Balance charging 3S lipos in parallel

[winchweight]

Hi guys. For my Mohawk I am using 2 x 2500mah 3S lipos soldered together in parallel. I have balanced charged them and have found that they don't seem to need charging seperately, that using the balancer connected to just one of the batteries does all the charging for both.

I tried to charge them seperately to check, even disconnecting them, but no, after a balnced charge in parallel, both were indicating fully charged.

Is this right or am I doing something wrong?

I assume that by having 2 x 2500mah batteries in parallel, I get 5000mah in effect?

[Robert Bromwich]

HI Shaun

If im reading this right then you have got both the reds and blacks (main power cables) soldered together to give you 11.1v 3s still ? 

then you are charging using just one 3s balancer lead to one of the batterys? the problem with that is your only balancing one battery as the power to charge the other is going down the power leads !

What you need to do is disconnect the power leads and use or make a 6s balancer lead using 2 x 3s leads this will charge both at the same time as a 6s battery and balance both the same.

You can then connect them back together as 2 x 3cells

 Rob

[winchweight]

Ahh.... of course. The second pack is still being charged by virtue of being connected to the first pack. But it's not being balanced as it's charge via the cables. I get it now.

I'll do them seperately in future.

Thanks

[Phil Winks]

just my 2p worth Shaun but would it not be best to keep the bty's seperate and wire 2 connectors to the esc so that the bty's are connected 1 at a time but are still in parralell when fitted. mind you I've seen somewher that wen used like this the bty's need to be fairly closely balanced as a pair or one may be depleted before the other as the esc can only see the best pack so altering the bal lead and charging together as a 6 cell pack may be the best way. think we need Timbo's imput here  so come on master of electrickery  what do you suggest

[winchweight]

Dunno..... I await the guru

[Phil Winks]

Like loyal believers we wait patiently in line Tim

[Tim Mackey]

Hi guys....'tis the funeral this morning, so I am just distracting myself for the next 10 mins.

The ONLY correct way to deal with this type of scenario is to connect things in such a way as to ensure that all cells are separated from one another by series wiring, for charging and balancing purposes.

If you really want to be able to guarantee levelled cells, then keep the 2 x 3s packs seperate, and use a connecting harness ( like a "T" piece ) to connect both packs together for flight. Then, separate the packs after use and  charge as 6s ( by re-connecting the packs back into series of course ) and insert each balance plug into a 3s balance socket on your balancing equipment, charging at 2.5A. Or again, make up / buy a little adaptor to convert the 2 x 3s balance plugs into one 6s plug. The method you choose will depend on the socketry of your balancer. In use, after connecting together, the main packs as a battery will even each other out of any minor potential differences.

Alternatively - you could ( and knowing you Shaun you probably will not want to ) permanently connect each battery together in parallel, and then find each cell designation of each battery and connect that cell to its "partner cell " in the second pack together and take out one balancing lead to a new 3s balance plug......thus creating one permanent larger capacity cell IYSWIM. Do the same for all, and end up with effectively a 3s pack again, used, charged and balanced as a 3s. The pairing off of the cells should ensure each pair keep themselves evenly matched, as it is actually impossible to have two cells or indeed two batteries connected in parallel and show anything other than one particular voltage at the terminals. One further consideration is the charging......a large capacity pack such as this ( 5000 m/a ) will require a charger capable of supplying 5A and 12.6V which equals 63 Watts ( in reality it will be slightly higher to allow for cable and component losses etc ) and many chargers are often only around 50Watt capable. The wattage of PSU driving the charger will need to be even higher at around 75Watts or so.

Of course you knew that didnt you grasshoppers, as you have all read my article in last months mag!!

I also think that with good quality packs, that have been made from well "matched" cells balancing may not be necessary every time. I have 2 x 3s Kokam packs here which are still behaving well after 5 years, and due to having no balance plugs fitted back in them olden days, have NEVER been balanced, yet were used mainly in parallel, and sometimes charged separately, sometimes in series, and sometimes in parallel !

[Phil Winks]

Thanks Tim very informative as usuall sorry to hear about the funeral had no idea take care Phil

[Tim Mackey]

Thats OK Phil, will all be over by midday, and the family can then start getting back into some sort of normality.

guess you missed this thread.

Would normally be "covering" for David as he is on hols for a week or so, but you guys will just have to behave while my back is turned

[Phil Winks]

I'm certain that while the cats away the mice will be good  boys and girls Tim

[winchweight]

Cheers Timbo. Sorry to hear about your loss, I have been there but a few years ago. I was 22 and out in the first Gulf War at the time. Came as a shock.

As for the packs, they are connected by a sort of Y harness, so I can seperate them for charging.

I guess I only need to pull one lead apart to break the parallel circuit?

[Phil Winks]

your right there shawn I assume your charging out of the plane of course  the advantage I see of keeping the packs seperate is they can then be used elsewhere as 3s 2500mah if you require as such I'd leave the Y harness in the plane and remove the bty's individually

[winchweight]

I always charge in a lipo sack, just to be sure.

As you say, the batteries can be used seperately, although as yet I have nothing suitable.

