Author Topic: Grounding a wireless VP2 station in addition to grounding the mounting structure  (Read 497 times)

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Offline klschmidt

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Having a nice open area for weather station siting, I decided to install my VP2 according to NWS standards (anemometer at 33 feet). I constructed a steel triangular lattice tower for station mounting. Having heard that static buildup can increase the chances of a lightning strike, I decided good grounding was important. I connected two grounding rods to each leg of the tower with #4 solid copper wire. The station ceased transmitting yesterday, so I went to investigate. Upon opening the transmitter cover and touching the battery, I received a significant electrical shock. It would seem that static had accumulated between the ISS and the structure it is mounted to. Is it ok to allow such static to accumulate? If not, how can I ground the ISS? It would seem to me that the ISS is completely isolated from the structure it is mounted to. All sensor mounting is plastic. Even where steel bolts are used, they hold plastic to the tower. The wire which goes up to the anemometer is, of course, insulated. With no electrical connection between the weather station and the structure it is mounted to, how can static accumulation be prevented? I find no green ground screw inside the transmitter cover.

Davis tech support suggested contacting a licensed contractor to help with grounding issues, but I'm not sure where to find a contractor familiar with the internal circuitry of a VP2.

As a side note, the station resumed transmitting after draining the charge.

Offline Aardvark

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why don't you drill a hole in the case, insert a screw and drop a ground lead as you have with the rest.  I have never had any such problems, but then again,  maybe it is lurking out there.

Definitely drilll the hole in the case, bolt and nut, moisture seal, drop a ground wire.
Davis VP2 Plus; 24h  FARS;  Soil Moisture/Temp Station;Weatherlink ;
https://www.desmoinesweather.org

Offline eyecue

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 :shock:  Have you checked all the bonding connections to be sure that they are getting a good low resistance flow to the ground rod?  How deep are the ground rods?  With that tower is it all one piece?  If not the joints need to be checked too. Clamps do hold the plastic housing to the metal tower so it could be an internal issue.  Ill check my spare unit and see
Cocorahs, Skywarn, Aficionado of weather. Davis VP2  pro wireless, Oregon Scientific and DIY.

Offline klschmidt

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Aardvark, when you mention "the case" are you referring to the transmitter or sensor housing? If so, mine are all plastic. I believe connecting a ground wire to some part of the station is a good idea, but I don't see many conductive surfaces.

eyecue, I measure 0.0 ohms between grounding wires. All six ground rods are ten and a half feet deep. The tower is one piece welded construction.

To continue my original post: After getting shocked removing the battery, I decided to drain any residual charge before replacing the battery. A jumper wire between the battery terminal and the tower produced a spark, so the electrical circuitry of the Davis is clearly isolated from the tower. Touching the tower did not shock me.


Offline Aardvark

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Aardvark, when you mention "the case" are you referring to the transmitter or sensor housing? If so, mine are all plastic. I believe connecting a ground wire to some part of the station is a good idea, but I don't see many conductive surfaces.

eyecue, I measure 0.0 ohms between grounding wires. All six ground rods are ten and a half feet deep. The tower is one piece welded construction.

To continue my original post: After getting shocked removing the battery, I decided to drain any residual charge before replacing the battery. A jumper wire between the battery terminal and the tower produced a spark, so the electrical circuitry of the Davis is clearly isolated from the tower. Touching the tower did not shock me.

The housing.
Davis VP2 Plus; 24h  FARS;  Soil Moisture/Temp Station;Weatherlink ;
https://www.desmoinesweather.org

Offline eyecue

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On the ISS board there is a screw in the upper right  corner that has a washer around it..  That screw is the electrical ground for the board that has all the electronics on it.  You could run a ring terminal under it and a wire from that to the outside to ground the unit.
Cocorahs, Skywarn, Aficionado of weather. Davis VP2  pro wireless, Oregon Scientific and DIY.

Offline dalecoy

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Given your relative humidity at approx. 10%, and rather continuous wind of 10 mph or more.......

Offline miraculon

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In my opinion, grounding the board as eyecue recommends is the best bet to eliminate your "shock hazard" when servicing the ISS battery. However, what is the "root cause" of the charge? Is it static buildup on the anemometer cups and/or vane passing the charge down to the ISS via the wires, or some direct buildup on the SIM transmitter housing?

For what it is worth (my 2 cents worth), my RM Young Wind Monitor Jr. has a small gauge ground wire that comes from the wind set and the purpose is to drain off static charge. The Young obviously takes the charge buildup into consideration, and I suspect that the internals of the speed and direction sensors are connected to this ground wire. I believe that this was to reduce damage to the vane potentiometer from arcing due to the static buildup.

I wonder if something like this would help: http://www.l-com.com/surge-protector-outdoor-high-power-telephone-dsl-lightning-surge-protector-rj11-jacks# This is the outdoor unit for a single line. If the charge is coming from the wind assembly, this might help dissipate the charge.




Greg H.




Blitzortung Stations #706 and #1682
CoCoRaHS: MI-PI-1
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Offline klschmidt

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On the ISS board there is a screw in the upper right  corner that has a washer around it..  That screw is the electrical ground for the board that has all the electronics on it.  You could run a ring terminal under it and a wire from that to the outside to ground the unit.
This is precisely what I needed. I hadn't realized that Davis supplied a ground screw for the circuit board.

Miraculon, I'm not sure of the source of the static. Conditions like dalecoy mentioned are common at this time of the year, and would certainly invite static. The incident I mentioned in the original post occured after a mostly dry thunderstorm (the ISS ceased transmitting during the storm). I understand those who are about to be hit by lightning often notice their hair stand up from static first. Maybe lightning considered my station as a target?

Does anyone know if the ground screw eyecue mentioned grounds one of the wires to each sensor in addion to grounding the circuit board? If attaching a ground wire to this screw grounds the anemometer, I'm thinking I might be ok without a surge protector. Any thoughts?



Offline dalecoy

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If this is a wireless VP2 (no cable connection to your house), then you don't need a surge protector. 

If lightning strikes your tower, the induced currents will almost certainly "fry" (technical term) the ISS circuit board and the anemometer and/or anemometer cable.  Nearby lightning strikes can have the same effect.

A surge protector would not "drain" static buildup from the anemometer, if that's present.  Surge protectors do have a good purpose - this just isn't one of them.
« Last Edit: June 09, 2018, 12:34:30 PM by dalecoy »

Offline klschmidt

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Thank-you to all for the suggestions. I have completed the grounding of the circuit board.

As a follow up for anyone who might wish to connect a circuit board ground: I found that the ground screw has a nut on the back side, so the circuit board will need to be removed to remove the screw. With the circuit board out, I traced the wiring and found that each sensor plug has a wire connected to the pcb ground. Therefore grounding the pcb should ground each of the sensors as well. Some of the solder mask had flowed into the screw hole and partially insulated the ground screw. I was unable to get a 0.0 ohm reading between the ground screw and solder joints connected to the ground, so I decided to remove the solder mask under the washer. The solder mask on this pcb is really thick and hard; access to a milling machine was beneficial. A small amount of dielectric grease was applied to prevent corrosion and the #4 ground screw was reinstalled through a ring terminal attached to a ground wire.

I suppose it will be difficult to determine whether or not a ground wire will save my weather station, but something does seem wrong with circuit boards that throw sparks. Thanks again for your help!

 

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