rzingsheim

My Feedback: (4)

I am considering hooking up two 3 cell lipos with 5800mah each for an electric powered plane instead of one 6 cell 5800mah. This will help with being able to put one battery in front and one battery behind the wing tube for balance and allow me to charge faster by separating them. Do I hook them up in series or parallel to achieve 22.2 volts? Will the milliamps stay the same or double also?. What happens to the milliamps if I was trying to stay at 11.1 volts with the 2 each 3 cell packs? I am converting from glow so some of this is new to me.
Thanks in advance,
Roy

ray foley

hi there from Toledo

Hi Roy


If you have two 3s packs of 5800 mah capacity you can hook them up is series to have a 6s equivalent pack. That is, nominal voltage of 22.2 VDC ( 25.2 VDC fully charged) with 5800 mah capacity. In series hookup the voltages add, the capacity does not.

And just to be complete, in a series hookup, the positive (red) of pack 1 goes to the ESC positive, the negative (black) of pack 1 goes to the positive (red) of pack 2, the negative (black) of pack 2 goes to the ESC negative connection.


If you hook the aforementioned packs in parallel, you would get 11,600 mah capacity at the 11.1 VDC nominal voltage (12.6 VDC fully charged). In parallel hookup the capacities add, the voltages do not.

And just to be complete, in a parallel hookup, the positive connections (red) of pack 1 and pack 2 go to the ESC positive connection, the negative (black) of pack 1 and pack 2 go to the ESC negative connection.



There is your answer, but ... there is more. Some serious warnings:

Never do a series hookup with packs of different capacities, NEVER EVER !!!

Never do a parallel hookup of packs with different cell count, NEVER EVER !!!

In either of the above cases there is a serious risk of fire and equipment damage.



SO, if you are new to this, have your wiring checked out by your club electric guru before actually going live.

Lipo fires are spectacularly energetic and destructive, be forewarned. However glow fuel fires are similarly destructive, six of one half dozen of the other, your choice.

ciao -rjf

chuckk2

As others have said, hooking up identical 3S packs in either series or parallel is possible.
Advantages to using two packs:
Weight distribution at the expense of slightly more weight.
Less problems obtaining large capacity batteries, due to shipping restrictions.
A failed 3 cell pack is less expensive to replace than a 6 cell, assuming the same capacity cells.
When you use two packs in series, make sure that you use the most negative battery lead as
the "ground lead".

siberianhusky

"When you use two packs in series, make sure that you use the most negative battery lead as
the "ground lead"."

What do you mean by this? There is only one negative lead in a series setup, or am I missing something?
Plug one battery + lead to the other battery - lead, leaves you with two batteries with one + and one - lead free.
Where is the "most negative" lead?

ray foley

hi there from Toledo

The "most negative lead" would be the "free ( - ) lead" of the series hookup as you have described it, this (-) lead would be hooked up to the ESC (-) lead and the (-) lead of an external BEC voltage regulator if you are using one. This is the system Ground.


A Good Sense of Balance:

In a series pack, such as a 3s lipo, the (+) to (-) joints and the (+) lead and the (-) lead are connected to the balance plug by a number of wires (four wires for 3s); starting at the free (+) lead (usually red) and proceding from joint to joint until the last connection is made to the "free (-) lead" (usually black). The "in between" balance wires may be any color, all manufacturers use different color schemes.


The voltage at each balance plug connection are as follows:

pin 1, V1, 11.1 VDC, +Vmax, the most positive lead

pin 2, V2, 7.4 VDC, "less positive or slightly more negative" than pin1

pin 3, V3, 3.7 VDC, "less positive or slightly more negative" than pin 2

pin 4, V4, 0.0 VDC, pack Ground, the most negative lead, "less positive or slightly more negative" than pin 3

For packs with more or fewer cells (N) there will be N+1 balance leads, similarly arranged.


ciao -rjf

rzingsheim

My Feedback: (4)

Thanks for the info. I am finding premade series wiring set-ups for 2 batteries that have almost no wires between them, and also ones that have short wires of various gauges. What do you guys recommend? I plan using 2 ea. 3 cell 5800 mah packs in series. Regarding the balance plug, I have never heard it described in the way that Ray did. Am I to understand that a 3 cell lipo pack is also wired in series? Thanks for your help guys. This is getting interesting.

ray foley

hi there from Toledo


Battery Pack Internal Issues:

Yes, a 3s lipo pack means 3 lipo cells (N = 3) wired in series ( s = series; p = parallel ) and connected to a balancing plug with 4 ( N+1 ) balance wires and the red (+) and black (-) power leads as described above.

