Power supply question

[peter_4059]

I recently purchased a G11 and due to rain up here I'm yet to use it. I've been reviewing my wiring and power supplies and have read a few threads that warn about using multiple power supplies.

The mount came with a 13.8V power supply unit rated for 11 amp peak/10 amp at 50% duty cycle. While this is ample to drive the mount I suspect it is not going to have sufficient capacity to drive the mount, QHY8 and dew controllers. Also I've read on the QHY website that 13.8V is too high for the TEC cooler.

So the question is what power supply do people recommend (needs to be suitable for a mount like the G11) and what is the thinking on using multiple power supplies for the mount, camera and dew heaters? I've never had any problems using multiple power supplies with my EQ6 but wondered if the G11 was going to be different?

Peter

[scagman]

I Peter, I havn't used my mount a lot, only got it early Nov.
At the moment I run my mount of a 15v 2a power supply I also run a power supply for the focuser and 1 for the lappy all from the same 4 plub powerboard and havn't noticed any problems sofar.

[cventer]

What you have shoudl do the job just fine. However I would not reccomend you run dew heaters off the same power supply that powers the mount and camera. The dew heaters osciallate power on and off and this can introduce noise into the camera and gemini may not be too happy about it either. I suggest a separate supply for dew heater.

[RobF]

I'm not an electrician or electrical engineer, but if I understand earlier threads correctly the worst case scenario may be to have multiple (grounded?) power supplies plugged into different GPOs? If there were all off the same powerboard going to same GPO, likely to be ok?

I'm running my QHY9 off a big battery at the moment Peter after the problems I had last year. Hasn't missed a beat so far, although it's probably overkill. Now I think back though, my problems may have co-incided with laptop (and USB devices) powered from inside the house and QHY9 powered from plug outside the house.

[peter_4059]

Rob,

I'd doubt the 240V side is going to be an issue but believe the problem is on the DC side of the power adaptors when a potential difference exists between the -ve terminals of the different supplies. Not sure why there would be a difference or how to check though? I've been running the EQ6, QHY8 and Kendrick dew controller from three separare power supplies for years without any issues but the G11 needs a bigger power supply than the EQ6 so I'm faced with using something new and I want to ensure I don't fry the Gemini!

It seems like there are quite a few people using multiple power supplies without any issues with G11's - typically running 14-15V.

Peter

[Jeffkop]

Pete ... I cant see why a 10 amp Supply wouldnt be plenty to run the items you have suggested ... You are correct ... ideally the G11 will be better running from 15v but 13.8v and a 10 amp supply would still be adequate.

Different DC Power supplies with their -ve terminals not referenced to each other or ground will vary ... most power supply -ve's will be fine referenced to anothers ... the PD of each will still be the same ... (Be warned though that there are some supplies that may not be able to be referenced to another voltage.)

[leon]

When I was powering my G11 I used one 13.8 regulated power supply for the mount and also one 13.8 power supply for the dew heaters, all was fine, and never had a issue.

Leon

[peter_4059]

Jeff,

I assume by "referenced" you mean the -ve terminals are made common? How do you tell if a supply is able to be referenced to another?

Peter

[Jeffkop]

Yes -ve terminals commoned.

A very good question Peter ... The recommended way would be by way of circuit diagram or circuit tracing the -ve side visually ... In the main most designs will accommodate referencing though. If I was going to try referencing I would measure the -ve output with respect to earth first ... this may or may not provide a voltage ... (if its 0 then the supply -ve is obviously already referenced to ground) ... if its above or below zero then I would get a low value resistor say 10ohms and connect that to the -ve terminal then connect the other end of the resistor to earth ... (if there is any kind of spark remove it straight away) measure the -ve and also the voltage between the + and - ... if all is OK you should have the correct output voltage and very little between the -ve and earth ... you can safely reference the supply -ve to any other reference if this is the case.

[adman]

Peter - I ended up running my camera off a 45Ah deep cycle battery - though I'm not 100% sure this solved the problem I thought I had with ground loops. The camera still needed a USB connection to the laptop which was running off the main supply.

