6S/8S Speedrun - Parallel vs Series: Which is better?

[Panther6834]

I've searched the forum, and (unless I missed something) I could find any thread(s) on this specific subject. So...I'm creating this thread to not only 'learn', but to (hopefully) prompt answers that will help other Speedrun nOObs.

In general, I'm quite familiar with running LiPos in parallel, as well as in series. As most know, when using two identical packs, running them in parallel doubles the output capacity (two 5000mAh 4S packs = 10,000mAh 4S), while running them series doubles the voltage (two 5000mAh 4S packs = 5000mAh 8S). For a couple of my crawlers, I'll probably run two packs parallel...and, with my boats, I run both ways (on different boats, obviously, dependant on the purpose/type of boat). Using two of my boats as examples, my P-Sport Hydro runs two mid-capacity 2S packs in series (as opposed to a single 4S, or two 4S parallel) to help keep weight as low as possible. However, in my P-Limited Cat, I run two high-capacity 4S parallel (one in each hull) to keep the cat 'balanced'.

However, where speedrun vehicles are concerned, I see, and read about, people using both...and, admittedly, I'm a little confused. For the purpose of the following examples, let's assume a person will be running 8S. On one hand, two 10,000 4S packs could be run in series. On the other hand, two 5000mAh 8S packs could be used parallel. Both examples result in the same capacity AND same voltage.

My questions are:
1) For the specific purpose of a speedrun vehicle, what are the advantages/disadvantages of each configuration?
2) For the specific purpose of a speedrun vehicle, is one configuration truly better than the other...and why?

 

[Hector_Fisher]

If im understanding your question correctly, youre asking which is better ideologically: two 4s batteries in parallel vs the same 4s batteries in series for fastest possible speed running? I'm going to assume so.
EDITED: @Panther6834 apologies, it was late and I misread your post!

Agreed that electrically, they both SHOULD be the same. Same voltage and same potential amperage. I have a feeling there will be a minor difference, but i don't have experience running both to say. Hopefully others chime in.

 

[Panther6834]

If im understanding your question correctly, youre asking which is better ideologically: two 4s batteries in parallel vs the same 4s batteries in series for fastest possible speed running? I'm going to assume so.

No, not what I was asking. If that were 'correct', one would result in 8S, while the other would still be 4S (albeit, double the capacity)...and, I clearly stated (in the thread title) they this is for 6S & 8S, thus 4S "total" is not 'applicable'. If you reread what I said, BOTH configuration options lead to 8S, as copied/pasted below:

"On one hand, two 10,000 4S packs could be run in series. On the other hand, two 5000mAh 8S packs could be used parallel. Both examples result in the same capacity AND same voltage."

I could have chosen packs of any capacity...but, to 'simplify' what I was asking, I chose to use 10,000mAh as the final/total capacity. Additionally, please ignore 'C' rating, as it has nothing to do with what I'm asking. In other words, whether two 5000mAh 8S packs, or two 10,000 4S packs, assume all packs just mentioned have the exact same 'C' rating.

 

[LibertyMKiii]

I've searched the forum, and (unless I missed something) I could find any thread(s) on this specific subject. So...I'm creating this thread to not only 'learn', but to (hopefully) prompt answers that will help other Speedrun nOObs.

In general, I'm quite familiar with running LiPos in parallel, as well as in series. As most know, when using two identical packs, running them in parallel doubles the output capacity (two 5000mAh 4S packs = 10,000mAh 4S), while running them series doubles the voltage (two 5000mAh 4S packs = 5000mAh 8S). For a couple of my crawlers, I'll probably run two packs parallel...and, with my boats, I run both ways (on different boats, obviously, dependant on the purpose/type of boat). Using two of my boats as examples, my P-Sport Hydro runs two mid-capacity 2S packs in series (as opposed to a single 4S, or two 4S parallel) to help keep weight as low as possible. However, in my P-Limited Cat, I run two high-capacity 4S parallel (one in each hull) to keep the cat 'balanced'.

