Tortoise 16v AC circuit problems

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Tony Wilkins
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Re: Tortoise 16v AC circuit problems

Postby Tony Wilkins » Wed Mar 15, 2023 11:09 am

Martin Wynne wrote:
Julian Roberts wrote:If this works better I wonder why it's not on the Tortoise instructions?

Hi Julian,

I'm struggling to see how that circuit can work. Current doesn't usually go round in circles. Tony?

But worth a try if you have some spare diodes. The current ratings don't matter for a trial if you have 4 diodes to hand.

cheers,

Martin.

Yes. Sorry chaps. Ignore that. That circuit won't work (brain fart). You need a center tapped transformer to do that. I have deleted the earlier post to avoid confusion.
To be honest I thought there was something not quite right about it at the time but couldn't see what. When I redrew the circuit in a different way the error became obvious.
Regards
Tony.
Last edited by Tony Wilkins on Wed Mar 15, 2023 4:11 pm, edited 1 time in total.
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Alan Turner
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Re: Tortoise 16v AC circuit problems

Postby Alan Turner » Wed Mar 15, 2023 2:25 pm

Martin Wynne wrote:
Alan Turner wrote:If you want to use DC but still use SPDT switches (which the use of microswitches requires) you could use this control board

Hi Alan,

That looks expensive if you need one of those for every motor?


What £1.25 is expensive!

regards

Alan

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Julian Roberts
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Re: Tortoise 16v AC circuit problems

Postby Julian Roberts » Wed Mar 15, 2023 2:43 pm

Hi Alan - you didn't put in a link for the control board in your post yesterday - if it's £1.25 that looks a no-brainer - I've just googled Tortoise control board but I'm not seeing what's in your photo.

I was going to say that having established there's nothing wrong I'm relieved to be able to put this behind me get on with the next stage; though I wonder Keith if you'd be up for making a video of your test rig working to show your guessed 20% change of motor speed?

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Martin Wynne
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Re: Tortoise 16v AC circuit problems

Postby Martin Wynne » Wed Mar 15, 2023 3:08 pm

Alan Turner wrote:What £1.25 is expensive!

Hi Alan,

You didn't previously quote a price but even so, 2 of these for £12.80 (less on ebay/Amazon if you don't want RS brand):

https://uk.rs-online.com/web/p/ac-dc-adapters/1753294

So that's cheaper than £1.25 each, for more than 10 motors.

And those control units still need a power supply.

cheers,

Martin.
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grovenor-2685
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Re: Tortoise 16v AC circuit problems

Postby grovenor-2685 » Wed Mar 15, 2023 4:08 pm

Julian Roberts wrote: though I wonder Keith if you'd be up for making a video of your test rig working to show your guessed 20% change of motor speed?

Not for now, I would have to recreate the setup and I'm very busy with Alexandra Palace then MERG committee away days.
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davebradwell
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Re: Tortoise 16v AC circuit problems

Postby davebradwell » Wed Mar 15, 2023 6:22 pm

I think the control board just adds more complexity and is something else to fault-find if there's a problem. You'll need connectors and a decent crimp tool, too, no doubt. Can't see why you would want to add something to every point motor when dual power supplies would be simpler if you have an aversion to 2 diodes.

Add the capacitors to your simple diode circuit, Julian. That might help even it up if it's a distortion of the waveform causing the issue. I just can't see the supply volts sagging 20% even though you can't measure them. Be sure you get them the right way round or they can go bang.

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Julian Roberts
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Re: Tortoise 16v AC circuit problems

Postby Julian Roberts » Wed Mar 15, 2023 9:40 pm

davebradwell wrote:
Add the capacitors to your simple diode circuit, Julian. Be sure you get them the right way round or they can go bang.

DaveB


They just went bang :D :o

Could anyone confirm this diagram which I followed?
20230303_205653.jpg
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Tony Wilkins
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Re: Tortoise 16v AC circuit problems

Postby Tony Wilkins » Thu Mar 16, 2023 9:34 am

Hi Julian.
Yes, at least that diagram IS correct.
What voltage and type of capacitor did you use?
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Tony.
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davebradwell
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Re: Tortoise 16v AC circuit problems

Postby davebradwell » Thu Mar 16, 2023 9:38 am

It's easy now - all you have to do, Julian, is put the new capacitors in the other way round. Have you sourced some cored solder yet?

