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AC DPM's -- are the all DPM'$?

I've been seeking some inexpensive AC digital panel meters; but thus far, there's as hard to find as a popular BP executive.

Marel sells some that are $100 each, gulp.

Or is there a $6.95 AC-DC addon I can use on my pile of old DC Analog Devices units?

-- A host is a host from coast to snipped-for-privacy@nrk.com & no one will talk to a host that's close........[v].(301) 56-LINUX Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433

Reply to
David Lesher
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David Lesher wrote in news:hukp1i$eqq$ snipped-for-privacy@reader1.panix.com:

An op-amp with diodes? Fullwave rectifier.. Or even halfwave, on a single supply. I don't know if anyone built those into complete sealed modules at low cost though, I suspect people usually build their own.

Reply to
Lostgallifreyan

MPJA is currently out of stock, but they carry this for $8.95

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--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.
Reply to
Michael A. Terrell

These guys have stock, but you'll pay a bit more if you're in a hurry:

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Reply to
JW

Thanks. Those will do fine, but I guess I'll need separate wallwart power supplies for each one. That, or isolation transformers which will cost far more.

[Unless you have a spare 8-channel isolated power supply.] 
--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433
Reply to
David Lesher

A 6.3 volt filament transformer, diode & electrolytic capacitor would be a better choice. They are available wit a 1500 V isolation rating

--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.
Reply to
Michael A. Terrell

Not the issue. My point is, each one needs a separate supply. If I could find very low current 277v primary xfmrs [I'm monitoring a 480 Y system]; then I could use one common supply. But such would be $$$ in quantity.

--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433
Reply to
David Lesher

Some of the meters use isolated power inputs, You can always build a simple DC to DC converter with multiple, isolated outputs. Then you can use any reasonable DC voltage you have available for the input, or a small transformer & diodes. It isn't rocket science.

--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.
Reply to
Michael A. Terrell

I've not found same at good prices.

Not sure where to find an xfmr with 6-8 identical windings...

I am thinking this would work. Find some old small B+ transformers. Use them to isolate and step down the 277V. Than an appropriate resistor or two per meter, and a lower range on the DPM would give me good data.

--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433
Reply to
David Lesher

A small inverter with a torroid output transformer. Wind your own, it isn't that hard to do.

--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.
Reply to
Michael A. Terrell

Why do you need 8 separate supplies? You should be able to run 8 (or N) of those DPMs from the same power supply using the isolated ground configuration.

Ed

Reply to
ehsjr

I'm less sure of that. I will be measuring 3 legs of 277VAC with them. Less then good isolation could get....noisy...

--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433
Reply to
David Lesher

Ok, I can't address how sure or unsure you are, but I can provide some general information that may assist.

To understand their isolated ground, google on "virtual ground". It should yield a _very_ high impedance (for practical purposes you can consider it op amp input impedance) between the DPM's DC supply and the input (the signal that is being measured) ground.

Also, this datasheet may help:

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I guess, for you to be absolutely sure, you'd have to try it. I have not done it with these DPM's myself.

Ed

Reply to
ehsjr

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