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 Post subject: Voltage Limiting
PostPosted: Tue Apr 29, 2008 4:01 pm 
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Roboteer

Joined: Fri Apr 04, 2008 2:34 am
Posts: 43
Hi

My current project requires that I step 12V down to 7.5V to power a wireless router. I have never done anything like this before and am a little nervous about it. Just need a little help.

Cheers,


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 Post subject:
PostPosted: Tue Apr 29, 2008 7:41 pm 
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Robot Guru

Joined: Tue Feb 28, 2006 12:27 pm
Posts: 2172
what current (in amperes) or power (in watts) does the router require? voltage is only half of the information required to determine what type of regulator or converter is necessary.


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 Post subject:
PostPosted: Tue Apr 29, 2008 11:58 pm 
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Roboteer

Joined: Fri Apr 04, 2008 2:34 am
Posts: 43
Ohh yeah that could be useful.

The router wants 1 amp. An I am using a 12V battery to power it so i am not worried about not enough power just to much.

Thanks for the help.


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 Post subject:
PostPosted: Wed Apr 30, 2008 2:47 am 
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Roboteer

Joined: Sun Jan 13, 2008 10:38 pm
Posts: 3
Have you opened the router and had a look at its power supply section? If it is using a linear converter such as a 7805, which sounds likely based on the 7.5V input requirement, you can connect it directly to the 12V supply.

Adi


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 Post subject:
PostPosted: Wed Apr 30, 2008 6:47 am 
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Roboteer

Joined: Sat Dec 23, 2006 3:03 pm
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That would mean the 7805 has to dissipate 7 Watts as opposed to 2.5 Watts, significant difference :wink:

_________________
Ok wait... that part isn't supposed to be smoking..


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 Post subject:
PostPosted: Wed Apr 30, 2008 10:04 am 
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Robot Guru

Joined: Tue Feb 28, 2006 12:27 pm
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ScuD has a good point. To use a linear regulator like a MC78M08 or LM317T (adjustable, set to 7.5V) you will need to be able to dissipate roughly 6W from the device (input to which could actually range from 13.8V to 10V or so if using a 12V battery). You also may want to consider that if running from a battery the efficiency of the regulator might be important. This all suggests a small dc-dc converter or switching regulator circuit might be a good idea. Has anybody seen any R/C switching BEC devices that output other than 5V or 6V?


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 Post subject:
PostPosted: Wed Apr 30, 2008 11:00 am 
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Roboteer

Joined: Fri Apr 04, 2008 2:34 am
Posts: 43
HI

Thanks for the interest.

The router is powered by a wall wart transformer:

MODEL NO:AM-0751000D41
INPUT:120VAC 60 Hz 15W
OUTPUT 7.5VDC 1000 mA

The router is a D-Link DI-524:

Where the plug from the transformer goes in to the casing 7.5V = 1A is stamped on it. On the inside the terminal is wired right onto the board.

Thanks again guys.

PS just thought of something could it be possible to run it on 6V instead of 7.5? Is there a danger in doing so with an electrical device like this?


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