Quote:
Originally Posted by Tandum
Yes that's right, Rob is a renegade, but show me a grounded power supply?
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Many supplies are grounded. Look for those with 3 prong cables.
Quote:
Originally Posted by DavidTrap
I thought a ground loop could occur if there is a potential difference between various the negative terminals of different power supplies, e.g., between the negative terminal of a USB plug connected to a laptop being powered from a 240V adapter, and the negative terminal of a CCD being powered from a 12V battery???
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Yes that's true. It seems quite strange that a battery powered device can fry as a result of an earth loop as battery powered devices by their very nature "float". I have a similar setup, my laptop is earthed by virtue of the powersupply it uses, and my telescope power floats. If I plug in a USB cable you can see a brief spark as everything is brought to the same potential followed by perfectly working equipment.
Quote:
Originally Posted by RobF
Would be interesting to hear what if any power supplies aren't "floating" design though? I thought regulated (versus switchmode) was best?
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There is no "regulated" vs "switchmode" a switchmode supply is a form of regulated powersupply. The alternative to switchmode is "linear". Both have their benefits.
Switchmode generates a stable voltage by rapidly switching a circuit on and off across a reactive component and then filtering the result. They are very stable, small, light, energy efficient, capable of large loads without getting hot, but they do exhibit noise typically within their switching frequency (often between 60kHz and 1MHz).
Linear regulates power (downwards only) in a resistive way, burning any difference between the input voltage and output voltage away in heat. They are not at all energy efficient. They rely on heavy transformers and get very hot very quickly as the current increases. They produce a very low noise output.
Both types of powersupplies can be floating, Both types of powersupplies can be grounded. Metal case powersupplies will nearly always be grounded types (for safety). As for which is better? Neither. Some people will swear that linear is the only way to go, others like myself have seen switchmode supplies power the likes of highly sensitive spectrum analysers costing in excess of $200k.
The answer as always is you get what you pay for.