Resisdence soldering or normal soldering whats the difference?

[Adrian]

 
 

Your last paragraph contains factual errors that are very wide of the mark.
Firstly you are not producing a 'short circuit' with an RSU - the carbon probe acts as a point of resistance (giving the unit its name) and effectively 'uses' the current in exactly the same manner as a conventional light bulb or an electric fire.
Secondly you are not doing anything with the mains current which is isolated from the soldering probe by the fact that the mains is on the transformer primary winding and the soldering probe is fed from the secondary winding.
Thirdly, the use of the unit does not cause undue heating of the battery charger transformer which is built to withstand considerable mistreatment in its intended field of use.
As I have said in a previous post, I have used my RSU to solder the rails (code 100) to pcb strips on an exhibition layout that involved continuous operation of the RSU for twenty second intervals over a period of aprox thirty mins while we did the work - very little heating of the transformer resulted which proves beyond all doubt the durability of the RSU as such a job a far beyond the normal use the a modeller would subject an RSU too - I am more than happy to demonstrate this application to anyone.
Fifthly, no knowledge of electircal design is needed to undertake such a conversion for oneself - all that is necessary is the same common sense that is applied to handling the electrics within our hobby as a whole.
 
Remember that according to the rules of aircraft design the bumble bee cannot fly - problem is nobody has informed the bee and so he keeps on flying !.

You seem to be getting very defensive and reading things into my post that was not intended. I never said that battery chargers wouldn't work I just said you had to be careful choosing the right one - you appear to "have chosen wisely". Also I never said the probe was at main voltage but you are plugging it into the mains and you are using it for a purpose not originally designed for which to me constitutes "taking a chance". Finally the definition of a short circuit is

 

an electrical circuit in a device of lower resistance than that of a normal circuit, especially one resulting from the unintended contact of components and consequent accidental diversion of the current.

 

In the electrical circuit you are replacing a lead-acid battery  with a carbon rod, I strongly suspect that the carbon rod is of a lower resistance than the batttery hence my comment that you "effectively creating a short circuit", which I don't think is that far wide of the mark.

 

Finally it's quite ironic that you quote the myth about the bumble bee's flight because this has been debunked several times and the aerodynamic understanding of it's flight now enables him to fly - which I'm sure is of great relief to the bumble-bee. 

 

There is no one situation where an RSU is the only tool you can use, nor is there one situation where only a conventional iron can suffice. Whether it be the manufacturers of RSU's or the snobbish attitude of users that have created the myth about RSU's I know not, but the popular myth that an RSU is better than a conventional iron is rubbish.

As always with tools, it's horses for courses. Hope that helps a little bit.

It does - and I think a suitable point on which I'll agree with totally and bow out of this thread.

 

[TheWeatheringMan]

Your last paragraph contains factual errors that are very wide of the mark.

Firstly you are not producing a 'short circuit' with an RSU - the carbon probe acts as a point of resistance (giving the unit its name) and effectively 'uses' the current in exactly the same manner as a conventional light bulb or an electric fire.

Secondly you are not doing anything with the mains current which is isolated from the soldering probe by the fact that the mains is on the transformer primary winding and the soldering probe is fed from the secondary winding.

Thirdly, the use of the unit does not cause undue heating of the battery charger transformer which is built to withstand considerable mistreatment in its intended field of use.

As I have said in a previous post, I have used my RSU to solder the rails (code 100) to pcb strips on an exhibition layout that involved continuous operation of the RSU for twenty second intervals over a period of aprox thirty mins while we did the work - very little heating of the transformer resulted which proves beyond all doubt the durability of the RSU as such a job a far beyond the normal use the a modeller would subject an RSU too - I am more than happy to demonstrate this application to anyone.

Fifthly, no knowledge of electircal design is needed to undertake such a conversion for oneself - all that is necessary is the same common sense that is applied to handling the electrics within our hobby as a whole.

 

Whilst as a former commercial supplier of RSU's I understand that you would not wish people to build their own but to buy a ready made unit but it is wrong to make statements that are not correct to put people off doing a worthwhile and relatively easy build.

The fact that many people have very sucessfully done such a conversion proves beyond all doubt that it works and all the reasons that are sometimes given why it wont work dont alter the fact that it does.

Remember that according to the rules of aircraft design the bumble bee cannot fly - problem is nobody has informed the bee and so he keeps on flying !.

Hi,

Having re read my post I felt that a couple of points needed expanding.

