Power distribution 2 lipo's

T

thijmen5

Member
Hello all,

I'm looking for a good power distribution for my DJI wookong octo. I received a lot of the parts and waiting for the carbon now.
The octo will be powered by 2 x 5000 4S lipo's independently from each other.

That means 1 lipo powering 4 motors. My though here was if 1 lipo fails the other 1 still powers 4 motors which might be enough for a more soft landing. But it also means if the lipo which also powers (see next question) the FC, receiver also stops being powered. Is there any solution for the other lipo to take over the power supply to the FC and receiver?

I will be using maytech 30A opto esc's. Does this mean I need to buy an extra BEC to power the wookong, receiver and so on?

I hope I have made myself clear.

Thanks

Regards,
Thijmen
 

BorisS

BorisS

Drone Enthusiast
Two ways you can do it second better.

attachment.php


Boris
 

Attachments

  • Distboatd.jpg
    Distboatd.jpg
    98.7 KB · Views: 246

T

thijmen5

Member
That means 2 power boards connected with each 4 engines. As far as my electrical knowledge reaches that means that if 1 lipo fails the voltage remains the same because the boards are connected and it still gets powered?

But what about the amps? Maybe a stupid thought, but arent both boards getting the amps of 8 engines? My guess is no since electricity always gets the shortest route, but im not sure?

Thanks for your fast and clear pictures!
 
Last edited by a moderator:

BorisS

BorisS

Drone Enthusiast
yes that the point of it. Not only the motor/escs will stay alive of one of the lips dies also every other component that get is energy from the diet board, for example RX PMU Ubecs etc.

Boris
 



T

thijmen5

Member
Great answers guys, thanks.

What high power connectors would you guys use for lipo?
For esc i thought about standard 3,5mm connectors.

Most bigger connectors are not having a case, just the connector. Do you just put shrink tube around it?

What bec is recommended?
 



T

thijmen5

Member
What bec and led's?

By this time I received a lot of other parts. Still I need to order a bec to power the fc and so on. I also want to use led's for oriëntation. Are there led's which can be connected directly to the power distri board on 4s?

What bec is suggested in combo with the wookong and maytech 30A esc?
 

BorisS

BorisS

Drone Enthusiast
thijmen5. The PMU actually power the WKM over the CAN-Bus, there is a separate BEC in the PMU that if connected to the MC the receiver is also powered either via the S-bus connection or the traditional connections.

Of course you could power everything separately with a bec although at the moment I am not sure what the can-bus voltage is and messing with the can-bus cables is a little annoying.

The separate BEC in the PMU unit i don't trust to a 100% i already had problems with it. So you could use a extra BEC to power the RC to be safe.

The ones prefer using a the castle creations BECs. They have their price but are of good quality and have the widest range when it comes to configuring the output voltage.

http://www.castlecreations.com/products/ccbec.html

The small one is enough, but also need though the Castle Link Usb adapter to let you program the BEC to the desire voltage.

Boris
 

T

thijmen5

Member
Ok,that means I would leave the PMU out?

And how do I connect the BEC to power everything? In a port on the DJI I don't use?
 

M

Mihnea de Vries

Member
BorisS said:
Most octo hover around 50 60 A with a payload around 5kG, with standard HL motors Axi QC torn tigers etc.s
Click to expand...

Hello Boris, when you say 5kg payload, you mean the added weight of camera and camera mount, or you mean 5kG total liftoff weight (frame, electronics, battery, camera, camera mount, and everything else?) In aviation the payload is only the cargo and passengers.

Mihnea
 

BorisS

BorisS

Drone Enthusiast
sorry i wasn't reading what i was writing ! Payload is wrong take off weight 5kg. Than of coarse the A is dependent on the props size Lipos 4s 5s 6s you are using etc. Thanks for pointing it out !

Boris
 

J

jes1111

Active Member
I hate to be the one to burst the bubble, but this idea simply will not provide the level of redundancy you are expecting. If two (or more) batteries are connected in parallel then any fault on one will directly influence the other(s), in particularly an internal short. Using two distribution boards doesn't change anything electrically-speaking. The only scenario against which you might gain protection is the accidental disconnection of one pack.

To achieve the "4+4 fallback" capability you refer to you would need to provide either an auto-switching circuit (similar to that in a computer redundant power supply unit) or run each set of four ESCs on an entirely separate circuit. But the difficulty with that second solution would be to avoid floating earths, ground loops or other electrical nasties that I don't fully understand.
 

BorisS

BorisS

Drone Enthusiast
thats good to know since its seems to be a general misunderstanding that two lips in parallel will compensate for each other if a cell in one of them dies !

Boris
 


BorisS

BorisS

Drone Enthusiast
jesss is indicating that thats not the case or the question is in what form it fails. Gonna try to find some info on it !
 

J

jes1111

Active Member
It depends very much on what "fail" means and, to some extent, on the particular configuration of the pack that's "failing". The two most common failure scenarios for a lipo pack would be one or more cells overheating (a runaway exothermic reaction which will inevitably result in a short-circuit) or "failing" in the sense of the output voltage dropping radically (and therefore offering a high resistance to its fellow cells). Either of these events would be catastrophic for the entire system.

"3S", "4S" etc. means 3 or 4 cells in series. So, just like one bad AA in your Walkman stopped the others working properly, so one bad cell in a Lipo will upset the others. Increasing the number of packs whilst keeping the voltage the same is connecting them in parallel, e.g. 4S2P. Electrically-speaking, that's all that matters: series and/or parallel. Exactly where/how those connections are made is irrelevant.
 

You must log in or register to reply here.
Top