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[Step-Down Power Supply] Wassup?


JavaLaurence
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I tried running my stack without USB for the first time. I've got the boards linked together as follows: Step-Down, Master Brick, Wifi Master Extension.

 

I've got a 13V DC transformer plugged into the Step-Down Power Supply. When the stack is hooked up via USB, I can see that the Master Brick can measure the stack's voltage as that supplied by the Step-Down. But when I pull out the USB cable, I would expect that the whole stack carries on happily as if nothing happens. Instead, everything falls dead.

 

Did I misinterpret the function of the Step-Down Power Supply? Shouldn't it be capable of powering the bricks?

 

When I try to start my stack without any USB, and I plug in the DC supply, then the Master Brick lights don't light up..

 

:-(

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You interpreted the function of the Step-Down Power Supply correctly.

 

The way you are describing it, it sounds like the 5V rail isn't working (which is used to power the Bricks).

 

Can you check if the Board-To-Board connectors are connected correctly?

 

We do test the 5V rail of each Step-Down Power Supply, so i don't understand why it wouldn't be working.

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I had a good look at the Step-Down board, and with bright light shining on it, I can't see any visual problems (with naked eye).

 

When I plug the Master into the Step-Down, I ensure that the triangular markings align. I have a multimeter, but I'm afraid its probe pins are much too big for the minute leads on your designs. Instead of measuring, I would be shorting things..

 

Is there any other way to diagnose a rail problem?

 

The system that I'm trying to put together cannot be powered by USB, and also has to be wireless, as the whole stack is going to live in our cellar, with the spiders and the mice.

 

So I need this Step-Down to work as advertised, or I cannot complete the solution I have in mind.  :-S

 

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No worries, if it is broken we will of course replace it. It is just so unlikely that the 5V rail isn't working. Can you measure the voltage of pins in the green connector? And are you using the black connector for input (Black is input, Green is output) ?

 

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:-) I'm actually using my only (very cheapo) multimeter's cables to connect my little DC adapter (bought from yourselves) to the Step-Down PS. So to do any measuring, I'd need to make a cable first. While I'm on the subject, I really think you should add a cable to your catalog that can connect a DC adapter to the Step-Down.

 

And yes, I only used the black connector. And I didn't swap + and - around. I'll try to make a cable, so that I can use my multimeter and measure the green connector's voltage...

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OK, made myself a crappy cable, so was able to measure the output voltage: looks like 5.6-5.7V. Definitely not a clean 5.0, though my meter is analog, so could be off by a few tenths.

 

5.6-5.7V is ok for a unstressed Step-Down power supply is ok (I would expect this). With load it should drop to 5.2-5.3V. The reason for the higher voltage (with respect to 5V) is, that we want to make sure, that if you use a Step-Down power supply, that it is used to power the stack (the higher voltage powers the stack since all supplies use diodes to supply the stack).

 

When I plug the DC supply into the Power-Down as part of a stack, the AC-DC transformer block changes its faint chirping noise to a higher-pitched noise. Unfortunately I don't know squat about electronics .. but sounds like a clue..

I guess this should be ok. Transformers can make sounds and change their behavior based on the load.

 

The weird thing is, that if the power supply works, everything should be ok. You have measured the output voltage at the green connector, right? Can you please do it when the stack is connected and the power supply should power the stack? Is there any chance that your DC transformer has not enough power? Can you test another supply, e.g. a battery?

 

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Yes, I did measure the green connector, not the black. The transformer is OK because it used to power a Wifi router until very recently. It's rated as producing 12V (see attachments).  I now measured the output voltage with a stack, and I'm afraid I get the same reading (see screenshot of setup).

IMAG2414.thumb.jpg.f4a0623301f4b26609ea89e46052e79a.jpg

DC_Supply.thumb.png.4b7c84f71d13c7816571bbb5198ad370.png

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The only reasonable explaination is that you have measured with an attached Master Brick, right? Please measure at the green connector without any Bricks attached.

 

The reason is, that the green connector is connected to 5V stack voltage. If the Step-Down Powersupply does not power the stack, but you have attached e.g. a Master Brick with USB connected, you will measure the voltage supplied by USB.

 

Weird is that if thats the case I wouldn't expect a voltage above 5.3V.

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I measured with and without the Power-Down as part of a stack. So I have measured it stand-alone, and with a Master Brick and my Wifi Extension (as the picture clearly showed). In both configurations, the measured output voltage is identical. Also note that in the stack config, Brickv shows a stack voltage and small current consumption. So clearly, as part of the stack, the Step-Down has some "effect" on the stack.. but it fails to power the whole stack when I pull the USB cable out. Also if I take my cold stack, and plug the DC supply in, then absolutely nothing happens. No LEDs, however briefly, light up.

 

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  • 4 weeks later...

Short "post-mortem" comment for people who are interested in this thread.

 

The final conclusion was that the Step Down was not broken at all. It was a Master Brick problem. I bought two Master Bricks, and the dead rail problem only occurs with one of the Masters. If both are in the stack, the stack also doesn't get any power.

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