Mac Mini Power supply upgrades

Paul Hynes · « **on:** 13 Jun 2010, 12:25 pm »

Hi folks,

Thanks to kenreau for starting the upgrade thread ball rolling with interest in the Mac Mini power supply.

There is very little information around for Mini up-graders so please feel free to post your own experiences in this thread and we can form a reference guide to upgrading the Mini.

Several of my customers have ordered regulator modules for the Mini power supply recently but they will not be able to give any feedback yet as they haven’t received their regulators. One of my customers (please feel free to join in Steve) has provided a very useful link to information about the DC connector and also a link to the source of a DC lead with a matching connector that can be adapted for use with linear power supplies. The links are :-

http://www.computeraudiophile.com/files/Mac%20Mini%20PS%20Cable_0.pdf

http://store.mp3car.com/MacPac_Power_Cable_Kit_p/cbl-002.htm

The first link is particularly interesting as it shows the requirements for the iSense connection to allow the Mini to boot properly. The two links solve the problem of interfacing a new linear supply to the Mini.

If anyone has links to additional useful information please let us have them.

The Mini requires a power supply with an 18v5 output and the supply that comes with the Mini is capable 6 amps continuous, to power the motherboard and allow the use of the usual peripherals that take power from the motherboard. A linear supply with these specifications will be somewhat larger than the standard Mini supply as it will be less efficient, demanding increased thermal management and a large mains transformer, which in turn will require a larger case to safely accommodate such a design. I will prepare some drawings to show the application of such a power supply using the heavy duty PR3HD-18v5 regulator module over the coming week as time permits. This can then be used as a starting point for assessment of what is involved when planning such a power supply project.

Regards
Paul

ferenc_k · « **Reply #1 on:** 13 Jun 2010, 08:50 pm »

Very interesting, keep us informed.

Paul Hynes · « **Reply #2 on:** 18 Jun 2010, 05:19 pm »

Hi Ferenc,

Is the power supply shown in the attachment what you are looking for.

SR7-18v5 rated at 6 amps continuous.

Regards
Paul

ferenc_k · « **Reply #3 on:** 20 Jun 2010, 07:25 pm »

Looks quite brutal

Paul Hynes · « **Reply #4 on:** 21 Jun 2010, 03:22 pm »

Hi Ferenc,

You have to get brutal with high power linear supplies because of the thermal management requirement and large transformers that are required to provide the high output current.

This power supply can deliver a lot more than 6 amps for transent loads.

Regards
Paul

ferenc_k · « **Reply #5 on:** 21 Jun 2010, 06:54 pm »

Sounds good

mintzar · « **Reply #6 on:** 22 Jun 2010, 04:36 pm »

What transformer did you use in that monster, if you don't mind me asking?

I was looking into this, or building a battery power supply for the mini. The problem is that because the Mini draws 6A of current it'd drain the battery too quicky so you'd need a very substantial battery. I was looking into wiring 3 6v batteries in series and finding a beefy regulator to make sure it maintains 18v, then putting a charger on the input to help keep it charged. Some of the nicer chargers will shut off when the battery is charged to prevent overcharging, and kick in once the battery gets below a certain threshold. I am still reading about the implications of these things, it's beyond my experience, but I figured I'd post it to see if anyone can take it and run with it.

Paul Hynes · « **Reply #7 on:** 22 Jun 2010, 05:13 pm »

Hi mintzar,

The transformer is a 160 VA low noise toroidal manufactured by Noratel.

Although a fully charged 6v battery will give more than 6v across it’s terminals, trying to regulate 18v5 from 3 x 6v batteries would leave you little window for operation before recharge even with a low dropout reg. You would be better of using two 12v batteries in series, to give 24v then regulating to 18v5.

If anyone else wants to run with this let us know and I will expand the project to include development of a working battery solution.

Regards
Paul

mintzar · « **Reply #8 on:** 22 Jun 2010, 05:33 pm »

Sure!

I just ordered a cheap Mini PSU brick off ebay. I'll crack it open and take some pictures if that'd be of interest to anyone. The primary reason that I bought it was to steal the DC connector from it. (Got it for $25 shipped, so it was cheaper than the MP3Car website).

I may start off attempting to build a Linear PSU for the mini and then try the battery as my PSU knowledge grows a little bit.

I was looking at the Antek TXs. The 300VA with 18v/8.3A looks good, but doesn't the PSU increase the voltage by 1.41? So i'd have 25v, which is more than I want. What am I missing?

