New power hub using desktop PC PSU?

[Stargazer33]

Hi, I think it's about time I upgraded my power supply box and I was thinking about using the power supply from a desktop computer. They have multiple power outputs of both 12v and 5v DC as well as a built-in cooling fan. I could step up one of the12v feeds or the mount (say to 13.4v) and step up a 5v supply or down a 12v supply for the DSLR feed (to about 8.4v).

Does anyone know of a problem with this? I am wondering if the PC power supply unit is stable enough.

Would be interested to hear your thoughts/views. 

[iapa]

Good quality PSUs for your desktop PC are stable - at room temperatures. 

You would need to check spec. sheet for your PSU of choice to confirm its working environment parameters.

I've a 1kW PSU that has goos specs - think I may investigate this further (great minds - fools seldom differ - monkey see monkey do !!! :):):):)

 

[Gina]

I would think that's fine.  I use "buck converters" to give me other voltages - mainly from my main supply of 13.8v down to other voltages but also to convert 3v from a Lithium Ion cell to 9v for my digital oscilloscope to make it a battery portable unit.  These buck converters are switching power supplies that change the input voltage to a different output voltage very efficiently.

[Stargazer33]

Thanks iapa, Gina.

I have got a couple of buck converters in my current power box which I was going to recycle into the new box.

One reason for the upgrade is due to my DSLR cool box, as the peltier cooling plate draws about 6 amps! The feed wire gets too hot also. It was a cheap unit from China I bought off eBay after reading an article in one of the astronomy mags. I am going to get a lower current draw one - I believe Maplins do a good one.

This could be my Christmas project for this year.

[SkyBound]

Computer power supplys are "switched" power supplys,  which means you can get lots of noise or interference from them which is not good for camera equipment, whereas a bench power supply is well regulated and so much cleaner....  

just something to think about

[iapa]

@SkyBound as are most of the mains - 12V 5A adapters we buy?

Agreed a bench PSU is the way to go - as long as it's metering is accurate

[SkyBound]

2 minutes ago, iapa said:

@SkyBound as are most of the mains - 12V 5A adapters we buy?

Agreed a bench PSU is the way to go - as long as it's metering is accurate

So how do you isolate the "noise" from them, do you just use ferrite beads on all input and output cables..?

[iapa]

Actually, yes, I did buy ferret cores for the PSUs used for the mount and cameras, but don't both on the focus motors, dew heaters etc..

 

http://www.maplin.co.uk/p/ferrite-clip-on-hem3017-n94ab

[SkyBound]

1 hour ago, iapa said:

Actually, yes, I did buy ferret cores for the PSUs used for the mount and cameras, but don't both on the focus motors, dew heaters etc..

 

http://www.maplin.co.uk/p/ferrite-clip-on-hem3017-n94ab

Why not on the focus motors and dew controllers, I would have though the motors and PWM control from the dew controllers would have needed them, certainly the motors would cause noise I would have assumed

i have used those ferrite cores, but far cheaper on eBay, I got 20 for £6

[Gina]

DC motors cause interference, stepper motors don't.  PWM certainly causes interference and needs RFI filtering as close to the switching device as possible.

[Stargazer33]

I thought RF was only a problem with audio signals or radio transmissions. How does a noisy power cable affect a mount? 

[iapa]

12 hours ago, SkyBound said:

Why not on the focus motors and dew controllers, I would have though the motors and PWM control from the dew controllers would have needed them, certainly the motors would cause noise I would have assumed

i have used those ferrite cores, but far cheaper on eBay, I got 20 for £6

Why use then on dew controllers? They only need power, its not really controlled is it?. You could run AC through them and still get the heat.

Ditto th serve focus noters that I have, all we need them to do is one in and out - software controlled to eyeball MK I - it will sort it self out as the image is checked - at least at my noob pre=beginner status.

I got some from eBay, and they shattered in the cold; -5c may be ok for camera (actually it's great :)) , but not cheap 'ferrrite' cores. When that happened, they look ed like they suffered from mental fatigues, shiny crystalline structure,

 

[SkyBound]

39 minutes ago, iapa said:

Why use then on dew controllers? They only need power, its not really controlled is it?. You could run AC through them and still get the heat.

Ditto th serve focus noters that I have, all we need them to do is one in and out - software controlled to eyeball MK I - it will sort it self out as the image is checked - at least at my noob pre=beginner status.

I got some from eBay, and they shattered in the cold; -5c may be ok for camera (actually it's great :)) , but not cheap 'ferrrite' cores. When that happened, they look ed like they suffered from mental fatigues, shiny crystalline structure,

 

I was a bit confused here, are there a few typos, or......??

[SkyBound]

1 hour ago, Stargazer33 said:

I thought RF was only a problem with audio signals or radio transmissions. How does a noisy power cable affect a mount? 

I didn't say affect the mount, more the data cables to and from cameras...etc...

[Gina]

Yes, interference can cause stripes in the camera image though I haven't experienced it myself. 

