In case it matters, I have a mixture of older and new locomotives. I’m new to all this but have tried to do my homework. I am particularly concerned if the amperage measurement limit will be enough. Is the amps setting something that I would definitely use?
I found this information from dstarr on this forum and wondered if it is a good solution for a novice. For instance, how would I attach the resistor?
“If your Radio Shack meter lacks a 1 amp or higher range (best current range on my Radio Shack meter is 600 mA or 0.6 Amps) and you need a higher range, you place a 1 ohm resistor in series with the locomotive, so that all the locomotive current flows thru the resistor. Measure the voltage across the resistor. By Ohm’s law, I = V/R. In the special case of R = 1, Ohm’s law reduces to I = V.”
The cheapo meters will work for most of our model railroading projects. I have about a dozen of the Harbor Freight meters laying around at arms length, I’m lazy!
I check out each one as I get them against my Fluke 179 and everyone has been very close, within .1 volts or so. Close enough for Government work.
I bought one of the DSO138 scopes (assembled) off eBay for under $20 and it works great for my hobby projects. It’s off -.27 volts at 12 VDC not too bad for $20. Works great for DCC and Arduino stuff.
Mel
Modeling the early to mid 1950s SP in HO scale since 1951
I didn’t pay a lot for any of my meters and I have some pretty fancy benchtop meters as well as handhelds, I also have a calibrated precision reference I use to compare them aprt from one that is nearly 40 years old andneeds some capacitors repalced, they are all quite accurate, even the worst is still more than good enough for model railroad use. But I still pull out a HF one for quick and dirty checks - the idea being that if I accidently touch the wrong thing and blow the meter up, I don;t really care because it was $3. Heck, new batteries cost mroe than HF charges for the whole meter, it’s almost not worth it changing the batteries when they die - although it would be a good place to use those massive boxes of 100 batteries you can get from China on eBay - cheap enough that even if half of them are dead before you get them, it’s still a bargain. a 10 amp range is almost a necessity for HO and larger scales. The method of using a resistor and measuring the voltage drop is exactly how the meter works internally, but not only do you need a resistor of sufficient wattage to handle the expected current, you also need a reasonably accurate resistor. 10% tolerance won’t really cut it unless you actually measure the resistor first and then do the full calculation. You’re better off just getting the HF meter and using the 10 amp range to check stall currents. On the AC setting is also reads DCC track votlage fairly accurately, mainly because it’s NOT an RMS meter tuned for sine waves.
Mel, another nifty and cheap gadget is one of those $20 or less LCR meter/transistor checker. Works pretty well and is pretty accurate, you can slap on a resistor or capacitor or inductor and itwill tell yo the value, or hook up a transistor and it will tell you NPN or PNP or N-MOS or P-MOS etc and give you the gain and some other specs. Or a diode and it will tell you the forward voltage. The slightly facier one with the graphical display ike mine will draw the scheatic symbol for the detec
I have one and keep it handy when I’m working on projects. I can’t tell one ⅛ watt resistor from another. The China paint on the newer resistors isn’t as easy to read as the good old US resistors were.
Mel
Modeling the early to mid 1950s SP in HO scale since 1951
The whole time I built the kit I kept one of my other meters fired up as well - to check the value of every resistor. I can;t tell some of thoses colors from one another either. Plus with many being 1% tolerance, they have 5 bands and they also aren’t very careful about offsetting them so you know which end to start at.
I have four beacuse I do misplace them at times. I sometimes keep one in the car for it’s 12 v system.
It cost more to make longer test leads with better probes, wire, meter plugs, alligator clips and flea clips some years ago. Made leads three feet long.
You might consider the below depnding on what kind of testing you do. The flea clips are nice for decoder testing, small diameter wire and tight spots.
I’ve also got around a dozen Harbor Freight meters…and all give slightly different readings.[;)]
You can however, open them up and there is a small adjustable capacitor on the circuit board that you can adjust them with. They also contain a 9 volt battery that might be useful in something. Free is always good.
To help the meter probes last longer from the wires breaking loose from continuous flexing I put a dab of Amazing Goop glue where the wires exit the probes. Amazing Goop remains slightly flexible and is a very good train relief. I also Goop the wires where they exit the connectors. I haven’t lost a probe since I started Gooping them.
Another helpful thing is to make a angle support for easy viewing. A simple block of angled wood wither Gooped or Velcro-ed to the back of the meter works very good.
