Transformer comparisons

[ikcdab]

I now need to acquire five 16v ac output tranformers for the new layout.

In the past I have very happily used gaugemaster openframe T1. 

The best price I can find is £24.50 

https://railsofsheffield.com/products/742/gaugemaster-t1-any-scale-open-transformer-output-2-x-16v-ac-1a

I would need three of these (They are twin output),  so  £75 cost.

 

However, I have also see this:

https://www.rapidonline.com/vigortronix-vtx-126-006-215-chassis-transformer-230v-6va-15v-15v-88-3907

 

Ok, only 15v as output, but I guess that will make little difference. At £7.50 each, I save around £50.

 

Are the Gaugemaster transformers that much better to justify the extra cost or would the cheaper ones be as good?

[Nigelcliffe]

Electrical (and electronic) items from model railway suppliers are often more expensive than from electrical component suppliers.

 

Beyond that, make your own engineering judgement on the specification.   Anyone installing bare transformers needs a decent understanding of electrical safety and engineering for the mains-side of things, with appropriate protection for people and equipment.  Multiple transformers make the safety issues higher. 

 

Unless you've a need for AC,  I'd be using DC power bricks.   Cheaper, all in one box, and simpler for electrical safety.   The last ones I bought (long established UK supplier's branded, so some comeback on quality) were under £12 for 12vDC at 5A or under £25 for 15vDC 6A. 

 

 

- Nigel

[Crosland]

45 minutes ago, ikcdab said:

Are the Gaugemaster transformers that much better to justify the extra cost or would the cheaper ones be as good?

 

Aside from the lower voltage the Rapid one is only 6VA so 30V @ 200mA or 15V @ 400mA or 2x15V at 200mA each.

 

Assuming the GM one is 1A on both outputs simultaneously, it is 32VA or 5x "bigger".

 

You need to compare like-for-like  Rapid have 2x15V 25VA and 50VA in the same range.

 

How much current do you need from each winding? 

[ikcdab]

1 hour ago, Crosland said:

 

Aside from the lower voltage the Rapid one is only 6VA so 30V @ 200mA or 15V @ 400mA or 2x15V at 200mA each.

 

Assuming the GM one is 1A on both outputs simultaneously, it is 32VA or 5x "bigger".

 

You need to compare like-for-like  Rapid have 2x15V 25VA and 50VA in the same range.

 

How much current do you need from each winding? 

I hadn't realised I wasn't comparing like for like!

Each winding will run one controller running one loco. So I Guess the 1amp is the max requirement.

Edited June 18, 2020 by ikcdab

[DCB]

2 hours ago, Nigelcliffe said:

Electrical (and electronic) items from model railway suppliers are often more expensive than from electrical component suppliers.

 

Beyond that, make your own engineering judgement on the specification.   Anyone installing bare transformers needs a decent understanding of electrical safety and engineering for the mains-side of things, with appropriate protection for people and equipment.  Multiple transformers make the safety issues higher. 

 

Unless you've a need for AC,  I'd be using DC power bricks.   Cheaper, all in one box, and simpler for electrical safety.   The last ones I bought (long established UK supplier's branded, so some comeback on quality) were under £12 for 12vDC at 5A or under £25 for 15vDC 6A. 

 

 

- Nigel

Agree but for heaven's sake get decent overload protection for your locos if you go for 5 or 6 Amps.  60VA won't do your pickups any good if you short it across an isolator for instance.

[Nigelcliffe]

18 minutes ago, DavidCBroad said:

Agree but for heaven's sake get decent overload protection for your locos if you go for 5 or 6 Amps.  60VA won't do your pickups any good if you short it across an isolator for instance.

 

There is adequate protection downstream, and I know where the current it going.    

 

- Nigel

 

 

[Grovenor]

Assuming these are for your homebrew controllers in the other topic, then I would go for 15V, 50VA units from Rapid, this will allow you around 1.8 Amps per circuit, comfortable for single controllers. Not as big a saving as you hoped but still around half Gaugemasters price.

