Observatory 12v power change?

[michaelmorris]

The planning of the new upgraded observatory setup continues.  At present the power to all the 12V devices in the observatory is supplied by a cheap Halfords 12v power supply.  Up to now this has sevred me well.  However, with a swapping of the mount from a Meade LX200 to an EQ8 and the addition of a CCD camera, is there any reason to suppose that this power supply may not still be adequate?

 

[barkis]

10 minutes ago, michaelmorris said:

The planning of the new upgraded observatory setup continues.  At present the power to all the 12V devices in the observatory is supplied by a cheap Halfords 12v power supply.  Up to now this has severed me well.  However, with a swapping of the mount from a Meade LX200 to an EQ8 and the addition of a CCD camera, is there any reason to suppose that this power supply may not still be adequate?

 

A lot will depend on what other loading you will add Michael What Power output limit does your  PSU have..
Has  the camera got Cooling, will  you be adding Dew straps, and any other devices that require powering up?
Current soon adds up, even though individual devices might draw small amounts.

[M106]

You need to work out the total current (marked in Amps/A) requirements of all the kit, add 20%, and then check that the power supply gives at least that much

[Scott]

I bought this. maybe overkill but I've never had a problem with it. 

http://www.maplin.co.uk/p/375w-linear-dc-variable-voltage-bench-power-supply-rp10l

[michaelmorris]

Thanks, I'll do the maths this weekend. Why do so many people use a a continuous power supply as opposed to a switched power supply?

[RayD]

2 minutes ago, michaelmorris said:

Thanks, I'll do the maths this weekend. Why do so many people use a a continuous power supply as opposed to a switched power supply?

Linear is cleaner than switched mode, which can be electrically "noisy" which with sensitive kit like CCD cameras can be a problem.  Downside is they are usually bigger and get warmer so need cooling (normally have slots in the casing).

You could keep a switch mode for things like your dew strips, and then add a smaller linear one for the sensitive stuff.

[barkis]

1 hour ago, Scott said:

I bought this. maybe overkill but I've never had a problem with it. 

http://www.maplin.co.uk/p/375w-linear-dc-variable-voltage-bench-power-supply-rp10l

Looks the part,  and obviously is. I bought two of the 10Amp units, one is a permanent fixture in  the Obs. The other is in the Star Party traveling kit. I'm sure it will be employed soon . 

[Starlight 1]

32 minutes ago, RayD said:

Linear is cleaner than switched mode, which can be electrically "noisy" which with sensitive kit like CCD cameras can be a problem.  Downside is they are usually bigger and get warmer so need cooling (normally have slots in the casing).

You could keep a switch mode for things like your dew strips, and then add a smaller linear one for the sensitive stuff.

I am with Ray on this one, my sw heq5 and az-eq6 -gt will not not run on switched units I get power lose all the time , use my 20 years old linear unit spot on .

[RayD]

The Nevada ones Flo do are pretty good value for money, and 2 of them to separate all the good bits (mounts from cameras etc.) is only £70 odd.

[Horwig]

2 hours ago, michaelmorris said:

Why do so many people use a a continuous power supply as opposed to a switched power supply?

Another vote here for linear supplies. I use two, one that runs the camera, and usb hub, ie, stuff that is sensitive to rubbish which might be picked up off the supply rail, the other powers the mount, dome and dew heaters. In reality, the "dirty" supply does not have to be linear.

I've continued this into my portable rig, I use two 12v batteries, one "clean", one "dirty". I've no evidence that it's required, but it did not cost a whole lot more, so just in case...

 

Huw

[michaelmorris]

3 hours ago, michaelmorris said:

Thanks, I'll do the maths this weekend.

Well I've done the maths and it doesn't make pretty reading.

I'm planning to now mount a powered USB Hub on the scope dual bar and hence it will run from the 12v distribution box also mounted on the dual mounting bar, as will the cooled CCD camera.  Assuming all the dew heaters are on at the same time (worst case scenario), I calculate the following peak consumption.

• Dew heaters = 4.5A
• USB Hub = 3A
• Focuser motor = 1.7A
• CCD camera = 1.5A
• Mount = 3.8A

This equals a whooping 14.5A  

With an output voltage of 13.8V,  I calculate this would mean I will need a power supply capable of supplying 200 watts.

If I powered the mount separately (easy to do), this would reduce the load to 10.7A (148W)

Do these calculations appear to be overly pessimistic?

[RayD]

1 minute ago, michaelmorris said:

Well I've done the maths and it doesn't make pretty reading.

I'm planning to now mount a powered USB Hub on the scope dual bar and hence it will run from the 12v distribution box also mounted on the dual mounting bar, as will the cooled CCD camera.  Assuming all the dew heaters are on at the same time (worst case scenario), I calculate the following peak consumption.

• Dew heaters = 4.5A
• USB Hub = 3A
• Focuser motor = 1.7A
• CCD camera = 1.5A
• Mount = 3.8A

This equals a whooping 14.5A  

With an output voltage of 13.8V,  I calculate this would mean I will need a power supply capable of supplying 200 watts.

If I powered the mount separately (easy to do), this would reduce the load to 10.7A (148W)

Do these calculations appear to be overly pessimistic?

You are probably a bit over on the calculations there I would think.  Personally I would power the dew heaters totally independently on a separate switched mode supply, and then get a decent 10A linear regulated power supply for the other bits

[RayD]

Just to clarify why I say a bit over is that you can derate the equipment which won't be running full tilt all the time, such as the mount, focuser and dew heaters.

