Parallel charging vs. series charging
 

I have looked online and notice there is A LOT of parallel charging boards out there. My question: Is there a Series charging board out there? I have only been able to find an adapter wire (had to order from china and on Ebay), but would like it to be more permanent. I have (2) 2S batteries that I would like to charge in series. Seems like this should be more common considering the 1/8 market moving to saddle packs again.

A little background, I have the 1/8 buggy from Kyosho Mp10E that utilizes the saddle pack battery method. Those batteries are run in series to make a (ONE) 4s battery. I would like those batteries to always charge together so they are very close in balance.

Thats because parallel charging is the best way to do it. The more cells you have in series the harder it is to balance them. Charging with a jumper wire also makes balancing harder, thats why when running 2 packs in series you have to be really careful about one pack or one cell getting over drained, SMC has a nice article about it on their website.

Basically one pack gets discharged more, so they should be rotated to each position in the circuit as you cycle them. The same would be for charging but to a lesser degree since chargers also balance while charging.

So is there an issue with running them in series in the RC. They usually discharge at same rate in the vehicle, then charge them in parallel with an icharger?

Ive used serial charging before and I dont see any problem in doing so. It might take longer to charge since your charger would have to balance more cells if your packs arent all at the same charge. Thats why I only serial charged my packs after they all have been stored.

But I went back to individual cell charging since it was DIY setup and there were wires EVERYWHERE and I was tired being in constant fear that I will short something. Also I have 2 dual port chargers so I could charge up 4 cells at a time, so theres really no need for it.

I see one problem with parallel charging.
If you have one empty and one full battery ad lets say you charge 2C basec on the capacity of both batteries toegether then the empty one will get almost 4C charge.

In seril you do not have that problem.

Just permanently wire them together and put a 4s balance connector on it. Treat them as a single 4s. Twin 2s LiPos used as a 4s should never be ran separate anyway.

The OP will never experience this problem, he's running both packs in the same car in series.


Far easier to charge them in parallel, though here's a wiring layout for charging in series yourself, note that the side with the true negative has the positive lead hanging off, this prevents the circuit from shorting:


https://live.staticflickr.com/5181/5...62acf07b_c.jpg


I will be happy to make you one of these series balance harnesses for $10 shipped in the CONUS if you want one, but honestly there's no difference with charging the packs in parallel with respect to keeping the cells balanced.


Here's the SMC article about the risks of running packs in series:
https://www.smc-racing.com/index.php...y&path=174_166

*** most important thing is to rotate the packs every cycle to even out the distribution of IR between both packs.

There is nothing inherently wrong with series charging. Consider that any multi-cell pack is being charged in series up until the balance portion of the charge. The "s" in the naming convention stands for series. The problem with charging these hard cased shorty 2s packs in series is there is only one independent balance lead, so you will need to build an oddball charge lead. It's possible, but TBH, pointless, since charge times will theoretically be identical (you'll save time not having to swap the packs though).

It's much easier with more standard type battery packs that have completely separate balance leads, assuming you also have a charger that can handle the new cell count.

Another thing to keep in mind is what your charger and PSU can handle. Lots of folks are near their limits charging at 40A. If you are near your limit at 40A and you double your cell count, you will now have to cut your charge current in half.

W=A*V

2S 5000mAh pack @ 2C is 8.4*10=84 Watts
4S 5000mAh (two 2s in series) @2C is 16.8*10=168 Watts.



To reach your goal here, you do not need to charge those packs in series.

I think the reason we don't see series charging multiple packs very often is because:
-There is no benefit
-In many cases, the resulting cell count will exceed the rating of your charger. Not the case with running 2p4s saddle packs, but it would be the case if you were to run 4s2p saddle packs.

I think maybe there is some confusion there. You cant properly balance a pack when parallel charging unless you independently balance the pack after the charge cycle is completed. It's impossible. When parallel charging, each balance lead splits into two cells which the charger sees as one cell, so there is no way it can accurately balance both of them. The general rule with parallel charging is, you should give them a normal balance charge every few cycles in order to balance them properly.


EDIT: IDK, I'm not buying it with that article. Most of it is great advice, but the parts about cell counts don't make sense. We have been using HV LiPos in series on RC helis for more than a decade. No problems such as what is described in that article. In theory, these would be grossly evident with RC helis. We pull 8000mAh in 4 minutes running 12s 6p2s saddle or stick packs. A 6s pack as what they describe is six cells in series. Assuming what is stated was true, then we would be seeing single multi-cell series packs also fail in the same way.... but we don't. Two 3S packs in series is the same thing as one 6s pack, aside from the added resistance you may get from the jumper.

The bigger issue with running series packs (especially stick packs) is the added ripple current you will see due to the extra-long battery leads. Capacitor banks help smooth that out.

A very funny story, as it only happens with sepparate packs in serie while all in one packs are nothing different.....

