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Old 06-18-2014, 08:52 AM   #1
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Default Doubling ... Tripling up LiPo packs ?

OK.. before anyone gets wrong idea ... my main point here is to get people to post their experiences so anyone looking to do this can gain some advice / info to help.

Lets take my LiPo inventory ......... I have literally a box full of 3S packs, mostly in the 2200 size... 25C

I am looking at maybe putting together a model that will take a 6S capable motor and that means 6S LiPo ... so why not double up some of my 3S jobbies to get the required.

Care of course has to be in the main wiring going to ESC as now we are talking over 22V etc. that with maybe 20 - 30A is a lot of power ...
The LiPo's series connection has to be made with care as well ... and of similar good grade wire.

So I'm now asking for examples of models ... type, size, weight along with some battery, motor, ESC details etc.

This will go a long way to help those venturing into this arena ...

It can also assist those who are considering altering a moderate sized or larger IC engine model to E-Power.

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Old 06-18-2014, 01:23 PM   #2
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Nigel,

Not sure of direct relevence but I run series connected packs on a couple of my helis. The 600 size heli runs two 6s 3000mAh packs in series to make a 12s 3000mAh. The 700 size heli is similar but uses 5000mAh packs.

Probably the simplest way to connect them up is by using bullet connectors on the battery and ESC leads, that way you dont need any special harness. But a harness is very easy to do if you want to retain the standard two pole battery connectors (Deans / XT60 etc).

They work just as you would expect, there really is no down side to running series packs other than a slight increase in wiring complexity.

As for power.. Obviously lots of power is potentially available when you start increasing voltage. The 700 heli will touch 6000W without even pushing very hard. The advantage of going high cell count is that you can keep current relativly low for the same power, so your ESC can be smaller. On the other hand if going above 6s you generally need a high voltage ESC which tend to cost more, for your 6s idea though a standard 'low voltage' ESC would probably be ok as many are rated for 6s, but it would have to have a switching BEC because a linear one wont cope with higher voltage input, or use an external BEC.

You obviously need a lower Kv motor than you would need when running lower cell count.
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Old 06-18-2014, 01:31 PM   #3
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PS.. I did also briefly run two 3s 2200 packs in series on one of my 51" span 3D aerobatic fixed wing models. I uses a 480Kv 170g Turnigy motor and a 14x7 (or 15x7) prop. It kicked out well over 1kW and performed very well.
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Old 06-18-2014, 07:16 PM   #4
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I have an old Goldberg Eagle 2 that has a been converted to E power. I run 4 2200/3s/30c cells wired to run 22V. I have them so i can disconnect them and use them in a normal 3 cell 2200 config. I built a special harness to connect the mess together with the heavier Deans plugs. I also have a 4400/6s/50C pack too.
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Old 06-18-2014, 07:32 PM   #5
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You can parallel same cell count as long as you want. No restriction on capacity or C rating but you should treat the result as if it was all the lowest C rating pack in the paralleled group.

Yes, you can parallel a 100 mah 1S with a 5000 mah 1S (if you can find a 5000 mah 1S) You get 5100 mah 1S.... or a 100 mah 6S with a 5000 mah 6S (if you can find a 100 mah 6S) You get 5100 mah 6S.

You can put packs in series only if they are the same capacity and C rating. Mixing capacity or C rating will lead to destruction of the lower current/capacity cells. The hither current cells will force the lower current cells to carry excess current. The lower capacity cells would deplete below minimum safe voltage before the LVC cuts in.

I commonly run 3X 4S or 4X 3S in series for 12S. 3300 mah to 5000 mah packs (always the same capacity and age packs bought as a set)

I occasionally parallel packs. I'm more likely to parallel charge than to operate a model with parallel packs though.
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Old 06-18-2014, 08:07 PM   #6
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I run parallel 3S and 4S in my Concorde ... sometimes I do run them split ... separated to each motor individually ...

I occasionally look at models that require 5S and 6S ... and look at the LiPo inventory I have ... 6S or 8S would not be a difficult thing for me to do ... only side is I do not carry really large mAh size ... largest in 3S I have is 2200 and in 4S is 2700 ... I have a couple of 5S 3000's ...

But loads of smaller stuff ...

