I haven’t tried this.

[Cheez ‘n’ Quackers]

Is this a good idea/efficient? I’m planning on using two shorty packs in my next build. I have several rigs that have the two batteries option and they all use Y adapters. Sorry if it’s a silly question but I’ve never considered this.

 

[bill_delong]

Yes that is a very popular setup among many racers in my area running TLR, AE and XRay

Only catch is I recommend reading the following article for understanding the extra maintenance involved and precautions:
https://www.smc-racing.net/index.php?route=product/category&path=166

 

[Cheez ‘n’ Quackers]

Yes that is a very popular setup among many racers in my area running TLR, AE and XRay

Only catch is I recommend reading the following article for understanding the extra maintenance involved and precautions:
https://www.smc-racing.net/index.php?route=product/category&path=166

Thanks Bill.

 

[KnowAir]

Yes that is a very popular setup among many racers in my area running TLR, AE and XRay

Only catch is I recommend reading the following article for understanding the extra maintenance involved and precautions:
https://www.smc-racing.net/index.php?route=product/category&path=166

The above link is an interesting read, thanks for sharing.
I am curious as to how there would be any significant difference between using 2x3s vs 1x6s? In a 6s pack, the cells are in fact wired in series, which means the resistance increases with each cell as current flows through..in this case, the order of the actual cells in the pack never change. Seems even more susceptible to problems than using 2x3s where the packs can be reversed each cycle?
Interesting..

 

[Cheez ‘n’ Quackers]

The above link is an interesting read, thanks for sharing.
I am curious as to how there would be any significant difference between using 2x3s vs 1x6s? In a 6s pack, the cells are in fact wired in series, which means the resistance increases with each cell as current flows through..in this case, the order of the actual cells in the pack never change. Seems even more susceptible to problems than using 2x3s where the packs can be reversed each cycle?
Interesting..

It’s a little confusing. What you’re saying seems to make sense.

 

[KnowAir]

Agreed. I'm no guru.. hell, I'm an idiot in some circles,LOL.
I'm just applying the theory that anytime we use batteries wired in series to increase voltage. As we go from one cell to the next, resistance increases right? Nature of the beast, ohms law..
Seems like a benefit to use multiple packs? I mean, we can in fact rotate the packs to "balance" the packs each cycle whereas with a brick pack, the order of the cells remains constant, so the same cells are working harder than the next one in every cycle.
Now, the fact that we need additional wire and connectors to utilize multiple packs has got to have some influence on the matter I'd guess. How much? I'm not sure.
I choose multiple packs for versatility, but I'm also not a racer. So all out performance isn't really my priority.

 

[nino]

I still think that SMC blurb (that originated the claim there's a difference in load on different cells in series) is plain wrong.

 

[bill_delong]

The above link is an interesting read, thanks for sharing.
I am curious as to how there would be any significant difference between using 2x3s vs 1x6s? In a 6s pack, the cells are in fact wired in series, which means the resistance increases with each cell as current flows through..in this case, the order of the actual cells in the pack never change. Seems even more susceptible to problems than using 2x3s where the packs can be reversed each cycle?
Interesting..

The best way to validate the SMC article is to use a temp gun.

1) Measure temp on a 1x6S pack which will yield the lowest temp reading proving that there is lower IR overall.

2) Measure temps among 2x3S packs where one pack (typically the true negative) will be significantly hotter due to the increased IR from the pig tail jumper between the packs where the pack on the positive side should be comparable in temps to the 1x6S pack measured above.

The net effect of packs in series will cause faster degradation of longevity regardless if you rotate the packs or not.

I have seen some saddle pack designs with the jumper wire being extremely short and these designs will not be nearly as bad as those with longer wires between the packs, however the temp readings will prove SMC knows what they are talking about regardless of jumper length.

I have already performed my temp tests long before the SMC article was published so I already knew running packs in series was causing premature battery failures for me but I had no scientific reasoning why until SMC explained what was happening.

Anyone who claims SMC is wrong has clearly not used a temp gun to validate their findings, simple as that.

 

[KnowAir]

The best way to validate the SMC article is to use a temp gun.

1) Measure temp on a 1x6S pack which will yield the lowest temp reading proving that there is lower IR overall.

2) Measure temps among 2x3S packs where one pack (typically the true negative) will be significantly hotter due to the increased IR from the pig tail jumper between the packs where the pack on the positive side should be comparable in temps to the 1x6S pack measured above.

