Ground Loop?

[adman]

Having just installed a Gemini on my G11, I think I am now getting problems with ground loops - stuff freezing, errors from QHY5 in PHD etc

I have drawn a diagram of all the connections in my setup - and now that I have done that it is easy to see where the problems might be - but what do you do about it? I understand there are USB isolators - does anyone else use these? And where do you get them?

If I did get one or more isolators, where in the diagram would be best? If I put them in the obvious places between the netbook and usb hub and netbook and gemini, it still appears there would be the potential for a groundloop through 550D Power --> 550D --> USB Hub --> USB Hub Power...? Is that right? I have only basic knowledge about this stuff, so go easy if I have got it completely wrong.

Thanks
Adam

[multiweb]

I have a similar setup. I would try that. What USB to serial adapter do you use? Are they opto-isolated?

[multiweb]

I also have bought a couple of these (http://www.keterex.com/kxusb150.php) in the past. They are very expensive but you think about it you are protecting equipment that is worth $$$. Here's an excerpt of an old correspondence on the Gemini Yahoo Group:

Hi all
I will once again put my 1 cent into this thread.
This is a message I have sent in the past.

The Gemini 1 is sensitive to Ground loops and static electricity. Of
course lighting is also a cause of failure.
I have had to replace about 20 RS232 chips and 3 guider chips do to
either Ground loop voltage, Static electricity, or
lighting in the case of 3 of them.
I would use an isolated adapter for the Guider input, if your camera
does not have isolated outputs.
If you are using a USB to serial adapter for the RS232 input, then one
of these 2 devices will help prevent
ground loops:
http://www.keterex.com/kxusb150.php (http://www.keterex.com/kxusb150.php) available from Mouser also.
http://www.poscope.com/product.php?pid=23 (http://www.poscope.com/product.php?pid=23)

I have both and they both work. You get a message that you could have a
faster connection
if you use a USB 2.0 device with the second less inexpensive device, at
least I did.
I use them with an FTDI based USB to serial adapter from Mouser called
the US232R-10
*http://tinyurl.com/l77sez (http://tinyurl.com/l77sez) *

Tom Hilton

[Poita]

I build my own from the kits here:
http://www.circuitsathome.com/products-page/usb-interfaces/adum4160-usb-isolator-board-bare-pcb-and-kits/

If you need a couple you can save a lot of $$ that way.

Or you can buy the board fully populated
http://www.circuitsathome.com/products-page/usb-interfaces/adum4160-usb-isolator-board-populated.

[cventer]

I have never been worried about ground loops before on either my G11 or MI250 both use Gemini level 4.

Maybe I have just been lucky.

Who else with Gemin has had ground loop isues ?

Is this something we really need to worry about ?

[Barrykgerdes]

I spent a lifetime in the electronics industry and while I knew of the effects of ground loops I never had any bother other than noise on secure data lines and this was cleaned by screens and single point earthing.

One interesting problem we often had with poor grounding was with mains equipment that had input filtering on the mains lines. If you did not have a good ground the gear would sit at half the mains voltage with respect to ground. Quite shocking!

Our G11/Gemini has no problems and runs in the field from the generator that also supplies a number of computers, telescopes, heaters, cameras etc.

Barry

[multiweb]

I've had arcing between my hands and the alu tripod in very dry nights enough to drop the USB communication to the lappy and have a bit of a jolt myself but I haven't had any major damage. Ever. Although I have heard and read many times on the Gemini groups people having to change specific fuses on the gemini board or components linked to local surge in voltage. One cannot be too cautious IMHO.

[jeff65]

As someone who has some amateur experience in electronics, I can say from looking at the wiring diagram there are many potential problems here. Add to this that you or your tripod acting as an earth return may present lower resistance than the earth returns in the electronics and you've got a potential nightmare. I'm not surprised someone might get a jolt once in a while. Operating this set up while standing in wet grass or on a concrete slab in bare feet could be a really bad idea.

I am not qualified or experienced enough to give advice regarding the approach to resolving this and ensuring its safe. I hope the thread attracts the attention of someone that feels comfortable doing this.

[adman]

thanks for the helpful replies everyone.

I did have some problems on the digital drive as well - if I ever looked through my cameras viewfinder I would get a little zap off the metal surround - felt like a pin sticking into my eyebrow (I keep the eyecup off so I can cover it when doing darks with that little rubber cover you find on the shoulder strap) This did sometimes upset the digital drive - the guidespeed and TVC would reset to their defaults.

But now with the G11 it is making the 550D not respond to on-camera button pushes (but will still control OK via USB), and I get an error out of PHD, and strange chopped up images from the QHY5.

Marc - that sounds like a good idea changing the USB-serial to go through the hub - actually very obvious - although it had't occurred to me :P. I do have a spare port on the hub.

those little poUSB things for $39 euros each might be the go...

cheers
Adam

[multiweb]

Yeah I think so. Everything helps. I forgot to mention I even blue screened the laptop once . I had my hand holding the mouse on the Alu table and reached for the focuser... Zap! :scared: But then again I'm prone to statics. On a windy day I'll always zap on the car door when getting out. I even zap people. My mum's the same. Even worse. Maybe it's biological? Some people retain charge more than others. I don't know..

