Question: Series vs Parallel

[Panther6834]

We've all seen questions having to do with a single large-capacity LiPo vs two smaller-capacity LiPo packs in parallel, with the same number of cells. We've also seen questions having to do with a single LiPo vs two LiPo packs in series of the same capacity, but half the cell count. This is a question of similar nature...but, at the same time, completely different.

I have the TFL Jet Boat, which comes with a single battery tray, centered directly in front of the motor. The ESC & servo are on the port side, while the Rx is on the starboard side. This causes the Jet Boat to be somewhat unbalanced, with greater weight on the port side (as most probably know, the TFL Jet Boat is not "self righting"). As such, I'd like to 'correct' the balance problem...and, I have an idea on how to do so.

My idea involves moving the ESC to what is currently the battery tray, and then installing two new (and smaller) battery trays, one on each side of the ESC (the Rx would remain on the starboard side, as its weight is almost equal to the weight of the servo on the port side). Although not a perfect 50-50 left/right balance, it would be about as close as anyone could ever get without adding weights. So, what's my question?

In switching from a single LiPo, to two LiPo packs, I have two options. For the purpose of the following examples, let's assume I want a total capacity of 6000mAh. On one hand, I could use two 2S 6000mAh packs in series. On the other hand, I could use two 4S 3000mAh packs in parallel. Obviously, both equate to 4S 6000mAh...but, what I'd like to know is, is one solution better then the other? For example, would one run cooler than the other? Does one provide greater "punch" over the other? Does one less battery sag when accelerating from a standstill? Does one provide less ripple? Or...should I leave it as it is, with a single LiPo centered in front of the motor (even though it causes the boat to be unbalanced)?

In answering, it might also help to know that I'll be replacing the stock 120A ESC with the OSE Raider 150A, and the stock 1620kv motor with a lower kv motor (probably in the 1300-1400kv range). Until now, I've always run the stock electronics on 3S, thus why I'll be going with a lower kv motor. When it comes to something like hydro, where low COG makes a huge difference, two 2S in series is the better way to go...but, with a mono like the TFL Jet Boat, I honestly don't know, thus the reason I'm asking for advise.


~ More peace, love, laughter, & kindness would make the world a MUCH better place

[Bande1]

i cant imagine there's a difference. I just grabbed a set of 2s 7200mah 100c packs off amazon for $25 shipped. I prefer wiring in series because I use 8mm bullets on my batteries and its easier to wire them with a short jumper than it is to deal with an obnoxious parallel Y cable.

think of it like this; the batteries cells are just being series wired inside the pack. when you hook 2 up externally its not really any different then the internal pack connections. is that making sense? its early as heck here. lol

lower CG in any boat is better. another reason 2s in series because of the versatility of configuration with smaller packs.

[ray schrauwen]

If your amp draw is low enough it doesn't make a big difference.

[jkflow]

Agreed, with low enough current, and it doesn't really make a difference. I'd always go for 4S, as I have nothing in the 2S range. As long as you keep brand, voltage and capacity the same, you can go series or parallel as needed.

In general, series will always be less efficient as you have the internal resistance adding up, therefore your max current will also be 'limited'.

[lohring]

The ultimate in series/parallel connections was Mike Bontoft's 98 mph electric hydro. It had 42 6S 5000 mah packs in 6 boxes. Each box had 7 packs in parallel with the six boxes in series. That gives 133 volts nominal with 700 amps at 20C. In reality we pulled a peak of 840 amps at around 135 volts. We needed to stay under 144 volts to meet the rules.

Lohring Miller

UIM runs.jpgCharging During Testing.jpgMike Checks the Charge.jpg

[paulejr]

Or, one could just stick on some wheel weight/s to make it sit right. As for the battery question, hello Pandoras' box.......

[Panther6834]

The ultimate in series/parallel connections was Mike Bontoft's 98 mph electric hydro.

