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Old 31-12-2011, 02:07 PM
JohnH's Avatar
Member # 159

JohnH is offline
Join Date: Feb 2005
Location: NSW
Posts: 1,205
USB Laptop Voltages - and a dead CCD

I have a wierd problem with powering my AP kit. I have worked with this setup ok for a couple of years but recently changed my ccd and since then have had issues - finally resulting in me smoking my ST2000xm - not good!

So I will share this information for those who might have similar setups and/or similar experiance.

My original setup was to have my laptop indoors and connected to a USB hub at the scope using an active USB extension cable. The hub then connects to the mount (a G11G) via a Belkin USB to serial convertor, to the ST2k via a USB cable and to a Moonlite stepper controller with another USB cable. The ST2k connects to the autoguider port of the G11G using RJ11 6P6C cable. All the remote kit is supplied with power from a single, regulated power supply (Jaycar unit providing 13.8V).

This has worked ok so long as I did not use the Sbig AC power supply.

Recently however when I connected my ST2K the red light did not come on the fan did not run and the camera was not visible from CCDSoft. I disconnected and re-connected - smoke from the CCD.

What I have found is that the USB 0 V level on my laptop is +12V with respect to the 0V at the power supply. If I disconnect my laptop from the mains this drops to 0V. I have no idea what causes this.

The bottom line seems to be - even though I have the newer Gemini 1 which isolates the autoguide port from the electronics the use of the relay box is a good precaution. I now want to re-configure so that all equipment is isolated.

I believe the usb/serial convertor will provide isolation from the hub, the relay box from Sbig will isolate the gemini from the ST2k as well, there is still potential for problems at the hub to the ST2K. I think you can get special USB hubs that isolate - does anyone use those, where can I get them? Do they work?

Is there a better option?

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