First point - when the current is passed through the carbon probe and the resistance comes into play the electical energy is converted to another form of energy - heat - which of course is what does the intended job of melting the solder. This is what comprisses the 'using' of the current and therefore does not constitute a short circuit any more than the working of a conventional soldering iron element does. 

 

Second point - it has become obvious, both from comments on this thread and in discussions elsewhere, that the level of current (amps) needed to produce the heating of the carbon probe is often very much over estimated. As has been proven over and over again the current required does not need to exceed aprox 8 amps and can be a little lower and remain sucessful.

It has been stated by one poster that 2mm wire would heat up. To do this would indicate either a direct short circuit held for a long period of time (remember that an RSU does not cause a direct short) or an amperage far in excess of that required.

The voltage used can be anything from 2 volts upwards provided that sufficient amps are available. However, as most will know, the lower the voltage the higher the amps required for a given task - this of course applies to all electrical equipment not just an RSU.

The use of 6 - 12 volts strikes a good balance and allows the use of a more reasonable level of amps.

Again if the amps are far higher the need arrises for heavier cables to connect the RSU to the work and probe to prevent loss of energy by heating those cables.

 

Another matter that has been raised is that it has been said that the resistance takes place between the 'interface' of the items being joined.

This is very clearly wrong as can be seen when an RSU is in use.

It is the resistance of the point of contact of the carbon probe that generates the heat that melts the solder in the same way that a hot conventional iron does.

In my example I quoted of soldering the rail ends to pcb strips with my RSU there were several joints where the rail did not touch the copper surface of the pcb and the small gap was filled with molten solder - conventional resin cored solder fed against and under the rail heated with the RSU probe - the molten solder transfering sufficient heat to the thin copper layer of the pcb. I think this rather proves the total falacy that the resistance/heating takes place at the 'interface' of the two parts being joined.

Additionaly if this happened at the 'interface' then my feeling is that it would more than likely oxidise the metals in the solder and destroy the flux rather than acheive the desired result.

I think we can sum up the RSU versus Soldering Iron like this -based on my experience of using both for very many years - but my thoughts only and likely to be different to others thoughts perhaps.

 

(1)  An RSU cannot and will not replace a soldering iron for all jobs - some jobs are totally beyond an RSU for various reasons.

(2)  An RSU is not essential by any means - it CAN be a very usefull additional tool for some jobs but not essential.

(3)  A soldering iron is a more universally usefull tool as it can do everything an RSU can do - the reverse is not true.

(4)  To say an RSU can do some jobs more easily or neatly is wrong - a soldering iron can achieve just the same in skilled hands.

(5)  An RSU will not improve ones skills - it might make some jobs quicker but the final quality of the work is down to the worker.

 

Its very much 'horses for courses'.

Most modellers who posess an RSU do find it an advantage in some circumstances but not all - and if a modelled finds an RSU is not for him (or her) he or she is no less of a modeller as a result. Its a very personal thing just like what you model.

 

Would I want to be without my RSU ?.

Personally no i'd prefer not to be as i'm an enthusiastic user of same - but that said if I lost it it wouldnt stop or alter how I model as i've got about six different soldering irons (mostly Antex) and a mini gas torch (another very usefull but non essential tool).

 

Dont rush out to build or buy an RSU but talk to other modellers at exhibitions and get a few opinions - better still try your hand at a demo - and only then decide if an RSU will be usefull to You.

 

Remember : can be very usefull - YES                      Essential to a workshop - deffinatly NO

 

Well the above is offered as what I hope is an unbiassed and fair verdict on the RSU.

If i'm biased slightly in favour of having one its only because i'm fortunate to own one - but I neither expect or would advise all and sundry to follow my example.

Hope that does seem a fair summing up.

 

Best Regards All

[TheWeatheringMan]

 

 

You seem to be getting very defensive and reading things into my post that was not intended. I never said that battery chargers wouldn't work I just said you had to be careful choosing the right one - you appear to "have chosen wisely". Also I never said the probe was at main voltage but you are plugging it into the mains and you are using it for a purpose not originally designed for which to me constitutes "taking a chance". Finally the definition of a short circuit is

 

 

In the electrical circuit you are replacing a lead-acid battery  with a carbon rod, I strongly suspect that the carbon rod is of a lower resistance than the batttery hence my comment that you "effectively creating a short circuit", which I don't think is that far wide of the mark.

 

Finally it's quite ironic that you quote the myth about the bumble bee's flight because this has been debunked several times and the aerodynamic understanding of it's flight now enables him to fly - which I'm sure is of great relief to the bumble-bee. 

 

It does - and I think a suitable point on which I'll agree with totally and bow out of this thread.

