Understanding Lithium Polymer batteries

[gtranquilla]

IMHO - I would avoid using an C rating below 35C for VTOL type aircraft...... and 12C is way too low.
And here is why......see attached. http://www.maac.ca/docs/2013/lipo_b...e_max_current_draw_true_crating__rev3_toc.pdf

I'm flying a heavy lift X8 that's roughly 7.5kg AUW. I've been using 6S 8000 30C Lipos but was looking at a 6S 10000 12C; it weighs less and offers more power. My question has to do with the discharge rate... will the 12C work for my set up?

 

[Bartman]

I'm flying a heavy lift X8 that's roughly 7.5kg AUW. I've been using 6S 8000 30C Lipos but was looking at a 6S 10000 12C; it weighs less and offers more power. My question has to do with the discharge rate... will the 12C work for my set up?

at your normal flying weight how many amps does your helicopter draw? if you can't say then look at the specs for the motors given the props you're running....you may be able to use table data to get a rough estimate for your application.

if you're running eight motors drawing 5 amps each hovering and 9 amps max then that is 40amps of draw hovering or 72 amps max. with a 12C battery, it's 12 times capacity as its max amps discharge capability. It would have to be at least 72/12 or 6 amps-hour, also known as 6000mah for it to be suitable but even then it's borderline. If you have two in parallel then it would be fine as they'd each be supplying half of the amps but if you lost a battery the second would be working hard to keep the helicopter flying.

Bart

 

[polylawman]

Here's my question. I fly stock F550. At first I used a 3S 5200Mah 45C lipo and was getting about 7 1/2 minutes flight time. I purchased a 4S 5000Mah 50C lipo and got over 15 minutes flight time. During the last flight with the 5000Mah lipo, I notice that as the lipo voltages dropped, it seemed to take more throttle to keep the copter in the air. It flew with a little pep in the beginning of the flight, but that pep went away as the flight progressed.
So to keep the throttle/power constant throughout the whole flight would you chose a lower C rated battery, like a 20 to 25C?
I hope my question makes sense.
I don't want to zip through the air doing tricks, just a normal smooth flight, hovering to take some videos and pics.


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[Motopreserve]

Actually, if anything, you might want more C rating to be able to discharge more. The higher the C rating. the more current it is capable of discharging. Of course, the higher the C rating, the heavier the pack, so that fights against/for how the MR will react. That being said, it seems that there is always going to be some lack of power towards the end of a pack, regardless of the C rating. How low was the pack when you began to notice a difference?

Here's my question. I fly stock F550. At first I used a 3S 5200Mah 45C lipo and was getting about 7 1/2 minutes flight time. I purchased a 4S 5000Mah 50C lipo and got over 15 minutes flight time. During the last flight with the 5000Mah lipo, I notice that as the lipo voltages dropped, it seemed to take more throttle to keep the copter in the air. It flew with a little pep in the beginning of the flight, but that pep went away as the flight progressed.
So to keep the throttle/power constant throughout the whole flight would you chose a lower C rated battery, like a 20 to 25C?
I hope my question makes sense.
I don't want to zip through the air doing tricks, just a normal smooth flight, hovering to take some videos and pics.


Sent from my iPad using Tapatalk

 

[Roger Ramjet]

The first thing you want to check is the prop you are using! You may very well fly a 10X5 prop with a 3S but you may have to reduce the prop i.e 9X5 or something along this line if you go with a 4S battery. It is all a matter of how much amps you motors and ESC can take. By going to a more powerful source of energy (4S vs 3S) your motors are going to develop more thrust but will also consume more current (amps).

The stock 920 KV DJI are certainly overworked with a 10X5 AND a 4S battery pack! I myself run the Sunnysky 800 KV with 4S 35C on my loaded 550 (3 Kg) and I use 10 X 3.8 props. Keep an eye on your motor temp upon landing, if you can not keep your hand on it it is likely running too hot. You have to reduce either the pitch and/or the span of your propellers to allow your motors to operate in the normal operating temperature range. An electric motor that gets too hot is far less efficient and the extra heat on the bearings isn't great either... Hope it helps!

 

[Motopreserve]

Roger is absolutely right. Sorry, I was taking for granted that the props matched the motors, and could be appropriate for the give batteries.

Thanks Roger!

 

[polylawman]

Actually, if anything, you might want more C rating to be able to discharge more. The higher the C rating. the more current it is capable of discharging. Of course, the higher the C rating, the heavier the pack, so that fights against/for how the MR will react. That being said, it seems that there is always going to be some lack of power towards the end of a pack, regardless of the C rating. How low was the pack when you began to notice a difference?

