Demoralised DCC newbie

[Pete the Elaner]

1 hour ago, melmerby said:

 

A £10 quid DMM? some even several times that price are pretty awful, my last few years of paid employment I worked at an instrument company that calibrated other firms electrical equipment and I spent a fair time

calibrating multimeters (including AVOs) and some of the Maplin and similar DMMs that were sent for calibration were truly rubbish accuracy.

Flukes were about the lowest priced DMMs that were really accurate and stable.

 

 

IIRTC, Flukes cost at least £100.

Most modellers will use a multimeter for finding faults & in most cases, the difference will be more important than the absolute reading.

Testing for a bad joint will show up as a jump in resistance so long as the meter is consistent with itself.

Why pay a huge amount more (& £10 to £100 is a huge difference) when the £10 one is good enough to find a fault?

 

If an accurate value is important, like when calculating capacitance requirements, then this will be a different matter.

[Bochi]

I got an Ultrics multimeter and once I worked out which end was up and deciphered the Chinglish instructions, got a straight 14v AC reading off the tracks.

[melmerby]

8 hours ago, Pete the Elaner said:

 

IIRTC, Flukes cost at least £100.

Most modellers will use a multimeter for finding faults & in most cases, the difference will be more important than the absolute reading.

Testing for a bad joint will show up as a jump in resistance so long as the meter is consistent with itself.

Why pay a huge amount more (& £10 to £100 is a huge difference) when the £10 one is good enough to find a fault?

 

If an accurate value is important, like when calculating capacitance requirements, then this will be a different matter.

As I was replying to the quote "a £10 DMM is more accurate" (than an AVO) I think my comments were more than justified.

 

Many basic DMMs can't read AC at anything other than 50Hz sine wave with any accuracy, the waveform of DCC can be particularly challenging.

The problem with very cheap DMMs  is that you don't know what you are getting, two the same price can be like chalk & cheese. One could be reasonably accurate, another total rubbish.

 

BTW You will be lucky to get a full function Fluke for anywhere near £100, I think the 113 is about the cheapest (£115 @ Amazon) and AFAIK it doesn't do current.

The nearest equivalent to the one I have is now probably the 177.

[RAF96]

Usually the spec for a DMM will give you the sampling frequency. The higher this is the more accurate it will be when reading pseudo AC such as DCC .

 

I have three DMMs and the cheapest (£10 from Llidl) also has the highest sampling rate, covers a 10Amp DC range (for motor stall checks) and is the most accurate for reading DCC when compared with my RRAMP meter. And it came with a rubber outer sleeve to protect against knocks and scrapes.

[Nigelcliffe]

I'm sticking with my view that for 99% of railway modellers, a cheap (sub £15, frequently sub £10) multimeter will do all they need. 

I've built accessory decoders, Loconet devices, Arduino hardware, put stay alives on stupidly small locos, debug layout faults, etc.. etc..   With my "two for £5" digital meter.   

 

I don't need to measure the DCC track voltage.   I can get a decent proxy for track voltage with a rectifier and measure the DC output from it.    If there is a problem, remove DCC system, and either measure wiring resistance (should be close to zero), or put a DC voltage onto it (9v battery) and measure that.  

 

I've experience of seriously expensive measuring kit: I used to work at BT's R&D facility. 

 

 

- Nigel

[Pete the Elaner]

3 hours ago, melmerby said:

As I was replying to the quote "a £10 DMM is more accurate" (than an AVO) I think my comments were more than justified.

 

Many basic DMMs can't read AC at anything other than 50Hz sine wave with any accuracy, the waveform of DCC can be particularly challenging.

The problem with very cheap DMMs  is that you don't know what you are getting, two the same price can be like chalk & cheese. One could be reasonably accurate, another total rubbish.

 

BTW You will be lucky to get a full function Fluke for anywhere near £100, I think the 113 is about the cheapest (£115 @ Amazon) and AFAIK it doesn't do current.

The nearest equivalent to the one I have is now probably the 177.

 

My apologies. I have re-read your post & interpreted it totally differently this time around.

It sounded like you were claiming £10 meters were no good, but I have interpreted it totally differently today & I don't believe you meant that at all.

& I wasn't even drinking last night... 

[melmerby]

1 hour ago, Pete the Elaner said:

 

My apologies. I have re-read your post & interpreted it totally differently this time around.

It sounded like you were claiming £10 meters were no good, but I have interpreted it totally differently today & I don't believe you meant that at all.

& I wasn't even drinking last night... 

