Power supply issues

[Gina]

The Tantronics PSU looks good at a good price - I may get one of those    And I certainly remember your elegant power box

[Gina]

I've been out and measured the current taken by the EQ8 under various conditions.  Worst case was 3A when slewing at full speed in both axes at once.  NS fast took 2A and EW fast 2.5A.  Any slower slewing took 1.2A to 1.5A.

[pete_l]

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.

If it was me. I'd be inclined to "divide and conquer" and have a few smaller PSUs rather than one honkin' big one.

The reason being that it makes it easier to isolate a suspected power problem when you can swap kit between supplies. It also allows you to run the high-current stuff separately from the delicate and sensitive stuff.

[ChrisLX200]

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.

Each port on a USB hub should be capable of supplying 500mA so really you need 2A for a 4-pot hub. I would offer the camera 2A as well, it will only take as much as it needs. TBH the most I see is about 5A drawn from my PSU at any time but there is 33A available on the line at the pier. I doubt my cable would carry all of that at the moment - I have yet to install the proper armoured cable which is sat in the Obs...

ChrisH

[Demon Barber]

HI Gina, i` have used these for 4 years,as recommended to me by a development electrician,and i can honestly say i`ve had not  one problem 

I run my whole obsy from one,and take one if leccy available when out and about,there is also plenty of room in the housing to put extra outputs/sockets.

Link here:http://www.rapidonline.com/electrical-power/rapid-smps-25a-40a-65063    

Regards

Mike

[Gina]

If it was me. I'd be inclined to "divide and conquer" and have a few smaller PSUs rather than one honkin' big one.

The reason being that it makes it easier to isolate a suspected power problem when you can swap kit between supplies. It also allows you to run the high-current stuff separately from the delicate and sensitive stuff.

Yes, I'm thinking that too.  I think I'll keep the 13.8v PSU for the mount completely separate as now.  The dew heaters I would like to power separately too either from the exPC PSU or just from a transformer - heaters don't need DC let alone regulated DC.  The mains supply is quite stable enough for dew heaters.

I like the idea of powering the cameras from 12v regulators at the pier head, avoiding any varying voltage drop in the 5m cable from the warm room.  In fact I've just ordered some L78S12CV +12v regulator chips.  I've already decided to use a 5v regulator for the USB hub which not only supplies the hub itself but also the guide camera via the USB cable and already have some L78S05CV chips for +5v supplies.

The L78S12CV is specified at 14.5v to 30v so a standard 13.8v PSU is not suitable.  OTOH I have a variety of transformers in my collection plus rectifier bridges and electrolytic capacitors, that I could use to provide an unregulated DC supply.  I'm not unfamiliar with designing and building power supplies

[Gina]

Each port on a USB hub should be capable of supplying 500mA so really you need 2A for a 4-pot hub. I would offer the camera 2A as well, it will only take as much as it needs. TBH the most I see is about 5A drawn from my PSU at any time but there is 33A available on the line at the pier. I doubt my cable would carry all of that at the moment - I have yet to install the proper armoured cable which is sat in the Obs...

ChrisH

I will be having 2A available for the USB hub and for each camera using L78S series voltage regulators as these are rated at 2A.  These are TO-220 packages which I plan to bolt to my hefty aluminium plate that carries the two Evostar scopes.  Fortunately the tab is the common terminal so doesn't need insulating from ground.  Heat sinking will thus be virtually perfect.

[Gina]

HI Gina, i` have used these for 4 years,as recommended to me by a development electrician,and i can honestly say i`ve had not  one problem 

I run my whole obsy from one,and take one if leccy available when out and about,there is also plenty of room in the housing to put extra outputs/sockets.

Link here:http://www.rapidonline.com/electrical-power/rapid-smps-25a-40a-65063    

Regards

Mike

Very nice Mike   If a little pricy   Thank you for the recommendation   I see the 25A one is out of stock though the 40A one is only a few pounds more.

[ChrisLX200]

I can fully recommend this one :  http://www.ebay.co.uk/itm/Powersolve-PSL400BP-12-400W-12V-33A-Baseplate-Cooled-Power-Supply-PSU-AC-DC-IN-/221565139199?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item33964fb8ff

Which is the one I use. I also added a cheap digital display for Volts and Amps (and another for Volts at the Pier).

The one listed above (my external supply) is to the left in this photo

ChrisH

[Gina]

It's only 12v-14v though and the regulators I'm using need 14.5v minimum

I guess there are numerous PSUs available on the 'net.  Probably a 15v one would be fine allowing for 0.5v cable drop.  Or 18v or 20v or even 24v.  I already have a 24v PSU I'm using for my big 3D printer I could get asnother of those I guess buying one would save me making one

[Tinker1947]

I would go with a single 30amp 13.8v mains PSU, then run it to the pier as 13.8v and do the voltage dropping ect.. keep it simple comes to mind.....

[Gina]

Yebbut... the regulator chips want 14.5v   OK I could make my own regulators but 1.8v is not much to play with and the voltage drop over cables has to come out of that.