DaveB

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Julian Roberts
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Re: Tortoise 16v AC circuit problems

Postby Julian Roberts » Thu Mar 16, 2023 11:55 am

Thanks so much for finding the time for this. Embarrassed to show the depths of my ignorance! - The diagram means the negative (nearest the stripe) goes on orange, positive on yellow; and negative on grey, positive on yellow****? That's what I've done.

20230316_111840.jpg

20230316_112706.jpg



Did they blow because they're not rated adequately? Got two of these bigger ones.

20230316_112747.jpg


More ignorance - cored solder does away with the need for tin of rosin?

*****
Edit I've mis-written this and meant grey to orange, not yellow. Fortunately Keith and Martin understood
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grovenor-2685
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Re: Tortoise 16v AC circuit problems

Postby grovenor-2685 » Thu Mar 16, 2023 12:02 pm

If they were wired as shown in your photo then they blew because they were the wrong way round. (Or actually in terms of your diagram the diodes are wrong way round, ie you have the grey wire positive and the yellow wire negative).
Diode Scan.jpg


And I agree witrh Martin that the 25V rating is low, but that is not why they went bang in a hurry, it would have taken longer!
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Martin Wynne
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Re: Tortoise 16v AC circuit problems

Postby Martin Wynne » Thu Mar 16, 2023 12:10 pm

Hi Julian,

Those capacitors are rated 25v max. You have already showed us a meter reading of 30v rms, and the wave peak for that could well be approaching 50v.

I suggest you need 100v rated capacitors. Also, I doubt 220uF is big enough to make much difference for multiple motors, maybe 1000uF would be enough:

https://uk.rs-online.com/web/p/aluminiu ... rs/7111769

(packs of 2)

p.s. why not just buy a couple of 12v power adaptors, and be done with it? No messing with diodes, capacitors, control boards -- and you get your 16vac power unit back for something else.

cheers,

Martin.
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Julian Roberts
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Re: Tortoise 16v AC circuit problems

Postby Julian Roberts » Thu Mar 16, 2023 12:32 pm

Argghh sorry I'd forgotten I'd wired it all up for Alan's experiment and not changed it back again (- it was still working). Thank you very much.

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Noel
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Re: Tortoise 16v AC circuit problems

Postby Noel » Thu Mar 16, 2023 2:54 pm

I'm not the best qualified to answer this, but, as no-one else has:
Julian Roberts wrote:More ignorance - cored solder does away with the need for tin of rosin?

Yes, for anything we are likely to want to do. Cored solder is standard for electrical or electronics connections, and will not normally need flux or subsequent cleaning. The technique for use is rather different though, in that the iron is applied first to heat the joint and the end of the solder wire is then applied to the joint to be made [not the iron]. Care is needed to use the iron for the minimum necessary time, and apply the minimum amount of solder to do the job, particularly if electronic components are involved, as they may be sensitive to heat. Practice on less sensitive items may be helpful. There are a number of more detailed explanations on the internet [search under "electrical soldering"], and the usual warnings apply. It's a good idea to test joints afterwards to check for mechanical integrity and electrical continuity.
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Noel

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Simon_S
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Re: Tortoise 16v AC circuit problems

Postby Simon_S » Thu Mar 16, 2023 3:56 pm

I've been playing with this circuit in a simulator http://www.falstad.com/circuit/ and noticed that if all the switches are in the same direction then the current to all the motors flows through one diode in the same AC half-cycle; if some switches are one way and some the other, then current flows in both diodes the and both halves of the AC cycle and the peak current is reduced. Overloading of the supply in the peak cycle could explain the varying speed behaviour.

davebradwell
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Re: Tortoise 16v AC circuit problems

Postby davebradwell » Thu Mar 16, 2023 4:41 pm

I don't think we're overloading anything here, Simon, as the 4 Tortoises will draw 68 mA according to the resistance measurement earlier. Have we had a rating for the transformer? It will be at least an amp. In any case, the volts are dropping when just one of the motors is reversed and stalls.

