Tortoise 16v AC circuit problems

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grovenor-2685
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Re: Tortoise 16v AC circuit problems

Postby grovenor-2685 » Sun Mar 12, 2023 5:08 pm

I have found 3 tortoises in the loft, brought them down, wired them up to an AC source via two diodes and 3 switches as you are doing. Everything behaves as expected. There is no visible difference in the speed of operation whether 1, 2 or all 3 are connected, whether moving normal to reverse or vice versa or whether operated singly or in pairs or all 3 together. So IMHO there has to be a connection problem somewhere.
The only time a voltage change is visible on the meter is when measuring the voltage on the motor and running it, the meter reads a couple of volts lower when running than when stalled.
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Keith
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Re: Tortoise 16v AC circuit problems

Postby Tony Wilkins » Sun Mar 12, 2023 5:22 pm

Hi Julian.
Thanks.
Allowing for the fact that your meter is not quite zeroed correctly in the first picture, those readings tally pretty well with mine. How consistent the motors are though is another question.
What that tells me is that on a 12v DC supply the stall current will be about 17milliAmps, on 7v it will be 10milliAmps. So the demands on the power supply are negligible. When the motor is running the current demand will be less than the stall current, so a 1 Amp supply should be capable of running at least 50 point motors even with them all stalled on the same half of the AC cycle although this would be an unbalanced load.
With such a low drive voltage, it is possible that the resistance to movement in the point mechanism may have an effect on the drive speed. It is certainly an effect I have notice with some of the points on my layout although I am using Cobalt point motors on 12volts.

For your information, the top scale is for resistance and is a reverse Logarithmic scale. What that means in practice is that the zero is to the right and as the resistance increases the scale becomes progressively more compressed toward the left. It takes a bit of getting used to as the Voltage and current scales are linear and start from the left.
Hope I haven't confused you too much. The best way to learn is to measure some known resistors and see how they read.
Whatever you do, don't attempt to measure a voltage with the meter on ohms as it won't do the meter any good at all.
Regards
Tony.
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Re: Tortoise 16v AC circuit problems

Postby davebradwell » Sun Mar 12, 2023 6:08 pm

While you have your meter out, Julian, you might as well check the diodes. Pull the loose ends of these out of the block and use the new found resistance ranges to confirm that in one direction it's almost a dead short (needle to right) and the other way (reverse meter probes) there's a high resistance - not much needle movement. All indications are they will be fine.

I wondered about a mechanical problem, Tony, but he's eliminated that by using loose Tortoises. Keith has confirmed that the theory is sound.

If the transformer has decent overload protection, you might replace diodes with wire links and one Tortoise with a link, disconnect the other, and just see if the transformer and wiring can pass any current. Monitor ac volts on the transformer while you make and break the circuit at the Tortoise stand-in and switch off quickly if the protection doesn't trip. You'll need to see what form this takes first. What do others think - it's the sort of desperate test I dream up when nothing is making any sense. I'm doubting if the transformer will give much more than 2-3 amps when shorted but someone else might know better as a result of experience, perhaps.

I've been suspicious of your soldered joints ever since you mentioned 140 solder. Don't you have any proper electrical cored solder.

DaveB

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Martin Wynne
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Re: Tortoise 16v AC circuit problems

Postby Martin Wynne » Sun Mar 12, 2023 6:16 pm

davebradwell wrote:I've been suspicious of your soldered joints ever since you mentioned 140 solder.

Wow -- I didn't notice that. I'm sure that will be the problem.

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Re: Tortoise 16v AC circuit problems

Postby grovenor-2685 » Sun Mar 12, 2023 6:41 pm

davebradwell wrote:If the transformer has decent overload protection, you might replace diodes with wire links and one Tortoise with a link, disconnect the other, and just see if the transformer and wiring can pass any current. Monitor ac volts on the transformer while you make and break the circuit at the Tortoise stand-in and switch off quickly if the protection doesn't trip. You'll need to see what form this takes first. What do others think - it's the sort of desperate test I dream up when nothing is making any sense. I'm doubting if the transformer will give much more than 2-3 amps when shorted but someone else might know better as a result of experience, perhaps.
DaveB

I can see no point in short circuiting the transformer as a test, it will tell you nothing and may well cause damage. We know that the transformer can supply current as the motors are running. The only apparent problem is the mysterious variation in speed which does not happen on my test rig.