If you are running multiple packs to create a larger pack (twin 2s to 4s). Shouldn't they all be balanced together? I would think having 2 cells at a different balance voltage than the other 2 cells would defeat the whole purpose of balancing.

No, because you are still balancing them. The charger dictates the end voltage, not the way the pack is constructed. Assuming the balance lead is wired correctly and the charger is able to charge each cell independently, then the main contributor to how your packs balance is the charger. This is of course assuming the pack itself is healthy.

That's the whole point of balance-charging. If it didn't work that way, then why would we pay extra money for a charger that can also balance? Back in the day when LiPo tech was new to the RC world, you would have a separate device to balance the packs. Charging LiPo batteries was a lot more of a pain in the ass back then.

This is simply not true, when parallel charging each cell is at the same voltage. Remember lithium charges are voltage controlled, the purpose of balancing is to equalize cell voltages. Hard to be different when they are directly connected. Note many packs contain paralleled cells, one might be parallel charging without being aware of it.

Some good info that covers many of the misconceptions regarding parallel charging.
How-To: Parallel Charging

I'm still trying to follow this bit:

The problem is mostly when you have a pack with a cell that's a bit off from the others before you start charging. Assuming everything is perfect, then you are 100% right, it does not matter. Nothing is 100% perfect though, so in practice, it can be a problem. If you have two identical 6s packs, and each cell is at 3.75 except one... one is at 3.65, and you parallel charge, you may have a problem. The link you shared cautions the user about this.

Packs with parallel cells are not too common these days for anything aside from lower C TX or RX packs. I've taken apart hundreds of LiPo packs over the years to see how they are assembled. Last time I saw a flight pack that was wired in series and parallel was a 20C Align flight pack from 2008.

The 2 different packs when connected would self equalize fairly quickly, and then charge normally. Usually the biggest concern is that equalizing current between packs, but many do it without noticing adverse effects.

More info on parallel charging and various questions and misconceptions that arise. Also discusses series charging some.

On the topic of parallel charging of Lixx / PB packs.

Yes it mentions best practice is to have cells within a couple tenths, but is not required. Some fly guys connect discharged packs and charged packs together to put them both in storage even, althou that might be pushing it for some wiring and connections.

I have personally experienced this first hand many years before SMC published their article... I had no idea what caused one of my packs to prematurely swell... I had no IR meter, nor was I rotating the packs, but I definitely experienced premature LVC issues and all kinds of reliability issues when running packs in series for 10 min mains... no issues with 5 min quals, but 2x2S-5Ah in series was a disaster and 1x4S-5Ah gave me no issues.

I believe the extra wiring/connectors for series wiring is what causes the additional IR on the circuit, totally different from having a single pack wired internally, plus a single pack has matched cells where you can't possibly guarantee matched cells from 2 separate packs. Simply put, running packs in series is just a bad idea all the way around :(

You may have had issues, I just don't think that quote I pulled explains why. I see people run series packs without issues in all kinds of RCs. Sure the packs should be reasonably matched and kept together to avoid a low cell. Recommend a higher than normal LVC setting.

An option to provide additional protection when running series packs: CellShield

Could have also just been a dud pack. Or could well have been a cold joint or some other issue.

If running packs in series is so bad, then we should be seeing constant failures in the RC heli world. Helicopters are far more power hungry and running series is pretty much the norm for large helicopters. Even our single stick packs are technically twin packs in series that you can charge independently or in parallel.


Dave H
You're right, I should not have used the word "impossible." I should have clarified... it's impossible to get a true reading, since pairs (or triplets or whatever) of cells are seen as one. Sure, it's possible to get a good balance when parallel charging, but you have no way of knowing if there is a problem because you cant see individual cell voltage, so as a safety precaution, I will run them individually once a week and monitor the pack. I've had instances where one cell was giving me trouble but after balancing it independently, it would go back to normal for a while.

I've also been parallel charging for many years, safely, with no problems. My biggest words of caution are, let the packs equalize for a few minutes and definitely get a fused paraboard. Usually not a problem if you don't let them equalize, but it only takes one unseen problem to cause a fire. Stay safe out there!

So are you are saying there is no point of having all 4 cells the same voltage in a 4s battery?

parallel charging is meant more for smaller packs for like Drones 1300mah or 1500mah packs etc. as you only get 3-5 min flight times so you have many packs 6 -12 is normal. so after you burn through your packs you can recharge them all at the same time. providing they are all the same cell count, MAH size, and preferably C rating.
when you get into bigger car batteries 5000mah and up most chargers do have the power to charge more than 2 at a time so its really irrelevant.

to charge a 1500mah at 1c is 1.5amps to charge 6 1500mah in parallel it is 9A
5000mah at 1c is 5Amps to charge 2 in parallel it is 10Amps!

better off getting a charger that can charge dual port(2 lipo at the same time)

you can't charge more than 1 lipo in series there is no way to balance it properly and you will damage the lipo at the very least. you have to make a harness that can take the lipos and connect them so that the charger can see the lipo as a single lipo (IE: 2 3S and make it a single 6S that the charger can recognize) but again once you get into bigger lipos most chargers cant handle the load. 2 5000mah 3s in series would be a 6s 10,000Mah load and 1c is 10Amps. bigger than that and your getting into 8s load which most chargers cant do, or over 10amps which most chargers cant do(not alot cant even do 10amps)

No, not at all what I am saying. How are you coming to that conclusion based on everything I have said?

