higher than that since because of its short duration (in the millisecond range) it is mostly limited by the resistance in the battery cell, not the thermal load the battery can handle. The internal resistance of a high quality lipo is usually around 1.2 - 8.0 mOhm.

So if you take ohms law V=IR or I=V/R you get I=8.4V/1.2mOhm so your short circuit current can be as high as 1000-7000 Amps, theoretically. In reality there are more factors at play than just internal resistance so for a pack that small I would expect a short circuit current in the range of 10 - 40 amps. Some of the largest high discharge packs (10 Ah 160C) that 7000 Amp short circuit current number is actually somewhat reasonable.

Usually where you will run into trouble with a lipoly and your electronics is if your altimeter doesn't have some sort of inrush current limiting. You can damage capacitors by charging them too fast, or burn out circuits.

If you want to play it safe, you can just limit the current on the lipo to a similar level compared to a alkaline. If I recall correctly the discharge limit for a alkaline battery is around 1-2 amps. So if you put a 3-4 Ohm resistor inline with just one of the battery leads, that would limit your battery current to the range of what an alkaline puts out. There are more efficient ways to limit battery current, but this is at least the simplest.

If you wanted to take advantage of the higher current a lipo will put out to make sure your ignitors will fire you will have to do a bit more of your homework. I think a stratologger can handle 10 amps, so you might be able to get away with no current limiting but it will depend. The ravens look like they can handle lipo's just fine since they are specified in the manual, just dont go a higher capacity than the 165 mAh specified in the manual.
 
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I fly lots of RC stuff on lipo's. some can be saved depending on how dead they are. if it is just "mostly dead" one trick is to put the battery in the freezer overnight and charge it in the morning. I just had to do this to a battery for a micro quad copter and it worked. I do recommend charging the battery in an explosive safe location. I set it in a coffee mug on the driveway. if it takes a charge and doesn't swell after a day or two I'll use it.
 
With the above noted would a 2s 120mAh 25C keep me in the safe zone in general? I have 4 different altimeters in mind that this battery may work with. Raven, Stratologger, Aim Usb, Marsa54L. Thinking of switching from 9v to lipo on all my dual deploy rockets.
The StratoLogger is basically a Pnut with dual deployment. It should work fine with a ~150-250 mah Lipo for real e-matches.
 
Hmm, not to sound negative, but given the extra issues (that we don't need when conducting already complex flights), plus the startup costs for a good quality charger and the lipo itself, I can purchase quite a few simple 9 volt batteries, and have some extra piece of mind while I am it...
 
Hmm, not to sound negative, but given the extra issues (that we don't need when conducting already complex flights), plus the startup costs for a good quality charger and the lipo itself, I can purchase quite a few simple 9 volt batteries, and have some extra piece of mind while I am it...



+1 Never had a problem with rechargeable Nimh's, always worked 100%.
 
Hmm, not to sound negative, but given the extra issues (that we don't need when conducting already complex flights), plus the startup costs for a good quality charger and the lipo itself, I can purchase quite a few simple 9 volt batteries, and have some extra piece of mind while I am it...
I really don't see costs as a big factor. If you have a big numb rocket with lots of room and in need of ballast then almost any battery chemistry will work, however if you are weight and size sensitive, the LiPos are the only way to go.

In the Pnut, PerfectFlite uses a 9 volt battery and an on-board regulator to recharge the built-in LiPo. If you're not trying to break any speed records, a simp1e low current 4.2 volt regulated voltage source will recharge any small LiPo in an hour or two. When you reach 4.2 volts, you disconnect the supply. In any case, good LiPo chargers can be bought for less than $20 so price really should not be an issue. HobbyKing has dozens of them, including ones that will charge from you vehicles power socket as well as line voltage.

Bob
 
I really don't see costs as a big factor. If you have a big numb rocket with lots of room and in need of ballast then almost any battery chemistry will work, however if you are weight and size sensitive, the LiPos are the only way to go.

In the Pnut, PerfectFlite uses a 9 volt battery and an on-board regulator to recharge the built-in LiPo. If you're not trying to break any speed records, a simp1e low current 4.2 volt regulated voltage source will recharge any small LiPo in an hour or two. When you reach 4.2 volts, you disconnect the supply. In any case, good LiPo chargers can be bought for less than $20 so price really should not be an issue. HobbyKing has dozens of them, including ones that will charge from you vehicles power socket as well as line voltage.

Bob



+1 There really isn't that much start up cost and the lipos seem to last a long time if you treat them right. Its nice to fly a 14 volt pyro/air start batt, that is half the weight of a 9 volt.



TA
 
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