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JamesF

Observatory 12V power supplies

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Having had a rethink about low-voltage power in my observatory, I'm now more in favour of running 13.8V to each of the three piers from a PSU in the warm room.  I'm thinking I'm unlikely to want more than 10A per pier except when slewing so perhaps something like this is worth considering:

https://www.radioworld.co.uk/power-supplies-23-40-amp-high-power/sharman-lm-40-variable-voltage-40-amp-linear-power-supply

Cost-wise it seems pretty much comparable to having a PSU on each pier, with the advantage of not having the supply anywhere it's likely to get wet.  The plan (as per Gina's suggestion) is to connect it across a battery with appropriate fusing and switches so I can as a minimum tidy up if the power disappears or the PSU goes pop, or even carry on imaging until sleep overtakes me.

Anyone care to offer thoughts or alternatives?

James

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I've just realised that one appears identical to the Nevada PS-40M.

James

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at 13.8v you're feeding the battery a topping charge voltage level or at least on the cusp of that level, not ideal if its already charged and left connected for extended periods I would think. You really need volts set to be in the float charge range so the battery doesn't warm or gas and reduce lifespan. Depending on the battery type the spec range may vary a bit but typically you'd be looking at 2.25-2.27v per cell so more like 13.6v might be better. That's assuming also that temp is in the low-mid 20C range and that you want the battery at max charge level. 

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With a variable voltage supply that should be possible.  I'm sure the mounts won't mind 13.6V instead of 13.8V.

I have just been wondering if a digital display for the voltage might make more sense though.  Microset have one of a similar capacity with an LED display that doesn't cost much more.

James

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Posted (edited)

digital display does make things easier, but bear in mind there'll be some volt drop over the length of the cable so the pier end may see a touch less. How much will depend on length and cable type but I see that was covered in your other thread 🙂 Ability to lock the adjust dial would be good too, to save any accidental large voltage changes.

Don't forget to fuse the runs at the feed end too, and if you plan on a battery between the PSU and the piers then fuse either side of the battery, better safe esp if any critters decide to enjoy a wee nibble of the insulation for their dessert...

Edited by DaveL59

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Having just blown my caravan one I have bought a new system which having read you question might be a solution to your problem.

its one of these (or something like as there are many different ones available) https://www.12voltplanet.co.uk/portable-power-technology-premium-battery-charger-12v-30a.html

They charge a battery very efficiently / safely but also provide a 12v DC(13-14v) power supply.

May not be as "quiet" as a ham radio power supply but still pretty good.

Just a thought.

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Posted (edited)

Rather than charge from the PSU, why not run the PSU from a UPS, smooth power and battery backup, designed for constant trickle? You can also hang your imaging PC off it, assuming it has the rating 😀

Edited by Yawning Angel

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Posted (edited)

UPS power will only be smooth if you get a sine-wave output type, a lot of the cheaper ones are a stepped approximation waveform. Might not cause any issues but in the past switch-mode PSU's didn't always get on with the stepped waveforms. You're also sacrificing some efficiency, perhaps but you do then gain surge protection in exchange. If you do decide the UPS route, the APC smartups range are sine-wave output and pretty good buys used on the bay etc, just needing new batteries in the main, just make sure they have the battery cables included. The APC SUA 1400/1500 will need 2x 17Ah batteries but they also have a fan that can be annoying. The APC SUA1000 uses 2x 12Ah batteries but its an easy upgrade to use 17Ah batteries in them. The XL models use the 17Ah ones tho are harder to find used. I've 5 of the 1000's around the house keeping the tech and security stuff powered 🙂

Edited by DaveL59

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19 minutes ago, Yawning Angel said:

Rather than charge from the PSU, why not run the PSU from a UPS, smooth power and battery backup, designed for constant trickle? You can also hang your imaging PC off it, assuming it has the rating 😀

There probably will be a UPS because I may well move my backup file server into the observatory where it stands a chance of surviving even if the house burns down, but one of the things I'm trying to avoid is making the power supply a single point of failure.  If it were just the one mount then I probably wouldn't worry to much, but to lose all three in one hit would be a bit frustrating, to say the least.  The weather is a big enough single point of failure as it is :D

James

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5 minutes ago, DaveL59 said:

If you do decide the UPS route, the APC smartups range are sine-wave output and pretty good buys used on the bay etc, tho the APC SUA 1400/1500 will need 2x 17Ah batteries but they also have a fan that can be annoying. The APC SUA1000 uses 2x 12Ah batteries but its an easy upgrade to use 17Ah batteries in them. The XL models use the 17Ah ones tho are harder to find used. I've 5 of the 1000's around the house keeping the tech and security stuff powered 🙂

Yes, I have a couple of the APC 1300 models protecting the kit on my desktop and file server/firewall etc.  They've proved very useful over the years, even if it just means I have time to shut everything down cleanly if we have a power outage.

