Getting Zapped when touching focuser?

[glend]

I have an un-usual problem with some sort of electric charge on my gear. I need some advice on tracking it down. This is on an imaging setup on a concrete pier in my observatory, CGX mount, MN190 scope, ASI1600MM-C camera, Starlight Express filter wheel, MBeat 7 port powered hub, ZWO guidescope and ASI290 guide camera. Heater straps on the MN and guidescope are powered by a Kendrick contoller with source from a 12V battery. All other devices are powered by 12V from two AC/DC power supplies, except the Mbeat and USB3 cable extension which run off AC plug packs ( output 5V). The pier top plate is not earthed but this setup has been running for three years without any issues, and the mount (with different scope and camera) was out at Mangrove Mountain the night before without any issues.

When touching the focuser knob I receive a small shock (consistent with a 12v supply being applied somewhere), in fact touching any part of the gear, scope and mount I receive this small shock. This is not normal. This stopped my imaging last night because it also seems to affect the ASI1600 ability to download an image to SGP, with SGP going into a loop trying to download but failing to get anything. The CGX PWI mount control software running on the laptop failed at the same time with an 'exception error'.

Any ideas on how to debug this in the daytime?
I will take my multimetre out and try to measure the potential, and probably disconnect one power supply after the other, and one accessory after another. Has anyone had something like this happen?:question:

[Atmos]

I’ve had something similar to this happen once a few days ago but that was not too long after I’d been zapped by my car so I likely was still holding some potential energy.

Could it be from your clothing that the static build up is coming from? That usually is the every day culprit.

[glend]

Hmm, never had that happen in the Obs before. The Obs is built off the ground on timber posts and has carpet tiles on the floor backed with rubber, and i was wearing my rubber sole shoes. No i don't think static was a factor, and it happened multiple time when I touched the gear (static usually discharges). It seems active if the gear is powered up.

[JA]

Hello Glen,

To potentially state the obvious, it's important to track this down, not only for human comfort reasons, who likes to be shocked anyway, but also for equipment protection reasons. If it is an electrostatic discharge this can be of considerable danger to the health of sensitive electronics, such as those in computers, cameras, etc..

Perhaps use a multimeter to look at the voltage differences in and around your gear, even relative to your own body. You might need to use a maximum hold function to possibly catch any transient discharge. You could also check current.

I'm not saying it is static, but if humidity is very low this can increase the incidence of electrostatic discharge. This is a consideration in building air conditioning and I've seen it more prevalent as relative humidity approaches 30%.

Failing all that and given its reoccurrence, maybe you have an excessive leakage current from one of your connected devices. Perhaps use a multimeter or a brute finger shock test to determine the culprit by the process of elimination as you remove one item of gear at a time and then retest your setup for the same shock/ESD.

The problem may stem from a difference in the ground potentials of your devices and this may provide a solution , i.e: adopt a common ground, but I wouldn't force that until I'd zeroed in on the culprit by elimination.

Good luck

Best
JA

[glend]

Thanks for those suggestions. Humidity last night was 65% in the Obs, which dies not normally encourage static build up. Will do a full powered up test with all devices today.

[glend]

Thanks Rowland, I am getting an idea about where this might originate from. The ASI1600 camera uses an external heater mounted to the front of the camera to prevent condensation on the sensor compartment window. I recall your effort to build something similar for your cooled DSLR. This ZWO heater element is an add-on to these original Version 1 cameras, subsequent later versions use a different approach. The heater element on the version 1 cameras, is sandwiched between the camera and the filter wheel housing, it maybe that the thin film element has shorted to the filter wheel case. I will start there.

[bojan]

Check AC/DC adapter.

Most likely it is not properly grounded.

[rcheshire]

Sorry Glen, I saw JAs response and deleted mine. A layman's approach. Check to see if you can short to ground. Check wires / connections.

A strip of kapton over the element and under any terminals solder joins will sort any shorts or leakage.

And yes, as Bojan says, check the adapter.

[multiweb]

Sounds like a dew heater of some kind. I get that buzzing feeling on any alu surface on my rig whenever I have the heaters on. I also get a lot of statics but that's me. I spark everything. Cars, laptops, even people in shopping centers when I touch their trolley.

[luka]

Glen, not sure about the Kendrick dew heater controller but most of the dew heater controllers switch the negative/ground terminal. This normally would not be a problem but most of heating tapes use the RCA plugs (https://www.altronics.com.au/p/p0200a-red-rca-plug-line/) which have one terminal (usually ground) exposed.

The combination of the two (switching ground and RCA plugs) is very bad and potentially dangerous. When the heater ground gets switched off the outside of the RCA plug will be at 12V. Due to the design of the RCA plugs (large exposed metal surface) it is just too easy for the 12V to touch the scope or the mount somewhere. This will put everything at 12V potential.

Unfortunately almost everybody is using the same bad design. Try wrapping something around the dew heater connectors to insulate them.

[glend]

I have spend some time going over everything and believe I have narrowed it down to the camera. With the camera off the scope, nothing else, ie mount, guide scope, etc is sparking. I tried removing the camera connections (there are 3) one at a time, and it seems that the camera cooling power to the TEC is where i am getting the zap, which can traverse metal to metal contact to the scope, mount, etc. It may have to go back to ZWO, but it's out of warranty. I will switch over to one of my other cameras for testing tonight. If all ok tonight I will have to make a quick decision, as I am suppose to be going to Astrofest in less than three weeks - not enough time for ZWO to turn it around I fear.

[multiweb]

Bit short notice for ZWO given the astrofest is coming fast. Meanwhile you can discharge any nasties by keeping a hand on your mount tripod prior to touching the focuser or any other part of your telescope.

[Stonius]

You haven't plugged in your laptop or something? Nothing's running off additional AC transformers or anything? it's all coming from the single 12v supply?

[glend]

No the laptop runs off AC adaptor in the Obs, as does the Hub power pack (5V) and the USB3 camera active extension cable (also a 5V plug pack). The camera TEC power does come off a AC/DC power supply, and perhaps I can switch that over to dedicated battery power for testing. The camera TEC power has come off the same power supply for well over two years now, without issues until now.
I have a DC/DC converter for the laptop which I use in the field, so I can switch that over as well but the laptop seems to be ok. I have run the camera TEC power off a battery powered pure sine wave inverter in the field and it has worked fine in that configuration, I could switch to that mode for testing.

Update: I have attached a heavy gauge earth wire to the mount top plate on one end and the other end to rebar driven into the ground. That should eliminate any further float in the assembly. We'll see if this makes a difference tonight.