Isolated power supply with protection from lightening strike

Thread Starter

PlasmaT

Joined Feb 19, 2015
61
I need to power an electronic device at an elevated height. I am thinking of powering the device via a power source from the ground level. The data from the device is transferred via RF module.

My question is whether the supply wires (from ground level to the elevated device) might increase the risk of a lightning strike. Appreciate any advice how to tackle this problem. At the moment I am thinking of using a transformer for isolation. Will this be enough?
Thanks.
 

Papabravo

Joined Feb 24, 2006
17,030
Enough for what exactly? In the case of a lightning strike it is likely that the device and the power supply will both be destroyed. The transformer might not survive either.
 

DickCappels

Joined Aug 21, 2008
7,905
Hmmmmm....given that some scientists shoot rockets into thunder clouds to cause lightning discharges that then follow the wire down to the ground, the answer is "probably".

Depending upon the amount of power you need you might be able to transmit the power by light or microwaves.
 

philba

Joined Aug 17, 2017
960
You need to provide a "low impedance" path to ground, AKA lightning rod. There a number effects from a lightning strike - the super high current discharge, thermal/mechanical shock from the explosion and induced secondary currents. Anything close to the strike will be toast, literally. It's only the last item that you can protect against. Your best bet is to have a lightning rod and locate the device some distance away (I don't know how far that is though). This is a decent overview of the issues and general approaches
 

Dodgydave

Joined Jun 22, 2012
10,063
Either power it from a local supply near to the device , or if you must run it from the ground floor, put the cables in metal conduit with an Earth rod six feet deep ideally from Copper at the ground .
 

Thread Starter

PlasmaT

Joined Feb 19, 2015
61
I accept that in case of a direct lightening strike the device and power supply could get destroyed. I just want to prevent a lightening from being attracted to this device as a preventive measure.

My thought was that, if the device is powered by battery as a single unit and elevated above, it does not make any difference to the attractiveness of a lightening (correct me if I am wrong).

Hmmmmm....given that some scientists shoot rockets into thunder clouds to cause lightning discharges that then follow the wire down to the ground, the answer is "probably".
Well... I am concerned about having a wire from the device to the power supply at ground and providing a path to act as a shortest path for the lightening.

So am I putting the device and nearby property at risk by just providing a wire to power the device? Instead, is it worth not to take the risk and power the device on battery and keeping on replacing/recharging the battery. Well I have to climb up to the device, so this is also not an easy task as well.

So can I use a coupling transformer? I could send an AC voltage across the transformer to the device. Static charge will not get across the transformer. So not attracting the lightening. Am I right?
 

MrChips

Joined Oct 2, 2009
24,458
A transformer is not going to protect your device.

You need:

1. A lightning rod.
2. Power cable inside rigid metal conduit.
3. Faraday cage around your device.
 

Thread Starter

PlasmaT

Joined Feb 19, 2015
61
Looks like my hobby project is going to be a major project. Is there any other alternative that i could settle for. I am a bit reluctant to go for a lightening rod. The device is a water level sensor on top of a overhead water tank (28ft above ground). At this elevation, there are no nearby structures except for some tall trees.
 

philba

Joined Aug 17, 2017
960
Is the water tower metal? If so, I'd pretty sure you aren't increasing the chance it will get hit. Has it ever been hit before?
 

MrChips

Joined Oct 2, 2009
24,458
Looks like my hobby project is going to be a major project. Is there any other alternative that i could settle for. I am a bit reluctant to go for a lightening rod. The device is a water level sensor on top of a overhead water tank (28ft above ground). At this elevation, there are no nearby structures except for some tall trees.
Your water tower, if it is made of metal, is your lightning rod.
Put your electronics lower than the top of the tower and it is somewhat protected.
 

Thread Starter

PlasmaT

Joined Feb 19, 2015
61
Is the water tower metal? If so, I'd pretty sure you aren't increasing the chance it will get hit. Has it ever been hit before?
Your water tower, if it is made of metal, is your lightning rod.
The water tank is of plastic. It is on a concrete slab. There are 4 small concrete columns surrounding the tank that was supposed to mount a roof to the water tank. The columns are about a foot above the water tank.

So will these reinforced concrete columns act as a lightning rod? I know that there is at least one 10 mm diameter reinforcement bar for each column. But the reinforcement is not exposed.
 