James

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I'm not electrically minded enough James, I run one to feed everything apart from my laptop and I give that a separate feed. For £79.95 they have proved to be very reliable.

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As an observation I have noticed that none of the power supplies mentioned have 4 wire outputs (plus minus and sense) which makes voltage setting a bit hit and miss...

Alan

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10 hours ago, JamesF said:

Would it be safe to couple the outputs together (in parallel), I wonder?

James

I wouldn't recommend doing that James, not without putting some levels of protection in there. You don't want to be back-feeding power from one into the other if there's any drift in output level and potentially introducing instability in the output regulation. Wonder if an option is gutting an old dual-PSU server as some can be picked up pretty cheap, tho they are more geared toward hi-current 5v rather than 12v  which would only be driving the fans and drives. If viable then could hang that off a UPS and the DC output side would auto-switch on failure of one PSU or load-share when both are running. But there's still a SPOF - the UPS unless you feed each PSU from a different UPS... ahh the costs will keep creeping up as you aim for resilience.

If you do figure on a UPS, the APC's run with 2x 12V or 4x 12v on the 2200 models. So that's £60 per UPS just on batteries unless you have the XL with external batteries too as I have (14 batteries every few years, ouch).

Ideally for the UPS side, don't run it at more than 50% load or when you lose mains feed it'll get pretty warm and could shutdown due to internal temp. At say 20% load I can see 1.5 hours runtime on the standard SUA1000's which is pretty decent. Didn't even realise power went a few months back as the desk gear and TV etc just carried on as if nothing had happened 🙂

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9 minutes ago, DaveL59 said:

I wouldn't recommend doing that James, not without putting some levels of protection in there. You don't want to be back-feeding power from one into the other if there's any drift in output level and potentially introducing instability in the output regulation. Wonder if an option is gutting an old dual-PSU server as some can be picked up pretty cheap, tho they are more geared toward hi-current 5v rather than 12v  which would only be driving the fans and drives.

That was my thinking about the outputs.  I was fairly sure it wouldn't be a good idea, but sometimes...

As it happens, I have an old dual-PSU disk enclosure sitting about somewhere.  I don't know if I fancy pulling it apart though.  Probably not in the short term.

James

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was kinds thinking something like an old HP server with hot-swap PSU but not sure the 12V would be at the level you're looking for. 

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No, you're probably right.  I shall go back to pondering...

James

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Decisions aren't coming easily on this one, so I have decided to run all the cabling and whilst I'm dithering I'll use the two 7 amp supplies I currently have ("7 amp", "currently", ho ho) to feed a couple of the piers.  They'll do whilst I sort my life out and it stops everything stalling whilst I dither as at least I can test stuff out and nothing at the pier end should change once I do make my mind up.

James

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You could always "sit on the fence" and run both mains and 12v to the piers.  Or use big enough pipes with easy bends so that you could change cables later.

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Ideally if you are running three setups you should be using 6 power supplies, 3 for the mounts and dew heaters and 3 for the cameras....

Alan

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Hi James,

I installed a UPS in each dome, probably more important here in rural France than the UK, as I sometimes lose the power without warning. The domes are not on the UPS, as they draw too much current and would drain the battery in a few minutes.

It is a stepped waveforem type (please don't judge me harshly, to protect all the IT, I needed five of them...) and they work fine with the switch mode PSU's for the PC, mount and camera. The dew heater is also not on the UPS.

There is also a UPS in the warm room, mostly for the 4g internet connection, as I get a stronger signal there than the house.

All the PSU's are local to the scope, to avoid running long lengths of DC power. It's all about volt drops...

Good luck,

Gordon.

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Hi James i have used these power supplies for almoast 10 years and can highly recommend them:https://www.rapidonline.com/rapid-ps1540s-smps-switch-mode-power-supply-15v-40a-with-digital-display-85-1828

There are a huge range in bench psu`s, i have always found them to be really reliable

Regards

Mike

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