Low voltage transformer

[tomparryharry]

Hello Folks,

 

Any idea where I can purchase a 3vdc transformer?

 

I'd like to motorise some signals, and I'm looking at using something like a mini-servo.

 

As usual, all help/knowledge gratefully received.

 

Regards,

Ian

[Oldddudders]

http://www.maplin.co.uk/ac-dc-fixed-voltage-6w-power-supplies-512208

[tomparryharry]

Hello Ian,

 

For the life of me, I couldn't find those earlier.....

 

Ian

[Crosland]

Hello Folks,

 

Any idea where I can purchase a 3vdc transformer?

 

I'd like to motorise some signals, and I'm looking at using something like a mini-servo.

 

As usual, all help/knowledge gratefully received.

 

Regards,

Ian

Why 3V? I would stick to 5V servos.

 

Andrew

[stewartingram]

Pedant mode - a transformer only works on AC....but I think I know what you mean, a 3v DC psu?

 

(Pedant mode off)

 

Stewart

[tomparryharry]

Why 3V? I would stick to 5V servos.

 

Andrew

Hello Andrew,

 

I've got some servos where the operating range is 3-4.8 VDC. I'm assuming that if I use the higher end value, they will function that more quickly. Hence the lower value. Semaphores don't 'whizz off'

 

Regards,

Ian

[tomparryharry]

Pedant mode - a transformer only works on AC....but I think I know what you mean, a 3v DC psu?

 

(Pedant mode off)

 

Stewart

Hello Stuart,

 

You are of course correct. I did indeed mean a DC supply. DOH!

[Crosland]

I've got some servos where the operating range is 3-4.8 VDC. I'm assuming that if I use the higher end value, they will function that more quickly. Hence the lower value. Semaphores don't 'whizz off'

 

A decent servo controller for model railway applications will let you control the speed and even add "bounce" to the movement.

 

Andrew

[richard-g8jvm]

One of the standard value LDO, low drop out regulator, is 3.3V which is ideal for you application.

If you servo motors takes less than 100mA you can use the three leaded TO-92 package , which is just Vin, Vout and ground.

You will need to put a capacitor on the input and output to ground, you can use small tantalum caps 1~2uF with wire leads,

So if you are really scruffy with construction you can just twist together the leads on the regulator and capacitors and twist the wires

on as well, cost under £2, use one with each servo motor, then just run +12v to it.

 

HTH

Richard

[Crosland]

T

 

One of the standard value LDO, low drop out regulator, is 3.3V which is ideal for you application.

If you servo motors takes less than 100mA you can use the three leaded TO-92 package , which is just Vin, Vout and ground.

You will need to put a capacitor on the input and output to ground, you can use small tantalum caps 1~2uF with wire leads,

So if you are really scruffy with construction you can just twist together the leads on the regulator and capacitors and twist the wires

on as well, cost under £2, use one with each servo motor, then just run +12v to it.

 

HTH

Richard

 

Totaly unsuitable for anything like 12V input at 100mA!

 

(12V - 3.3V) x 100mA is 0.8W which in a typical TO-92 package will lead to a junction teperature rise of 120 deg. C. The device will shutdown when it hits it's internal thermal limit.

 

Andrew

[Stevelewis]

Try  looking  at  mobile  phone  chargers  there  are  usually  a  few  lying   around in  many  households,  they  provide  usually  around  5 volts DC lowish amperage

 

i am currently  using  some  to  provide   power  for  lighting  buildings,   providing  power  for  Eckon  clour light  signals

and   providing  power   for  Kato \\\\\unitrack  motorised points in a  fiddle  yard!!

[richard-g8jvm]

T

 

 

Totaly unsuitable for anything like 12V input at 100mA!

 

(12V - 3.3V) x 100mA is 0.8W which in a typical TO-92 package will lead to a junction teperature rise of 120 deg. C. The device will shutdown when it hits it's internal thermal limit.

 

Andrew

You are assuming its going to take 100mA continuously, which it wont. And if it gets too warm put a series resistor in line, or use a LF33cv which is in a TO-220 package which you can still twist the leads together, and they are 0.73 p each, As its got a tab with a hole on it, its easy to get rid of any heat,

I see this is going to turn in to a flame war.

Richard

[14Steve14]

If its in a 220 package put a heatsink behind it and do it properly.

[cpman46]

So if you are really scruffy with construction you can just twist together the leads on the regulator and capacitors and twist the wires

on as well, cost under £2, use one with each servo motor, then just run +12v to it.