[michaelmorris]

1 minute ago, RayD said:

You are probably a bit over on the calculations there I would think.  Personally I would power the dew heaters totally independently on a separate switched mode supply, and then get a decent 10A linear regulated power supply for the other bits

i could do that, but my aim was to have just two cables going to the mount head, one 12v power supply and a USB cable going to the powered hub. If I did go down your suggested route, what 10A power supply would you recommend?

[RayD]

1 minute ago, michaelmorris said:

i could do that, but my aim was to have just two cables going to the mount head, one 12v power supply and a USB cable going to the powered hub. If I did go down your suggested route, what 10A power supply would you recommend?

I only suggest that as dew heaters, being resistive, can cause their own issues with a nice clean power supply.

As for linear supplies, there are a number of suitable ones, like some of the ones Maplin do (Barkis noted having a 10A one), or like the one below:

10A Linear Power Supply

You can definitely use a single supply, but you would need a 20A one, which is fine, and also if a dew heater gives up, as they can and do, it could take out a fuse which will knock out everything.

Either way will work, but if you just want the single cable then the bigger supply is the way, but then definitely linear without doubt and the price takes a fair jump:

Maplin 25A Power Supply

[BargeGazer]

Personally, and I know it is only a personal thought, I would think along the lines of my primary source being a 12v leisure battery then all types of current needs can be catered for.

Make it a decent size one. And then I would connect a good quality battery charger that will keep it at a healthy voltage all the time. The battery will smooth out any ripples caused by the charger or any devices as it acts like a huge smoothing capacitor to these. An 85Ah Leisure battery and a CTech charger would be my first choice. You could even get away with an ordinary car battery if you charger is left running while observing. I am assuming you have space in the observtory and can leave everything in place when not observing.

David

[RayD]

39 minutes ago, BargeGazer said:

Personally, and I know it is only a personal thought, I would think along the lines of my primary source being a 12v leisure battery then all types of current needs can be catered for.

Make it a decent size one. And then I would connect a good quality battery charger that will keep it at a healthy voltage all the time. The battery will smooth out any ripples caused by the charger or any devices as it acts like a huge smoothing capacitor to these. An 85Ah Leisure battery and a CTech charger would be my first choice. You could even get away with an ordinary car battery if you charger is left running while observing. I am assuming you have space in the observtory and can leave everything in place when not observing.

David

Hmmmm not so sure that's advisable.  The second you put any load on the battery the charger will jump to bulk charge which is 14.4v.  

[BargeGazer]

Ray

Oops, that's a point. The one I use in a different application has a programmable boost voltage which I generally set to 13.8v in case boost switches in while I have other things in use. You don't want to pay that price though! As I say it is for a different application where cost is either justified or you go cold!

I just like to be independant of any mains power intermitents so find a battery in there solves the problem.

David

[RayD]

31 minutes ago, BargeGazer said:

Ray

Oops, that's a point. The one I use in a different application has a programmable boost voltage which I generally set to 13.8v in case boost switches in while I have other things in use. You don't want to pay that price though! As I say it is for a different application where cost is either justified or you go cold!

I just like to be independant of any mains power intermitents so find a battery in there solves the problem.

David

Yes I agree with the independence definitely.  Best way to do this though would be to use a properly sized UPS (I think Sara has just got one for this specific reason), which then only kicks in if you lose power, and if it's a long outage can give you chance to shut things down or do a controlled shut down for you.

[iapa]

On 07/01/2017 at 00:09, michaelmorris said:

Well I've done the maths and it doesn't make pretty reading.

I'm planning to now mount a powered USB Hub on the scope dual bar and hence it will run from the 12v distribution box also mounted on the dual mounting bar, as will the cooled CCD camera.  Assuming all the dew heaters are on at the same time (worst case scenario), I calculate the following peak consumption.

• Dew heaters = 4.5A
• USB Hub = 3A
• Focuser motor = 1.7A
• CCD camera = 1.5A
• Mount = 3.8A

This equals a whooping 14.5A  

With an output voltage of 13.8V,  I calculate this would mean I will need a power supply capable of supplying 200 watts.

If I powered the mount separately (easy to do), this would reduce the load to 10.7A (148W)

Do these calculations appear to be overly pessimistic?

you'd probably not want to run the USB hub from the same supply, it is likely to be 5V the rest are 12V.

11.5A fo the rest does still seem high.

the mount rating may be the maximum when slewing, so you could look into a lower rated PSU that runs at, 9-10A (whatever your base current is) with a max load short term current up to 12A to cover the increase requirement for the short time you are slewingc?

 

[michaelmorris]

7 minutes ago, iapa said:

you'd probably not want to run the USB hub from the same supply, it is likely to be 5V the rest are 12V.

 

It's a powered hub with a 12v supply.

[RayD]

What about 2 single 6A supplies and a single 4 core cable so you still only have the 1 cable going to the mount?

[timwetherell]

One of the cheapest ways to get a high power switch mode 12V DC supply is to use a power supply from a computer. I use a 12v unit from a PC mounted indoors with about 10m of 3mm2 heavy duty cable running to the observatory. Works a treat! the lights and everything in there are 12V which saves the hassle and potential danger of running mains to an outbuilding. 

[michaelmorris]

On 07/01/2017 at 00:30, RayD said:

I only suggest that as dew heaters, being resistive, can cause their own issues with a nice clean power supply.

As for linear supplies, there are a number of suitable ones, like some of the ones Maplin do (Barkis noted having a 10A one), or like the one below:

10A Linear Power Supply

Thanks Ray.  Just ordered one.

[patm]

Switching or linear doesn't mean much, both can be very noisy depending on how well the transformer/switching output is filtered. Switching usually gives more of a square wave while linear is sine - neither is great if the filtering is bad. The good thing is if you think noise is a problem you can toss in your own capacitor to clean it up.