If you have the technical skills I would highly recommend running the tests that Jeff has pointed out - would really pay to get it right before you start in earnest.

Adam

[peter_4059]

Thanks for the info Jeff. The QHY8 power supply is double insulated so does not have an earth connection so not sure if it can be referenced to earth in this way?



Thanks for the heads up Adam - what were you using to power the camera before you opted for the deep cycle battery?

Peter.

[adman]

I was using a cheap eBay 240v adapter. I ended up cannabalising that (for the dummy battery connector) and a Jaycar dc-dc converter to power it from the depp cycle battery

Adam

[peter_4059]

I wonder if it was the ebay 240V adaptor causing the issues? The GME PSA1210 power supply seems pretty robust.

[Karls48]

Most of DC power supplies sold (but not all) are floating. Meaning that there is not DC connection to the earth. Some especially the ones with earthed metal chassis have high value resistor and small capacitor in parallel connection to the chassis to reduce high frequency noise. For most of purposes they can be regarded as floating.
To find out if your PS is floating or not - use multimeter! Switch it to low Ohm range – buzzer or diode test. With PS not connected to power connect one probe to common, negative or – (whoever it is called on your PS) terminal of your PS and the other probe to the Earth pin of the mains socket on your PS or (in case of fixed power cord) to the Earth pin of the mains lead. If your multimeter reads open circuit – your PS is floating.
Now if you have a number of single output (meaning – 0 +12V, 0 +13.8V, 0 +6V and so on) floating Power Supplies it is safe and preferable to connect all 0V together. It will not matter if those PS are plugged to different Power points. But it must be done with PS being physically as close to each other as possible (side by side). Running a meters of wire to connect one PS to other would defeat whole point of exercise.
Unless you know what are you doing do not connect multiple outputs or Negative zero Positive PS together.
Personally I would not use non floating Power Supplies for my astronomy gear and regardless what I said about PS the Battery is the best power source especially for cameras as it provide cleanest DC.

[RobF]

Karl, if the problem with floating supplies is lack of a common earth (possibly), what's the downside with non-floating if I may ask?

[Brisbane]

Peter,

my two cents worth, although it may look a little messy, I would still run independent power supply systems for each application as each system has its own voltage operating range requirements. You wouldnt want to damage the sensitive electronics in the G11. I'm not sure if your scope is still under warranty but I'm guessing the fine print specifies use only original equpiment manufacturer accessories.

[Karls48]

One of the functions of DC power supply (beside giving you steady (regulated) DC voltage) is to provide isolation from mains supply. By connecting the mains Earth to the common or negative terminal of the PS you broke that insulation and your PS is (under some circumstanced) electrically connected to the mains.
Look at it this way. Some people build really good piers with deep concrete base. The pier itself may have a similar or even better Earth resistance then your house wiring Earth. Now what will happen if some appliance in the house has leakage or short circuit? The fault current will go along your house mains wiring to the Earth point in your switchboard and blow the fuse or trip the circuit breaker on offending circuit. But, some part of that fault current will also (and it can be significant part - depending on ratio of the Earth resistance on your switchboard and the pier Earth resistance) will pass thru your wiring to the pier and the Earth somewhere on power pole in your street.. As the fault current passes thru your common terminal of your PS it changes ground reference for the voltage regulator and the possible outcome is blown up CCD camera.
All of this is much more complicated then what I have written. I just want to make it reasonably easy to understand to the people with no electronics./ electrical background.
To put it in nutshell. Best option to power Astronomy gear is a battery. Second best are floating PS – analogue PS is well ahead in terms of clean DC, but way behind in terms of costs, efficiency and weight. Switchmode PS are cheap and very efficient but not as clean as analogue. I would not use non floating PS on my Astro gear.

[Karls48]

I would not call it common Earth as it may cause confusion with connecting Power Supply's common or negative terminal to the mains Earth.
Lets call it common 0 Volts terminal.

[RobF]

Thanks for clarifying further Karl :)
(Hopefully I'll be slightly less dangerous to myself and gear now :whistle:)