Midland in Tewkesbury

[Tricky]

On another matter, I’m not sure if I’ve mentioned here or elsewhere that I intend dipping my toe into DCC. I’ve been talking to a potential supplier who just needs me to tell him the stall current of the motor in my 0-6-0 which I will be converting. I have one of these:

....but I’m a bit baffled as to how to wire it and use it! Any (positive..ha ha) suggestions? Bearing in mind my electrical knowledge is mostly confined to straightforward household wiring, this is unfamiliar territory! 

[O-Gauge-Phil]

Set your meter to the lowest resistance range, on your meter this is 200.  Then with the leads in their position as shown, ie. not in the 10 amp position, touch the two leads together and check that the resistance reading is zero.  Now measure the resistance of the motor and if necessary subtract the value you have got when you touch the leads together. 

 

Then using ohms law calculate the maximum current.  The voltage is set within the decoder, usually 12 volts, (however I normally set mine to 9 or 10 volts)

eg.  WIth a motor resistance of 100 ohms and 12 volts, then I = V / R  = 12 / 100 = 120mA.

 

This will give you the maximum current that can be drawn by that motor.   As the motor rotates it will generate back emf which will reduce the current drawn.  You don't usually see this level of current as you normally start on a reduced voltage.  Modern  motors don't as a rule draw much current and a one amp decoder is okay for most O gauge locomotives.

 

I thought this might also be of interest to others.

 

Phil

[colin penfold]

I have two projects on the go and am about to get chips for both so this was timely for me. I have just measured a Canon MT motor from MSC models at 7 ohms and a Mashima 14/20 at 18 ohms. Using Phils sum I make the figures 1.7 and 0.66 amps respectively. I have the same meter as you Tricky. Hope this is useful. Thanks both.

[Tricky]

1 hour ago, O-Gauge-Phil said:

Set your meter to the lowest resistance range, on your meter this is 200.  Then with the leads in their position as shown, ie. not in the 10 amp position, touch the two leads together and check that the resistance reading is zero.  Now measure the resistance of the motor and if necessary subtract the value you have got when you touch the leads together. 

 

Then using ohms law calculate the maximum current.  The voltage is set within the decoder, usually 12 volts, (however I normally set mine to 9 or 10 volts)

eg.  WIth a motor resistance of 100 ohms and 12 volts, then I = V / R  = 12 / 100 = 120mA.

 

This will give you the maximum current that can be drawn by that motor.   As the motor rotates it will generate back emf which will reduce the current drawn.  You don't usually see this level of current as you normally start on a reduced voltage.  Modern  motors don't as a rule draw much current and a one amp decoder is okay for most O gauge locomotives.

 

I thought this might also be of interest to others.

 

Phil

Hi Phil,

Thanks for this. I'm a bit thick, but how do I measure the motor current? I've read somewhere that measuring the stall current involves stopping the loco dead in its tracks. I f this is the case, how do I go about that - i.e. step by step?

I'm sure this will indeed be useful to others to know.

Thanks,

Richard

[O-Gauge-Phil]

No problem, move the black lead to the terminal marked "10A MAX". 

Then 1) connect one side of the motor to one terminal on your controller, then 2) connect the red cable to the controller's other terminal and 3) the black lead to the other side of the motor. Whilst holding the motor so it doesn't rotate, set the controller to MAX .  The motor will now produce quite a lot of force so don't let it pinch your fingers in the gears.  You should now be able to read the current with a stalled armiture.  As soon as you have got a reading - no more than a second or two - disconnect the wires and let go of the motor. This will then be your stalled motor current.   Personally I would not use this method because it is complicated and could potentially burn your motor out. My calculated method described previously is far easier, less risky and will give the same result

 

As a caveat, decoders have a constant current and a short term rating.  The continuous rating may be say 1.2 amps and the short term 15 or 25 amps for 20 seconds.  The chip has an overload function.  Therefore the short term rating is more than enough and the main criteria is how much current the motor will draw when it is pulling the biggest load.  No eight coach trains on Tewkesbury!  From Colin's  observations the Canon motor would be quite happy with a 1.2 amp unit but the big beast may demand something a bit bigger.  As your loco was battery powered it most likely doesn't take much current and after the removal of the radio, space shouldn't be a concern.  Low current decoders cost  about the same but are a lot smaller.

Give the first method a go and let us know what you get. You can always send the supplier a picture, they should  be able to work it out from past  experience.

 

Hope I've helped and not made it more complicated?

 

Phil

 

ps. Don't forget to move the 10 A leads back or you could burn your meter out if you go to test something with a voltage on it.

