**Before I begin, I want to state that I am completely aware that in older Athearn locomotives the motor is not isolated from the frame and it needs to be to do decoder installations.
Anyways to my actual post, I am trying to get familiar with my multimeter as I want to check if the motor is isolated in older non-DCC locomotives. Since I know that older Athearns have motors that are not isolated, I am using them to test my multimeter.
I put my multimeter in the lowest OHMs and one probe to either the motor terminal or the motor brush and the other probe on the frame, however I am getting no continuity, but I know I should. What am I doing wrong?
I want to make sure I use my multimeter properly before I install decoders in older non-dcc locos (not just Athearns).
Thanks in advance,
Hi gpharo:
This is probably a stupid question, but have you tested the meter by touching the probes together? It should read zero ohms.
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
Not a stupid question at all. I don't get exactly a reading of zero, I always get something like 00.4, which I've read online, that it is close enough to zero.
gpharoI put my multimeter in the lowest OHMs and one probe to either the motor terminal or the motor brush and the other probe on the frame, however I am getting no continuity, but I know I should. What am I doing wrong?
You should not get continuity to the top motor terminal from the frame, only the bottom terminal/brush. Place the locomotive on a scrap piece of track. Check continuity from the track to the frame.
If there is no wire going to the bottom of the motor, you have a hot frame, and its probably connected.
gpharo I don't get exactly a reading of zero, I always get something like 00.4, which I've read online, that it is close enough to zero.
Mine never reads exactly zero either.
I have used analog and digital meters for years. When we say zero ohms, it is very close to zero. The meter probes have resistance.
I always touch the probes togeter first to check the probes and meter.
Did not do that many years ago and when I did not measure any voltage I thought the circuit was dead. It was not. Low voltage so no shock.
Below is a link on motor isolation but I suspect you are aware of the details but still good to put into Favorites.
http://www.dccwiki.com/Decoder_installation#Isolating_the_Motor
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
The weirdest thing, as suggested I tried connecting one probe to the frame and the other to the rails of a seperate piece of track and nothing, no continuity
Then I tried putting both probes on the frame and again, no continuity, but there should be.
So I thought maybe the problem is the paint, maybe the black paint that Athearn uses does not conduct. So I grabbed my Dremel and I sanded off the paint on a small part of the frame. Then I tested that part of the frame with the rails, bottom motor terminal and motor brush and voila...I got a reading of conductivity, proving that the motor is not isolated from the frame. (even though I knew this already).
Does this conclusion make sense?
Valueable information moving forward into future decoder installs.
gpharoDoes this conclusion make sense?
Yes you have to remove the paint, on some locomotives.
hon30critterMine never reads exactly zero either.
Some of the analog meters I've used in the past had "zero-adjust" pots.
Maybe they have been eliminated on newer models?
Good Luck, Ed
Just because there is coontinuity from the rail to the frame does NOT mean the motor is not isolated. Is this loco an older Blue Box oone, or is it one of the newer RTR models that has a circuit board clipped on top of the motor instead of those big metal clips? The newer RTR models fo have the lower motor brush isolated fromt he frame - it's not a bad idea to verify this, but the ones with a PC board clipped on top of the motor are designed for plug-in decoder installs with no rewiring.
Frame to rail but no frame to motor = perfectly fine, just possible coupler issue depending on how the coupler is mounted.
Frame to motor but no frame to rail = not good, a derailment could push a wheel into the frame resulting in rail to motor conduction and a blown decoder.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
gmpullman hon30critter Mine never reads exactly zero either. Some of the analog meters I've used in the past had "zero-adjust" pots. Maybe they have been eliminated on newer models? Good Luck, Ed
hon30critter Mine never reads exactly zero either.
Part of the reason analog meters need a zero-adj for the ohms scale is because the battery inside is directly part of the circuit. As the battery depletes, the meter indication will change. Most digital meters, the battery feeds a voltage regulator circuit so the voltage applied for the ohms range is constant right until the battery gets too low to work, better ones will have a low battery indicator so you know when it is time to replace the battery. With an analog meter, it was battery replacement time when you shorted the probes and even with the zero adj at the extreme as far as it would turn, you still couldn't get a 0 reading.
rrinker Frame to motor but no frame to rail = not good, a derailment could push a wheel into the frame resulting in rail to motor conduction and a blown decoder.
