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 Post subject: Info on Sterling ammeter sought
PostPosted: Jun Tue 11, 2019 2:54 pm 
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Joined: Dec Sat 22, 2012 3:20 pm
Posts: 723
Location: Marenisco, MI
Bought a Sterling AC ammeter off that %$&# auction site. It doesnt work. The original box
says it is model 70-818 and the meter face has printed on it 9981. Does anybody have any
technical info on this one? I am wondering if it might be made for a different voltage than 120 V.
It seems in good condition and I have examined the inner parts and it doesn't seem to be defective
but get I cant get any current draw when in an ac line. Inside it says Sterling Mfg Co Cleveland Ohio.
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 Post subject: Re: Info on Sterling ammeter sought
PostPosted: Jun Tue 11, 2019 3:33 pm 
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Joined: May Tue 30, 2006 4:46 pm
Posts: 9904
Location: Santa Rosa, CA
I don't understand the question about 120 volts. It's an ammeter, not a voltmeter. Non-linear scale, for some reason.

Since the scale is 50 Amps, an important question would be whether the shunt is internal. You could blow it out if it needs an external shunt.

Sterling used to make a line of "pocket" meters for testing radios.

Rich


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 Post subject: Re: Info on Sterling ammeter sought
PostPosted: Jun Tue 11, 2019 7:43 pm 
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Joined: Jun Fri 19, 2009 6:34 pm
Posts: 8538
Location: Long Island
How much current is your load drawing through the meter? These were neither the most sensitive nor linear meters made and if you are only drawing a couple of amps, it may not deflect the needle at all.

Ammeters generally do not have voltage ratings; they are connected in series with a load and measure the current in the circuit regardless of voltage (within reason). Of course the voltage has to be sufficient to overcome the internal resistances of the meter and the load, and it cannot be so high as to cause insulation breakdown, but between those extremes, it's irrelevant.

Most meters of this variety consist of a few turns of heavy copper wire around a soft iron core; the core is shaped to produce magnetic replusion of an egg-shaped disk on the same shaft as the pointer. If that's the case here, there is no shunt and the full load current passes through the coil.

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 Post subject: Re: Info on Sterling ammeter sought
PostPosted: Jun Tue 11, 2019 8:33 pm 
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Joined: Dec Sat 22, 2012 3:20 pm
Posts: 723
Location: Marenisco, MI
Yes I am quite aware it is an ammeter and not a voltmeter. And yes it was tested in series
and I drew 2 amps by using a healter for testing with another meter but this one shows nothing. The inside is, as Chris says, an heavy copper surrounding an iron core. I was hoping I was missing something with my voltage question but it seems that as is the rule now and not the exception on ebay I was ripped off. Yeah I know. Buyer protection blah blah---just have to jump through hoops and then wait for refund. Im all through with ebay.


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 Post subject: Re: Info on Sterling ammeter sought
PostPosted: Jun Wed 12, 2019 12:56 pm 
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Joined: Jun Fri 19, 2009 6:34 pm
Posts: 8538
Location: Long Island
Maybe you got ripped off and maybe you didn’t but two amps is way below what this kind of meter can register accurately. Try drawing 20-30 amps through it and it might just work.

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Thomas A. Edison


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 Post subject: Re: Info on Sterling ammeter sought
PostPosted: Jun Wed 12, 2019 1:02 pm 
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Joined: Sep Tue 30, 2014 6:08 am
Posts: 4226
Location: Norfolk, VA
......Does it require an external shunt?.......without instructions, I'd never hook up an panel ammeter before knowing just that.

50 Amperes - the shunt would be quite large, so I'd assume it would require an external shunt, and is likely more a voltmeter (measuring voltage drop across that external shunt). Most are 50mV or 60mV shunt ammeters.

Note, for reference only..... https://www.ebay.com/sch/i.html?_nkw=50 ... 0&_fosrp=1

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"Capacitor Cosmetologist since 1979"
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 Post subject: Re: Info on Sterling ammeter sought
PostPosted: Jun Wed 12, 2019 2:23 pm 
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Joined: Dec Sat 22, 2012 3:20 pm
Posts: 723
Location: Marenisco, MI
A lot of good info here, thank FindmKeepm and Chris.

I got the meter working---Chris was right-its not a sensitive meter and the needle
doesn't come off the peg until over 2 amps is drawn. Beyond 2 amps it is responsive
and tracks with a better meter I have been testing it against.


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 Post subject: Re: Info on Sterling ammeter sought
PostPosted: Jun Sat 15, 2019 10:49 am 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 11420
Location: Powell River BC Canada
Remove the tip from a soldering gun. Hook the ammeter across the tip holders .

Now plug the soldering iron into a Variac and increase the voltage to make the
meter read.

Meters are often specified for testing ferro resonant transformers ( CVT) because they
are true RMS and not affected by waveform.

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Steve Dow
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 Post subject: Re: Info on Sterling ammeter sought
PostPosted: Jun Sat 15, 2019 6:12 pm 
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Joined: Jan Tue 16, 2007 7:02 am
Posts: 2978
Location: Lexington, KY USA
I don't think this sort of meter can accurately respond to the RMS current. In this meter's era, you would need a thermocouple type RF ammeter.

Ted


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 Post subject: Re: Info on Sterling ammeter sought
PostPosted: Jun Sat 15, 2019 8:43 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3265
Location: Seattle WA US
AC ammeters dont use shunts, they use current transformers. The most common setup I have seen uses a 5 ampere movement and provides for other ranges with current transformers. Having said that, I see I have several cheap 25 amp AC ammeters, with no transformer.
-
Chuck


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