• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

Fat Shark TX Power board/module draws from only one cell, don't use it

hastiado

Junior Member
#1
My experience comes from the PREDATOR V2 RTF FPV KIT from Fat Shark.

I'm writing so others can avoid severely unbalanced battery packs on their plane/copter.

Here is the device I am writing about, it allows you to quickly plug in your FPV TX to the balance plug on your battery in order to power the device from the same battery which is running your aircraft. Other's use an independent battery pack to power the device.

IMG_20140604_140757.jpg

Here's a diagram showing the pin to pin wiring between the black port (power to the TX) and the 3 white ports (battery connection).

Code:
Red to Red

Black to Black

Blue is left floating, this means that you are only using one cell of the battery.
IMG_20140604_140804.jpg

This is bad with a single battery setup, as your aircraft will be equally drawing from each cell through the main connector and a leech will be drawing from a single cell causing it to lose capacity at a faster rate than the others. This will severely shorten your flight times as the total series voltage output of your battery will drop faster than it will when distributing the load of the TX across all three cells.

This is bad with a separate battery for the TX unless it is a single cell battery, as you will be continually discharging and recharging one cell while the other stays full... quickly destroying your battery.

When using this module, you gain a capacitor which will reduce the ripple - http://en.wikipedia.org/wiki/Ripple_(electrical) - on the input voltage to the TX. In practice this is covered by a high quality BEC or ESC (what's powering your receiver) and is negligible directly from the battery.

Actual Draw Readings

@ 5v the TX draws ~.42 amps

IMG_20140604_143146.jpg

@ 11v the TX draws ~.21 amps

IMG_20140604_143124.jpg

Roughly 2.1 watts which on a 3S battery at 11.1v would be 210mA. That's not too bad if you are drawing energy equally from all 3 cells.

However, when using the dongle/adaptor/ripple reducer you are going to be pulling that entire 2.1 watts from a single cell @ ~3.7v which is ~.56 amps. The voltage reduction rate on this single cell will be much higher (faster) in real terms and as batteries for the most part (3S, 4S, etc) wire the internal cells together in series, you will notice the voltage drop much more quickly than it should for the entire cell pack of the battery.

Normally you are drawing power equally from all of the cells of the battery by using the main connector. If for example you have a 3S battery you would be drawing 3.7+3.7+3.7=11.1v. When using this adapter you will have something like 3.7+3.7+3.0=10.4v (with the low cell dropping at a faster rate than the other 2) at which time your aircraft will report a dead battery much faster than it actually is.

Flight times will be decreased more than they should if you use it.

This cell will wear out much faster than the others, especially if you are not balance charging which will drastically shorten the life of your batteries.

As you can see from the current readings, the TX operates fine from 3.7v to 12v so you should have no problem connecting it directly to the battery. You can also use a BEC or an additional output from an ESC to resolve this problem.
 
#2
My experience comes from the PREDATOR V2 RTF FPV KIT from Fat Shark.

I'm writing so others can avoid severely unbalanced battery packs on their plane/copter.

Here is the device I am writing about, it allows you to quickly plug in your FPV TX to the balance plug on your battery in order to power the device from the same battery which is running your aircraft. Other's use an independent battery pack to power the device.

View attachment 24696

Here's a diagram showing the pin to pin wiring between the black port (power to the TX) and the 3 white ports (battery connection).

Code:
Red to Red

Black to Black

Blue is left floating, this means that you are only using one cell of the battery.
View attachment 24697

This is bad with a single battery setup, as your aircraft will be equally drawing from each cell through the main connector and a leech will be drawing from a single cell causing it to lose capacity at a faster rate than the others. This will severely shorten your flight times as the total series voltage output of your battery will drop faster than it will when distributing the load of the TX across all three cells.

This is bad with a separate battery for the TX unless it is a single cell battery, as you will be continually discharging and recharging one cell while the other stays full... quickly destroying your battery.

When using this module, you gain a capacitor which will reduce the ripple - http://en.wikipedia.org/wiki/Ripple_(electrical) - on the input voltage to the TX. In practice this is covered by a high quality BEC or ESC (what's powering your receiver) and is negligible directly from the battery.

Actual Draw Readings

@ 5v the TX draws ~.42 amps

View attachment 24699

@ 11v the TX draws ~.21 amps

View attachment 24698

Roughly 2.1 watts which on a 3S battery at 11.1v would be 210mA. That's not too bad if you are drawing energy equally from all 3 cells.

However, when using the dongle/adaptor/ripple reducer you are going to be pulling that entire 2.1 watts from a single cell @ ~3.7v which is ~.56 amps. The voltage reduction rate on this single cell will be much higher (faster) in real terms and as batteries for the most part (3S, 4S, etc) wire the internal cells together in series, you will notice the voltage drop much more quickly than it should for the entire cell pack of the battery.

Normally you are drawing power equally from all of the cells of the battery by using the main connector. If for example you have a 3S battery you would be drawing 3.7+3.7+3.7=11.1v. When using this adapter you will have something like 3.7+3.7+3.0=10.4v (with the low cell dropping at a faster rate than the other 2) at which time your aircraft will report a dead battery much faster than it actually is.

