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New guy battery question

Khaptin

Junior Member
#1
Hey, I've been working on tuning and getting my flame wheel 550 flying better. I'm an adventurer and tend to jump into things, so I added a cheep camera gimbal to the rig. When I get out in the air I can see right away that me video is more smooth. However that's the extent of the pros...

Here's what I've run into. with everything installed my craft seems to be really heavy, and I think my 3 cell battery is having a hard time lifting it. I've read on other forums people saying that you really need to use a 4 cell with the flame wheel 550.

I was wondering if anybody here had any opinions on the topic? My craft weighs about 5.25 pounds with everything. My current battery is very heavy. it's an 11000 mAh battery and is 645g if I'm not mistaken. I get about 12 to 13 minutes of flight time with it without the gimbal and just the GoPro.

Would I get good flight times with a lighter smaller battery? such as a 4 cell 5000 mAh? I'm wondering if the lighter battery would reduce weight enough to offset the fact that it has less "Juice". I notice that some of these batteries are only about 100g lighter than mine.

Would there be an advantage to using much smaller batteries and wiring in a series (say using 2 cell) or parallel (using small 4 sell)?

Thanks

P.S. I'm using 9443 carbon fiber props
 
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#2
Rule of thumb: you want to be able to hover around 50% throttle. I suspect you're nowhere near that?
4S will give you considerably more power, but Im just assuming the motors and ESCs are designed for it.

Battery size is always a tradeoff with diminishing returns. Generally you will fly longer with a bigger battery, but not (nearly) as much longer as the capacity would suggest, because of the added weight. At some point the return may even be negative. Only way to find out for sure, is give it a try.

Putting 2S batteries in series is not a good idea, but putting 2 or more 3/4S in parallel is often done. Advantage is that you can chose to fly, say, one 4AH battery at a time, or two simultaneously. The latter will (probably) give you longer flight time, but not nearly 2x as long so if you dont need a single long flight, you'd be better off landing and swapping the battery.
 

Khaptin

Junior Member
#3
Yeah, the mid throttle thing is what clued me in that I wasn't getting enough power. Usually I can hover at mid throttle, but was having to give it more and still having a hard time keeping it in the air. The ESCs and motors can take a 4s depending on prop size.
 
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Craftydan

Hostage Taker of Quads
Moderator
Mentor
#4
DO NOT GO 2S.

A pair of 2S packs in series will work as a 4S pack, but a dedicated 4S pack of the same capacity will be lighter. A 2S supply will reduce your efficiency.

4S packs will increase your weight for the same capacity, but they simultaneously increase the power available for lifting. effectively they move you up to a different thrust/power curve, and if you substute weight-for-weight you'll be much farther down on that next-higher-curve, possibly in far more efficient regions for your motors. If the motor runs more efficiently, it'll run cooler, have more authority, and use less current to generate the same thrust -- better use the lower capacity.

If your current setup has the quad in a fairly inefficient state (possible, but could be fine -- don't know anything about your motors, but 5#/2kg is a bit heavy) the lower capacity may still increase your run time because the power available remains the same and the motors are running with greater efficiency. Even if this isn't so, it's just increased your thrust, and in turn increased your efficient payload capacity . . . meaning you can carry an even larger battery extending your efficient flight time even further.

It's all a balancing act, but the balancing gets easier at higher voltages, assuming your electronics can handle it.

That being said, prepare to re-prop. You'll likely have to drop an inch in the props to accommodate the higher RPM's needed. She should still fly fine on the original props at lower throttle levels, but as you add weight (increase battery capacity) the hover RPM will increase and your current demands will increase with them. lowering the props size will nudge around that power/thrust curve, but if you're already on the long end for props, higher voltage may drive you down a size as you move up in weight.
 

Epitaph

Ebil Filleh Pega-Bat ^.^
Mentor
#5
What are the motors you are using? And how heavy is the whole setup? You might be able to go with some bigger props even, depending on the specs...
 
#6
DO NOT GO 2S.