 

 

Hi,

I totally refute the suggestion that i've got 'deffensive'.

What i've sought to do is state facts that offer a correction to wrong statements so that those reading this thread are presented with correct information.

I note that my accuser does not respond to the matters I pointed out such as the very wrong statement that an RSU is causing a short circuit.

The definition of same can be interpreted in several ways but the 'replacement' of a lead acid battery by a carbon probe does not constitute a short circuit for the very reason that was stated in my post.

I simply felt that to say that an RSU is a short circuit could end up putting people off the whole idea to the detriment of those who seek to sell such a product (I dont for one moment expect everone to follow my chosen way to own an RSU) and that this statement needed to be corrected.

The other poster has apparently chosen not to partake further of this thread - this I feel is a great shame as differences  of opinion, correction of statements made and input from others ideas is what makes RMWeb one of the best sources of information, inspiration and exchange of ideas in the world.

Our hobby would be very much the worse if RMWeb and its debates did not exist.

Every single Member is as valuable to our hobby as any other - long may it continue.

 

Regards

[Jol Wilkinson]

Your two posts contain some contentious statements and your claims as to how resistance soldering works are at odds with what I believe is the generally held view.

 

My understanding of how resistance soldering works is based on the personal research carried out by the late Mike Grey while he was designing the London Road Models unit. He was a member of the IEE and a Head of Department at a large college so didn't take his approach to things electrical lightly. From his research he developed the view that the heat generated at the joint interface was created by the current passing through the joint interface and the solder.

 

Wikipedia has this definition.

“Resistance soldering is soldering in which the heat required to flow the solder is created by passing an electric current through the solder. When current is conducted through a resistive material a certain level of heat is generated.”

 

Another analogy would be spot welding “Resistive spot welding  is a process in which contacting metal surfaces are joined by the heat obtained from resistance to electric current.”

 

However, you seem to be saying that the heat generated where the carbon probe contacts the metal is what melts the solder. While that may have some effect, it is only a part of the process.

 

You also say “As has been proven over and over again the current required does not need to exceed aprox 8 amps and can be a little lower and remain sucessful.” Where has this been proven? By who?

 

Your statements regarding volts and amps seem ambiguous. If you increase the voltage the current will rise. The “standard” RSUs operate a maximum of about 5 volts with 100va capapcity, i.e. 20 amps. Using a similar circuit, carbon probe etc. you are claiming that 12 volts will drive about 8 amps. It may be that the transformer you have used has a limit of 8 amp output, dictated by its windings, but that would not in itself prove that 8 amps at 12 volts is optimum for resistance soldering.

 

Your description of soldering rail to pcb sleepers is also misleading, the rail/solder and solder/pcb interfaces both provide a point at which heat is generated, so melting the solder. If you want an example of how resistance soldering works using track, look at Mike Grey’s article in MRJ 82. He demonstrates how using two probes located into the rail web either side will raise the temperature of the rail metal between the probes sufficiently to melt solder paint under the rail and attach it to a track rivet in a wooden sleeper under the rail. No doubt you will claim it is heat from both probes, but I don’t consider that you can provide any proof of that, any more than I can definitively prove Mike's view. In addition he would ensure that the probe tips didn't get red hot by selection the correct RSU settings and ensuring good probe to metal contact.

 

Furthermore, your probe heat view is also contradicted by soldering such items as handrail knobs into boilers by placing the probe on top of the knob. The heat path down the knob is restricted by the narrow section and that approach certainly wouldn't work well with an ordinary soldering iron. It is the current flow through the solder/knob – boiler interface that generates the heat to melt the solder.

 

No doubt the technique of getting the probe tip red hot – advocated by some – will create some heat transference. However, with thinner materials in 4mm (and especially 2mm) it will cause surface burning and pitting, especially on half etched metal sections. I refer you to the picture in post # 8 as an example of a brass kit that has been assembled using a LRM RSU and 145 deg without excessive probe tip temperature as evidence of the results that can be obtained.

 

You say “ I think this rather proves the total falacy that the resistance/heating takes place at the 'interface' of the two parts being joined.

Additionaly if this happened at the 'interface' then my feeling is that it would more than likely oxidise the metals in the solder and destroy the flux rather than acheive the desired result.”

 

The recommendation when using an RSU is to turn off the power when the solder “flashes” around the joint being  made. The flux will already have done it’s job and the solder will just have reached/passed its melting point. So how will the solder be oxidised and the flux destroyed?  You could say the same about using a standard soldering iron operating at 420 degrees with 145 solder. 