Sometime you may see a pack description like "3s2p lipo" ( NsMp, M is the number of paralleled series sets of N cells each ), this means that there are 6 lipo cells ( N=3, M=2; N x M = 3 x 2 ) wired as a series-parallel network. This used to be fairly common in years gone by, not so much any more. if the cells were 2000 mah each then this pack would have 11.1 VDC ( 3 x 3.7VDC ) and 4000 mah capacity ( 2 x 2000 mah ), and four (N+1) balance wires.

An Example:

Now just to muddy the waters a bit, imagine a 7s6p A123 battery pack. I actually built one of these for a Ford Trimotor scale project.

Given: An A123 cell has 3.3 VDC and 2300 mah capacity.

How many individual cells are in the 7s6p pack?

What is the output voltage of the pack?

What is the capacity of the pack?

How many balance wires are there at the balance plug?

What are the balance wire colors?


Series Harnesses:

Regarding a series harness, It depends on where the packs need to be for C/G concerns. I generally fabricate a series harness from wire and connectors after locating the packs. Sure, each plane has is own custom wiring harness. You will want some 12 awg very flexible wire ( red and black ) and appropriate male and female connectors for the ESC and the batteries. You will need a serious soldering iron, rosin core solder, heat shrink tubing, a heat gun, and associated tools, parts, and pieces. Your Club probably has someone who can help as needed.

Less wire = less resistance = better performance, so keep the harness as short as reasonably possible and long enough for easy access and handling.


ciao -rjf


Answers: There are 42 cells (7 x 6 =42), 23.1 VDC (7 x 3.3VDC), 13800 mah (6 x 2300 mah), 8 wires (7 + 1), V1 red (probably), V8 black (probably). The rest? They may all be red, they may all be black, they may be the colors of the rainbow. Who knows? The manufacturers are not consistent. .

ray foley

hi there from Toledo

So Roy,

I think the discussion of series and parallel pack construction as well as series wired packs is fairly complete at this point but... (there is always a "but" right?)
there are always more issues.

Do you understand the idea of balancing a pack and why it is important?

Or perhaps parallel charging from a single output charger?

Or perhaps the various lithium cell chemistries and their characteristics?

This is your thread, What do you need to know?

Happy New Year -rjf

rzingsheim

My Feedback: (4)

Thanks for all your help guys,
I have some answers for Ray and some questions for anyone. I do understand balancing lipo packs. I have a number of electric planes but this is the first one I am selecting the components that go into it. I have a Hitec Multi Charger 4X and I always balance charge.
I would like run past you guys the set up I plan to use. Airplane- Aeroworks extra 300 63" wingspan. (I have 1/4 scale Extra 300-gas motor-experience). Weight with batteries should come out to 8lb 8oz. motor Rimfire 120 size outrunner. Prop APC 16x6e. Speed control Castle 90amp. Batteries 2 ea. Zippy 3 cell lipo's wired in series, 5800 mah ea. The reasons I want to use two 3 cell batteries are that I can use them in other projects, I can charge them with my Hitec charger, and balancing the plane will work out better. The battery needs to be on the spar (which is a problem) so by splitting them I don't need to add extra weight. Now for another question. I have used Deans connectors in the past and would like to for this plane also. Are there any problems you guys can see using Deans with my set up? I'd be interested in what you guys think. I have run this past some "electric fliers" in my club and I have not received any red flags. One more thing. I have an Electrifly Power Match Power Meter but I haven't received the batteries yet to check things out.
Thanks in advance,
Roy

ray foley

hi there from Toledo

Based on the motor specs and the recommended prop and battery, you should be good to go.

The Dean's connectors will be fine.

Also consider using an arming jumper between the batteries and the ESC. With the jumper out you can hook up everything safely, turn on the TX, turn on the rcvr, check all the surfaces, then last thing before you fly, install the jumper and only then does the motor/ESC boot up. And when you are done flying, pull the jumper and the motor/ESC are totally disabled and handling the plane is completely safe. I use a power jumper on all planes, safety first. (This assumes you are using a separate rcvr pack with the red lead from the ESC disconnected from the rcvr. )(or use a 3" servo extension between the ESC and the rcvr with the red wire cut out, either way will do.)

From a system architecture point of view, I use the ESC as a speed control only, I don't use the ESC's internal regulator or external BEC for power to the servos and rcvr (too many eggs in one basket, as it were). I use a separate battery pack and switch assembly for the servos and rcvr such as a 5 cell nicd/nimh or a 2 cell A123 LiFe pack.

Ciao -rjf

Jetdesign

My Feedback: (8)

I agree, system looks good. I was about to use basically the same on my 66" airplane until I realized 8S would work better for the batteries I have (5S + 3S in series). No problem with Deans. I have used them in the past but prefer a different connector. You may get more of a 'snap' with the higher cell count than you're used to on 3S.

