Power supply issues

[Gina]

I am currently using two PSUs sited in the warm room and feeding DC power via cables to the pier head and imagiing equipment.  13.8v for the EQ8 mount plus 12v and 5v feeding cameras, filter wheel, dew heaters, USB powered hub and Arduino focussing system. 

The problem I am having is horizontal interference lines/stripes in the Lodestar guide scope images at times.  The cable length for the power is around 3m and I am getting voltage drop.  The mount seems acceptable at 13.5v versus the 13.8v supply (minimum usable is 12.5v) but the 12v is down to 11v and the 5v is down to 4.5v.  I suspect that 4.5v may be causing problems with USB devices such as the Lodestar which uses USB power.

Initially I was thinking of adding extra decoupling for the power supplies at the scope end but now I think the voltage drop may be the problem (or both).  Two possible solutions as I see it.  Beef up the cables and add scope end decoupling or move the 12/5v PSU to the pier head.  The 12/5v PSU is an ex PC one rated at 370W with oodles of amps to spare and will just about fit between the pier head plates that support the mount.

Moving the 12/5v PSU to the pier head would be easy enough electrically but I am rather concerned about the environment for it.  For insatnce, last night by midnight everything was literally dripping with dew (except the scope lenses which were being kept clear by the dew heaters).  This is NOT the environment the PSU was designed for and I think I might be courting trouble by using it in a very damp environment.  I presume that the astro equipment viz. mount, camera, FW, are expected to be used in heavy dew.

All comments welcome

[ChrisLX200]

I keep my PSUs in the warm room which I set to 13.8V, a long (15M) cable runs to the pier and voltage drop gives 13.6V there, then use a voltage converter located on the pier to drop the voltage to 5V for the USB hub. You can get weather-proof converters designed for automotive use.

That's the converter stuck to the inside of the socket box...

ChrisH

[Alien 13]

Hi Gina i suspect the problem may be a combination of volatage drop and crosstalk on the supply lines.

If it where me i would use the 12V output from the PC supply to power a number of DC-DC convertors for the 5V supplies so each was independent these could be mounted very close to the mount in 3D printed boxes (with or without potting compound) the 12V supply would have to be taken off the 13.8V PSU again using DC-DC convertors.

The problem could possibly be cured by just having a seperate feed via a DC-DC convertor to the camera.

Hope that helps.

Alan

[knobby]

Is it a switch mode psu ... You'd be amazed how much interference they give out ... Stuck one on an amateur radio and it wiped out with mush most channels ?

Regulated would be better

[steppenwolf]

Noise (your banding) on imaging gear is often a sign of a USB issue caused by lower voltage, low signal or even a PC that isn't processing the input data quickly enough.

Assuming a voltage drop for now, you could run a very heavy duty cable from your modified PC PSU into the observatory and have a boxed 'busbar' system to distribute the power to individual components using more manageable cable to allow for the movement of the mount.

[Ptarmigan]

5v down to 4.5v is one serious voltage drop !
What current is being drawn by your devices and what diameter and length of wire, I guess you have looked up your SWG/Amps tables ?
Yes, beefing up the wire would be one thing to try, but I wonder if there is a resistance problem, can you test each side of the (various?) joints (soldered or screw-terminal ?) along the route to see if you have a localised or distributed drop ?
Another thought, have you spare wires long enough to measure the resistance of the DC path with a meter ? ( dont forget to measure and subtract the resistance of your test wire loop !! )

Before buying new beefier wire - if you have a spare length of wire of similar gauge,  run that in parallel with the existing wire to see if the drop changes

As for decoupling, hmmm, that should be at the PSU end. If the devices are causing noise than that suggests that they are not themselves decoupled and are able to contaminate adjacent devices via the power because of a DC source resistance problem, maybe.