[adman]

my next question is - do the ground loops only occur through USB connections - what about the power supplies - or are these isolated already by their transformers?

The path I am worried about (from my diagram) is

USB Hub Power --> USB Hub --> 550D --> 550 Power

for the isolators I imagine that if all USB stuff comes off the hub, then a single isolator between netbook and hub should be sufficient - surely I wouldn't need one off each hub port? It also looks like the isolators reduce the USB throughput a little...would this upset anything?

Adam

[mithrandir]

That implies the generator is providing the common ground.

The 240VAC is all on one power board? Not multiple power points which could be on different circuits and floating at different grounds.

Maybe start by opto isolating the ST4 cable (if you can find one of those) between the Gemini and the QHY5. If you can't find one of those, a USB one between the hub and the notebook. You might need more than one, maybe as many as three, or experiment to see which USB most needs it. The QHY5 gets its power from the USB so i guess you can't put an isolator between the hub and it.

Andrew

[multiweb]

To confirm with Theo but I am pretty sure the QHY5 ST4 output is already opto-isolated.

[adman]

I am pretty sure that the biggest issue is with the netbook --> gemini connection. If I pull that one the problem goes away.

I have just ordered 2 of the USB isolators - will have to make do till then - but will give it a try moving the gemini connection to the hub

Adam

[adman]

Yes - all off the one board

Adam

[adman]

the QHYccd website says the ST4 port on the QHY5 is optically isolated.

Adam

[cventer]

I believe QHY5 and Starshoot autoguiders do have an Opto Isolated ST4 port from everything I have read.

I am confused by post below. If what I am reading is correct does this mean if everthing runs off same power source and same powerboard then ground loops are not an issue ?

[jeff65]

Does it go away if you run the netbook off its battery?

[adman]

hmm - good thought -not sure I will give it a try and post the result. Thanks for the suggestion.

Adam

[adman]

I think if you are not having any problems with connected gear, then you probably don't need to worry. But with mine, it was affecting my laptop (the trackpad was almost unusable), and the camera (did not respond to any on-camera button presses, and would disconnect randomly which has never happened), and god know what it would do to the gemini over time.

Like Marc says - the stuff we have wired up is worth many thousands, if I can protect it with a $50 isolator, I'm in.

Adam

[adman]

OK - did some testing the other day. Findings:

1. it doesn't help to just run the laptop off its battery.
2. I have moved the USB-Serial to the hub - thanks Marc!
3. The main problem looks like it was the 550D power supply - although I did not test running the camera on its battery with the USB-serial in its original position (as per pic in original post)

I have ordered 2 usb isolators, one of which I will put in front of the hub, and if I still get problems I will put one between the 550D and the hub.

Will update once they are delivered.

Adam

[multiweb]

Some more information I had saved in an old text file:

/////////////////////////////////////////////////////
Ground loops and power supplies are tricky things. Take these steps to find out if you have a possible ground loop.
1. Turn off all power supplies. Leave the power supplies plugged into the house current.
2. Disconnect all power supplies from the Gemini and camera. Leave the one to the computer plugged in.
3. Measure with an ohm meter between the Gemini power pins of the VCD OUT GND pin (see page 131 of L4 manual) on the Gemini to the Ground pin of the Camera and then a ground spot on the Computer. Also measure between the camera and computer. A reading of NO ohms would be perfect. Any low reading could mean you might have a ground loop. This means that the power supply input is not isolated from the power supply output.
4. Next turn all power supplies on. Measure for voltage between the ground outputs to each other. A zero reading is good. anything above 1 volt is bad. Voltage between 0 and 1 volt can also be bad, but depends on how large your wires are. Remember that you are doing this with no/very little current flowing.
5. Reconnect the camera, Gemini and computer. do step 4 with them connected. and see what you have. They should not have changed much. Again voltage between the units is a bad thing.
Computers can cause ground loops because they normally get connected to many other powered devices like monitors, networks and printers through wires.
The best way to eliminate ground loops is to have all the neutral (ground) DC output of every device tied to a central point, through a heavy (12 Gauge) wire. The central point when using a Gemini would be the Gemini ground input pins. This is not easy to alway do. The next best is opto or magnetic isolated inputs to the Guider and RS232 inputs.
If you do do a central ground between your devices, consider puting in a ground rod at least 8 ft deep next to the central point into the ground. This can help prevent static damage.
The best preventive is to use Isolated RS232 or USB adapters and Guiders into the Gemini. They can eliminate ground loops. I use one on all inputs to my Gemini. Of course I manufactured my own.
One word on note: The Gemini's with the slide switch for power do not have the electronics grounded to the case. The Gemini's with the Toggle switch do have the electronics grounded to the case.
//////////////////////////////////////////////////

[adman]

Any chance you might know where I can find GND on the 550D? What about the netbook - are there any obvious ground points on USB ports or monitor outputs?


Do you mean no resistance, or very high resistance. No resistance will mean the current will flow very easily - or is that what you want to stop differences in potential? I am so not an electrician...

I guess this would be DC voltage?? I don't want to upset my multimeter...


