General > General Technical Chat
Do you guys use an isolation transformer for your lab/workbench?
nctnico:
--- Quote from: bigfoot22 on February 01, 2023, 07:13:48 pm ---Yeah I have no intentions of using it for my lab/workbench after reading your helpful replies. If it doesn't pass through earth then its dangerous anyway. I'll get an RCD/GFCI for my setup.
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And get CAT rated high voltage differential probes. These are very affordable (from MicSig for example) and will provide safety while measuring in mains powered circuits.
Also think long and hard if you even need to provide mains power to a mains powered device. Switching power supplies always have a low voltage supply in the primary side. If you use a bench power supply to power the primary side (and a different channel to apply some power to the secondary side) you can test 99.9% of a power supply without even connecting it to mains.
NiHaoMike:
I have one that does about 100W, made by taking apart two halogen lamp transformers and reassembling one with two primary windings. I use it more for the current limiting although the isolation is definitely a plus.
For more power, I run a 1000W power inverter from a surplus 1400W server PSU. It's rare that I have to do that, even working on fairly large PSUs the 100W isolation transformer is sufficient to see if it at least powers up correctly.
Electro Detective:
Study isolation transformers in detail till you understand what type for what task,
how to test the actual level of input to output 'isolation', chassis relations,
and that it will do the task before using it,
but not before understanding the source of the incoming power from your mains switchboard first, the earth bond/grounding thing etc
It's actually SUPER SIMPLE even using generic isolation transformers once you have understood the above,
with the wiring option of various degrees of 'isolation' from the mains and or connected suspect equipment etc
My rig has the option of any type of isolation needed,
regulated, varied or limited AC,
and options to use GFCI or RCD,
and be able to externally test trip them also to ensure they actually do work
i.e. If risky business 8) I simulate the snafu first, then hook up and power up
and there's a UPS rig too but that's another story as to how it's transformer works on backup disconnected from the mains
My intentions when learning about this stuff were really to be personally 'isolated' from hospital beds
and or a one time permanent earth/ground connection, after a few good overconfident idiot zaps and walkaways over the years. :phew:
'Isolation' has way too many variables for people unfamiliar with all the voodoo and confusion,
to either zap their equipment and themselves,
or cop spark shrapnel in the eyes,
or worse still, send panic'd kitty and fido packing down the street :scared: :scared:
into an oncoming beer swilling, bad hair day, 'friday tradie' ute, with cranked up mindless detuned metal mayhem trash. :palm:
Isolation: No research? = No Do ! \$\Omega\$
Brumby:
--- Quote from: AVGresponding on February 01, 2023, 06:55:52 pm ---
--- Quote from: tooki on February 01, 2023, 06:46:35 pm ---Let’s put it this way: if you don’t thoroughly understand why and when you’d want an isolation transformer, and what it does and doesn’t protect you from, then you shouldn’t work on mains-powered stuff yet, specifically, things with a live chassis.
If you get one, make sure you don’t let it lull you into a sense of false security, such that you actually let your guard down around mains voltages.
As for the specific question of using one to isolate all of your test equipment: an emphatic no!!!!
If you want to add safety to your bench, install a sensitive GFCI (more sensitive than the one your home may already have installed).
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This ^ 100%
Simple quotepost because it bears repeating.
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I was going to do exactly the same - for the same reason.
rstofer:
--- Quote from: tooki on February 01, 2023, 06:46:35 pm ---If you want to add safety to your bench, install a sensitive GFCI (more sensitive than the one your home may already have installed).
--- End quote ---
In the US, UL standard 943 covers GFCI devices and they trip at 4 to 6 mA of ground current. I don't think you will find anything more sensitive. These are used for individual branch circuits, we do not trip the panel main breaker with a GFCI nor do we use something like the UK RCD device. Typical ratings are for 125/250V up to 50A
It is my understanding (from a quick read on Google) that UK RCD devices trip at 18..23 mA (30 mA max).
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