 

Edited August 9, 2019 by O-Gauge-Phil
ps

[Tricky]

On 09/08/2019 at 10:57, colin penfold said:

I have two projects on the go and am about to get chips for both so this was timely for me. I have just measured a Canon MT motor from MSC models at 7 ohms and a Mashima 14/20 at 18 ohms. Using Phils sum I make the figures 1.7 and 0.66 amps respectively. I have the same meter as you Tricky. Hope this is useful. Thanks both.

Still not sure I’m on the right track (ha ha) but I get a reading across the leads of 0.7 and across the motor terminals of 5.6, so working the sums through assuming 12V = 2.4 amps. This sounds quite a lot...? 

[colin penfold]

55 minutes ago, Tricky said:

Still not sure I’m on the right track (ha ha) but I get a reading across the leads of 0.7 and across the motor terminals of 5.6, so working the sums through assuming 12V = 2.4 amps. This sounds quite a lot...? 

My results were 7 and 18 across the terminals so your 5.6 sounds feasible. 2.4a is high but not outrageous? Hopefully Phil may advise. I will update with the results of my visit to Digitrains.

[O-Gauge-Phil]

Yes, I would concur, 2.4 amps is high but not outrageous, as a standard size decoder can handle 15 to 20 amps stall current.  Controllers have overloads built in because it wouldn't take that long to burn a motor out when stalled.  Normally when running, due to the back emf this would probably restrict to 200-300 mA.  One of my friends, who is a motor mechanic, used a windscreen washer motor, this ran okay for a minute or so before conking out because it was only designed for short runs.  

 

I have just measured a normal O gauge can motor and that was 77 ohms, all my other motors are coreless, so it does seem very low, something doesn't seem quite right. 

 

The radio controller you are replacing - what make and model was it?  Because if this was okay working from the radio control, a decoder of a similar value shouldn't be a problem.

 

One question I have is - is this a 12v motor or was it running off battery voltage, 4 or 8 volts?

 

I'm off to the train club now, they have a Dapol loco so I'll measure that.   

 

Phil

[Tricky]

1 hour ago, O-Gauge-Phil said:

Yes, I would concur, 2.4 amps is high but not outrageous, as a standard size decoder can handle 15 to 20 amps stall current.  Controllers have overloads built in because it wouldn't take that long to burn a motor out when stalled.  Normally when running, due to the back emf this would probably restrict to 200-300 mA.  One of my friends, who is a motor mechanic, used a windscreen washer motor, this ran okay for a minute or so before conking out because it was only designed for short runs.  

 

I have just measured a normal O gauge can motor and that was 77 ohms, all my other motors are coreless, so it does seem very low, something doesn't seem quite right. 

 

The radio controller you are replacing - what make and model was it?  Because if this was okay working from the radio control, a decoder of a similar value shouldn't be a problem.

 

One question I have is - is this a 12v motor or was it running off battery voltage, 4 or 8 volts?

 

I'm off to the train club now, they have a Dapol loco so I'll measure that.   

 

Phil

It is running off the Gaugemaster controller at 12V now that it’s 2 rail. 

[colin penfold]

My motor which measured 1.7a by Phil's method had a stall current tested by Digitrains at 0.9a. They confirmed that a standard decoder would be fine for that so I'm sure yours will be too. They also showed me the size of a 2amp decoder and it would fill the entire tender on my Ilfracombe Goods!

[Tricky]

49 minutes ago, colin penfold said:

My motor which measured 1.7a by Phil's method had a stall current tested by Digitrains at 0.9a. They confirmed that a standard decoder would be fine for that so I'm sure yours will be too. They also showed me the size of a 2amp decoder and it would fill the entire tender on my Ilfracombe Goods!

Very interesting....I have just phoned Digitrains and placed an order for an NCE Powercab, decoder with sound file and stay alive capacitor. They were telling me about a customer they had just had in, whose symptoms sound remarkably similar to yours...!!!

As you (and they) say, the standard decoder will handle it.

Looking forward to their package turning up and getting going...

[Tricky]

In other news, the first sod has been cut so to speak. A solid start made on the baseboard this evening. At the moment just positioning three main ribs so that the change in levels can be assessed. 

Here I hope you can see the line dropping gently towards the flour mill and the lower bit which will be water.  

This is the current view from beneath. Nothing is glued at the moment, just screwed so if I need to cut bits away for wiring and/or point control I can remove ribs to do so. 

The front fascia will be added once the back is built up, very similar to Bristol. 

[Tricky]

Just trying to get to grips with the DCC gubbins I’ve bought. The stay alive capacitor has two wires, black and blue. Which is positive and which is negative? Any help gratefully received. My scalp is getting sore from all the head scratching...! 

[lezz01]

Hi Tricky. 

The BLUE wire is connected to the Function Common - DC Positive
The BLACK wire is connected to the DC Negative of the decoder.