However, where speedrun vehicles are concerned, I see, and read about, people using both...and, admittedly, I'm a little confused. For the purpose of the following examples, let's assume a person will be running 8S. On one hand, two 10,000 4S packs could be run in series. On the other hand, two 5000mAh 8S packs could be used parallel. Both examples result in the same capacity AND same voltage.

My questions are:
1) For the specific purpose of a speedrun vehicle, what are the advantages/disadvantages of each configuration?
2) For the specific purpose of a speedrun vehicle, is one configuration truly better than the other...and why?

We run parallel solely to combat voltage sag. Although weight is bad it is not as harmful as in boats. The reduced voltage sag and improved amperage delivery will always outperform a single series setup. With that said not all batteries are the same. I am sure you have already experienced some of this with your boat racing....


I would also like to say again that someone new to speed running might want to avoid 6s or 8s setups.

I have learned much more by working my way up in voltage:

• With the 1/7 scale I hit 99mph on 2s
• Then went to 3s and have a current world record at 126 mph with the VTE2. (CNHL G+ 6Ah packs in parallel)
• Next I will be going to 4s and fully expect to be up around 150.

The point is if you are new.... 6s is 150+ capable and just that much easier to crash. I highly recommend starting with 4s that later could be used for 8s runs.

Working your way up in speed allows you to learn gearing needs, reading logs, tuning the car for your road and learn how to control the car as it goes higher and higher speeds. Just like in boats there is many many many little details that go into it and crashes happen.

 

[Panther6834]

We run parallel solely to combat voltage sag. Although weight is bad it is not as harmful as in boats. The reduced voltage sag and improved amperage delivery will always outperform a single series setup. With that said not all batteries are the same. I am sure you have already experienced some of this with your boat racing....


I would also like to say again that someone new to speed running might want to avoid 6s or 8s setups.

I have learned much more by working my way up in voltage:

• With the 1/7 scale I hit 99mph on 2s
• Then went to 3s and have a current world record at 126 mph with the VTE2. (CNHL G+ 6Ah packs in parallel)
• Next I will be going to 4s and fully expect to be up around 150.

The point is if you are new.... 6s is 150+ capable and just that much easier to crash. I highly recommend starting with 4s that later could be used for 8s runs.

Working your way up in speed allows you to learn gearing needs, reading logs, tuning the car for your road and learn how to control the car as it goes higher and higher speeds. Just like in boats there is many many many little details that go into it and crashes happen.

Good thing I already have quite a few high-quality/high-'C- 4S & 6S packs...can hold off investing in 8S packs, as well as an 8S-capable charger.

 

[LibertyMKiii]

Good thing I already have quite a few high-quality/high-'C- 4S & 6S packs...can hold off investing in 8S packs, as well as an 8S-capable charger.

I have never seen a quality 8s pack for speed run use yet. People just run 4x 4s packs

 

[Notoriousone]

Paralell will give less voltage sag than series, and I see more of the real fast guys, guys doing over 170 mph, running 8s parallel systems as opposed to wired in series.. Question, if perfect technology batteries that had no voltage sag existed, would it then make sense to run those in Series instead of Parallel?

 

[LibertyMKiii]

Paralell will give less voltage sag than series, and I see more of the real fast guys, guys doing over 170 mph, running 8s parallel systems as opposed to wired in series.. Question, if perfect technology batteries that had no voltage sag existed, would it then make sense to run those in Series instead of Parallel?

Absolutely unless you needed the weight to avoid blow overs.

 

[Panther6834]

I have never seen a quality 8s pack for speed run use yet. People just run 4x 4s packs

Sounds like a combination of parallel AND series. Two 4S in series to equal 8S, and two more 4S in series to equal 8S, followed by each 'series' running parallel to double the capacity. Only problem is, that configuration won't fit inside the Limitless.

