Today's Message Index:
----------------------
1. 02:57 PM - Pitot Heat Ground (JDA_BTR)
2. 03:26 PM - Re: Pitot Heat Ground (Charlie England)
3. 03:42 PM - Re: Pitot Heat Ground (JDA_BTR)
4. 04:14 PM - Re: Re: Pitot Heat Ground (Charlie England)
5. 04:26 PM - Re: Re: Pitot Heat Ground (Daniel Hooper)
Message 1
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Subject: | Pitot Heat Ground |
I read the faqs, and know the recommendation to just take the pitot ground to the
chassis.
But I have a specific situation in mind, and would like some thoughts on it. I'm
building an RV14 and the pitot heat controller will be about 4 feet outboard
of an ADAHRS in the wing with a built in magnetometer. I figured if I ran the
14V/Gnd pair together as far from the magnetometer as possible I stood a chance
of not interfering with it when the heater is on.
I've gotten a Dynon heated pitot tube with controller. In this controller the
aluminum controller box is connected to ground as is the ground lead leaving the
box. Dynon says to a) not use the box for ground, and b) run a ground wire
all the way to the battery.
So I'm struggling with the idea that my ground wire will return the current to
the battery in a sufficient way to stifle interference of the ADAHRS magnetometer.
I figure a lot of current will take the controller box path and a lot will
take the wire path, but since I don't own two ammeters I won't be knowing for
sure.
So if the controller box is going to ground, seems like taking the ground wire
to a lug near the box might as well be done, because I won't get an interference
benefit running the ground wire back to the battery. Lots of people ground
the controller locally without trouble despite the reccs by Dynon to run a wire
all the way back.
Anyone have an expert opinion?
I'm about at the point of blowing off the long ground return and just getting a
remote magnetometer if it makes a difference.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=446897#446897
Message 2
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Subject: | Re: Pitot Heat Ground |
On Tue, Sep 8, 2015 at 4:55 PM, JDA_BTR <dudley@jdatkinson.net> wrote:
>
> I read the faqs, and know the recommendation to just take the pitot ground
> to the chassis.
>
> But I have a specific situation in mind, and would like some thoughts on
> it. I'm building an RV14 and the pitot heat controller will be about 4
> feet outboard of an ADAHRS in the wing with a built in magnetometer. I
> figured if I ran the 14V/Gnd pair together as far from the magnetometer as
> possible I stood a chance of not interfering with it when the heater is on.
>
> I've gotten a Dynon heated pitot tube with controller. In this controller
> the aluminum controller box is connected to ground as is the ground lead
> leaving the box. Dynon says to a) not use the box for ground, and b) run a
> ground wire all the way to the battery.
>
> So I'm struggling with the idea that my ground wire will return the
> current to the battery in a sufficient way to stifle interference of the
> ADAHRS magnetometer. I figure a lot of current will take the controller
> box path and a lot will take the wire path, but since I don't own two
> ammeters I won't be knowing for sure.
>
> So if the controller box is going to ground, seems like taking the ground
> wire to a lug near the box might as well be done, because I won't get an
> interference benefit running the ground wire back to the battery. Lots of
> people ground the controller locally without trouble despite the reccs by
> Dynon to run a wire all the way back.
>
> Anyone have an expert opinion?
>
> I'm about at the point of blowing off the long ground return and just
> getting a remote magnetometer if it makes a difference.
>
>
> My 1st inexpert reaction is, why is the magnetometer 'built in' the same
wing as the heated pitot? And 2nd reaction is, why can't it be built into
(moved to) the other wing? Never built a -14 or installed a Dynon, but I'll
bet their install instructions for the magnetometer say to keep it as far
away from high current wires and RF as possible.
Message 3
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Subject: | Re: Pitot Heat Ground |
It's a good thought. The ADAHRS location in the wing is very convenient to the
pitot for AOA. The magnetometer can be had as a remote unit and put elsewhere.
Nonetheless I would like to know about the situation as presented, because I'm
curious - why would the controller box be grounded if it is so important to carry
a ground wire all the way back to the battery; and when the faqs here say
the ground can be local and simple. Would running that wire reduce magnetometer
interference even if I ran it?
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=446901#446901
Message 4
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Subject: | Re: Pitot Heat Ground |
Again, inexpert opinion...But with a high-current device like a pitot tube
heater, they are probably trying to guarantee a solid ground path for the
heater. With all the variations in building techniques, and hundreds of
'joints' between the pitot & the battery negative, it's conceivable that
one could have several ohms of resistance in the ground path when using the
airframe. Could be worse with a tube/fabric airframe, through the steel.
Another thought is that the instructions are intended to be 'universal', so
no matter the airframe material, a good ground is provided.
But I'd hope someone at Dynon could give you the real answer.
If the magnetometer is built into the ADAHRS, you could just prepare for
having to remote it (a few extra wires), and just try it before purchasing
the extra magnetometer.
On Tue, Sep 8, 2015 at 5:37 PM, JDA_BTR <dudley@jdatkinson.net> wrote:
>
> It's a good thought. The ADAHRS location in the wing is very convenient
> to the pitot for AOA. The magnetometer can be had as a remote unit and put
> elsewhere.
>
> Nonetheless I would like to know about the situation as presented, because
> I'm curious - why would the controller box be grounded if it is so
> important to carry a ground wire all the way back to the battery; and when
> the faqs here say the ground can be local and simple. Would running that
> wire reduce magnetometer interference even if I ran it?
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=446901#446901
>
>
Message 5
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Subject: | Re: Pitot Heat Ground |
There are a couple of potential answers to this. One simple one is that the ground
connection between the chassis of the box and the power ground inside the
box is not low-impedance. In designing circuits, you do what you can to minimize
radiated and conducted noise, and one of these ways is to segregate grounds
internally. The connection between the two may be a giant bonding braid, a screw
through the board, or even a 1 MOhm resistor.
Another reason that the installation manual may encourage a wire pair instead of
a single conductor and chassis ground is that high current devices create larger
magnetic fields. Magnetic fields are proportional to several things, two
of which are current and current loop area. By taking two wires back to the battery,
you minimize loop area. When using the chassis ground method, you have
no real control over the loop area.
There may be another line of reasoning, but that is only known to the engineer
who wrote the installation manual unfortunately.
I am not that guy, so I have no idea, but that should give you some possibilities
to consider.
Daniel
> On Sep 8, 2015, at 5:37 PM, JDA_BTR <dudley@jdatkinson.net> wrote:
>
>
> It's a good thought. The ADAHRS location in the wing is very convenient to the
pitot for AOA. The magnetometer can be had as a remote unit and put elsewhere.
>
> Nonetheless I would like to know about the situation as presented, because I'm
curious - why would the controller box be grounded if it is so important to
carry a ground wire all the way back to the battery; and when the faqs here say
the ground can be local and simple. Would running that wire reduce magnetometer
interference even if I ran it?
>
>
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=446901#446901
>
>
>
>
>
>
>
>
>
>
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