The only suggestion I have is to recheck all wiring connections, especially soldered joints using dodgy solder. Better, I think to fit the diodes to a terminal block rather than soldering together.

IMHO its not appropriate to describe this supply arrangement as a 'kludge', using half wave supplies in this way is a standard technique and recommended by the motor supplier.
Regards
Keith
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Martin Wynne
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Re: Tortoise 16v AC circuit problems

Postby Martin Wynne » Sun Mar 12, 2023 6:48 pm

grovenor-2685 wrote:IMHO its not appropriate to describe this supply arrangement as a 'kludge'

Does that mean I can't present "Match of the Day"? :)

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Re: Tortoise 16v AC circuit problems

Postby Jol Wilkinson » Sun Mar 12, 2023 7:54 pm

Julian,

I suggest it would be better to quote the meter readings as figures, rather than relying on people reading your meter in a photo. I can't make out what is what on those scales. Or else buy a meter with a digital readout which is easier to read.

Jol

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Re: Tortoise 16v AC circuit problems

Postby Julian Roberts » Sun Mar 12, 2023 9:17 pm

Well, thanks very much chaps. Tony, I've measured the other Tortoise of this pair and the reading is very much the same. I don't think it's the turnout mechanism - here is a video of moving it with my 5th finger. Strong enough spring to hold the blade securely against the stock rail though.



Dave Martin and Keith I've rearranged the diodes so that they are screw in at each end. And checked them with the meter as you suggested Dave.

20230312_210111.jpg


All the terminals are screwed down hard.

I've replaced the twisted orange/grey wires in case the twisting had broken the strands at any point.

Still no change in the working!!
I really appreciate the help here. Jol, thanks, I put the picture as I'm still learning how to read the scales.

I'll reread Alan's suggestion from this morning but -

No more time this evening!
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Re: Tortoise 16v AC circuit problems

Postby Tony Wilkins » Mon Mar 13, 2023 9:46 am

Hi Julian.
I thought it unlikely to be the turnout mechanism as this would only affect individual turnouts, but it can be a factor.
Having more or less eliminated the switch wiring as a source of problems, I have gone back to your original description of the fault.
I woke up in the small hours with this going round in my head.
In summary your symptoms are: whichever lever is pulled first the motor runs at normal speed, any subsequent lever pulled the motor runs slow (in both directions). This certainly suggests voltage drop somewhere in the circuit. The only part of the circuit common to all these situations is the common return wire, so I would check each and every joint in the common return wire between the power supply and the distribution block for a high resistance. I can see no other possible cause and using 145 solder rather then proper electrical solder definitely won't help. If the solder does not wet the metal surface well then a dry joint (equals high resistance) can result.
Regards
Tony.
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Alan Turner
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Re: Tortoise 16v AC circuit problems

Postby Alan Turner » Mon Mar 13, 2023 9:59 am

Julian Roberts wrote:W

20230312_210111.jpg



That picture does not make sense as the diodes have to be connected together at one end.

This how I would have done it:

Tortoise AC Wiring.JPG


The green wires to the Transformer.

Other colours as per your original diagram.

NOTE the orientation of each diode.

regards

Alan
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Last edited by Alan Turner on Mon Mar 13, 2023 10:27 am, edited 3 times in total.

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Re: Tortoise 16v AC circuit problems

Postby davebradwell » Mon Mar 13, 2023 10:09 am

I'm including the wiring to the microswitches as well, Tony, as it's symmetrical and adds 3 joints pre leg. We're looking for a significant resistance to drop a volt or so at 20mA - 100 ohmsish - which should be measurable with the meter. Perhaps just 10s of ohms per joint, though.

Encouraged by others sharing my suspicion of your soldering, will you confess which joints have been done with 140 and what you used as flux, Julian. Test above should indicate if there's anything in this so you might yet be spared.

