how do you charge more than one lipo

[gary watson 2]

I was looking to buy a charger that i could charge 4 x 3 cell lipos at once because at the moment it is taking me at least 40 minutes a battery so i am wasting valuable flying time.I know i could probably charge them in parallel i dont want to do that.I was thinking about something like the hitec h4 quad charger and this will do me when i get on to the really big lipos.

Gary

[crispin church]

just buy extra charger like imax B6 charger that do 4 battery at once normally cost loads more then cost of another 3 B6 and if one breaks you have not lost the only charger

[Tony F]

Hi gary , slough models do a 4 x charger , check their site for info. So do hobbyking but stock levels on their chargers is pretty poor unless you order from their international warehouse.

Tony

[Tony F]

Or as cc says

Tony

[Kevin Wilson]

Gary, you either parallel charge or you get multiple chargers.

The quad charger you refer to will do the job, there are other multiple output chargers you could consider.

You do not say what size 3S LiPo you are charging. But check the charger output for your expectation of 'really big' LiPo. (mAh capacity / 1000 * batt volts = watts. eg 3s 5000, 5000 / 1000 * 12.6 = 63 watt charger)

Personally I have a single 50w charger that I parallel my batteries before a flying session. Then use the same charger to top up each cell as it comes out of the plane. This works for me as I am a cheapskate and am prepared to accept the compromises of this setup.

My generic FBC (four button charger) (B6 clone) will do a 1C on a 4000 4S. Or in my case a 1C parallelling my 2x 2300 3S.

Of course it breezes a fist full of 300 2S for my indoor foamies.

You pays your money and takes your choice

Best of luck, Kevin

[IanR]

I also was miffed about the time taken to charge a number of 3S 2200 batteries but the multi chargers I looked at all required a separate power supply, which I don't fancy so, to go with my Sigma EQ2 50w charger, I bought an Overlander - RC6-VSP 80watt 7A output charger for only £40. Works a treat and I can plug both my chargers into the mains and charge 2 batteries at the same time. As Crispin says, if one of them breaks I've still got the other one.

Ian

[GrumpyGnome]

I too use multiple chargers: IMax B6, an old JP one, an eflite one that came with my blade heli and an FMS one that came with my FMS Tempest.

Rats nest of wires but possible safer (?) than parallel charging .... ?

If one breaks, I still have three left ! I did think my B6 was broken but I think it must have an internal battery that was completely flat as having left it on for a while (afetr not using it for a few weeks) it burst into life.

GG

[John Lee]

I'm just back from flying and have 5 x 6s 5000mah, 1x 2s 1300mah and 2 x 2s 2200mah to charge. I went through the same dilemma and eventually bit the bucket & bought a Hitec H4 and a 600watt power supply. Best thing I did since going mainstream electric. All the above will be charged within 2 hours, the Hitec is brilliant, does everything I need, easy to use and you can mix batteries on charge, including NiMh & Pb.

[gary watson 2]

I know it is early days yet but i have been using the hitec quad smart charger for over a week now and i dont know why i did not get one when starting out with electric flight. I charge up 4 x 3 cell 2200 at 1c in 40 minutes, using the single charger it would take me 2 hours just to charge 3. If you are serious about electric flight i recommend you get one it should cater for when you start using the bigger lipos.

[Phil Green]

Why the reluctance to parallel packs Gary?

Having several cells wired in parallel is exactly the same thing as one large cell, only the interconnection is through wires rather than through a continuation of the electrodes.

Heres a silly theoretical example. Say you had a laser and you cut a big lipo cell in two. Lets say the laser cuts the internal electrodes cleanly without shorting the pos & neg layers, and it also re-seals the plastic. So now you have two small lipos, and each one can be used and charged as such.

Now parallel these two small lipos by connecting the neg electrodes back together with one bit of wire, and then another bit of wire to connect the pos elecgtrodes. Now you have your big lipo back as it was, same capacity, but instead of the the foils being continuous, they're connected via wires.

Electrically, its exactly the same before or after the cut & shut, and you'd charge it just as you did before!

A crucial point is that you might not cut it exactly in half - say you chop it into a third and two-thirds.

