Transformers

[Isaac Newton]

Hy guys,

That's a simple question but, since I don't have any experience with production... So, how do I get a costumized  transformer manufactured?

[PA0PBZ]

First ask yourself if you really need a customized one, there are so many different for sale that there should be something that you can use out there.

Then, is it a one-off or do you need a lot? If it is only one you could make it yourself, either by getting a DIY package or stripping an existing one, you can probably leave the primary on.

If you need a lot, just contact a company specialized in this.

[Isaac Newton]

I need a lot. Do you know any company that make transformers?

[Kremmen]

Transformers are heavy (unless real tiny) and you may want to have them made relatively close to where you are to save on delivery costs. Seeing how you fly the Brazilian flag this one could be a tough one for most of us to answer. I could easily tell you who make trafos here in Finland but that could be less than useful info for you...
I agree with those who recommend a standard part. It would be worth it to revise your design a little to accommodate such a standard component. That way you make long term maintenance also feasible / far easier.

[mariush]

Look in the well known online stores (digikey, rs online, farnell/newark/element14 , mouser) what manufacturers of transformers are there, then get some random datasheets for them and get the contact information.

Send emails etc ...

Just from the top of my head I can think of Hammond Manufacturing, Triad Magnetics.. simply because I checked Digikey a while ago and their inventory.

But if you're thinking of making a small switching power supply for your device, you may be better off to get an OEM power supply, with or without the plastic case and optionally strip the plastic out.

[Bloch]

That's a simple question but, since I don't have any experience with production... So, how do I get a costumized  transformer manufactured?

That i do is give the manufacture my requirements (I only buy 50/60HZ transformers)

• VA
• Pri.  voltages
• Sec. voltages
• C-Core / Toroid / EI
• Approvals

They will give you the size /price / delivery time for the transformer.

Transformers are heavy (unless real tiny)

Well the box we get the 4,5VA in is ....    HEAVY 

I agree with those who recommend a standard part. It would be worth it to revise your design a little to accommodate such a standard component. That way you make long term maintenance also feasible / far easier.

well if the order is big enough e.g. 500VA in > 100 pcs Then there are not much differens in price.

[Isaac Newton]

I was thinking the same thing: The weight.

The aplication I'm intending to use just have a pic16f, a couple of latching relays, some LEDs and a couple of opto-couplers + the good and old pacives.

I'm still in the prototyping stage with this project, but I like to let the minimum to the stage of refining for production. I basicly have 3 options:

1- Use a transformrless powersuply (subject of an other post i started), which I thing is a little bit risky because it does not isolate the circuit;
2- The old and hungry, but still usefull, linear regulator with a transformer and a voltage regulator;
3- A sitching-mode power suply, which I believe is the best option for the power consumption, but I guess It needs lots of ajustments and headichs to get it right.

Well, I found the Rohm BP5041a5, but I'm a little worried about then because I could not  find any similar on the market so, for production, I think it's not very good...

[Kremmen]

Think very very carefully before deciding on a nonisolating mains supply for your application. That is appropriate only in very specific cases and absolutely a no-no if this gadget of yours is anything you are supposed to operate in some way. The Rohm part you mention is a very small device but it is also nonisolating and i believe most on this forum would agree with me when i recommend against considering it for any "ordinary" purpose.
The components in your application are in themselves not an obstacle to using such a component but the intended end use might very well be.
A safe and easy option would be to use a small regular mains transformer followed by a buck switcher. It will not be anything like the Rohm part in size, but the big benefit is that nobody dies and the house won't burn down (or check AcHmed's suggestion below)..

P.S. After reading your other post let me emphasize that powering a circuit directly from the mains should not be considered a "neat trick" or an easy way to save on component count or anything like that. It is a quite dangerous decision and should only be taken after competent evaluation of the risks involved. Based on the information so far, i am not sure if you can make such a competent evaluation. I may be mistaken of course but it would be good to get more data on your application in that case.

