Help - Bachmann 170 Turbo threatening National Grid

[Ravenser]

A few months ago I bought a rolling road . Today I have been giving various models a brisk run on it , to clear the cobwebs

 

The Bachmann 170 , in store for several years , has just given me a fright. Put it on the rollers , and static, at speed-step 000, it draws 1.02amps according to the ammeter

 

Crank it up to step28 , and this drops to a "mere" 0.82 amps

 

It isn't the Powercab ammeter - remove the 170 and the reading drops to a normal background. 0.08 amps

 

What on earth is going on? How can a static loco with no sound or lights draw an amp???

[34theletterbetweenB&D]

I would have the decoder out pronto, and have the ohmmeter on the loco circuit as a first step.

[Pete the Elaner]

& then,

If you have a 10A multimeter, connect it as an ammeter to check the current draw while still on DC.

[Ravenser]

I would have the decoder out pronto, and have the ohmmeter on the loco circuit as a first step.

 

Thanks. My difficulty is that this is an older Bachmann mechanism , and therefore the decoder is hard-wired. Since a TCS T1 is fitted , the decoder itself is unpluggable, but that doesn't mean I can run it without a decoder. As a T1 is rated at 1.2amps continuous/2 amps peak the decoder is probably not at immediate risk of blowing  

 

The only ammeter I have /used is the feature on the NCE PowerCab - someone pointed out this facility to me a little while ago . I do have a multimeter , and could therefore do a resistance check from motor terminal to motor terminal, without power, and also from connection to decoder back through the pickups. The multimeter has a 10A facility, but please bear in mind that I'm a Bear of Very Little Brain when it comes to electricity with only a very limited understanding of what the multimeter can do , so I would need things explaining very slowly in words of one syllable

 

The mechanism was given a little lubrication with plastic-safe oil beforehand , on motor bearings and axle bearings . Pickup is by wipers on wheel-backs  . The lighting has been disconnected so cannot be imposing any load

 

The chassis ran well enough - if you ignore the current readings - from about step 2 or 3  up to full speed . Without the ammeter function I wouldn't have guessed  there was an issue

 

There is a little history, which now starts to seem a bit sinister....

 

I also have a 158, which is stopped, damaged. This unit always was a bit difficult and would refuse to move until speed step 10 (of 128) . More recently it seemed to have lost power/required a lot of grunt to start. Before Shenfield last year I was trying to get it going , and resorted to running it back and forth on the layout at speed. Since the layout is 8'6" long , this probably wasn't too smart - and after a couple of minutes it popped a drive shaft out and would not move on one bogie . Attempts were made to reinstall the shaft , it kept coming out and the whole thing was abandoned as a bad job at 1:15am on the Friday. (That was when I decided to buy a rolling road....)

 

And when I was involved with a club project, I recall another member having a couple of motor failures on Bachmann 158s/170s   

 

I'm starting to worry that there may be an underlying motor issue, and maybe the 170 is going the same way.... 

[Ravenser]

I've just had another go, while sorting out other locos. I oiled the  motor bearings and the accessible gears before trying it

 

The results remain terrifying.

 

Current drawn while totally static is now a "modest" 0.90A to 0.95A , measured by the NCE Powercab. This falls to a current draw of 0.79A - 0.72A  when running very fast. (At least this is below the T1 decoder's continuous rating of 1.2A...)

 

Two Bachmann 158s - a very similar mechanism - result in a static current draw of 0.08A to 0.11A (this will be point motors and other locos lights) (I've just sorted out the damaged unit referred to above)

 

I unplugged the T1 , and connected a Gaugemaster DC controller across the motor terminals . It ran fast and freely without problems

 

I've got out the multimeter. I am a bear of very little brain when it comes to electricity and continuity/resistance testing is all I know how to do… So I plugged the red probe into the 10A socket - as opposed to the 200mA one - selected 10A range and held the probes to the motor terminals while it was running under DC power. The meter read a shocking 5.1   [Amps?!!?] and the motor slowed right down

 

At this point I started vaguely wondering if exorcism would be relevant

 

I am getting a resistance of 29.0-29.5 ohm across the motor terminals reported by the multimeter - for what that's worth.

 

The mechanism runs fine , is totally controllable and the decoder seems fine - if it wasn't for the ammeter readings I wouldn't suspect anything was wrong......

 

 

 

[Suzie]

The meter in current mode needs to go in series with the motor! Connecting it across the motor is applying a short circuit and the decoder will not last very long, especially when drawing 5A.

[Dungrange]

I'm no expert with electrical things, but to get an accurate current measurement from your multi-meter, you need to ensure that the meter is in series with your electrical circuit.  That is, the meter needs to replace one of the wires between one side of the motor and the controller.

 

When you are connecting it across the motor terminals, which is what you would do if you are trying to measure voltage, that is connecting in parallel.  As Suzie has indicated above, what you have effectively done is applied a short circuit across the decoder and it would record 5 Amps because that is probably what your NCE Powercab can supply, although I'm not sure why it didn't see that as a short circuit and shut down.

[Ravenser]

The current test was conducted using my DC controller with the decoder removed (it plugs into the harness , so I simply unplugged it - I was trying to eliminate any decoder issues)

 

I'm not sure why this didn't trip the DC controller, but at least the decoder is safe . The probes were in contact with the terminals for only a couple of seconds, until my jaw came back up off the floor....

 

I think I can do a proper current test the correct way .. Apologies for the stupidity , but there's no documentation with the multimeter and the little book I bought on multimeters has diagrams of meter circuits but no practical instructions on how to use a meter or what to test and what it means.

Edited February 11, 2019 by Ravenser

[mossdp]

There is a thread on here or possibly elsewhere about slow running Bachmann Voyagers. Someone had investigated this in detail and found that the brush springs had lost their "springiness" and this caused excess current consumption. Once the brush covers were removed by gently levering them out and the springs stretched slightly then performance was restored. It may be that poor commutation is causing arcing and this is causing a build up of carbon in the commutator slots leading to excessive current consumption or that the brushes have stuck in their tubes against the armature. There are multiple reports of this sort of fault and it nearly always seems to be that a model has been in store for sometime. The lack of springiness may be the effect of the excessive current consumption rather than the cause as excess heat seems to cause springs to loose their springiness and possibly stuck brushes are the underlying cause.  It is also important that the rest of the mechanism is also running freely and cleaned and lubricated.