The connectors between ESC and motor are usually 3.5mm bullet connectors. For Rx batteries you can use the JST (red 2 pin) connectors that come on the small lithium batteries, or use a standard servo plug. I have used Micro Deans and found (the hard way) that they can accidentally plug into each other.

I also use separate Rx power in the airplanes I care about, which is most. In the planes I care a lot about, I use two separate battery packs for the Rx for redundancy (these are $1000 and over airplane setups, or anything that is particularly special to me).

There are series adapters available for Deans. I personally would use this:
http://www.f3aunlimited.com/webstore...roducts_id=312

This is probably a little more traditional (a little heavier than linked above):
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXNKY9

There are arming switches available as mentioned above:
(14ga.) http://www.f3aunlimited.com/webstore...roducts_id=628
(12ga.) http://www.f3aunlimited.com/webstore...roducts_id=603
(Build your own) http://www.f3aunlimited.com/webstore...roducts_id=604

rzingsheim

My Feedback: (4)

Thanks for the info guys. For the series connector, I purchased one that each deans plug is separated by about 3 inches of 10 gauge wire in sort of a triangle shape. I figured this would give me a little more flexibility in battery placement. Not sure if the 10 gauge wire is overkill but it wasn't much more in price that lesser gauge. I have used arming jumpers like you pictured before (bought them at Toledo, forget the vender). Your answers brought up some more questions, If I go the jumper route, is 12 gauge sufficient? Is it best to use the red positive wire with for this or doesn't it matter? If I do use a jumper, should I leave the series connector hooked up to it all the time and just plug and unplug the 2 batteries into the series connector, or is it better to do it another way?
I was not planning to use a separate battery to power the servos. If I did this I would probably use a short servo extension between the ESC and receiver. Am I understanding that all I have to do is cut the red wire on the extension and the power doesn't get to the receiver, just the signal controlling the throttle? Than just use a regular battery plugged into the receiver to power the servos through a typical Electrodynamics type charge plug/switch? My Castle 90 ESC says it provides 20 amp peak with 9 amp continuous for the servos. Are you guys thinking that's not sufficient? Any enlightenment you guys can give me would be appreciated. I was hoping to avoid more weight.
Thanks,
Roy

Jetdesign

My Feedback: (8)

I think most guys that use the series adapter leave them in the plane. I personally wire my 2 battery packs together so I don't need to use one, but to each his own.

10 gage is overkill in most situations, 12 is probably more than enough.

I don't think it matters if you put the arming plug in the pos or neg side. I think most guys put it on the red wire, and that's where I would have put it not even thinking about it. It is a DC circuit, so power will not flow until the loop is closed. (ESC to motor is AC, but that is a different topic and not relevant to this).

The fewer connections you have, the better. If you can somehow incorporate the arming switch into your series adapter, that would be nice.

You have to check your ESC manual about the BEC power. With Castle Creations, I believe you are correct in that you disengage the red wire between the ESC and the receiver, and only use the signal and ground.

If you use a separate Rx battery, it is the same as with a glow plane: you can use a switch between the battery and receiver, and you always want to turn the Rx power on before the motor is powered and off after the motor power is cut. Most ESC's have a safe design where they don't send power to the motor until they see power and signal from the Rx. I don't know about cheaper/Chinese brands, I would think so but you never know.

It's not that the BEC from your ESC isn't enough, it's just a safety thought. If for some reason you lose connection between your flight pack and ESC, or ESC and receiver, you still have power to land the plane. One thing people are doing is using a small lipo on a regulator set to 5V. This uses the power from the BEC. If there is a failure and no BEC power, you have the little battery to get you home. It's up to you how you want to do this, tons of guys use the BEC because it's easy and light. I don't take the chance with projects that cost a lot of time and/or money.

I fly precision aerobatics and there is a weight limit. While I have not had to worry about weight with my previous planes, the current one I am building (now painting) is known to be heavier. To reduce weight, I eliminated the series adapter and wired my packs together (can use a bullet connector from pack 1 red to pack 2 black, I use Anderson Powerpoles). I don't use a switch between the Rx and Rx battery, I just plug directly in then put canopy on when I'm ready to fly. Arming switch would keep you safe if you are using one.

Electric planes use very little Rx power. I fly a 2000-2500 watt setup on 10s lipos. I use about 90mah per flight in Rx power. I use two 450mah lipo batteries each on a regulator, and I can fly all day with this. In other words, a 75" aerobatic plane can fly with a 900mah receiver pack. You don't need 2000mah packs like you did with glow or gas because the plane doesn't shake and make the servos work hard. There is some more weight savings.

chuckk2

Electric planes can have problems with BEC's that are in the 2A class. Peak currents can cause the same problems that can occur with a 2000mah battery pack.
I have two models that by luck and chance survived the experience, and I installed 5A BEC's that eliminated the problems.

sportflier62

??