 

You also said;

“Our hobby would be very much the worse if RMWeb and its debates did not exist.

Every single Member is as valuable to our hobby as any other - long may it continue.”

 

I agree entirely.

 

[martin_wynne]

The question some of us are wondering (mostly, it appears, those who already feel comfortable soldering with a conventional iron and have developed the requisite skills to use it effectively)  is the converse of your comment: In what situation is there a need to use an RSU where a conventional iron can suffice? (Not just suffice, but do the job entirely satisfactorily) So far I have not seen anything described as an advantage of an RSU which I don't already do with a conventional iron and in pretty much exactly the same way, bar the means of applying the heat.

 

Hi Graham,

 

Buried several times in this topic but not sufficiently emphasized is the essential difference between an RSU and a conventional soldering iron. With an RSU:

 

  the tool remains in firm contact with the work while the joint cools

 

You can therefore use it to hold the part in position, and do not need to improvise other means of holding or clamping. This makes the RSU ideal for adding detail parts:

 

1. apply solder cream, preferably 2% silver 179-degree SMT paste.

 

2. apply tool to work while cold and hold firm.

 

3. switch on with foot switch.

 

4. watch solder flow.

 

5. switch off with foot switch.

 

6. continue to hold firm until cold.

 

If you do the same job with a soldering iron, as you remove the hot iron the part is likely to move, needing some method of prior clipping or clamping to be devised. Holding it place with a cocktail stick while it cools is often sufficient, but needs an extra hand.

 

Martin.

[raymw]

Resistance welding, seam or spot welding is an entirely different situation. For spot welding it generally uses water cooled copper electrodes, high currents and physical pressure. The heat is generated at all metallic interfaces, depending on the relative resistances (I*I *R) and once the steel sheets are melted, pressure forces them together and the ratio of the resistances change, being mainly at the copper clamps/steel sheet interfaces, current is then shut off and pressure is released. Total time, generally less than a second. Metals other than steel can be used. There is surface resistance involved, but the dynamics are different to using an rsu for soldering.

 

In an RSU system, there are a number of resistances that come into play, and over time these will change, as the joint progresses. Initially, there will be a high resistance between the metal sheets and solder/flux interfaces. Once solder has flowed into that joint, then the resistance at those interfaces will significantly reduce. The main resistance will then be at the carbon tip to metal contact - that will be where the heat is generated, and that allows seams to be soldered. The two sheets are electrically connected by the molten/solid solder at the previously made joint, and electrical current takes the easiest path which will be through the already soldered part of the seam, and most resistance will therefore be at the carbon tip. If it was the case that the only heating took place at the metal/solder interface, then instead of a carbon rod, a copper or other rod could be used, or no rod at all, just connections straight to both sheets of metal.  (Talking about current flow here, not arcing with poor contacts to metal rods)

 

Now, for a quick dab of a joint, perhaps fitting a lamp iron, then a metal rod could be used, but I've had little success with that, maybe I should try harder.

 

There is much more to this, but I just can't be bothered to go into the detail.

 

I have, about three posts ago, already asked that this thread should be locked, since I believe the discussion had gone away from the original question, and it was becoming such that some folk were talking about things that were not relevant and were quoting half truths.

 

Best wishes,

 

Ray

[Bruciethefish]

Hi, no disrespect intended * and not directed specifically at you (just using this as an example) but to be honest I'm not surprised you have not used your 25W iron, but I would suggest that this is because I would consider the 25W iron seriously underpowered for the jobs you indicate. For thick brass components I would suggest at a bare minimum a 40W iron, but an 80W iron would be preferable. So to be honest I'm not surprised the RSU was significantly better. Soldering is very simple it's just a case of getting sufficient heat into the job so I'd suggest that you wouldn't see much difference between a bigger iron an an RSU.

 

An RSU is what I would term a "marmite" tool - you either love it or you hate it. For myself I'm in the "hate it" camp. I use an ERSA RDS-80 iron and this does everything I need for soldering. As I mentioned soldering is very very simple, all it needs is heat in the joint and the solder will flow. I can solder quite small detail using solder paste with a standard iron and I can control where the solder flows, I struggled with the RSU because the hottest point wasn't always where the probe was, it's where the resistance is the highest - hence the name! I always struggled to get the solder to flow cleanly along a seam with the RSU's I have used. When I see all these guides about RSU's using earthing plates and magnets I despair sometimes, as I believe it shows a lack of understanding about the fundamentals of soldering. As I will repeat time and time again it is all about getting heat into the job. Witness the craftsmen who solder white metal with a blow torch! They have the confidence to get heat in just where it is needed. So all this messing about with earthing plates and magnets is an anathema to me.