All the above thoughts are quickies off top of my increasingly useless head, cos I know you like to get on with things pdq :) so hope something might help
 

[Gina]

I keep my PSUs in the warm room which I set to 13.8V, a long (15M) cable runs to the pier and voltage drop gives 13.6V there, then use a voltage converter located on the pier to drop the voltage to 5V for the USB hub. You can get weather-proof converters designed for automotive use.

That's the converter stuck to the inside of the socket box...

ChrisH

Thank you Chris   A voltage regulator for the 5v supply for USB devices at the scope end is a very good idea   Just wondering why I didn't think of it myself   Guess I have a lot on my mind

BTW Just measured my cable length and it's nearer 5m than 3m!

[Gina]

Hi Gina i suspect the problem may be a combination of volatage drop and crosstalk on the supply lines.

If it where me i would use the 12V output from the PC supply to power a number of DC-DC convertors for the 5V supplies so each was independent these could be mounted very close to the mount in 3D printed boxes (with or without potting compound) the 12V supply would have to be taken off the 13.8V PSU again using DC-DC convertors.

The problem could possibly be cured by just having a seperate feed via a DC-DC convertor to the camera.

Hope that helps.

Alan

Thank you Alan   Yes, 4.5v is below the standard voltage spec for computers so definitely a likely source of trouble.  Again, a DC-DC converter and voltage regulator at the scope end is a really good idea.  The Lodestar is USB powered and gets its power from the powered USB hub.

[Ptarmigan]

 it's nearer 5m than 3m!

Ooops I missed the 3m earlier,

said I had a useless head !

If the electric companies had that kind of % drop over that length then we wouldnt need central heating in the UK lol!

[Gina]

Is it a switch mode psu ... You'd be amazed how much interference they give out ... Stuck one on an amateur radio and it wiped out with mush most channels ?

Regulated would be better

Yes, it is a switched mode PSU - a standard PC supply.  Sounds like it's time I bought a regulated supply for the cameras and associated gear an kept switch mode supplies away from sensitive equipment.  A relatively small price compared with everything else I've bought   Thank you for pointing that out again 

[Gina]

Noise (your banding) on imaging gear is often a sign of a USB issue caused by lower voltage, low signal or even a PC that isn't processing the input data quickly enough.

Assuming a voltage drop for now, you could run a very heavy duty cable from your modified PC PSU into the observatory and have a boxed 'busbar' system to distribute the power to individual components using more manageable cable to allow for the movement of the mount.

Thank you Steve   Yes, I'm convinced low voltage is the problem or at least part of it.

[Gina]

5v down to 4.5v is one serious voltage drop !

What current is being drawn by your devices and what diameter and length of wire, I guess you have looked up your SWG/Amps tables ?

Yes, beefing up the wire would be one thing to try, but I wonder if there is a resistance problem, can you test each side of the (various?) joints (soldered or screw-terminal ?) along the route to see if you have a localised or distributed drop ?

Another thought, have you spare wires long enough to measure the resistance of the DC path with a meter ? ( dont forget to measure and subtract the resistance of your test wire loop !! )

Before buying new beefier wire - if you have a spare length of wire of similar gauge,  run that in parallel with the existing wire to see if the drop changes

As for decoupling, hmmm, that should be at the PSU end. If the devices are causing noise than that suggests that they are not themselves decoupled and are able to contaminate adjacent devices via the power because of a DC source resistance problem, maybe.

All the above thoughts are quickies off top of my increasingly useless head, cos I know you like to get on with things pdq :) so hope something might help

Thank you  

I've been checking the wiring and what loads I have on which power lines.  The imaging camera (460EX) and filter wheel run off a separate pair of wires back to the 12v supply.  Another 12v line supplies dew heaters and ancilliary devices.  BUT the dew heater for the Esprit I have on the 5v line so I think this explains the large 5v voltage drop.  Must change that.  Also, the 12v and 5v use the same return/ground wire (except 460EX and FW which have their own ground wire).   The 12/5v cable is 5amp flexible mains cable. 

