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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Good question, if both packs delivered exactly 8000mAh (80%) then the weight saving will have the biggest influence on flight time.

(Just a correction: 2 x 5000mAh 4s 25C (in parallel) is equal to 10000mAh 4S 50C - the C rating also doubles.)

But in this case the heavier pair will have lower internal resistance and should last longer but as the extra weight will cause the overall amp draw to be greater, the 8Ah may be used up faster.

It will depend on how much greater amp draw the extra weight causes.

Without measured data from both packs the only way you'll get accurate real world information is to test them.

Going for heavier batteries usually gets one into the law of diminishing returns.

Since you don't want theory, you should provide links to the actual batteries you are comparing.
(They will have the same max amps draw when you parallel the 5000's)

The 4 x 2500mAh  batteries combined will have a lower internal resistance than the 10000mAh battery and so will produce a much lower volt drop across the battery, Each battery will also be supplying 1/4 of the total current and so they will be less stressed and last longer. 

With the lower volt drop the measured voltage at the power module will be higher and so the aircraft will fly for longer before you reach the lower limit. 

It is also a safety feature as one battery failing will not bring down the aircraft. on a side note this also causes less structural damage in the event of a sudden arrival. the batteries can be secured individually and some may not detach. 

Been doing this for a long time. never had a problem with this at all. 

Are you sure @Graham?! Is not 2 x 5000mAh 4s 25C (in parallel) is equal to 10000mAh 4S 25C not 50C?!

Graham misspoke technically speaking, but in essence he is correct and your math is wrong calculating max current because you failed to double the max output. Putting two 5Ah batteries in parallel gives you 10A X 25C = 250A. This would be the same as 5Ah X 50C. This is where Graham's 50C figure comes from.

Thanks for your input Graham, That is precisely the issue that is not sitting right in my brain, therefor the reason I asked the question.

I was hoping that someone had already tested this and had an answer for me.  This is an expensive exercise, just to test which one will last longer.  I already get 13 to 14 minutes of flight time with 2 x 5000mah batteries and I am in the market to get some more.  I think that I am better off with two vs a single larger battery.

Thanks for your view

Aussie

I was lead to believe the C rating stayed the same also?  In any case, 125A is plenty for my needs.

Thanks for correcting my figures though.  I am leaning towards 2 5A batteries rather than 1 x 10A.  

Aussie

Thanks mate for your input.  As per my response above, I am currently using 2 x 5A 4s batteries.  My Hex is a bit crowded for 4 x 2.5's so I think, after reading all you guys' comments, I will stay with 2 x 5A vs 1 larger.  Maybe upgrade to 2 x 6A :) if the weight isn't to much different. 

Cheers

Aussie

What is the weight of your hex ?

How much Watt  / Ampere do you need to hover ?

Yes, sorry, that is correct. Each 5000mAh pack can theoretically deliver 25c or 125A, so in parallel they can theoretically deliver 250A (or 25C of 10000mAh)

Spot on

If the batteries are of the same type then there is no resistance difference in 4 batteries at 2500mah in parallel and one of 10,000mah. For a given chemistry/construction resistance is inversely proportional to the mah of the battery.  Many high MAH batteries actually use cells in parallel.  The extra wire and connector increasing your overall weight is probably the biggest flight time issue with 4 versus 1 batteries.

But different battery chemistry/construction may have different inherent internal resistance factors.  Higher C rate batteries tend to have lower internal resistance then low C rate batteries.  

However lower C Rate batteries tend to be lighter for a given capacity.  One of the big reasons the Phantoms get good flight time is they use a low C rate battery with good energy density.  They are about 30%-40% higher energy density than a typical RC 35 C Lipo Battery.  So you typically want the lowest C rate that will safely power your copter given its setup. "Multicopter batteries" marketed by some tend to be lower C rate batteries particularly the high mah batterise where caqpacity adds to total amp output capability as some have noted.

The relatively new High Voltage LiPo batteres with 4.35 volts per cell tend to give about 7 or 8 percent higher energy density than average RC batteries so these may be a good solution for applications where a higher C rate is needed. They are great for performance flying as well.  Many FPV racers are going this route due to the higher voltage giving some performance increase and the higher energy density.

Number of batteries is not the key.  C rate, energy density, mah and weight  coupled with you copter setup are the factors.  E-calc is a good tool to look at these issues.

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