Regards Lez.Z.

[colin penfold]

The blue wire from the chip goes to the + terminal of the capacitor, grey to the -

 If you are using the zimo supplied capacitor the longer tail is the +  if you got a big black slug capacitor from Jeremy my assumption would be blue to blue and grey to black, but it's probably worth calling them to double check. Edit to say I am assuming you bought Zimo as I know you got it from digitrains. In which case NB they have the two dedicated wires from the chip for the stay alive.

Edited August 17, 2019 by colin penfold
Addendum

[Tricky]

Getting a bit frustrated...! I’ve programmed the chip to the loco number rather than 3, and I can tell something is happening because the loco ‘jitters’ for want of a better term when I’m doing it. Having done that, it doesn’t move! Argh! I had to try several times though as it kept coming up cannot read cv. 

[lezz01]

Sounds like it's not connected properly Tricky. Try programming on the main and make sure the start and max voltage is high enough. and check that you have the wiring correct and that all of the wires are intact.  

Regards Lez.Z. 

[Tricky]

Hi Lez, thanks for the replies (and no doubt your patience!). What sort of values should I start with?

[Tricky]

1 hour ago, colin penfold said:

The blue wire from the chip goes to the + terminal of the capacitor, grey to the -

 If you are using the zimo supplied capacitor the longer tail is the +  if you got a big black slug capacitor from Jeremy my assumption would be blue to blue and grey to black, but it's probably worth calling them to double check. Edit to say I am assuming you bought Zimo as I know you got it from digitrains. In which case NB they have the two dedicated wires from the chip for the stay alive.

I got a large ‘slug’ capacitor as supplied with the decoder but also supplied another tiny one - looks like 4 tiny batteries connected together. The ‘slug’ has rigid wire connectors but the tiny one has the blue and black wires. Must confess I’m still unsure where to stick the wires!!!

These are my options...

Or maybe I send the whole

lot to Digitrains and get them to install it?!

[colin penfold]

Which decoder do you have Tricky?

[lezz01]

Well mate you really need to start by measuring the starting voltage of the motor on DC and then make the starting voltage the same or 0.1 or 0.2 higher than that and set the max voltage to around 11 volts assuming that it's a 12 volt system. I only have experience of 4mm so I don't know much about the power requirements of 7mm models. Well not with DCC anyway. I only know about DC in 7mm from back in the day when I used to operate the old MKMRS exhibition layout and some of the locos had a skate underneath as they were stud contact. Shows how long ago that was. 

I have a rolling road/progaming track that I built from an old layout control panel that has a voltage meter built in to measure the start voltage.   Regards Lez.

[Tricky]

2 hours ago, colin penfold said:

Which decoder do you have Tricky?

MX696

[colin penfold]

Wiring diagram here

https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.zimo.at/web2010/documents/MX-GrosseDecoder_E.pdf&ved=2ahUKEwi66pr53orkAhWjSxUIHRXFDokQFjAAegQICBAC&usg=AOvVaw2eml0USHjYeIN3HAZ0xxjk

 

[Jintyman]

Hi Tricky,

 

It's a Zino MX696KS with a screw terminal adaptor board, absolutely dead easy to wire up.

I will PM you an easy wiring diagram as the markings on both the decoder and the adaptor board are next to useless unless you understand Zimo!!!

 

The other thing is that the orientation of the decoder in the adaptor board is crucial. I've done some that have not worked that have simply been installed the wrong way around,

The easiest way to make sure that the decoder is fitted correctly is that the ebd of the decoder with the fewest pins is fitted to the adaptor board where the speaker wires go.

 

Regards

Jinty

[Tricky]

So here’s an update on the current state of play (pun intended...). Jintyman very kindly has dug me out of my particular hole and wired up the loco for me, including replacing the stay-alive capacitor and speakers and has done a wonderful job- thanks! 

This evening I popped it on the tracks and yes it works! After a fashion. There is obviously a knack to operating and it’s very different to DC - obviously. Is it my imagination or does it respond better when the sound is on?! Without sound I can’t seem to get it to stop in time and keep having to press the Emergency Stop button to prevent it falling off the end of the test track! With sound, it coasts nicely and has a delightful brake-squeal as it comes to rest. There are also numerous buttons on the Powercab relating to increase, decrease, momentum etc but the instruction manual might as well be in Chinese for all the use it is. At the moment I can’t even work out how to decrease the sound volume! There’s another thing - I somehow managed to start off the sound of a scraping coal shovel  and a blower I think but once started I can’t stop them! 

I know, I know, I can hear the sniggering from the back row as a novice tries to grapple with technology that is now old hat to most of you but to me it is totally baffling. Is there an Idiot’s Guide somewhere for this combo of decoder and control system...?