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Old 06-18-2014, 08:30 PM   #7
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You can do parallel AND series... just make up series for capacity and duplicate it to put in parallel.

EG 3S 2200 + 4S 2200 in series for 7S. Do it again and parallel it and you have 7S 4400

You just have to equal the rules for paralleling and putting in series at the same time... so mixing capacities gets difficult.
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Old 06-18-2014, 08:51 PM   #8
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This is all good and I hope that any newcomers who are looking at this can learn from it ...

Cheers
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Old 06-19-2014, 05:58 AM   #9
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Now here's an interesting point ...

Lets say you have a 6S combo or higher ... made up from 3S packs ... and a uBEC that is not capable of connecting to such a high voltage source ... why not plug into the balance lead of one pack. Then that will be a 3S source to the uBEC but still a high voltage pack for the motor ... with all packs connected and staying relatively same power level ...

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Old 06-19-2014, 12:03 AM   #10
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For the 4400 pack I series (2) 2200 packs for 22V and do the same to another 2 then parallel the 2 packs together. I can take them apart so i can still use them individually if needed.
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Old 06-19-2014, 02:05 AM   #11
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Main problem with doing a parallel-series connect is its SOOO easy to mis-connect and blow up 2 or more packs.

You can build a harness to prevent that.
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Old 06-19-2014, 03:33 AM   #12
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i have batteries to be used for specific planes and in all different sizes of c and mah ratings.

now as for the main batteries i run as series packs has always been my preference over buying larger cell count packs. theory is as follows. all zippy batts from hk.

i have six 4000mah 40c -3cell
four 4000mah 40c - 4cell
three 4000mah 40c - 2cell

i run series for the hog bipe on 6cells,the greatplanes extra 300s runs on 7cell,lastly the greatplanes rv 4-40 runs on 5cells.

a plus is the greatplanes edge 540t uses the 4cell 4000mah packs to fly 10+minute flight with tons of throttle and vertical climbs.

i used two 4cell 2200mah 20c batteries in parrallel in the towerhobbies uproar as they fit perfectly in the fuel tank compartment with my conversion kit build and the weight gave cg without adding lead anywhere.it crashed last year and i have the 8 old 2200mah 20c packs laying in storage with many cycles run through them.


the main reason i like series is if one cell goes bad in the pack i don't loose the use of a 5,or6,or 7cell lipo that cost more to purchase than the smaller packs run in series. also i can easily build for a 8cell or 9cell or 12cell running 3 packs in series. it a win win situation. even though my battery storage cabinet looks over filled,i use these packs often enough to keep them charged and cycled. then held in cool storage at storage charge level.

i also use the deans series plug from headsuprc and i made one as its easy to do. i also made my own parallel harness.


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narrow is the place to land...wide is the space to crash....choose the narrow way!
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Old 06-19-2014, 04:29 PM   #13
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Originally Posted by fhhuber View Post
Main problem with doing a parallel-series connect is its SOOO easy to mis-connect and blow up 2 or more packs.

You can build a harness to prevent that.
I work in the electrical industry, so DC wiring is easy for me. I build 200-500 amp alternators from scratch.
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Old 06-19-2014, 07:07 AM   #14
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Nigel,

To power the BEC you can just tap into the wiring harness between the two series batteries (for BEC positive) and to the negative harness wire (for BEC negative). This is exactly how I power the BEC on my 600 size heli. I'm personally not use the balance wires as they are fragile and not necessarily rated for the current a BEC might pull.

Castle have a wiring diagram showing how to do it (and how not to): http://www.castlecreations.com/produ...multicell.html
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Old 06-19-2014, 07:44 AM   #15
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Both are valid ... balance lead or tapped of main.

Why I would look at using the balance lead .. is to lessen the wiring clumped around the battery bay.
The balance lead of one pack could slide out from the mess and be used with uBEC away from the rest.

I agree that odd packs do have leads that are less flexible and can break of ... but I've only had that happen on one pack in many. That was principally my fault anyway - pack was jammed in hard in a model due to puffing slightly. I pulled on it - then used the balance lead as well ... I know - we shouldn't do that ... but be honest - I bet we've all done that at some time or another !!
The pack had the lead resoldered and soldiered on.