Not trying to be sarcastic...but, how, exactly, does that have anything to do with my question? I'm not trying to power the Empire State Building with LiPo batteries...just a simple 4S jet boat.

Or, one could just stick on some wheel weight/s to make it sit right. As for the battery question, hello Pandoras' box.......

In RC, almost everything can be a 'Pandora's Box'...especially when someone asks the "What connector should I use?" question...lol


~ More peace, love, laughter, & kindness would make the world a MUCH better place

[Panther6834]

Deleted - dbl post

[Peter A]

It really doesn't matter which way you go with this. Perhaps more relevant would be pack sizes and weight as to what fits best. The one advantage of series over parallel is less wiring and connectors with a series set up. Balance that with will the packs you choose be useable in other applications also?

[Panther6834]

It really doesn't matter which way you go with this. Perhaps more relevant would be pack sizes and weight as to what fits best. The one advantage of series over parallel is less wiring and connectors with a series set up. Balance that with will the packs you choose be useable in other applications also?

I'm guessing "Balance that with" was possibly meant as the beginning of one sentence, and "will the packs you choose be useable in other applications also" was meant as a separate sentence. While I can't make heads or tails of what that first sentence would have been, I can try to answer the second. Since I'm probably be sticking with XT60 connectors on the Jet Boat, the answer would be, "Yes, they could be used in other vehicles/vessels."

But, that's not guaranteed. Right now, not counting my helicopter & Mini-B (both of which use EC2), a variety of connects are in use: XT60, Deans, EC3/IC3, EC5/IC5, Castle, 7mm bullet, 4mm bullet, 5mm bullet. There might be others, but at I'm currently out-of-state on a 3-day job, I can't check, nor can I remember. I'm just about to start the process of 'minimalizing' the number of connectors used, for which the 'plan' is to only use XT60 & QS8 - smaller and/or less powerful vehicles/vessels getting XT60 & larger and/or more powerful vehicles/vessels getting QS8. Land vehicles using XT60 will consist of 2S, 3S & 4S, while those using QS8 will consist of 4S, 6S & 8S (6S & 8S using two 3S/4S). As for boats, the Jet Boat, Recoil 17, Drifter Micro & Tenshock Mini Eco will all use XT60, while all others (SonicWake, Skater X2, Pursuit CF, Shockwave & hydro) will use QS8...tho, in regards to the Shockwave, that could end up with XT60.

The 'point' is, I've gotten tired of having to deal with so many different connectors, and trying to remember which vehicles/vessels each is "compatible" with, this the decision to 'limit' the connectors to just those two (ok, three, is you count the EC2). Not only does it mean easier management of batteries, but also easier in charging (my charging case has XT60 & 5mm bullet, plus I recently got two custom-made QS8 charging leads with XT60 connectors for the charger end, and 6S balance connectors w/ 3S & 4s notches).

I'm thinking, before deciding, the LiPo dimensions & weight (as mentioned by Bande1, ie. lower COG) is what I need to consider most. I have a LOT of LiPos, and (since moving) I REALLY need to go through ALL of them...determine which ones might not linger be good, get dimensions & weights, etc. I should have the next two days off (I get back to Vegas tonight), which should give me time to get through most of them. Still undecided whether to go series or parallel for the Jet Boat...but, once I have a better idea of what's in my LiPo collection, that might help make the decision for me.


~ More peace, love, laughter, & kindness would make the world a MUCH better place

[Peter A]

Perhaps a comma would have been clearer to ya. Balance that with, will the..... What I meant was in considering what batteries to buy, balance the decision with is there any further application and use for them. Are you going to get a separate set of batteries just for this boat, or ones that are useable in multiple models. Seems like you actually understood the point anyway.

[Bande1]

8mm bullets on everything. even if its overkill. on boats they are not.

[Panther6834]

8mm bullets on everything. even if its overkill. on boats they are not.