It comes down to the saying - "when you've eliminated everything else....blah.....no matter how improbable"

DaveB

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Re: Tortoise 16v AC circuit problems

Postby Tony Wilkins » Mon Mar 13, 2023 10:13 am

Alan Turner wrote:
Julian Roberts wrote:W

20230312_210111.jpg



That picture does not make sense as the diodes have to be connected together at one end.

regards

Alan


I think they are, by the black wire.
Regards
Tony.
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Re: Tortoise 16v AC circuit problems

Postby BorderCounties » Mon Mar 13, 2023 10:30 am

Julian

You are probably not going to like what I'm about to say, but read on.

You have gone to the trouble of making a nice, working lever frame and slapped a lot of electrical bits on the back of it. Why did you not use it as intended and make it mechanical with rods and cranks, and using the micro-switches to change the crossing polarity? It would have been so much more tactile - actually moving the levers to change your turnouts instead of an over elaborate electrical switch.

It probably doesn't help at all, but I know what I would do now. Classic example of the KISS principle.

John

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Re: Tortoise 16v AC circuit problems

Postby davebradwell » Mon Mar 13, 2023 11:13 am

It seems these are points worked by ground levers so not even any need for a frame - a knob on the edge of the board would have done. We'd have met the problems when he did the real frame, though.

DaveB

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Re: Tortoise 16v AC circuit problems

Postby Tony Wilkins » Mon Mar 13, 2023 11:25 am

grovenor-2685 wrote:
IMHO its not appropriate to describe this supply arrangement as a 'kludge', using half wave supplies in this way is a standard technique and recommended by the motor supplier.

It is not an arrangement I am particularly enamored with for a power supply, but it does have its uses and I agree in this situation it should work.
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Re: Tortoise 16v AC circuit problems

Postby Julian Roberts » Mon Mar 13, 2023 11:41 am

Thanks everyone. John - I set out with that intention but realised for my particular layout design the mechanical option was going to be far harder than this, which I still think!

Tony, Dave, Alan - as I've tried all sorts of set ups with exactly the same problem could we perhaps think about what else might be going on rather than a duff joint? - although I know you said there seems to be nothing else to explain it. I use 12% phosphoric acid for any solder joint with 145 solder. I've used electrical solder for fixing the wires to the motors where the instructions warn against using any flux. Any cable ends I solder the strands having twisted them before screwing in to any terminal or soldering to a tag.

I've tried Alan's set up as you posted yesterday morning Alan but nothing changes!!

Yes there's a loop on that photo from last night joining the diodes.

Tony - (of course I'm sorry this is disturbing your sleep!) could you check on my OP videos about what's happening? Any one motor runs just fine. As soon as two are in the circuit, yes, the first runs fine one way, then slow the other, BUT run it one way: normal, run the other, that is slow; NOW run either back again and it runs normal, then the other one runs slow back again. Add more turnouts to the mix, once all have been set, the first to be thrown back again runs properly, the others all slowly. If I throw all the points at the same time they all behave as the single one did when it was in its own circuit - i'.e. they all move at the proper speed together, and back again.

I'm wondering if simply these motors take more current on the stall than they're meant to? I surely need to measure that, but not absolutely sure how to. So -

After the Alan set up didn't yield anything I've started what must be the only thing to do, Martin's close examination of everything. I'm not sure if this is the proper procedure he meant - and sticking to these two motors for now which aren't linked to any crossing Vs in the case of the catch point, and no wiring at all on the unused one except the two connections for the motor:

With the meter on 50V AC in all cases (having set the needle to zero on the 10 ohms setting joining the probes to each other as in the instructions - very little adjustment required)

Both motors disconnected from each other, joined to the diode arrangement singly one at a time.

Both motors behave almost exactly the same.

The probes (doesn't matter which way round) on the red and black wires stay constant at around 17v whatever I do.

Remember I'm just pressing the microswitch now, it's not in the lever frame.

Red Probe to grey and Black probe to yellow 50v ac setting

1. at rest
2. While motor moves when Switch pressed
3. With switch pressed motor not moving..
4 while motor moves on releasing switch

1. 16 or 17v

2. 27 or 28v

3. As (1)

4. As (2)


Catch point the same except 30v rather than 27 or 28

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Re: Tortoise 16v AC circuit problems

Postby Tony Wilkins » Mon Mar 13, 2023 11:44 am

BorderCounties wrote:Julian

You are probably not going to like what I'm about to say, but read on.