 

 

Richard

Not a 'flame war' but I think we should encourage all fellow modellers, even those with perhaps limited soldering skills, to use proper soldered joints when constructing electronic component circuits. Twisting wires together is not good for long term reliability. A strong well soldered joint wins every time and takes little time to do.

Just my threepenneth!

Mike

[richard-g8jvm]

twisting wires together is very satisfactory, it was a method widely used for telecoms in the old telephone exchanges, and also on military equipment.

the term used was wire wrapping.

Having seen how some people can solder, and what they use to solder with, a twisted or wrapped joint , not the ones you smoke, with last longer than a dry joint.

 

Soldering is not difficult, but if you cant do it, its better to make a wrapped joint instead of something that looks OK but the solder hasn't flowed and the joint is actually

held together by the flux.

Just because it looks scruffy does not mean non functional

Richard

[ZiderHead]

wire-wrapping is usually wire to square post and requires a special tool and some technique (like soldering). just twisting wires together is not the same as you don't get the required cold-weld that you do with real wire wrapping or crimping.

 

If you really dont want to solder wire-to-wire connections, use those 3M screw on jobbies, although the cold-weld is hard to achieve with them, they are fiddly, bulky and not reworkable (unlike a solder joint) so leave plenty of spare wire just in case.

[richard-g8jvm]

the only reason a square post is used is to break though the insulation, and you dont need a special tool,, its only to make the joint easier to make,

its only to speed up the process.

[ZiderHead]

The square post and the tool are designed to create multiple cold welds - 4 per loop. Insulation must be stripped as it is compressible, which means it is impossible for the tool to generate the pressure required to form the cold weld.

[richard-g8jvm]

You really want to pick an argument dont you

 

Cold weld ... if it welded you would not be able to unwrap it, which you can, so there can be no weld, it is a pressure contact, nothing more

[ZiderHead]

My intention is not to pick an argument but to encourage good practice, as cpman said earlier, and explain why one method may be better than another. There are few things more frustrating than having to trace and fix intermittent electrical faults, especially when crawling around under your baseboard.

 

Twisting wires together is just asking for trouble later because although it may be a viable low-pressure contact connection when its made, over time with vibration, heat cycles etc it will become less so. Unlike connectors designed for low pressure contact connections there is no method to maintain the pressure, and hence the contact.

 

Scotchlok or screw on connectors are a decent alternative if soldering isnt an option, and they cost pennies.

 

If you are interested theres plenty of info on the web about how the high pressure cold welded joint in a wire wrap or crimp is fundamentally different from a low pressure contact.

[richard-g8jvm]

every list has its pre-madonnas, guess we know who it is on this list, I'm not wasting any more time further with you

[Crosland]

twisting wires together is very satisfactory, it was a method widely used for telecoms in the old telephone exchanges, and also on military equipment.

the term used was wire wrapping.

I've tried to resist, to avoid accusations of fanning the flames, but...

 

There is a world of difference between wire wrapping and just twisting two wires together.

 

The materials, tools and techniques used for wire wrapping are designed to provide a secure gas tight joint that will last a long time, something you simply canot do with simple twisting.

 

Andrew

[Crosland]

every list has its pre-madonnas, guess we know who it is on this list, I'm not wasting any more time further with you

Every list also has those who refuse to learn when confronted with something beyond their experience and go off in a huff. Google wire wrapping and cold welding to get a clue.

 

Andrew

[richard-g8jvm]

you couldn't be more wrong if you tried Andrew.

I was using wire wrapping on prototype boards back in the early 1970's, probably before yore left school.

After wrapping the wire continues to stretch and the contact pressure decreases, but because there are so many contacts, there is only milli ohm change in

conductivity.

And the reason wire wrapping was used on computer prototype boards was package density. and difficult to get a soldering iron in for modification.

Back in the days when if you wanted to make a printed circuit board, you had to manually layout with tape on a light box, normally  twice the size, then photographically reduce to size,

then photo etch, but no pre-sensitised board  then. So that had to be done by hand as well.

 

There were few pcb design packages then, If   you found a computer that could run one, it cost a lot of money, and was big,

TVs were monochrome, some of the newer were dual standard and colour,

and the 405 line TV transmitters were still operational

And the wrapping was done with hand tools, the posts were not strong enough for any power tool. power wrapping was mostly a production process

Not everything on Google is accurate, and  not written by the guys that used the method professional,

They are mostly from the older part of the population that have nothing to do with computers.

[Crosland]

you couldn't be more wrong if you tried Andrew.

Whatever.

 

You just carry on believeing that twisting two wires together is the same as wire wrapping.

 

Andrew