I really don't remember how low the pack was, but will pay attention next time.
Thanks everyone for the helpful info.


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[polylawman]

The first thing you want to check is the prop you are using! You may very well fly a 10X5 prop with a 3S but you may have to reduce the prop i.e 9X5 or something along this line if you go with a 4S battery. It is all a matter of how much amps you motors and ESC can take. By going to a more powerful source of energy (4S vs 3S) your motors are going to develop more thrust but will also consume more current (amps).

The stock 920 KV DJI are certainly overworked with a 10X5 AND a 4S battery pack! I myself run the Sunnysky 800 KV with 4S 35C on my loaded 550 (3 Kg) and I use 10 X 3.8 props. Keep an eye on your motor temp upon landing, if you can not keep your hand on it it is likely running too hot. You have to reduce either the pitch and/or the span of your propellers to allow your motors to operate in the normal operating temperature range. An electric motor that gets too hot is far less efficient and the extra heat on the bearings isn't great either... Hope it helps!

What are your average flight times with your setup?


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[Roger Ramjet]

As previously stated, I use a 6000 mAh 4S on a fully loaded F-550 that weighs in at 3.0 Kg. It is basically a video Platform that features a Gopro camera and a DJI H3 3D gimball using AVL58 for video downlink. Add the landing gear, few strobes light, a Spot Trace Locator and a small battery for the video transmitter and you are inevitably approaching the 3 Kg mark. My flight time is a solid 10 minutes with a 20% reserve upon landing (80-20% rule). I feel that I could fly for 13+ mins if I was flying the frame naked, still landing with a decent reserve.

I much prefer doing 6 X 10 mins flights than 3 X 15 mins when in video capture mode. Quite demanding to fly and monitor what is being shot at the same time. Maybe I am getting old... Ha! Ha!

 

[johnsonsten]

very helpfull and information rich

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[patrickwin]

A very good post

Hey, you have done a good job, very good post, you must be hardworking. I have one question, what do you think of Tattu battery?

 

[AK1990]

Great Post Bartman! That was very informative and helpful. Thanks for sharing.

 

[Ian]

I have a question or two

Can you calculate how much capacity you have used from how much the battery takes to reach full charge ? is there any losses in capacity it takes to recharge ?

secondly the 3v per cell lower limit, does this include under load ? battery voltage can recover have a volt after resting

 

[Bartman]

Can you calculate how much capacity you have used from how much the battery takes to reach full charge ? is there any losses in capacity it takes to recharge ?

I suppose if a cell has a high internal resistance then the MAH going in (as measured in the charger) would actually be higher than the actual MAH absorbed by the battery in the charging process since some is being lost to the heat generated by the higher than normal internal resistance. But the programming in a charger could be factoring in some loss to internal resistance so it's hard to say exactly what is happening. If a cell is rated at 6000 mah and the charger says it's putting back in 5000 mah after a normal flight, you can say with a reasonable amount of accuracy you replaced 83% of the capacity and this is a worthwhile strategy to know what you're using so as to not damage your batteries.

secondly the 3v per cell lower limit, does this include under load ? battery voltage can recover have a volt after resting

it's usually 3.3 and yes it would be under load as measured while flying. the voltage recovery you see after landing isn't really factored in. when you reach 3.3 volts while under normal flying loads it is recommended that you land to prevent damage to your packs.

 

[Kratos]

Thank you Bart for putting together such a comprehensive & easy to understand guide. It's an awesome reference!

However, I still have some really basic questions that I just can't find the answers to anywhere (I've read the entire thread, browsed the newbie area, searched the site, used Google/YouTube, etc - nothing).

Most pressing is this...



How long is "a while"? A day, 2 days, 3 days, a week? I've seen countless warnings, threads, & videos showing how these things can puff up and spontaneously ignite if they're left either fully charged or empty and I want to make sure I'm not sharing my house with a handful of little bombs that could go off while I sleep (I don't have a fire-friendly place like a garage to store them).

At the moment I charge them in the morning and fly in the afternoon but I now need to charge my batteries the night before a planned flight so that they're ready for an early start (balance-charging 5x 4s 5000mAh packs takes about 4 hours). Is it safe to charge them the night before and not worry about them puffing/burning overnight? What if I didn't use all the batteries that next day and didn't have time to discharge them? Would it be safe sleeping next to them for a 2nd night? Are the fully-discharched batteries a danger too if not given a storage charge quickly? Worst-case, what if I 'lost' a fully-charged LiPo around the house - would I have to spend 24 hours tearing my place apart to find the ticking time-bomb?

