RCME - Parallel Universe in January 2017

[Bryan Anderson 1]

This article glosses over the danger and problem with serial charging. The warnings at the end, where they might be missed by readers who skim read, seem to be aimed at parallel charging cases.

1. There is a possibility of shorting out one of the batteries in Figure 2 if the balance leads are crossed over. It depends on exactly how things are wired internally in the charger and whether any of the balance wires are connected to the negative terminal.

2. Rather than speed up charging it can slow it down. If the batteries are of different capacities or charge states then the higher capacity or more deeply discharged one ends up being charged slowly once any one of the lower capacity cells is charged.

Ideally, one would want all cells being charged to be in identical batteries and in the same state of charge.

Serial charging is bad advice and a safety hazard. Cell manufacturers specifically warn against serial charging. Battery manufacturers take care to match the cells in batteries to try to minimise these problems.

[Mike Freeman]

Thanks for the feedback Bryan,

I wanted to describe the series charging option as it is a legitimate method of charging cells. If I had just talked about parallel charging with no reference to series I wouldn't have been giving readers the whole story.

I agree that series charging isn't ideal and I say this in the article calling it "the least favourite option" and "pretty restrictive". I also raise the points/concerns you eluded to ie the states of charge and capacities of the packs.

You mentioned the risk of a short circuit in the balance plugs. There are balance connectors commercially available that allow the balance plugs from two individual packs to be joined to make a single pack so this is a recognised method of connecting packs.

Series charging is only mentioned early on in the article and, I thought, having described the principle and rubbishing it early on would help readers focus on the much better option of parallel charging that followed. I'm sorry if you disagree. The rest of the article is geared around parallel charging, Indeed, the title uses the word "Parallel" so I'm confident your concern of someone skim reading the article and ploughing straight into series charging is pretty unlikely.

Whenever I skim through a document I usually read the Conclusion first and it gets my full attention. I'm sure I'm not alone in this practice and the first two words in my Conclusion are "Parallel charging". Anyone who did skim through the article and had a mind to give it a go would surely go back through it in detail. I know I would!

I hope this puts your mind at rest,

Regards,

Mike

[Trevor Crook]

Yep, I disregarded serial charging as soon as I got to the second part of the article. I use 2 chargers at the moment so I can charge my various sizes of pack in the minimum time, so didn't think this method would help much. However, having recently bought a pre-owned Black Horse Mosquito, which is configured to power each motor from a seperate 3s pack, it will be an ideal solution as each pack should be at the same state of discharge. I've already been looking at paralleling boxes on ebay. They are very reasonably priced and come with the XT60 connectors that I use. Didn't even know such things existed - thanks for the article Mike.

[Mike T]

I haven't read the article yet (maybe I should!), but I've always struggled with parallel charging as the cells in parallel aren't 'seen' by the charger and the method relies on the parallel'ed cells 'self-balancing' as the charge progresses.

I have a //el charge board and I've never managed to get packs to charge in less then the time it would have taken if they'd been charged separately!

When series charging, OTOH, all the cells are 'seen' by the charger and individually monitored. E.g. series charging two 3S packs, the charger sees 2 x 3 = 6 cells, just as if it were charging a 6S pack. Providing you use a correctly configured adaptor, I fail to see the problem. The series adaptors I have do the job much quicker and I can monitor each individual cell.

Or - am I failing to see the problem?

[Bryan Anderson 1]

The most likely danger is from dual 3S to 6S balance converters. There are 4 wires from each 3S connector but only 7 wires on a 6S connector. If you google for "3S to 6S balance converters" you will find examples where they connect a pair of these wires together - red wire to black wire. Use one of these and the danger I described is very evident. Cross over the balance connectors and you short the batteries. Don't try this at home.

[Martin Harris - Moderator]

I haven't used or seen one of these but aren't the connectors fitted with keys to avoid incorrect insertion? Ideally, there should of course be a physical bar between orifices or separate connectors and then the scenario I think you're describing couldn't occur.

If this is one (no recommendation etc. just the result of a Google) which can be misused, please outline how as it's escaping me!

While it might be possible to force a misaligned connector together with some effort, the gauge of wire/pin connector used is likely to act as a fuse anyway so there would be minimal danger unless your eye was very close to the action.

