A topic often discussed in FPV is regarding batteries. The option of using another separate battery from the main flight battery dedicated to the video.This topic is thrashed out on many forums on a weekly basis. Here is what my personal finding have been on the subject.
So if this option is available then its the best route ?
Well that depends. What we have found instead is the there are pro`s and con`s to each system. Lets look at the differences
1 Battery system :
Only one lipo to charge and remember to charge.
Only one failure point
More room available
2 Battery system :
Separate supply for both flight and video system for cleaner signal and redundancy
More stable operating voltage with no voltage drop during motor running
If flight lipo fails video will still run enabling flyer to see impact point
1 Battery system
Only one lipo to depend on whole system working
If the flight lipo dies control of plane is lost
If a 12v video system is used with no step up voltage supply for it and lipo dies video is lost
2 Battery system
Both batteries have to be charged each flight
Both batteries have to be monitored
Double the failure points of the power system
More weight in the plane for less capacity
If flight battery dies flight control is lost
Lets breakdown the pro`s :
1 Battery system :
Only one lipo to charge and remember to charge – Running off the single supply as it says only one battery to charge – On a dual battery system two lipos to charge and monitor
Only one failure point – One set of connectors to fail, one set of cells to fail – On a dual system, two sets of connectors and cells are now potential hazards – Double the risk
Lighter aircraft – If using a single lipo system the aircraft can if chosen be lighter – On a dual lipo system it will either be heavier or you will have to sacrifice some flight capacity to keep the weight down
More room available – With a single lipo system more room is available for RTH devices or OSD units. In most FPV planes space is tight or space between components is desirable – On a dual lipo system more room is taken up by the additional lipo reducing flexibility for equipment placement
Less connections – As failure points on a single lipo one set of connections – On a dual twice as many to fail mid flight
Simpler system – On a single lipo system, one source of power less complication, easier to fault find – On a dual system, twice as many points to fault find
2 Battery system :
Separate supply for both flight and video system for cleaner signal and redundancy – On a single system a simple LC Filter is used to clean the supply to components – On a dual system the filter is not needed
More stable operating voltage with no voltage drop during motor running – On a single system a step up can be used, or if using a highly recommended 5v system then the voltage never drops below operating voltage anyway – On a dual system this is not needed
If flight lipo fails video will still run enabling flier to see impact point – On a single lipo system using a step up or 5v system this is also the case – So no additional benifit from a dual lipo system
Lets breakdown the con`s :
1 Battery system
Only one lipo to depend on whole system working – On a single lipo system with a step up or a 5v system this means video works even after a cell has failed. If main lipo fails then the system goes down – On a dual lipo system the video works if second lipo is charged but if flight pack fails control is lost so that doesn’t really matter anymore
If the flight lipo dies control of plane is lost – On a single lipo system this is true – On a dual lipo system this is still the case
If a 12v video system is used with no step up voltage supply for it and lipo looses a cell the video is lost – On a single lipo system this is why we use a 5v video system so its not – On a dual lipo system as long as video lipo is charged this does not happen
2 Battery system :
Both batteries have to be charged each flight – Not so with a single lipo system – True with a dual, forget to charge the video lipo and you are in for a surprise mid flight
Both batteries have to be monitored – With a single lipo you can time your flights or use a lipo alarm – On a two lipo system you have to monitor both at the same time, either two lipo alarms to use or an OSD with two separate readouts and two values to concentrate on while flying as well as everything else
More weight in the plane for less capacity – On a single lipo system, one lipo full capacity for the weight – In a dual lipo system either the plane has to weigh more or the flight lipo has to be reduced in capacity to keep the weight down
So looking at it on face value, at first glance the two battery system seems to have an advantage over the single in the video will still be active if control is lost. But having said that most video systems will run on 5v or be 12v systems that will still continue to work below 9v ( failure point of a 3S system. ) What is recommended is using a 5v video system, camera and Vtx. This way you can run a lipo till its dead or loose a cell and your video will still work absolutely fine so this then now fails to be an advantage for two separate lipos.
The second advantage is having the video supply isolated from the flight supply thus isolating any interference in the video. Yes this is partly true, but then even if it is isolated if the two separate systems wires are run in parallel with each other at any point in the aircraft the interference can transfer over to the video supply anyway. With a single lipo system sometimes you don’t get any interference ( if you lucky ) if you install a ferrite ring or an LC Filter it will cure this. So that’s another advantage that`s not actually viable.
So as we look further into this the more apparent that the initial pro`s of a dual lipo system seem not really that good after all. Now take into account charging. How many times have you forgot to charge your transmitter before going to the field ? Now you have to remember to charge your video lipo too. If you forget, that’s your FPV flying out the window for the day. With the single system if you have charged your flight pack your great to go.
If you run two separate lipos on board you have now doubled the chances of failure.
We can achieve the same result as running two lipos with one. By running a 5v video system.
Some argue that with a separate lipo for video if your flight lipo fails you can still watch the impact and find the plane. You can on a 5v system too. Either way the same thing will happen. If flight controls lost the plane is no longer under control. The plane is coming down and chances are not to a nice smooth landing. No amount of video is going to save that from happening.
Here’s an example :
Take 2 planes, If you use two batteries you have less capacity in the flight battery ( if both were identical planes ie weight ) because the video battery would take up space. Therefore even though your video would be fine your flight times are now reduced. Now take the 1 battery plane with a larger capacity flight battery, the video still works as its on 5v through the whole pack but the pack is bigger. Bigger pack = longer flight. 5v system means video always works so advantages of running a second battery now seems insignificant
So from what we see, every advantage of a second lipo on board can be matched by a single system on every account. Thus negating the need for running a separate lipo