Afternoon Everybody…

Quick Question…

I just finished up a new 8inch GEPRC Mark 4 Build, with the SB F7V3 Stack (50ESC) and now I’m debating on Voltage and Batteries and what not, And the batteries I currently have, (2 sets) that I’m planning on using till I can afford a couple really nice ones are:

• 14.8V LiPo 1800mah 4S 120C (26.64wh) (X’s 6 Batteries)
• 11.1V LiPo 5000mah 3S 50C (X’s 2 Batteries)

If you were in my shoes and and cool with 4S, but ultimately wanting to venture into 6S, What might you do?

And am I correct in thinking that if I were to run those in series, I’d be left with: 2 - 11.1V 5000mah 3S 50C Batteries - Would I be left with an end result of:
22.2V 10,000mah 6S 100C Battery????

Or can or should I even think of running the 1800mah batteries in parallel, which I think should then leave me with a
14.8V 3600mah 120C set-up?

Is that Right ?????

   

The maximum discharge ""C" rating of a battery does not alter whether single, parallel, or series, its fixed by the chemistry and construction used. A pack can through its internal resistance only deliver to a limit, basically you can only "suck" so much current.  Its also an area where label cheating is rife!

Thus your two 11.1V LiPo 5000mah 3S 50C will in series be (roughly) double the voltage, with the same capacity and discharge ability as before singly.

I say roughly as a lot will depend on your wiring loom quality.

Your 14.8V LiPo 1800mah 4S 120C , if connected in parallel, will roughly double the capacity, with a nominal 3600mAh. Again though, you are adding wiring and connections and the quality of those will affect the result.

In both cases you will need to pay attention to the minimum voltage per cell as batteries, especially used batteries, will have some cells better than others. The BALANCE of paired packs becomes more critical, as a weaker cell can drop away without the obvious to user drop in performance to warn till you have run that cell under a safe voltage with consequent risk of damage.  

The Betaflight "Average voltage per cell" display is less than ideal to display this variation during discharge.  Basically, keep a safety margin above minimum.

There's an obvious loss compared to a single cell pack, as you'll have more construction material so more weight, but its not usualy critical.


I have successfully run twinned 3S to get 6S in the past, and twinned 6S to get 12S, both on Helicopters (12S currently used, that is).  I run twinned 1S to get 2S on whoops all the time.

On the Heli I run a couple of lightweight battery alarm "screamers" on the balance ports, set to my chosen min voltage. Some latch once triggered, the better ones to use reset after a current surge.  They are loud enough for my use even if there are i.c. planes also up at the time, but then I do not go outside club boundaries.

Hi Cole,

As you have shown in the picture, you can connect the 2 x 3S batteries in series to
form an effective 6S pack. I have done this in that past and it works much better
than most folks might think. It is a good way to see how the quad flies on 6S.

In fact, I have connected up to 3 Li-Po packs together, sometimes series and 
sometimes parallel depending on my application. This works much better than
folks might believe and actually comes pretty close to using a single pack of
the same configuration. Yes, any variance comes from the connector, but I
have found this to be a minor. In fact, the performance of my "connected" 
packs is pretty close to a factory assembled pack. Very close. Certainly,
close enough to use; I have and still do. It works.

Now, let's think about it. A Li-Po pack (from the factory) is actually comprised
of single, 1S, cells connected in series to form 2S, 3S, 4S, 6S. Oh yeah, that
is also how Li-Ion packs are made. Plus, their are larger builds that are using
multiple packs connected with adapters. 

In short, go ahead. The connected packs will be fine and work well.
Will the performance exactly match that of a factory 6S? Maybe not, but it
will likely be close enough that you might not be able to tell the difference
when you get a real, factory assembles, 6S Li-Po.

Later, iFly  

Never run Lipo batteries in parallel. One set will always have a smidge more resistance than the other, so the discharge will be uneven. Even 0.01 ohm difference can cause this. You can even get to the point where the first-discharged pack gets reversed by the second pack. This kills batteries. Series fine. Parallel not fine.

You could overcome the back charging issue by throwing diodes on the output of each pack. That would get rid of any back flow. But the unbalancing side of it, i can see a way using something custom that allowed you to connect say x number of packs in parallel, but only allowed one pack to be connected between a range of voltages and then energised the second pack when first packs voltage hit's whatever the min voltage is that you set.

So for instance each pack is connected via a relay. First pack is operational until it's average voltage hits say 3.6V, then second pack is energised between 3.6V and 3.55V, at 3.55V first pack is cut off and the cycle continues for each connected pack. You could probably build something around a PIC or Arduino with several relays connected to it to achieve that, since we aren't asking it to do anything really complicated besides monitor voltage and energise relays based on conditional statements. Whether you would want to, is a whole different question.