[ikcdab]

3 hours ago, DavidCBroad said:

Agree but for heaven's sake get decent overload protection for your locos if you go for 5 or 6 Amps.  60VA won't do your pickups any good if you short it across an isolator for instance.

I have built this into the controllers circuit

https://uk.rs-online.com/mobile/p/resettable-wire-ended-fuses/6478673/

It appears to be the same at that in the gaugemaster W controller.

[ikcdab]

So I have now bought two of the rapid 50va 15vac open frame transformers.

I do understand the safety issues and the wiring.

But as for a casing? In the past I have used small plastic storage boxes. I have also used metal boxes. I could easily make a casing out of ply. 

Is there a preferred material? Plastic, metal or wood?

[WIMorrison]

On 18/06/2020 at 16:25, ikcdab said:

I have built this into the controllers circuit

https://uk.rs-online.com/mobile/p/resettable-wire-ended-fuses/6478673/

It appears to be the same at that in the gaugemaster W controller.

 

The spec for those would suggest to me that they are no use for a model railway - 8.2s to trip @ 2.2a is too slow. I fear that by the time these trip you will have melted whatever you are trying to protect

Edited August 8, 2020 by WIMorrison

[ikcdab]

On 08/08/2020 at 14:39, WIMorrison said:

 

The spec for those would suggest to me that they are no use for a model railway - 8.2s to trip @ 2.2a is too slow. I fear that by the time these trip you will have melted whatever you are trying to protect

Yes I spotted that. Yesterday I was wiring up and I created a short circuit. The controller tripped out immediately. However, I cleared the short and very soon it came back to life. So now I wonder if the technical spec for the breaker is wrong and should mean "8.2s to reset".

Thoughts?

Ian

[WIMorrison]

Perhaps they meant 8.2ms or 8.2us?

[Crosland]

2 hours ago, ikcdab said:

Yes I spotted that. Yesterday I was wiring up and I created a short circuit. The controller tripped out immediately. However, I cleared the short and very soon it came back to life. So now I wonder if the technical spec for the breaker is wrong and should mean "8.2s to reset".

Thoughts?

Ian

 

The data sheet linked from the RS page explains it, in figures and graphs, and will be correct. It is seconds, but that is a maximum at a given current (5.5 A). At 40 A the trip time is 20 milliseconds.

 

The trip time will depend on what current the transformer will deliver into a fault or overload.

 

[ikcdab]

28 minutes ago, Crosland said:

 

The data sheet linked from the RS page explains it, in figures and graphs, and will be correct. It is seconds, but that is a maximum at a given current (5.5 A). At 40 A the trip time is 20 milliseconds.

 

The trip time will depend on what current the transformer will deliver into a fault or overload.

 

Thank you. I have a transformer delivering 15v AC to the controller via a 2a fuse. The controller delivers a max of 12v DC to the track. I short circuited the track. I wonder how many amps that would create. I'll look at the data sheet 

Many thanks again

[Crosland]

3 hours ago, ikcdab said:

Thank you. I have a transformer delivering 15v AC to the controller via a 2a fuse. The controller delivers a max of 12v DC to the track. I short circuited the track. I wonder how many amps that would create. I'll look at the data sheet 

Many thanks again

 

So where did you fit the polyfuse? Between the transformer and controller or after the controller.

 

What sort of controller? Does it not have some overload protection of its own?

 

[ikcdab]

1 hour ago, Crosland said:

 

So where did you fit the polyfuse? Between the transformer and controller or after the controller.

 

What sort of controller? Does it not have some overload protection of its own?

 

It's home made. Based on circuits I found on here. I fitted it directly after the diode bridge. I opened up my gaugemaster hand held and I fitted the same circuit breaker as they seemed to have used. Same ref number, anyway.