guillaumekh
Posts: 12
Joined: Fri Dec 21, 2018 6:42 pm

Sourcing & testing alternative power supplies

Fri Dec 21, 2018 7:40 pm

We love the official Raspberry Pi power supply, manufactured by Stontronics. It's reliable, modular, and bears loads of certifications for export. You can't ask much more from a PSU.

Image

...which is why we're super bummed we can't use for it for a current project which requires a DC barrel jack connector (picture below) instead of the usual micro USB.

Image

We found a "medical-grade" PSU [edit: link removed] that checked all boxes, plugged a few to some heavily stress-tested Raspberry Pi 3 B+ to test them, and then ordered hundreds. A few months later, we have about 10% of them that are unable to sustain proper voltage, triggering under-voltage warnings across the board, which happens when output voltage dips below 4.63V, well below this PSU's 5V±5% supposed output.

In your opinion :
- how/where should we source our next PSU ? Experience just taught us that specs don't tell the whole story.
- how can we test the reliability of our next PSU ? We found some voltage multimeter-dataloggers but were floored by how expensive they are (e.g. Fluke)
Last edited by guillaumekh on Thu Mar 28, 2019 3:37 pm, edited 1 time in total.

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
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Joined: Sat Jul 30, 2011 7:41 pm

Re: Sourcing & testing alternative power supplies

Fri Dec 21, 2018 8:10 pm

Not sure what use case requires a barrel connector since the Pi doesn't have one, but I would simply take a Pi supply and change the plug.

Or this could just be a sophisticated spam post.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
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guillaumekh
Posts: 12
Joined: Fri Dec 21, 2018 6:42 pm

Re: Sourcing & testing alternative power supplies

Fri Dec 21, 2018 8:21 pm

Hello James,
We use a DC barrel jack because it's lock-able, preventing accidental disconnection (example below). It also has the benefit of looking more "pro", which is admittedly more a marketing benefit than an engineering one.

Image

We could change the plugs one by one but doing that at our scale (few hundreds units) would not make much sense: it would cost way more than simply buying barrel jack PSUs.

mfa298
Posts: 1387
Joined: Tue Apr 22, 2014 11:18 am

Re: Sourcing & testing alternative power supplies

Sat Dec 22, 2018 10:48 am

guillaumekh wrote:
Fri Dec 21, 2018 7:40 pm
In your opinion :
- how/where should we source our next PSU ? Experience just taught us that specs don't tell the whole story.
- how can we test the reliability of our next PSU ? We found some voltage multimeter-dataloggers but were floored by how expensive they are (e.g. Fluke)
Where - Find a trusted source (I'd probably look at the likes of CPC/Farnell/RS). At least then you should be able to get the same device on each order and the specs are more trusted. (Compared to the likes of eBay, Banggood, Aliexpress).

As for testing:

As a first step I'd probably setup something that can easily monitor the voltage and current at the same time with a variety of switchable loads. This could be as simple as a couple meters and some switchable load resistors (ensure adequate wattage). This should at least pull the really bad choices out with an easily repeatable set of tests.

For something more advanced I might add something that can switch part of the load quickly (simple micro-controller running a PWM loop) where the PWM speed and load can be altered as well as a static load. This might also require a scope so you can check for momentary blips on the voltage.

You might also want to run the PSU at a high percentage of it's maximum ratings (or at least slightly over the normal load) for a while to see how it copes.

That's just my thoughts, There might be better ways and I'm sure there are plenty of (probably expensive) boxes out there to do some of that type of testing for you.

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 26383
Joined: Sat Jul 30, 2011 7:41 pm

Re: Sourcing & testing alternative power supplies

Sat Dec 22, 2018 12:34 pm

If you are building product in those sort of quantities, I would have thought the cost of a decent datalogging multimeter should be factored in to pricing - for example, we have some hugely expensive scopes* in the lab that are simply the cost of doing business.

As for suppliers, if Stontronics make ours, can you not aporoach them and see if they can provide? Although the quantities may be a little low to get decent pricing.


*more expensive than my house.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Contrary to popular belief, humorous signatures are allowed.
I've been saying "Mucho" to my Spanish friend a lot more lately. It means a lot to him.

guillaumekh
Posts: 12
Joined: Fri Dec 21, 2018 6:42 pm

Re: Sourcing & testing alternative power supplies

Thu Mar 28, 2019 3:51 pm

Sorry for necroposting

After learning a few more things about electronical design, we found out that our PSU was blameless. :oops:

What happened to us was some components (i.e. a Bourns MF-MSMF250 polyfuse, and some thin aluminium wires) between the Pi & DC jack were introducing a voltage drop.

If it's in anyone's interest, to curb the voltage drop in our product, we've:
- replaced the internal wires with shorter, thicker, copper wires
- removed the polyfuse since we noticed the PSU does overcurrent protection already

Thanks @jamesh & @mfa298 for your feedbacks.

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