Re: higher current ammeter sources

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "S&JY" <youngsters-at-konnections-dot-net> 

David,

You can adjust the current through your smaller ammeter to read full scale,
say 10 amps.  Then add your shunt and trim it until your meter reads 1 amp,
for example.  Then full scale on your meter with shunt will be 100 amps.  Be
sure to use some large (e.g. #10) brass bolts and nuts on your home-made
shunt to handle the high currents.

Your primary shunt can be one that makes your meter read a little high, then
trim it by adding low value resistors in parallel with the main shunt until
the meter reads correctly.

You don't need another ammeter to calibrate it using this method, but if you
can borrow an accurate one, then do so.  Calibrate your shunted meter near
the load current you will usually run.  For example, plug in a toaster and a
couple of hair dryers for a 30 amp load, then trim your shunt(s) until it
reads the same current as the meter you borrowed.
--Steve Y.

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, May 09, 2004 9:14 PM
Subject: Re: higher current ammeter sources


 > Original poster: DRIEBEN-at-midsouth.rr-dot-com
 >
 >
 >
 > ----- Original Message -----
 > From: Tesla list <tesla-at-pupman-dot-com>
 > Date: Sunday, May 9, 2004 9:18 pm
 > Subject: Re: higher current ammeter sources
 >
 >  > Original poster: "S&JY" <youngsters-at-konnections-dot-net>
 >  >
 >  > David,
 >  >
 >  > Just make your own from a lower range meter and a home-made shunt.
 >  > You can
 >  > use a length of copper or iron wire or strap and keep reducing the
 >  > length of
 >  > it, shunted across the meter, until your full scale reading is
 >  > what you
 >  > need.  For example, for a 0 to 100 amp meter, it is best to use a
 >  > 0 to 1 or
 >  > 0 to 10 amp meter with a shunt to make reading the actual value
 >  > from the
 >  > meter scale easier (x10 or x100).  You can also buy meter shunts
 >  > from some
 >  > electronic distributors.
 >  > --Steve Y.
 >
 > Steve,
 >
 > Ok, so you're saying that you can use another coil of
 > wire as a shunt in parallel with the input terminals
 > of a smaller ammeter to make the full scale reading a
 > given fraction of the total amperage? I suppose that
 > you'd have to use another ammeter or clamp-on to cali-
 > brate the shunt?
 >
 > David Rieben
 >
 >
 >