Why would the two packs be at different voltage per cell? If they are identical packs, in identical health, and charged with the identical parameters, why would their balance differ if not charged together?

Fairly simple way to check on the fly, connect each pack in turn and check each cells discharged voltage, before connect all and charge away. A good idea for any cell or pack charge. Agree monitoring each pack occasionally can also be useful. And for others don't do anything you are not comfortable with, the links I posted earlier include concerns to be aware of and times it may not make sense to parallel.

That's not quite how it works. When you plug it in, the charged pack will discharge into the empty pack before you even turn the charger on. You want them to be at similar voltage levels before you plug them in.

Additional wiring won't affect the IR, which is the Internal Resistance. By definition it excludes any external wiring. Extra external resistance won't damage the batteries or cause puffing.

Clearly the difference between 2 packs wired in series vs a whole single pack has some sort of effect, otherwise many people wouldn't notice this phenomenon. Not like the guys at SMC are inexperienced, clearly they know something about power systems.

There's definitely a significant difference in what the cells see in the 2 scenarios. Cells soldered tab to tab vs 2 connections (could be high resistance if dirty/loose) a bit of wire on top of the cell tab connections would look different under a big load.

That leads to some cells discharging more than others and could cause some to dip below 3-3.2v and get damaged.

End of the day if everything goes right, and you swap the packs so they arent in the same position, there shouldn't be a problem. But thats not always the case.

Adding resistance in series won't make certain cells discharge more than others. If there's no parallel path for the current to flow then the exact same current will flow through the cells.

The main advantage to pre assembled packs in series is that they can match cells that have comparable capacities and resistances. Unmatched cells can lead to unbalanced voltages. No 2 cells are identical due to manufacturing tolerances.

If you are running 2 2s packs in series then it would be the same as a 4s pack. If you need to balance all 4 of the 4s cells then you should also need to balance all 4 cells of the 2 2s packs. Im not seeing the difference here.

Same reason you would have 1 or two cells off in a 4s pack. They should in theory be identical as well, but you still have to balance them so they are the same.

Umm... man, I'm sorry, but you are starting to confuse me. I'm not sure why you think I said you don't need to balance two s2 packs but would need to balance one 4s pack. I did not say that, nor did I imply it in any way. I just went over everything I posted and I've been really clear, so I really have no idea what you are talking about at this point.


I was referring to packs that have already been balance charged. Why would there be a difference, and more importantly, why would balancing them together have an impact on their final resting voltage?

Balancing a pack makes all the cells the same voltage. How exactly can a charger balance all 4 cells if you balance them separately? If you balance charge 2 2s batteries separately and run them as a 4s you won't have 4 balanced cells you will have two pairs of balanced cells.

From iCharger manual:
If one pack gets balanced to a lower voltage you run the risk of running 2 of the cells under voltage.

....but why would it get balanced at a lower voltage? If it gets balanced at a lower voltage, it's user error... because the user selected a lower voltage. The iCharger does not make you select end voltage every time you charge. I've had a 306B since it came out.

Standard voltage for a LiPo battery is 4.20 volts. That's what any charger will default to, unless you manually change the setting. Unless there is a problem with your batteries, balancing the packs separately will have the same effect as balancing them together.

In balance mode, the charger applies voltage to the cell that needs it, then backs off and lets them equalize. The process is repeated till all cells maintain their target voltage for a predetermined period of time... and then your charger goes DING, and it's done.

You do You I guess.

LMAO dude, I'm doing it the normal way. I think you are just misunderstanding something.

You must have some serious kit if every time you charge a battery its coming off the charger at precisely the same voltage and the same as all of your other batteries. You must have won the charger lottery and run those new unobtainium LiPos.

Yep, that must be it.

It's the amps that is different between 2S in parallel vs series... in parallel you need to double the amps in order to charge the pack in same amount of time as you would with 2S in series.

.

Let's not forget cell phones, laptops, and of course your TV remote control... even the 12v Lead Acid battery in your car is actually 6 cells in series.

Tesla is far from perfect, they are forced to provide additional heat shields from all the fires started from the extremely dangerous battery configurations in their cars... shrug


https://abc7news.com/tesla-electric-...factory/21997/