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Topic: measuring current not working (Read 556 times) previous topic - next topic

Dane

Hi! :)

I'm trying to measure the current draw of a wireless doorbell to see if I can power it directly from my Arduino (with external 1A power supply) alongside a servo and some LEDs. Also to find out what if any resistor it would like used in line.

I'm using three the double 'A' batteries it is normally powered by and I have put the multimeter in line. So I have the black lead in COM and the red line in the 10A socket.

The circuit works - the doorbell works - but I don't get any reading on the multimeter, which is very sad. Any ideas? The multimeter, the Elit 70A, is pictured below. I have it on the 'A' setting.



THANKS

robtillaart

How did you connect - schematic?
Can you measure the voltage?
Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

retrolefty

You appear to have your red test lead in the 10A, but you are selecting a millamp scale? I'm pretty sure you need to move the red test lead to the other lower current position jack, but the picture is not complete.


Lefty

Dane


You appear to have your red test lead in the 10A, but you are selecting a millamp scale? I'm pretty sure you need to move the red test lead to the other lower current position jack, but the picture is not complete.


Aha! In that case, I must have a blown fuse on the milliamp socket...thanks for helping me figure that one out.

Dane

Yep - confirmed.

Weirdly, the 10A fuse is not at all easy to get out or at, whereas the 0.5A fuse is held by the usual easy to detach clips...

retrolefty



You appear to have your red test lead in the 10A, but you are selecting a millamp scale? I'm pretty sure you need to move the red test lead to the other lower current position jack, but the picture is not complete.


Aha! In that case, I must have a blown fuse on the milliamp socket...thanks for helping me figure that one out.


That's happened to the best of us. A very important rule when measuring current is that once you have made your measurement remember to immediately remove your test lead from the current jack, as if you forget and subsequently go to make a voltage measurement, the internal shunt resistor used for current sensing will cause high current to flow through the meter leads and blow open the protection fuse.

John_S

Quote
A very important rule when measuring current is that once you have made your measurement remember to immediately remove your test lead from the current jack
I learned that the hard way. A 12V SLA battery makes big sparks that way. It was like DC welding :smiley-eek:
http://jsrintervalometers.blogspot.ca

retrolefty


Quote
A very important rule when measuring current is that once you have made your measurement remember to immediately remove your test lead from the current jack
I learned that the hard way. A 12V SLA battery makes big sparks that way. It was like DC welding :smiley-eek:


My Fluke model 87 DVM has a very nice feature that if there is a test lead plugged into a current jack, but you turn to a voltage function on the function selector knob, the meter starts making a sharp beeping noise to try and warn you that you are telling it to do something very stupid.  ;)

Lefty

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