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Earthing the mount....


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A relatively boring thread in SGL has turned interesting when several people have talked about getting a tingling from their mount when they touch it, and presumabely earth it!


I've yet to put the multimeter on my mount and see what happens.


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When powered by a mains adapter this is quite normal. Just measured mine from the mains earth to the tripod leg and I get around 90V RMS AC.

It can give you a bit of a tingle but there is not enough current to shock you.


I have noticed this quite a bit when using mains adapter powered test equipment at work.

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yea 90 Volts but extremely low current.


Its strange, the leg nearest the transformer measures 6V AC but the leg furthest from the transformer measures nearly 90V AC. Not sure I fully understand it but have seen it a few times before.



Edited by TasKiNG
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This explains a lot - I once had the CPC rigged up to the battery and a couple of dew bands on EHU. The scope wouldn't do anything it was told when using the goto handset. I guess the current interfered with the scope electronics somehow and sent the encoders crazy?

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  • 3 months later...
Guest Alien 13

This effect is due to the use of a switch mode power supply that has no earth refrence and the measured 90V is not uncommon, it is not in itself lethal but can play havok if you have a number of items on the mount powered bu such supplies and they are allowed to touch.


The best option is to ground the mount and all of the negative connectors (can be done with a low value resistors for better noise imunity) or use a linear power supply which will normally have an earth connection.


The thing to consider is that a lot of PSUs are not designed for outdoor use so could easily exceed there stated leakage current and then become a safety hazard when in a humid environment so i would allways make sure my mount is earthed.



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