One power supply to "rule" them all

[NenoVento]

Hi all,

In my little observatory right now I'm using three different power sources, one for the telescope, one for the 12V mini-computer and another one for the 12V USB-hub (and sometimes even another one for the dew shield). I was wondering if it won't be simpler to have just one power supply to "rule" them all (please, allow me a little LOTR joke here) such as these ones:

Both of them are switching power supplies. The one above is the Lrs-200 series 200W, with 17A and 204W rated power (and three DC outputs). The one below is the Lrs-350 series 350W, with 29A and 348W rated power (and also three DC outputs). You can find them here.

Does this make sense or is it better to have a power supply for each device?.

Best regards,

NV

 

Edited February 23, 2021 by NenoVento
typos

[fifeskies]

I use a single supply for everything , just fuse every section when using a big supply.

Those bare skeleton supplies will need to be built into a suitable external box however.

[discardedastro]

Single supply is fine. I will say those boxes branded "NVVV" are trying to rip off MeanWell (branded MW in a quite stylised fashion on their units), who are a well-regarded manufacturer of SMPS. I'd stick to the real ones, e.g. https://uk.rs-online.com/web/p/embedded-switch-mode-power-supplies-smps/7059857/ - a little more dear, but you don't want a dodgy PSU blowing up all your kit when it decides to short the incoming AC across the DC outputs...

Any of those encapsulated/skeleton PSUs will indeed need boxing up, but that's very doable - just consider heat dissipation (you may want to think about hot airflow around your scope in an obsy - SMPS are obviously much better in this regard than linear supplies, but something to think about nonetheless)

 

[wxsatuser]

Just buy a decent supply like this one, you get 20amps with peak of 30Amps, more than enough for most.

https://www.nevadaradio.co.uk/product/nevada-psw-30h/

or this one, I use these to power my hamradio gear.

https://www.nevadaradio.co.uk/product/nevada-psw-30/

[pete_l]

There's no reason not to use a single power supply. Though I have to say I'm not keen on fans in outdoor equipment. You never know what they will suck in to the equipment . In addition, they seem to me to be the weakest link - often cheap units that cannot withstand long periods of use before becoming noisy (poor quality bearings, or ones that fill up with dust) and unreliable. Plus with a unit like this, it's meant to be incorporated into a "finger proof" cover, so you have to plan for airflow when designing your enclosure.

When the fans do fail then your heat dissipation stops too. I prefer passive cooling. It needs larger heatsinks and external ventilation, but fewer moving parts are always a good thing. Especially when you have a potentially damp environment or a shed that is home to creepy-crawlies or larger "guests".

[fireballxl5]

This is the beast that I got to power my dual scope/camera setup with plenty of spare capacity for a future IT and maybe mount refresh

https://www.nevadaradio.co.uk/product/nevada-ps-30m/

[Carbon Brush]

May I make a few suggestions on power supply choice?

Visit the manufacturer (not seller) web site. Is it a professional appearance?
Or are they an 'under the railway arches copy' of something else?
Is it a known name that has been around for a while?

Does the manufacturer list safety and EMC (electrical interference and more) certification?
If in doubt, it should be in the downloads area, as well in as downloadable data sheets.
If he is selling into the professional world, he needs this. If he sells (potentially unsafe and unreliable) product to the hobby market......
There have been plenty of imported product confiscations on safety grounds. Few recalls by proper manufacturers. 

What warranty does the manufacturer state? If you look at good names (Cosel, TDK Lambda  and Meanwell are examples), you see 3 to 5 years.
That is the measure of confidence the manufacturer has in his product.

Try to avoid a PSU with fan. These are often the least reliable component in a PSU. At least in a well designed PSU!
Think about this. A bench top supply may be used in a 25C room and have papers piled on top.
A chassis mount PSU, intended for inclusion inside equipment may have to handle a cabinet that is already at 40-50C.
Heat loss from your PSU in a cold shed is much less of an issue.

Buy with spare load capacity. You will buy a heavier mount with more powerful motors, add dew heating to more glass, want to power a mount computer of some sort. It all grows with time.
In addition, a 50% loaded PSU will in general last a few years longer than a 100% loaded PSU.

Chassis mount supplies, like those shown in the OP are not necessarily an unsuitable construction for an observatory.
It is very difficult (well impossible) to put a finger into contact with live parts.
However, they do need external methods of securing cables, and need fastening down.
On housing or location, just ask yourself what happens if you are a bit slow getting the roof on and there is a sudden downpour.