 

So my recommendation would be to invest in a good quality soldering station first, I'd highly recommend the ERSA RDS-80. Practice soldering on scrap etches and after you have built your loco(s) and want to try an RSU find someone or a club where you can practice with one before committing to buying one. I've had two RSU's over the years because I thought I needed them to improve my modelling - they both got sold as I never used them, one on eBay, and I actually got more value for money signing up for an evening class in jewellery making where I learnt how to silver solder, lessons learnt from that are very transferable to soft-soldering.

 

Regards

 

Adrian.

 

* sorry to use the "no disrespect intended" option as that usually means that the person saying it is being disrespectful but wants to claim otherwise and I detest using it - however in this respect it is meant honestly, there are quite a few articles on the web that talk about the 'black art of soldering' and claim to clear up 'myths and facts' of soldering and then go onto to talk, in my opinion, some utter claptrap. So my post is aimed at them rather than Bruciethefish posting per se.  

I know this post was a few days ago, but having done this stuff professionally for 35 years following an educational background in both engineering & silversmithing, I consider I've had a reasonable amount of experience which qualifies me to comment. I have, within my armoury of tools such things as  big, high-wattage irons, though I've never bothered to use them, as they are huge, heavy & unwieldy things requiring special precautions while they are on. I've always found the 15 & 25 watt Antexes sufficient for most purposes, with the added advantage of not taking up too much space on the bench, where they would always be switched on ready for use whenever I was at work. If extra heat was needed, I'd light up a gas pencil torch to provide it.

The RSU takes up no space at all on the bench, as I have the probe & earth lead hanging on hooks, & gives me the option of all the heat I'm likely to need, instantaneously at the flick of a switch, thus saving me the cost of the 25 watt iron constantly burning power for at least 50 hours a week, & giving an annual saving of 62.5 kilowatt hours. 

I've never felt the need of a temperature-controlled iron, having evolved my own techniques through experience, using the simple, lightweight Antex products which I've found reliable & economical, only needing replacement every 10 years or so.

Apart from electrical means of producing heat, I also can bring a standard plumber's blowtorch or an oxy-propane set into play if I need to get anything really seriously hot;- I've not needed them much in a modelling context since acquiring an RSU either... It's the convenience of the thing that I feel is its strong point, in that it saves someone like me time & money, though I could easily manage without it.....

[martin_wynne]

I have, about three posts ago, already asked that this thread should be locked

 

Heaven preserve us from self-appointed moderators. You don't want to read any more of this topic, so no-one else should be allowed to?

 

How about just not reading it?

 

Martin.

[raymw]

Martin, sometimes self appointed are more knowledgeable  than 'officially appointed' . My point was that it seemed the replies were going off track, into areas that people had little understanding of, needless arguments were developing in an area that would be difficult to get at the facts. As you said in post #105, the real answers to the question were buried in the nonsense about whether the carbon rod was the heat source, copper wire being dodgy because it got 'toasty', and other comments implying that folk were lying. 

 

Anyway, who moderates the moderators? seems it may be you.

 

Best wishes,

 

Ray

 

edit  - the 'official' moderators can't see all the threads, I suggested that Andy looked at this thread, to decide if he thought it had run it's course. Is it worth while you coming back in a weeks time to repeat you post #105? do you care that much?

[martin_wynne]

Martin, sometimes self appointed are more knowledgeable  than 'officially appointed' . My point was that it seemed the replies were going off track, into areas that people had little understanding of, needless arguments were developing in an area that would be difficult to get at the facts.

 

Ray, if you exclude from RMweb topics which stray off course or contain needless arguments there would be hardly any left. Anyone who is not interested in the direction which a topic is taking is entirely free not to read it.

 

I'm extremely irritated when topics in which I have posted get locked, but ultimately that is a decision for those who have been appointed by Andy Y to make such decisions. Not me. Or you.

 

Martin.

[Andy Hayter]

Several people have commented on the high cost of an RSU - including me obliquely by suggesting that it might be considered a luxury.

 

However, something to consider if you are not fully experienced with conventional soldering (as indeed we all are at some stage of our development) is how many kits do you need to spoil in developing your skills in conventional soldering to pay for the cost of an RSU.

