physically mounting resistors for voltage monitoring

[nigelsheffield]

Is there a good way to mount the resistors for monitoring cell voltages.
I thought of putting one set through the board with other end all linked to gnd, and the other resistors on a lead to a plug socket for the lipo balance plug,
My only reservation is everything is then permanently fixed and then quite bulky if I want to just use the vario with no voltage monitoring.
Another idea is put all resistors on the plug wiring so as plugs into the arduino.
Obviously I need to link the gnd too.

[mstrens]

If you do not want a permanent assembly, one option could be to use pin headers connected to pins Gnd, A3, A2, A1, A0 (skipping pin vcc).
Pin header could be at 90° in order to keep it as flat as possible.
When you want to measure the lipo cells, you can connect a cable to the pin headers.
In this cable you can insert a small board that should support all resitors.
Eventually the board could be directly connected to the pin headers via a connector.

FYI, I made a PCB to be put on top of Arduino. The pcb is just a littel longer than arduino and can support:
- a connector (or a cable) for a 4S lipo (balance plug)
- all resistors for this 4s (size is 0805)
- a connector for a current sensor
- a direct connection (pin header) for 1 or 2 barro sensor(s) to be put on top of the pcb
- a airspeed sensor (4525D0)
- a Sport/hub cable
- a ppm cable (or connector).
If you are interested, I can send some PCB (without the component) and or the PCB design (in Eagle format).

[kalle123]

I am using those here.

Top is for a 2S Lipo battery, bottom for a 3S Lipo. Connects directly to the balancer connector.

Brown is ground.

br KH

[mstrens]

If the same lipo is used to power the Rx, is it not better (safier) to avoid connecting the Gnd (in order to avoid a loop)?

[kalle123]

Hi mstrens.

Did my tests till now with gnd connected. Would would be the effect of a gnd loop?

If that is a issue, correct me, but then a lot of people are having it.

See -> https://www.google.de/search?q=frsky+vo ... AQ&dpr=0.9

br KH

[nigelsheffield]

Thanks guys, I need some surface mount resistors to make a nice small job!
I have hundreds of normal resistors from my TV repair days!

[nigelsheffield]

Regarding the ground loop, so if I leave out the gnd and just rely on the gnd from the bec will this work well?
I remember j did a similar thing with a2 for pack volts on a d8r but ended up connecting the gnd as the results were better.

[nigelsheffield]

Oh, other thing,
The first lipo cell will have 4.2v Max, so does this need any resistors at all?
Maybe just one to limit current?

[mstrens]

If you use Vcc (about 5 volt) as voltage reference, you normally do not need resistors for the first cell.
Still a resistor between cell and arduino pin can only help making it safier.
A high value resistor can also be added between arduino pin and ground in order to avoid that arduino pin remains "open" if no lipo is connected.

About the ground loop, there is more info in this thread:
viewtopic.php?f=95&t=4293

[jhsa]

Connect the ground to the sensors on the battery side. The ground is already on the receiver through the BEC.
so, only 2 wires for the 3 cell connector and 3 wires for the 3 cell connector.

João

[nigelsheffield]

OK , so I guess it depend a bit on the bec as to the gnd working through bec without a gnd connector on the battery.
So if no gnd is connected to balance connector port this would be easier to wire up without having to break out the gnd again, if it works OK I just wonder what happens if battery is plugged into balance port without the main plug powered, will this cause damage with no gnd connected at all?
Should then the main pack always be plugged in first?

[kalle123]

Should then the main pack always be plugged in first?

First, switch on the TX

But Nigel, I think in most cases nothing will happen.
I like Mikes idea with a 1k resistor and give it a try here...

br KH
Have a look at that video on youtube. https://www.youtube.com/watch?v=xTo40NnQAE8

[jhsa]

After he install the second BEC he could have removed the ground between the current sensor and the OSD. So he resolved one and created another.

João

[nigelsheffield]

TX on first OH YES LOL.
That video cleared up the ground loop for me , I had a farily good idea of what ground loop problems might be but now I know for sure and exactly how to avoid them.
The 1k resistor will not actually do anything different to open circuit in normal operation but is there to hold the gnd to near 0v when no proper ground is there then.
Certainly a good idea for safety.

The whole loop thing is obviously BAD, ohms law does not just say the current will take the least resistive path but is proportional, so with a ground loop there will be SOME extra current going through the second path when more power is drawn from motor.

I tihnk the average rc flyer is completely unaware of this problem.

[MikeB]

The 1K resistor also provides a second benefit, depending on where everything is connected. If the ground connection between the flight battery and the ESC goes open (or high resistance), then the motor power would run to the receiver, via the power sense ground, and from there through the receiver and out to the ESC via the throttle servo connection. This usually blows tracks on the receiver. The 1K resistor limits the current and protects everything. In the worse case, the 1K itself gets destroyed, opening the circuit.

Mike.

[nigelsheffield]

So, if that ground connection from bat to ESC breaks in flight, would the 1k to gnd provide enough power to keep the RX working I wonder?
Probably not, the servos would be underpowered at the least.

[kalle123]

Nigel, if that happens and you don't have a separate power supply for your RX, you plane is going down so or so ..

[nigelsheffield]

Yep, no point thinking about that one, I try to make sure my wiring is sound to avoid that!
Its one reason I have not yet fitted my cheapo 30amp sensor, I just worry it will go o/c on me , but from what I have read they seem rated well over the 30amp and I usually only draw something like 22amps for about 20 seconds at a time.
Though my 3m gliderman is gonna use more I think so I do without till I get a bigger one. I just test on ground and a few short flights will get me a good idea of run time.

I've ordered some 805 assorted resistors and have some proto typing PCB board on the way too so when it all arrives I will make a small board to connect to lipo balance plug, I have proper balance socket already so will have an choice of using those or pin header.
Gonna have to get my specs and magnifying glass out and find some steady hands!

[kalle123]

In the picture, I am using 1206. A little easier to fit

[nigelsheffield]

Oh I see, oh well when I have used up the 500 mixed lot that I ordered I'll go over to 1206.
By then I should either be blind or really good at soldering 0805 size!