Here's the TX I was looking at: http://www.antekinc.com/details.php?p=62.

Paul Hynes · « **Reply #9 on:** 22 Jun 2010, 05:51 pm »

Hi mintzar,

18 vac when bridge rectified and smoothed will give around 25.5 volts minus the diode drops plus the regulation factor of the transformer at the load drawn. There will also be a ripple waveform on the smoothing caps caused by the cap charging cycle that needs to be factored in for headroom. You can regulate down to 18v5 from this DC voltage, with reasonable headroom on the regulator, which will require a heat-sink.

Regards
Paul

mintzar · « **Reply #10 on:** 22 Jun 2010, 06:02 pm »

Good deal.

Another interesting question... is it possible to power two Mac Minis from one of these power supplies or would I need to build two power supplies?

Paul Hynes · « **Reply #11 on:** 22 Jun 2010, 06:21 pm »

Hi mintzar,

At present I am not sure what the actual current draw of the basic mini is without any peripherals connected (anyone know this let us know) so cannot answer the question for the SR7-18v5 power supply. The maximum continuous current for the SR7-18v5 is transformer limited to 6 amps. Transient current can easily exceed 50 amps as there is no current limiting on the IXIS output mosfet and there is plenty of drive voltage available to drive the mosfet gate.

For a battery supply it should be possible but working time before recharge would depend on the mini power draw and how many current drawing peripherals you use with the minis and the additional load would drain the batteries more rapidly.

Regards
Paul

mintzar · « **Reply #12 on:** 22 Jun 2010, 06:41 pm »

Paul,

Would your PR3HD-18v5 regulator work with both the battery supply and the linear supply? If size isn't a big issue, is there a way to design this supply without knowing the current draw -- i.e. overcompensate?

Here is a link for those looking to learn about regulation/PSU/etc...
http://knol.google.com/k/electronic-circuits-design-for-beginners-chapter-4#

I'm reading it now in the hopes that it will help avoid some of the obvious questions. I figured it would help others looking to undertake this project as well.

mintzar · « **Reply #13 on:** 23 Jun 2010, 12:56 am »

Another question...

Does the Mini need 18v5 Peak to Peak or does it need +18v5, -18v5?

I am figuring out what TX to get still. If the TX has dual secondaries, then I could use a 2x 12v for Center Tap to get 24v and then regulate that down to 18v5. That's only if the Mini needs 18v5 peak to peak. If it requires +18 - 18 then I'd have to get a 20-24v TX rather than the 12v TX. Thoughts?

Paul Hynes · « **Reply #14 on:** 23 Jun 2010, 09:51 am »

Hi mintzar,

The PR3HD-18v5 regulator would need to be re-configured for use with a 24 volt battery.

The PR3HD-18v5 regulator cab be configured to provide more power by selecting a suitable output device and ensuring the heat-sink the module is bolted to can dissipate the heat generated. The transformer rating would also have to be increased. I am afraid to say that this gets into rather costly heavy engineering very rapidly and it would be more sensible to use one supply per mini. This will also remove a source of HF noise from each mini cross coupling through the power supply ground.

Thanks for posting the link. This will benefit many who wish to understand more about the basics or power supplies.

The mini needs 18v5 DC. An 18 vac transformer winding is an ideal match for this configuration. You could use 2 v 18 vac in parallel or 2 x 9 vac in series.

Regards
Paul

BPT · « **Reply #15 on:** 23 Jun 2010, 01:14 pm »

Mintzar:
The Mini will run on DC voltage between 12-19.

Paul Hynes · « **Reply #16 on:** 23 Jun 2010, 08:44 pm »

Thanks Chris,

This is useful information. Can you provide a link to this data so we can analyse the current requirements over the operating voltage range?

Regards
Paul

Mike Nomad · « **Reply #17 on:** 23 Jun 2010, 09:29 pm »

You know that the minis no longer use an external power supply...

http://www.apple.com/macmini/

Paul Hynes · « **Reply #18 on:** 23 Jun 2010, 10:35 pm »

Hi Mike,

Yes I am aware that the mini has moved on. This does not mean that previous versions are obsolete for audio server purposes. The goal of this thread is to work out a first class power supply solution for those who own an older version of the mini, with external power supply options, and there are many out there.

Regards
Paul

mintzar · « **Reply #19 on:** 23 Jun 2010, 11:12 pm »

Plus I'd imagine it wouldn't be impossible to bypass the Mini's new internal power supply with this one we're building...