Two 4S parallel still equals 4S. Guess I'm just not "getting it". As 8S packs are far & few between, I'm not understanding how "8S parallel" to a single ESC/motor is possible.

 

[Diem Turner]

We run parallel solely to combat voltage sag. Although weight is bad it is not as harmful as in boats. The reduced voltage sag and improved amperage delivery will always outperform a single series setup. With that said not all batteries are the same. I am sure you have already experienced some of this with your boat racing....


I would also like to say again that someone new to speed running might want to avoid 6s or 8s setups.

I have learned much more by working my way up in voltage:

• With the 1/7 scale I hit 99mph on 2s
• Then went to 3s and have a current world record at 126 mph with the VTE2. (CNHL G+ 6Ah packs in parallel)
• Next I will be going to 4s and fully expect to be up around 150.

The point is if you are new.... 6s is 150+ capable and just that much easier to crash. I highly recommend starting with 4s that later could be used for 8s runs.

Working your way up in speed allows you to learn gearing needs, reading logs, tuning the car for your road and learn how to control the car as it goes higher and higher speeds. Just like in boats there is many many many little details that go into it and crashes happen.

+1
I can only confirm...moving to 3S from 6S really pushed my understanding of speed running and what is involved instead of the old "more power" adage.

Sounds like a combination of parallel AND series. Two 4S in series to equal 8S, and two more 4S in series to equal 8S, followed by each 'series' running parallel to double the capacity. Only problem is, that configuration won't fit inside the Limitless.

Two 4S parallel still equals 4S. Guess I'm just not "getting it". As 8S packs are far & few between, I'm not understanding how "8S parallel" to a single ESC/motor is possible.

You'd need to wire up two 4S packs in series (times two) which you then connect in parallel for 8S parallel.

You're correct, 4x4S won't fit in a Limitless. The chassis is too narrow and the body too low slung. But it will in a GT conversion.

 

[rotauq]

Sounds like a combination of parallel AND series. Two 4S in series to equal 8S, and two more 4S in series to equal 8S, followed by each 'series' running parallel to double the capacity. Only problem is, that configuration won't fit inside the Limitless.

Two 4S parallel still equals 4S. Guess I'm just not "getting it". As 8S packs are far & few between, I'm not understanding how "8S parallel" to a single ESC/motor is possible.

8S parallel would need 4 batteries. 2x2 in parallel, ran in series.

I've also tried 4 in parallel, but that's where they get more busy charging each other rather then feeding the motor.

Fun facts. When we talk about batteries and their voltage, we talk about the amount of cells in Series
Especially bigger batteries that already have cells in parallel, the battery spec will say 4S2P
edit: Like Diem's picture above

 

[Diem Turner]

8S parallel would need 4 batteries. 2x2 in parallel, ran in series.

I've also tried 4 in parallel, but that's where they get more busy charging each other rather then feeding the motor.

Fun facts. When we talk about batteries and their voltage, we talk about the amount of cells in Series
Especially bigger batteries that already have cells in parallel, the battery spec will say 4S2P
edit: Like Diem's picture above
View attachment 246276

Or 2x2 in series, ran in parallel Shouldn't make a difference performance wise but what you're suggesting might be easier to wire up now that I think about it. I think you might have just saved me some time. I didn't even think about that. Thx

 

[Panther6834]

You're correct, 4x4S won't fit in a Limitless. The chassis is too narrow and the body too low slung. But it will in a GT conversion.

Great...except that I'm not yet (and won't be for a while) running a GT chassis. So, while I can run 4S & 6S parallel, once I reach 8S, the only 'option' will be two 4S in series.

As for those who "claim" to be running 8S parallel, I take it that the "reality" is they're running two 4S in series, the other two 4S in series, and those two 'series' in parallel...so, they're still running packs in series. At least I'll be able to run 4S & 6S in TRUE parallel.

