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Quick tip: How to NOT Puff Batteries

colorex

Rotor Riot!
Mentor
#4
If you are building a quad or a hexacopter, you should be fine with that setup. The calculation is as follows:

Max amps that the motor will use - motor specs say 10 amps with a 9x4.7 prop (they recommend 8x4 though)

So max amps per motor = 10 A so 18 amp esc's will run cool enough at around 60% load. (It's good to have a bit bigger ESC than needed)

And for the battery the motors max amps = 10 x 4 motors = the quad will draw 40 amps max from the battery. So how much can the battery take?

The battery is 2200mAh (or 2.2Ah), and the discharge capacity is 30C - so 2.2 x 30 = 66 Amps and you'll only use 40 Amps at WOT, so yes that's a nice combo for this quad.

The motors with a 8x4.7 prop are stated to produce a bit more than 500 grams of thrust, so if your quad stays at or under 1 kilogram it should fly really well.
 

xuzme720

Dedicated foam bender
Mentor
#5
The best insurance is a wattmeter to determine total draw and make sure you have some headroom with your battery and it's C rating. Colorex has already given you the rest.
 
#6
So..... were talking about total current draw VS what the battery can provide?

I'm just building a simple airplane, not a multi rotor(although now I see why your asking about that). So with a 30C rating on my 2200 means i can put out MAX 66 amps, as long as I don't draw more than that, i should be good?

Josh said something in a recient video that flying with less than 10% might do something? what was he referring to?
 
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pgerts

Old age member
Mentor
#7
C-rating is not to take all to serious - but more C is generally better.
I have some 30C batteries lasting better than 45-90C ones. (Your E-flite is one of the best i have regarding capaicity and keeping hard).

Do not exceed the recommended amps (capacity in mAh * C (continous)) - better have some margin.
Do not get the batteries to warm (cooling in the plane).
Do not discharge to low - half charge the batteries as soon as possible after using (but let cool down first).
Do not store batteries fully charged over extended periodes without using them.
 
#9
C-rating is not to take all to serious - but more C is generally better.
I have some 30C batteries lasting better than 45-90C ones. (Your E-flite is one of the best i have regarding capaicity and keeping hard).

Do not exceed the recommended amps (capacity in mAh * C (continous)) - better have some margin.
Do not get the batteries to warm (cooling in the plane).
Do not discharge to low - half charge the batteries as soon as possible after using (but let cool down first).
Do not store batteries fully charged over extended periodes without using them.
Oh. Well, thank you for the info! I wasn't aware they were so sensitive.
If LiPos commonly have problems like this, why hasn't society switch to nuclear batteries yet? Or single point energy? I'm just kidding, although these are good facts to know when it comes to their longevity. If I were to wrap them in a nice strong tape/resin infused carbon fiber, would they be a threat?
 

jetpackninja

More combat please...
Mentor
#10
If I were to wrap them in a nice strong tape/resin infused carbon fiber, would they be a threat?
Yes- wrapping them will not mitigate the risk of a fire or explosion.

Make yourself familiar with the risks then manage the risks.
I have moved all of my charging outside and field charging is done with a deep cycle marine battery to move the charging out of the engine compartment of my truck.

 
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xuzme720

Dedicated foam bender
Mentor
#12
There is a lot to try to keep in mind when you first switch to lipo power, but they are still the lightest power supply available to provide us with the burst amperages we need to fly. They are also safe when treated with a modicum of respect, and can have long productive lives when used properly.
First thing to consider is charging. Lipo's need to be charged with a reliable balance charger to maintain the balance of voltage across all the cells in a pack. If you always charge with a balance charger, risk of fire or a pack detonating is reduced almost to zero, but NEVER charge unattended! All it would take is a charger or pack malfunction, and the house goes up in smoke. Always babysit those charging batteries like they are the neighborhood pyromaniac with matches in a gas station.
If you see any damage to a pack from a crash or they puff, pay special attention to them as they will most likely be the one that fails. Usually, it's best to just write off the pack and be safe. If you do have a suspect pack, you can safely discharge it by immersion in saltwater for a few days to a week.

