Converting my 7740 from 12v to 9v

[Alexland]

Hi - first post so please be gentle!

I have seen a few discussions here about converting 12v trains to run on 9v motors with metal rails but not the steps required to get it working.

I have figured out my 7740 needs a new 6x28 base plate as the 9v power connector jams on the underside of the correct 4093b so have found a spare blue 92339 which works until I can buy a black 4093a or 92339. Does it matter which I buy as the 4093a looks cheaper? Also I have fed the ends of the 12v light wire into a 9v connector and it seems to work well powering the lights on both ends but is there any electrical reason that I shouldn't be doing this? While its a lower voltage is there any risk the current, etc could damage the lights long term?

Thanks

Alex

[Alexland]

Also does anyone know the spec of the 12v wire to buy more new? It's impressive how well it has lasted over 40 years compared the the 9v wire which tends to go flaky.

[zephyr1934]

7 hours ago, Alexland said:

I have figured out my 7740 needs a new 6x28 base plate as the 9v power connector jams on the underside of the correct 4093b so have found a spare blue 92339 which works until I can buy a black 4093a or 92339. Does it matter which I buy as the 4093a looks cheaper?

From the outside they all look the same, so go with the cheaper as long as the inside meets your needs.

[Andy Glascott]

6 hours ago, Alexland said:

Also does anyone know the spec of the 12v wire to buy more new? It's impressive how well it has lasted over 40 years compared the the 9v wire which tends to go flaky.

I don't, but I use speaker wire on my 12v layout and it works fine. I've used several different brands/types over the years with no problems. 

[Alexland]

Thanks guys so I'll go with the cheapest nice condition black base and just get find some good looking cable that looks right.

Nobody has told me that I am doing anything electrically wrong with the lights so I will just leave it alone and hope they don't go pop.

I have my 4.5v 7720 running on 9v too although it looks a bit sad without it's battery box so I am building up some old wagons including the Shell 7813 to keep it busy.

Just listed my old 12v track including electrically operated points, crossover, isolating rail, etc in a few ebay listings if anyone in the UK is interested.

Alex

[Alexland]

Has anyone tried similar powering a more valuable 12v signal light brick from from a 9v controller?

Ideally I would like to put an inline non-lego switch on the end of the cable (not sure the name of the type of switch required?) to flip beteen red and green.

I would be gutted if 9v makes it go pop as it's a really nice condition part.

[Andy Glascott]

You can use these on 9v track to stop/start trains. I’ll post the how later, I have 2 on the 9v part of my layout. 

[Andy Glascott]

I posted a thread 6 years ago about how to use 12v signals on 9v track, here's the link:

 I'm working on the assumption you have both a 12v power pack and the red/green switch for those signals, if not, there are probably other ways to do it. There's no fear of the two power supplies coming into contact as the circuit on the green button is isolated from the one on the red button. If you have questions, feel free to ask, but ask here rather than bump the original thread. 

[LEGO Train 12 Volts]

The conversion from 12 volts to 9 volts has always fascinated me

On 10/21/2020 at 9:33 AM, Alexland said:

While its a lower voltage is there any risk the current, etc could damage the lights long term?

I think not

[Alexland]

Thanks but not looking to keep the 12v controller or implement automatic stop/start - my ambitions are just to have vintage trains from my childhood running on 9v with a good set of accessories.

I found the courage to connect the signal light and it works fine even when the 9v controller is set to max.

So I just need to find a nice inline switch to put on a new cable to switch the wires around to switch the colour.

It would help if I knew what such a switch was called!

[Toastie]

On 10/21/2020 at 9:33 AM, Alexland said:

While its a lower voltage is there any risk the current, etc could damage the lights long term?

 

2 hours ago, LEGO Train 12 Volts said:

I think not

100% right: U = R x I. R = resistance of the 12V "bulbs". When U goes down, I goes down. Linearely. Which increases the lifetime of the 12 bulbs as they are under less "stress".

Stress? Let's make stress = wattage P. I know: Sort of. So: P = I^2 x R. Which means: Your 12V bulbs life is not linearly scaling with the voltage you apply, but quadratically. The less the better.

I guess.

Thorsten. 

[Alexland]

Thanks that's all very reassuring on the lights!

After some research I believe a Double Pole Double Polarity (DPDT) switch would reverse the polarity of the 9v DC on the wire to the 12v signal light brick so that it can be remotely switched between green and red.

After some more digging do you think Lego 9v part 6551c01 Polarity Switch would do the job?

Thanks, Alex

Edited October 22, 2020 by Alexland

[LEGO Train 12 Volts]

15 hours ago, Toastie said:

Your 12V bulbs life is not linearly scaling with the voltage you apply, but quadratically. The less the better.

