Power supplies

lefizz
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Power supplies

Postby lefizz » Tue Jan 29, 2013 6:19 am

Poor power supplies. I have heard many people say that they are having stabilty issues with these sticks and others. The usual response to this is suggesting get a larger PSU. I was thinking that most of these devices use effectively mobile phone chargers as PSU. These have very little need for much smoothing capacitance because they are use to charge a battery which acts like a huge capacitor.

However in stick PCs which also have next to no capacitance to smooth the supply you have the situation that neither the PC nor the power supply has enough micro farads to properly stabilise the supply so when the machine draws some current the supply voltage droops and the machine crashes. I think PSU modding could be a great way to make them more stable.

Just an idea




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trssho91
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Re: Power supplies

Postby trssho91 » Tue Jan 29, 2013 7:58 am

Good morning. My father and I just had this conversation yesterday! My only concern with a PC power supply would be it tends to have some voltage dips and spikes under no or low load. I would think what we need is cap like you said for it to be stable enough. This should act like the battery in a phone or tablet and smooth everything out. I personally use a ipad charger for most of my toys (raspberry pi, MK808, MK803 III, haven't gotten the video working on the gk802 - but I can't see it requiring more power than the rest). I have a Logitech G105 keyboard, G500 mouse, usb sound, usb ethernet, usb 4-port hub, and a kyb/mouse kvm switch and I never have stability issues. I found ipad chargers give very stable power and are very inexpensive on ebay. I also think a PC power supply draws too much in (if you care about UPS battery life or power cost on this low scale). If the 2A from isn't enough, how about the power supply for an external hard drive, HP printer, or my dad uses a pitney bows label printer power supply. All good 5 volt switching power supplies putting out more than 3A.

lefizz
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Re: Power supplies

Postby lefizz » Tue Jan 29, 2013 8:30 am

I have a lot of power supplies about. I might trying either modding a reasonable 2 a PSU with a few hundred uFarad's in various values. Eg 100, 10, 1, 0.1 or taking a 12v 2a psu a building a really good regulated 5 v supply from it. Again using a wide range of cap sizes to filter the supply and drop ESR.

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trssho91
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Re: Power supplies

Postby trssho91 » Tue Jan 29, 2013 9:02 am

You know, taking a larger power supply and stepping it down with your own conditioning never occurred to me, thats a really good idea. If you take a good solid 9-12vdc switching power supply, it could be something as simple as a 7905 regulator, a diode or two for isolation, and the right combination of caps. This would also let you use a automotive automatically resetting circuit breaker in line for safety. I had another idea, reducing the about of caps (just one or two to protect against spikes and dips) and using a 5 or 12 volt battery (depending on where in the circuit), this would create very smooth power and protect your device from data corruption if the power is lost abruptly for some reason. The part I am not 100% sure of off the top of my head is the right charging circuit for the battery. This could even maybe act like a portable battery pack for travel, if you assemble the whole works in a old network switch case or something. Just thinking out loud.

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trssho91
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Re: Power supplies

Postby trssho91 » Tue Jan 29, 2013 9:05 am

On a side note in case any device OEMs read these forums - the raspberry pi has a lone cap right behind the power connector for just this sort of an issue. It would be cool to see something like that in future devices- :)

lefizz
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Re: Power supplies

Postby lefizz » Tue Jan 29, 2013 9:37 am

The trouble is the form factor doesn't allow it. Sticks are a bit stupid really, no space for smoothing caps and very poor heat dissipation. Very small cubes such as the ouya and odroid make far more sense. You can clock the CPU much high whilst having no heat issues because you can fit a decent heatsink and ventilate properly. But the heat issues often happens with big brand routers so we can hardly blame Chinese no brand makes for following the same silly mistakes.

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lefizz
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Re: Power supplies

Postby lefizz » Tue Jan 29, 2013 9:40 am

The pi is very well designed a robust, if only they had Gig of Ram and a decent SOC. I use mine for xbmc and hardware decode is great but the menus etc run so poorly.

Still its a very cool because they can do so much. If only they had a bit more power.

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bogolisk
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Re: Power supplies

Postby bogolisk » Tue Jan 29, 2013 10:22 am

lefizz wrote:The trouble is the form factor doesn't allow it. Sticks are a bit stupid really, no space for smoothing caps and very poor heat dissipation. Very small cubes such as the ouya and odroid make far more sense. You can clock the CPU much high whilst having no heat issues because you can fit a decent heatsink and ventilate properly. But the heat issues often happens with big brand routers so we can hardly blame Chinese no brand makes for following the same silly mistakes.

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Agree. for a TV-box, the odroid-u2 has a great design. That's how you do case-as-heatsink design, the thermal design of the gk802 and most sticks just doesn't work. My gk802 keeps rebooting due to overheating after 45min of 2D gaming and about 20min of 3D gaming.

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trssho91
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Re: Power supplies

Postby trssho91 » Tue Jan 29, 2013 10:25 am

That's true about the design. I personally put mine in a dlink switch enclosure and replaced the heatsink with a mobo nb hwatsink. That also let me put my USB hub, sound card, and Ethernet in one nice little unit. I also use my pi for raspbmc, menu doesn't seem so slow when you use a rc6 remote exclusively, :)


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