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.