Charging in series

[ltaylor88]

Hi i'm looking for a new charger that is capable of charging 4 x 2 cell 7000mah batteries at once at 1c.

I'm not a noob when it comes to charging I just have a question I'm unsure about. Do the cellpro chargers when charging in series balance all cells of the different batteries indepently? On my skyrc charger I get massive swings in cell voltage levels and I cant see how one of these expensive chargers can do it any better. If they can how does it work?

My other option it to buy a quad charger, but i'd prefere not to have to have a external power supply so that limits my options. I am open to suggestions.

My main priority is being able to charge 4 individual 2 cell batteries while being FULLY balanced.

Thanks in advance

[jimmyhorns]

If you are looking for a charger that will charge 4 x 2S 7000mAh at 1C then you are going to need a reasonably high powered charger if you are to charge in PARALLEL, which is the norm for charging multiple packs at once.

4 x 2 x 4.2V x 7A = 235.2W , so allowing for losses you are going to need at least a 250W charger

If you want to charge in series, then you are effectively making 1 8S (8 cell) battery, and so would need one of the high end chargers like the PL8 to do it like this, and its not a very sensible way of doing it to be honest, as you cannot buy commercially available balance boards to make this work properly without significant modification.

I suspect you mean charging in Parallel - so I will carry on down that line.

Once you get over 50W output power, your choice of charger with a built in power supply is very limited. There are some 50W per channel quad chargers that have a built in PSU, but these are not the best in terms of quality and I would steer clear.

I would get either an Icharger or a PL6 and a separate PSU (you can get a modified server PSU from Coolice on here for sensible money), and you will have a setup that is accurate, safe and practical.

[Grumpy]

Yes, as per last reply, series charging is not recommended, it's fraught with danger of connecting the balance leads incorrectly.

Parallel charging is far more straightforward but will require a charger with high amp output if you want to charge 4 x 7000mAh batteries. You would need 28 Amps to do a 1c charge on those batteries in parallel, which drives you to a pretty high end charger. It's the amp output not the power that will be limiting for those batteries as no 250W charger will be able to deliver enough amps.

Of the 'brand name' chargers the iCharger 306b is probably the cheapest option that meets the need. Hobbyking also do a good one: Turnigy Reaktor 30A 1000W Balance Charger

You could also use two 300W Turnigy Reaktors: Turnigy Reaktor 300W 20A 6S Balance Charger (UK Warehouse) (which is actually a very cost effective solution and gives you power and amps to spare)

There are various other options such as the PL6 but cost is higher.

[ltaylor88]

Yes I did mean parallel, sorry always get them mixed up. So if I go down the PL6 what is different about charging them on any other high watt charger, re them staying balanced?

Example, if I put two 2cell 6600mah in parallel(on on my parallel charging board) on my Skyrc 16amp charger. One battery can end up at 3.50,4.10 while the other is at something like 4.30,3.90. Which is obviously bad(this happened yesterday. Please note the batteries have never showed any fault when balanced separately.

Why would this not happen on a PL6

Thanks for your help.

[jimmyhorns]

Are the two batteries of a similar age and cycle number?... Are they from the same manufacturer?..

[Grumpy]

Something is seriously amiss if the cells are not the same when they come off the board. On the parallel board (with balance lead connections) cell #1 on the first battery is directly connected to cell #1 on the second battery, likewise cells #2 on both batteries are also connected together and so on.... So it's actually impossible for them to be at different voltages because they are directly connected, if one was at a higher voltage it would just discharge into the other.

I suspect that whatever you used to measure cell voltage is giving you incorrect readings.

If any cell does genuinely charge above 4.2V then the battery is in real danger and should be discharged down below 4.2V immediately. Over charging is the 'best' way to get a LiPo to explode!

[myxiplx]

Massive swings in cell voltage levels means your packs aren't being balanced properly, and that's the kind of thing that worries me personally on LiPos, especially on a big pack, it's easy to end up with a single cell over voltage which has potential to cause a runaway failure. And that could be either down to your charger, or down to charging packs in series. Personally I always do a balance charge on my LiPos, it's too risky otherwise, and my biggest packs are only 1450mAh...

To answer your question, I suspect the biggest difference change with the big chargers is that most people are doing parallel charging. Parallel charging is definitely recommended, when the batteries are connected in parallel the cells in the packs equalize themselves (eg: if cell 1 in your first pack is at 3.8V and in your second pack cell 1 is at 3.9V, they're going to naturally balance out so they're both at something like 3.85V), and that allows the charger to monitor the cell voltage levels via the balance lead. The only time you could ever get a cell going out of balance in a parallel charging setup is if your balance leads to one pack aren't properly connected.

While it doesn't sound like the PowerLab is what you're looking for, it might be useful as an illustration of what's possible. I can parallel charge all six of my 6S 1450mAh packs in 20 minutes, and the cells on all the packs are generally within 0.05V of each other, and if you monitor the cell voltages through the charge they're even all the way through, if cell 1 is at 4.1V, all six cells on all six packs are sitting there at 4.1V.

It was a huge, huge difference from my previous charger which could take an hour or more to try to balance packs, and which never got results like that no matter how long I left it.

[myxiplx]

Aaah, seems there were a few replies being posted while I wrote that. Ignore the stuff about series charging then :-)

If you are parallel charging and getting such huge voltage swings then you've either got a bad lead on your parallel setup, or a bad charger, or a bad measuring device. I would suspect a bad lead or bad connection though since even if the charger isn't balance charging, the packs should naturally equalize their cells when connected in parallel.

Please do check whether you are parallel or series charging, as those results do sound a bit weird.

[GravityKills]

Hi,

one problem with parallel charging is that if one cell fails (short circuits), it gets toasted by all the parallel cells, and a fire is much more likely.

[Grumpy]

The only time you could ever get a cell going out of balance in a parallel charging setup is if your balance leads to one pack aren't properly connected.

Good point, that might be the explanation.

The balance leads were connected.... yes?

[ltaylor88]

I thought they should equalise. This is why I am confused. I suppose it is a possibility that one balance lead wasn't in right as I have only seen it happen once. The batteries are turningy nano techs(I know not the best!) but they have been great up till this mishap Only has maybe 10-15 cycles never taken below 3.5 per cell and always kept in pairs and stored at 3.8 per cell as I run them in series to get 4cell in a buggy its only the last few weeks I have started parallel charging to save time.

So just clarify, it is not ideal to charge batters that are not of a similar charge states. as I usually want to charge two at a time, but with races overlapping I might want to put another two on while the first two are still charging.

[ltaylor88]

Anyone selling a nice charger and supply?

[ltaylor88]

I want to get a decent one as I have been long due one.

[jimmyhorns]

Hi,

one problem with parallel charging is that if one cell fails (short circuits), it gets toasted by all the parallel cells, and a fire is much more likely.

Depends if you use something like the MPA balance board which is fused to prevent these kind of issues....

[Grumpy]

So just clarify, it is not ideal to charge batters that are not of a similar charge states.

Correct, when connecting batteries in parallel they should be roughly similar charge state, otherwise you get a large inrush current into the low battery. If that's something that would cause you problems the option of getting the two 300W Reaktor chargers might be the way to go, or a dual output charger such as one of the iCharger Duo range.