Question about a clamp meter with a low range

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I need a clamp ammeter but it's for very occasional use and I'm  
trying to decide between a few cheap Chinese products. One has  
ranges of 2A, 20A & 200A while the others have 20A, 200A and  
400/600/1000A.

In the unlikely event that I ever need the higher ranges, I can  
always borrow a meter from the power company, so I'm attracted to  
the one with the 2A range. But I have a question about the  
practicability of measuring down to a few mAs with a standard  
non-contact technique. Is it likely to be usefully practical or  
about as practical as, say, a milliohmmeter with a two-wire probe?

Re: Question about a clamp meter with a low range

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I'm not sure this is going to work out, but I just bought an AN8802 TRMS  
Clamp Multimeter 6000 Counts Temperature Auto Range AC/DC Ammeter for US  
$29.68.

Here are two ebay item numbers:

282421973048
332087546732

They claim AC and DC current measurement from 600uA to 1200A, True RMS  
readings, plus a bunch of AC and DC, capacitance, frequency, resistance  
capability. Here are the specs:

Description:
Features:
Auto/manual ranges.
True RMS measurement.
550V protection in resistance and capacitance ranges.
Large LCD display,MAX display 6000 counts.
Sample rate: 3 times per second.
Backlight
Data hold
Polarity identification
Low voltage indication
1200A high current measurement, low current measurement
Auto power off
Main measurements: AC/DC Voltage, AC/DC Current, Resistance, Capacitance,  
Diode and Continuity Testing, Temperature, Frequency and duty cycle.

Specifications:


+15)

5.0%+5)





Measurement mode: Double-integral style A/D transform
Over range indication: OL
Working environment: 0~40?, relative humidity < 80%
Supply power: 3V (1.5V AA batteries * 2 Pcs)(Not included)
Frequency: 1Hz to 10MHz
Temperature: -20C to 1000C(-4? to 1832?)
Capacitance: 10pF to 6000uF
AC volts: 0.1mV to 750V
DC volts: 0.1mV to 1000V
AC current: 0.1uA to 1200A
DC current: 0.1uA to 1200A
Resistance: 0.1 to 60M
Duty cycle:1% to 99%
Product size: approx. 238*90*45mm/9.37*3.54*1.77''
Gross weight: approx. 286g

Note:
Please allow 1-3mm differs due to manual measurement.
Due to the different display and different light, the picture may not  
reflect the actual color of the item. Thanks for your understanding.

Included:
1 x Multimeter
2 x Test Leads
1 x Temperature Sensor Cable
1 x Storage Bag
1 x User Manual

Even though the uA range is printed on the case, I suspect the uA values  
should really be mA. Then it would keep the progression from 600 mA to 6A  
and 60A to 1200A.

I don't know how they claim to measure DC current, but if it's true, it  
will pay for itself quickly on problems with my car battery charging. If  
not, then True RMS and a wide current range is still very useful.

Re: Question about a clamp meter with a low range
Steve Wilson wrote:

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** Read the specs very carefully.

 Using the clamp, the ranges are 60, 600 & 1200 amps.  

 It's not clear if the clamp works with DC at all and I bet it does not.  



.....  Phil  


Re: Question about a clamp meter with a low range
On Tue, 9 May 2017 00:40:22 -0700 (PDT), Phil Allison

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In addition to the DC issue, one should remember that the AC _current_
waveform can be far from sinusoid these days with all kinds of SCR,
Triacs and SMPSs.

What do you want the meter to display and what is it actually
displaying ? Ipeak/1.41, some quasi-peak or trueRMS ?

Thus read th specs really carefully.



Re: Question about a clamp meter with a low range
On 5/9/2017 12:10 PM, Steve Wilson wrote:
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The specs are nice but it's way above my budget. What I'm looking  
at are in the US$6-7 range.

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I once read a long time ago - long before the internet age -  
about a technique used by one manufacturer for making DC amp  
measurements with a clamp. It involved biasing the clamp's  
magnetic property with a multivibrator (discrete of course). The  
measured DC current shifted the operating point along the  
non-linear portion of the B-H curve. I don't remember what the  
claimed accuracy was but I get the impression that it was quite  
reasonable.

Re: Question about a clamp meter with a low range
On a sunny day (Tue, 9 May 2017 15:38:25 +0530) it happened Pimpom

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Any LC oscillator with a ferrite core coil an be used to sense large
DC magnetic fields (causes a frequency shift when core saturates).
1 $ componenst, if you have a frequency counter...
Then it is a question of calibration / lookup table.

Re: Question about a clamp meter with a low range
On 5/9/2017 3:08 AM, Pimpom wrote:
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Current technology uses a hall device to measure the DC current
using the clamp.  For RMS, they might also have to sum in the AC
component from the coil, depending on frequency response required.

