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I have a Rasberry Pi device (a Helium miner, a Bobcat 300), and I'm now on my 6th power adapter for the device, as all of the previous adapters have burnt out after 1 or 2 weeks.

Here is the pertinent information:

I live in Canada in a single detached home, and have not had power problems in the past at all. The device itself takes a DC12V, 1 ampere input. I have a surge protector device at the outlet (Amazon link here.)

Originally, the device was directly plugged into the wall, and ran for about 2 months. I then installed a large 8dBi antenna on my roof that connects to the device by a long LMR400 cable, and pretty much since then its been burning out power adapters.

I buy equivalent adapters from Amazon, and the device works again as normal for a week or two, and then one day it is as dead as a doorknob.

I opened up one of the burned out adapters and there is nothing obviously burnt or broken (and tried different devices to confirm they are really dead.) I had an electrician come to my house and check the outlet I was using, and he said it was completely normal for the voltage and Hz.

I tried different outlets, including running an extension to another room. Other devices are plugged in the room INCLUDING other power adapters and they have not failed the same way.

Here are my basic questions:

  1. Could the connection to an antenna somehow cause just the power adapter to burn out?
  2. Could the Raspberry Pi/Bobcat miner device be causing it to burn out?
  3. Is it possible to diagnose HOW the power adapters failed if I take it to an electrician or electronics repair shop? (And therefore get a clue as to what is happening.)
  4. Is it possible to get some kind of power adapter that would be more impervious to any of the possibilities that might be burning these out?

I'm getting really tired of shelling out 20 bucks every 2 weeks for another crappy Chinese power adapter (I've gone through 5 brands too), and I'm hoping someone can at least give me some ideas.

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    \$\begingroup\$ For one, stop buying cheap Chinese power supplies. They're absolutely notorious for falling over. Is the supply getting hot? Have you measured the actual power consumption / current draw of the device, with or without the new antenna? \$\endgroup\$ Commented Sep 20, 2021 at 5:42
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    \$\begingroup\$ Outlet power meters can be had in the 30 CA$ range. Cheaper than calling out an electrician and very useful things to have in general! You just plug it into the wall and plug the device into the meter. Ideally look for one that measures current and "power factor" and has min/max functions. You can see if something is occasionally overloading the transformer and knocking it over. 5 cheapo supplies failing is NOT unheard of though, especially if running near their stated power. \$\endgroup\$ Commented Sep 20, 2021 at 6:14
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    \$\begingroup\$ This sounds like a problem: I buy equivalent adapters from Amazon \$\endgroup\$ Commented Sep 20, 2021 at 7:05
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    \$\begingroup\$ If the original supply failed after 2 months I'd be expecting the manufacturer to replace it. \$\endgroup\$ Commented Sep 20, 2021 at 8:44
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    \$\begingroup\$ You have an external antenna - do you have a lightning protector and earthing for the antenna? If not, i’d suggest you get one. And get yourself a better psu. \$\endgroup\$ Commented Sep 20, 2021 at 10:18

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I would offer a 3 pronged approach to solving the problem. Please forgive me if I get too basic in any of this:

  1. The band specification for LoRa in Canada is the 915mHZ band. Verify your device is for that band and the antenna is also for that band. An antenna needs to be grounded and also best to have a lightning arrestor as mentioned in the comments. A static charge can build up on the antenna and apply a dangerous voltage to your device instead of it passing harmlessly to ground. Look for a high frequency grounding block that will pass a 915mHz signal. A tutorial is here: https://www.groundedreason.com/how-to-ground-an-outdoor-antenna/

  2. Also mentioned, connect your adapter to power through a power usage meter such as a "Kill A Watt" so you can watch it "live". You can also see if the power factor is negative, which means power is feeding back into the power supply. These meters also store the power used over time. You can see if the mains voltage is correct or fluctuating. If you have a multi-meter, you can measure the voltage and current at the input to the Bobcat. You would need to make or buy an adapter that would allow you to get to the power wires. You could buy one male and one female "2.1mm barrel jack to terminal screw adapter". You plug the female onto the end of your power supply and the male into your device. You can then connect wires straight through to the correct +/- screw terminals, plus to plus and minus to minus. Measure voltage just by connecting your voltmeter across the plus and minus terminals on one adapter. To measure current, you need to wire the meter in series by removing the positive wire where it connects to the device, connect that to the positive lead of the meter. Then connect the negative lead of the meter to the positive terminal on the adapter where you just removed the wire. Make sure when measuring voltage and current, you select the right range and have the probes plugged into the correct ports on the meter. Good video on doing this here: https://www.youtube.com/watch?v=om85DYMyYBA

  3. Antennas, especially at that frequency with a lead length that must be long to get to your roof, should be matched to the transceiver. First make sure it is the correct antenna AND cable rated for that frequency and the correct impedance. It is possible that you have a high SWR, which means your signal to the antenna is reflecting back into the transmitter causing the voltage to rise and have it draw more current. Usually, this causes the final output stage of the transmitter to fail before the power supply though. Due to the expense of an SWR meter / Antenna Analyzer for your 915mHz LoRa signal, this may not be practical.

  4. Go for more amps on the power supply. Yes, a 12V, 5W device should be drawing less than half an Amp. But make sure the power supply really can deliver at least 1A continuous. Don't go above 2 or 3A just in case since if there is an issue with the device drawing too much current, you don't want that to fry your device. The manufacturer would obviously supply the correctly rated power supply, so that with the number of different power supplies have failed suggests something else.

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  • \$\begingroup\$ Assuming it is 1) above, and assuming it would be difficult for me to access the antenna externally (at least in the short term), is there any way to dissipate this static charge easily from inside the home? \$\endgroup\$ Commented Sep 20, 2021 at 16:24
  • \$\begingroup\$ 1) I have a lightning arrestor arriving, could I connect this to a grounded plug and plug it into a grounded outlet? (excuse me if that's insane or something, this is all pretty new for me) 2) If the power adapter itself has a grounded plug, does that mean it might be better able to dump the static discharge? \$\endgroup\$ Commented Sep 20, 2021 at 16:29
  • \$\begingroup\$ Further note: I'm not aware how easy it is to access the house ground from an arbitrary room on my second floor. \$\endgroup\$ Commented Sep 20, 2021 at 16:33
  • \$\begingroup\$ Inside the home is not good. you want it discharged outside. And no, you don't want the ground inside the home. I know it's a pain, but ideally, you have a big 3' copper rod right outside where the lead enters the house and you drive it into the ground until just a few inches of the top sticks out and you connect to that. \$\endgroup\$ Commented Oct 11, 2021 at 18:19

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