4mm terminal posts, cigar plugs and similar are good for a quick disconnect.
They are not really good for long term connection. I won't go into plating choices, current rating, etc.

Outside of a single PSU. Arrange for several power out connections, preferably each with a lower current fuse or PTC thermistor, or circuit breaker protection.
If you have a 30A rated PSU it may deliver 40A or more on overload. What happens if the (cheap unsuitable) little DC plug for your mount develops a short?
The short (no pun intended) answer is the cable and plug will heat to the point of melting the plastic cable insulation. You gave a burn hazard if you don't realise and start feeling around wiring.
Further, heating in a mount plug may conduct through to the socket inside the mount and damage the PCB. It gets expensive.
If you have a low current fuse in the line to the mount, this blows and there is no further harm done.

You can the see the two paragraphs above are hinting at building, or buying some sort of power distribution panel or box.

HTH,

David.

 

 

[SamAndrew]

I've got 3 of these, started off with one for my EQ6, that's been going fine in the obsy without issue for over a year now. Then I got a second one for my pegasus pocket power box and a 3rd for the actuators on my obsy doors.

[NenoVento]

Thanks a million to you all for your inputs! (special kudos go to @Carbon Brush for such a detailed explanation). I've been looking for a water-tight electric board since I made my little observatory, but they don't seem appropriate for heat dissipation (from the power source and the mini-computer) and it makes no sense to install one and then have it open when observing, I think. If I see clouds rolling in, I'll simply close the lid of the obsy.

I also have been looking into the DC power distribution box idea and, to be honest, having just two cables (power and data) to the mount does make a lot of sense. As far as I can see, their wiring should be something like this:

 

 

I'm not so sure about the DC fuses, though. Is there a rule of thumb to establish what kind of fuses I should use?. Right now I'm looking at the automotive ones, with 3A-20A and 32 VDC.

Regards,

 

NV

[NenoVento]

On 24/02/2021 at 01:44, wxsatuser said:

Just buy a decent supply like this one, you get 20amps with peak of 30Amps, more than enough for most.

https://www.nevadaradio.co.uk/product/nevada-psw-30h/

or this one, I use these to power my hamradio gear.

https://www.nevadaradio.co.uk/product/nevada-psw-30/

Hi @wxsatuser, these power sources that you are using are rated 13.8 VDC, if I am not mistaken. Isn't it dangerous to use your astrogear above 12 VDC or is there something I am missing here (that you can regulate these power sources down to 12 VDC)?.

Best regards,

 

NV

[wxsatuser]

1 minute ago, NenoVento said:

Hi @wxsatuser, these power sources that you are using are rated 13.8 VDC, if I am not mistaken. Isn't it dangerous to use your astrogear above 12 VDC or is there something I am missing here (that you can regulate these power sources down to 12 VDC)?.

Best regards,

 

NV

No most electronics will go to 15 or 16Volts

[wxsatuser]

21 minutes ago, NenoVento said:

Thanks a million to you all for your inputs! (special kudos go to @Carbon Brush for such a detailed explanation). I've been looking for a water-tight electric board since I made my little observatory, but they don't seem appropriate for heat dissipation (from the power source and the mini-computer) and it makes no sense to install one and then have it open when observing, I think. If I see clouds rolling in, I'll simply close the lid of the obsy.

I also have been looking into the DC power distribution box idea and, to be honest, having just two cables (power and data) to the mount does make a lot of sense. As far as I can see, their wiring should be something like this:

 

 

I'm not so sure about the DC fuses, though. Is there a rule of thumb to establish what kind of fuses I should use?. Right now I'm looking at the automotive ones, with 3A-20A and 32 VDC.

Regards,

 

NV

Yes you can use car fuses, they come in standard or fast blow.

Also you can get ready made DC power blocks like in the link below

https://www.hamradio.co.uk/accessories-by-manufacturer-west-mountain-radio-accessories/west-mountain-radio/west-mountain-radio-rigrunner-4005-horizontal-58312-1041-pd-7866.php

[wxsatuser]

8 minutes ago, NenoVento said:

Hi @wxsatuser, these power sources that you are using are rated 13.8 VDC, if I am not mistaken. Isn't it dangerous to use your astrogear above 12 VDC or is there something I am missing here (that you can regulate these power sources down to 12 VDC)?.

