Getting an amp meter to work

Thread Starter


Joined Nov 22, 2015
I am a model railroader. The type of power that i use, called DCC- produces an AC wave that cannot be read accurately with a multi-meter. A website recommended using a full bridge rectifier to change teh wave to a DC wave that the meter can read. I have built the rectifier and it measures both peak and average voltage well -- after adjusting for the loss of V by virtue of the inclusion of a CAP in the circuit. The site also advises that you can use a full bridge rectifier to measure amps. My power supply puts out about 13 V and 3.3 A. I first built a rectifier out of 4 1n4001 diodes but it got hot very fast -- since as it turns out the diodes are only rates at a fraction of an amp. However, I did get a reading near 3.3 A. I then bought a Vishnay full bridge rectifier # KBU4D. When I use it the max amps I can measure is 0.3 amps, even with a very heavy load on the circuit. I though that there might be a cap built into this recitifier but I cannot see one in the spec sheet.

Any advice?


Joined Nov 29, 2011
The 1N4000 series diodes are rated at 1 amp max.

Your bridge rectifier is probably bad. Look for some 6 amp diodes and build another bridge. Capacitors are not normally built into bridges.

You don't use DC PWM for train control? What is DCC? Why can't your multimeter read AC accurately?

Thread Starter


Joined Nov 22, 2015
DC is a straight dc flat dc signal. DCC is a square wave signal that both delivers power and allows one to control many function on a model train engine -- sounds, lights, engine characteristics etc. Does it matter what diode I get as long as it is rated 6 amp?


Joined Feb 5, 2010
Doesn't even need to be 6 amps could be 4 or 5 or 8 etc.
It MUST be rated for more than the system max output if you want it to last a reasonably long time.

A single diode followed with a cap of a few hundred micro farad will be enough to get a decent average DC voltage level reading if digital "hash" is causing problems with your meter. (Polarity must be obeyed for meter connections).


Joined May 20, 2015
Sinewave is only example.
My rectifier bridge can also work the other waveform. A more detailed description of your signal.I I do simulation of your process.