Re: [Electronics_101] Re: Safety question about current...
- On Sun, 02 Jul 2006 08:32:50 +0200, Bob Hyland-PMP
>I second that opinion and will add the suggestion of using an isolation
> Um Jack... help me out here. You shun the power outlet, but you
> create one by using a 300W power inverter? How is this "safer"? You
> are still looking at 120V @ 300 Watts. I would assume that using a
> standard GFI outlet would give you better safety than using this
> home-brewed option. That is, unless there are additional safety
> mechanisms built-in along the way that I don't know about.
> Also, 300 Watts is a lot of power to be delivered by batteries. Just
> how many are you using to power this thing, keeping in mind the
> eficiencies of each component along the trail?
> As an alternative, you could just use a standard 12V power supply
> that connects to the mains, and plug in the inverter to that! Seems
> like it would give you the same "safety" and you would not have to
> keep replacing / recharging the batteries....
> Bob H.
Sometimes GFI protection is better, sometimes isolation.
Basically if you are somewhat grounded (feet, chassis, etc) a GFI will
protect you and switch the power off if you touch the hot side. You would
still feel a zap though. If you use a GFI make damn sure it is 30mA fault
current or less. I was trapped once on a GFI protected circuit with an old
200mA GFI that did not trip. You wouldn't believe you can pull out the
plug of a power strip lying on the floor with your feet, but you can if
you have no use of your hands! (Note to self: Next time just walk/jump
back until the connection is pulled away you stupid idiot!).
Anyway, an isolation transformer in comparision will not do anything if
you touch hot and earth, no current flowing. No zap, but no power-off
either so it makes sense to add either an isolation monitor or test
everything you repair after an isolation transformer with an isolation
tester for ground faults.
Now that was the hot/ground fault. What if you touch hot AND neutral? Well
If you have a GFI you might be grounded, and it would have tripped as soon
as you touched the hot wire. But if you got in this situation to touch
both you are probably not grounded. An isolation transformer wouldn't help
So this is one mistake you need to avoid.
The isolation transformer can save you from one mistake - but you mustn't
ever rely on it because that'll let you make the second mistake. For
example if there is a ground fault in the unit and one mains wire is
shorted to the chassis - and you do not know about this - the one single
fault the isolation transformer can forgive is USED UP!.
- On Tuesday 04 July 2006 04:01 pm, Jack Giammerse,Jr. wrote:
> Thanks,Roy,For me as well. :-)
> I have heard the phrase Sealed Lead-Acid before,but do not remember
> seeing the acronym SLA until here in this thread.Here in the U.S.,the
> acronym SLA only brings to mind the "Symbionese Liberation Army",
> The lady did get out of prison after several years and go on to live a moreInteresting, as I'd never heard any of that. But as you say OT. :-)
> normal life,and she did all this with her dignity intact. I admire her
> greatly for that,because it is a testament to her true character.
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, a critter that can
be killed but can't be tamed. --Robert A. Heinlein, "The Puppet Masters"
Information is more dangerous than cannon to a society ruled by lies. --James