How to connect FrSky Battery Voltage Sensor (FBVS-01)

[Nadim]

I am not really an expert in electronics, so please bear with me. I was searching infos on the FBVS-01 and found this thread, but I am now even more confused.

I have been instructed NOT to connect the black wire from sensor to A1/2 on the D8R Rx, buth rather from sensor to battery, and have done so since. But does this apply even if the battery I want to check the voltage of is a different one, on an entirely separate circuit from the one that is feeding the Rx? So with a scheme, would the following be the right way to wire up the system?

Thank you guys.

[jhsa]

The ground from Battery 2 is alteady going to the receiver through the kill switch connection. So, in my opinion there is no need for connecting the ground from the voltage sensor to the receiver.. That could create a ground loop anyway, and that is also not good..

João

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[Nadim]

I see, I actually kind of "imagined" so.

So I'll be OK if I wire it up as in the picture, will I?

[jhsa]

In my opinion, yes. Unless the kill switch is somehow isolated. But that could be measured.

João

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[Nadim]

In my opinion, yes. Unless the kill switch is somehow isolated. But that could be measured.

Is this "measurement" something that a noob in electronics like me can do?

BTW the kill switch is the ever popular one from RcExl:

https://www.flyinggiants.com/forums/sho ... 1533037083

[jhsa]

It is easy to measure.. Just measure the continuity between the ground on the Kill switch battery connector, and the ground on the kill switch receiver connector. if it measures close to zero Ohms, then you are good to go..

João

[Nadim]

I don't have the equipment to do so...

In the case the kill switch WAS indeed isolated, what should I expect if I wire up the system like that? Just not to work, or am I going to fry something?

[Kilrah]

Just some nonsensical reading.

[Nadim]

Just some nonsensical reading.

Could you please elaborate?

[Kilrah]

Not the correct battery voltage, an unstable/fluctuating reading,...

[Nadim]

I had totally misunderstood your previous post: I thought you were talking about this thread, whence my question. Sorry

[jhsa]

If you want to configure and calibrate voltage sensors, I strongly recommend that you buy a digital multimeter..
If you can't measure your batteries voltages, how do you know the sensors are reading correctly?

João

[Nadim]

I do have a couple of cheapo voltage sensors like this one: https://www.amazon.co.uk/Battery-Tester ... B011SE9DB8

I know it's probably not 100% accurate... but not too far off either, as per checked with my charger.

[jhsa]

As I said, I would buy a multimeter. They can be found very cheap, and if you are into model flying (special big birds ), you should have one anyway.
Easy to troubleshoot bad parts, measure voltages, etc.

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[Nadim]

I thought I'd report about this, in case anyone is interested.

It turns out that the kill switch is indeed insulated, so I had to connect both wires from the sensors to the Rx (and of course from sensor to battery) to get the reading.

This regardless if the kill switch is actually feeded (thus ON) or not. Without the black wire, it doesn't work.

[Kilrah]

Just be aware that it is then no more insulated, and ignition switches usually are in order to reduce potential interference from the ignition on the radio. So check everything well to make sure you're not getting ignition noise that reduces your RC range.

[Nadim]

Ah, right... I couldn't think about that.

Is a reduced range the only potential downside of this scenario? Or am I risking to damage the Rx or other components?

Or... I would have to find another solution to check the voltage of the ignition battery, but at this point I wouldn't see how.

[Nadim]

I was wondering: what Kilrah said about the switch not being insulated anymore seems to me to imply that the noise doesn't only come from the CDI module to the kill switch, but also from the switch to the battery, as in:

Because if this is the case, then forget about voltage sensors and stuff, every single battery setup on a gas plane would cause the same issue, as in:

Single battery setups seem to be very common though, especially on small planes, due to weight saving, and as far as I read online on forums there haven't been problems related to noise. I also have used it on a couple of planes without issues.

Is there anyone who understands electricity a bit better than I do (shouldn't be difficult to find ) who can comment on the above?

[Kilrah]

Of course, noise gets carried everywhere if there is no insulation. It might work for some setups, not for others. Some CDIs are very noisy, some aren't.

[Nadim]

I understand that but my question was rather whether the kill switch filtering can work also against the noise being passed from the CDI back to the battery, not only from CDI to Rx. I'm not even sure this is physically possible.

[Kilrah]

No it doesn't.
It is technically possible, but complicated and kind of overkill.

If you used an FLVSS sensor to measure the battery you'd keep the separation since it is isolated as well.

[Nadim]

That's good to know, thanks.

Unfortunately I'm still using the old D series Rx on all my planes, so I don't have SmartPort. I guess it's time for an upgrade to the X series sooner or later.

In the meantime, would one of these: https://www.amazon.com/VSKEY-Anti-inter ... B075G2P5SW work?

If so, I guess it should be applied at the very source of the noise, namely on the wire from CDI to the switch. Is that right?

Thanks as always Kilrah

[Kilrah]

No idea about the efficiency of ferrite cores in this case.

[Nadim]

By the way I can't find on FrSky website nor anywhere in the Internet about the FLVSS being insulated. Could you please give me some references? Thanks

[Kilrah]

It isn't mentioned anywhere in the specs which is stupid becasue it's a great selling point, but it is.

The MLVSS however is not, and in its manual you can see a whole host of warnings about not reversing the connector or not using multiple for measuring series batteries with it becasue of it. No such problems in the FLVSS thanks to the isolation.

[Nadim]

Indeed it would be a great selling point.
Well then, I guess it's time to upgrade to the X8R and get a FLVSS.

Thanks!

[jhsa]

I know it is a bit off topic, but I wonder if the DIY openXsensor could be made isolated as well..
Need to look into it

João

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[Nadim]

I didn't know such thing existed, but please keep up posted.

Speaking of the FLVSS, I see it comes branded as "LiPo" sensor, and I am wondering whether it's equipped with some sort of buzzer that will beep automatically below a certain voltage.

I ask this because I would rather use it with LiFe batteries, so I hope it doesn't have LiPo-specific features that can't be disabled and would be unconvenient when used with LiFe.