If you look carefully at the specs and the front panel,
you might conclude that the clamp has a lowest range of
60A FS and the test leads measure up to 6mA.



Would be more useful if the leaded range went two decades higher
to 600mA.

Just verified that both my similar units limit at what would
be 6mA on this one using the wired input.

The Tektronix P6042 current probe can do 1mA/division from DC to
50 MHz, but the size of the clamp will barely accept
a #12 wire.  The instrument is maybe 50 years old.  It's a hall device.



Re: Question about a clamp meter with a low range
On Tuesday, 9 May 2017 11:08:33 UTC+1, Pimpom  wrote:
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Why buy one when you can just wind a current transformer on an old core? Use that with your current meter.


NT

Re: Question about a clamp meter with a low range

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Congratulations.  Welcome to my style of cheap.

I bought 7 of these for $7.35:
<http://www.ebay.com/itm/152252187798
because I was tired of loaning my good clamp ammeter to friends,
neighbors, customers, visitors, friends of visitors, etc.  It would
usually take weeks and ocassionally a burglary to arrange for it to be
returned.  I gave 5 of them to the worst offenders and haven't heard a
word for about 2 months.  That means either they are satisfied with
the gift, or the meter exploded when they tried to use it.  I haven't
bothered to ask (or care).

The meters a junk, but adequate for the purpose.  It takes 3ea AAA
batteries which I guess is cheaper than the usual 9V battery.  It does
AC only on the clamp, not DC.  It is NOT a true RMS meter and will
produce weird results with non-sinusodial waveforms (which is just
about everything I would want to measure).

The maximum current is 400 amp.  If you ever find something that
actually draws 400 amps, I would hesistate to use this meter to
measure it.  I don't know what might happen, and I don't want to find
out.  Use a better meter for high currents.

Mostly, I use these for much lower currents.  20A full scale is not
sensitive enough.  So, I use a 10 turn wire loop in series with an AC
power plug/jack adapter to increase the sensitivity to 2A full scale.
Radio Shack (Micronta) used to sell them.
<https://www.picclickimg.com/00/s/MTIwMFgxNjAw/z/jY8AAOSws4JW8ARk /$/Micronta-7-Range-AC-Volt-Ammeter-Catalog-No-22-161-_57.jpg>

Good luck and don't forget to buy a spare to loan (or sell) to your
cheap friends.



--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: Question about a clamp meter with a low range

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Someday you may need a spot welder or a stick welder. Measurement of 800A  
to 1200A would be useful. Youtube has plenty of examples:

DIY Welders

Home Made Spot Welder Pt 1 - YouTube

https://www.youtube.com/watch?v=jydUZ5OUWAk&t21%4s


Tiny and compact powerful spot welder - YouTube

https://www.youtube.com/watch?v=McKbU9Bu_30


spot welder Mk 1.wmv - YouTube

https://www.youtube.com/watch?v=RnjF5Hj2Udg


Homemade welding machine !!! Very cheap ! - YouTube

https://www.youtube.com/watch?v=XxgX9LHNfg4


Step by step how to make a welding machine (Part 1)  

https://www.youtube.com/watch?v=0ZTH02b18AM


Re: Question about a clamp meter with a low range
On 5/9/2017 8:34 AM, Steve Wilson wrote:
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Typically, a spot weld short enough to weld a small
item is too short for the sample rate of the meter.
Mine don't have display hold functions either.

Microwave transformer welders certainly have their place,
but to do small stuff without overheating the attached
pieces, like for battery tabs, you need a short pulse.
For short pulses, the amount of energy actually delivered
to the weld is strongly dependent on the where you left
the core on the B-H curve at the last weld.
To get useful repeatability, I had to count cycles of AC
and start/stop at repeatable core magnetization positions.
Even then, welds were reliably unreliable.

My real CD spot welder does a 7000 amp pulse.
Measuring that with a scope proved difficult.
When it fires, every scope on the bench triggers whenever
it wants to.

http://i.imgur.com/ZWSYAKQ.png
shows the output pulse and how they reset the core between
hits.


Re: Question about a clamp meter with a low range

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I have a commercial sheet metal AC spot welder.  I don't recall the
current but it's well past 400 amps.  It draws enough current that it
will probably demagnetize tools.  If I wrap the clamp meter around the
copper electrodes, it would probably be destroyed.

I also have several stick arc welders.  One is a cheap junk 85A AC arc
welder that is heading to the local thrift shop.  AC welders spray
metal and slag everywhere and produce some really ugly welds.  While
the clamp meter should work with this AC welder, I've never found a
reason to do so.  I can usually guess(tm) as to the arc current by its
appearance or by measuring the 240v AC input current.

My other stick arc welder is a 100A DC model.  Unlike the AC model, it
doesn't sputter or spray metal and slag all over the work.  It's also
easier to strike an arc, maintain the arc, and penetrates better.  The
clamp meter only measures AC current, not DC and will therefore not
work with this welder.

