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[John Mk2]

I have X 2 4s 2600Mah Lipo paks same make , age ect. As i need a bit more run time i was toying with wiring them  in parallel.  The voltages / balance readings are identical. Safe or not

[grasshopper]

Yes - should be fine if they are identical - that applies to discharge 'c' rate as well as voltage and current rating.

[snowwolflair]

Only if you are wearing an asbestos suit

If a LiPo goes wrong it happens very quickly and the resulting explosion and fire wille wipe out your model and possibly you.

If you have to put any battery in parallel put the outputs of each battery through an individual high current diode.  You will lose 0.6 of a volt but you will be much safer.

[grasshopper]

Manufacturers wire Lipo's in series and parallel as a matter of course to get voltage and ampere/hour capacities to their required ratings.
xS means wired in series giving increases in voltage
xP means wired in parallel giving increase in A/hr ratings

Lipo's listed as xxC (20C, 30C, etc) shows the potential discharge the battery can supply,  20C in the case of a 3200mAh battery would be 20 x 3200 = 64000mAh or 64Amps

An example available:
http://hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=8580

If you have 'issues' with Lipos make sure you buy hard-case ones - and only use them as instructed, use a low voltage cutoff device and don't over charge.
Everything has potential to cause damage, but it can be avoided by being sensible and following the rules!

[nick_75au]

Safe as houses no diodes, only proviso is make sure wiring is in good condition, and keep all the paired wiring equal length.

Best way to charge them is in paralleled as well, this ensures all cells are balanced together, there are vendors selling balancing boards especially for parallel charging. (obviously they need to be the same voltage and capacity).

Cheers
Nick

[snowwolflair]

Gentlemen we are dealing with amateurs on this website not qualified electronic engineers.

I am a graduate engineer and a Fellow of the Institute of Electrical Engineers and my professional experience tells me it is a very bad idea on the grounds of safety to put LiPo batteries in parallel.  What battery manufacturers do is a design in issue not an afterthought.

Before you give such advice ask yourself whether you are prepared to compensate personally for the injuries that result from your advice.

Sorry if this seems a bit serious but death and injury it is a very serious matter.

[HS93 (RIP)]

Thank you for that  snowwolflair , it needed your post to tell people not to do it, theoretically you can in practice with model product NO

Peter

[nick_75au]

The best option is to buy bigger batteries, there is no reason for the scare tactics

A little research, common sense and if you are unsure or uncomfortable then don't do it.

OK maybe my safe as houses comment was a little flippant, batteries are dangerous.

cheers
Nick

Good info here,
http://www.rcgroups.com/batteries-and-chargers-129/

In ten minutes of searching I couldn't fine one thread with problems from running batteries in parallel, knowing that forum if it was a problem there would be a massive amount of "don't do it" threads

[HS93 (RIP)]

The best option is to buy bigger batteries, there is no reason for the scare tactics

A little research, common sense and if you are unsure or uncomfortable then don't do it.

OK maybe my safe as houses comment was a little flippant, batteries are dangerous.

cheers
Nick

Good info here,
http://www.rcgroups.com/batteries-and-chargers-129/

In ten minutes of searching I couldn't fine one thread with problems from running batteries in parallel, knowing that forum if it was a problem there would be a massive amount of "don't do it" threads

nick_75au  how do you set a voltage cut of on a  speed controller Parallel batteries that is a must if you want to use cells more than once?

Peter

[mattycoops43]

I know a lot of pilots, flying large electric models on 8 or 10s lipos in Imac competition, the price of 8 or 10 s packs is prohibitive, so many people run 2 x 4s or 5s as a matter of course. I have never heard of an issue with this ever.

Obviously you need to keep an eye on discharge levels, but then you have to do that if you run one lipo.

Matt

[snowwolflair]

Because some idiot does it does not mean it is safe.

OK let me explain.

A three cell LiPo is 11.1volts, put two in parallel when they are new and you might be ok.  After some use you will eventually get a cell failure on either battery dropping one pack to 7.4volts.  you now have a 11.1 volt and a 7.4 volt pack in parallel.

The 11.1 volt battery will discharge with a 3.7V potential into the 7.4volt battery at twenty to thirty times the maximum safe current charge rate and in seconds you will have a fire and explosion.


If it is a 30C battery rated as 5Amps thats a potential rate of 150Amps and the power equasion is "I" squared times "R" which is under a tenth of an ohm for a LiPo.

Power is 2.25KWatts in a fraction of a second.

[nick_75au]

nick_75au  how do you set a voltage cut of on a  speed controller Parallel batteries that is a must if you want to use cells more than once?

Peter

Peter,

The voltage cut off will still cut off at the set voltage regardless of number of packs in parallel, small imbalances in packs sort them selves out, It is possible to have individual cells become out of balance, this happens on single series pack as well hence the need for balance charging. Parallel charging is a valid way to charge, and is proffered to series charging Lipos as the possibility of connection error is lower.

Nick

[HS93 (RIP)]

How , two cells in parallel will be viewed as one cell by a speed controller so if one pack is better than the other or had more use one will discharge faster but the better pack will tell the speed controller that it's OK so there goes the pack. unless you pay a lot of money most individual pack alarms just beep or flash a light that you wont see or hear in a high speed boat

Peter

[John Mk2]

I know i started this thread But its sorted now on X1 4s  Just one more thing. Iam pretty sure you can use Lipos at any angle ie in helis/planes ect. Any long term damage by doing this ?

[nick_75au]

What will happen is the good cells will support the bad cells, both will show the same voltage while paralleled, when they are separated the difference will show.

Relying on just a alarm is not best practice, a li-po protection circuit is always better whether its built into the ESC or a separate unit that shuts down when the level is reached

Its not a big problem, there are threads with people who have deliberately put mismatched in capacity cells in parallel, in their case it shortened the life of the weaker cells but did not end in fire and brimstone as has been suggested.