The resulting two small lipos are clearly different capacities, and individually you'd charge the larger one at twice the current of the smaller one.  But parallel them back up and you're back to the one big cell, which you'd charge as you did before before the chop!

Cheers   

Phil

PS dont chop lipos up with a laser

Edited By Phil Green on 26/05/2014 21:10:29

[Paul Marsh]

I've got one of these. Only problem it can only charge 5A per channel, or 50W each, but good enough for most stuff.

[John Olsen 1]

Phil, your theory is all very well as far as it goes, but what about the situation where I have been flying with two packs. (one at a time.) The first flight was cut short for some reason, the second went a bit longer. So now I have the two packs with one at say 3.9 Volts per cell and the other at 4.1. What happens when I parallel them up for charging? I notice that my charger says that the resistance of each cell is of the order of milliohm or so, so a difference of 0.2 Volts could drive a current of the order of 100 Amps between the cells. So although my charger is supposed to be able to parallel charge I have never actually tried to do it. It might be different if I was using two packs in series, eg 2 4S to make an 8S. Then they would have seen the same discharge, so should be at the same level for charging in parallel. I would still probably make up device to allow them to be paralleled with some resistance first, eg parallel them with maybe a 1 Ohm resistor between each balance point, and leave them like that for a minute or two before paralleling them on the charger without the extra resistance.

I'm actually using one of the big Fat boy chargers from HK. This allows me to charge my biggest cells (6S 5000mAh) in about half an hour, depending on how hoonish I have been during the flight. That is actually plenty fast enough as usually there is a bit of chatting with the guys between flights, and I have two batteries for that plane. So by the time I have talked to the guys and done a flight on a battery, the other will be pretty well ready to use.

John

[Tim Mackey]

I have advocated parallel balance charging of same cell count batteries for years - theres simply no good reason not too. As for imbalance with packs before you start, then providing the voltage difference is not huge, then just plug in the main plugs to the balance board first, and any "rush of current" from the high pack, to the low pack, will be via the main leads, not the balance leads. people often worry about this, but frankly its not an issue as any current flow from one battery the other will be over in a fraction of a second, and both batteries are now seen as one - its IMPOSSIBLE for two or more batteries to be at different voltages if their terminals are all connected to common nodes.

I have been doing this for years, and sometimes with some quite large variances in voltages, and have never even seen a spark!

Parallel charging boards have a lot going for them, as not only are the packs equalizing themselve, but also, so are the individual cells. Only one caveat - occasionally do each pack separately, preferably on a discharge /charge cycle and ascertain exactly what charge is being put into it from "empty" as well as spotting any potentially weak cells.

Of course, irrespective of whether you parallel charge, fast charge, or whatever........ the real limiting factor of any charger, single or multi port, is WATTAGE - as well as the supply thats feeding it

[gary watson 2]

Phil i am not against parallel charging its just that i dont know enough of how to do it safely !

[IanN]

Genuinely nteresting thread.

It might seem a strange thing to say in 2014 when many modellers are electric only, but I'm "on the fringes" of electric so far as my knowledge is concerned, and my approach is very much to use budget components and operate them well within their stated limits.

I hadn't heard of parallel charging, but having done a few internet searches this evening I'd convinced myself it was the way to go. If I've read it right, my (no doubt in many peeps' eyes) modest 80w charger will cope with three 2200 3s packs at a small fraction under 1c

If Tim says its all good, then that's good enough for me. Only q is how. HK do cheap enough balance boards, but the shortness of the balance leads on most LIPOs looks like its going to be a bit awkward to use them. So, I guess I'll buy a board and some balance lead extensions and give this a go

[Lazygit]

Posted by Tim Mackey on 26/05/2014 23:12:37:

I have advocated parallel balance charging of same cell count batteries for years - theres simply no good reason not too. As for imbalance with packs before you start, then providing the voltage difference is not huge, then just plug in the main plugs to the balance board first, and any "rush of current" from the high pack, to the low pack, will be via the main leads, not the balance leads. people often worry about this, but frankly its not an issue as any current flow from one battery the other will be over in a fraction of a second, and both batteries are now seen as one - its IMPOSSIBLE for two or more batteries to be at different voltages if their terminals are all connected to common nodes.