Flight times will be decreased more than they should if you use it.

This cell will wear out much faster than the others, especially if you are not balance charging which will drastically shorten the life of your batteries.

As you can see from the current readings, the TX operates fine from 3.7v to 12v so you should have no problem connecting it directly to the battery. You can also use a BEC or an additional output from an ESC to resolve this problem.
So I got one of these and running it off the balance connector isn't an option since my battery alarm goes there. Google brought me here in search of options.

After reading this, I whipped out my multimeter and measured my battery output on the balance connector, and the output from the fatshark filter device.

On my 3S balance connector I got roughly, 4v, 8v, 12v. This tells me that with the pins you've highlighted, it really uses all three cells at once. I plugged in the battery to the filter and measured it's output to the video TX and indeed, it's also 12v.

I always install a spare 12v connector on the battery mains, so I'll tap that and run the filter that way. But I don't think it's an issue to run it off the balance connector either. If I'd got 4v off the filter, then yeah, I'd worry.
 

Jael

Junior Member
#3
sounds perfect

Hi
Would it be possible to get more detail on your wiring connections for this fatshark filter

you mentioned that you were tapping 12v straight from your battery wiring harness to the 3s balance connector on the fatshark filter. can you confirm this works with no issue?

I am in the process of building my quad and like you I would like to put a battery low voltage alarm on the balance lead of my battery.
So if I understand correctly I could tap 12v from my battery wiring harness, using a custom made 3s plug with just the +&- pins in use, to supply 12v to the filter and on to the transmitter and camera.

Thank you
Jay
 

Balu

Lurker
Staff member
Admin
Moderator
#4
Hi cyberbillp and Jael,

welcome to the forum.

The balance port doesn't work like it was described in the first post. I've made a scribble once how it is wired:

LiPo.png

You can see that between the black ground and the red plus of cell 3 you will have the same voltage as the main connector: 11,1 V. So as long as you use the outer ones, you will draw power from all three cells with the maximum voltage.
 

Jael

Junior Member
#5
Hi Balu. Thank you

Thats great.
I will make a connection come off of my main battery wiring harness to the fatshark filter, using only the 2 outer pins of a 3S plug
That way i can have my batteries balance lead connect straight to my low voltage alarm, and supply 12v power the fatshark setup straight off the battery wiring harness.

Thank you for your quick response.
 
#6
The first post is COMPLETELY misguided (to put it nicely).

Using a bal connector for power will not damage your batts.
If you only use 2 cells from a 3cell batt, so what....thats what balance chargers are for.
If you are worried about the current drain from a fpv TX, use a separate batt or a bigger batt.
 

joshuabardwell

Senior Member
Mentor
#7
If you are worried about the current drain from a fpv TX, use a separate batt or a bigger batt.
There is really not much reason to be worried about the current drain from a camera and vTX. I worked out the math once, and on my quad it is a difference between something like an 8 minute flight and a 7:30 flight. Well worth the convenience of only dealing with one battery. This is doubly true if you have telemetry or an OSD, since it means your telemetry is monitoring the battery for your entire system.

IMO, if you are going to use the vTX regularly on the plane, best course of action is to permanently wire in the vTX's power lead to the ESC's main power lead.
 
#8
I noticed the voltage of cell one on my 3s batt becoming unbalanced with cells 2 and 3 after fabricating a y-harness for my batts balance lead to power both my voltage checker/alarm and my fatshark filter board. Running a Versacopter btw, thus I plan eliminate the y-harness and solder a JST connector to one of the Versacopters aux power pads like Josh did in the build video to solve this cell balancing issue.

But my question is, what voltage does the filter board put out to the VTX? I'm running a Lumenier 600mW VTX with a Fatshark 600TVL cam(yes I made sure the dust cap is not still on the cam) and cannot get any video to appear on my Fatshark Attitude V2 goggles. I have cycled thru all 32 channels numerous times and the display shows everything from blank black screen to white/black dots fuzzy when cycling thru the channels. Currently using the whip antenna that came with the VTX until the spironet antennas I ordered arrive.

My best guess is either the filter board is not supplying enough power to the VTX(VTX has plainly printed on it 7~19V) or the stock whip is not playing nice with the spironet on my goggles??? Help
 
#9
Back in business. I found the link below on fpvlab about the lumenier vtx not putting out +5V. Which is what my fatshark cam requires. I removed and cut off the power wire pin to the cam at the vtx connector, soldered and folded back a jumper wire and heat shrinked. Then connected the other end to the +5V pin of my naze32 FCB.

I also did away with the 3s balance lead y-harness i made. Then used another 3s connector, removed the two middle wires leaving only the power and ground wires. Soldered the other ends to one of the aux pads on the Versacopter PDB....And now my FPV system is working swimmingly. The above posts definitely helped me find a cleaner and better way to connect my filter board without messing with two connectors coming off my batts balance lead.


http://fpvlab.com/forums/showthread...ier-5-8g-600mW-transmitter-to-fatshark-camera!