 

Having messed up a half etch overlay on a not cheap brass kit due to clumsy use of the 50W iron, I invested in a RSU and have had no failures since.  The average cost of my French kits is probably in excess of 200€ and the average life of producers seems to be around 4 years (my best guess) - so the chances of getting a replacement etch are generally zero.  Of course e will never know what might have happened if I had stayed with conventional soldering for everything, but I reckon my RSU has paid for itself several times over.

[JeffP]

LNWR Modeller said:

 

Your statements regarding volts and amps seem ambiguous. If you increase the voltage the current will rise.

 

I'm not sure that's how it works with transformers.

 

When I was taught the transformer rules, many years ago, we were told that the "VA Rating" of the transformer was it's maximum. Given by Current x voltage, or, in other uses, wattage.

 

Thus, if you have, say a maximum VA of 100, you could have 100V, 1A;  50V, 2A;  25V 4A;  right down to 1V, 100A; or less?

 

Each time the VA is the same, but in the case of a transformer, DEcreasing voltage really does INcrease current.

 

Or so I was told.......I stand to be corrected.

[raymw]

Jeff, Better not tempt me

[JeffP]

You reckon I'm wrong, then?

[TheWeatheringMan]

Your two posts contain some contentious statements and your claims as to how resistance soldering works are at odds with what I believe is the generally held view.

 

My understanding of how resistance soldering works is based on the personal research carried out by the late Mike Grey while he was designing the London Road Models unit. He was a member of the IEE and a Head of Department at a large college so didn't take his approach to things electrical lightly. From his research he developed the view that the heat generated at the joint interface was created by the current passing through the joint interface and the solder.

 

Wikipedia has this definition.

“Resistance soldering is soldering in which the heat required to flow the solder is created by passing an electric current through the solder. When current is conducted through a resistive material a certain level of heat is generated.”

 

Another analogy would be spot welding “Resistive spot welding  is a process in which contacting metal surfaces are joined by the heat obtained from resistance to electric current.”

 

However, you seem to be saying that the heat generated where the carbon probe contacts the metal is what melts the solder. While that may have some effect, it is only a part of the process.

 

You also say “As has been proven over and over again the current required does not need to exceed aprox 8 amps and can be a little lower and remain sucessful.” Where has this been proven? By who?

 

Your statements regarding volts and amps seem ambiguous. If you increase the voltage the current will rise. The “standard” RSUs operate a maximum of about 5 volts with 100va capapcity, i.e. 20 amps. Using a similar circuit, carbon probe etc. you are claiming that 12 volts will drive about 8 amps. It may be that the transformer you have used has a limit of 8 amp output, dictated by its windings, but that would not in itself prove that 8 amps at 12 volts is optimum for resistance soldering.

 

Your description of soldering rail to pcb sleepers is also misleading, the rail/solder and solder/pcb interfaces both provide a point at which heat is generated, so melting the solder. If you want an example of how resistance soldering works using track, look at Mike Grey’s article in MRJ 82. He demonstrates how using two probes located into the rail web either side will raise the temperature of the rail metal between the probes sufficiently to melt solder paint under the rail and attach it to a track rivet in a wooden sleeper under the rail. No doubt you will claim it is heat from both probes, but I don’t consider that you can provide any proof of that, any more than I can definitively prove Mike's view. In addition he would ensure that the probe tips didn't get red hot by selection the correct RSU settings and ensuring good probe to metal contact.

 

Furthermore, your probe heat view is also contradicted by soldering such items as handrail knobs into boilers by placing the probe on top of the knob. The heat path down the knob is restricted by the narrow section and that approach certainly wouldn't work well with an ordinary soldering iron. It is the current flow through the solder/knob – boiler interface that generates the heat to melt the solder.

 

No doubt the technique of getting the probe tip red hot – advocated by some – will create some heat transference. However, with thinner materials in 4mm (and especially 2mm) it will cause surface burning and pitting, especially on half etched metal sections. I refer you to the picture in post # 8 as an example of a brass kit that has been assembled using a LRM RSU and 145 deg without excessive probe tip temperature as evidence of the results that can be obtained.

 

You say “ I think this rather proves the total falacy that the resistance/heating takes place at the 'interface' of the two parts being joined.

Additionaly if this happened at the 'interface' then my feeling is that it would more than likely oxidise the metals in the solder and destroy the flux rather than acheive the desired result.”

 

The recommendation when using an RSU is to turn off the power when the solder “flashes” around the joint being  made. The flux will already have done it’s job and the solder will just have reached/passed its melting point. So how will the solder be oxidised and the flux destroyed?  You could say the same about using a standard soldering iron operating at 420 degrees with 145 solder. 

 

You also said;

“Our hobby would be very much the worse if RMWeb and its debates did not exist.