You may be correct, the pulse of current between batteries of differing voltage will be over in a fraction of a second, The questions are, how big is the pulse, and how long is it and what effect does it have? Until those questions are answered saying it is not an issue is without foundation. Batteries are not capacitors which store charge directly, they are miniature chemical processing factories. Even charging batteries on their own, well within their specified limits they will never lay down the chemicals in they they were when first manufactured. This is one reason batteries have a life that eventually comes to an end, and the battery fails. Slamming high current pulses in will shorten their life, just as does fast charging, fast discharging, deep discharging, overcharging. Do these high current pulses make a battery more likely to fail catastrophically? If your answer is no, you should provide supporting evidence. If the answer is "possibly" you should stop doing it. Catastrophic lipo failure is, well, catastrophic. Ask someone with no house as a result. If the manufacturers say it's ok to parallel charge, that's fine, they have done the work to justify it, otherwise just buy another quad charger. Even at £100 it is still a pretty low cost, one time, insurance premium to help give batteries the best care possible, maximise their life and reduce the risk of catastrophic failure.

[Phil Green]

You're right LG in that its pertinent to treat lipos with respect.

The ESR under charge is much higher than the discharge ESR. This is one reason why you charge at a much lower current than your motor draws in flight. Hence paralleling cells of different charge state will not result in a huge inrush current. Say the discharge ESR is 10mΩ and the charge ESR is 90mΩ, and there's a difference of 1v between the two cells you're about to parallel. The result cant exceed a momentary 10 amps which will drop exponentially in a fraction of a second - and a 1v difference is quite an extreme case, its the difference between fully flat and fully charged.

 

 

Edited By Phil Green on 27/05/2014 08:32:56

[Peter Beeney]

Just for what it's worth, if anything, my take on this is just that the current flow between batteries when connected in parallel in different states of charge is proportional to the voltage differential between the packs and the total resistance of the circuit.

I did a practical check on this once upon a time, just to confirm what I thought would happen. Two 2,200 mAh 3S lipos, one fully charged to 12.6V, the other totally flat at 9V. With both negatives connected together the voltage difference between the positives was, as I remember, slightly less than 3.6, the voltage on the flat battery is always going to start to recover, if only by small parts of a volt.

On connecting the positives together the instantaneous current was 15 amps; however this immediately began falling at the rate of about 2 amp/second for about three seconds, it then started to slow and after 10 seconds there was slightly less than 5 amps changing places. From then on the rate of change, amps per second, really began to decline but nevertheless getting smaller all the while. This is simply is a result of both voltages equalising. In the normal course of events I’d have thought that it’s unlikely 2 batteries will normally be connected together in this state anyway, it would most likely be accidental. I personally don’t consider this has damaged my packs in any way, they are both still going strong, along with the others. Theoretically a half charged battery and a half flat battery would have the same voltage, therefore no current transfer, so from say both packs being flat up to this point it should be possible to parallel them together without too much bother.

Any number of packs can be connected in parallel for charging, providing they are all the same voltage. To get an accurate charging rate, add all the capacities together, lets say that might be 10,000 mAh, then if they are then charged together at 10 amps they will all be charged at the 1 hour rate, 1C, irrespective of their individual capacities. The balance leads are also connected in parallel, if all the voltages in adjacent cells in the individual packs are the same there will be no current flowing in the balance leads anyway. Usually there is a few millivolts difference, though, therefore any current flowing will be proportional to this, very small. It’s only the end pair that might have to carry all the current, but they are in parallel with the big power leads, so no problem there, either.

I’ve always considered that the consumer cells, of which there are a great many varieties, can tend to have have a built in obsolescence. They are ideal candidates for this. I’ve checked numerous new tx and rx packs over the years, and occasionally they come with one faulty cell; I think too many to be a coincidence. I’ve also bought some cheaper high capacity nimhs, just to see what they can do, and they can be so useless that they might be rejected at the local tip as unsuitable for scrap! Industrial types can be much better, I have a rechargeable torch with nicads from circa 1980, still using the original pack, (and bulb), and that’s still going strong. It gets used regularly, mostly in the winter, of course. Bigger installations can also last for many tens of years, although the progress in technology of the equipment they inevitably serve says that everything is upgraded every few years. At least, that’s how it used to be…

I’d consider that flying a lot of electric soon makes me familiar with it, so I’d try and make it as foolproof as possible. Such as making connections impossible to get the wrong way round; polarised is the technical term; also when doing the actual linking if I’m not entirely satisfied by checking the voltage difference to be on the safe side. It could be up a bit, between two 6 packs, say, up to a possible 7.2 volts, although the total circuit resistance will also be proportionally higher, too.