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Old 06-19-2014, 08:33 AM   #16
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Nigel,

Yes, both should work but as i said, the balance leads are not rated for much current so personally I'd not use them for something as critical as powering a BEC. But i dare say it would work ok most of the time.
The other hazard with doing it that way is you could very easily connect to the wrong balance lead and leave the BEC receiver and servos floating above ground voltage making the system prone to shorting. This is why the Castle instructions warn against wiring to the positive side of the series harness.

The advantage of wiring into the harness is that the BEC is on automatically when you plug in the flight battery. It's impossible to power up the ESC and still have the BEC isolated, as would be possible if you wired the BEC off the balance lead.

As for clutter, it really makes no difference wherever you connect the BEC wires. They can be routed away from the battery bay either way.
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Old 06-19-2014, 09:31 AM   #17
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Originally Posted by JetPlaneFlyer View Post
Nigel,

Yes, both should work but as i said, the balance leads are not rated for much current so personally I'd not use them for something as critical as powering a BEC. But i dare say it would work ok most of the time.
mmmmm I'll take a rain-check on that ... some high power chargers balance at high amps through the same lead ...
I wouldn't advocate pulling steady 10A through a balance lead ... but 4 or 5A is well within it's capability I'm sure... with occasional spike high demand. Lets be honest - the balance leads wires are usually larger gauge than the BEC's - they are on mine anyway !

The other hazard with doing it that way is you could very easily connect to the wrong balance lead and leave the BEC receiver and servos floating above ground voltage making the system prone to shorting.
?? Sorry - you've lost me there ... Lets take 2 x 3S packs connected ... doesn't matter whether parallel or series. We connect BEC to a balance lead of either of the packs ... the MOST the supply will be is the full 3S pack .. which is well within capability of the BEC. You could if you wanted to use other pins on the balance plug to tap of 2S ... but no need .. 3S is fine.

This is why the Castle instructions warn against wiring to the positive side of the series harness.
+ve side of harness ? A balance lead is a balance lead .. I'm not sure what is meant there ... I'm going to read through and see what they mean there ... I have a dicky internet connection and downloads are difficult - but will try !

The advantage of wiring into the harness is that the BEC is on automatically when you plug in the flight battery. It's impossible to power up the ESC and still have the BEC isolated, as would be possible if you wired the BEC off the balance lead.
I wasn't aware that any ESC would 'fire' up now if no signal .. If Rx is not powered up - there is no command to initialise the ESC.... But if there is an ESC that could fire up without Rx - then point taken ... but is there such an ESC ?

As for clutter, it really makes no difference wherever you connect the BEC wires. They can be routed away from the battery bay either way.
Actually my Concorde has this problem and I removed the BEC for this very reason - clutter. I reverted to built-in BEC. I did look at BEC via the balance lead ... the space is long and thin .. and the balance lead allowed me to lay it and the BEC lead alongside the nosewheel unit... too slim there for power leads etc. But in the end did away with it and squeezed the main leads in where best I could get them. It is also part of the reason why sometimes I parallel the packs and other times not. Some packs have main and balance leads exit same place ... others have them opposite corners same end - this is enough to alter my installation.
My big F16 ... I used the balance lead - again to clear the limited space ...It was easier than removing more foam from the area.

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Old 06-19-2014, 09:51 AM   #18
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OK ... looked again at the CC BEC schematic ....

a) It does not in any way show Balance lead use.

b) The +ve side as said - of course no-one would do that unless total voltage is within BEC capability.

Use of balance lead for power ........... mm it 'could be possible' on reflection to connect badly .. I'll have to wait till I get home to check this out ... easily done.

Connect up two packs and then meter the balance leads ...
In parallel - it will not make any difference which balance lead you use - you will only get maximum of a single pack voltage - not combined.
In series ? That needs to be checked because the -ve leads of BEC and ESC will be common through Rx bus, with +ve ESC from the total pack ... mmmmm

EXCEPT ... the CC BEC diagram is specific to a BEC that is max. 25V in and the combined pack is 12S ... over 44V....

For any combined pack of 6S or less as I am considering - you can take total voltage of the combo or individual pack to the BEC ... all my uBEC's are 6S with some up to 8S capable.

Interesting..... the real crux comes down to max voltage of the combo and what voltage the BEC can accept.

I will still look at combo results via the balance lead of each ... out of curiosity ..