Sorry if this sounds like a panic - it's not, but I've seen videos of them burning on YouTube and spotted a few hundred warnings from manufacturers and multirotor-pros like this ( http://www.multirotorforums.com/showthread.php?7898-Storing-Lipos-at-full-charge-warning&highlight=store charged lipo ), coupled with the fact that members here seem divided with some saying it's fine and others saying you're asking for trouble (note: I don't mind the batteries going bad, I just don't want them going 'bang'). I can't find a clear answer and it seems like a pretty important question. Any help would really be appreciated.

Heh this is my problem too...
Is there any other type of battery that have similar specification like this LIPO? Why is this so important compared to others? Is there more simple batteries to plug and play? Like phone Li ion or Gopro or some other ? I really don't like this Time Fire Bomb in my appartment... I Dont want to go outside on work or a meeting and think subconsciousness about batteries are they going to get fire... Also how to store them.. Use mother flowerpot on balcony LOL and install sprinklers in my appartment..., also in my country winters are cold -20 was for new year how does that affect battery and multirotor (isnt better to be more cold like superconductors)? I dont like these batteries so much that now I dont want to assemble my quadricopter...
For all fire comrades here is old hit from highschool

Fire starts on 2:34 or 2:07 depending on what you like more

Dont get me wrong I am beginner

 

[Motopreserve]

Keep in mind that most issues happen during incorrect discharge or charging (too much or too little is not a good thing).

For storage safety, keeping them in an ammo box (can be purchased for under $20) is a decent option.

 

[Kratos]

Keep in mind that most issues happen during incorrect discharge or charging (too much or too little is not a good thing).

For storage safety, keeping them in an ammo box (can be purchased for under $20) is a decent option.

aaa my brain hurts because lipos
How can you charge too much ? why it doesnt stop automatical? And you have led indicator is it full or not... Dont get it, is it because human impatience and inattention ? Man this lipos, I wont sleep because of them, this is like bad nightmare

 

[Motopreserve]

Take a deep breath...

Your charger should have an automatic shut-off at the set voltage. But many you have to set up correctly. Most will have a safeguard so you don't get nightmares.

Discharging is where it gets dicey. People push the envelope too far which can create issues.

You should try to follow the 80% rule - meaning do not use (discharge) the battery more than 80% (leaving 20% in reserve). You can calculate that based on voltage (4.2v cell multiplied by .8 gives you 3.36v) so that you don't dip too low. Very inexpensive alarms are available to tell you you've hit a set voltage under load. Most people will only fly down to 3.6v or 3.7v to be safest.

Then when you get to charging, keep track of the mAh put back to the battery. It should not be more than 80%.

If you have to put back more than 80% mAh or your voltage sags under 3.36 in flight, you're probably pushing it. Best to play it safe.

Following this rule should keep you as safe as can be....

Keeping the lipos in special storage bags or the ammo boxes I mentioned is for peace of mind.

 

[Kratos]

Take a deep breath...

Your charger should have an automatic shut-off at the set voltage. But many you have to set up correctly. Most will have a safeguard so you don't get nightmares.

Discharging is where it gets dicey. People push the envelope too far which can create issues.

You should try to follow the 80% rule - meaning do not use (discharge) the battery more than 80% (leaving 20% in reserve). You can calculate that based on voltage (4.2v cell multiplied by .8 gives you 3.36v) so that you don't dip too low. Very inexpensive alarms are available to tell you you've hit a set voltage under load. Most people will only fly down to 3.6v or 3.7v to be safest.

Then when you get to charging, keep track of the mAh put back to the battery. It should not be more than 80%.

If you have to put back more than 80% mAh or your voltage sags under 3.36 in flight, you're probably pushing it. Best to play it safe.

Following this rule should keep you as safe as can be....

Keeping the lipos in special storage bags or the ammo boxes I mentioned is for peace of mind.

What about plug and play bateries, why this lipos are so important?

 

[Motopreserve]

I'm not sure what you mean by plug and play, but these lipos come ready to go other than charging. You may need to swap plugs if your MR has a different type to the onboard power.

I'm no expert, but I think the advantage to the lipos is that they provide a high discharge rate capable of handling the power draw that these MRs require.