Variable Power Supply

[dyl_jo]

TL:DR version: looking for recommendations for a cheap and basic variable/adjustable DC power supply for amateur use.
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First time in this forum so apologies if I'm asking in the wrong place.
Additionally, I'm a novice and so I'm not even sure if I'm asking the right questions or using the correct language: happy to be coached!

I have a number of powered kids toys around the house - eg. lego motors, hot wheels car launchers, and other misc toys - and they chew through batteries. Initially I solved my problem by finding an old variable voltage DC adaptor (plugs into the wall and lets me choose between 3 to 12V in 1.5V increments - ideal for nearly all the toys in the house) and then adding a plug that I can switch around to different toys when they are in use. Each toy then gets its own plug (connected to the battery terminal in various ways depending on the toy) so all I have to do is plug it in to the transformer, select the correct voltage and off we go.
For Christmas my son was gifted a Hot Wheels toy that launches his cars around a track, but after about 2 hours of play the batteries (4xD size) weren't up to the job anymore.
Rather than buy more batteries I wired up the adaptor as I had before, but found out that the power to the projectile launcher was inadequate. My guess is that the output current from the transformer (“500mA max”) was inadequate for the task at the required voltage.
I started looking at “upgrading” from my variable voltage adaptor to variable power supply in order to get more control over what I’m pumping into things.
Obviously I checked out what I could on the EEV Blog Youtube channel but the explainers for the power supplies are nowhere near as comprehensive as Dave’s rundown on multimeters so I’m kind of stabbing in the dark and wondering what to look for?
In terms of specs, I’ve guessed that I should be looking at the following

• Output
• • 0 – 30V
  • adjustable in 0.01V steps
  • resolution 0.01V
  • accuracy +/- 0.5%
  • 0 – 5A (3A?)
  • adjustable in 0.001A steps
  • resolution 0.001A
  • accuracy +/- 0.5%
• Input voltage capability should be higher than output demand if not boosted
• Max output power: up to 150W(?) (But I’m conscious of minimum load requirements for some units given my intended use)
• Digital display for both V and A
• Single Output (won’t be doing more than one thing at a time)

Ideally also has (but not critical):

• coarse and fine controls for both voltage and current
• the ability to lock the voltage and current (so the kids don’t blow up one of their toys)
• voltage output control (so I don’t blow up one of their toys)
• output enable/disable
• NOT giant/heavy – this is to be portable around the house, not fixed to a bench
• I’m guessing because of my intended use that noise, ripple and power density aren’t a concern (not that I know what any of that means) and so a switching supply will likely be cheaper and do the job fine (over and against linear)?

• I’m also not too fussed about efficiency, and don’t need to be able to program it.
• I don’t want to build one myself, I’d like a complete kit. I just want to plug it in and fiddle around at the toy end not the power supply end.
• I’m based in Australia.

In terms of cost, my main motivation is to stop chewing through batteries (and I don’t like rechargeable batteries) so the cost for a unit needs to be in the ballpark of $100 to $150 AUD (roughly the cost of the batteries I won’t need to buy!).
Here’s some units I’ve found that seem like they fit the bill, but I’ve no idea about brands, or what to look out for. Any help or advice would be appreciated.
https://www.amazon.com/Dr-meter-Single-Output-Switchable-Alligator-included/dp/B00O8DJ8QC/ref=ex_alt_wg?_encoding=UTF8&pd_rd_r=60b643c9-c935-4609-abf2-b93ba420db9a&pd_rd_w=YxRuI&pd_rd_wg=cL7hK&pf_rd_r=K31TTW0XSHH48VXWQ3Z4&pf_rd_p=0bdfe557-f174-4fcd-92b4-fe942ad9b326&pd_rd_i=B00O8DJ8QC&psc=1

