Connectors when running batteries in series?

[MasterOfPupets]

So, some background. I currently run my car on 3s with several batteries that I switched a few years back to all use EC5 Connectors (upgraded from deans and adapters). My son's car runs on 2s (or nimh) and all his batteries run EC3 connectors (what came with the truck and batteries.). Well, I'm looking at possibly running some 4S in the (nearish) future but don't want to invest in new batteries right now. I know I can run 2 2s batteries in series to equal 4s, however I'm not sure how the amperage stacks up throughout the system when using multiples. I know the EC3 aren't recommended for 4S, but would I be ok running 2 2s using a series adapter with the current connectors (2 EC3 in series to one EC5 output to the ESC,) or should I go through and change all the 2S (and my son's car) to EC5?

 

[bill_delong]

don't want to invest in new batteries right now.

I hate to be the bearer of bad news but this is a really bad idea... trust me,, been there, done that and I wasted a lot of money destroying a bunch of my packs when LiPo first came out and there wasn't any information sharing the do's and don'ts with series.

After I damaged 4 packs plus 1 brand new pack, I gave up running packs in series. Many years later SMC would publish the following artricle which confirmed all the woe's I was experiencing:
https://www.smc-racing.com/index.php?route=product/category&path=174_166

Long story short:

You MUST buy 2 brand new "identical" packs (from the same manufacturer and same manufactured date) as a "Matched Pair", label them so they remain a matched pair. It's imperative that you rotate each pack every cycle so they wear evenly... I found that the pack on the true negative would get the majority of the abuse and you can confirm this by taking temp readings after a long run where the pack on true negative side will be significantly hotter.

Many racers are running saddle packs with great success today, however there is more maintenance and care involved than I am willing to put that level of effort into right now.

So to answer the rest of your questions, yes it is fairly easy to make an adapter to run 2 packs in series, here's an adapter to make this simple, but use extreme caution:
https://www.amazon.com/BDHI-Connector-Battery-Adapter-Flite/dp/B095LY1GR2

 

[MasterOfPupets]

I hate to be the bearer of bad news but this is a really bad idea... trust me,, been there, done that and I wasted a lot of money destroying a bunch of my packs when LiPo first came out and there wasn't any information sharing the do's and don'ts with series.

After I damaged 4 packs plus 1 brand new pack, I gave up running packs in series. Many years later SMC would publish the following artricle which confirmed all the woe's I was experiencing:
https://www.smc-racing.com/index.php?route=product/category&path=174_166

Long story short:

You MUST buy 2 brand new "identical" packs (from the same manufacturer and same manufactured date) as a "Matched Pair", label them so they remain a matched pair. It's imperative that you rotate each pack every cycle so they wear evenly... I found that the pack on the true negative would get the majority of the abuse and you can confirm this by taking temp readings after a long run where the pack on true negative side will be significantly hotter.

Many racers are running saddle packs with great success today, however there is more maintenance and care involved than I am willing to put that level of effort into right now.

So to answer the rest of your questions, yes it is fairly easy to make an adapter to run 2 packs in series, here's an adapter to make this simple, but use extreme caution:
https://www.amazon.com/BDHI-Connector-Battery-Adapter-Flite/dp/B095LY1GR2

I have at least 1 brand new "pair" of 2s that haven't been used.
Basically, I'm looking to test the new setup on 4s to see if the performance gains are worth it (or possibly "too much truck" for my current uses) without having useless batteries laying around should I decide to just stick with 3s. I was mainly worried about getting too much heat in the EC3 connectors. If I test it and like it/prefer it, I'll start spending the money on some new 4S packs

 

[bill_delong]

True brand new pair of packs that can be matched will be perfectly fine to run all the way down to LVC.