I'm with segler999 on this, running multiple packs in series is fine and done all the time, I have an EDF jet that uses 4x3s packs in series and after 15 years and 6 sets of batteries they stay very healthy with just occasional balancing. Note that I always run them together, I mean I treat the 4 3s packs as one pack. Do not run them in parallel unless you are willing to only use a fraction of their total capacity and watch the discharge characteristics very carefully. If one pack is doing more work stop paralleling them. And even if they share the load that will change over time as the cells age. Maybe you can borrow a 4s 5000/6000 from a friend to test?
Maybe you already know all this but anyway I'll say it. A 7" is a big quad, so the motors will draw a lot of current, as the voltage goes up amperage goes down so if I was building a big quad I would rather run 6s, it would run cooler for the same flying style. But motor kv and prop pitch will all come into this. For the same prop lower kv motors and higher cell count will give the same rpm as higher kv motors and lower cell count. But it's easier to change the props than the motors so lower pitch props at higher rpm and 6s will equal the lift of higher pitch props and lower rpm on 4s. Just food for thought.

(17-Feb-2024, 04:59 PM)segler999 Wrote: Never run Lipo batteries in parallel.  One set will always have a smidge more resistance than the other, so the discharge will be uneven.  Even 0.01 ohm difference can cause this.  You can even get to the point where the first-discharged pack gets reversed by the second pack.  This kills batteries.  Series fine.  Parallel not fine.

Hi Segler,

Meaning no disrespect, I disagree from the perspective of actual use and years of 
research. Let's start with the EMAX TinyHawk Freestyle that comes with a dual 1S 
battery connector. Now, let's consider that the long range guys and others have 
been doing this for years with higher cell count Li-Po and Li-Ion battery packs. 
In fact, I still run some dual parallel packs with no issues. It has been common 
practice for years to run LiPo packs in parallel.

I also have a project where I intend to connect 2 multi-cell LiPo batteries in
parallel; one on the top deck and one underslung. It should be interesting. 
Just as a test, I will start with two (2) new batteries and run them for as long
as they last; of course keeping records of the data collected for future reference.

By the way the chemistry of the Lithium Ion Polymer (Li-Po) battery is the same
as any other Lithium Ion battery. Just saying. 

While there may be (?) some "technical" accuracy in your theory, in practical use, 
any differences (smidge) of resistance is minor, one can't tell the difference, and 
there is no obvious detrimental effect; it does NOT Kill batteries. Rather, it has not 
made any appreciable difference in any of my batteries and you are the first one
that I have seen suggesting it. None of the batteries that I have run in parallel 
have suffered any ill effects as a result of paralleling Li-Po batteries. Most of them 
are several years old and still going strong. Of course, I also don't split hairs to 
see which packs last longer than others. Plus, none of the research or advice that 
I have seen even suggests that it is a bad idea to connect Li-Po batteries in parallel.

Of course, folks mention things like, being the same brand, size, capacity, and 
all that, however, there is more leeway than what is suggested. The primary thing 
is that the voltage (cell count) be the same and about the same level of charge. 
That said, any difference in charge voltage will quickly equalize across all cells.
While this may not result in the absolute maximum voltage, it will not harm the
batteries. In fact, this is how charging works.  

Maybe, take a look at information in the links below...and these are but a few 
of the many on connecting Li-Po batteries in parallel; common practice for 
years. Also, I found nothing to corroborate the "resistance" theory of that it
adversely effects battery life.

                       
Connection of two LiPos

Series and Parallel Battery Connections

Wiring LiPo Batteries in Parallel


The short answer:  Connecting Li-Po batteries in Parallel is fine.

Later, iFly  

(17-Feb-2024, 07:06 AM)BadRaven Wrote: The maximum discharge ""C" rating of a battery does not alter whether single, parallel, or series, its fixed by the chemistry and construction used. A pack can through its internal resistance only deliver to a limit, basically you can only "suck" so much current.  Its also an area where label cheating is rife!

Thus your two 11.1V LiPo 5000mah 3S 50C will in series be (roughly) double the voltage, with the same capacity and discharge ability as before singly.

I say roughly as a lot will depend on your wiring loom quality.

Your 14.8V LiPo 1800mah 4S 120C , if connected in parallel, will roughly double the capacity, with a nominal 3600mAh. Again though, you are adding wiring and connections and the quality of those will affect the result.

In both cases you will need to pay attention to the minimum voltage per cell as batteries, especially used batteries, will have some cells better than others. The BALANCE of paired packs becomes more critical, as a weaker cell can drop away without the obvious to user drop in performance to warn till you have run that cell under a safe voltage with consequent risk of damage.  