A cheap DMM is certainly one of the basic tools I would recommend all railway modellers to purchase, just don't expect  a reading of 12.00v to be 12.00v (although it might be!)

As you say relative readings are more valuable than absolute, which can be inaccurate.

Some way of testing continuity is invaluable and comparable readings from known good circuitry can help.

 

I'm fortunate, due to my work, to have acquired some scrap quality DMMs which after I repaired and serviced them do (or did!) give a pretty accurate reading, not everyone is as fortunate.

[Ray H]

19 hours ago, Bochi said:

Thanks for all the advice which did enable me to track down some mistakes - hadn't installed one decoder properly after all, and misunderstood some aspects of programming.

I still have a mechanical issue with the 4-4-0 which has developed a stutter in reverse. It runs (but with a stutter) on DC but in the much slower DCC mode it grinds to a halt with a horrible ratchet sound as the motor, presumably, is spinning or trying to spin without engaging properly.

 

You do really need to sort out dc running first. Adding a decoder is very very unlikely to address dc performance issues.

[Bochi]

53 minutes ago, Ray H said:

 

You do really need to sort out dc running first. Adding a decoder is very very unlikely to address dc performance issues.

 

It was running OK on DC before I fitted the decoder. Now it isn't running OK on either.

[Ray H]

I'd check that the wiring hasn't been disturbed.

 

Set it up for dc and then ease the blanking plug/plate out a little in case it's touching somewhere it shouldn't. You're far better off trying the address problems on dc first then you know you should only need to tweak some CVs on dcc. 

[melmerby]

2 hours ago, Bochi said:

 

It was running OK on DC before I fitted the decoder. Now it isn't running OK on either.

Are you trying to run it on DC with the decoder in place?

Theoretically it should work OK but it's better to take the decoder out and try it on DC with the blanking plug in place

[Bochi]

44 minutes ago, melmerby said:

Are you trying to run it on DC with the decoder in place?

Theoretically it should work OK but it's better to take the decoder out and try it on DC with the blanking plug in place

 

It's on DC with the blanking plug in place but it still has this graunchy sound coming from the loco when it runs in reverse - sweet as a nut forward though. It is much, much faster on DC (old H&M kit) and doesn't stop and start but powers on through while making its unpleasant noise, which I guess might be a pickup issue? I'll just note that the blanking plug sits in the tender with this model, I've never had the main loco open.

[melmerby]

It sounds like a mechanical problem with the loco's mechanism, using DCC wouldn't cause it.

It seems to be an unfortunate co-incidence that after you fitted a decoder it went pants.

 

Comparing speed on DC and DCC is a red herring as the power getting to the motor could be quite different between the two systems.

[rockershovel]

A propos DCC locos running on analogue, I’d be very cautious about that. I had a DCC converted Bachmann 2-8-0, very nice it was but it did NOT run on analogue, although it would sit there making “start-up sequence” sounds. 

 

My two MMI 2-8-2s have been converted to DCC etc by Paul Martin, who advised me NOT to put them on analogue, so I have taken him at his word. 

 

My Broadway Lines 2-8-0 runs quite happily on either, being set up that way from the factory. 

[Sir TophamHatt]

On ‎06‎/‎05‎/‎2020 at 20:03, Joseph_Pestell said:

Very difficult to build a layout without a multimeter. It's the best fault-finding tool.

 

I've managed two...  I wouldn't even know how to use one.
The only faults I've had is where I accidently swapped the positive and the negative.  After turning on my PA2 and discovering it, a quick look at the soldering I've just finished and problem solved.

 

It's funny as I see them mentioned all over the forum, yet I don't think I've ever needed to use one.
 

 

 

@Bochi - don't worry.  I can imagine it's hard to start with.

What's the latest update?  Did the loco you re-fitted work properly on DCC?

 

[Bochi]

16 hours ago, melmerby said:

It sounds like a mechanical problem with the loco's mechanism, using DCC wouldn't cause it.

It seems to be an unfortunate co-incidence that after you fitted a decoder it went pants.

 

Comparing speed on DC and DCC is a red herring as the power getting to the motor could be quite different between the two systems.

I agree, it's probably coincidental - but confusing for a noob! It may be of course that I knocked something while fitting/unfitting the decoder and blank. That seems the most likely explanation.

[Bochi]

16 minutes ago, Sir TophamHatt said:

 

@Bochi - don't worry.  I can imagine it's hard to start with.

What's the latest update?  Did the loco you re-fitted work properly on DCC?

Latest is that I'm putting together a DC test circle so I can properly run in the locos. Framing a 4' x 4' baseboard for it atm. 