You have gone to the trouble of making a nice, working lever frame and slapped a lot of electrical bits on the back of it. Why did you not use it as intended and make it mechanical with rods and cranks, and using the micro-switches to change the crossing polarity? It would have been so much more tactile - actually moving the levers to change your turnouts instead of an over elaborate electrical switch.

It probably doesn't help at all, but I know what I would do now. Classic example of the KISS principle.

John


Each to their own.
I have a Society 42 lever frame to build with full interlocking and it will use micro switches to connect electrically with the turnouts and signals, however they will switch relays that will power the turnout point motors and signal servos. This is mainly due to the turnouts being spread over several baseboards and electronics was my stock in trade.
I was though responsible for designing and building the mechanical point operating system used on the storage sidings of Heckmondwike. As the turnouts at each end spanned two baseboards, it was possible to group each pair of lever frames either side of the baseboard joint at either end to effectively make one frame. These were rather novel as the longitudinal rodding twisted to transmit the force to the transverse rods to the point blades. These proved very reliable in service, so I have had some experience with both systems.
Regards
Tony.
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Re: Tortoise 16v AC circuit problems

Postby Tony Wilkins » Mon Mar 13, 2023 12:04 pm

Julian Roberts wrote:
Tony, Dave, Alan - as I've tried all sorts of set ups with exactly the same problem could we perhaps think about what else might be going on rather than a duff joint? - although I know you said there seems to be nothing else to explain it. I use 12% phosphoric acid for any solder joint with 145 solder. I've used electrical solder for fixing the wires to the motors where the instructions warn against using any flux. Any cable ends I solder the strands having twisted them before screwing in to any terminal or soldering to a tag.


This paragraph jumped out at me straight away.
1) Using acidic flux for any electrical work is not a good idea as it is corrosive and any remnant will continue to corrode the joint over time.
Resin flux is the correct flux to use although the iron needs to be hot enough for it to work.
2) Pre-soldering the stranded ends of cable before inserting them into any type of screw terminal is bad practice. For solder tags this is permissible, although I rarely do so. The solder being soft can creep under pressure from the screw resulting in poor contact.
Regards
Tony.
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Re: Tortoise 16v AC circuit problems

Postby Tony Wilkins » Mon Mar 13, 2023 12:23 pm

Julian Roberts wrote:
I'm wondering if simply these motors take more current on the stall than they're meant to? I surely need to measure that, but not absolutely sure how to. So



That's not possible.
The stall current will be a product of the resistance of the motor and the applied voltage (Ohms Law) and will be the maximum the motor can draw.
When running, the motor will draw less current because it is also acting as a generator and produces a voltage opposite polarity to the applied voltage. This is called the back EFM (Electro Motive Force) and is what is measured by feedback controllers to adjust the power pulses to try to make the motor do what is wanted in terms of RPM.

I wouldn't worry about trying to measure current until you are more familiar with test meters. For a start that meter has a maximum current range of 100mAmps or 1 / 10 A and it will be very easy to overload it. I lost count of the number of times I have picked up a meter at work to measure current only to find the internal fuse blown because someone had forgotten it was on amps and tried to measure volts with it. Especially the case with digital meters.
Regards
Tony.
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Martin Wynne
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Re: Tortoise 16v AC circuit problems

Postby Martin Wynne » Mon Mar 13, 2023 12:23 pm

Julian Roberts wrote:Catch point the same except 30v

Hi Julian,

Are you sure? Without any smoothing in this circuit, and the typical meter response, that will be the RMS output from the power supply.

Which means the peak wave voltage and/or inductive spikes from other motors might be reaching around 45 volts or more -- which might be exceeding the reverse breakdown voltage of the diodes, or one of them.

I tend to go for a minimum of 100 volts rating for any diodes or rectifiers in model railway circuits, e.g. 1N5401:

https://www.switchelectronics.co.uk/1n5 ... de-3a-100v

Having eliminated all other possibilities, I would be going for replacing the diodes.