No...not a good way to go. In certain vehicles, such a on-road & off-road race vehicles, where even a few extra grams can be bad, your 'suggestion' would be the difference between winning, and losing. Besides, let me set you put 8mm connectors in a Mini-B, SCX24, or Blade Nano S3.


~ More peace, love, laughter, & kindness would make the world a MUCH better place

[Bande1]

No...not a good way to go. In certain vehicles, such a on-road & off-road race vehicles, where even a few extra grams can be bad, your 'suggestion' would be the difference between winning, and losing. Besides, let me set you put 8mm connectors in a Mini-B, SCX24, or Blade Nano S3.


~ More peace, love, laughter, & kindness would make the world a MUCH better place

the higher resistance from smaller connectors could also be the difference between winning and losing.

[Panther6834]

the higher resistance from smaller connectors could also be the difference between winning and losing.

You've, obviously, never raced. Show me any 1/10...or even 1/8...land RC with 8mm connectors that has won races. But, this is taking things COMPLETELY off-course from the question originally asked, so, it would be greatly appreciated if you refrained from continuing down that road to and bring things back to the asked topic.


~ More peace, love, laughter, & kindness would make the world a MUCH better place

[lohring]

I race at the NAMBA National Championships. I, and many others run 8 mm connectors on our batteries these days. The new Castle ESCs have 6.5 mm motor connectors, and they may be fine for P limited. I ran 8 mm connectors on my 1/8 scale and on the full size electric hydro mentioned above. That hydro was built in 2008.The current draw from the 1/8 scale two lap record run is below. That boat won the 2012 NAMBA Electric Nationals with 4 4S packs connected in series and parallel.

Lohring Miller

[Panther6834]

I race at the NAMBA National Championships. I, and many others run 8 mm connectors on our batteries these days.

Again, please stop with ANY responses having to do with connector size...that had NOTHING to do work the question originally asked. I am trying to keep this thread on-point to the question asked, and not have it going in other 'directions'. The only reason I even mentioned connectors was because someone else asked if the batteries used in the Jet Boat would be used in any other vehicles/vessels. And, as for me mentioning 1/8, that, as with 1/10, was in reference to off-road vehicles, not boats. The question is, specifically, about parallel vs series connection in boats (or land vehicles, as it could also apply to them) of this size/power.


~ More peace, love, laughter, & kindness would make the world a MUCH better place

[Bande1]

8mm connectors

[lohring]

I'm just trying to answer both questions. I have a lot of experience with series and parallel connections. The expected current draw has a lot to do with the connector size. If you are using connectors sized for the expected current, you can connect the batteries any way you need. It won't matter. Below is a 6S setup with batteries in both series and parallel. That was what would fit.

After all single cells are assembled into packs using internal connectors. These connectors are surprisingly thin. I have burned through them at too high current draws.

Lohring Miller

P1010002.jpg

[Bande1]

its excruciatingly easy to pull mega currents in a boat.

[Panther6834]

its excruciatingly easy to pull mega currents in a boat.

True, true...especially in larger/faster boats with high kv motors and/or high voltage setups. My first SonicWake was originally set for series (the second, which I'm just starting to build, started life as just a hull)...but, the person who built the hydro I bought set it up for parallel. I can only assume that, in regards to the previous he & his wife preferred, the 5000mAh 4S packs must have been shorter than the 10,000mAh 2S packs (and, before anyone says he didn't know what he was doing, understand that he was one of the top racers in the country, as well as a former IMPBA Officer).

Anyway...getting things back on track (yes, even I can get myself off-track at times)...I'm thinking, the best 'solution' (at least, for the Jet Boat) is to compare the heights & weights of the 2S & 4S packs I'd consider using, to see which is shorter and/or lighter, so as to 'assist' in obtaining the lowest COG.

Case closed?


~ More peace, love, laughter, & kindness would make the world a MUCH better place

[Bande1]

I mean 10mm is even better.