16 minutes ago, Sir TophamHatt said:

 

 

[Philou]

I've had problems in the past in just removing blanking plates, especially the 21 pins one. They were very tight and the danger is that by using a little leverage (think screwdriver) suddenly the plate will come off at an angle resulting in a few bent pins. How do I know? Check your pins that none have been  - er - modified. With care, they can be straightened using fine tweezers, but gently does it! Haven't permanently lost any (yet!).

 

Cheers,

 

Philip

[Bochi]

Sigh. I've built a test track, a circle of 4th radius set track on a nice solid frame. The Compound runs fine forwards but stutters going backwards. I fiddled with the blanking plate to no avail A previously unused (but quite old) tender driven 4F ran fine for half an hour forwards and then after one good lap in reverse the tender started smoking and now it won't run at all.

I'm burning through locomotives just trying to test the little wretches on DC!

(It's clearly not the track circuit which is very simple and in any case, ancient warhorses such as my GWR pannier and Bachmann Royal Scot ran in well both ways).

Edited May 26, 2020 by Bochi

[Brian]

What are you using as the DC power source for testing?

[beast66606]

For continuity testing I had an "operation" guy, which came in Bart Simpson mode, and each time continuity was found he used to say "Doh!" - but we digress.

[Matt C]

When laying and connecting up my tracks I've used two simple visual guides. My layout is a bit of a hybrid so three sides are accessed from the outside and one from a well in the middle so the normal principal of 'black to the back' gets interesting depending on where you are working.

   First visual Aid is a simple four wheel wagon with red masking tape on one side and black on the other. This starts out at the front of the layout with 'black to the back' and then moves around with me to where ever I Am working, doesn't matter whether I'm working from inside or out, a quick glance tells me where red and black should be on that section. Second to aid when wiring up is an old rear bicycle lamp I cut up and added two external wires with crocodile clips on the end. If you switch it on and then touch the clips together it lights up. Clip these to each rail in a section already laid, switch on and it should be unlit. Carry on laying and wiring in new track sections and if you inadvertantly cross wires the light comes on ...   Simples.

    you can do the same thing with a battery box, buzzer, clips and wire if you prefer an audio warning but I like the light option better.  Mine took half an hour to knock together and has saved me LOTS of cross(ed) wires 

[34theletterbetweenB&D]

On ‎26‎/‎05‎/‎2020 at 18:59, Bochi said:

Sigh. I've built a test track, a circle of 4th radius set track on a nice solid frame. The Compound runs fine forwards but stutters going backwards. I fiddled with the blanking plate to no avail A previously unused (but quite old) tender driven 4F ran fine for half an hour forwards and then after one good lap in reverse the tender started smoking and now it won't run at all.

I'm burning through locomotives just trying to test the little wretches on DC!

(It's clearly not the track circuit which is very simple and in any case, ancient warhorses such as my GWR pannier and Bachmann Royal Scot ran in well both ways).

Don't feel too despondent, that's what tender drives do. It was probably about to burn out when you happened to reverse direction. The rule with any older model that has been out of operation a good while is to use caution, and first try the mechanism for satisfactory freedom of movement before applying power. Test run it body off and check for heating very regularly over whatever will be its expected running duration.

 

(And with old open frame motors like the XO4, beware of sudden field loss. I have seen one which had sufficient magnetic field to lift the mechanism quite literally die after a few minutes operation. The armature wasn't damaged because power was chopped swiftly after it slowed and the unmistakable hot smell occurred. And the magnet had an extremely weak field, presumably all its domains gone wibbly wobbly and unaligned, just like that.)

 

 

[Bochi]

On 27/05/2020 at 14:03, Brian said:

What are you using as the DC power source for testing?

 

Old Hammant and Morgan controller. Tests fine on the multimeter.

[GoingUnderground]

On 06/05/2020 at 20:03, Joseph_Pestell said:

Very difficult to build a layout without a multimeter. It's the best fault-finding tool. The cheapest are only about a tenner so you will soon make it pay for itself.

 

I am a bit puzzled about the idea of motors that will work on either DC or AC. 

Many AC motors will work on DC, and are sometimes referred to as Universal motors for that very reason. They will work on DC, but only in one direction as reversing the polarity also reverses the magnetic polarity in the field coils so the motor still turns in the same direction no matter what polarity is applied. This also happens when running on AC as the polarity is continually reversing.

 

To change direction you need to change the polarity of either the commutator feed or the field coil feed, but not both. I don't know about modern Maerklin locos, but British Trix locos used AC up to mid 1950s and they incorporated a field coil polarity switching relay.