Thanks for the info Marc. Will try to find out some more info and give it a go.

Adam

[multiweb]

Here's some info (http://pinouts.ru/Slots/USB_pinout.shtml)on USB wiring. No idea on the 550D.



Very low resitance to no resistance. It's very unlikely you'd get no resistance at all though.

[Hagar]

I have been using a G11 and lots of other bits like you and have only ever had problems with the USB to seal adapters. I have tried quite a few with very spasmodic results. The only way I have been able to eliminate all my problems was to firstly get the Qhy5 off the hub and on a single USB connection and secondly get the Gemini connected to a true RS232 connection and everything worked. My observatory rotation also posed problems with the USB to serial adapter and a swap to rs232 fixed that as well.

[adman]

thanks Doug - when you use the QHY5, do you have the guide cable connected to the gemini, or do you just have a USB cable connected?

Adam

[Hagar]

Adam, I have the guide cable connected to the St4 port on the Gemini and the USB cable connected to the laptop.

We did find there can be a lot of timing issues using USB to serial adapters where they didn't report back to the Gemini or laptop with stop bits and effectively just disconnected USB items at random.
At times either the little LED on the Gemini hand controller would just go off while the gemini power led kept running. This was the Gemini disconnected and likewise the qhy5 would do similar.

[JohnH]

Hi Adam did your USB isolators arrive yet? Did they fix your problems?

I am having very similar issues here with a G11G (new type - rocker switch and round motor connections) and a similar setup.

In my case I have the G11G powered buy a Jaycar 13.8V regulated PS, that also provides power to the dew heaters and my moonlite stepper focus controller.

Also running off the same mains socket are a PS for a powered usb hub and the camera power supply.

The laptop connects to the G11G via the usb hub and then a Belkin usb to serial converter, the camera and focus controller are also connected to the hub.

What I found was USB timeouts when image downloads were in progress. I thought to fix that with a second USB cable direct to the camra but when I made the connection at the laptop I got a spark from the USB shield. That stopped me in my tracks!

I measured a 24.7 V poterntial difference between the usb shields on the camera usb cable and devices connected to the Jaycar PS.

I think I can avaid this issue if I swap the ST2k power supply for the DC version and run everything of the Jaycar PS but I am reluctant to experiment for fear of blowing up something expensive. So far I only seem to have fried the USB hub.

Can anyone confirm if this idea is sound?

Regards

[frolinmod]

Do you really expect anyone to venture an answer knowing that no matter their answer, you could potentially fry your camera? Who wants to be involved with such a disaster? Not me!

[mill]

I also have a G11 with Gemini 2 and i run everything from one power supply and have no problems at all.
I made a power supply box that is fitted to the telescope and has 8 x 13.8 volt outputs and 1 x 5 volt for usb and 1 x 8.4 volt for my Canon 10D.
My power supply is a 13.8 volt 12 Amp switch mode like the one from Jaycar.
Also why are you running usb to the G2? Lan is much faster now the new firmware has been posted to the general public and it wont hog up precious usb bandwidth.
Hooked up to the box are 3 dew heaters, QHY9m with filterwheel, G2 and my Canon 10D.
One power supply means no ground loop and having everything insulated helps too :thumbsup:
I have this setup now for over 2 years and have had no problems at all.

[mill]

PS: here is my wiring.

[tlgerdes]

24.7v difference is not a "ground Loop" problem, you just have some strange/crappy wiring. :lol:

[JohnH]

Thanks that gives me hope ! I may have confused you it is not a G2 but a G11 mount with a Gemini v1 controller.

[JohnH]

Yup I find IIsers a most helpful bunch!!

[mill]

G1? Bleh!!!! :rofl::rofl:

[tlgerdes]

Also, 2 pin 240v power supplies can give problems as they dont have a local ground reference.

[tlgerdes]

Yeah well at least they work :P

[mill]

Hehe the G2 works flawlessly now and we will have loads of features later :P
Just joking, i know that the G1 is working well :)
The G2 will have more options because of all the feature ports build in.

[adman]

Hi John - yes my isolators did arrive, but I wasn't very happy with them. For a start they only ran at USB 1.1 speeds - not great. Then secondly I was still getting problems even with them connected. By trial and error I was able to localise the problem to the dodgy eBay power supply for the 550D. If I ran the camera off its battery, I had no problems.

So my solution was to buy a DC-DC converter from Andrews Communications that gives me the correct voltage for the Canon, and use the dummy battery from the dodgy power supply. Then it was snip-snip solder-solder and hey presto I can now run my 550D off my 45 amp hour AGM deep cycle battery - should last several days before needing recharge. Not the most elegant solution - I would like to have been able to solve it with my setup as it was (now I have to lug said battery with me on field trips...) but I am no electronics whiz by a long shot, and so took the path of least resistance (pardon the pun)

My theory is that if I paid the big bucks for a genuine canon power supply, I wouldn't have had any problems...maybe?

Regards
Adam

[JohnH]

I am now powering all my equipment from a single DC source (except the latop) and that seems to have cured the problem but I have another with my guide cable. I will make a new post for that though.

Thanks to all for your help!

John