A pair of 2S packs in series will work as a 4S pack, but a dedicated 4S pack of the same capacity will be lighter. A 2S supply will reduce your efficiency.
Hmm.. The S in 4S stands for Series. Its short hand for "4 lipo cells in series". Putting 2x2S batteries in series is really the same thing as putting 4 cells in series, it doesnt really matter a lot how you package it, its not like the shrink wrap is very heavy. Of course, there is also no obvious benefit and balancing the cells will be more tricky, so I agree its not a good idea, but in principle its no different as using a 4S battery and assuming similar C ratings, weight difference would be limited to a few slightly longer wires.
 

Khaptin

Junior Member
#7
What are the motors you are using? And how heavy is the whole setup? You might be able to go with some bigger props even, depending on the specs...
My whole setup is about 5.2lbs. the motors I am using are the 960kv DJI e300.

Dan, thanks for the tips. Corect me if I'm wrong but what your saying is that it could be to my benefit to go with a a smaller 4s battery as apposed to a really big 3s. Before I added the gimbal I could fly pretty well and hover at mid throttle until my battery reached about 11.3v, which wasn't to bad since I figure I should start thinking about landing anyway by the time I hit 11.1.

SO my thought with the 4s is that since I'd want to try and stay above 14.8v I should be able to hover all the way until I want to land and re-charge my LiPo.

This brings me to another question, since in my research I find different schools of thought. How low can you safely drain a LiPo? is the 11.1v or 14.8v limit to high?

I'm guessing I'll just have to experiment with different pack sizes to figure out the weight vs capacity trade off that works for me.
 

Craftydan

Hostage Taker of Quads
Moderator
Mentor
#8
Yes, 2x2S and 4S are electrically identical, but Weight is weight. In fairness multirotors are sloppy overpowered brute force beasts when it comes to weight, but the extra packaging to the extra pack is still weight that could be better spent in lithium goo.

You also run the issue of mis-matching your packs -- a 4S pack is guaranteed that the 4 cells will be charged/discharged/abused together. 2x2S you can start matching and mismatching them as they age and you'll forever be limited by the weaker of the two packs, while making the weaker packs weaker. careful management of pack sets can negate this, but having the packs shrink-wrapped together at the factory is easier.

There's also the cost -- depends on the market for batteries, but it costs less to build, package, and ship a 4S pack than a pair of 2S packs of similar stats . . . how much you're gouged or one pack to the other affects whether those savings are passed on to you or not.

I'm still recommending, DO NOT GO 2S.
 

Cyberdactyl

Misfit Multirotor Monkey
#9
I agree with CD. Two 2S in series is not worth 4S power. Too much added material and added harness adaptation (plugs).

Where buying multiple slightly lower mAh batteries DOES come in handy is 3S and 4S where you have the option of using them individually or in parallel.
 

Craftydan

Hostage Taker of Quads
Moderator
Mentor
#10
This brings me to another question, since in my research I find different schools of thought. How low can you safely drain a LiPo? is the 11.1v or 14.8v limit to high?
Never below 3.3v/Cell loaded. Never below 3.7v/Cell resting.

My reason for this depends on the chemistry.

If you look at the discharge accumulation curve (how much "energy" is left in the pack vs the voltage) you'll find that at 3.7v resting there's a sharp knee in the curve -- above this, drawing a small amount of "energy" (current over time) causes a small change in voltage. below this drawing the same amount of "energy" will cause a MUCH larger drop in voltage.

why?

Below 3.7v resting, the chemistry is changing. there are two sets of simultaneous reactions occurring as the battery discharges -- Reversable (rechargeable) and irreversible (damaging). you'll ALWAYS have a small amount of both, but how much of each will depend on the pack voltage. the knee in the curve tells me I'm running out of the reversible reactions and starting to rely on irreversible reactions (DAMAGE!) to generate the current.

So why 3.3v loaded? the disparity between the loaded and resting voltage is caused by the fact it takes time for energy to move out of the pack -- internal resistance. The "stuff" closer to the contacts dumps it's energy readily and must allow the "stuff" behind it to recharge it some to pass it out to the contacts. Below 3.3v you're MOSTLY running irreversible reactions, so dropping that first layer below this will decreases it's own ability to pass the charge along from the stuff behind it . . . increasing the overall internal resistance nearer the contacts and damaging your pack.

Others may disagree -- they're free to do so -- but I'm comfortable with my reasoned approach to this.
 