Best regards,

 

NV

The second link down the psu is adjustable from 9 to 15volts

[Tomatobro]

Switch mode power supplies are low cost, small and efficient but not very good at dealing with transients whereas Linear are expensive, large and relatively inefficient but are very good at coping with transients. Either will work but the power supply of choice would be the Linear.

Adjustable voltage outputs allow compensation for the volt drop caused by cabling and load variations, again not essential but good to have if you can have it with the power supply.

 

[Carbon Brush]

@NenoVento Yes your fuse box shematic is essentially correct.

Given the low voltage and low fault current (tens of amps) automotive fuses are fine.
The benefit of these is that you can easily buy them. Maybe even pick up a power distribution box to suit your needs.
Whether you go for a fuse box, or a fuse & switch, or even with led indicators, is your choice.
Here are examples (though not the best choice) of something I saw a few days ago.
https://www.sotabeams.co.uk/powerpole-fused-dc-connector-box/
https://smile.amazon.co.uk/Qiorange-Blade-Holder-Circuit-holder/dp/B0752H5DC6/ref=sr_1_3?dchild=1&keywords=fuse+power+distribution+unit+12v+boat&qid=1614280428&sr=8-3

In my earlier post I mentioned fault currents of tens of amps being enough to cause heat damage. But if the fault current flows for a second or less till the fuse blows, there is little heating.
A lead acid battery (favoured by many for astro kit) will provide a fault current of hundreds of amps. Fusing is therefore extremely important.

On fuse values, a couple of amps is fine for a mount. More for dew heaters.
If you invest in a multimeter (change from £20) you can actually measure the current draw of your various devices and choose fusing to suit.
As a rough guide, choose a fuse about double the actual current draw. This gives a margin for surge/inrush at power up with 'electronics' type loads and the broad tolerance of low cost automotive fuses. 
The meter comes in handy for loads of other things. You will wonder how you ever managed without.

Astro kit manufacturers used to shy away from providing electrical specifications for the their products. Even avoiding temperature range specifications!
That meant if Mr. Skyestron said his mount needed a 12V supply, and you found it didn't work at 11.9V he could blame you!
Same if you said it ddn't work on a cold night. He didn't say that it would.
Things have improved now. Recently I bought a Skywatcher solar tracking mount and it had a very wide range stated for the 12V supply.

As a general rule, mounts powered from a nominal 12V supply use the 12V for the motor and an internal regulator to provide 5V or 3.3V for the electronics/logic.
Depending on the display lighting method, it may be powered from 12V or the logic supply.

This means that in practice mounts are quite tolerant of 12V supply variation. But if you can provide 13V to 14V, similar to a fully charged 12V lead acid battery, it can provide various benefits that depend on the mount design.
But that is another topic enirely.

I disagree with the idea of increasing above 12V just to overcome cable or connector voltage drops.
When load changes significantly, for example dew heaters turning on/off,  you will get step voltage changes on the 12V line at the point of load.
These can work their way through to the low voltage elctronics.
If you suffer this problem, you should use thicker cables to reduce voltage drop and/or different connectors.
Your power supply will be (near enough) constant voltage.

The switcher vs linear argument is a bit more complex.
Response to both mains transients and load transients is very much dependent on the individual power supply design.
If you buy the cheapest, you get what you pay for. Which comes back to my original comment about checking the manufacturer specifications.
A correctly designed switcher supply will provide a stable output over a wide input voltage range (not an issue in the UK) and rapidly correct for load variations.
A correctly designed linear supply will do the same.

Where the switcher supply wins is on efficiency (not heating the observatory), size, and weight.

I used to say that the switcher supply was more expensive than linear. But that difference has been very much eroded in the last few years.
Large scale manufacturing of switcher supplies has brought prices down.
At the same time linear supplies have significantly increased price due to the expensive copper and high grade iron used in the large transformers.

Where a linear supply has the potential to beat a switcher is on long term reliability and repairability. Potential is the key.
After many years of use, a linear supply will have degraded electrolytic capacitors, that can be replaced for a few, or perhaps tens of pounds on a large supply.
At this point the supply will give 12V on light load, but less on heavy load. A good clue for your fault finding.
Everything else will probably be OK - if it has been designed correctly. That is components not run too hot.
Against you on linear, significant cost saving is making the transformer from cheap iron and thin copper wire. This causes heating, which degrades everything else.
Another big cost saving is using cheaper shorter life expectancy electrolytic capacitors.
So linear reliability depends on the designer.