 As has been mentioned before, the aircraft guys parallel lipos flying around with $1000+ worth of plane. If it was such a big deal don't you think there would be warnings all over the forums. Fiery crash of plane is a much bigger deal than a boat catching fire in the water.

Anyway, said my piece, there is a pile of information to read on the thread I linked to both the good and the bad of lipos.

John, Lipo wont care what direction its in, its a package sealed under vacuum.

Cheers
Nick


 

[malcolmfrary]

Iam pretty sure you can use Lipos at any angle ie in helis/planes ect. Any long term damage by doing this ?

There should be no problem at all, just avoid changing the angle too suddenly, or the speed & direction (i.e. dont whack it).
The only problem with adding cells in series is ensuring that charge state and performance of all the cells matches, if they start at different charge states, at the end of discharge, some may have gone too far, the probability is that the monitor only looks at the overall voltage, and a few marginally low cells might well be masked by the good ones.
Paralleling is another story.  Done by the manufacturer and sealed in its pack, there is no problem.   Anywhere else, they have to survive being connected, and even a minute difference in voltage will result in a massive circulation current on connection until things even out.  This is also true for lead acid, NiCad and NiMH batteries, which can be a hazard, but lithium cells are capable of much more current delivery, and any weak point in the circuit is much more liable to damage, which will manifest itself by suddenly getting hot.  If its a poorly cell, it will show itself by bursting into flame, but if its wiring to a cell that is getting hot, then there is a good chance of that cell also overheating as a result.  Not good news in either case.

[nick_75au]

I just tried a parallel connection with 2, 5000 mAH 3 cell batteries that had a difference of 1.6 volts, Im still here, what did I see, wait for it...




 nothing, not even a spark, unlike when connecting to the esc, which gives a significant crack, that is like connecting a battery with 0.0 volts to a fully charged battery, the capacitors are capable of holding significant charge, and are wired in parallel with the battery......

think about it, you want to run your boat, your going to charge both batteries on your balancing charger right, they are supposed to charge all the individual cells to within a few millivolts of each other. so the total difference is going to be say worst case 0.25 of a volt, how many milliamp does it take for your charger to raise the voltage from 4.15 to 4.2 volts per cell, its in the order of 100 milliamps or so, how can that possibly equate to many amps flowing for enough time to create heat and fire.

Remember we are talking li-pos, Ni-xx are not recommended for parallel connection as they much more likely to unbalance from each other during discharge.
 Lead batteries, I connect in series and parallel 200 Ah batteries every week, I don't check the voltage of each battery to make sure they are the same voltage, there is no need to

Nick

[snowwolflair]

 

http://video.google.com/videoplay?docid=3690260570423705609
http://www.youtube.com/watch?v=SQ0SNESIkWk

[RaaArtyGunner]

http://video.google.com/videoplay?docid=3690260570423705609
http://www.youtube.com/watch?v=SQ0SNESIkWk

Seems if you want to simulate naval battle in a model just use a Lipo 

Nick's link above also has dire warnings of Lipo fires.

Interesting thread.

[brodjack]

Nick is spot on.
Paralled lipos for use and charging for many yrs.In cars,helis,boats and planes.

[snowwolflair]

So are Nick and you prepared to state on this forum you will back this guarantee of safety with your money to compensate people relying on your assurances when they get injured? 

[malcolmfrary]

nothing, not even a spark, unlike when connecting to the esc, which gives a significant crack,

Thats the difference between a very small voltage difference and a large one, especially a large voltage difference with plenty of current generating ability behind it, and a device waiting to sink infinite current.  The pro-connecting up group are all, I presume, knowledgeable about things electrical, but they have to bear in mind that many of the members here, while they make models that I can only drool about, really know very little about electrical matters, and, given their skill set, why should they?  There is also the occasional typo where series and parallel get confused, and the occasional person who doesn't know the difference, and, maybe the majority, for whom things electrical are a black art (see the section title). 
I was taught the wonders of low voltage high current DC by a guy with slightly less than the normal number of fingers, a condition gained by over-confidence.  Having decided back then that I like having all of mine, I never quite lost the idea that caution is no bad thing.  Working on the assumption that most of the folks on here also like keeping their fingers and eyebrows, I tend toward caution when offering advice.  There are safe ways to connect batteries in parallel, but they fall into the category of "if you need to ask, its probably best to do it another way".
How much current was actually flowing into the stick with the missing 1.6 volts?  When things settled, what was the overall voltage?  Was the 1.6 volts missing from one cell or evenly spread over the stick?

[Timo2]

Hi All

         " snowwolflair " Ref :-   Pack for Cars or Boats  twin saddle packs

          ZIPPY Flightmax 5700mAh 2S3P 25C saddle pack

         http://hobbycity.com/hobbycity/store/catalog/F5700-2s3p-25.jpg

    it must work  

   Timo2

[HS93 (RIP)]

Timo 2  yes they are in SERIES to give 7.4 no problem the post is about the dangerous use of them in Parallel

Peter

[snowwolflair]

Hi All

         " snowwolflair " Ref :-   Pack for Cars or Boats  twin saddle packs

          ZIPPY Flightmax 5700mAh 2S3P 25C saddle pack

         http://hobbycity.com/hobbycity/store/catalog/F5700-2s3p-25.jpg

    it must work  

   Timo2

If you read my comments above, I said if it is designed to work that way by the manufacturer it is a different matter, these packs will have been designed by the manufacturer to be safe.

Not wired together by an amateur.

As Peter says they are series, and not knowing the difference between Parallel and Series points up the danger of amateurs getting "BURNED"