Next thing to consider is the power draw of your system. We talk of headroom. All that means is having a buffer or running a system that is lower than max draw from the battery. Say you have a 2200mAh 30C battery like you mentioned above. Let's take a look at what you can expect from it.
Usable capacity: this is what the battery can supply in time and power and is considered 80% of rated capacity. With your 2200 mAh battery this means you should have 1760mAh of useable power. 2200 x 80%=1760
Now this can either give you 1.76 amps for an hour or about 10 amps for about 10 minutes. How do you get that? Milliamps are 1000 per amp so 1760mAh=1.76Ah or amp hours so if you take the hour amp rate and multiply it times 6, you'll get a 10 minute amp draw.

Another thing to consider and a more accurate gauge of when to stop flying is voltage. Lipo cells have a nominal voltage of 3.7 v per cell and if you aren't flying for a few weeks, your batts should be charged or discharged to that voltage. When flying, it's a good idea to stay above 3.3v per cell but down to 3.0 volts can be done but just keep in mind that when a lipo drops close to 3V per cell, it's also very close to damage. 2.7V per cell is completely dead and lipos have a sharp drop-off, or when they are close to dead, they drop in voltage quickly! So most people set up any alarms for 3.3 to 3.7 depending on draw of the system. Also keep in mind, these voltages are per cell, so with a 3S or 3 cell battery, you need to fly no lower than 9.9 volts for the pack.

So back to amp draw. Like you said earlier, 2200 30C pack can provide 66amps of current but if you are using all of that 66amps, you'll have less than 2 minutes of flight time. It should be spectacular but short! So if you plan on just going to the max on the "C" rating, you'll also shorten the battery lifespan as they don't care for maxing out in any aspect. Main thing to consider is that your C rating can supply what you expect the max draw to be plus whatever you think is a good buffer, I usually try to have at least 10-20% of wiggle room. So I would use that battery with a max planned draw of around 40-45 amps. Keeps me well within the limits and also keep the battery cool but not pushing it to it's limits.

Hopefully this helps and I haven't completely confused you. Let me know if anything needs more clarification...
 
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xuzme720

Dedicated foam bender
Mentor
#14
Usually overcharging. Damage can also cause it also, like in a crash. Most overcharging comes from not balance charging and doing what's called quick charging, where the only voltage that's monitored is the overall voltage. If you have a cell that discharges or charges faster, you can easily get the cells in a pack to different voltages in just a couple of cycles. Say you have 2 cells only at 3.9 volts and you are setting the charger to charge to 12.6 volts which is what a fully charged 3S lipo will be. You'll have a cell at 4.8 volts which doesn't sound like much over, but that is over enough to cause damage and possibly fire. If you follow a few simple rules, you will likely never see a lipo fire in person. The best thing is not to leave them unattended when charging. And it's best to charge outside, or at the very least, close enough to the outside that you can get a battery out the door in a hurry if it does go postal.
 

jetpackninja

More combat please...
Mentor
#15
So what exactly causes the fires in the video? Overcharging? Overheating? Charging a puffed battery?
The fires in the video were done intentionally. Charger was set to a high rate and higher voltage. Most of the batteries were already puffed. Overcharging creates a runaway chemical reaction that releases a bunch of heat. the runaway reaction can be from charging a damaged battery, incorrect charger settings or a charger malfunction.
 
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skeplin

Senior Member
#16
So I think the second most important thing to discuss is how to put out a fire should one occur. I would assume that a standard fire extinguisher would not work. What type of fire extinguisher should you have on hand?
 
#17
There is a lot to try to keep in mind when you first switch to lipo power, but they are still the lightest power supply available to provide us with the burst amperages we need to fly. They are also safe when treated with a modicum of respect, and can have long productive lives when used properly.
First thing to consider is charging. Lipo's need to be charged with a reliable balance charger to maintain the balance of voltage across all the cells in a pack. If you always charge with a balance charger, risk of fire or a pack detonating is reduced almost to zero, but NEVER charge unattended! All it would take is a charger or pack malfunction, and the house goes up in smoke. Always babysit those charging batteries like they are the neighborhood pyromaniac with matches in a gas station.
If you see any damage to a pack from a crash or they puff, pay special attention to them as they will most likely be the one that fails. Usually, it's best to just write off the pack and be safe. If you do have a suspect pack, you can safely discharge it by immersion in saltwater for a few days to a week.

