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rubecula

Equipment power supply

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I'm about to change from DSLR imaging to a CCD and will also add a filter wheel and focuser.  I've got too many 12V transformers as it is, with this extra kit it will become impossible.  I intend to get a single output power supply that will provide 300W, something like this:

https://www.mouser.co.uk/ProductDetail/MEAN-WELL/SPV-300-12?qs=bXBibfwyPRGop1klGb8bvQ==

but I was wondering if I should go for 12V output or something a little higher, say 13.5V.

 

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Hi Robin.

I agree with the idea of going a little over 12V, for various reasons.

The Meanwell supply from Mouser is adjustable to 13.2V.
Though it looks like you might have to add a couple of external resistors to do this.
Don't foget though that this is intended for mounting inside a case.
The live terminals are exposed and you can drop things into the ventilation slots.
If you are happy with this construction, then you have a lot of choices - not just this Meanwell supply.

If you think an enclosed (bench top) supply is more what you need. Take a look at these:

https://www.rapidonline.com/rapid-sps-9250-209mg-smps-switch-mode-power-supply-15v-25a-with-digital-display-85-1824

Beware of products offered from retail type outlets.
They often struggle to meet specification. For example a headline '10 amps' might be only for a short time with 5 to 7 amps available for continuous use.
Maplin used to be a major player in this - you only found out when you checked the small print or equipment stopped working.
This was done especially on CB radio power suplies. The idea being you were not transmitting continuously so they could play 'specmanship' and keep cost down.

Mouser is principally an industrial supplier so tends to sell products that do what they are supposed to do.
Rapid sell to industry and to education.

Do you really need 300W (25 amps). High power costs high money in general.

Hope this helps, David.

Edited by Carbon Brush
Additional info
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Thanks all for your replies.

I think I need 300W. At the moment it looks like this:

Mount = 4A, Camera = 2.5A, Filterwheel = 0.3A, Dew Heaters = 10A, Focuser = 2.4A, total = 19.2A So allowing a bit of headroom I thought I'd go for a 25A.

The focuser is a guess, I'm not sure after all this whether I can afford a Moonlight or similar so was thinking of having a go at making  an arduino based one.

Do you think I could get away with 20A?

Thanks

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10A seems a lot for dew heaters (that's 120W altogether! - usually a watt or two per dew heater is sufficient unless it's extremely cold and damp) and 2.4A is a lot for a focuser - mine use a few hundred milliamps.  Please check you calculations again.  I think 20A should be quite sufficient on the assumption that you've overestimated.

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For my normal 'garden' setup, I just tap off power from the local computer PSU (250watt 12v & 5\3.3v very well regulated & clean), which drives the computer (full PC), mount, heaters (2), cameras with coolers (2\3), focusers (2), filter wheel etc., and I've never had any issues with low power, on any device

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On 12/12/2018 at 15:03, rubecula said:

I think I need 300W. At the moment it looks like this:

Mount = 4A, Camera = 2.5A, Filterwheel = 0.3A, Dew Heaters = 10A, Focuser = 2.4A, total = 19.2A So allowing a bit of headroom I thought I'd go for a 25A.

I don't think you'll be slewing, focusing and changing filters all at the same time. And, as Gina wrote, 10 A for dew heaters is an awful lot. I have the 150 W meanwell, and "room to spare".

Edited by wimvb
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You may want to consider consolidating to two supplies, a larger capacity model for the drives, heaters, filter wheel and focuser, and a smaller, very clean supply for the camera. While the camera will certainly incorporate internal linear regulators for the critical rails, keeping the input voltage as stable as possible can only eliminate some potential noise sources. As for voltage levels, I would review the specifications for each piece of equipment to be sure that you're supplying a value which is within design limits. Some telescope drives which will operate at 12 V can tolerate and may perform a bit better at higher voltages, but that may not be true for other equipment in your inventory.

I've found re-purposed laptop power supplies to be suitable for applications requiring stable DC voltages across a range of load conditions. Most of your equipment won't be affected by a small AC component or occasional voltage spikes superimposed on the DC level, but it isn't a bad idea to measure the AC voltage level at the load end when everything is operating. This would be most important for your camera, but if you dedicate a good quality supply to that device, you should encounter no difficulties.

As discussed in James's build thread, be sure to adequately size your DC supply cables if they are of any significant length to avoid series drops.

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