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flygal6
journeyman
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Reged: 03/03/13

Meade 12V pwr cord tip polarity
      #5841730 - 05/05/13 01:51 PM

I have a meade 12v pwr cord and one of the wires pulled out of the tip. I unscrewed the collar with the intent of making repairs and resoldering the wire to the tip. To make a long story short, then the connection tip broke off totally. Off to radio shack I go. I purchased a 12v 5amp power cord and the correct adapter tip (this was the only type they sold). My first question is this power cord safe to use as a replacement? Second does anyone know if the original cord has a positive or negative tip polarity? I need to know this to make sure I put the tip on correctly and not get it reversed.

Thanks Carol

Edited by flygal6 (05/05/13 03:37 PM)


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Whichwayisnorth
Pooh-Bah
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Reged: 07/04/11

Loc: Southern California
Re: Meade 12V pwr cord tip polarity new [Re: flygal6]
      #5841746 - 05/05/13 02:03 PM

Center is positive, outside ground.

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highertheflyer
professor emeritus
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Reged: 07/08/05

Loc: Aledo, Texas
Re: Meade 12V pwr cord tip polarity new [Re: Whichwayisnorth]
      #5842533 - 05/05/13 09:44 PM

Quote:

Center is positive, outside ground.



This statement so true, and never ever, to cross the polarity!
Make certain you find a way to always connect the positive to the positive, red to red, big prong to little prong, etc....!

Perhaps someone here on Cloudy nights can come up with a way that would protect your choices in the wee hours of the night and as a backup, not allow you to cross connect.
Jim


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flygal6
journeyman
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Reged: 03/03/13

Re: Meade 12V pwr cord tip polarity new [Re: Whichwayisnorth]
      #5842549 - 05/05/13 09:58 PM

Thanks - it worked!

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nitegeezer
scholastic sledgehammer
*****

Reged: 11/27/07

Re: Meade 12V pwr cord tip polarity new [Re: highertheflyer]
      #5842675 - 05/05/13 11:24 PM

Quote:

Quote:

Center is positive, outside ground.



This statement so true, and never ever, to cross the polarity!
Make certain you find a way to always connect the positive to the positive, red to red, big prong to little prong, etc....!

Perhaps someone here on Cloudy nights can come up with a way that would protect your choices in the wee hours of the night and as a backup, not allow you to cross connect.
Jim




I have thought of putting a bridge rectifier on the inside of that connector to make it a don't care. That would protect polarity issues, but I am not sure if the 1.5v drop across the bridge would be too much. I don't want to protect myself from one problem and just create another. It all depends what the lower limit is on the power requirements.


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OzAndrewJ
scholastic sledgehammer
*****

Reged: 11/30/10

Re: Meade 12V pwr cord tip polarity new [Re: nitegeezer]
      #5842682 - 05/05/13 11:38 PM Attachment (6 downloads)

Gday NiteGeezer

Quote:

but I am not sure if the 1.5v drop across the bridge would be too much.




You also need to be careful re ground loops doing this as well.
ie items coming off the same battery/supply, then directly connecting to the scope, like guiders etc.
One way to protect agains reverse polarity is to use a reverse biased PChannel Mosfet in the supply line, and wire it up so it will only ever open if the polarity is correct.
A simple test utility is to get a multi colour LED ( or wire 2 LEDs back to back ) in a plug unit.
Put the cable into the unit and one of the LEDs will always glow
and the colour tells you the polarity.

Andrew Johansen Melbourne Australia


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nitegeezer
scholastic sledgehammer
*****

Reged: 11/27/07

Re: Meade 12V pwr cord tip polarity new [Re: OzAndrewJ]
      #5842735 - 05/06/13 12:20 AM

That looks like a great idea.

Up to now I have not worried about ground loops because I was pretty much a visual user. I am now going to get serious about ap, so I know there are issues. My Canon camera by itself would be no problem as there would be no interesting current paths to worry about, but I have decided to operate my camera remotely from a laptop so I know I am going to have to be careful. I am going to see how well I can do without guiding, I consider this more a learning experience rather than going for the perfect shot that first night. I will spend this summer learning what I can do with what I have, and then during the winter look at guiding to see how that would help. By taking little steps, I hope to avoid the ground loop issue. I have put large systems together in the past, and tracking down a ground loop with a large system is a nightmare, so I like to grow things a little at a time.


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