The Betaflight "Average voltage per cell" display is less than ideal to display this variation during discharge.  Basically, keep a safety margin above minimum.

There's an obvious loss compared to a single cell pack, as you'll have more construction material so more weight, but its not usualy critical.


I have successfully run twinned 3S to get 6S in the past, and twinned 6S to get 12S, both on Helicopters (12S currently used, that is).  I run twinned 1S to get 2S on whoops all the time.

On the Heli I run a couple of lightweight battery alarm "screamers" on the balance ports, set to my chosen min voltage. Some latch once triggered, the better ones to use reset after a current surge.  They are loud enough for my use even if there are i.c. planes also up at the time, but then I do not go outside club boundaries.

"On the Heli I run a couple of lightweight battery alarm "screamers" on the balance ports, set to my chosen min voltage. Some latch once triggered, the better ones to use reset after a current surge.  They are loud enough for my use even if there are i.c. planes also up at the time, but then I do not go outside club boundaries."

That awesome, And TY for the info. Im happy to hear things might work out for the better when I do so. 
I do have a question, and in that Im also eager to get a little bit of clarity on the "Screamer Set-up" you mentioned prior. 
Can you shed a lil light on that, maybe evan a picture as to how you have that wired up?

(17-Feb-2024, 12:26 PM)iFly4rotors Wrote: Hi Cole,

As you have shown in the picture, you can connect the 2 x 3S batteries in series to
form an effective 6S pack. I have done this in that past and it works much better
than most folks might think. It is a good way to see how the quad flies on 6S.

In fact, I have connected up to 3 Li-Po packs together, sometimes series and 
sometimes parallel depending on my application. This works much better than
folks might believe and actually comes pretty close to using a single pack of
the same configuration. Yes, any variance comes from the connector, but I
have found this to be a minor. In fact, the performance of my "connected" 
packs is pretty close to a factory assembled pack. Very close. Certainly,
close enough to use; I have and still do. It works.

Now, let's think about it. A Li-Po pack (from the factory) is actually comprised
of single, 1S, cells connected in series to form 2S, 3S, 4S, 6S. Oh yeah, that
is also how Li-Ion packs are made. Plus, their are larger builds that are using
multiple packs connected with adapters. 

In short, go ahead. The connected packs will be fine and work well.
Will the performance exactly match that of a factory 6S? Maybe not, but it
will likely be close enough that you might not be able to tell the difference
when you get a real, factory assembles, 6S Li-Po.

Later, iFly  

I really Apprechiete the info, As Im Stooked to hear this.. Ive always wondered what I would do with these long ass 11.1V 3S 5000mah batteries I had laying around from an older quad that went by the name of Traxxas Aton... That was my 1st quad that got my brain Jacked into this world.... 

-Thanks Again

(17-Feb-2024, 04:59 PM)segler999 Wrote: Never run Lipo batteries in parallel.  One set will always have a smidge more resistance than the other, so the discharge will be uneven.  Even 0.01 ohm difference can cause this.  You can even get to the point where the first-discharged pack gets reversed by the second pack.  This kills batteries.  Series fine.  Parallel not fine.

+1

-Thx for the Info....



[quote pid='214095' dateline='1708185563']
 "Series fine.  Parallel not fine."
[/quote]

[quote pid='214095' dateline='1708185563']
 
[/quote]

(17-Feb-2024, 05:30 PM)Pathfinder075 Wrote: You could overcome the back charging issue by throwing diodes on the output of each pack.  That would get rid of any back flow.  But the unbalancing side of it, i can see a way using something custom that allowed you to connect say x number of packs in parallel, but only allowed one pack to be connected between a range of voltages and then energised the second pack when first packs voltage hit's whatever the min voltage is that you set.

So for instance each pack is connected via a relay.  First pack is operational until it's average voltage hits say 3.6V, then second pack is energised between 3.6V and 3.55V, at 3.55V first pack is cut off and the cycle continues for each connected pack.  You could probably build something around a PIC or Arduino with several relays connected to it to achieve that, since we aren't asking it to do anything really complicated besides monitor voltage and energise relays based on conditional statements.  Whether you would want to, is a whole different question.

So for instance each pack is connected via a relay. First pack is operational until it's average voltage hits say 3.6V, then second pack is energised between 3.6V and 3.55V, at 3.55V first pack is cut off and the cycle continues for each connected pack. You could probably build something around a PIC or Arduino with several relays connected to it to achieve that, since we aren't asking it to do anything really complicated besides monitor voltage and energise relays based on conditional statements. Whether you would want to, is a whole different question. 


-That's an Awesome Idea....

If there was a way I could get One wish to bring back a Favorite Store of mine - " I'd Wish for Radio Shack" to come back to life....

God I miss that place.... "Got an Idea"??? Cool, hop in car, goto Radio Shack - Done...