Edited By Martin Harris on 21/12/2016 10:39:46

[Bryan Anderson 1]

Yes, Martin, that is a good example of one that can cause problems. You are right, the connectors are polarised to prevent them being plugged in the wrong way round but there is nothing to stop them from being plugged into the wrong battery of the serially-connected string.

Red and black wires are connected to a common pin at the middle of the 6S connector. If the black lead shown at the right-hand side of the picture is connected to the balance plug of the most negative battery then all is well. But connect it to the balance plug of the most positive battery and those balance wires connected to each other short circuit the entire 6S pack. Not good.

A mantra of safety is that, if it can be done, it will be done. So better not to allow the possibility.

[Bryan Anderson 1]

Correction: If the black lead shown at the bottom of the picture, not the right-hand side.

[Martin Harris - Moderator]

Thanks Bryan, I can see the problem now - sketching it out on the back of an envelope confirmed it to me. I'd assumed that you were talking about two adjacent connected pins shorting a cell.  

Even parallel charging, which I do on occasions, has it's dangers though e.g. a failed balance connection on one cell may not be detected by the charger.

Edited By Martin Harris on 21/12/2016 11:58:31

[Trevor Crook]

Yes, but if, as the article suggests, you use a battery tester to check the packs are at a similar state of charge, if the balance connector is used for this check it should reveal any anomalies.

[Mike Freeman]

Posted by Trevor Crook on 20/12/2016 23:12:21:

Yep, I disregarded serial charging as soon as I got to the second part of the article.

Thanks Trevor,

That is how I intended the article to be read..... Introducing the reader to the two options of multiple lipo charging - quickly dissing the Series option, saying there is a better option.. "Parallel" charging and going into the detail.

I know there are folks that prefer series charging but the only benefit I can see is the individual measuring of each of the cells voltage in each of the multiple packs. The limitations on number of packs a charger can charge and risks of incorrect connection, as described by Bryan, are not worth the hassle IMO - parallel charging is the way for me!

As Martin says above, a faulty balance plug would not be picked up with parallel charging and you are quite right in your post above that this would be picked up when checking the charge state of the packs to be parallel charged.

Parallel charging is safe to do as long as we are vigilant, treat the Lipos with respect and follow the golden rules! BTW the Paraboards are good value for money and save the hassle of knocking up a homemade set of leads.

I could do a similarly detailed article on Series charging if there was a demand but I think most will agree that Parallel charging is the better option!!

[Mike T]

I'll repeat my lack of success with //el charging, using reasonable quality kit. As a time-saver, for me it just doesn't work. Furthermore, it relies on the //el'ed cells self balancing over the course of the charge and the voltage of any group of //el'ed cells is only the aggregated voltage of each group - you can tell nothing of the voltage on each cell until it comes off charge.

I have better results using commercially available series connectors (see pic) and which is more, I can monitor the voltage of each individual cell throughout the charge.

[MattyB]

Well that's not entirely surprising given your charger can only put out 150W at a max current of 7A. You'd max it out charging two 3S 2200s at 1.5C.

You need more power to make parallel charging worthwhile - if you fly parkfliers on packs in the 3S 2200 ballpark then 250-350W is ok. Move beyond that to 4S 3300-4000s and I'd recommend a 500-750W setup, and if you are charging large numbers of 6S 5000s a 1KW setup with a 24V server PSU is the way to go. The other advantage with the higher wattage chargers is that they generally offer much higher balancing currents, meaning the balancing phase at the end of the charge is faster - important if you are paralleling a fair number of packs.

Edited By MattyB on 22/12/2016 20:51:42

[Willyuk]

Matty is spot on about having a sufficiently powerful charger. With the right gear, parallel charging is a godsend. I use 10s flight packs made up of two 5s, 5000 mah lipo packs. These are not cheap and so having more than 8 or 10 battery packs, i.e. 4 or 5 flight packs is prohibative. When i go flying i like to have more than 4, 8 minute flights so parallel charging is the way to go. I use a powerlab cellpro 6 with the parallel charge board. With that set up and a decent leisure battery i have managed to fly more than enough. I usually put the first pair of batteries on charge immiediatly they have been used, add a set after a further flight and have even had six packs being charged at once, thats a 30 amp plus charge rate. The only issue i have had is the need to balance charge the batteries individualy from time to time. That ensures that the cell voltages are matched and helps bring the ir into line.