[Gina]

OK...  several things are wrong with my power supplies

1. Running a dew heater off a 5v line shared with USB devices
2. Having a common return wire for dew heaters and USB devices
3. EM noisy PSU

Items 1 & 2 are easily fixed and I'll try those before buying a new PSU.  The trunking between warm room and pier is 40mm ID plastic waste pipe with plenty of room for multiple cables.  So I can run separate power cables as appropriate.  Some things will have a common ground (eg. everything with a USB connection) but this doesn't apply to dew heaters - they can have seperate return wires (or one dew heater return, separate from other loads).

I think I'll use the 3way cable for the dew heaters and provide a separate regulated supply for the USB hub.  The Arduino has it's own internal regulated supply so that can run straight of the 12v supply.

This gives the following feeds :-

1. 13.8v supply for mount - 2 wires
2. 12v supply for camera(s) - 2 wires
3. 12v supply for Arduino and USB 5v regulator - 2 wires
4. 12/5v dew heater feed - 3 wires

I see no reason why the cameras, Arduino and USB regulator shouldn't use the same pair of wires.  They have a common ground anyway and earth/ground loops cause problems.  That would mean I already have enough cables running through the trunking   I may want to beef up the camera supply when I add two more cameras for a triple imaging rig as that would then be at least 3A.

[Gina]

I missed something from the 5v supply line and that's the stepper motors for focussing.  I think I'll change them for the 12v version then I won't need 5v for that.

[Ptarmigan]

A few more thoughts,

Ok on the 5v dew heaters, good move, that would explain some of the ( high-ish load) volts drop, but even so it still seems very big (what watts, amps are they, 5A cable should be more than enough I'd 'av thort) You could move it/them up to 12v by including a resistor within the dew sleeve, dont want to waste watts

Still think you need to look for resistive losses in the supply.

With all that damp around what state are the screw terminal joints in ? Some choccolatblocks are not good in this respect, I wouldnt dare suggest that you may have a dry-joint solder, would I , >>> runs&ducks

Then, when you shift the dew heaters, on the light-load usb stuff consider a filter at the sm-psu to get rid of hash, a ferrite core (torroid pref.) choke (or two) can be liberated from redundant electronics (power side.)

Then a few, liberated, small capacitors(s) from the output(s) of the ferrite choke(s) to psu ground.

Might save the cost of a new psu.

and with several earth returns should we be considering earth loops and star earthing, just for belts&braces ?

[Gina]

A few more thoughts,

Ok on the 5v dew heaters, good move, that would explain some of the ( high-ish load) volts drop, but even so it still seems very big (what watts, amps are they, 5A cable should be more than enough I'd 'av thort) You could move it/them up to 12v by including a resistor within the dew sleeve, dont want to waste watts

Still think you need to look for resistive losses in the supply.

With all that damp around what state are the screw terminal joints in ? Some choccolatblocks are not good in this respect, I wouldnt dare suggest that you may have a dry-joint solder, would I , >>> runs&ducks

Then, when you shift the dew heaters, on the light-load usb stuff consider a filter at the sm-psu to get rid of hash, a ferrite core (torroid pref.) choke (or two) can be liberated from redundant electronics (power side.)

Then a few, liberated, small capacitors(s) from the output(s) of the ferrite choke(s) to psu ground.

Might save the cost of a new psu.

and with several earth returns should we be considering earth loops and star earthing, just for belts&braces ?

With the dew haeter unplugged the voltage goes up to 4.88.

Connections are XLR with a chocolate block in the distribution box in the warm room.

I have a few ferrite rings I can use for interference suppression also a good collection of ceramic capacitors.

I shall use one signal/data earth return and may upgrade this to a larger size wire.  The dew heaters will have a separate return wire.

I shall use an L78S05CV voltage regulator for the USB hub - 5v at 2A with the tab screwed to the big aluminium plate that takes the two Evostar 80ED scopes either side of the MN190 with Esprit 80ED on top of the MN190 tube rings.