[kxenos]

Or something like this http://export.farnell.com/myrra/47133/power-supply-3-2w-9vdc-unreg/dp/1825786
A complete SMPS in the form of a small trasformer. Mind you, it will require some linear post regulation to get 5Vdc.

[Isaac Newton]

A safe and easy option would be to use a small regular mains transformer followed by a buck switcher. It will not be anything like the Rohm part in size, but the big benefit is that nobody dies and the house won't burn down (or check AcHmed's suggestion below)..

Yeah, I really need to use some sort of insulation.

Maybe the little transformer and the buck regulator is the best option. Both for safety and power consuption...

[ptricks]

You don't need to go custom on a transformer for a small current device like that. You can get already produced transformers very cheap. I always tell people to go with a transformer design over a switched design if the current is small. I recommend linear vs switched because linear at low currents is cheap and the parts count is low as well as the complexity and chances of something failing in the long term are much lower.

I use a lot of the tamuracorp transformers and if you get one that is low voltage and add a LDO regulator your waste or heat generation at low current isn't anything of concern.
http://www.tamuracorp.com/

Check surplus sites too, they often have transformers cheap. I got some of the tamura for about $2 each, retail is $9 each.

[Kremmen]

I specified small Tamuras as well for a recent design for a +24V linear / +5V buck aux pwr combo. Easy as pie and the trafos were just 2,28 € in lots of 50 from Mouser (their code 838-3FD-336).

[Isaac Newton]

I use a lot of the tamuracorp transformers and if you get one that is low voltage and add a LDO regulator your waste or heat generation at low current isn't anything of concern.

An other thing I'm a bit concerned is the current peaks when the latching relays are setted or resetted. Shure I can put a transformer that can handle that but, since I'm looking for something cheep and the latching relays won't be setted or resetted frequently, I'm thinking in putting a small capacitor bank after the LDO to handle that. I think this way I can minimize the costs with the transfomer... I know the relays won't consume very much but I think It will reduce the size of the transfomer.

[IanB]

An other thing I'm a bit concerned is the current peaks when the latching relays are setted or resetted. Shure I can put a transformer that can handle that but, since I'm looking for something cheep and the latching relays won't be setted or resetted frequently, I'm thinking in putting a small capacitor bank after the LDO to handle that. I think this way I can minimize the costs with the transfomer... I know the relays won't consume very much but I think It will reduce the size of the transfomer.

Regulators don't like big capacitor banks on the output side. Follow the data sheet and don't make the output capacitor any bigger than recommended.

Small current surges are no issue at all for a transformer. Transformers are big lumps of iron and copper. They can supply multiples of their rated average current for short periods without breaking a sweat.

Of more concern to you is the regulator. You need to make sure the absolute maximum current is not exceeded, but many regulators have current limiting to protect them in the case of a temporary overload.

Since you seem to be a little over your head in design skills, I'm wondering what kind of production quantity and market you are thinking of for your device? Is it for your own use or do you want to sell it?

[ciccio]

You write that you need a lot of these transformers, so I believe that your design is for a commercial product.
This means that you will be obliged to have it made in compliance with the relevant (in your country) safety regulations.
I don't know about them (Brazil in not Europe (no CE marking) nor USA or Canada (no UL or CSA marking), but surely there are regulations (I believe that  INMETRO is the name of the regulatory body) and they will be enforced (think about product liability in case of damages  to people or goods due to a transformer that burst in flames...).
My suggestion is to look for a local, reliable manufacturer. They will know how to make a compliant product.
It should not be difficult to search for one: the Chamber of Commerce could help you,   or you can find a label glued to some transformer inside some product...
Another option is to contact an international manufacturer and ask if the can supply a product that is compliant with Brazilian regulations.
Best regards

[Isaac Newton]

Yeah, I'm thinking in selling it.
I'm a Electrical Engineering student and have been a electronics hobbyist since I remember. I don't have very much experience in production, but I'm intending to start learning this by my self since my college sucks in the pratical side of engeneering, which is kind of a paradox, since It is, well, Engeneering... Well, but this is a problem in most of the colleges here in Brasil...

