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12 vdc to 5 vdc converter

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#1 darkman

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Posted 08 April 2012 - 12:35 PM

I have a 7-port powered USB hub on my scope, instead of using the ac transformer I’d like to power it from the 12 vdc already at the scope supplied from my deep-cycle battery.

I’ve done a little searching but can’t find a suitable dc to dc converter/regulator: I need 5 vdc @ 2.5a, any ideas?

#2 Denimsky

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Posted 08 April 2012 - 12:46 PM

I've been using this for my powered USB Hub used for my imaging rig without any problem.

http://www.powerstream.com/dc6.htm

#3 darkman

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Posted 08 April 2012 - 12:53 PM

Are you running at the 4.5 or 6v setting?

#4 Micheal

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Posted 08 April 2012 - 01:59 PM

If you are handy with a soldering iron and have a radio shack nearby, you can buy a 12v to 5v voltage regulator, some resistors and a heat sink and make your own.

#5 Denimsky

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Posted 08 April 2012 - 04:03 PM

I think I'm using with 4.5v but I can confirm it tomorrow when I get home.

#6 ccs_hello

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Posted 08 April 2012 - 04:08 PM

Rusty,

DIY version:
Use this LM2596 based module described here in CN. Set it to 5V output.

Also the detailed DIY steps: this CN thread.

Clear Skies!

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#7 Arctic_Eddie

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Posted 08 April 2012 - 07:53 PM

Here's the regulator link. I've used several now and they work great.

http://www.ebay.com/itm/260858526297

#8 Denimsky

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Posted 09 April 2012 - 04:53 PM

Are you running at the 4.5 or 6v setting?


I checked and the setting I use is 6v.

#9 darkman

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Posted 09 April 2012 - 07:44 PM

Thanks, and to everyone

#10 Mike Clemens

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Posted 09 April 2012 - 09:22 PM

I think i'm going to pull the pot off a few of those ebay boards and put some resistors down selecting 3.3V, then run a bunch of loads on em and see how well they regulate.

#11 Phil Sherman

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Posted 09 April 2012 - 09:42 PM

I just purchased a bunch of these for use with my scope and some other projects. I ran into two issues with them.

1. There's no mounting holes for the board. Resolution - get a 1/2" strip of thin brass from a hobby shop ($1.00) and make a mounting bracket that's soldered to the bottom of the board. This also provides a good heat sink.

2. I needed two of these in my scope power box. One for 5v (USB) the other for 8v (Canon camera). I decided to simplify the mounting by attaching both to the same heat sink. There's an interaction between the two units that disables the current limiting and locks both to maximum output current, 3A. I also had to electrically insulate the heat sinks from each other, even though the grounds for both boards are all connected to the same ground bus. I still don't understand why this was necessary since the heat sinks are attached to the ground plane of each board and the ground planes are connect at the ground bus. A friend of mine who spent a lifetime designing electronics for aircraft, where interference is a major issue, said that we'd have to set up a test bed with a pair of them to figure out where the feedback between them is occurring.

The same suppliers also have a buck-boost regulator that may be of interest to EQ6 owners. I added one to my power box for the mount and now don't have to worry about low battery voltage to the mount.

Phil

#12 Mike Clemens

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Posted 10 April 2012 - 10:37 AM

I have been using a Pololu buck converter ( http://www.pololu.co...og/product/2110 ) to power the logic in a dew heater controller project I am working on. It is painfully expensive at $15 each. I thought i would try one of these cheap converters so I bought a small pile of them.

I put both units on the scope last night and found this cheap ebay converter had a slightly cleaner looking output with less apparent ripple and less high frequency noises.

Unfortunately though when I powered up the device with it (3.3V device ~100ma) the display would flicker when powered by the cheap unit only, and periodically reset on its own.

Maybe my application is too low current for it to perform to spec? Not sure but my display is solid on the Pololu board.

Also I found that when hooking up _the input power only_ to the ebay switcher that I could make a dead short by scraping the wall of the IN+ through-hole with a mini-grabber hook. I need to get the board under the microscope to see if it's not a plated through hole and if there is a middle ground plane exposed inside that hole!

#13 bassplayer142

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Posted 10 April 2012 - 11:12 AM

Keep in mind that any regulator above 2.5Amps will work. The circuit will only draw as much current as it needs which is up to 2.5Amps. In fact, staying above the 2.5Amp limit will stress the circuit less and probably increase the longevity and operation of the regulator.

If you really want a clean output use a older generation linear regulator rather than a switchmode regulator. The linear regulator will be a lot cleaner of a signal but will be less efficient as a drawback. Either that, or the cleanup of a switch mode high frequency signal can be cleaned by a pi filter. This will remove the high frequency harmonics that bring noise into the system.

http://en.wikipedia....or-input_filter

#14 Mike Clemens

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Posted 10 April 2012 - 01:07 PM

I have avoided linear regulators for this solution since the input voltage could be anywhere from 9V - 16V and with an output of 3.3V that is a lot to drop on the regulator. I just switched to an OLED display though so my power requirement has dropped a lot. I'll need to just try it and see how much it heats up.

#15 Arctic_Eddie

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Posted 10 April 2012 - 06:19 PM

You can mount the eBay switchers using two ring type crimp lugs. Take the insulator sleeve off and split open the inner part. Bend each lug to 90° and slide the split part over the edge of the board and solder. The ring part will now bolt to the side wall of a box. This also becomes part of the heatsink.

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#16 ccs_hello

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Posted 10 April 2012 - 10:55 PM

...Unfortunately though when I powered up the device with it (3.3V device ~100ma) the display would flicker when powered by the cheap unit only, and periodically reset on its own. ...

Mike,

For your 3.3V 100mA application:
I'd suggest adding one additional 330uF 20V capacitor on the input side and one additional 220uF 6V on the output side.
(It's based on some suggested values on LM2596 datasheet.)

Clear Skies!

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#17 Mike Clemens

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Posted 11 April 2012 - 04:19 AM

appreciate the advice, I'll report back






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