G'day DIY Drones,

I have a question about batteries, yes, I know this has been done to death, but I would like some real world experiences rather than the math.  

I have used the search bar but I guess I am not using the right keywords, hence the reason for this post.

I am considering using 1 10000mah 4s instead of 2 5000mah 4s batteries to get more flight time from my 690mm photography rig.

A bigger battery of the same C rating or close to it.

Here is the math (feel free to correct me if I'm wrong)

2 x 5000mah 4s at 25 C = 125 max amp draw and has 10000mah. Weight, approx 1300g

1 x 10000mah 4s at 25 C = 250 max amp draw and has 10000mah. Weight, approx 800-850g

I only need about 115 max amps so both will do the job.

My question is about flight time and battery voltage sag.

I don't want theory but real world experience please.

Will the 10A, lighter battery give me more flight time because of the weight saving or will the voltage drop off sooner because it is only a single battery?

Another way to put it would be, would the 2 5A batteries hold the voltage longer than the 1 10A battery given the same flight situations?

Another way to put it is, are two batteries that equal the one in MAh, better?

I hope I am making sense here 

Cheers

Aussie

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Thanks for your replay Alasdair,

I am using Zippy 30C 5000mah High Discharge "Flightmax" LiPo batteries.  I use 2 at a time and get about 13 to 14 minutes before I hit 13.7v (my personal get the hell home voltage)

Maybe that is a good time and I am just being greedy wanting more?  I still think, from the comments here and my gut feeling, that 2 is better than one larger battery.

Zippy do have an 8000mah 30c.  Two of those might get me the extra I need.

Cheers

Aussie

Personally my experience is "lower cost" multiple batteries in series/parallel has two fold benefit. If a cell in a pack goes bad, your only out 1/2 the pack (unless you know how to assemble packs with a simple spot welding technique, 99% don't). I have used the Turnigy hardcase 4S-5000 packs (at $21/ea on sale shipped) for my AP 600mm deadcat quad and electric bikes for years now (I buy them for her bike, but mostly get used for my quad, lol), I have not found a better bang for buck yet, if you find something please post, tia.

Here is the pack I get for $21 shipped when on sale

http://www.hobbyking.com/hobbyking/store/__18631__Turnigy_5000mAh_4...

This discussion really sheds a light to me.

Currently i'm rebuilding my quad from a serious crash.

I'm using a 6000 mah 6s lipo and now considering of using 2 x 6000 mah 3s lipo in series.

Would it be better in term of amperage draw on each batteries as well?

The reason i'm asking is because things discussed is in parallel configuration and i want to apply a series configuration.

Thanks

The biggest factor for flight times is weight. So everything else being similar or good enough, the one with less weight will always win.

Hi

@ Joe Gordon  You are correct the resistance is the same for 4 x 2500 or 1 x 10000 of the same type. my error. 

So a typical 5000mah 30C 3S battery has a internal resistance of approx 1.3mohm. and a 10000mah has an internal resistance of approx 0.65mohm.  The 2 x 5000 packs in parallel have the same 0.65mohm as the 10000 pack but the total current from both packs is the same and so each of the 5000 packs is only producing 1/2 the amps and 1/2 the watts. This will have a smaller effect on heating the packs as they have a larger surface area to cool them . I still prefer to have the 2 (or more) packs from the security perspective, If one pack fails the copter can still fly and if this happens your financial loss is reduced. 

interestingly the packs with a higher C rating have a lower internal resistance (0.24mohm for a 50C 10000mah )and so the volt drop will be less for the same total current equaling longer flight times. 

I have been flying a home built Y6 for 3 months now.  My design uses 3 5000mah 25c lipos wired in parallel.  Ecalc predicted max output at 20c each for each of the three batterys, for a max load of 300A.(rough numbers)  I hover around 45% throttle or 90A.  The max reported current ever, has been 150a and over 100A I get serious voltage lag that triggers a battery failsafe.  If the available current actually was additive from the three parallel packs I should have 120Ax3=360A available current.

I have found a few important bits of information,  One battery site gave the advice that if voltage lag is not acceptable then you need to  only use 1/2 the C rating for your battery.  I'm beginning to be convinced.

Second, I emailed the vendor that sold the battery, they responded that they conclude parallel lipo packs do not actually provide additional current and that my setup will provide 120A max.  (I could not get a more technical explanation) but I suppose internal balancing between packs could consume some of the overall current capacity.  My reaction to this was to wire a parallel balance connector between each pack to better balance the cells during discharge.  This has extended my flight time, perhaps reduced the voltage lag a bit, but the max reported current is still the same.

My conclusion would be to use a single lipo pack with the highest C rate you can get, rather than parallel the lipos.  I agree that the current in the parallel arrangement should be additive, but that has not been my experience.

I Plan on a new set of 60C lipos.  Perhaps I wont see this much voltage lag.

beware, if one of the batteries has a voltage drop, you are dead while in parallel not.
So be shure to use fresh and good quality batteries.
Always stay far from voltage limit of the battery.
Amperage draw correspond to the battery lowest Ampère rating , it will not add as for parallel.
So in series, if a battery as 3A and the other has 10A , you will have a 3A system.

90 A to hover ?
I will be scared to use such high currents.
Your conclusion IMO is wrong, check your connections and cable size because currents are very high.
Beware, one of my customers, with his monster okto setup got solderings that melt due to high current and heat generated by current flow.

What is the weight of your copter ?
What props are you using ?

Without this information it is hard to help you to increase flightime.

A quad with average efficiency and no payload will fly 60 minutes with one 5000 mah 4S battery while only 69 minutes with two 5000mah 4s batteries.

Luc:

I'm actually happy to hear you disagree with my conclusion.  I'm heavily vested in the 3-pack parallel arrangement.  I have the current issues under control with my power distribution, All 10ga wire and heavy distribution board.  Any heat generated is in the esc's and the batterys.  After a flight the batterys are always hot, and that concerns me.  So I figure my biggest risk now is a failing battery from drawing near max current most of the time.  Now that I made a parallel balance cable things look more stable.  New  "different" batterys are in my future

Their comment that parallel packs do not increase current capability is absolutely incorrect. Either the person who made the comment does not understand the issue or may not have understood the question.  Packs in series will not increase current capability but do increase voltage,packs in parallel are additive in current and capacity

C rating for current are not standardized.  So many values may be inflated for marketing purposes.

I am running a 10C 16,000mah and pull about 70 amps at hover. No issues with excessive voltage sag or overheating battery. I do take into account some voltage sag when setting warning and failsafe values for battery voltage.  The batteries are warm after flight but not excessively so.  The heat is a consequence of current and battery resistance.

Your setup should easily work.  When you check battery voltage after flights and look at how many mah you put back into the battery when recharging - what are these values.  It could be a matter of adjusting your failsafe trigger point.

I have run into a issue on 3.3 where there seems to be a issue with battery monitoring and calibration but don't know if it is a issue with a defective part or as I thin a firmware issue.  When I arm one copter I have on 3.3 the measured voltage immediately drops with no increase in current flow.  This did prematurely create a failsafe.

All you wrote is correct Harry, but if there is not a bottleneck in cable size or power transmission chain it is not possible that Ampere of the three parallel batteries do not add .
I might have not understood correctly your words since english is not my native language, if it is the case , I apologize for that.

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