Quadratically  ...wow, I never stop learning! 

[Toastie]

1 hour ago, LEGO Train 12 Volts said:

I never stop learning! 

Ha! You knew it anyway, Emanuele ! And: It is a very rough estimate from even rougher presumptions plus a shaky "P is proportional to lifetime" assumption ...

Spoiler

But I for sure know that for filaments we use in mass spectrometry. Such a filament is nothing more than the thing in an old-school light bulb. The ones that make 5% light and 95% heat from electricity ...  when we run our filaments at about one half of their nominal current (or electron emission rate), they live >>way<< longer than twice the time they would live otherwise. Which gave me some reassurance in that very rough estimation. However, running things a half their performance is sort of uncool. So we learned to make our own ion source filaments from plain vanilla tungsten wire, which you get 10 or 100 m wise for very little money. Each filament is 2 cm >max.< in length. So now we run the instruments at 200% and burn them out about monthly. Replacement cost when you buy such a thing from a manufacturer: $200. Our replacement cost: About 10c.

Best wishes,
Thorsten

 

 

[Alexland]

Hi,

Unsure if it's a coincidence but th 9v motor on this 7740 has now started to play up.

I was running it with 1 carriage and 4 wagons and it started running very slowly and then eventually stopped with just the lights working.

It's now intermittently going slugish (even with just the loco top on and lights disconnected) and sometimes stops but occasionally going fast before slowing and stopping again.

It's not the track as I don't have this problem running my other 9v motors.

Has the motor failed, is there any way to fix it and could it have been caused by the 12v lights and/or cable conversion?

Thank you in advance,

Alex

[Toastie]

1 hour ago, Alexland said:

Has the motor failed, is there any way to fix it and could it have been caused by the 12v lights and/or cable conversion?

Well. I tried to read through this thread ... but can you pleas recap, what the actual configuration is?

(Guessing: 9V track. 9V motor. Conversion cables that let you hook up the 12V lights to the 9V motor. Is that right? Did you manipulate the 9V motor? Or just the "outside" wiring? You said other 9V motors don't show this behavior. When the motor showing this behavior is unaltered, it is this motor, right?)

Yes there is a way to fix a 9V motor. It is invasive though. But chances are good.

Just need a bit more input here.

Best
Thorsten

[Alexland]

Yes 9v track/motor + a 9v connector on the end of one of the 12v lighting wires (and 12v lighting bricks) coming out the bottom of the 7740 (see top photo).

The motor is original unmodified recently acquired 2nd hand and never really tested under the load of pulling carriages/wagons before.

Seems to run well in a circle under no load but now even with just the 7740 loco top on it it can become sluggish stop for a bit then start working again. It wasn't like that in the previous few weeks since buying it. So either testing it under load of pulling wagons and/or the lighting configuration and/or bad luck has caused it to develop a problem.

I've been watching a few videos on Youtube of people swapping out the motor from a more modern one but there's a bit of me that's tempted to sell it as part-working on ebay (maybe it wasn't working well for the previous owner...) and just buy a brand new unused one and pay the difference however I'd be annoyed if my bespoke lighting setup caused it to burn out again. Maybe I would be better replacing the 2 wires and 2 light bricks with proper 9v parts even if they won't line up tightly against the 12v light prism bricks?

Thanks Alex

[Toastie]

But then you can swap this particular motor causing trouble with another one, you have at hand, right?

Same behavior?

Best
Thorsten

[Andy Glascott]

I don’t know much about the motors, but for lights you could use the PF lights in the 1x6 bricks that hold the prisms. You’d need a 9v to PF converter cable as well but they do fit. 

[Alexland]

Thorsten - another motor is fine to pull the wagons and carriages with the 7740 on top but I haven't wanted to connect up my 9v lights connector / 12v light bricks for fear of damaging another motor in the same way. I really wish I had put the motor under the load of wagons before connecting up these light so that I could determine the cause of the problem. The motor is now just problematic under small loads with no lights connected.

Andy - your prompt caused me to find the below excellent article however this experieince of possibly damaging a motor (if only I knew if it was already damaged...) has put me off using converter cables and I am tempted to just go to standard 9v cables and light bricks. I guess it would take 3x cables as there isn't enough height to stack the 9v connectors at one end so the stack would need to be in the middle. Might be possible with 2 cables and a long 9v plate..

https://questforbricks.wordpress.com/2013/08/31/12v-lights-vs-pf-lights-vs-tin-foil/

Edited October 28, 2020 by Alexland

[Toastie]

38 minutes ago, Alexland said:

The motor is now just problematic under small loads with no lights connected.