The net effect of packs in series will cause faster degradation of longevity regardless if you rotate the packs or not.

I have seen some saddle pack designs with the jumper wire being extremely short and these designs will not be nearly as bad as those with longer wires between the packs, however the temp readings will prove SMC knows what they are talking about regardless of jumper length.

I have already performed my temp tests long before the SMC article was published so I already knew running packs in series was causing premature battery failures for me but I had no scientific reasoning why until SMC explained what was happening.

Anyone who claims SMC is wrong has clearly not used a temp gun to validate their findings, simple as that.

I'm not disagreeing, trying to understand it. So, the resistance of the jumper is the actual culprit it sounds like? I won't be changing anything in my regimen but, good to know.
I've been using the 2xX setup for several years, and satisfied with the battery life I'm getting.
However, I do have several 2,3 and 4s packs with bad cells. Sounds like some research is in order. Keep an ear open for any lipo fires in upstate NY,LOL..

 

[bill_delong]

...So, the resistance of the jumper is the actual culprit it sounds like? ...

Correct as explained by SMC:

This is due to the flow of current, the current from one pack must flow ‘through’ the second pack meaning that the current sees virtually double the resistance of the first pack.

When you "double" the resistance, it's fairly nominal, which is why so many people are perfectly satisfied with saddle packs, but it doesn't mean that resistance isn't there, anyone can verify this with a temp gun to confirm both packs come off at different temps. If you're concerned that the hotter pack may be due to motor placement, then swap the wiring around to force the hotter pack to be farthest from the motor

 

[KnowAir]

SMC said:
This is due to the flow of current, the current from one pack must flow ‘through’ the second pack meaning that the current sees virtually double the resistance of the first pack.

But isn't this already going on in any battery pack that consists of more than one cell? Whether we're talking about a 2s or 6s, the current must flow through each cell, which are connected in series. Cell number 1 will always see more resistance than the next..and so on?
I didn't see it worded by SMC as though it is the jumper used between 2 seperate packs that's the cause of increased resistance, but believe it to be true.
At the end of the day, the main reason I've stuck with the 2 pack setup is versatility. I simply don't have the finances to buy each cell count I use..I'm not sure it even makes financial sense, I can buy 2x2s 5.2Ah batteries for far less than one 4s of equal specs. If I sacrifice some longevity in doing so..

 

[bill_delong]

SMC is implying the jumper wire doubles the resistance when they say the flow goes from one pack to the next.

You bring an excellent point that 2S packs can be more economical so one could argue that it's a wash if less expensive 2S packs need to be replaced sooner, but if they are cheap enough to offset the difference in longevity then it could be a moot point.

I run Zeee brand 4S packs which go for around $57 ea, but note these are 120C packs:
https://www.amazon.com/gp/product/B09CMHWHLL

I found some $17 2S packs here but they're only 50C which is a double whammy for shortened lifespan
https://www.amazon.com/Zeee-5200mAh-Battery-Truggy-Airplane/dp/B06ZYRCPS3

 

[tudordewolf]

I still think that SMC blurb (that originated the claim there's a difference in load on different cells in series) is plain wrong.

I agree, whether that phenomenon exists or not, the explanation they give is nonsensical at best, misleading at worst. It was also discussed in this thread earlier this year.

Resistance doesn't "add up" in subsequent cells like that; each cell has no idea where it is within the stack in terms of how they experience load.

If anything it just goes to show that even reputable hobby-oriented battery companies are first and foremost in the business of marketing, not engineering.

 

[bill_delong]

The only people wrong are those who refuse to take temp readings, they choose to be blind of scientific facts proven by SMC, simple as that

 

[nino]

I immensely appreciate your knowledge and experience in RC and even more the fact that you've been sharing it for years. But like you said somewhere, Bill, you're not an engineer nor a scientist.

Anecdotal evidence is not "scientific fact" and a short article by a battery distributor is not "proof" (or the other way round). I just want to see a single mention of cell position in a series connection having an effect on anything. Something actually backed with science or a formula or something. I'm not even saying it's wrong, just that I'm sceptical of the claim!

