Lipo 6s packs / Parallel and Series


#1

I found locally a great deal on some big 6s lipo’s…

My plan is to use 4 x 22000mAh on the frame and 4 x 16000mAh in a flight cockpit/ballast bag.
Open ppg electric 89

If you are going to use batteries in series, they should be of the same age, manufacturer, capacity and type.
That’s because all cells in a series pack have to be able to support the full load current which is running through every one of them.

Since I have to parallel them as well it is important that all paralleled packs must have the same charged voltage… They don’t have to be the same capacity (mAh).
If batteries are connected in parallel, each will stay at exactly the same voltage as the other at all times. If your packs are different capacity (mAh), the larger one will provide a greater share of the power than the smaller one, in order that it’s voltage drops at the same rate.

I will also use on each balance lead cell voltage checker, which are buzzing if any separate cell is going below a certain voltage (3.3 volt default). They are really loud…

The weight of the 4 x 22000mAh would be 9960 gram and the 4 x 16000mAh would be 7728 gram.

This would be a total 76000 mAh in 12s. I think this is a versatile combination since I can use whatever
capacity i need in parallel mode.


#2

Do you mean this tattu 22000 6s and 16000 6s ? and what frame do you use these batteries on?


#3

Exactly… I have these battery packs. But I paid for the 6s 22000mAh new only 240$ and I bought 8 batteries in bulk second hand.

On the frame from OpenPPG>

Nothing fancy… Velcro self adhesive 2 inch tape and Velcro straps, like on the picture for the 4 x 6s 22000mAh.

The 4 x 6s 16000mAh are tiny - they fit into my 8.5x6.5x6 inch fireproof bag.I want to use them in flight in
a flight deck with ballast bag.



#5

What is the current rating of the connectors on the batteries, and wire gauge? Length of the wires will be important due to voltage drops from the further packs, and the temperature of the cables will also be high potentially. The video link is a little frustrating to listen to, but it shows cables and XT90 connectors being stressed - maybe someone did the same for your batteries? https://youtu.be/4rcCdCVBXAI


#6

Worth considering that the power loss in the connectors and cables is I2R, so double the current, quadruple the power loss, and there will be a point where that runs away as there is a linear relationship between temperature and resistance for the power loss equation.


#7

Hi. Paul, how many Bonka batteries packs can you put on the OpenPPG maximum?


#8

These connectors are rated for 190 A continue and 230 A peak…

I like the 3 color coded connectors for the 2 x 6S series connection to have a 12S pack>

They are easy to solder as well…


#9

I’m a bit concerned about people thinking it’s ok to extend the wires between their batteries and ESCs. Do the ESCs used on this project not specify a maximum wire length between battery and ESC?
The Turnigy dlux 250A I used on my project specifies the wires should be no longer that 6 inches, not because of current concerns, but EMF generated in the wires supplying the ESC. The longer the battery wires the more the ESC gets pounded to destruction.
It’s supposed to be ok to extend the wires between the ESC and motor though.

I expect one or two of you have seen this video, note the extended wire running from the ESC down to the batteries.

https://www.youtube.com/watch?v=52K8PKqSxkM


#10

There could be a number of reasons that an ESC can burn up. Top of my list being… Well… Turnigy…

The EMF your referring to, I know as ‘voltage ripple’. In practice, I’ve never seen it rise above 2 volts (as logged on a Castle Creations HV160, with 1.5 meter battery wire run pulling 200A)

Say your ESC is rated to 12S or 50V.
Hot off the charger your battery is 50.4V. Add an extra 2-5 volts induced for long cable ripple voltage and your ESC input could be spiking as high as 55v. Your capacitors and MOSFETs are the voltage sensitive components inside the ESC. They will be the bits that fail violently.
You could add additional capacitors at the ESC to absorb the hammering if you have data confirming it’s a problem.

Turnigy and other ‘Lucky Dragon’ brands are built to a price with components running on the edge of their spec. That additional couple of volts from a long cable run could be enough to tip it into the grave.
Pull one apart and get the model numbers off the MOSFETs and capacitors. Compare their data sheets to say one out of a known, quality brand like Castle Creations. Be curious to hear back from any one who has done this.

I’m not sure where these Hobby-Wing ESC’s sit. I’ve never used them before, but their quality has crossed my mind


#11

Primary concern is the bridge capacitors. With higher series resistance due to the cables, they will be doing more work, will get hot, and are more likely to fail. Most ESCs have questionable capacitors, both in terms of working voltage (must be significantly higher than nominal supply voltage), and ESR (if they are to be useful to the bridge).


#12

Cheers Lukas.
In my case it was only the three external 470uF 100v 105º of the ESC that burst thus stopping the unit from working which, was handy, as I was in the air at the time; and naturally wouldn’t have wanted the fireworks shown in the link I pasted earlier.
The two internal 470uF caps of my ESC were ok, but unfortunately replacing the three external caps with the correctly rated types didn’t get my unit working again so, the internal control circuit must have sustained some damage.
The Turnagy dlux 250A that I have uses 36 IRFB3207 MOSFETS.

The bloke in the link below seems knowledgeable on the subject of long battery wires, it is from 2008 though.

too long battery wires can kill ESC: precautions, solutions & workarounds


#13

Had a look on the Castle website and found this:

Warning: Do not exceed more than 18 inches of total wire between the battery and ESC (this includes the wire already on the ESC and battery).