https://www.amazon.com/LW-K3010D-Adjustable-Switching-Regulated-Spectrophotometer/dp/B07512KQDW/ref=ex_alt_wg?_encoding=UTF8&pd_rd_r=b97f6122-9e4f-408d-8c60-aef2d51d0cda&pd_rd_w=MIBVX&pd_rd_wg=Xm76b&pf_rd_r=KRYCT2TAHZFGHPY55EAV&pf_rd_p=0bdfe557-f174-4fcd-92b4-fe942ad9b326&pd_rd_i=B07512KQDW&psc=1


https://www.amazon.com/YaeCCC-Variable-Adjustable-Bench-Supply/dp/B074C86DSY/ref=sr_1_5?ie=UTF8&qid=1538633829&sr=8-5&keywords=test+bench+supply&dpID=510YGDhhV5L&preST=_SX342_QL70_&dpSrc=srch

Thanks in advance

[nightfire]

In short, as I have had some time ago some similar thoughts/concerns, back then based about powering lots of LED lights and other devices for photography:
You don't need such fancy stuff and can save some money.

Because: Devices need to deal with the changing voltage from the supplying batteries. A 1.5V battery can deliver 1.6 Volts when really fresh out of the box, and cutoff voltage usually is around 1.0 Volts, when they are empty. Similar stuff goes for NiMh rechargeables, the can have about 1.3 Volts and again a cutoff at around 1.0 Volts when empty- this is theoretically the limit where the device should stop working in a controlled way to keep the rechargeables intact.

My solution: For all devices I could power with AA (or AAA) batteries I bought good quality NiMh (Eneloop rules, by the way) and a very good quality charger (MEC AV4m). There are adapters available to C or D cells, which can take up to 3 AA cells, IIRC.

Only stuff that needed more than 6 V I bought power supplies, and as they were quite few in number, each got its own Power supply. When looking carefully at the input specs, lots of gear accepts a wide range of inputs, so that in most cases some 12V or 15V supplies were sufficient.

Current: The Power supply should have some overcurrent protection, but as current is drawn from a supply, there is no need to regulate it- those stuff is IMHO only needed in a lab power supply for testing purposes, but not in the real world with tested devices.

Such "high-quality wall warts" were obtainable with my favorite online retailer for about 15 € each, and i have a variable setting PSU with interchangeable adaptors in the closet for the "just-in-case" scenario.

As I am also in the progress of building my own little lab at home, I had a look at good lab PSUs, and came to the conclusion, that whether I have the sub-100 €€€ category and live with 100 mV and 10mA acccuracy (and no remote control), or I have to spend at least 300 currency tokens for a good quality one.
(Went for a somewhat affordable Peaktech 6225A, which is small, and has a mixture of linear and SMPS electronics mangled together according to some reviewers)

[ledtester]

A recent forum thread on this topic:

https://www.eevblog.com/forum/beginners/cheap-power-bench-supply-any-recommendations/msg3210760/#msg3210760

Another option is to build one from an existing fixed power supply and a buck regulator like this:

https://youtu.be/IJFBvMMltQw

Your fixed power supply could be an old laptop charger, for instance.

[elektrolitr]

Get a GOPHERT NPS-1601. It's a neat little unit, cheap (around $40), lightweight and compact, and meets all your specs exactly.



The unit is well worth the money, just be sure to throw away the banana wires included, these are total crap.

[bob91343]

I am surprised that your specifications are so stringent for a device intended for toys.  Maybe I misread your message.

To run motors and lamps you don't need a high tech power supply.  In most cases you don't even need close regulation.

Having said that, low cost and very effective units proliferate, both new and used.  But now you are committed to make careful adjustment when you move to a different load.  And you still have only one power supply so can only run toys that require a single voltage setting.

I would suggest a different solution.  Make up cheap power units for each toy rather than try to make one unit power them all.  Beyond the annoyance there is the chance of making an error and damaging something.

[dyl_jo]

Thanks for all the contributions
I ended up getting a Wavecom 30V 5A Power Supply - PS3005D.
It seems to meet my needs nicely.