Getting back to the topic: Yeah,   INMETRO is the regulatory body and I think they have similar standards to most of the countries arround the world. 

[SeanB]

For most latching relays they only need a 20-50mS pulse to change, easy to do with a 2200uF capacitor on the secondary side to provide the energy. Even if it is charged with 1mA it will drive the relay to change if it is at the rated voltage or the pulse voltage.

[Kremmen]

Yeah, I'm thinking in selling it.
I'm a Electrical Engineering student and have been a electronics hobbyist since I remember. I don't have very much experience in production, but I'm intending to start learning this by my self since my college sucks in the pratical side of engeneering, which is kind of a paradox, since It is, well, Engeneering... Well, but this is a problem in most of the colleges here in Brasil...

Getting back to the topic: Yeah,   INMETRO is the regulatory body and I think they have similar standards to most of the countries arround the world.

OK, selling your design should be doable - lots of companies and individuals do it all the time. I have no idea about the applicable product liabilities in Brazil so this is just based on how things are roughly done here. There are 2 things you really need to sort out for yourself:

1) the requirement for formal conformity to code and regulations. That i guess is where INMETRO would/could enter the picture. In Europe we have the CE mark, what you have is for you to find out and then act as you see fit.

2) the actual product safety and compliance in real life. This is largely associated with sound design principles and best practices, not so much rules and regulations, although the 2 have a strong correlation. To cover this point, you need to find out the relevant design rules, recommendations and practices that directly apply to safety and Electromagnetic Compliance (EMC). Things that come to mind here are:

- As a mains supplied device, your design automatically comes into the scope of such standards as  IEEE 587 and IEC 60664;1-5. Now you get rules: these standards have strict requirements for things such as overvoltage management, impulse voltage and current tolerance, minimum flashover and creepage distances in circuit boards and other structures in high energy circuits. And lots more. Your mains input automatically by its nature becomes a circuit classified at least as IEEE 587 Cat A / IEC 60664 Cat II. It would be good for you to understand what that means.

- For EMC the device needs attention to EMI filtering and power factor correction. The latter in this particular case is hardly needed but wherever there are switching power supplies, interference is possible. It would be good if you at least understand the intent and aim of such documents as EU Directive 2004/108/EC, CENELEC EN 61000-6-1, -6-3 and VDE 0871. In your case the power levels may be low enough not to worry, but at least understanding that this legislation exists is your advantage.

In my country the local electrical code and legislation states something like this (not verbatim) "It is permitted for individuals to maintain such plugged electrical devices they have constructed for themselves for their own use...". The code specifically allows maintenance, by extension it must allow construction, because if not, there can be nothing to maintain. I have not the slightest idea if this applies for you or if it is relevant to your product. However, offering the product as a kit that plugs into the mains would fulfill the wording of that code. And limit your liability at the same time, since it would be the buyer who builds the device. In case of accidents, it would probably/possibly be enough if you can demonstrate that the design fullfills the stipulations of the standards as far as safety is concerned.

I don't mean to scare you but really, do think carefully about safety when thinking about selling products connecting to the mains. Lots of the chinese onehunglow manufacturers do not, and as the old Romans used to say - vestigia terrent.

[IanB]

If you look at almost anything you buy these days that is mains powered it comes with a wall plug low voltage power supply that is packaged separately. This is a very good way of separating mains power concerns from the design of your product, as well as providing significant user convenience (convenient since the low voltage DC power cord can be thin and flexible rather than thick and bulky in the case of a mains cord).

If you are thinking of selling a small volume kit or product you should consider the same option. Find a wall plug type power supply that already has the appropriate safety features and design approvals and purchase it ready made.

[Kremmen]

Excellent advice 

[Isaac Newton]

Thanks, guys.