Merging power supplies

[Jon86]

To find if you've only got one rail, you'll just have to read the specs, normally they're single 12v rail I think.

[Jon86]

I think the problem you're going to have with these ATX supplies is that you're not using them for how they're designed, therefore you're not going to have a great amount of success or reliability.
If you can afford it, you'd be much better off just getting a dedicated 12V supply that can handle what you need in one unit, then you won't have to screw around with balancing.

http://www.ebay.co.uk/itm/12V-10A-120W-16-7A-200W-20-9A-250W-29-2A-350W-PSU-Power-Supply-Transformer-/190899007235?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&var=&hash=item2c7277af03

[axero]

I know I'm seemingly jumping between subjects here but that is because I've been wondering a lot about this.

A common scenario where it is tempting to merge power supplies into one is for low-voltage halogen lights. I think it was this particular scenario that started these thoughts. There are mechanical AC transformers and there are electronic transformers. Many of the electronic transformers for halogen lights are really bad and they even make the filament burn out prematurely. I think one should be careful with the electronic ones even though many of them do have overload protection. The mechanical ones which are just simple transformers should be similar to the DC transformers when it comes to merging as long as they are using the same phase. But with AC voltage we can now use coils and capacitors as ballasts if we want to. I'm open to input about this. But then again, power supplies for halogen lights are not that expensive...

The main reason for starting this thread is for a project that I'm discussing in this thread

https://www.eevblog.com/forum/projects/acpi-power-saving-circuitry-for-150-w-pci-devices-%28ie-gpus%29/

I wanted to get through the basics here before moving on with that project. There are pretty good posts in there already. I myself always use good PSUs for computer hardware but I cannot assume that *everyone* is. So therefore it is good to know what is required to meet the plain vanilla ATX specifications and what is not so that I cover as many user scenarios out there as is reasonably possible. There are good posts in that thread already discussing this but maybe I should give the ATX whitepaper a good read too. The intention with merging the input terminals as described in the project is to save on components.

There are PSUs that are merged into one when I come to think about it. They are found in enterprise-grade hardware where you can hot-swap each should one fail. Most likely a load sharing controller is being used to put them together.

[AG6QR]

Ok, let's go back to ordinary power supplies. I've read a prior comment that ATX PSUs are bad. Sure a cheap one is bad but a certified one must be good ríght? There are bronze, silver, gold and platinum certified PSUs. I don't know much about them more than that a higher certification implies better components inside the PSU and higher energy efficiency.

A certification is only as good as the certifying agency and the certification criteria.  Be careful that you're not putting a lot of faith in a certificate that comes from a thinly disguised marketing agency.  Be sure to read the certification criteria to determine whether it's relevant to your use.

At best, certifications would concentrate on the factors that are relevant to the intended use.  That is, using one ATX supply to power one computer motherboard with accessories.  Good ATX supplies are good at what they're supposed to do, but they may not be so good at operating in parallel, or charging batteries, or providing low ripple, or operating with an external source of voltage on their output.

[AG6QR]

There are mechanical AC transformers and there are electronic transformers. The mechanical ones which are just simple transformers should be similar to the DC transformers when it comes to merging as long as they are using the same phase.

I think you may want to study up on transformers:

http://en.wikipedia.org/wiki/Transformer

None of them are mechanical.  They're all electromagnetic.  Since they work via induction, there are no "DC transformers".

While we're at it, we don't "merge" power supplies.  Occasionally, we may want to operate them in parallel, but that's generally a very bad idea unless they were explicitly designed with parallel operation in mind.

[axero]

Back where I live, transformers for low-voltage lighting are classified either as 'mechanical' or 'electronic'. I can assure you that it wasn't my idea to give them that name. The distinction is made especially for dimmers where some supposedly don't work for the former and other don't work for the latter transformer type.

[tehmeme]

Back where I live, transformers for low-voltage lighting are classified either as 'mechanical' or 'electronic'. I can assure you that it wasn't my idea to give them that name. The distinction is made especially for dimmers where some supposedly don't work for the former and other don't work for the latter transformer type.

where do you live?

[axero]

Ok, look here then;

http://www.el-grossisten.com/pl/Halogenbelysning_Transformer_1407.aspx

[AG6QR]

Ok, look here then;

http://www.el-grossisten.com/pl/Halogenbelysning_Transformer_1407.aspx

In English, those are not "transformers".  OK, perhaps the Danish term "Transformer mekanisk" could be translated to the English "transformer".  I'm not sure what is in it, but it looks like it might be a transformer.  It's not mechanical, though, at least not in the sense of the English word "mechanical".  It has no moving parts; no gears, levers, inclined planes, pulleys, ball bearings, four-bar mechanisms, or similar devices.  It works based on electromagnetic principles.

Similar languages often have "cognates", words that have similar sound and meaning in the different languages.  But beware of the "false cognates", words that sound similar but mean different things.   I could tell stories about misadventures involving the English "embarassed" and Spanish "embarasada" (pregnant); or "excited" and "excitado" (aroused).

I'm sympathetic to the problems of a second language, but when we post on an English language board in English, we should use English words with their English meanings.

[Eddie]

Trying to run power supplies in parallel is asking for trouble unless the power supplies are designed to be used that way (as in a telco installation).

If you need higher amperage than what you can get from what you have buy / build a power supply that can supply what you need for your project. Remember linear power supplies are easier to make but thay weigh a lot more and tend to be more reliable (in my experience) switch mode are nice and light but can have voltages I shy away from now a days, also switch mode power supplies can have harmonics on the output and can have other undesirable (for RF people like myself) frequency radiated from the cct.

What are you trying to run and what amperage are you looking at needing for your project?

Cheers Eddie

[lapm]

Ok, let's go back to ordinary power supplies. I've read a prior comment that ATX PSUs are bad. Sure a cheap one is bad but a certified one must be good ríght? There are bronze, silver, gold and platinum certified PSUs. I don't know much about them more than that a higher certification implies better components inside the PSU and higher energy efficiency.

A certification is only as good as the certifying agency and the certification criteria.  Be careful that you're not putting a lot of faith in a certificate that comes from a thinly disguised marketing agency.  Be sure to read the certification criteria to determine whether it's relevant to your use.

At best, certifications would concentrate on the factors that are relevant to the intended use.  That is, using one ATX supply to power one computer motherboard with accessories.  Good ATX supplies are good at what they're supposed to do, but they may not be so good at operating in parallel, or charging batteries, or providing low ripple, or operating with an external source of voltage on their output.

Lol, i was about to ask this too. Certified by who and to do what exactly... Without knowing that certificate is not worth paper its printed on.