As a general rule, a switcher supply works until it stops. Though you can get degradation (similar to a linear) where the supply works on low load, but not frull load.
Repairing a switcher supply is much more difficult. Often best regarded as throw away.

You might ask about my choices on new astro build?
A switcher supply from a reputable manufacturer. Using no more than 50% of the rated power.
This helps reliability, provides continuous power on momentary mains loss and gives capacity for future additions.

When you look at power supply prices, they are often not straight '££ per watt' within a manufacturers range. Extra watts can cost only a few extra ££.
As an example I was recently looking at 300W and 600W supplies for industrial projects needing both ratings.
The 600W supply was only 20% more money than the 300W supply. size and weight were similar.
Buying spare capacity does not necessarily beak the bank. I bought the 'one size fits all' option.

Apologies for the long ramble. I hope there is something in there useful to the community.

David.

 

 

[xthestreams]

On 25/02/2021 at 21:02, NenoVento said:

Hi @wxsatuser, these power sources that you are using are rated 13.8 VDC, if I am not mistaken. Isn't it dangerous to use your astrogear above 12 VDC or is there something I am missing here (that you can regulate these power sources down to 12 VDC)?.

Best regards,

 

NV

this reminds me of my quest into Mordor a year ago. 
 

a few things;

- 13.7VDC is what most “12V” supplies generally output, for a variety of reasons a;ready mentioned here. Most everything seems to cope fine, or in some cases prefer slightly higher voltages

- the fact this is “news” leads me to conclude you’ve possibly not metered your existing supplies, worth investing in one if yiu are about to embark down this path

- think about your distribution strategy, for passive distribution, a RigRunner is a great and affordable investment

- don’t forget about switching things on and off independently, having to reboot and re-home a mount when  your NUC ( which will also run on 13.7V) needs a hard reboot, for example,  is painful (same is true vice versa)

- look into,something like a Pegasus UPB or a Denkovi for remote control switching and distribution 

- I eventually decided to go from “one to rule them all” to a DIN rail with four MeanWell power supplies - one for my Denkovi, one for my UPB riding on my mount/OTA (along with NUC, camera, focuser, heaters, fans etc), one 48V for the mount (paramount) and another just for the observatory/dome/lights/shutter battery charging etc - just because I like to know that it’s not all relying on one device AND they can be switched separately 

- AC switching to each supply controlled through an APC 7920 smart PDU, it also controls the dehumidifier and is the master switch for each DC supply 

- DC switching for the observatory through the Denkovi (for anything not on the OTA)

perhaps a little complicated, but I’ve found it gives me the flexibility I need

Edited February 28, 2021 by xthestreams

[Zakalwe]

Pay a bit more and get a regulated power supply. Personally I'm leery of using those cheap eBay PSUs (often badged as CCTV supplies). They need casing and they aren't designed to be used in condensing environments. They have the potential (geddit?) to have exposed contacts at mains voltage. One slip-up with a finger in the dark and you could be found dead the next morning. How many times have we tripped or banged our heads in the dark?

 

Also get a decent Anderson powerpole  splitter and convert all your gear to Anderson plugs. it#s well worth investing in a proper Anderson crimper too.  The Anderson plugs are handed so they cant be plugged in the wrong way and are very solid, unlike crummy cigarette plugs.

Anderson PowerPole splitter

 

[ollypenrice]

On 24/02/2021 at 08:10, pete_l said:

There's no reason not to use a single power supply. Though I have to say I'm not keen on fans in outdoor equipment. You never know what they will suck in to the equipment . In addition, they seem to me to be the weakest link - often cheap units that cannot withstand long periods of use before becoming noisy (poor quality bearings, or ones that fill up with dust) and unreliable. Plus with a unit like this, it's meant to be incorporated into a "finger proof" cover, so you have to plan for airflow when designing your enclosure.

When the fans do fail then your heat dissipation stops too. I prefer passive cooling. It needs larger heatsinks and external ventilation, but fewer moving parts are always a good thing. Especially when you have a potentially damp environment or a shed that is home to creepy-crawlies or larger "guests".

The counter argument would be that fans discourage condensation. I honestly don't know which side wins this one...

Olly

[DaveS]

I have three PSUs in my obsy, for mount, camera and electrically noisy accessories.