You'll still need rosin for soldering droppers to rail, Julian. No acid flux allowed here either, or on any electrical connection.

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Noel
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Re: Tortoise 16v AC circuit problems

Postby Noel » Thu Mar 16, 2023 5:51 pm

davebradwell wrote:You'll still need rosin for soldering droppers to rail,

I've never found it necessary, so long as the rail is properly cleaned beforehand. I've never used steel rail, though, only NS, which may make a difference?
Regards
Noel

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Re: Tortoise 16v AC circuit problems

Postby davebradwell » Thu Mar 16, 2023 6:45 pm

I suggest use of a separate flux for these heavier jobs as it makes it easier to control the amount of solder that ends up on the joint. With cored solder you don't get the flux until the solder melts and the whole thing can run away - usually a good thing with an electrical connection but we usually try and make it neat. We're not talking about huge amounts of cash here nor does it seem to go off so I think it's worth having some rosin about.

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Julian Roberts
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Re: Tortoise 16v AC circuit problems

Postby Julian Roberts » Fri Mar 17, 2023 8:30 am

davebradwell wrote:It's easy now - all you have to do, Julian, is put the new capacitors in the other way round. Have you sourced some cored solder yet?

DaveB


Despite Martin's warning I did try the pair of larger capacitors (the right way round) on the circuit of two motors - the effect was quite dramatic, the motor threw at an alarmingly fast speed - but the good news is that the return throw seemed to be the same speed (I wasn't going to investigate by repeating the process for fear of damaging the motor). Nigel (who is out of the country just now) when sending them to me suggested just one small one might do the trick but wasn't clear which one in the diagram that would be.

He sent this diagram in case it was needed

20230317_084349.jpg


Regarding flux etc, Noel thanks for your answer too, here are the options from one place. I've found that solder tags, microswitch terminals, etc, take the solder very easily, acting as though they are already tinned - is that likely? I assume that a tin of "Fluxite" isn't what I should be after.
Flux https://www.esr.co.uk/shop/contents/en- ... _Flux.html

Regarding electrical solder I have got one of those packets of Carrs that contain sufficient for someone of a more anorexic approach than mine. None of these say "electrical" -
https://www.esr.co.uk/shop/contents/en- ... older.html

Oh - and Simon, thanks, a new member of our club has an oscilloscope and is interested to investigate what's going on too.
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jim s-w
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Re: Tortoise 16v AC circuit problems

Postby jim s-w » Fri Mar 17, 2023 8:39 am

Just throwing this in there. While a tortoise is a stall motor you don't need to power it all the time. On New Street, Brettell Road and the universal fiddleyard we've used lenz ls150 decoders ( which have an ac output) set to a 3 second throw without any problems at all.

It significantly reduces the power requirement if you have a lot of point work.

Might not be relevant to this discussion mind you
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Martin Wynne
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Re: Tortoise 16v AC circuit problems

Postby Martin Wynne » Fri Mar 17, 2023 8:58 am

Julian Roberts wrote:Despite Martin's warning I did try the pair of larger capacitors (the right way round) on the circuit of two motors - the effect was quite dramatic

Hi Julian,

With all the motors set the same way, measure the voltage across each capacitor. The one not supplying any motors will be higher than the one which is. But how high? If it's less than 25 volts, the capacitors will probably continue working ok. If it's more than 25 volts they might not.

Use the 50v DC setting on the meter -- red probe to + side of capacitor.

You could bring the no-load voltage down below 25V by adding a dummy load as a resistor in parallel with each capacitor. Say about 4.7K which will draw about 5mA and dissipate about 1/8W continuously, so needs to be safely rated at say 1/2W max:

https://uk.rs-online.com/web/p/through- ... rs/7078280

cheers,

Martin.
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Martin Wynne
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Re: Tortoise 16v AC circuit problems

Postby Martin Wynne » Fri Mar 17, 2023 9:26 am

jim s-w wrote:Just throwing this in there. While a tortoise is a stall motor you don't need to power it all the time. On New Street, Brettell Road and the universal fiddleyard we've used lenz ls150 decoders ( which have an ac output) set to a 3 second throw without any problems at all.