Cyberdactyl

Misfit Multirotor Monkey
#12
The other thing frequently asked is how to charge a Lipo that has fallen too far in voltage for the charger, set to LiPo mode, to recognize.

You can set your charger on NiCd on its lowest amp setting, and charge it up to around 3.1V/cell. After that is reached, switch over to a normal balanced LiPo charge.

The caveat is you MUST personally monitor the battery while in the NiCd charging stage, and it's highly recommended to use a charging bag for a least that battery afterwards.

A "resurrected" Lipo most likely has lost a considerable amount of life, but many times can still be used for a while longer. If too puffy, but still holding some decent charge, it can be retired or re-purposed as ground base use such as a FPV ground station.
 

Khaptin

Junior Member
#14
Ok, I ordered a 4s 5500 mAh LiPo battery. It's an "off brand" so I'll post back it's condition and what my initial thoughts are when I get it. I'll also try to remember to post back if it gives me plenty of re-charges or is a miserable mistake of mine.
 
#16
not sure what you call "off brand"; if you mean something from hobbyking/turnigy/zippy or similar instead of a DJI (re)branded one, then fine, you should be ok, but I hope it doesnt mean some dodgy no name from who knows where. My point being, a faulty battery can cost your entire craft, gimbal, camera, not too mention possibly the house where you charge it or the well being of the people you fly over. It can happen with any brand, but Id rather not save the last $2 on a battery for a heavy hexacopter.

Also, what C rating did you get and how did you determine it?
 

jipp

Senior Member
#17
i have a bag but i end up charging at 1a on top of it.. because my balance leads were not long enough.. but i have a extension coming.

so i can start charging in the bag.


i try to charge in the same room also.
chris.
 
#18
I charge mine when I'm in the room, so I feel relatively safe charging without a bag. But I do have a metal pot if I leave the room.
Id lie if I said I always used a bag, and its far from certain a bag will actually prevent a fire, but surely its what I would always recommend (to myself too!). A bag and a smoke alarm. And being around the house. At least the latter two I always do, no exceptions, because Ive had a large lipo explode while charging (user error, forgot to disconnect one battery from those huge multiple charge looms, then charged a higher cell count battery on a different plug on the same charger, that didnt end well); Ill tell you that being in the same room isnt all that much use, and possibly even not such a good thing, if there is no bag.
 

Khaptin

Junior Member
#19
The battery I ordered

not sure what you call "off brand"; if you mean something from hobbyking/turnigy/zippy or similar instead of a DJI (re)branded one, then fine, you should be ok, but I hope it doesnt mean some dodgy no name from who knows where. My point being, a faulty battery can cost your entire craft, gimbal, camera, not too mention possibly the house where you charge it or the well being of the people you fly over. It can happen with any brand, but Id rather not save the last $2 on a battery for a heavy hexacopter.

Also, what C rating did you get and how did you determine it?
I ordered a Floureon 4s 35c. It actually cost me more than some of the Turnigy packs I was looking at. I ordered from Amazon, so may be able to cancel. What do you think? Is it worth trying out?

Sorry, I'm pretty new to this LiPo thing. I just know I can't afford to buy maxamps for experimentation.

P.S. I went ahead and just changed my order to a Hobby King (pretty sure it's a turnigy) battery
 
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Cyberdactyl

Misfit Multirotor Monkey
#20
Id lie if I said I always used a bag, and its far from certain a bag will actually prevent a fire, but surely its what I would always recommend (to myself too!). A bag and a smoke alarm. And being around the house. At least the latter two I always do, no exceptions, because Ive had a large lipo explode while charging (user error, forgot to disconnect one battery from those huge multiple charge looms, then charged a higher cell count battery on a different plug on the same charger, that didnt end well); Ill tell you that being in the same room isnt all that much use, and possibly even not such a good thing, if there is no bag.
99.95% of the time charging is no problem, especially with idiot proof chargers and always, ALWAYS use the balance leads. . . and use a reasonable amount of awareness of not keeping obviously physically damaged LiPos (damage other than merely puffy).

Being in the same room will allow you to smell and hear the hiss long before 99% of that remaining 0.05% becomes a conflagration.

NOT being in the same room pretty much guarantees any battery that goes that route will be a serious problem.

But I DO admit, there's that 0.005% that can ruin your day.


 
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