I also have a home made battery terminal spot welder.  It's a CD
(capacitive discharge) type, which is DC, and will therefore not work
with an AC clamp ammeter.

"Measure Arc Welding Machine Current with clamp meter Deadshort 300+
Amps"
<
https://www.youtube.com/watch?v=XP2BpwkMxZA



--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
We've slightly trimmed the long signature. Click to see the full one.

Re: Question about a clamp meter with a low range
On a sunny day (Tue, 09 May 2017 20:16:54 -0700) it happened Jeff Liebermann

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Nice video.


Re: Question about a clamp meter with a low range
On Tuesday, May 9, 2017 at 11:20:25 AM UTC-4, Jeff Liebermann wrote:
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Hmm lotsa choices, I wonder if Dave of the EEVblog has done a review of  
cheap clamp meters.  

George H.  

Re: Question about a clamp meter with a low range
On Tuesday, May 9, 2017 at 11:20:25 AM UTC-4, Jeff Liebermann wrote:

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Just for grins, I looked on AliExpres and found the lowest price to be  $5.90 with shipping for a similar looking multimeter.  

But the Ali one is shipped from China.

                     Dan

Re: Question about a clamp meter with a low range
On Tue, 9 May 2017 13:19:14 -0700 (PDT), " snipped-for-privacy@krl.org"

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Not always.  I order quite a bit of electronics on eBay that allegedly
is shipped from China.  However, instead of the usual 2 to 4 weeks
delivery, it arrives in a few days from a random US location.
Apparently, some of the vendors have become big enough to warehouse
their stuff in the US.  I haven't checked, but my guess(tm) is that it
is shipped from someone's garage or house, who has relatives in China.




--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: Question about a clamp meter with a low range
wrote:

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I just found the proper name for this contrivance.  It's an "AC
current line splitter".
<https://www.google.com/search?tbm=isch&q=ac+current+line+splitter
There is not much inside.  Just some magnet wire:
<https://www.eevblog.com/forum/testgear/extech-ac-line-splitter-and-amazon-promotion-20-40-off/?action=dlattach ;attach17%4051;image>
However, if you're dealing with devices plugged into an AC wall
receptacle, it probably makes more sense to use a Kill-a-Watt or other
AC power meter instead of a clamp meter:
<http://www.p3international.com/products/energy-savers.html


--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
We've slightly trimmed the long signature. Click to see the full one.
Re: Question about a clamp meter with a low range
On 5/10/2017 8:16 AM, Jeff Liebermann wrote:
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I longed to have the functions of a Kill-a-Watt for a long time,  
but it's not available in India. Even if it were, the original  
Kill-a-Watt couldn't be used in our 230V system.

Then came the Chinese knock-offs for 220/240V. I got one as soon  
as the imported/smuggled ones had dropped from the initial  
exorbitant prices to a more reasonable level. It has served me  
well for the past several years.

Still, it's not always possible to plug in a device into a wall  
socket through the meter. And there are times when the measured  
load takes more than the rated 10A of the meter. In fact, I don't  
feel comfortable going to much more than 5A.

Re: Question about a clamp meter with a low range

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I never noticed that Kill-a-Watt wasn't available for 220-240VAC
service.  The device is very popular in the USA and is being sold
retail at some hardware stores.

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I haven't found any complaints online of Kill-a-Watt meters melting or
exploding under excessive current conditions.  Well, just this one,
which seems to be a collection of dubious complaints:
<https://www.smokstak.com/forum/showthread.php?t10%1985

There's quite a bit available that might do as a 230VAC power meter.
For example:
<http://www.ebay.com/itm/AC-100A-Power-Meters-Monitor-Volt-Amp-kWh-Watt-Digital-Combo-Meter-AC110v-230V-/231602812752
<https://www.banggood.com/EPM8200-Digital-AC-Watt-Meter-Energy-Meter-KWH-Meter-Voltage-Current-Power-Factor-Tester-1000W-4A-p-1102521.html
<http://www.ebay.com/itm/AC-Power-Meters-Monitor-Volt-Amp-kWh-Watt-Digital-Electric-Combo-Meter-110v-230V-/192003673329
<http://www.ebay.com/itm/LCD-AC-230V-Analyzer-Energy-Power-Meter-Socket-EU-Plug-Voltage-Monitor-/252866023417
<http://www.ebay.com/itm/LED-Multi-Function-DIN-RAIL-Volt-AMP-Meter-Active-Power-Factor-220V-230V-BI629-/311828822079
etc...  

--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
We've slightly trimmed the long signature. Click to see the full one.
Re: Question about a clamp meter with a low range

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On a higher range clamp on ammeter you can wrap 10 turns around the clamp  
and get a 10X multiplication of the range sensitivity.  



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