 

[bill_delong]

• Question: Does running 2x2S cause batteries to degrade faster than 1x4S?
• Research Topic Area: Locate documented research paper written by reputable source who is in fact a battery manufacturer who has done extensive testing on dozens if not hundreds of battery pack configurations and provides details on how to minimize the damage caused by running packs in series
• Hypothesis: After previously experiencing problems running packs in series long before the SMC article was published, I knew there was something fundamentally wrong with the concept so I stayed far away from this practice to avoid the same problems published in the article
• Test with experiment: While not explained in the SMC article, I had discovered that the pack on the true negative side would tend to run hotter with the variable being time and the longer you run the batteries down to LVC the true negative pack would get exponentially hotter. VERY IMPORTANT... HEAT is the #1 killer for degradation of batteries, 1x4S will tend to run lower battery temps proving they will last longer than 2x2S
• Analyze data: Observations of one pack consistently running hotter is undeniable proof that pack is experiencing higher resistance than the other pack as cautioned by the published SMC article.
• Report Conclusions: SMC article is correct

*** side note... I am not affiliated with SMC and while I used to be a customer of SMC, I have not purchased any of their batteries in many years. They provide a quality product and I have high confidence in the brand, though I am currently a sponsored driver for Trinity where I have higher confidence in Trinity quality so I am recommending Trinity batteries to anyone who asks me which brand of battery is the best.

 

[Jerold]

I'm not disagreeing, trying to understand it. So, the resistance of the jumper is the actual culprit it sounds like? I won't be changing anything in my regimen but, good to know.
I've been using the 2xX setup for several years, and satisfied with the battery life I'm getting.
However, I do have several 2,3 and 4s packs with bad cells. Sounds like some research is in order. Keep an ear open for any lipo fires in upstate NY,LOL..

The bad cell are a problem in any configuration. They are basically infinite resistance.

It's series vs parallel resistance aka Ohm's Law. This a simplified model. The IR is not actually a constant. It's a function of a lot of variables, but for discussion purposes we can just pick a number an run with it.

If you have two batteries in series, the resistance (IR) of both packs added together is your total IR. But you will double the voltage. When they are parallel, resistance is cut by approx 1/2 with the same voltage, but provides more current because of two source and lower internal resistance. You also get to double the capacity.

Two 3S batteries in series, you add the IR from each cell and total voltage. The mAh stays the same.

For each battery

When they are in parallel you have two batteries with 15 mΩ (IR) each battery and 10,000 mah. The total Voltage is the same.

If you have a battery with a bad cell it's like an open circuit (no connection) or infinite resistance.

If R=∞ then I is infinitely small. Meaning you an have voltage with no current.

 

[Jerold]

I still think that SMC blurb (that originated the claim there's a difference in load on different cells in series) is plain wrong.

I believe they are correct or at least he math says that. They are saying that cells with different IRs will discharge at a different rate.

The current draw for each node through a series circuit is constant, meaning that it's the same for both. When they are in parallel the voltage drop for each node is constant.

Again a very simplified model. I think we all agree that if I have two 1S batteries with different IRs, they will perform differently. One would expect the battery with a lower IR to have more current providing capability. Now if I put them in series, why would I expect the lower IR battery to hold back on current?

It won't and I it can't with out a BMS on each cell.

So here's the problem, voltage is NOT constant which makes this model a bit wonky. Also we are talking about charge not current. Current is the change in charge during a time period. As I pull charge from the battery the voltage drops. Since everything is changing it's not linear and the models aren't accurate. The concept is still true but the exact math is not right.

The point of the article is if you want maximum performance, you want everything to be identical and predictable. Including batteries cells. One point they make is the LVC is the average of all the battery cells. If one cells voltage drops more than the others, you can still average 3.2V and have a bad cell in the pack.

If you set your LVC for 3.2, you could have one cell below 3.0V and still have an average of 3.2V.

In an ideal world with infinite money, this is the best practice. If you are racing competitively or need absolute performance this is a must. For the rest of us slouches, it's would be nice.

​

Think of it as tires on a car. If I replace one tire with 50% wear; the new tire will be larger and have less RPM than the the other three smaller tires. This means your car is not at it's maximum performance, because one wheel is spinning slower than the other three. It "could" cause darting, weird braking or acceleration, stress the drive train, etc. You probably won't notice it much at all and after a week it's a non-issue.

In an ideal world you would keep all of your tires exactly the same diameter. Since we are not made of money, we don't need every last drop of performance for going to work (i.e. it's not a Formula 1 car) it doesn't work that way in the real world.

​

​

​

 

[Cheez ‘n’ Quackers]

Guess I opened it….

 

[nino]

Jerold, I know all of that. I studied electronics for 4 years. Now a scientific article OR ANY OTHER THING IN THE WORLD that mentions what SMC claims would be nice.