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dendad

Joined Feb 20, 2016
3,926
You could try a solar panel and battery powered sensor and a radio link. It would only need to transmit a signal once a day just to make sure it is still working, otherwise if the water level changes by a set amount so as to limit power consumption. You may even do away with the solar panel if your receiver will generate an alarm if it does not hear from the sensor at least once a day. Then you can change the batteries. The sensor spends most of the time asleep.
 

Dodgydave

Joined Jun 22, 2012
10,063
How does the water tank get a fresh supply of water, with a ballcock valve?? just wondering why you need to monitor the level,..
 

Tonyr1084

Joined Sep 24, 2015
6,374
How about a different approach? Since water weighs 0.43 pounds per foot of elevation (https://www.rcgroups.com/forums/sho...oes-water-pressure-increase-per-vertical-foot) use a pressure sensor to determine how much water (in feet of elevation) is present. You can do this from ground level.

Also keep in mind that many things can be conductive to lightning. Likely the water in your tank will be very conductive. Any lightning strikes will channel to ground through your water system. That's why they say not to shower or bathe during a thunder storm. Hard wired telephones have also been known to channel lightning to those using the phone at the moment of a strike. Albeit, not fatally, but lightning can go many places. Water is more conductive than the plastic tank. However, how does that water get down to the point of use? Via copper pipe? If so - I'd HIGHLY recommend a grounding rod tied via 10 to 6 gauge wire to your plumbing. If you're using PEX plumbing I'd suggest you plumb in a short length of copper and use that to ground the system. Regular home plumbing that comes to the house does so via under ground plumbing. Hence, the cold water pipes in your house is a good grounding source. However, with PEX, the grounding potential is not acceptable. Hence, you can not ground to cold water PEX tubing. It's not allowed. You MUST provide a solid ground to devices within the home via a good (and approved) grounding method. Using a short length of copper pipe will prevent lightning from following the path into any structures seeking a path to ground.

I'd go with a pressure transducer AFTER the copper coupling to ground point. That'll help protect your system from lightning strikes. And it can be powered from standard house current. No need for isolation. Though you can isolate if you feel better that way. Use a 12 volt transformer. Then your circuitry is completely isolated from the house ground, and your ground coupling will direct any energy from a lightning strike to ground.
 
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Tonyr1084

Joined Sep 24, 2015
6,374
Further, since your tank elevation is 28 feet - that's 12 PSI. I'm assuming you're going to have a pressure boost pump and tank so you can boost the water pressure to around 40 to 60 PSI. Your sensor would have to be before the boost pump. And you'd be protecting your pump from lightning by grounding the tank through the ground coupling.
 
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Thread Starter

PlasmaT

Joined Feb 19, 2015
61
I'd go with a pressure transducer AFTER the copper coupling to ground point. That'll help protect your system from lightning strikes
Currently in my house the pipes are of PVC and the earthing is presumed to be via the water motor pump. The motor is connected to the "Earth" wire of the House ground. Hope this is sufficient. Anyway, as per your detailed diagram, I am going to add the copper tube and earth it with an additional grounding rod for additional safety.
 

Tonyr1084

Joined Sep 24, 2015
6,374
You said your plumbing is PVC. That concerns me a little because PVC is not rated for potable water (drinking). Perhaps you have CPVC, which IS safe for consumption and looks just like PVC. Or if you have PEX, something that is fairly new to the market, that is rated for consumption as well. Safe for drinking. Sometimes people mistake PVC for PEX . PEX is flexible and comes in standard white, blue and red. I suppose you can find it in other colors too but those are the only colors I've seen.

If you don't mind a question, what is the purpose of this tank? Are you collecting rain water, purifying it and storing it or are you just keeping it full in case of an emergency? Really curious.
 

Thread Starter

PlasmaT

Joined Feb 19, 2015
61
You said your plumbing is PVC. That concerns me a little because PVC is not rated for potable water (drinking). Perhaps you have CPVC, which IS safe for consumption and looks just like PVC
It's uPVC. only cold water so no need for CPVC.

If you don't mind a question, what is the purpose of this tank? Are you collecting rain water, purifying it and storing it or are you just keeping it full in case of an emergency? Really curious.
the tank is for drinking water.
 
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