Using acid flux and non-electrical solder is a no-no for electrical work, but on the other hand it does seem to be working for a single motor, so can't be the cause of the problem.

cheers,

Martin.
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davebradwell
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Re: Tortoise 16v AC circuit problems

Postby davebradwell » Mon Mar 13, 2023 12:35 pm

I don't agree with your analysis of the situation, Julian. The problem is in the side with one stalled motor. Once the motor stalls it seems to be pulling the volts down for the rest. Remember that until the first point is changed this side has no load and while the first motor is running has very little load. It's when it stalls that the volts drop for the remainder which consequently run more slowly.

I can't see that your readings on ac tell us anything. What we want are the dc voltages across the motor under the different conditions to support my initial assertion. Before that you might measure the resistance from one diode terminal through the 3 soldered joints and closed microswitch to the Tortoise terminal. It should, of course, match your zero setting exactly.

I suggest you chuck out any component that you've used acid flux on. It's probably run down inside the microswitches and will cause havoc - perhaps it's already doing that. Go out and buy some cored electrical solder and a pot of rosin for connections to rails and the like.

DaveB

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Re: Tortoise 16v AC circuit problems

Postby Tony Wilkins » Mon Mar 13, 2023 12:51 pm

Martin Wynne wrote:
Julian Roberts wrote:Catch point the same except 30v

Hi Julian,

Are you sure? Without any smoothing in this circuit, and the typical meter response, that will be the RMS output from the power supply.

Which means the peak wave voltage and/or inductive spikes from other motors might be reaching around 45 volts or more -- which might be exceeding the reverse breakdown voltage of the diodes, or one of them.

I tend to go for a minimum of 100 volts rating for any diodes or rectifiers in model railway circuits, e.g. 1N5401:

https://www.switchelectronics.co.uk/1n5 ... de-3a-100v

Having eliminated all other possibilities, I would be going for replacing the diodes.

Using acid flux and non-electrical solder is a no-no for electrical work, but on the other hand it does seem to be working for a single motor, so can't be the cause of the problem.

cheers,

Martin.


Hi Martin.
If you look back to Julian's first meter pictures, he was getting similar readings then and I was suspicious of them from a 16V AC output.
The later DC readings made more sense.
I have a cheapy analogue test meter of similar vintage and that can sometimes give odd readings on AC settings.
Remember he is measuring 1/2 wave DC on an AC setting.
Regards
Tony.
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Martin Wynne
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Re: Tortoise 16v AC circuit problems

Postby Martin Wynne » Mon Mar 13, 2023 12:58 pm

davebradwell wrote:Once the motor stalls it seems to be pulling the volts down for the rest.

Hi Dave,

A stalled motor on half-wave is a static inductor. The spike voltage might be all over the place, and the diodes won't like it. If the diodes are breaking down, the motor will see part of the opposite half of the wave and run more slowly. I called this half-wave method a kludge for a reason. :)

Julian, if this is the problem, a quenching resistor wired across the motor terminals might cure it. The resistor will need to be suitably rated for the power dissipation (it will get warm).

If you have some 12v grain-of-wheat bulbs (not LEDs) you could try using those as quenching resistors just to try out this theory.

cheers,

Martin.
Last edited by Martin Wynne on Mon Mar 13, 2023 1:10 pm, edited 1 time in total.
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davebradwell
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Re: Tortoise 16v AC circuit problems

Postby davebradwell » Mon Mar 13, 2023 1:00 pm

Yes, I've ignored all anomalous readings and we have a one-sided load here.

I've changed tack and am suggesting that the resistance out to be measurable. As this requires the power to be turned off it's much clearer.

DaveB

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Re: Tortoise 16v AC circuit problems

Postby Alan Turner » Mon Mar 13, 2023 2:10 pm

Julian Roberts wrote:
I've tried Alan's set up as you posted yesterday morning Alan but nothing changes!!

Yes there's a loop on that photo from last night joining the diodes.



In that case please confirm to me that you have looped the Orange wire to one Tortoise motor connection on every motor?

Please confirm that you have looped the grey wire to every NC tab on the micro switch and the yellow wire to every NO tab on the microswitch (or NO and NC - that doesn't matter).

Finally you have taken the blue wire from the C tab of a micro switch to the remaining Tortoise motor terminal of the motor you are controlling for each Tortoise motor you have?

regards

Alan


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