How to measure the current need for an unknown device?

Thread Starter

Kelvin Lee

Joined Oct 22, 2018
110
Dear Sir/Madam,

I know how to use the multimeter to measure the current through a circuit but how can I know the minimum current need for an unknown device? What is the proper way to measure the current need for an unknown device if I don't have the datasheet?

Best regards,

Kelvin.
 

rsjsouza

Joined Apr 21, 2014
214
Kelvin, a golden rule of measurement (mostly applicable to manual range multimeters) is to always start with the largest range available and then decrease it as soon as you get a feel of the levels used by your equipment or system under test.

For measuring current on modern DMMs with auto-range, you always start plugging your test leads to the "A" and "COM" terminals and setting its dial to the "A" range.

An alternative is to insert a small resistor in series with the circuit (also called "shunt") and measure its voltage with the meter.

Obviously that you can't tell from above that I am unaware of your prior experience and skills, thus my answer may be very basic for you.
 

dl324

Joined Mar 30, 2015
9,321
What is the proper way to measure the current need for an unknown device if I don't have the datasheet?
You can't. You'll measure a current for sure, but you have no idea if it represents the maximum current draw. If you wimp out on the current capacity, it will likely result in unreliable operation.
 

MaxHeadRoom

Joined Jul 18, 2013
19,388
What is the nature of the "Unkown Device'"?
If this is a piece of equipment a very Rough idea is the operating voltage and the physical size and what its end function is.
Max.
 

BobaMosfet

Joined Jul 1, 2009
883
Dear Sir/Madam,

I know how to use the multimeter to measure the current through a circuit but how can I know the minimum current need for an unknown device? What is the proper way to measure the current need for an unknown device if I don't have the datasheet?

Best regards,

Kelvin.
Unless it is a very simple component where you can test using a voltage and current source and a measuring tool (meter or scope), you can't. If you know what it's for, and the pinout, you might make an educated guess. If it's more than a component, like and actual device comprised of several or many components and component subsystems-- all bets are off.

Every component in electronics is _designed_ to work within a specific or a range of voltages and current levels, and a tolerance. And in some cases, the ability of an item to withstand the electromagnetic forces arrayed against it literally comes down to the materials it's made of and their intrinsic ability to act as a dielectric.
 

Reloadron

Joined Jan 15, 2015
4,682
If you want to know the power consumption of a device, in the interest of keeping things simple just buy one of these or maybe one of these. I use the latter and both are available for a wide voltage input range. I only suggest a simple turn key solution as I have no idea what your skill level is using other instrumentation. The latter is available globally as far as I know and such devices or similar are inexpensive and plentiful pretty much globally.

Ron
 
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