Or 2x2 in series, ran in parallel Shouldn't make a difference performance wise but what you're suggesting might be easier to wire up now that I think about it. I think you might have just saved me some time. I didn't even think about that. Thx

That's true. Running two sets of parallel in series vs two sets of in series parallel...the two sets in series parallel would not only be easier to wire, but also would require less physical wire.

 

[Diem Turner]

Great...except that I'm not yet (and won't be for a while) running a GT chassis. So, while I can run 4S & 6S parallel, once I reach 8S, the only 'option' will be two 4S in series.

As for those who "claim" to be running 8S parallel, I take it that the "reality" is they're running two 4S in series, the other two 4S in series, and those two 'series' in parallel...so, they're still running packs in series. At least I'll be able to run 4S & 6S in TRUE parallel.

Correct.

I don't think it's them claiming to be running 8S parallel. It is 8S parallel. If you wanted to nitpick you could say it's a hybrid setup, but at the end of the day, it's 8S parallel. Personally, I don't see running 2x4S in parallel as "untrue" parallel. Two 4S packs in series is "seen" as one 8S pack by the ESC so it's the same thing as a single 8S pack in my view. Electrically it's two 33.6V battery blocks in parallel...whether that's in one pack or separated into two is more of a distinction without a difference. You could take an 8S pack apart and fold it out into two halves, but it doesn't stop being an 8S battery if you do. If I run the car as pictured above, that's 8S parallel. But that's just me. If it's something else to you, that's fine.

 

[rotauq]

Great...except that I'm not yet (and won't be for a while) running a GT chassis. So, while I can run 4S & 6S parallel, once I reach 8S, the only 'option' will be two 4S in series.

As for those who "claim" to be running 8S parallel, I take it that the "reality" is they're running two 4S in series, the other two 4S in series, and those two 'series' in parallel...so, they're still running packs in series. At least I'll be able to run 4S & 6S in TRUE parallel.

That's true. Running two sets of parallel in series vs two sets of in series parallel...the two sets in series parallel would not only be easier to wire, but also would require less physical wire.

8S is 8x 1 cell of 4.2V in series. It doesn't matter if they are soldered directly or if there are cables in between.
As for parallel it could be each individual cell, full amount of cells or some random in between.

You would call for example running 6 x S2 batteries as 2x2x2 in parallel (regardless how its wired) not TRUE parallel?

 

[Panther6834]

Correct.

I don't think it's them claiming to be running 8S parallel. It is 8S parallel. If you wanted to nitpick you could say it's a hybrid setup, but at the end of the day, it's 8S parallel. Personally, I don't see running 2x4S in parallel as "untrue" parallel. Two 4S packs in series is "seen" as one 8S pack by the ESC so it's the same thing as a single 8S pack in my view. Electrically it's two 33.6V battery blocks in parallel...whether that's in one pack or separated into two is more of a distinction without a difference. You could take an 8S pack apart and fold it out into two halves, but it doesn't stop being an 8S battery if you do. If I run the car as pictured above, that's 8S parallel. But that's just me. If it's something else to you, that's fine.

I guess, it all depends on how the entire wiring is done...especially considering you mentioned how the ESC "sees" the packs. Two sets of 2 in series, and then those two series to the ESC in parallel, it could be said the ESC "sees" the packs as 'parallel'. But, wired the other way...two sets of 2 parallel, and then those two parallel to the ESC in series...it could be said the ESC "sees" the packs as 'in series'. Both configurations involved both methods ("hybrid", as you put it...which I like).

Obviously, both configurations only apply to a GT...but, what I'm now curious about is whether one configuration causes less voltage sag compared to the other. I know (with the standard Limitless chassis) I'm just starting down the 2-pack road...but, this 4-pack matter raises a very interesting question:

As has already been said, when dealing with only two packs (total), 'parallel' causes less voltage sag (compared to 'series')...but, what about when four packs are used in these "hybrid" configuration? Is the voltage sag the same under both wiring configurations? Or, does one "hybrid" configuration causes less voltage sag...and, if so, which?