[Gina]

I know I have some tramsformers with 8+8+8+8 volt separate windings plus a couple of others.  So using two 8v windings to give 16v RMS is 22.6v peak and about 21v after FW rectification.  If we allow for 1v drop in the cables we have 20v.  Now if we say we want 15v supply minimum to the 12v regulators we can afford to drop 5v in ripple.  Roughly, a current of 5A will drop 5v with a 10mF capacitor with FW rectification (100Hz).  (10mF is 10,000 microFarads.)

I could have either one supply using a series/parallel arrangement of windings or two separate supplies with a pair of windings each.

[Gina]

I feel tempted to buy this 24v 10A PSU from Amazon at £20 ish.  I know it's switch mode but I can place it well clear of other equipment and add some interference suppression on the output.  Save me the effort of finding transformers etc. and building a PSU

[Guest]

I would go with a single 30amp 13.8v mains PSU, then run it to the pier as 13.8v and do the voltage dropping ect.. keep it simple comes to mind.....

Plus 1 for that idea

[Gina]

That would mean I have to design and make my own regulators with a very small voltage overhead.  To my mind keeping it simple involves using the L78S12CV 12v regulators which require 14.5v minimum so allowing some leeway means at least a 15v PSU.  I can't seem to find an analogue supply for 15v or more but there are a number of switch mode supplies.

I'll see what's involved in making 4 12v analogue regulators from discrete components

[sloz1664]

Hi Gina,

I use the following on my setup. Ruggedly manufactured to run 24/7.

http://www.ebay.co.uk/itm/HP-DL380-G4-REDUNDANT-POWER-SUPPLY-321632-501-367238-501-406393-001-/390945165506?pt=UK_Computing_Other_Computing_Networking&hash=item5b0625d0c2

Steve

[Gina]

Thanks Steve   What voltage is it?

[Gina]

Been looking into a voltage regulator that will work with just over a volt drop.  It's not easy!  A series power transistor would struggle - not sure about a power FET.  More research needed - this is straying beyond my experience.

One possibility would be a shunt type with a series resistor.  The series resistance could be the cable.  To put some figures on it, if I allow for 1A per camera as specified by Atik the cable would drop 1.8v at 1A ie. 1.8W.  This would be no problem.  I don't think 4x that would be too much for 5m of cable.  Of course it means 4 wires back to the warm room.  The shunt would dissipate up to 12W per supply - a total of 48W - that would keep the mounting plate warm   I have a few 2N3055s around that could be pressed into use.  They would need insulated mountings though.  Alternatively I could buy some PNP power transistors and then the case/collector could be earthed to the plate.  Can't say I'm happy with this approach though.

[Gina]

No - that won't do!  

Have another idea.  I have several exPC PSUs so I could use two of them in series viz. 5v + 12v giving 17v to feed to the pier.  A volt or so dropped in the cable would still give a very suitable voltage to use as the supply to the L78S12CVs.  The raw supplies could be used for the dew heaters and stepper motors.

[Gina]

Here is my proposed circuit diagram for the power supplies using two exPC PSUs.

[Lonestar70]

Hi Gina,

Power supplies can be a real pain can't they.

Roughly, a current of 5A will drop 5v with a 10mF capacitor with FW rectification (100Hz).  (10mF is 10,000 microFarads.)

How did you arrive this figure... I make the capacitive reactance of 10,000uF =  0.159 Ohms at 100hz... this would only drop 0.795v at 5amps.

To put some figures on it, if I allow for 1A per camera as specified by Atik the cable would drop 1.8v at 1A

Same question here... you must be using EXTREMELY thin cable... even thin cable with 0.5mm cross section would  have a typical max resistance of 0.18 ohms in 5 metres which means 0.18V drop at 1 amp... or am I missing something?

The series connection of 2 computer PSU's would only work if the psu's have totally floating outputs... if the Ov connections are connected to the chassis, and to earth... then they will effectively short each other out... best to double check this before trying it... better safe than sorry girl.

Finally have you seen these?

http://uk.rs-online.com/web/p/low-dropout-voltage-regulators/5339381/

12v x 3amp with 1 volt max drop out (typically 0.5v)... they would work well with 13.8volts input and are not too expensive.

Hope this helps.

My very best regards.

Sandy.

[Guest]

Hi Gina,

I have to say I think you are really over complicating what is essentially a simple fix, don't you think??

Olly

[Tinker1947]

Just a thought on the Atik voltage i am sure it used to be listed 12-14volts, i know my 428 run fine on 13.8v.........

[Gina]

Thank you everyone for your replies

I think I'm suffering from a period of confusion   I have a lot on my mind at present

Of course, the Atik cameras can run off more than 12v - people run them directly off power tanks with 13.8v batteries (the nominally 12v lead acid battery is 13.8v) so a 13.8v bench supply will be fine   Also, I have checked the Atik web site and according to their FAQs

What is the maximum voltage that can be used to power the cameras?

13.8V

So yes, using voltage regulators to provide exactly 12v is overkill.  13.8v with a little voltage drop in the cable will be fine