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Old 06-19-2014, 05:55 PM   #19
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Originally Posted by solentlife View Post
?? Sorry - you've lost me there ... Lets take 2 x 3S packs connected ... doesn't matter whether parallel or series. We connect BEC to a balance lead of either of the packs ... the MOST the supply will be is the full 3S pack .. which is well within capability of the BEC. You could if you wanted to use other pins on the balance plug to tap of 2S ... but no need .. 3S is fine.
It's a hard thing to explain but I'll have another go....
The BEC must be grounded to zero volts on the negative side, so you must connect it to the negative wire in the series harness. The positive BEC wire then goes to the jumper wire in-between the two batteries.

If you do it the other way and connect the BEC negative to the jumper and the positive to the battery positive then you still get the same voltage to the BEC, but the BEC earth is now floating at the voltage of the jumper wire (25 volt for a 2 x 6s flight pack). This means that the earth of the Rx and the servos is at 25v which gets really bad when you consider that the earth of the ESC is at zero volts. So when you plug the signal wire of the ESC into the Rx... POOOF
If the ESC is 'OPTO' (optically isolated) you might get away with it but if not it's curtains for pretty much all your electronics.

This is why CC instructions specifically say NEVER DO THIS in big red capital letters in a big yellow 'flash'.


Same thing would happen if you connected to the balance lead of the wrong series battery pack, which would be VERY easy to do.
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Old 06-19-2014, 04:39 PM   #20
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Same rules for use when its a pack all in one shrink wrap. Don't tap a partial voltage for the BEC. If you need partial voltage then you need a separate RX pack.

Most balance leads are only good up to appx 5 amps. Some RX systems can demand over 12 amps...
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Old 06-19-2014, 06:08 PM   #21
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Originally Posted by fhhuber View Post
Same rules for use when its a pack all in one shrink wrap. Don't tap a partial voltage for the BEC. If you need partial voltage then you need a separate RX pack.
Tapping partial voltage is perfectly ok providing you do it the right way, as per Castle Creations wiring diagram posted previously. I've been flying my 600 heli that way for ages, it works perfectly. IMHO, even if the BEC is rated for full voltage it's better tap off partial voltage for the following good reasons:
  1. BEC current output will be higher with lower voltage input due to less switching losses. In the case of the CC Pro BEC the constant output at 24v input is 13A but at 48v it drops to 8A
  2. It allows powering up of the BEC and radio without powering the ESC and motor (by just plugging one battery), which is a good safety feature when setting up the model.
  3. BEC is less stressed and runs cooler which seems according to many reports to increase reliability.
  4. Saves weight, complexity and clutter of a separate pack, and removes risk of forgetting to charge the separate pack.

There is no downside. The mAh used by the BEC is so low that the effect on battery depletion is un-noticeable. As far as I'm concerned the only time it makes any sense to run a separate Rx pack is if you power the Rx direct from the pack without a BEC. These days that's easy by using a 2s LiPo and HV servos.
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Old 06-19-2014, 05:04 PM   #22
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For more then 4 standard servos i use a buss bar and a separate RX pack
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Old 06-19-2014, 06:37 PM   #23
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The Cub I'm building I have a separate motor batt and RX/SX batt. The ESC only runs the motor and the RX/SX are only run from their own batt and the RX has it own batt on a buss bar system. It has 7 SX's and the ESC so I don't want to tax the RX and lose signal. A lot of plugging in but I did this on another plane with good success till Some moron at the field turned his TX on the same freq (FM of course) and snuffed the plane. Oh well , to the next plane. That why they produce kits.
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Old 06-19-2014, 06:50 PM   #24
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Originally Posted by propnut48 View Post
till Some moron at the field turned his TX on the same freq (FM of course) and snuffed the plane.
Sounds like you need a 2.4GHz system.

On the 700 heli I run four 75g high power, high voltage, core-less, digital servos which especially on a heli pull pretty high current. I run these direct from the receiver (FBL controller actually) and it's fine, but I have rigged up dual power input wires from the Rx battery (no BEC). This is because each connector on it's own is only rated around 5A, so no point having a 13A BEC if you have it connected to the Rx with one 5A plug
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Old 06-19-2014, 07:40 PM   #25
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I do now, that was 5 yrs ago
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