*Two* FBVS01 with *two* batteries: which wires to connect to where?

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Nadim
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*Two* FBVS01 with *two* batteries: which wires to connect to where?

Post by Nadim »

Hi there,

I'm setting up an electric setup where I'm using two batteries, one for the motor (6S lipo) and one for Rx / servos (2S lipo).

I'd like to use *two* FBVS01 to check the voltage of both batteries. Now the thing is: so far I've been using only one battery for everything, and, as often stated on various online resources, I have never connected the black wire of the FBVS01, with no issues. (Actually, I was connecting both wires from sensor to Rx, and only the red wire from sensor to battery - it seems that this was the wrong way to do it, but anyway...)

Now, though, using two batteries, I'm little puzzled as to which wire I should connect to where.

My setup is as follows:

- D8R-II Plus

- I've removed the red wire of the ESC to bypass its BEC and only connected the black and white wire to the Rx. As for functioning itself, I already tried and everything works fine.

- For the Rx / servo battery, it's a 2S lipo so I'm making it pass through a BEC set to 6 V.

Thank you :)

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Nadim
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Re: *Two* FBVS01 with *two* batteries: which wires to connect to where?

Post by Nadim »

It seems it's a difficult enigma, considering that nobody has answered :D

I've made some tests in the meantime, and I'm posting the results, in case anyone else were interested, in the future.

For both sensors, I connected both the red and black wire from the battery to the sensor, but only the red wire from the sensor to the receiver.

So in conclusion, no grounding for any of the two sensors.

Everything seems to be working fine. I get both readings, and they seem fairly accurate.

I can't strictly 'recommend' this to anyone because I understand little to nothing about electronics and I wouldn't want anyone to follow random advice. This is just what it seems to be working in my setup. Will let you know if I fry something!... :lol: But if it hasn't happened in one hour of flight, I'd like to think I'm pretty safe.

***

On a side note, the only thing that's a bit strange, to me at least, is that when only one sensors is activated, the other one, while being off, seems to be receiving some kind of noise too. This didn't happened when the port A1 was self-shorted to get Rx internal voltage reading (default settings of the D8R-II Plus).

Now, if for example only the Rx battery sensor is ON, the motor battery voltage is displayed as well, and varies while I open the throttle. Note that this isn't just an afterimage of what the sensor was reading right before it was switched off, it's a number that, despite being not the real voltage, it's 'alive' and varies while for instance I operate the servos or the motor. Probably the two sensors are interfering in some way. But when I switch on both sensors, I suddenly get the right readings, so no big deal really.
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Re: *Two* FBVS01 with *two* batteries: which wires to connect to where?

Post by MikeB »

See here: viewtopic.php?f=95&t=4293&p=60766&hilit ... png#p60766, for how I connect voltage sensor(s) to a D8R.
If the A2 input is "floating" (nothing connected), then it will typically return a similar voltage to the A1 input. This is normal.

Mike.
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Re: *Two* FBVS01 with *two* batteries: which wires to connect to where?

Post by Nadim »

Thank you Mike.

I don't see a link in your message though, where you say "here".

Thank you
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Re: *Two* FBVS01 with *two* batteries: which wires to connect to where?

Post by MikeB »

Link added.

Mike.
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Re: *Two* FBVS01 with *two* batteries: which wires to connect to where?

Post by Nadim »

Ah, yes, I had already read that thread.

I'm not used to electronics schemes, but I could definitely get my head around it if it can help. It's not immediate though... what is C1?

I understand adding a resistor in the circuit like you did could improve accuracy, but that's really not needed in my case: I can live with slightly far off measurements (which by the way don't seem to be that far off).

Am I risking some damage to Rx or servos with my current setup?
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Re: *Two* FBVS01 with *two* batteries: which wires to connect to where?

Post by jhsa »

I connect the sensor's ground to the battery, and only the signal wire to the receiver..

João

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Re: *Two* FBVS01 with *two* batteries: which wires to connect to where?

Post by Nadim »

jhsa wrote: Wed Aug 23, 2017 9:45 am I connect the sensor's ground to the battery, and only the signal wire to the receiver..
I guess you mean the positive, not the signal. But anyway: I've always connected only the positive as well, but in this case I have two sensors connected to two different batteries, only one powering the Rx. That's why I thought it might be different.
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Re: *Two* FBVS01 with *two* batteries: which wires to connect to where?