[MattyB]

Here is my setup - iCharger 406 Duo with a dual HP server PSU @24V. ~1200W charging power means I can charge 5x 6S 5000s at 2C if I wanted to; well I could if I actually had that many of the big packs!

Edited By MattyB on 22/12/2016 22:26:08

[Mike T]

Yeah, I'm aware of the limitations of the charger, but //el charging doesn't work for me even within that limitation. I usually (or used to) charge 2 x 3S 2200 packs at 1C. I'd expect a balance charge at that rate to take an hour 20 mins tops, but its usually well over 2, sometimes 2 1/2 hours. That's why I tried serial charging and found it much better - yes I'm limited to 2 x 3s or 3 x 2s, but it suits me at the moment.

My charger cost me about 35 quid. If I was into models requiring large capacity 6s batteries, I could probably justify a Rolls-Royce charger. My electric powered operation is centred on the ubiquitous 3s 2200 (or multiples thereof). If I need more power than that, well I have strayed into 4s occasionally, otherwise, if I want more power, I go glow/petrol!

However, the main point in posting was to challenge the notion that series charging was 'rubbish'!

Edited By Mike T on 23/12/2016 19:53:05

[MattyB]

Posted by Mike T on 23/12/2016 19:52:36:

Yeah, I'm aware of the limitations of the charger, but //el charging doesn't work for me even within that limitation. I usually (or used to) charge 2 x 3S 2200 packs at 1C. I'd expect a balance charge at that rate to take an hour 20 mins tops, but its usually well over 2, sometimes 2 1/2 hours. That's why I tried serial charging and found it much better - yes I'm limited to 2 x 3s or 3 x 2s, but it suits me at the moment.

You are remembering to increase the current from 2.2A to 4.4A when charging the two 2200 packs in parallel, right? What you are describing would tend to indicate not. If you are and it's still taking over two hours then something in you setup (most likely the charger, but possibly the para board) is clearly faulty or incorrectly configured. There is no other possible explanation.

Edited By MattyB on 23/12/2016 20:26:33

[MattyB]

Just checked your charger instructions and the max balance current is 300ma, about what I'd expect for a charger of this wattage. If the packs have a similar voltage at the start (within 0.1V) and are well balanced at the outset then this will be fine, but if not it could take a long time to complete the final balance phase. To find out the root cause just take to well matched and balanced packs and watch them on charge; if they charge at 4.4A for 40-50 mins you know it's the final balance phase taking longer because of the 300ma limit, but if it only sustains 4.4A for a short while then drops off it's likely to be something more fundament wrong with the charger or paraboard.

[gangster]

I havent fully digested the article but it did inspire me to think further into parallel charging and at the moment dont think it is the answer to my needs,

Just one caveat which forumites might like to agree or refute is the current capability of some chargers, some are pretty cheap these days and may be optimistically specced, in the same way as cheap ESCs

Whist the charger may be happy to charge a single 3300 at a 1c charge paralleling up you may wish to push the current up to ,say, 6A,( otherwise there would be no point in charging in parallel)

I was prompted to this thought by the melting of the DC input plug on my Imax B6 (probably a clone) It claims to be able to deliver up to 6A, I was charging a single 4S pack at 5.5Amps So the 12 Volt input current would have been considerably higher, maybe 8-10 A

Looking at the DC input plug on that charger it was a little 5mm coaxial job probably designed for 1A max. many of the cheaper chargers, and also some more expensive ones use this type of plug, rendering it a little risky to parallel charge any cells above say 2200mAh

[MattyB]

Posted by gangster on 24/12/2016 13:13:37:

I havent fully digested the article but it did inspire me to think further into parallel charging and at the moment dont think it is the answer to my needs,

Just one caveat which forumites might like to agree or refute is the current capability of some chargers, some are pretty cheap these days and may be optimistically specced, in the same way as cheap ESCs

Whist the charger may be happy to charge a single 3300 at a 1c charge paralleling up you may wish to push the current up to ,say, 6A,( otherwise there would be no point in charging in parallel)

I was prompted to this thought by the melting of the DC input plug on my Imax B6 (probably a clone) It claims to be able to deliver up to 6A, I was charging a single 4S pack at 5.5Amps So the 12 Volt input current would have been considerably higher, maybe 8-10 A

Looking at the DC input plug on that charger it was a little 5mm coaxial job probably designed for 1A max. many of the cheaper chargers, and also some more expensive ones use this type of plug, rendering it a little risky to parallel charge any cells above say 2200mAh

I agree that can be an issue with lower end chargers, but it's not a parallel charging issue. The input and output connectors should be rated to take the max currents the charger is capable of taking/putting out, pure and simple - whether that is to a single pack or multiples in parallel is really irrelevant.