Any other mix matched packs of varying brands and capacity can also be used for short periods of time, roughly 5 min or less... you don't want to risk going anywhere near LVC with mix matched packs... so yes they are doable for testing purpose. In my case, 5 min quals never presented any problems, but 10 min mains would cause me to hit premature LVC only to discover the pack on true negative side had swollen to the appearance of a round sausage

EC3 will be fine for 4S in general, in fact the higher voltage will improve efficiency so you'll pull nominally more current.... I've ran 6S on Deans connectors which are far worse performing than EC3. The EC3 will create some unnecessary resistance where EC5 will be better, but EC3 will certainly "giterdone"... in contrast a "perfectionist" would not run EC3 on 4S unless it was for a small aircraft. I would occasionally have to replace my Deans connectors on 6S where they would get hot enough to melt the solder, that was the only connector I had available at the time so that's what I ran, ha!

 

[tudordewolf]

I found that the pack on the true negative would get the majority of the abuse and you can confirm this by taking temp readings after a long run where the pack on true negative side will be significantly hotter.

I'm super curious about that detail in particular. It defies everything I understand about current and circuits. From the link you provide:

"the current from one pack must flow ‘through’ the second pack meaning that the current sees virtually double the resistance of the first pack."

At the risk of contradicting the expertise of a reputable battery company, that's just not how electricity works. I'm not denying the phenomenon exists, I just want to understand the mechanism behind it.

Does that mean the last cell in any pack is under more stress than the others? A 4S pack is never "swapped" top to bottom the way that recommends, but we don't get lower cells in that stack dying. EV's have upwards of a hundred cells in series and they wear evenly.

I would hazard a guess that it's not an electrical phenomenon, but an external physical one? Maybe more heat from the ESC travels up the negative lead, subjecting one battery to more heat? Maybe one side gets better airflow? It just doesn't jive with any physics I've ever learned that the *order* of a string of components in series would matter.

 

[bill_delong]

I am not an engineer, nor an electrician but will be happy to share my personal experience and what I believe may be causing the phenomena.

I think packs with internal solder tabs have such a short distance between the cells which use spot welds to get near zero internal resistance. When you run packs in series, you drastically increase IR by using bullet connectors and shielded wire which can starve the flow of current so the packs are not working as equal as if they would with the spot welds being internal.

That said, I know of MANY racers who swear that they don't have any issue with running saddle packs, though most of them are aware of the warnings that SMC has provided and I see them mark their packs and rotate them. What these guys won't share is that their saddle packs aren't going to last as long as a single 4S pack... the vast majority of racers I see running saddles are newish looking packs, I've yet to see anyone running packs that appear to be more than 6 months old. I believe racers running saddle are willing to splurge for the higher expense and maintenance for their perception that they believe it's a better layout configuration.

Final note, of the racers I see a DNF from LVC toward the end of a long main, they seem to happen most often to guys running saddle and I'll bet that's when they swap out to new packs and will continue to swear they never have issues running saddle... shrug

 

[Greywolf74]

This tracks with what I've personally see from the handful of rigs I've got that run dual 3S or dual 4S packs. One pack always wears out faster than the other one. That being said I dont track which battery is on which side in order to swap sides every run. I dont even have them set up for dedicated use on any one particular rig although I do tend to keep them married. I've honestly never thought to much of it cuz I only bash and if one wears out a lot faster than the other Ill retire the one pack and then convert the other pack to single pack use.

 

[Donnie533]

Most of my rigs run dual packs (3S, or 4S). I have not noticed much of a change from the 2 as far as end voltage is concerned. I do keep the pairs married together, but never track which sequence they are connected. I will also use the married packs individually, but try to keep the same number of cycles on each - if running a 3S car, I will charge both of the married pair. For bashing, I don't feel it is much of an issue. Crashing is probably a factor in shorter battery life.

 

[Greywolf74]

Most of my rigs run dual packs (3S, or 4S). I have not noticed much of a change from the 2 as far as end voltage is concerned. I do keep the pairs married together, but never track which sequence they are connected. I will also use the married packs individually, but try to keep the same number of cycles on each - if running a 3S car, I will charge both of the married pair. For bashing, I don't feel it is much of an issue. Crashing is probably a factor in shorter battery life.

Are you keeping tabs on IRs? Its imperative to keep series packs close together in IRs in order to minimize pack failure.