"Problematic" or "not problematic"? When the first, I am puzzled.

Best
Thorsten

 

[Alexland]

The 9v motor is problematic now. It was showing no problems before connecting up both the 12v lights and putting it under the load of wagons but is now running fast then slowing and stopping etc. That even happens now under light loads with no lights connected.

Could it have been the combination of 12v lights and some wagons that caused it to develop a problem? Or maybe it was just weak to start with and has got worse?

Thanks Alex.

Edited October 28, 2020 by Alexland

[Andy Glascott]

I suspect it was just coming towards the end of it’s natural life when you got it.... I’ve had a 9v motor just stop running on me in the middle of a show and despite reading several threads on here about repairs etc I haven’t been successful, which is probably as much down to my electronics limitations as anything else. 
 

I haven’t tried it yet, but there is apparently a possibility of taking the motor out of the 9v unit and using it as a power pick up for a PF or PU train motor. One of my locos needs 2 motors so I have a working 9v motor connected to a PF train motor and it runs fine. I think I had to bodge the connections but it works. 

[Alexland]

Yes there seems to be a good market on ebay for broken or part working motors around 15 GBP. Having watched various videos for things that can be done with broken 9v motors I don't fancy my chances either. I will probably just convert the 7740 to normal 9v cables and lights as although it won't be as good I won't be worried about killing another motor. I'll will still power that 12v signal brick from a 9v connector.

[Toastie]

3 hours ago, Alexland said:

Could it have been the combination of 12v lights and some wagons that caused it to develop a problem? Or maybe it was just weak to start with and has got worse?

Now I believe this has nothing to do with the 12V light at all.

Am I correct that your 9 - 12 V conversion cable you made pops (on the motor side) onto the 9V contacts that are also used for e.g. operating 9V lights?

When that is the case, and I am almost certain it is, then any lamp or other current drawing elements attached here can't damage to the motor. The power is picked up from the rails via the wheel flanges is funneled directly to the 9V motor outlet via "spring loaded" pieces of metal. There are many pictures on the net; here is one from the HispaBrick magazine:

Two things:

1) The motor is running in parallel to your lights (any 9V, 12V, LEDs) so nothing can damage it. When the lights are steadily emitting light but the motor is stuttering or simply slowing down under some load (or now no load at all - please check with the light again - you can't damage the motor that way!) then something is wrong is either in the path from the spring-loaded pick-ups to the motor (losing mechanical contact etc. - there is no welding/soldering, the piece are just in contact with each other)

2) OR - and I suspect this is the case here: The thermal over-protection thingy kicks in way too early (= is faulty). This is the piece sitting "on" the motor contacts, in the picture above seen close to the left brass gear of the motor. On Philo's motor comparison page: https://www.philohome.com/motors/motorcomp.htm, which is an excellent(!!!) resource you'll find this:

"(*) The train motors also contain thermistor limitations." That is the thing I am referring to (thermistor = thermally sensitive resistor). Philo's text goes on with:

"For the PF train motor, this protection trips too fast and prevents direct measure of the stalled current." OK, you don't have a PF motor, but this tells you what the thermistors do: When the current (caused by increasing load) is too high, the thermistor becomes too hot and then trips, i.e. "disconnects" power from the motor. This is in analogy to what you are observing. The 9V motor outlet is not part of this branch though. When the motor stutters and the light remains on (steadily) then as said, the thermistor may kick in.

Next: Thermistors do naturally age. As all 9V train motors are of historical value, so are the thermistors inside. The longer the motor was operated in his history, the less reliable the thermistor works. Aging means that the chemical substance responding to heat by increasing its electrical resistance has degraded over time. This degradation process is driven mostly by "time x current" going through it.

Solution: Out with it. None of my 9V train motors have them anymore. You can just pop them off as they are pressed-in as well. OK, you are losing the thermal protection, but then: With, it doesn't work. Your choice of course Without the motors do work like a charm. You can also try and replace the thermistor, but I would not know which one to choose.

And finally: The aging process is not linear with time; in the end it goes rapidly bad. Particularly when the current going through this device is rather high = high load. So I suspect that this behavior was caused by high load and not the 12V lights.

Opening up the motor is pretty much straight forward.

And as always: Not 100% sure; all is from literature and own experience. But when you want to go that route: Just ask, everyone here will be glad to help.

Best
Thorsten 

P.S.: Of course also the motor may have gone bad but first things first. And also this would nothing have to do with the lights but the load. There are (cheap!) replacement motors available as well.

Edited October 28, 2020 by Toastie