[Gina]

If the switch mode PSU still proves troublesome I could make up my own analogue supply.  I have a large transformer or two and the regulation could be provided by ready made chips.  L78S05CV for 5v and L78S12CV for the 12v for cameras etc.  With the cameras taking 1A each I would have a seperate regulator for each mounted on the big ali plate.  I'd probably use a separate one for the 4 12v stepper motors and Arduino Mega.

I would think dew heaters could be run off low voltage AC direct off the transformer.  That would mean the unregulated supply would only need to cope with around 5A or so reducing the size of electrolytic capacitors required.

[Alien 13]

I use devices similar to these http://www.ebay.co.uk/itm/5pcs-LM2596S-DC-DC-Buck-Converter-Adjustable-Power-Supply-Step-Down-Module-UK-/141210161794?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item20e0c81282#ht_1108wt_1164for powering my DSLR/Phone/Mount they are efficient so dont even get warm, you can get versions with screw terminals and built in voltmeters too.

Alan

[Gina]

Thank you Alan   But yes, I have several of those and have used them in the past but I'm a bit wary as they are switch mode and will produce some interference.  The price is little different from the L78S series of chips.

[russellhq]

Don't know if this will help but I used a left over piece of speaker cable to make my power runs. It was pretty cheap per m but had quite a meaty core! There's tons on ebay for around £1/m

[Gina]

Thank you Russel - that is indeed the sort of cable I'm using for the camera, FW and mount power

[Guest]

Hi Gina,

I think you really need to supply just the 13.8v to the pier and to the conversions at the pier, 12 to 5v and so on, that is what I do.

I have a 13.8v bench supply powering my DIY power mount hub which is 12meters away, the voltage drop is 0.6v when drawing 7amps, so 13.2v is getting to the power hub, then all the voltage converters are in the power mount his at the pier, 12v to 5v and 12v to 8v, which then have no voltage drop in them, you can get away with a voltage drop when using a 13.8v supply but not when using a 12v. So,I guess the only way round is to send 6v down the line and allow for a voltage drop to give you 5v minimum at the pier.

I think you have seen my power mount hub on another thread.

Hope that makes sense

Olly

[Gina]

Thank you Olly   Yes, that may be the best way to do it - if my PSU gives enough current for all my gear.  I like the idea of regulating the 12v to the cameras at the pier end (as well as the 5v for USB hub)

[Gina]

EQ8 mount - 4A

Atik 460EX camera - 1A

USB hub - 1A?

Dew heaters - not known ATM but could be run from the PC PSU.

I eventually intend to have three 460EX cameras so 3A.

Total 9A - and 13.8v PSU rated 5A continuous (7A @ 50% duty cycle)   Oh dear    BUT I suspect the mount takes nothing like 4A except when fast slewing and the cameras probably take an amp only when cooling.  I'll have to put ammeters in the feeds and check.

[Guest]

EQ8 mount - 4A

Atik 460EX camera - 1A

USB hub - 1A?

Dew heaters - not known ATM but could be run from the PC PSU.

I eventually intend to have three 460EX cameras so 3A.

Total 9A - and 13.8v PSU rated 5A continuous (7A @ 50% duty cycle) Oh dear BUT I suspect the mount takes nothing like 4A except when fast slewing and the cameras probably take an amp only when cooling. I'll have to put ammeters in the feeds and check.

Hi Gina,

Get yourself one of these (I have one). http://www.tantronics.co.uk/acatalog/fusion_15A_13.8V_200W_Bench_Top_Power_Supply_Twin_Output_PS200T.html

And it has a voltmeter and ammeter already built into it, so,it can be monitored from your warm room.

Then run that straight from your warm room or where ever you do you imaging from, to the pier into something like this (which I built) which has all the regulators fitted to give the different outputs, looking at some of the DIY stuff you have done in the past, this should be a walk in the park for you

https://www.dropbox.com/sh/of0yarei2bbrtvp/AAAEehy82Sj1RUpsClCwS30Pa?dl=0

Regards

Olly