Optical Isolation on USB Port

General Discussion of the 4 Cell Charger that Paul is working on.
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Mark
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Optical Isolation on USB Port

Post by Mark » Fri Oct 18, 2013 7:50 am

Since the 4 cell version of the charger will be powered by an external power source, I think it would be a good idea to include optical isolation on the USB port so that a ground loop doesn't cause damage to either the charger or a connected PC.

Paul.Allen
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Re: Optical Isolation on USB Port

Post by Paul.Allen » Sat Oct 19, 2013 5:01 pm

that is a great idea. I have been thinking about isolation and wish I could have been able to do it with the 2 cell version (it would have been one more thing added to the cost After I already had the money).

Mark
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Re: Optical Isolation on USB Port

Post by Mark » Sun Oct 20, 2013 1:08 am

I don't think it's as important for the 2 cell version since it can be powered from the same computer/hub that is connected via an FTDI port, so there's no chance of a ground loop.

(Of course, it's still possible to connect the charger to an external power source and the computer at the same time and end up with a ground loop)

DeweyOxberger
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Re: Optical Isolation on USB Port

Post by DeweyOxberger » Mon Oct 21, 2013 3:10 am

I'll have to look but I was under the impression that most wall-wart switchers are elv or selv. If that is true have a good ground connection between the supply and the usb port and you shouldn't need any opto-isolation. Opto-isolation is surprisingly hard to do well (the hard case is fast transient immunity).

Mark
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Re: Optical Isolation on USB Port

Post by Mark » Mon Oct 21, 2013 4:35 am

According to:
http://en.wikipedia.org/wiki/Extra-low_voltage

ELV allows up to 60V DC between any conductor and earth - I'd expect that would be more than enough to fry a 5V controller if there was sufficient current leakage.

Paul.Allen
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Re: Optical Isolation on USB Port

Post by Paul.Allen » Thu Oct 24, 2013 4:33 am

I am working on a little optoisolator board to go between an FTDI adapter and the charger. That way for those who are interested in monitoring real time with their computer (not just programing the charger) can do so.

Mark
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Re: Optical Isolation on USB Port

Post by Mark » Thu Oct 24, 2013 4:50 am

Sounds good!

Maybe just do the whole FTDI chip and optoisolator on the same board? Would make it a neater solution. Might be a more expensive option though - it wouldn't surprise me if it cost you more for the FTDI chip than the Chinese sellers on Ebay are able to sell them for including the board, a cable and postage!

Paul.Allen
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Re: Optical Isolation on USB Port

Post by Paul.Allen » Thu Oct 24, 2013 5:02 am

Mark wrote:it wouldn't surprise me if it cost you more for the FTDI chip than the Chinese sellers on Ebay are able to sell them for including the board, a cable and postage!
Probably!

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