True. Don't ask me how I know.
Gary
Proto 2000 Alco S1 or was it the S3...memory slipping on that one..
Probably both. That Atlas S2 (newer one, not the old Roco one) has the same problem, additionally compounded by having the metal frame of the motor connected to a brush, requiring a new nylon motor mount screw. On my P2K S1 the lower brush holder is in no way connected to the motor frame, so I just added a wire, cut off the tab that rubbed the frame, and put a piece of Kapton tape over it.
rrinker Probably both. That Atlas S2 (newer one, not the old Roco one) has the same problem, additionally compounded by having the metal frame of the motor connected to a brush, requiring a new nylon motor mount screw. On my P2K S1 the lower brush holder is in no way connected to the motor frame, so I just added a wire, cut off the tab that rubbed the frame, and put a piece of Kapton tape over it. --Randy
Even the Atlas Master Gold ones with DCC/sound already in them?
On one of the Protos, one has a pair of plastic nubs on the trucks that prevent wheel-frame contact. Im thinking the S3 has something like that.
Would be interesting to check the Gold ones. Those are like the third series, the originals were the Roco ones, then there is the one that internally looks almost exactly like the P2K - purple motor endcap and all. Those are the ones that need isolation.
Sorry to be pedantic BMMECNYC, but you will get continuity to both motor terminals if either one is connected to the frame. This is because the motor itself is a low DC resistance, especially older motors. One motor lead will be closer to 0 ohms than the other, but it may not be by much. Test each motor wire to the frame and the lowest resistance one will be the one you need to disconnect from the frame. As the OP discovered you always need a shiny metal part of the frame to test as most paints do not conduct electricty.
Alan Jones in Sunny Queensland (Oz)
Hi Randy, I just want to confirm I understand these two points...if I misunderstood them, can you please clarify.
"Frame to rail but no frame to motor = perfectly fine."
- It is ok to have continuity from the frame to the rail, as long as there is no continuity from the frame to the motor???
"Frame to motor but no frame to rail = not good."
- But anytime there is continuity from the frame to the motor is a bad thing regardless of the frame to the rail?
Thanks.
Alantrains Sorry to be pedantic BMMECNYC, but you will get continuity to both motor terminals if either one is connected to the frame. This is because the motor itself is a low DC resistance, especially older motors. One motor lead will be closer to 0 ohms than the other, but it may not be by much. Test each motor wire to the frame and the lowest resistance one will be the one you need to disconnect from the frame. As the OP discovered you always need a shiny metal part of the frame to test as most paints do not conduct electricty.
I agree with your point, once I sanded the paint on the frame, I had continuity from both the top and bottom motor terminals to the frame. BTW, the locos that I'm testing are older BB Athearns.
gpharo Hi Randy, I just want to confirm I understand these two points...if I misunderstood them, can you please clarify. "Frame to rail but no frame to motor = perfectly fine." - It is ok to have continuity from the frame to the rail, as long as there is no continuity from the frame to the motor??? "Frame to motor but no frame to rail = not good." - But anytime there is continuity from the frame to the motor is a bad thing regardless of the frame to the rail? Thanks.
Yes, exactly.
Besides BB Athearn locos, is there any other non-DCC locos that need some sort of modification in regards to motor isolation for decoder installs?
I'm thinking of the older Proto 2000s, the ones in the beige and/or greyish blue box, Atlas Classic and Proto 1000s?
A few years ago I bought, used, a Walther's HO H12-44, non DCC ready that has both halves of the motor connected directly to the brushes. One half bolted to the bottom frame and the other bolted to the top weight.
Used Kapton tape to isolate the motor halves and replaced metal machine screws with nylon screws. The original screws where Metric so I tapped for 2-56.
I had to machine a little with a Dremel and carbide bit for 0.002 inch thick phosphor bronze strips to rout power to the brushes.
Squeezed in a Tsunami TSU-AT1000 and a 25 x 35 mm speaker in a styrene baffle.