 

[Diem Turner]

I guess, it all depends on how the entire wiring is done...especially considering you mentioned how the ESC "sees" the packs. Two sets of 2 in series, and then those two series to the ESC in parallel, it could be said the ESC "sees" the packs as 'parallel'. But, wired the other way...two sets of 2 parallel, and then those two parallel to the ESC in series...it could be said the ESC "sees" the packs as 'in series'. Both configurations involved both methods ("hybrid", as you put it...which I like).

Obviously, both configurations only apply to a GT...but, what I'm now curious about is whether one configuration causes less voltage sag compared to the other. I know (with the standard Limitless chassis) I'm just starting down the 2-pack road...but, this 4-pack matter raises a very interesting question:

As has already been said, when dealing with only two packs (total), 'parallel' causes less voltage sag (compared to 'series')...but, what about when four packs are used in these "hybrid" configuration? Is the voltage sag the same under both wiring configurations? Or, does one "hybrid" configuration causes less voltage sag...and, if so, which?

I don't think the ESC "sees" series and parallel. All the ESC "sees" is voltage. How the batteries deliver what the motor is asking of them is where the two systems differ. We, as outside observers, see and know where things are connected in parallel and series. The ESC is just the mediator between consumer and supply side. That's the way I see it anyways. That's not etched in stone, that's just my working understanding of the system.

My gut instinct is that it should be the same as you'll have the same voltage and capacity on both sides. Just speculative on my part but, to my mind, it stands to reason.

As for converting your Limitless to GT format, Raz made it a lot easier and cheaper with his CF battery trays. Just add a GT body...done. @Notoriousone just posted this thread.
https://www.arrmaforum.com/threads/raz-pp-side-skirts-battery-trays.55987/

 

[Panther6834]

I don't think the ESC "sees" series and parallel. All the ESC "sees" is voltage. How the batteries deliver what the motor is asking of them is where the two systems differ. We, as outside observers, see and know where things are connected in parallel and series. The ESC is just the mediator between consumer and supply side. That's the way I see it anyways. That's not etched in stone, that's just my working understanding of the system.

My gut instinct is that it should be the same as you'll have the same voltage and capacity on both sides. Just speculative on my part but, to my mind, it stands to reason.

As for converting your Limitless to GT format, Raz made it a lot easier and cheaper with his CF battery trays. Just add a GT body...done. @Notoriousone just posted this thread.
https://www.arrmaforum.com/threads/raz-pp-side-skirts-battery-trays.55987/

I didn't mean 'see' literally...it was meant more 'figuratively'. The primary objective/point was related to to voltage sag of each 4-pack configuration. Either way, I think we each get the point, and ideas, that the other was trying to point out...we are, essentially, "on the same page".

As for the CF trays from Raz, yeah, I saw those. I had already figured, when ready to go with a GT body, that would be my 'intermediate' plan (before a full CF GT chassis).

 

[Diem Turner]

lol...yeah I know, that's why I initially put see in quotes But yeah, I'm pretty sure we're on the same page

Yeah, they appear to be the perfect stepping stone to a full GT build as they mitigate the upward flared edges of the stock chassis. Should be perfect

 

[Panther6834]

lol...yeah I know, that's why I initially put see in quotes But yeah, I'm pretty sure we're on the same page

Yeah, they appear to be the perfect stepping stone to a full GT build as they mitigate the upward flared edges of the stock chassis. Should be perfect

Even though I won't be using them for a while, once they're back in-stock, I'll probably get them ordered. I have an old saying, "Better to have and not need, than to need and not have.". Tho, truth be told, I will eventually need them (I have a Slash 4x4 roller that I've had for a few years, and still haven't decided what, exactly, to do with it).