Next thing to consider is the power draw of your system. We talk of headroom. All that means is having a buffer or running a system that is lower than max draw from the battery. Say you have a 2200mAh 30C battery like you mentioned above. Let's take a look at what you can expect from it.
Usable capacity: this is what the battery can supply in time and power and is considered 80% of rated capacity. With your 2200 mAh battery this means you should have 1760mAh of useable power. 2200 x 80%=1760
Now this can either give you 1.76 amps for an hour or about 10 amps for about 10 minutes. How do you get that? Milliamps are 1000 per amp so 1760mAh=1.76Ah or amp hours so if you take the hour amp rate and multiply it times 6, you'll get a 10 minute amp draw.

Another thing to consider and a more accurate gauge of when to stop flying is voltage. Lipo cells have a nominal voltage of 3.7 v per cell and if you aren't flying for a few weeks, your batts should be charged or discharged to that voltage. When flying, it's a good idea to stay above 3.3v per cell but down to 3.0 volts can be done but just keep in mind that when a lipo drops close to 3V per cell, it's also very close to damage. 2.7V per cell is completely dead and lipos have a sharp drop-off, or when they are close to dead, they drop in voltage quickly! So most people set up any alarms for 3.3 to 3.7 depending on draw of the system. Also keep in mind, these voltages are per cell, so with a 3S or 3 cell battery, you need to fly no lower than 9.9 volts for the pack.

So back to amp draw. Like you said earlier, 2200 30C pack can provide 66amps of current but if you are using all of that 66amps, you'll have less than 2 minutes of flight time. It should be spectacular but short! So if you plan on just going to the max on the "C" rating, you'll also shorten the battery lifespan as they don't care for maxing out in any aspect. Main thing to consider is that your C rating can supply what you expect the max draw to be plus whatever you think is a good buffer, I usually try to have at least 10-20% of wiggle room. So I would use that battery with a max planned draw of around 40-45 amps. Keeps me well within the limits and also keep the battery cool but not pushing it to it's limits.

Hopefully this helps and I haven't completely confused you. Let me know if anything needs more clarification...

Ya, this is Great!, Thank you! I read through the manual for my charger, and it appears to not auto balance, so i need to get an auto balancer. I know Josh and Josh did a video on that, like 20 bucks, Totally worth it!. So i guess its an 80% rule hua? Thats good. Do you have any suggestions for a battery charging setup? Like.... a cinder block or something? (In the event something were to go wrong.)
 

colorex

Rotor Riot!
Mentor
#18
So I think the second most important thing to discuss is how to put out a fire should one occur. I would assume that a standard fire extinguisher would not work. What type of fire extinguisher should you have on hand?
Class D for Metal fires:

http://en.wikipedia.org/wiki/Fire_extinguisher#Class_D


Note that you could use a standard fire extinguisher to keep a fire controlled (prevent it from spreading) until the LiPo burns down.
 
#19
If LiPos commonly have problems like this, why hasn't society switch to nuclear batteries yet?
Atomic batteries have three downsides:
* The commercial use of radioactive substances is so regulated it would be hopelessly messy for gobal trade until regulations change.
* Even though they have enormous capacity, the "C-rating" is very low.
* They degrade relatively quickly, as the radiation damages the cathode (I think). There is research around liquid anodes that would help here, though.
 

cranialrectosis

Faster than a speeding faceplant!
Mentor
#20
I haven't seen any discussion about what 1C or 2C is or how to calculate it.

I use 3S 2200mAH batteries. When I charge them I use a Turnigy Accucel 6. I balance charge at 3.3A. At what C rating am I charging and what is the formula to know so I can convert to a 4S?