Hi all. I’m starting to think that a pretty essential piece of kit for a Restart Party or Repair Cafe is a bench power supply. We’ve seen a number of instances where people have;
Brought an to fix item but forgotten the adapter
Been using an incorrect power supply (‘hey - the plug fits in but it doesn’t work properly now!’)
Don’t want to replace the blown power supply unless they known the device itself is OK (laptops for example)
I’ve got a bunch of ‘tips’ from a cheapo older universal power adapter, so maybe soldering wires to those for use with croc clips is a better solution (assuming I get the polarity correct ).
If you search eBay for universal laptop charger tips you’ll find various sets. Some of them have 2 pins so you can reverse the polarity to the tip - sounds like A Bad Idea. I can’t be sure from the pics but I think some other sets have a coaxial connector on the back end which would seem to be much better. For other devices you’d want to have 2.1 and 2.5mm circular tips, and miniUSB, microUSB and USB C, though for USB powered devices a separate USB PSU would probably be preferable, to avoid supplying such a device with anything but 5V.
There are universal laptop PSUs which come with their own comprehensive set of tips. Each contains a resistor which sets the voltage to that normally expected by that type of tip. That, plus a USB PSU with the various USB plugs, plus a wall socket type regulated variable voltage PSU with a set of tips for radios and other miscellaneous items would cover you more cheaply than the Farnell one.
Thanks Philip. I’ve not seen those before so i’ll check them out as an option.
Will save having to lug a larger piece of equipment around as well… enough of that already… !
For cheap bench power supplies, I bought one of these: https://www.aliexpress.com/item/4000381475010.html. I would never recommend buying a bench power supply without an output on/off switch because you’d have to keep disconnecting the supplied device to set it up. There is also a concern about the electrical isolation of these non-approved supplies - I tie the earth terminal to the negative output so at least it will trip the RCD if there is insulation breakdown. This particular one has good creepage distance on the PCB but you can’t tell what’s going on inside the transformer(s).
The Tenma that you mentioned is decent for the job, or something like https://a.aliexpress.com/_mM27cQS (note that PSU controller and actual SMPS come separate, so ~£100 total)
Combine with something like https://a.aliexpress.com/_m0FS7Po and adapters to different barrel sizes and you should cover most options — but do be mindful of polarity as mentioned above.
I’m hoping to use it for other electronics projects in the future so I didn’t mind spending a little bit more to get something that wasn’t just for laptops.
I didn’t particularly wanted to buy it from Amazon but I was having issues getting something shipped from the other electronics suppliers to the Channel Islands.
@Matthew_Marks Noted your comment about a separate on/off for the supply, this unit can do that. Thanks.
Looks good. Seems it has the same rather weird voltage/current setting system as mine, where the rotary encoder initially makes fine adjustments (10mV/10mA) and you press it in to move to coarser control. Takes a bit of getting used to but quite clever. It means it probably has the same issue someone pointed out with mine that while adjusting the voltage, the current display shows the set current rather than the actual current drawn (and vice versa). Or maybe they’ve fixed that?
*In 30+ years as a school physics lab technician, I found the best power supply was a Unilab model 022.314. In my time not one unit failed and I still have one at home that I bought used on ebay. They deliver 5a AC/DC up to about 28 VDC. The nominal Vmax is 20V AC , adjustable in 1v intervals by moving 2 plugs to different terminals (4mm sockets) on the LV side of the mains transformer… They were discontinued, I think because the mains fuse was accessible to pupils without the need for a tool - the fuseholder had a cap which uncrewed by hand. I got round that by opening the box, disconnecting the fuseholder, and wiring in a 2amp self-resetting fuse instead. After opening, the fuse would reset in a few minutes. You can still find these units on Ebay but you may have to wait a while.
That of course is a different class of machine! All these cheap switchers are electrically noisy so not suitable for working on sensitive RF circuitry. But they’re amazingly light and portable.
I agree, you want a linear PSU really, rather than a switcher, but they are quite heavy. Secondhand off eBay is the way to go (I got mine from a previous job, they were throwing out because of a damaged front panel).
As for the barrel jack tips, reversible ones are indeed useful, because don’t forget that some items that need powering are centre negative!
Also I can recommend getting a female 12V car lighter socket - its much better than crock clips, for those car items that need powering.
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