Post by jhsa »

You will also need to connect the signal wire from the sensor to the receiver so you have telemetry, right? ;)

I power my receivers from the BEC normally. I still haven't used two batteries, that is why I didn't refer to the "Positive"

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Re: *Two* FBVS01 with *two* batteries: which wires to connect to where?

Post by Nadim »

No, wait, there must be some misunderstanding here... :shock:

There's no "signal wire" whatsoever on those sensors. Are we talking about the same item? The one I refer to is the FBVS01, as in the thread title.

So far, I've always used one single battery, with which I powered up everything. I used to connect the sensor to the balance charger of the battery, just for convenience (instead of bridging the ESC wires...).

I don't see why that sensor would also need a "signal" to get telemetry back to the receiver. It's just a voltage divider, the telemetry processing in itself is inside the Rx.

So yes, either in this current setup as well as in my other setups in the past there has always been only ONE wire going from the sensor to the Rx, and that's the positive pole. (Whether I grounded the Rx-sensor circuit or the sensor-battery circuit is another story, but again, that's just the ground, not the "signal".)

Here's a pic of my scheme:
Attachments
Double battery and double sensors setup scheme
Double battery and double sensors setup scheme
Last edited by Nadim on Wed Aug 23, 2017 12:02 pm, edited 1 time in total.
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Re: *Two* FBVS01 with *two* batteries: which wires to connect to where?

Post by jhsa »

Ok, I called it "signal" not to confuse it with the battery positive. And yes, it is an analog signal, which happens to be a voltage.. I know those sensors of course. I build my own. :)

And yes, connect the ground from the sensor to the battery, but NOT to the receiver, to avoid a ground loop.. The receiver is already receiving the ground directly from the battery, or through the ESC or external BEC, depending on your setup.

This is standard procedure for these sensors. Actually, it should be standard for most sensors, including the ones that output a digital "SIGNAL" (not analog voltage) and connect to the receiver..

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Re: *Two* FBVS01 with *two* batteries: which wires to connect to where?

Post by Nadim »

Thank you. :)

You see, I'm not really expert in electronics, but here: https://hobbyking.com/media/file/431064 ... 211X11.pdf

it says that, if you are using a separate battery for the Rx, then you may ground the voltage sensor *of the motor battery*.

They write this, I think, because they assume that there are no crazy people like me who want BOTH the batteries monitored. :D

So I was puzzled because now that I'm using two sensors, I don't know which one I could fully ground to the Rx, if any one of them.

I attached a picture of my current setup. I do hope I'm not jeopardizing the health of the Rx or the servos... What do you think? :cry:
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Re: *Two* FBVS01 with *two* batteries: which wires to connect to where?

Post by jhsa »

Can't see your picture? :)

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Re: *Two* FBVS01 with *two* batteries: which wires to connect to where?

Post by Nadim »

Really?? :o :o

It's in the above post... I think I posted it while you were already writing your next post.. :D
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Re: *Two* FBVS01 with *two* batteries: which wires to connect to where?

Post by jhsa »

Ahhh, in a post above :) I thought you meant your last post :)

Yes, your connections look good.. I would do exactly the same.. :)

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Re: *Two* FBVS01 with *two* batteries: which wires to connect to where?

Post by Nadim »

jhsa wrote: Wed Aug 23, 2017 12:31 pm Ahhh, in a post above :) I thought you meant your last post :)

Yes, your connections look good.. I would do exactly the same.. :)

João
Thanks! By the way, there's a slight change in what I actually do, which for simplicity I omitted in the picture - that is, with the 6S, I don't actually connect the positive to the last pin of the balance connector, but to the fourth, so that I get the voltage as if it were a 3S. :D :D Just a matter of convenience with alarm settings, and also, that sensor is actually rated for a maximum of five cells.

P.S. You know what? Concerning the ground, I'd been doing it in the wrong way for years... I was grounding the sensor to the Rx and then only connecting the positive from the battery to the sensor... Luckily I didn't damage anything, and I've never had a problem actually, neither with servos nor with the Rxs... Still, I'm not sure as to what exactly changes... I mean, if only the positive of the battery is connected to the sensor, then, even if the sensor in turn is connected and grounded to the Rx, the Rx should still be getting no ground from the sensor... right? :?

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