With the correct necessary connection items to hand parallel charging is a doddle.

PB

[Peter Beeney]

I said ‘providing they are all the same voltage’. To be absolutely clear, it would have been better if I’d said ‘providing they are all the same number of cells. Slightly differing voltages is not a problem, if they’ve been discharged a bit they will connect together without even noticing it.

PB

[Tim Mackey]

Posted by IanN on 26/05/2014 23:31:25:

Genuinely nteresting thread.

It might seem a strange thing to say in 2014 when many modellers are electric only, but I'm "on the fringes" of electric so far as my knowledge is concerned, and my approach is very much to use budget components and operate them well within their stated limits.

I hadn't heard of parallel charging, but having done a few internet searches this evening I'd convinced myself it was the way to go. If I've read it right, my (no doubt in many peeps' eyes) modest 80w charger will cope with three 2200 3s packs at a small fraction under 1c

If Tim says its all good, then that's good enough for me. Only q is how. HK do cheap enough balance boards, but the shortness of the balance leads on most LIPOs looks like its going to be a bit awkward to use them. So, I guess I'll buy a board and some balance lead extensions and give this a go

I have several of the HK boards, and have only come across one that belonged to friend which showed evidence of poor soldering - and it was easily rectified in a few minutes. The biggest cause of problems with them, is in my experience, operator error ( as usual LOL ) in so much as due to the way the individual pins are connected up, on a PCB, then each long edge of the board will have the balance sockets orientated at 180 degrees to each other, so the balance plugs are positioned in opposite orientation.

Having read that last paragraph, its very poorly worded, so I will attach a few pictures shortly to illustrate

Basically people try to force plug the balance plugs in the wrong way around and this causes a short, which inevitably burns out the PCB track underneath the surface - again, easily repaired if your handy with a fine tip soldering iron.

Ive done a few of these repairs for friends

[Tim Mackey]

First up, general view of a couple of parallel balance boards connected to chargers.

One is a commercially available HK board that will take up to SIX batteries., and the other is one I made myself as I need to be able to do 10S batteries occasionally and couldnt source a suitable board.

[Tim Mackey]

The home made board can do up to 4 x batteries at once, and accomodates any battery from 2s right through to 10s. Obviously, only multiples of the SAME VOLTAGE batteries can be done on a parallel board, although battery capacity may vary. If for instance, I am doing a 4s 2200mahr, and a 4s 4000mahr together, then the combined capacity and voltage as seen by the charger, will be a single 4s ( 16.8v ) at 6200mahr capacity. If I wanted to charge this at 1C I would set the charger to 4s 6.2A.

Here you see me charging 2 x 9s 4000m/a packs in parallel, and I am fast charging them at 2c.

2 x 4000ma packs in parallel = 8A capacity, and to charge at 2C = 16 Amps

[Tim Mackey]

As you will see from the last two pictures below, the main lead XT60 plugs and sockets are arranged in a straight line down the middle, and it doesn't matter at all which sockets you choose - as like the balance sockets on the boards THEY ARE ALL IN PARALLEL and therefore just "piggy back" each other.

This only applies to PARALLEL charge style boards.

However, as I so poorly attempted to explain a few posts back, the layout of the board circuitry necessitates ( for easy track wiring ) that the balance sockets are "reversed" in their physical placement on the board - forcing a battery balance plug in the wrong way around WILL burn out the copper track, and as recently happened to a friends board, also "blasted" a pin out of the offending socket too!

Now Im never one to scaremonger, and as stated several times, am a BIG fan of all things lipo, and will restate, that parallel balance charging is fine - all it needs, as with lipo maintenance and use in general, is care and attention to what you are doing!

[Tim Mackey]

This crudely photo-shopped texting may serve to illustrate even further the socket orientation

[steve-richards]

**LINK**

I use one of these and suits me