Every single Member is as valuable to our hobby as any other - long may it continue.”

 

I agree entirely.

[TheWeatheringMan]

 

Your two posts contain some contentious statements and your claims as to how resistance soldering works are at odds with what I believe is the generally held view.

 

My understanding of how resistance soldering works is based on the personal research carried out by the late Mike Grey while he was designing the London Road Models unit. He was a member of the IEE and a Head of Department at a large college so didn't take his approach to things electrical lightly. From his research he developed the view that the heat generated at the joint interface was created by the current passing3 through the joint interface and the solder.

 

Wikipedia has this definition.

“Resistance soldering is soldering in which the heat required to flow the solder is created by passing an electric current through the solder. When current is conducted through a resistive material a certain level of heat is generated.”

 

Another analogy would be spot welding “Resistive spot welding  is a process in which contacting metal surfaces are joined by the heat obtained from resistance to electric current.”

 

However, you seem to be saying that the heat generated where the carbon probe contacts the metal is what melts the solder. While that may have some effect, it is only a part of the process.

 

You also say “As has been proven over and over again the current required does not need to exceed aprox 8 amps and can be a little lower and remain sucessful.” Where has this been proven? By who?

 

Your statements regarding volts and amps seem ambiguous. If you increase the voltage the current will rise. The “standard” RSUs operate a maximum of about 5 volts with 100va capapcity, i.e. 20 amps. Using a similar circuit, carbon probe etc. you are claiming that 12 volts will drive about 8 amps. It may be that the transformer you have used has a limit of 8 amp output, dictated by its windings, but that would not in itself prove that 8 amps at 12 volts is optimum for resistance soldering.

 

Your description of soldering rail to pcb sleepers is also misleading, the rail/solder and solder/pcb interfaces both provide a point at which heat is generated, so melting the solder. If you want an example of how resistance soldering works using track, look at Mike Grey’s article in MRJ 82. He demonstrates how using two probes located into the rail web either side will raise the temperature of the rail metal between the probes sufficiently to melt solder paint under the rail and attach it to a track rivet in a wooden sleeper under the rail. No doubt you will claim it is heat from both probes, but I don’t consider that you can provide any proof of that, any more than I can definitively prove Mike's view. In addition he would ensure that the probe tips didn't get red hot by selection the correct RSU settings and ensuring good probe to metal contact.

 

Furthermore, your probe heat view is also contradicted by soldering such items as handrail knobs into boilers by placing the probe on top of the knob. The heat path down the knob is restricted by the narrow section and that approach certainly wouldn't work well with an ordinary soldering iron. It is the current flow through the solder/knob – boiler interface that generates the heat to melt the solder.

 

No doubt the technique of getting the probe tip red hot – advocated by some – will create some heat transference. However, with thinner materials in 4mm (and especially 2mm) it will cause surface burning and pitting, especially on half etched metal sections. I refer you to the picture in post # 8 as an example of a brass kit that has been assembled using a LRM RSU and 145 deg without excessive probe tip temperature as evidence of the results that can be obtained.

 

You say “ I think this rather proves the total falacy that the resistance/heating takes place at the 'interface' of the two parts being joined.

Additionaly if this happened at the 'interface' then my feeling is that it would more than likely oxidise the metals in the solder and destroy the flux rather than acheive the desired result.”

 

The recommendation when using an RSU is to turn off the power when the solder “flashes” around the joint being  made. The flux will already have done it’s job and the solder will just have reached/passed its melting point. So how will the solder be oxidised and the flux destroyed?  You could say the same about using a standard soldering iron operating at 420 degrees with 145 solder. 

 

You also said;

“Our hobby would be very much the worse if RMWeb and its debates did not exist.

Every single Member is as valuable to our hobby as any other - long may it continue.”

 

I agree entirely.

 

 

Hi All,

 

May I ask anyone interested in this subject to read my earlier posts, my explanations that are based on both practical experience of using an RSU and the writings and agreement of a number of people (not by any means all modellers) who I have talked to about this subject.

 

Having read my previous post I would then ask that you compare the points raised therein with this reply.

I have to say that this is a clear case of a person failing to read my previous post.

 

Take for example my explanation of the job of soldering rails to pcb strip and then read this reply.

I stated very clearly indeed that some of those joints had NO CONTACT between the rail and the copper strip and yet here we have the poster telling me that such a joint provides two points of contact that would be the heat source. Really, pray tell how this can happen when a 1mm gap existed as was explained very clearly in my post.

