Author Topic: Ammeters, anyone?  (Read 3738 times)

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Offline Ejohnson

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Ammeters, anyone?
« on: October 11, 2015, 05:52:29 am »
I work in critical systems.  I.e., power systems that are highly redundant and won't dump critical loads when utility power is lost.  I regularly have to measure current up to about 1000 AAC or 1000 ADC - voltage at 480 or more. 

I purchased a Amprobe NAV-54 for an ammeter.  I'm pretty happy with it except the jaws won't fit around really big cables.  (The only other one I seriously considered buying was the Fluke iFlex.  The reason I didn't chose the Fluke was that I couldn't just get an iFlex for my 87V.  I would have had to buy a whole new meter just for the iFlex.  Grrr.  Plus the Amprobe is built like a tank and has some features the Fluke doesn't...)  They are both rated to 1000 A and are roughly the same price.  Obviously safety is essential!

Anyway, I have enjoyed watching Dave's videos on DMMs...  Especially when they get blown up!  Any plans to do any similar reviews for ammeters?  Does anyone else have anything interesting to say about ammeters? 

I was working with some guys from Liebert on a UPS.  Their technician put a relatively old Fluke ammeter around a 600 Volt cable and the force on the meter was so high he couldn't get the clamp off.  We couldn't turn off the UPS, of course.  It was a little sketchy!
 

Offline thefamilyman

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Re: Ammeters, anyone?
« Reply #1 on: October 11, 2015, 06:15:23 am »
I work in a similar industry as you with UPS and MW+ generators.
The clamp meter I use when working on the big stuff is the Fluke 376 with the iFlex. The clamp is good for 1000A and the iFlex up to 2500A and us very easy to use especially around big and tricky conductors and busbars. I tell you its worth every bit of money.

You can sometimes find the Fluke 353 or 355 secondhand but they're quite a big and bulky clamp meter
 

Offline HighVoltage

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Re: Ammeters, anyone?
« Reply #2 on: October 11, 2015, 08:40:41 am »
I would also suggest the Fluke 376 with the iFlex.
Even at extreme high currents, you will not have a problem in separating the probe under load.
It is well worth the price.
And if you look second hand, and have a little time, they do show up on ebay for a very good price from time to time.

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Offline Ejohnson

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Re: Ammeters, anyone?
« Reply #3 on: October 12, 2015, 03:13:59 am »
The Fluke meters all have the reputation for being safe and reliable meters.  That is certainly a big consideration!
 

Offline oldway

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Re: Ammeters, anyone?
« Reply #4 on: October 12, 2015, 10:18:35 am »
I also worked in a similar industry as you with high power UPS (I am now retired) and I was using a Metraclip 1000A  ac/dc clamp.
Never had any problem with it.
 

Offline WCarp

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Re: Ammeters, anyone?
« Reply #5 on: December 05, 2015, 03:16:32 am »
The Fluke meters all have the reputation for being safe and reliable meters.  That is certainly a big consideration!

I just did a test with three Fluke clamp meters, a 36, 355, and a 376. All three clamp meters, the Fluke 36, 355, and 376 were set to Min-Max mode DC Amps to test the starting current on a 2011 Ford Ranger with a 4 L engine this afternoon. The first test was with the 355 so the engine, because it was cold, would be expected to take more current to turn over. After each clamp meter test the engine was run a short time, then stopped. For each test, the clamp meter jaws were positioned similarly over the two positive cables near the battery.

The results:

1.   Fluke 355—176.6 A
2.   Fluke 376—255.7 A
3.   Fluke 36—747 A

Why should there be such a significantly wide range of values? Which one is correct or are any of them correct? The first two clamp meter results should be very close to each other since the 355 was just calibrated, and the 376 is brand new, just taken from the box I received today. My concern is how can I be assured then when I measure current with the jaws of any Fluke clamp meter, I will get the correct value?
 

