Multimeter-ing Help

H

Herc Driver

Active Member
Apr 18, 2005
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North Carolina
I posted this on the Tech thread but would like to open it up here as well.

How do I test the track for the correct voltage with a multimeter? I'm running straight DC, but have no experience using a multimeter. I read the directions, but they didn't answer the basic question of what do you actually touch with the test probes? Do you only touch one rail? Both? Do you need to ground one testor while the other touches the rail? I'm just trying to figure out if the rails I soldered today are doing a better (or worse) job of carrying power along the rails than those that are not soldered yet.

- Thanks guys -
 
S

Squidbait

Recovering ALCO-holic
Jan 27, 2007
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Paris, ON
Herc,

The short answer (no pun intended) is that you need to touch one probe to each rail. Power flows from one rail to the other through your loco's motor.
 
E

e-paw

Member
Mar 16, 2007
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saylorsburg pa
To check the track voltage on regular dc. Turn up the power pack, touch one probe to one rail and one to the other with the meter set to a range of at least 12 volts dc. Now with an analog meter (one with a moving needle) the needle may not move or pin all the way to the left past the zero mark. This means the polarity of the leads does not match that of the track. You can reverse the power pack or the leads and if you have power at the track it will show at the meter. With some of the newer digital controlled packs you may not see voltage unless there is a load on the track. In that case just place a lighted car on the rail.
 
P

pgandw

Active Member
Jul 9, 2005
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Reading the voltage on the track with no load does not tell you if your joints are good enough. With no load, the extra resistance of a poor track joint does not come into play. Reading voltage just tells you whether there is a connection or not, not the electrical quality of the connection.

There are two relatively easy ways to check the resistance of your track joints.

1) Measure the resistance of the joint directly using your multimeter. Remove or turn off all power to the track. Set your multimeter to ohms scale, use the X1 scale for more sensitivity if that is an option. Calibrate the multimeter by touching the probes together and adjusting until ohms read zero. Now place probes on either side of rail joint (same rail) to be measured and check for zero ohms. Anything more than 0.2 ohms is a poor joint. Note that if you have feeders properly attached on either side of the joint, the feeders will parallel the joint and reduce the resistance to zero, regardless of the quality of the joint. That is the whole point of the feeders.

2) Use an automotive 10 watt bulb with 2 wires attached to it. Turn power on full - should be around 12 volts - and put one wire on each rail. Light bulb should light. If you get a poor, but still conducting rail joint, between the power feed and the light wires, the bulb will have reduced brightness. The load of the bulb causes the resistance of the poor joint to force a voltage drop beyond the joint.

hope this makes sense and helps
 
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