[Phil Winks]

one thing is certain Shawn you would have the minute you committed to soldering them into a 6 cell pack lol. actually the free plan this month would be a most likely subject for a 2500 3s running a 20a motor 200w ish should do a proper job of getting that one round the sky me thinks

[Rick Brayford]

Hey guys

Very informative dialogue regarding 3s 2xp. I am relatively new to Elekrickery but now have the opportunity to jump to 6s using my two Evo lite 4250ma(Kyosho Spit 50 EP). I would like to charge seperately but cannot work out the configuration of the Y or T lead? I usully use Deans plugs but are willing to change plug design if needed.

Phil, you suggets leaving the harness in the plane and removing the batteries seperately but I am unsure of configuration and set-up f wiring.

Any advice gratefully acepted.

Rick

[Phil Winks]

ok rick it's not really that difficult wen you see how (hard if you don't know though lol) if your good at soldering then from the esc bring 4 wires (2 red from the +ve & 2 black from the -ve) these simply go to 2 deans as normal (ie: 1 red and 1 black to each) if you don't want to mess with solder on the esc circuit board simply buy one of these and insert it between the deans on the esc and the 2 bty packs voila as they say be aware that this is effectively lengthening the bty to esc lead though and so get some ferrite rings for your esc to rx lead to deal with any potential rf spikes that may occur

[Rick Brayford]

Phil, your thread on the deans set up looks acheivable to me. It seems to be saying that utilising that parellel connector will double milliamps. Will this also take me from 3s to 6s ?

rick

[Phil Winks]

No in parralell what you will get is same volts ie 11.1v but double cappacity ie: 2 1200mah will give you 2400mah to increase to 6cell voltage you need the connect in series this will double the volts but not the affect mah so to summerise from two 1200mah 3cell packs you can in paralell get 11.1 v x 2400mah and the same packs in series will give 22.2v x 1200mah hope this makes it clearer

[Rick Brayford]

Many thanks Phil. Clear.

I am going to solder up a lead based on your thread.

The ESC is Hacker SB 70 prowith ferro ring fitted. Do you think that is sufficient?. At this stage I hope to not have to run a seperate flight bty.

rick

[Tim Mackey]

I dont think Phil ( or indeed any of us ) could give an answer to that Rick. The parameters to "worry" about with the ESC suitability are

1) Current rating is sufficient ( with a good margin ) for the expected current draw.

2) That it is suited to the cell count being used - many are limited to 4 cells or so.

3) The BEC if used is capable of working from the cell count, and also capable of supplying the radios requirement.

4) The LVC is programmable to correctly match the cell count - or auto detects them correctly.

As for the ferrite ring / interference situ - this in itself may not be sufficient. careful  installation, and isolation as far as practical from the radio is required, long leads should be avoided, and so on...but no guarantees with this stuff I am afraid.

2.4Ghz does offer the very best solution to leccy flight, and IMO is pretty much the only almost guaranteed route to glitch free R/C flying.

We are now drifting somewhat off topic of OP however

[Phil Winks]

thanks for that Tim. and glad I could help rick  have to say though tim that after some fettling and a little good luck I've got 4 leccy planes now that I can hand on heart say are glitch free on 35 mhz however do still suffer external sources such as the wellington wobble suffered as we pass over an electric fence at the edge of our flying field (every 35mhz plane drops about 3' as if passing through turbulence) and getting shot down by a fellow flyer who's tx crystal went of tune by 2, yes 2 channels confirmed by the appropriate bench test equipment now there 2.4 is clearly better and so is definately on my wish list now how long till santa arrives oops of topic sorry lads and Tim

[Rick Brayford]

Hey guys. I now have my two x 3s 4250ma wired in series, connected to 70amp ESC and 1100 watt motor.Set up isturning out 55amps at 1000watts on 13x8 prop (7min time). Getting alittle hot in the fuse so probably changing prop to 13 x 7. Spitfire weighs in at 2.9kg AUW. Shouldn't need too much full throttle here I'm thinking.Almost redy for maiden flight.

Thanks again for help.

Rick

[Tim Mackey]

Hi Rick Just a small point, but those packs dont seem to be holding up too well under what is really only quite a moderate load. I always reckoin that a half decent cell should be able to hold at least 3.5V under approx 75% C rate load. Some quick numbers show that at 1000 Watts and current of 55A your 6 cells are giving just 18V which is only 3V each. At 55A the packs are working at 13C ( 55/4.25 ) which is not a heck of a lot for a decent quality Lipo these days. Perhaps the use of the Evolites is the reason....after all they are only 18C rated cells, unlike the reglular FP stuff which is 25C or so. Just wondered ...thats all

My 8lb Spit flies very well on a 13 x 8 so I should think your 6lb+ model should be fine on a 13 x 7

I reckon 120 watts per pound should suffice, after all it doesnt want to be flown like a hotliner does it....therefore around 750 Watts should be ample. Please keep us posted on the flight testing 

[Phil Winks]

Tim said it all there my 1st thought was that a 1000w was a little ott for a 6lb / 2.9kg model but as long as you don't wind the trottle up to quickly on take off I guess you'll have a nice flier there with plenty in reserve under normal flying conditions