Jump to content

sgl_imaging_challenge_banner_31.thumb.jpg.b7a41d6a0fa4e315f57ea3e240acf140.jpg

AC Voltage present on the tripod


Recommended Posts

Hi All,

After much deliberation, I finally bought myself the Celestron C8-SCT and a Skywatcher HEQ5 Pro mount and decided to take it round to a friend’s house and set it up on his lawn. When the mount was powered (from a standard mains powered 12VDC supply), there was a noticeable “tingle” felt when touching the tripods legs. I immediately disconnected and checked all the wiring but everything seemed ok. I retired to the garage and connected a multimeter between the DC ground (outer part of the plug) and mains earth and was alarmed to measure about 98VAC. I measured a similar voltage between the tip (+12v) and mains earth/ground so assumed my PSU must be faulty. We continued without power and finally managed to look through my new telescope and I was delighted.

The next day, I tried a different PSU and the exact same AC voltage was present. I’ve since tried three other PSUs, from three separate locations and they all exhibit a rather high AC voltage between the DC terminals and mains earth/ground.

I’m assuming the “tingle” was down to the wet lawn I was standing on, but why would there be any AC voltage present in the first place? I had thought about using an earth rod and bond it to the tripod, but that seemed a bit extreme for a 12VDC system.

If anyone could help restore both my sanity and safety, I’d be grateful.

Link to post
Share on other sites

Unfortunately the manufacturers don't seem to think power supplies need to use the earth pin on the mains plugs these days. Switch mode power supplies should ALWAYS use the earth but they never seem to :(

I really don't understand why manufacturers do this, it's dangerous, especially when the equipment is used outside. You should also always use an earth leakage unit (unless your house has a built in one in it's circuit breaker box).

Earth your tripod, and also earth the negative (0V) line coming from your power supply. It could save your life if the PSU develops an internal circuit from the power supply output to the live mains wire (say via dew/moisture on it's PCB).

Edited by Cath
Link to post
Share on other sites

There are a few threads discussing this issue...I will dig them out when I fire up the PC later...

The DC Output of the psu is floating with respect to earth and yoy are expeincing a tingle as the psu's leakage currebt fibds its way to earth through you... It will (or rather should) only be a few microamps...

Peter...

Link to post
Share on other sites

Since you're setting up on "wet lawn" you could try connecting an earth wire to your tripod and staking it into the ground. You can get an earth rod (and clamp) from Screwfix for a couple of quid.

Link to post
Share on other sites

3 different DC power supplies? do you still get 90 VAC to earth when you plug in at a different location? Are you using a mains extension to supply the 12VDC supply? if so i would check the wiring on this as it may have wires crossed!

Link to post
Share on other sites

Yep, I had one of those, my mains-tester screwdrive lit up nicely when I tested it on the tripod legs.

Stumped up for a skywatcher power tank after that.

  • Like 1
Link to post
Share on other sites

Thanks for all your help and advice, I think I'll be building a sturdy DC power supply, ground the 0V rail AND use an earth rod. (and wear wellies and rubber gloves)

@Lorne: I tried different PSUs on different extensions and plugged directly into the wall outlet and still the voltage was present. I guess I'm just lucky :laugh:

Link to post
Share on other sites

I even wrapped the leg in insulating tape and taped the PSU to the leg with more tape. Still got a tingle.

There's a good reason for people using Power Tanks, I'd still go with one of those rather than building a custom PSU. But that's me.

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.