WBJr over current reading for low battery current

[phonetic]

I have checked WBJr reading with DC clamp meter, if battery current is under -2-3 amps shown by DC clamp meter, classic is showing -6-9 amps changing aprox 1 sec period.

When loading Inverter  2400 W, getting -129 amps showing from classic display & local app, DC clamp meter showing -128 amps.

WBJr with low currents have scaling errors, what resolution the A to D converter WBJr have ??

[Vic]

Hi phonetic,

I have no specific knowledge of the WBjr's resolution or accuracy,
however,  Clamp-On DC ammeters are notoriously inaccurate,  are quite unstable  and have poor repeatability.    There are good Clamp-Ons that are quite good (and you may be using one of these)  which can be quite expensive.

Personally,  I would suspect the Clamp-On ammeter.

Also,  what is the exact Shunt that you are using?   I assume that it is the Deltec 500 A.   Just my opinions,     Vic

[tecnodave]

To get the best accuracy from an amp clamp meter it is necessary to center the wire in the jaws and it must be at 90 degrees both ways to get full accuracy, both Fluke and Amprobe (owned by Fluke) have wire alignment marks on the jaws. Listed specs on accuracy is 3% of full scale reading on most better grade amp clamps, so a 400 amp clamp meter could be off by 12 amps when reading at less than 10% of full scale.

td

[boB]

The current resolution of the WB Jr. with one of those 500 amp 50 mV shunts is 0.078125 amps.

To get a +- 0.1 amp reading, it has to be scaled and rounded, which is what is done inside the Classic.

Clamp-On meters are not going to be all that great, normally.

However, I am pretty amazed at the Extech $75  clamp-on DC/AC ammeter for
that price.

Either way, you really have to be diligent about resetting the clamp on probe to zero
at every chance.  Also, whenever you turn its polarity around.

One trick you can do when measuring low currents is to wrap multiple windings
of the cable you are measuring the current of around the clamp-meter jaws.
That is, if the wire is small enough or the jaws large enough to allow that.
Then, divide the ammeter's reading by the number of turns to get the actual current.

boB

[TomW]

However, I am pretty amazed at the Extech $75  clamp-on DC/AC ammeter for
that price.

Either way, you really have to be diligent about resetting the clamp on probe to zero
at every chance.  Also, whenever you turn its polarity around.

One trick you can do when measuring low currents is to wrap multiple windings
of the cable you are measuring the current of around the clamp-meter jaws.
That is, if the wire is small enough or the jaws large enough to allow that.
Then, divide the ammeter's reading by the number of turns to get the actual current.

boB

boB;

I really like my clamp on Extech meter. Appreciate you recommending it.

For anyone interested it is available on Amazon over here:

http://www.amazon.com/gp/product/B000BEZV5O/ref=wms_ohs_product?ie=UTF8&psc=1

Good trick with the multiple loops for small current reading.

Tom