Using a multimeter

[richg]

How to use a multimeter. Store this link in Favorites. Pass it on to others.

http://www.jameco.com/Jameco/workshop/techtip/Multimeter.html?sp_rid=MzEyMjY2MjcyMDAS1&sp_mid=4268910

Rich

[poliss]

If you want to measure the stall current to check which wired decoder is suitable, then you need the dial switch pointing to 10A and the leads , one in the common and the other in the 10A socket, as most motors stall at half an amp on n gauge and 1 Amp on H0.

[Len]

One other tip, when measuring voltage do it across a load, e.g., a lamp, motor, or resistor. Most multimeters have a high impedance input, which means they don't put much load on a power source, whether it's a battery or power supply.

So you may have a battery that's almost dead, but the multimeter will still read voltage from it. There's just no current behind that voltage. Which is why battery testers for common batteries have a load built in to them.

Len

[CNE Runner]

RichG - Thanks for the interesting and valuable hyperlink. I have been using multimeters for years and yet even this old brain learned a thing or two from that website. The international symbols on the newer multimeters has led to considerable confusion...that website addressed them all.

Len and Polliss - Very useful information...thanks!

If you are in the market for a decent multimeter, try Harbor Freight (aka The Chinese Tool Store). Their top of the line model #37772 sells for around $19.99 and is outstanding. Their most economical model (#98025 - selling for $4.99) will probably serve most of us just as well. On the other hand you will probably only purchase one multimeter...why not get a good one?

Ray

[richg]

I have three of the cheapest one for some time. They compare very well to a $200.00 meter for MRR use, checking my car. Cheap to replace if mis-used.
They do not measure AC current but I have never found that to be an issue.
They have a diode position but it does not work for LED's.

Rich

[poliss]

As a further note, a multimeter won't work properly on DCC. You will be able to get a general reading, but it won't be very accurate.

[Joe Satnik]

Dear All,

In case anyone was curious why DVOM diode checks won't work for LEDs:

The meters usually switch in a 1.5 volt battery and a series resistor (to limit current) for diode checks. 

The 1.5 V is enough to overcome the 0.6V or so Vf (forward voltage) of a regular diode.

Vf is the voltage needed to start a diode conducting current, or "turn on".     

LEDs, on the other hand, have forward voltages much higher than 1.5V, and vary by color.  (Guessing between 2 and 4 volts.)

The lowest Vf occurs on the red end of the spectrum (lowest frequency, lowest energy),

the highest on the violet end of the spectrum (highest frequency, highest energy).

Hope this helps.

Sincerely,

Joe Satnik 

[richg]

As a further note, a multimeter won't work properly on DCC. You will be able to get a general reading, but it won't be very accurate.

Older analog might not.

The digital ones do very well. 13.7 VAC on a NCE DCC system which is quite close to what my digital Oscope measures. I have used it at our club many times. This is not rocket science.

Rich