[gangster]

Indeed so Matty . It certainly isn't a parallel charge issue however parallel charging might be the last straw that breaks the back of a charger that happily charges a 3 or 4ah battery singularly

[Peter Jenkins]

I'm with Matty on this. I started parallel charging when using an iCharger 208b when I got into F3A aerobatics. It used to take me ages to charge 3 flight packs (2 x 4S for an 8S pack) at one 4S at a time. As they were 5000 mah packs that was 1C = 5 amps so each charge was around the hour mark or 6 hours total. By parallel charging I was now down to 3 charge cycles - 2 x 4S at 10 amps were charged within the hour at Fast Charge rate - roughly 95% capacity. If you wanted a 100% charge then it would drift out to 1:15 to 1:20 per charge. Anyway, 3 hours of charging beats 6 hrs into a cocked hat.

I now have 2 twin 500 watt output chargers - Emperor Fusion L712 both bought second hand - and so I can charge 4 flight packs (now 2 x 5S 5000 mah) in an hour. I use 6 flight packs so the second hour sees the remaining 2 flight packs and the 2 x 2S 800 mah Rx batteries charged. I gave up charging at the field so aim for 6 flights during the day and swap the Rx batteries after 3 flights. So far, this has worked fine.

The iCharger now does a great job parallel charging the 2 x 2S LiFe cells in my petrol birds. At 1C, they rarely take more than 20 mins to charge as packs are only used for ignition and Rx/servos respectively.

I use a 600 watt power supply for the each of the two 500 watts per channel chargers and a converted HP UPS power pack (rated at 1200 watts!) for the iCharger. Nothing gets hot when charging is in progress.

[Mike T]

@MattyB: Thanks for your input. Yes, I'm aware of the current/voltage requirements involved with //el and/or series charging. I'm using the appropriate settings for the packs being charged (whichever way) and I as I tend to fully discharge all packs in use, they are all pretty much at the same level when they go back on charge. I even make sure I'm only charging the same brand/c-rating packs at the same time. Although I prefer to stick to a 1C charge rate, I suppose I could try increasing it to 2C - I could probably go as far as the charger will allow without damage.

However, I want to reiterate that the main reason for my initial responses here was to question the rather blase dismissal of series charging as dangerous and/or crap. It can be, if you use a DIY lash-up based on an imperfect understanding of the principles - but this also applies to //el charging. The hazards can be mitigated by using a properly constructed connector (//el or series), with the caveat that you still have to understand what it is you are doing as the charger will only protect you, itself and your packs, up to a point!

[Bryan Anderson 1]

@Mike T.

I am sorry you have not enjoyed Christmas but I must protest. As the originator of this thread, I feel that I did not make a "blase dismissal of series charging" nor did I or anyone else, I think, call it "crap". I am sure that neither of us would ever misuse or misapply anything but I am not so sure about others with inferior abilities. Hence my warnings.

Is not education the essence of safety? The fact that a 6S battery can be short circuited by simply plugging in two identical-looking connectors the wrong way, in the wrong socket,  when using a commercially-available dual 3S to 6S converter is surely worthy of a warning.

This is not the time of year to be uncharitable but you might care to take a look at your writing and ask yourself who is being blase. Hint: count how many qualifications you make after dismissing the dismissal.

Edited By Bryan Anderson 1 on 27/12/2016 18:21:16

[MattyB]

Posted by Mike T on 27/12/2016 16:58:42:

@MattyB: Thanks for your input. Yes, I'm aware of the current/voltage requirements involved with //el and/or series charging. I'm using the appropriate settings for the packs being charged (whichever way) and I as I tend to fully discharge all packs in use, they are all pretty much at the same level when they go back on charge. I even make sure I'm only charging the same brand/c-rating packs at the same time. Although I prefer to stick to a 1C charge rate, I suppose I could try increasing it to 2C - I could probably go as far as the charger will allow without damage.

So can I ask one question - when you are charging your 2x 3S 2200s and they were taking over 2-2.5 hrs to reach a full charge state, what max current were you selecting on the charger?

Edited By MattyB on 27/12/2016 18:32:39