Charging batteries in series on a hobby charger? (And measuring IR)

Batteries and Chargers Rechargeable Batteries
1

Hi,

I’ve been busy charging some batteries that I just pulled from a pack, and have been using both some “normal” chargers (a Jetbeam i4 and a TF one) and an Accucel.

The Accucel is faster, so I’ve been charging 2 at a time in series (2S), but not letting it finish, and then before it’s done, moving the batteries to either the i4 or TF to finish charging.

The main reasons I do that is that it’s faster, and also I notice that, in the past, when the Accucel terminates, the battery voltages are usually a little lower than 4.20V.

I had one pair on the Accucel, and I thought I had checked voltages before putting them on the Accucel, but I happened to pull them off before the charger stopped, and measure the voltages, and one of them was at 3.98V and the other was at 4.38V!

I think that I know that answer to this question, but why was that (maybe I forgot to check voltages before charging)?

Also is it a bad thing to charge batteries in series on a hobby charger, in general? I thought that RC guys do that a lot?

Thanks,
Jim (still learning!)

2

It (the Accucel) does charge in series without doing balance charging (at the menu, you get to select 1S, 2S, 3S, etc.). I’ve actually charged 3S before with no problems, which is why I was surprised by what happened today.

For balance charging, I think you have to hook up some extra cables, including, I think, a lead to between the 2 batteries that are in series, which I haven’t tried before.

3

Absolutely right. Don’t do series charging on a hobby charger with li batt’s unless they’re balance charged. That’s why you have 2 different voltages, one of which is perilously high. All your doing is putting voltage in one positive end of the first batt and it goes full circle out of the other batt, the charger can’t tell you the voltage of both batt’s seperately just the total voltage. That’s why balance charging is the only way to go, you get both voltages of each batt and they charge without being destroyed in the process.

4

You have impeccable timing Ohaya. I was just researching balance charging for my Accucel. I've learned you need JST cables. I'm wondering if an 6S cable like the link below can be use for less cells, like 2S.

http://www.ebay.com/itm/330991813979?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

Does anyone know? I'm not finding much guidance out there.

EDIT: If yes, which wires do you connect to the cells. I'm looking at thread pictures, but none are clear. I'm guessing you connect the far right and far left wires to the positive and negative end of the series of cells. Which of the inner wires do you connect to the places where the cells make contact. The wires that are on your left when looking at the Accucel port or the wires on the right?

5

I knew i’d seen pic’s on here, Hobby Chargers

6

Yes it can be used for 1 - 6 cells.

7

Cool. Thank you StyXSIS. I have read that thread, but I can't make out the pictures good enough. Which wires do you connect to the cells. I'm guessing you connect the far right and far left wires to the positive and negative end of the series of cells. Which of the inner wires do you connect to the places where the cells make contact. The wires that are on your left when looking at the Accucel port or the wires on the right?

8

Yes, RC guys charge in series all the time, but, we BALANCE charge.
You don’t HAVE to balance charge BUT the cells need to be identical in performance and charge when you hook them up.
You could look at parallel charging.
2*18650 Serial/Parallel Battery Holder Case w/Lead Wires
The cells are unsuitable for series charging if they are unprotected or you go through the hassle of hooking up a balance system.

System Wiring

9

Seems like that happens occasionally between us, huh :)?

I don’t know if I’ll try this, but rather will just stick to 1-at-a-time. My wife is already ticked with the counter space I’m taking up :(.

But, in case, I have question: That page was for 10 cables. Do you need 10 cables to balance charge 2 batteries in series?

10

I thinking of getting 10 because I want to set up several spotlights with permanent cells. I will use one half of the cable to create a charging port on the light and the other half to connect to the Accucel. Actually, I will need 1 1/2 cables for each light I set up. The one cable will not be cut and will be the one that connects the Accucel to the light's port. I only need one of those for all the lights, but I want to have a couple as I imagine that one will eventually wear out from being plugged and plugged to the various lights. The lights will need the male end of the cables.

The cost is not much more than buying 1 cable for 2S. So this way gives me more options for not much more money.

11

Look at my post above.
You need a JST-XH cable appropriate for the series you want to charge.
Or get a holder like my 2nd link and wire it appropriately, which won’t work for a permanent pack.

12

Thanks for your input flydiver. Isn't that the type of cable I have linked above? I feel like I'm missing something.

13

Those are marked 6S (series).
Look at the links below that for other sizes.
You want the ‘S’ appropriate for the cells you are linking together. Each wire goes to a separate battery. The charger ends up balance charging single cells fro it’s perspective. The plug that goes into the balance port on the charger is very specific for THAT size cell.
You will end up with 2 plugs > a POWER plug, and a BALANCE plug. You need both for that style charger for balance charging.

You can’t use a 6S on a 2S or 3S battery.

14

So you and StyXSIS have opposite opinions. Which of you is right?

15

ImA4Wheelr,

A little off-topic, but one thing I forgot to mention is that, at least on my Accucel, if you have cables setup for balance charging (I think), the/some Accucel chargers have a function for measuring battery internal resistance (the one I have does).

16

StyXSIS is ‘wondering’.
I use them and have built them. In fact I just tore an old one apart (4S) to see if the (old) 18650’s would be good for my new lights……nope, too old.

Please look at the [System Wiring] link.

17

Assuming you are to balance-charge 3 loose 18650 cells, you need balance cable leads designed for 3S. This 3S connector has to be connected to your charger’s 3S socket balance port. This 3S connector has 4 leads, with one outermost lead being RED (connected to the outermost cell’s positive ). The next wire after the RED in connected IN-BETWEEN the 1st and 2nd cell, and the next succeding wire in again connected IN-BETWEEN the 2nd and 3 cell, and 4th and last BLACK wire connected to the outermost negative side of the series.

The main RED and BLACK output from the charger are of course and ALSO connected to the OUTERMOST + and - sides of the 3S connected cells. (adjacent to the RED and BLACK wires of the 4-wire balance cable)

18

I read that in a post somewhere you lucky dog. Mine doesn't have anything in the menus that sounds like resistance measuring. I looked and looked. I thought about sneaking into your place and swapping our chargers. Lucky for you, I don't know where you live.

19

For loose Li based cells I would really say parallel would be easiest if you don’t want to buy the cables. Just use some magnets and stuff you have lying around. NiMH is the opposite and should be done in serial.

20

Nice clear directions tatasal. Thank you. Now the question is, Do you know for sure or are you assuming you can't use a 6S cable and stop connecting at the at say the second black wire for 2S? The Accucel does ask how many series is connected. It would seem it could just auto detect which port was connected if it was port specific. All those different ports may be there for convenience of the consumer to be able to used different xS connectors.