I was stating facts based on actual happenings not thereory that dosn't stand up when the ACTUAL situation is examined. Fact not fiction i'm afraid.

 

You will all be glad to know that I now see no purpose in adding further to this thread as it is clearly apparent that common sense and actual facts are not accepted by those who spout missinformed thereory when actual proven practice shows otherwise.

It is also noticeable that many of the FACTS that I offered are neatly avoided.

 

I will continue to use my RSU in the knowledge that I know what goes on.

 

However I will add nothing further to this thread as it now seems pointless trying to argue proven facts and actual experience against incorrect thereory.

 

May I bid you all Compliments of the Season and depart.

 

Regards All.

[Graham Hughes]

 

However, something to consider if you are not fully experienced with conventional soldering (as indeed we all are at some stage of our development) is how many kits do you need to spoil in developing your skills in conventional soldering to pay for the cost of an RSU.

 

That's a fair point. I honed my ability to solder whitemetal kits with the 50W iron without turning the temperature down when, if I melted a bit, I threw it back in the melting pot and got another one out of the tub. After a while I got so I could judge the heat from the iron and get it right every time, but it would have cost a bit if I'd been buying the kits. I think that is the conclusion I have reached from this discussion; that it is probably easier to become accomplished with an RSU, although how much of that is down to the intrinsic merit of the RSU and how much is down to the myth and misinformation that seems to surround soldering I am not sure. 

[Bruciethefish]

From a practical point of view, it's not necessary to understand why or how resistance soldering works in order to benefit from the fact that it does. Familiarity with its use is all that's needed to produce practical results...

[martin_wynne]

Thus, if you have, say a maximum VA of 100, you could have 100V, 1A;  50V, 2A;  25V 4A;  right down to 1V, 100A; or less?

 

Hi Jeff,

 

Yes, but not all from the same transformer. All 100VA transformers will be a similar physical size, but each one is made for a specific output voltage and maximum current. The output voltage is determined by the number of turns of wire in the secondary winding. The maximum output current is determined by the thickness of that wire. You cannot get as many turns of thick wire in the same physical space as thin wire. Lots of turns of thin wire = high voltage, low current. A few turns of thick wire = low voltage, high current. The latter is used in RSUs.

 

If the current multiplied by the stated voltage exceeds the VA rating for continuous use, the output voltage will be reduced and the transformer will overheat. The VA rating is determined mainly by the physical size -- the size and number of laminations in the iron core.

 

Martin.

[JeffP]

Hi Martin, thanks for the above, I think I was being misled in my own head by ideas on transmission losses.

The RSU I have is the LR one, it must have different windings, (I've not had it in bit to see), but by plugging 4mm "banana" plugs into different sockets, I can get anything from 1V to about 6V (iirc).

 

That seems to give differing currents too, since it is used to choose the right amount of power for a given application.

[Grovenor]

 

That seems to give differing currents too, since it is used to choose the right amount of power for a given application.

Yes, for a given resistance (ie the job you are soldering) the current and thus the power is directly proportional to the voltage, so when you need more power you use the higher voltages to put more current through the work.

Keith

[naugytrax]

Hi, Keith:

 

I'm sure you meant to say:

"...the current is directionally proportional to the voltage and the power is proportional to the square of the voltage"   ...

[martin_wynne]

The RSU I have is the LR one, it must have different windings, (I've not had it in bit to see), but by plugging 4mm "banana" plugs into different sockets, I can get anything from 1V to about 6V (iirc).

 

That seems to give differing currents too, since it is used to choose the right amount of power for a given application.

 

Hi Jeff,

 

Yes, the different sockets are connected to different number of turns of the secondary winding. For the same job and bit dimensions, the higher voltages (more secondary turns) will drive more current through the work and hence deliver greater power (greater speed of heating), always subject to the VA limit of the transformer.

 

Practical use of the RSU requires choosing the most appropriate bit dimensions as well as the voltage setting. Too high a voltage with a fine pointed bit can melt a hole through thin components if you are not careful.

 

You may be interested in this:

 

 http://www.rmweb.co.uk/community/index.php?/topic/84521-king-street-goods/page-2&do=findComment&comment=1525588

 

regards,

 

Martin.

[Grovenor]

Hi, Keith:

 

I'm sure you meant to say:

"...the current is directionally proportional to the voltage and the power is proportional to the square of the voltage"   ...

Not quite! but nearly! trouble with trying to keep it simple late at night.

Keith

[naugytrax]

Ow!

I really need to pay closer attention to where my fingers are going - especially when I'm "correcting" other peoples' posts!