Now a Days - Got an Idea.... Grab laptop, Order.... WAIT WAIT WAIT...... 

Hate That Shiete...

(17-Feb-2024, 07:18 PM)husafreak Wrote: I'm with segler999 on this, running multiple packs in series is fine and done all the time, I have an EDF jet that uses 4x3s packs in series and after 15 years and 6 sets of batteries they stay very healthy with just occasional balancing. Note that I always run them together, I mean I treat the 4 3s packs as one pack. Do not run them in parallel unless you are willing to only use a fraction of their total capacity and watch the discharge characteristics very carefully. If one pack is doing more work stop paralleling them. And even if they share the load that will change over time as the cells age. Maybe you can borrow a 4s 5000/6000 from a friend to test?
Maybe you already know all this but anyway I'll say it. A 7" is a big quad, so the motors will draw a lot of current, as the voltage goes up amperage goes down so if I was building a big quad I would rather run 6s, it would run cooler for the same flying style. But motor kv and prop pitch will all come into this. For the same prop lower kv motors and higher cell count will give the same rpm as higher kv motors and lower cell count. But it's easier to change the props than the motors so lower pitch props at higher rpm and 6s will equal the lift of higher pitch props and lower rpm on 4s. Just food for thought.

Great Input, And Thank You for your thoughts on this, But after reading or while reading Im curious as to what you ment when you said
" I have an EDF jet that uses 4x3s packs in series and after 15 years and 6 sets of batteries they stay very healthy with just occasional balancing."

Only balancing occasionally?

* Do you mean, You only use the balancing feature on your charger once in a while, when needed?


Another quick question, When charging do you charge those 3 batteries all at the same time as one battery? 
or
Do you charge them ALL TOGETHER, As "ONE Battery"???

And if I may, What charger are you currently using?

I have a small POS charger that does Balance charging, But only 1 battery atta time..

-Thanks

So just to reiterate everything mentioned above, without me over thinking it...lol

If I ran -
2 - 11.1V 3S 5000mah 50C batteries in "Series", Id be left with a 1 - 22.2V 6S 5000mah 50C Battery (in theory) ????

If I ran -
2 - 11.1V 3S 5000mah 50C batteries in "Parallel", I'd be left with 1 - 11.1V 3S or 6S 10,000mah 50C or 100C Battery (in theory) ???

Im just wanting to be Absolutely 110% certain Im looking at this correctly.. Sorry if anyone thinks Im repeating myself..
I just want to make sure Im On-Point when doing this...

I tend to overthink sometimes, and wind up making things more of pain in the ass...lol

And then the same theory when it comes down to the 14.8V scenario..

If I ran 2 - 14.8V 4S 1800mah 120C batteries in "Series", I'd be left with 1 - 29.6V 8S 1800mah 120C or 240C Battery??

and

If I ran 2 - 14.8V 4S 1800mah 120C batteries in "Parallel", Id be left with 1 - 14.8V 4S or 8S 3600mah 120C Battery??

Again, Sorry if confusing....

But I Really Appreciate the Read and Response......

-Thanks

(19-Feb-2024, 06:18 AM)Coleon Wrote: So just to reiterate everything mentioned above, without me over thinking it...lol

If I ran -
2 - 11.1V 3S 5000mah 50C batteries in "Series", Id be left with a 1 - 22.2V 6S 5000mah 50C Battery (in theory) ????

If I ran -
2 - 11.1V 3S 5000mah 50C batteries in "Parallel", I'd be left with 1 - 11.1V 3S or 6S 10,000mah 50C or 100C Battery (in theory) ???

Im just wanting to be Absolutely 110% certain Im looking at this correctly.. Sorry if anyone thinks Im repeating myself..
I just want to make sure Im On-Point when doing this...

I tend to overthink sometimes, and wind up making things more of pain in the ass...lol

And then the same theory when it comes down to the 14.8V scenario..

If I ran 2 - 14.8V 4S 1800mah 120C batteries in "Series", I'd be left with 1 - 29.6V 8S 1800mah 120C or 240C Battery??

and

If I ran 2 - 14.8V 4S 1800mah 120C batteries in "Parallel", Id be left with 1 - 14.8V 4S or 8S 3600mah 120C Battery??

Again, Sorry if confusing....

But I Really Appreciate the Read and Response......

-Thanks

If in fact that is the case, How would I go about charging?

* Charge both seperatly, using the XT60 and the balance plug into charger?
* Or as 1 unit, and I'd have to combine the balance plugs of both batteries into 1, torun together of 1 chip?
* Or eliminate 1 balance plug, and Have 2 batteries running of of 1 balance plug? That dosent seem right?

So Yes, I guess I have a couple charging questions too... Sorry