My way of "fixing" the 5V power supply problem...

[Andrew Jergens]

UPDATE - As Chris and Warren were quick to point out, this first post contains some incorrect terminology and also a typo regarding the barrel jack size.  However, the linked products are specifically the ones I used with great success.  Please read a few posts following this one to make sure you fully understand the idea conveyed.  The original unedited post proceeds below:

I want to quickly let everyone know that I too was initially bitten by a power supply that outputs more than 5V, even though it claimed 5V.  For anyone experiencing nonsensical switch operations, you might want to verify that your power supply is outputting exactly 5V (or something darn close).  I discovered that my power supply of choice was outputting 5.35V because the switches operated in a weird fashion.  The other giveaway was that in a dark-ish room, all the LEDs were slightly illuminated.

After learning my lesson (thanks Oscar!), I want to share my "fix" with the community.  I purchased a step-down transformer that will take any voltage up to 30V and let you convert that voltage to any other voltage as long as the output is lower than the input.  Additionally, I purchased a 12V/2A switching power supply adapter for my input on the transformer.  So, by feeding the transformer 12V, I could "step-down" the voltage to a perfect 5V.  And because 12V * 2A = 24W, I knew my transformer would have plenty of power and not stress the supply. This particular transformer can deliver 5V * 3A = 15W, which should be more than enough for the PiDP8i system.  Heck even the official Raspberry Pi power supply only delivers 10.5W.  Anyway, I lastly purchased a USB Type A female breakout board to create a typical USB Type A port from the transformer's output.

So, power goes from the 110V/AC wall, through the 12V/DC power supply, through the step-down transformer configured to 5V, and finally through the USB breakout board to give a clean 5V on a regular Type A connector.  I guess I should also mention that a right-angle micro-USB cable is helpful too! The PiDP8i kit box has enough space to house the step-down transformer and the USB breakout board, along with all wiring.  To get the power INTO the box, I purchased a panel mount 2.1mm x 2.5mm barrel jack.  This barrel jack mates with the power supply barrel perfectly.

Hope this solution helps others!

-Andrew

[Chris Smith]

That's nice setup - and since I think I have two similar step-down units in my parts box, I will keep it in mind if I see oddities.

My only suggestion would be to refer to it the same way the Amazon page does - as a "step down converter". When I first read your description, I was trying to figure out how you were feeding 5 volts AC (!!!!) to your Pi, since transformers only work with alternating current. Once I reread it and opened the links, all was clear.

On the oh-well too-late-now, it would have been really nice if the Pi designers had been a little more careful about USB power handling with the Pi. I think I have been reading about USB power issues since the day it came out!

[Warren Young]

On Thursday, May 11, 2017 at 7:08:30 PM UTC-6, Andrew Jergens wrote:

I purchased a step-down transformer 

That's a DC-DC buck converter, not a step-down transformer. The two are very different items with different functions. For one thing, a proper transformer blocks DC voltages, rather than converting them; you have to use AC with transformers.

A buck converter is a type of switching power supply, as opposed to a linear-regulated or unregulated power supply.

Transformers are much simpler linear devices than switching power converters, dating back to the dawn of electrical power distribution. Switching converters didn't become broadly practical until transistors started to become inexpensive, so you didn't see them in wide use until the late 1960s and into the 1970s. Yes, the PDP-8 line straddles this transition towards switching power conversion, with only the later models using switching power supplies.

Today, it's uncommon to see anything but switching power supplies of one form or another, with today's focus on energy efficiency and the availability of cheap electronics.

 Additionally, I purchased a 12V/2A switching power supply adapter for my input on the transformer.  So, by feeding the transformer 12V, I could "step-down" the voltage to a perfect 5V.  And because 12V * 2A = 24W, I knew my transformer would have plenty of power and not stress the supply. This particular transformer can deliver 5V * 3A = 15W, which should be more than enough for the PiDP8i system.

Except for the terminology problems, this is a sound plan.

Relegating the dangerous wall voltage conversion to an external power supply simplifies things considerably, and shunts most of the risk of dealing with wall power from the DIYer to the power supply provider.

 

To get the power INTO the box, I purchased a panel mount 2.1mm x 2.5mm barrel jack.

5.5x2.1, you mean. That's the outer and inner diameters of the barrel plug.

2.1mm and 2.5mm are the most common pin sizes for this sort of jack, with 2.1mm being far more common. It's a small difference, but the two are very much not compatible: a 2.1mm barrel plug won't even insert into a 2.5mm jack, and a 2.5mm plug won't make reliable contact if inserted into a 2.1mm jack. So, be sure of which one you've got when buying parts.

[slob]

I used two of these in my case, shown in the "show us your setups" thread. These are available at much lower prices on eBay direct from China if you are willing to wait. Someone on the Internet tested this design (basically from the manufacturer's reference design) and pushing it to three amps is, well, pushing it at the edges of input/output voltages and output loads. There is an uprated version on eBay that uses a vertically-mounted toroid and an improved controller, that is better. The one shown here powers just my Pi, and the uprated model powers my seven-port USB hub mounted in the box.

There is also a mini version of this type of converter, not much bigger than a postage stamp, good for an amp of so. I use this nowadays instead of, for example, a linear 7805 regulator on smaller projects. It can be adjusted to 3.3 volts. When I'm happy with the voltage, I generally glue the pots. So far, I've not been sorry about doing it.

I generally use "orphaned" laptop power supplies with my projects. They are usually rated at 17-23 volts and 3-4.5 amps, definitely enough for most projects of this type. Also, with higher input voltage, the efficiency of the DC-DC converter tends to go up. IBM/Lenovo power supplies are especially compact.

