On Sun, 01 Nov 2009 15:53:30 -0500, "Michael A. Terrell"
wrote:


Winston wrote:

Michael A. Terrell wrote:
Wild_Bill wrote:
Adding AC powered instrumentation to utility-source line voltage equipment
is somewhat complicated, and a little more complicated for 3-phase circuits,
where one needs to be aware of peak voltages.

Winston offered a practical and safe solution. Stormin's suggestion would
also work if you utilize 3 separate battery holders, one for each meter.
Holders for 6 C or D cells are fairly common (6x1.5V = 9V).

FWIW, many small AC adapters and DC chargers aren't designed for line
voltage isolation.


Then they aren't safe for any application.

But what is 'totally safe'? Even KANO kills thousands a year.

PV was operating three digital mulimeters, each one floating hundreds
of volts above ground, and he lived to tell about it.


What is the lost voltage rating you've seen for magnet wire? For the
nylon bobbins? Even the old waxed paper separators were good for 600
volts. Any reputable manufacturer Hi-pot tests at 500 volts.


I think you meant "lowest" voltage rating.

I don't know where the FWIF came from but I don't know of
ANY walwarts, AC adapters or DC chargers which do not isolate
the low voltage output from the line voltage. In the UK at least
any such a device would be illegal.

Twice working voltage plus 1000V is a pretty common
acceptance standard and this is well below normal device
capability. Out of interest I tried but was unable to breakdown
a Motorola cell phone walwart even at 2,850V (the highest
available voltage) for half an hour.

Jim

wrote:
On Sun, 01 Nov 2009 15:53:30 -0500, "Michael A. Terrell"
wrote:

Winston wrote:
Michael A. Terrell wrote:
Wild_Bill wrote:
Adding AC powered instrumentation to utility-source line voltage equipment
is somewhat complicated, and a little more complicated for 3-phase circuits,
where one needs to be aware of peak voltages.

Winston offered a practical and safe solution. Stormin's suggestion would
also work if you utilize 3 separate battery holders, one for each meter.
Holders for 6 C or D cells are fairly common (6x1.5V = 9V).

FWIW, many small AC adapters and DC chargers aren't designed for line
voltage isolation.

Then they aren't safe for any application.
But what is 'totally safe'? Even KANO kills thousands a year.

PV was operating three digital mulimeters, each one floating hundreds
of volts above ground, and he lived to tell about it.

What is the lost voltage rating you've seen for magnet wire? For the
nylon bobbins? Even the old waxed paper separators were good for 600
volts. Any reputable manufacturer Hi-pot tests at 500 volts.


I think you meant "lowest" voltage rating.

I don't know where the FWIF came from but I don't know of
ANY walwarts, AC adapters or DC chargers which do not isolate
the low voltage output from the line voltage. In the UK at least
any such a device would be illegal.

On several notebook computer power supplies I tested, the negative
D.C. output was bonded to A.C. ground which as you know has a low
impedance connection to A.C. neutral. In the intended application,
this is safe and moral and legal *and* proper. To power instruments
(that are also connected directly to alternating current), not so much.

Twice working voltage plus 1000V is a pretty common
acceptance standard and this is well below normal device
capability. Out of interest I tried but was unable to breakdown
a Motorola cell phone walwart even at 2,850V (the highest
available voltage) for half an hour.

"I tested 'Z' so you can safely use 'A' 'B' or 'C' in your application."

Hmmm.

--Winston


--
The good news is that you have a new lawn mower.
The bad news is it's rated in 'Sears horsepower' and the
warranty is in 'AT&T months'.

Winston writes:

On several notebook computer power supplies I tested, the negative
D.C. output was bonded to A.C. ground which as you know has a low
impedance connection to A.C. neutral.

Really? I've never seen a notebook power supply that had a grounded plug.

On Tue, 03 Nov 2009 12:36:38 -0600, Richard J Kinch
wrote:

Winston writes:

On several notebook computer power supplies I tested, the negative
D.C. output was bonded to A.C. ground which as you know has a low
impedance connection to A.C. neutral.

Really? I've never seen a notebook power supply that had a grounded plug.

Yes, really. Older ones were not this way IME.

Richard J Kinch wrote:
Winston writes:

On several notebook computer power supplies I tested, the negative
D.C. output was bonded to A.C. ground which as you know has a low
impedance connection to A.C. neutral.

Really? I've never seen a notebook power supply that had a grounded plug.

Yup.

First time I saw that, it was on a 'Voodoo Envy' gaming notebook:
http://www.voodoopc.com/#/productsenvy

I see that their modern product has a two - prong power plug, though.
Perhaps they decided that ground loops were a Bad Thing (TM).

--Winston

--
The good news is that you have a new lawn mower.
The bad news is it's rated in 'Sears horsepower' and the
warranty is in 'AT&T months'.