Offline johansen

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Re: Ammeters, anyone?
« Reply #6 on: December 05, 2015, 03:23:01 am »
both the 176 and 255 amp readings are plausible.

my parents 2.5L 4 cylinder 1994 jeep pulls only 105 amps starting current.

Also for DC current measurements you can use a  Rogowski  coil.
http://www.powertekuk.com/dcsnapshot.htm
 

Offline PedroDaGr8

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Re: Ammeters, anyone?
« Reply #7 on: December 05, 2015, 03:35:16 am »
The Fluke meters all have the reputation for being safe and reliable meters.  That is certainly a big consideration!

I just did a test with three Fluke clamp meters, a 36, 355, and a 376. All three clamp meters, the Fluke 36, 355, and 376 were set to Min-Max mode DC Amps to test the starting current on a 2011 Ford Ranger with a 4 L engine this afternoon. The first test was with the 355 so the engine, because it was cold, would be expected to take more current to turn over. After each clamp meter test the engine was run a short time, then stopped. For each test, the clamp meter jaws were positioned similarly over the two positive cables near the battery.

The results:

1.   Fluke 355—176.6 A
2.   Fluke 376—255.7 A
3.   Fluke 36—747 A

Why should there be such a significantly wide range of values? Which one is correct or are any of them correct? The first two clamp meter results should be very close to each other since the 355 was just calibrated, and the 376 is brand new, just taken from the box I received today. My concern is how can I be assured then when I measure current with the jaws of any Fluke clamp meter, I will get the correct value?

You are using these clamps in a situation that is VERY difficult to measure properly. Startup currents are VERY high slope currents. They rapidly jump from zero to an extremely high instantaneous value and then rapidly drop to more reasonable values. This high very short peak can cause issues for any type of ammeter.
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Offline dom0

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Re: Ammeters, anyone?
« Reply #8 on: December 05, 2015, 03:36:10 am »
And all those meters have only 400 or 1000 Hz bandwidth which is probably far too slow in this application.
,
 

Offline cs.dk

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Re: Ammeters, anyone?
« Reply #9 on: December 05, 2015, 10:16:44 am »
The results:

1.   Fluke 355—176.6 A
2.   Fluke 376—255.7 A
3.   Fluke 36—747 A

I've got a Brymen BM089 Clampmeter, which has a "5 ms crest (peak) mode", it shows numbers like your Fluke 36, if I use "Crest-mode"

From top of my head;
Citroën Xantia 2,0 16V - ~530A
Citroën Xantia V6 - ~650A
Citroën C5 V6 - ~650
VW Transporter 2,4 Diesel - ~800A

I'll try later to see what the starter is pulling when it has the engine up cranking. It may only be 100A or so.

It would be nice with a mV/A (or similar) output from the meter, that way i could hook up the scope to see how long (or short) the peak current are.

EDIT: I have just mounted a new starter on my C5, it should be a 1,3 kW unit, so roughly 110A @ 12V. Will test that later.
« Last Edit: December 05, 2015, 10:23:55 am by cs.dk »
 

Offline HighVoltage

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Re: Ammeters, anyone?
« Reply #10 on: December 05, 2015, 11:02:32 am »
I'll try later to see what the starter is pulling when it has the engine up cranking. It may only be 100A or so.
The starter can take up to 1000A on a bigger V8 engine and then drops very fast down to 80-100A
Here is the math formula to calculate the current:

It is a quadratic equation and the solution will give two real values
I1 = Peak Crank current
I2 = Sustained Crank current
 
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Offline HighVoltage

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Re: Ammeters, anyone?
« Reply #11 on: December 05, 2015, 11:08:13 am »
And for measuring the starter current, I am using a good quality but relative low cost current clamp, made by TEXA, the BICOR 3
Two settings for max current:
200A and 1200A
And a 2 m cable with BNC connector
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Offline cs.dk

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Re: Ammeters, anyone?
« Reply #12 on: December 05, 2015, 11:25:30 am »
@ HighVoltage - Do you have a scope screenshot of a car starting? Would be interesting to se how long/short the inrush peak is.

Nice current clamp btw.
 


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