I've tossed most of my older, inefficient linear wall-warts.

[Oscar Vermeulen]

By the way, you can use a *crappy* 5.35V power supply quite comfortably if you put in the diode #27 under the IC, and cut the trace that shorts its footprint. That will cause a voltage drop sufficient to be in-spec again. And allows you to use cheap, cheerfully crappy, 5.35V bricks safely. The Pi 3 itself loves 5.35V.

The diode with a crappy 5.35V PS is in fact safer than using a *proper* 5.00000V power supply on a Pi 3 - see below.

On 12 May 2017 at 03:08, Andrew Jergens <ajer...@gmail.com> wrote:

I want to quickly let everyone know that I too was initially bitten by a power supply that outputs more than 5V, even though it claimed 5V.  For anyone experiencing nonsensical switch operations, you might want to verify that your power supply is outputting exactly 5V (or something darn close).  I discovered that my power supply of choice was outputting 5.35V

No commercial company could get away with what the Pi Foundation did. But because they are a Foundation, I guess publicity is kind to them. Which is wrong.

Because on the Pi 2 and especially the Pi 3, the crappy power regulator circuit they put on is no good. And instead of adding $0.02 to the production cost to fix it, they force 5.35V bricks into the world to mitigate the problem. 

The problem is, if a Pi gets <4.9V even for a brief moment, it can corrupt its SD card. Decent, normal brick PS's will fluctuate their voltage a tiny bit if the power consumption spikes briefly. Like, when the SD card is used. And that would be OK and acceptable behaviour for a cheap PS. 

Except that the Pi's onboard power regulator causes a voltage drop. So a perfect on-spec 5.0000V PS means the Pi sees only 4.9V behind that crappy regulator circuit. Even the tiniest voltage fluctuation of the wall wart can cause the 4.9V to then become 4.85V - and boom.

[Rant On]

If Volkswagen would have produced the Pi 3, it would face a class action... But the Pi is made by a Foundation... awww, nice nonprofit people with flowers in their hair... let's not criticise them for putting 5.35V power supplies in the world even though that is an out-of-spec and potentially damaging voltage for TTL logic. Which, of course, the Pi Foundation encourages you to hook up to their GPIO. Bah!

[Rant Off]

Kind regards,

Oscar.

[Obsolescence]

Maybe two other points are good to mention:

First, the PiDP circuit is not at risk of 5.35V power. It may be out-of-spec for 5V electronics, but the PiDP circuit is so simple nothing is at risk.

Secondly, the problem of Raspberry Pi's best living off 5.1V+ is due to an on-board polymer fuse which causes a voltage drop before the power reaches the rest of the Pi. It has been a source of misery for years now: people wonder why one Pi works fine for them, and another does not. These fuses vary a bit in the voltage drop they cause. So one Pi is more prone to corrupting its SD card (once a month?) and others seem trouble-free on the same marginally-OK PS brick.

The good thing is that if you feed the 5V through the Pi's GPIO instead of the micro-USB connector, you bypass this fuse. On the PiDP, that's the reason for a 5V power input pin on the normally unused 'serial connector' at the side of the PiDP.

[Chris Smith]

Rather interesting.

I have a Type B keystone module to bring USB power into the box. But it (although common) is a little strange - it is back-to-back Type B. I had been looking - VERY unsuccessfully - for a Type B to micro B short cable to bring power to the Pi inside the case.

It appears I would be much better off, for a number of reasons, just getting a short Type B terminated cable, cut off the other end, and run the USB power lines to the PiDP power input. that will take less space, too!

[Oscar Vermeulen]

Chris,

On 12 May 2017 at 23:02, Chris Smith <cjs...@gmail.com> wrote:

 It appears I would be much better off, for a number of reasons, just getting a short Type B terminated cable, cut off the other end, and run the USB power lines to the PiDP power input. that will take less space, too!

Yes, I think so. In fact, if you use a Pi Zero you can just power from a laptop's USB cable. A Pi B+/2/3 will give you trouble that way, though.

Kind regards,

Oscar.

[AB]

Love the "flowers in hair" rant!

[Rant On]

If Volkswagen would have produced the Pi 3, it would face a class action... But the Pi is made by a Foundation... awww, nice nonprofit people with flowers in their hair... let's not criticise them for putting 5.35V power supplies in the world even though that is an out-of-spec and potentially damaging voltage for TTL logic. Which, of course, the Pi Foundation encourages you to hook up to their GPIO. Bah!

[Rant Off]

[Andrew Jergens]

Chris and Warren,

Thank you for correcting my terminology and sizing!  I updated the first post to reflect your corrections.

Oscar,

Rant on, brother!

-Andrew

[Tom Stewart]

Chris- like this:

https://www.adafruit.com/product/937

?

On Friday, May 12, 2017 at 5:02:01 PM UTC-4, Chris Smith wrote:

... I had been looking - VERY unsuccessfully - for a Type B to micro B short cable to bring power to the Pi inside the case.

[Chris Smith]

Oooo - so close. Now if only they made this as a keystone instead of a panel mount.

I feel somewhat lucky, actually, NOT to have found what I was looking for. After the power handling discussion, I expect I will run power direct to the PiPD pins, not via the USB connector. Since I also have the parts to run the Pi remote from the PiDP, that also makes some of the internal wiring come together better.

... Chris

[Ed Thierbach]

Me, too ... especially since here in the States, Volkswagens were once strongly associated with flowers in one's hair. :-)

-Ed-