It significantly reduces the power requirement if you have a lot of point work.

Might not be relevant to this discussion mind you

Hi Jim,

If you do that, the internal polarity switches are not reliable because without the constant drive force the internal operating arm relaxes back from the stop position, lifting the contacts off the copper track.

Several years ago when I suggested on here that this was a problem with the Tortoise motors which demonstrated the generally crappy nature of the internal switches, I got a roasting for rubbishing a product while not using it in compliance with the manufacturer's instructions.

However, since they are so crappy that I never would use those internal switches anyway, it's ok to kill the current after a few seconds. For reliable polarity switching, use an additional pole on the control panel switch, or for SPDT switches slave a relay and diode across the connection from it.

There is a long topic on here about the poor internal switches on the Tortoise motors, and Andrew Jukes even went as far as getting replacement internal circuit boards made for them.

https://www.rmweb.co.uk/topic/168051-andrew-jukes/

Martin.
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jim s-w
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Re: Tortoise 16v AC circuit problems

Postby jim s-w » Fri Mar 17, 2023 9:34 am

I can honestly say we've never had a problem with that. I dunno how many tortoises were on the UFY (70ish rings a bell) and never had a single failure on either it or my 2 layouts.
Jim Smith-Wright

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davebradwell
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Re: Tortoise 16v AC circuit problems

Postby davebradwell » Fri Mar 17, 2023 10:55 am

It's certainly true that there was a problem with Tortoise switches and nearly all of mine failed quite quickly but these were bought over 20 years ago. I've not seen any problems on significant quantities bought more recently.

Cure is to strip down and drill and tap arm to take a 10BA screw to retain contact plate. Others have used 14BA but you might as well do the job properly and the coarser thread is better in the soft plastic.

DaveB

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Re: Tortoise 16v AC circuit problems

Postby grovenor-2685 » Fri Mar 17, 2023 1:38 pm

Julian Roberts wrote:Despite Martin's warning I did try the pair of larger capacitors (the right way round) on the circuit of two motors - the effect was quite dramatic, the motor threw at an alarmingly fast speed - but the good news is that the return throw seemed to be the same speed (I wasn't going to investigate by repeating the process for fear of damaging the motor). Nigel (who is out of the country just now) when sending them to me suggested just one small one might do the trick but wasn't clear which one in the diagram that would be.
If you use capacitors then they will charge up to the peak voltage, likely around 20V, the size won't make much difference (unless really very small). Tortoises are usually to fast at 12V, best at about 9V which is why the half wave circuit is quite good for them. If you use capacitors it has to be two, just using one will give the motors a smooth 20V in one direction and leave them with the half wave 10V in the other. I doubt he meant that.
He sent this diagram in case it was needed

You can add more diodes like that to reduce the voltage, each diode in the chain dropping about 0.7V, so to drop from 20V to 10V you would need a chain of 14 diodes! IMHO accept the speed variations or can the half wave system and get two small PSUs, ideally 9V ones as as has been suggested.
Regarding flux etc, Noel thanks for your answer too, here are the options from one place. I've found that solder tags, microswitch terminals, etc, take the solder very easily, acting as though they are already tinned - is that likely? I assume that a tin of "Fluxite" isn't what I should be after.
Definitely not fluxite. Usually component leads, solder tags etc. are pre tinned, microswitches not always as some are intended for push on connectors. But clean copper will solder well with cored solder, no need of extra flux.
Regarding electrical solder I have got one of those packets of Carrs that contain sufficient for someone of a more anorexic approach than mine. None of these say "electrical"
In an earlier post you did say you had used electrical solder, was that the Carrs? I didn't think he did any cored solder.
For any electrical wiring I would recommend old fashioned lead 60%/tin 40% solder with rosin flux core. eg. https://cpc.farnell.com/duratool/d01681/solder-wire-sn60-pb40-0-7mm-100g/dp/SD01535?st=60/40%20100gh
Regards
Keith
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