My observatory PSU is a switch mode type but charges a car battery which then supplies all the power for the astro equipment.  Also, the PSU and battery are in the warm room and a couple of metres from the pier and sensitive equipment.  Power is supplied through a couple of heavy duty cables and I have a 4700µF electrolytic capacitor plus a 100nF ceramic for RFI blocking, in my power distribution box on the mount.  This may be overkill but it works

[Alien 13]

A lot of switching PSUs regulate the output voltage by shifting the frequency, cable inductance/capacitance can cause delays to the high frequency noise component of the output voltage which on their own might not cause an issue but can set up changing beat frequencies which will be visible to a sensors electronics as well other kit connected to it.

Alan 

[iapa]

14 hours ago, SkyBound said:

I was a bit confused here, are there a few typos, or......??

So, I only use them on cameras and mount. Why use them on dew controllers etc. ? They only need power, its not really controlled is it?. You could run AC through them and still get the heat

Ditto the servo focus motors that I have, all we need them to do is one in and out - software controlled or checked by yeball MK I - it will sort it self out as the image is checked - at least at my noob pre=beginner status.

I got some from eBay, and they shattered in the cold; -5c may be ok for camera (actually it's great :)) , but not cheap 'ferrrite' cores. When that happened, they looked like they suffered from metal fatigue, showing shiny crystalline structure,

 

[SkyBound]

10 hours ago, Gina said:

Yes, interference can cause stripes in the camera image though I haven't experienced it myself. 

My observatory PSU is a switch mode type but charges a car battery which then supplies all the power for the astro equipment.  Also, the PSU and battery are in the warm room and a couple of metres from the pier and sensitive equipment.  Power is supplied through a couple of heavy duty cables and I have a 4700µF electrolytic capacitor plus a 100nF ceramic for RFI blocking, in my power distribution box on the mount.  This may be overkill but it works

Hi Gina,  can I ask where do you put the capacitors you use in your power control box, would it be across the incoming power + & - wires..? As that is something I could do on mine.

[Gina]

Yes, precisely

[SkyBound]

1 hour ago, Gina said:

Yes, precisely

And would that mean there would be no need for loads of ferrite cores on all the possible wires that could cause interference, inside my power hub,  or would I still need those...?

my power box is fed by a bench supply of 13.8v 

[Gina]

I don't use any ferrite beads.  I used to when I had PWM for something but I don't use PWM anymore.

[RayD]

10 minutes ago, SkyBound said:

my power box is fed by a bench supply of 13.8v

Is your "bench" supply not a linear one?  If it's a fairly reasonable one I would think it would be, and doubt that you would need any additional ferrites or caps as the ripple is generally not enough to cause issues associated with switch mode supplies (noise, heat etc.).

[Stargazer33]

23 hours ago, SkyBound said:

I didn't say affect the mount, more the data cables to and from cameras...etc...

Sorry SkyBound, I was referring to iapa's comment on using ferrite beads on his mount cables; but I guess he meant to stop any rf generated by the mounts motors affecting sensitive equipment and not as I interpreted it as stopping rf from affecting the mount itself. 

[Stargazer33]

12 hours ago, Alien 13 said:

A lot of switching PSUs regulate the output voltage by shifting the frequency, cable inductance/capacitance can cause delays to the high frequency noise component of the output voltage which on their own might not cause an issue but can set up changing beat frequencies which will be visible to a sensors electronics as well other kit connected to it.

Alan 

I think I need to go back to school! 

[RayD]

In response to the original question I would say yes it will definitely work, no doubts about that, but in my personal opinion it's not an ideal solution for a couple of reasons:

• I would doubt very much that an older PC supply will be a regulated linear supply.  Linear ones normally have great big heat sinks on them as they burn off the non used energy as heat.  Be mindful that each leg and its associated circuits are designed to run at that voltage and changing this will affect the current.  It will already be operating via a DC-DC convertor so be carful when doing any further mods.  It may be unregulated, or even switch mode, neither of which is ideal, and not what you could consider a real "upgrade".
• A PC supply is designed to work in a pretty controlled environment, not really one conducive to the ones we generally experience with AP (cold, damp etc.), unless you are planning to mount it in an obsy. 

To consider a power supply a real upgrade, as you have mentioned, you may want to look at a reasonable quality linear regulated supply.  The Nevada one FLO sell seems reasonable for the cost (£35), and for a few quid more you could get one with adjustable and metered output voltage.  I have one of the FLO ones and another 30A one (amateur radio) from which I run 2 separate supplies.  If not suited to external use it can be mounted inside, with a DC extension lead to a power distribution box at the mount (this is what I do and it works a treat and at relatively low currents you don't need to worry about voltage drop).  If you can't find one suited to outside use, and this is what you need, then reality is you are not going to beat the safety and guaranteed clean supply from a decent and properly rated battery (accepted that this is probably not what you're after).  Alternatively there are some externally rated supplies available for astro use, but they are expensive (relatively per Amp).

Regarding noise and alike as mentioned above, I would say the only way on a generated DC bus to totally eliminate it is to run multiple supplies for each piece of very sensitive equipment, which starts to get very costly.  If you really want no noise, then you are looking at VERY high end supplies, which are very expensive, and even on these there is still some ripple, so it's still not a totally clean or smooth DC supply like you would get from a battery.  You could run a cheaper switch mode for non critical items such as dew heaters if you hit problems, but with a decent supply I would doubt that very much.  

Ultimately I guess the only way to see would be to try it and see how your specific equipment behaves.

Keep us posted if you go the route of the PC supply as it will be really interesting to see it working