RM5 Transformer Range

[Western]

Hi guys ... I’ve often wondered if there is a supplier anywhere that sells a range of transformers in the RM5 size ... see pictures


There’s one board I fix that often has a faulty transformer ... and winding new ones by hand gets old very quick.


If there were ready made transformers close enough to the specs I need ... it could save me a lot of time and angst.


Thanks.

 

[ronsimpson]

What goes bad with the transformer?
Is it a broken core?
Broken wire?
Shorted insulation?

 

[Western]

What goes bad with the transformer?
Is it a broken core?
Broken wire?
Shorted insulation?

Usually open circuit ... broken wire.

By the time I get them out I have to start again anyway. Of all the ones I've removed, I've never got one fully apart without breaking something else ... usually the core .. or the former pins.

I'll take some photos to show you why.

First photo it's potted in the box with 3000 on top ... and second photo it's just potted with everything else. Really helpful!

 

[ChrisP58]

Transformers don't fail very often.

When they do it's usually because the original design was poor, or the construction was shoddy.

But to answer your original question, unfortunately no. Or at least I'm not aware of any source of any ready made switch mode transformers for general use. There are too many variables, and the design processes that we power supply engineers use tend to encourage choosing custom core-material-shape-size/inductance/turns ratios/pin outs/etc. (sorry about that)

What are the symptoms of failure, besides the board stops working? Any signs of overheating, etc.?

Does the broken wire look like it was stressed (stretched) that might have caused it to break?

 

[Western]

Thanks for your input Chris.

Transformers don't fail very often.

I certainly agree

When they do it's usually because the original design was poor, or the construction was shoddy.

That could easily be correct, in general. In this case I have a feeling it is more a hostile environment that causes the grief ... despite the encapsulation. The ones that fail have mostly been running for some years already ... and only perhaps one out of the 20 - 60 units in a dairy may go faulty.

But to answer your original question, unfortunately no. Or at least I'm not aware of any source of any ready made switch mode transformers for general use.

Actually I wasn't really sure how to describe it ... it is not a switch mode tx ... it's more of a signal transformer.

It operates at around 4.7kHz and puts out a signal of around 4 volts unloaded. It has a centre tapped primary and a single secondary winding.

I have looked occasionally over the years for suppliers, but have never found any. Certainly I could get some wound ... but I'd need to buy maybe a thousand ... and I'm only likely to use 20 -30 a year perhaps.

I did recently build a coil winder out of an old battery drill ... with a foot control for speed and reverse ... which helps a lot ... but it's still a pain in the butt.

What are the symptoms of failure, besides the board stops working? Any signs of overheating, etc.?

Does the broken wire look like it was stressed (stretched) that might have caused it to break?

The sensing circuit just stops ... all the rest still works ok.

I've haven't really been able to get one apart without inflicting lots more damage ... so I haven't worked out what goes wrong. It took a number before I could actually tell how it was wound and how many turns etc,

There is one model where the designer used an output socket the same size as the boards 27v power socket ... right alongside each other mind you. No prizes for guessing why some of those die.

 

[rjenkinsgb]

You have next to zero chance of finding an exact matching part - but you do not need to get vast quantities made.
The winding company we use are happy to do small quantities.

Just have eg. 25 or 100 bobbins wound and add the ferrite cores yourself as and when you need them. That minimises the up-front cost.

 

[Western]

You have next to zero chance of finding an exact matching part -

That was kinda what I was expecting.

but you do not need to get vast quantities made.
The winding company we use are happy to do small quantities.

Just have eg. 25 or 100 bobbins wound and add the ferrite cores yourself as and when you need them. That minimises the up-front cost.

They're more my numbers. Any idea on a price range approximation?

Thanks for your help.

 

[ronsimpson]

Coilcraft.com

 

[rjenkinsgb]

For the place we use, at 100 off for complete assembled E-I core signal transformers, they charge around £6.50 each.
That's including vacuum impregnation of the finished units etc.

A good part of that cost is the laminations [an unusual type] and assembly, so just having a bobbin wound and vacuum impregnated would be more like £2 - £3 at a guess.

If you are in the UK, give them a try:
https://www.trans-tronic.co.uk/

 

[ChrisP58]

Thanks for your input Chris.

Actually I wasn't really sure how to describe it ... it is not a switch mode tx ... it's more of a signal transformer.

It operates at around 4.7kHz and puts out a signal of around 4 volts unloaded. It has a centre tapped primary and a single secondary winding.

Could be a push pull switcher, but that frequency is pretty low. What does that 4V signal look like? (o'scope image) Can you get at the pins of an operating board with two scope probes to look at the two outside legs of the primary winding? I'd be interested to see the waveform and timing of those two signals.

- - - - -
I use https://coilws.com/ for small batch production.

But also post here everything that you know about the transformer winding and construction.
Also the core material. The n30 marked on the cores in your first post is the core material. Does that match the material of the original transformer, or did you just get whatever was available in the same shape?

 

[Western]

Could be a push pull switcher, but that frequency is pretty low. What does that 4V signal look like? (o'scope image) Can you get at the pins of an operating board with two scope probes to look at the two outside legs of the primary winding? I'd be interested to see the waveform and timing of those two signals.

Sorry for slow reply ... I'd already sealed up the last ones.

Here are 3 shots ...

First is of outer legs of primary ...

2nd is of same ...

3rd is of secondary ... unloaded

 

[Western]

But also post here everything that you know about the transformer winding and construction.

Primary is centre tapped ... 65 turns each ... 130 total

Secondary 40 turns

Both .125mm

Also the core material. The n30 marked on the cores in your first post is the core material. Does that match the material of the original transformer, or did you just get whatever was available in the same shape?

Most originals have been N30, though occasionally there have been other numbers. There can be a lot of difference with other material ... but now I have a good supply of N30, I'm sticking with that.

I use https://coilws.com/ for small batch production.

If you are in the UK, give them a try:
https://www.trans-tronic.co.uk/

Coilcraft.com

Thanks for the links as well guys.

I am in Australia.