Advice on hobbiest power supply

Hello,

I'm still quite new to electronics, but I'm getting into situations where sometimes 5v logic is convenient, other times 3.3v. Or I'm powering several motors and it would be nice if I needed to to just turn up the amps a bit on my power supply. It would be nice to have One Power Supply To Rule Them All. Am I wrong to want this?

For example, I'm looking at this guy:

It seems like it would be ideal. Kinda pricey though, so I thought it might be a good idea to consult with folks who know a lot more than I do :slight_smile: It'd be good to find a slightly more economical option, as well, but they seem to be tricky to search for, even...any input would be greatly appreciated!

Best,
lee

That is quite pricey, but I would trust the Sparkfun recommendation. Having an adjustable current limit may save you from some disasters. It would be great for building and testing robots with big motors.

A drawback is that it has only one output, and if you do much experimentation with analog circuits, you will often need 3 outputs (+/- 15V), 5V or 3.3V etc.

If price is a concern, you should start with computer power supplies. They'll have 12V, 5V, and 3V3.
The notion of 'turn up the amps' as you say, is quite indicative of a lack of understanding of a fundamental quality of electricity.
Start by looking up how current works, then look for some computer power supplies. Craigslist tends to have a bunch from people who have upgraded their packaged comps.

You mean I might need three different voltages at once? I had no idea! That's a great point to consider then. /me ponders.

You are absolutely right about my lack of understanding. I've been doing a lot of fundamental reading and video watching, and just when I think it's all starting to make sense, some new zinger comes along and I'm back to zero again.

I thought that's what you would do if you couldn't, say, turn all the motors you wanted at once, though?

A great source of power supplies are the power bricks found in thrift stores ($5 or less) or computer recycling centers, especially for LCD monitors.

They tend to be well made, with current limiting and come in a variety of fixed voltages (24, 18, 12, 5 etc.) and a wide range of current capabilities, up to 10 Amperes or so. Some have 12 and 5V outputs, so you get two for one. Just check the fine print right on the brick.

I use them for projects that have beefy motors or will be near house AC outlets at all times.

I’d go with a PC power supply. They’re cheap and strong. Probably stronger than anything you’d throw at it. The ones I’m working on today are running from a 650W Corsair ATX power supply. According the the sticker, it can give …

+3.3V 25A, 130W
+5V 25A, 130W
+12V 51A, 612W

The total peak load capacity is 650W.

612W is way better than that 80W.

I’m not saying that you have to buy this particular one. There’s nothing special about it. Get a cheap one, or salvage a mostly-working one from an old computer.

Look around for info on using it as a DC power source. The magic is jumpering the green wire in the main ATX plug to ground. Use any of the many pinouts to find which wires have the power you want.

I’ve seen some little adapters that break it out for you, with a power button. You don’t really need them. There is no dangerous output from the power supply. It’s all nice safe low voltages. Even if you mess up and short it, most recover gracefully with a power cycle.

The only real advantages I’d see with the Sparkfun power supply is that it’s ina pretty package, and gives outputs higher than 12V. If you don’t actually need 24V, don’t bother. Buy for what you need, not for what you might use someday. If the need comes up later, get a bigger one later.

When you learn a bit more, you could explore the fun of transformers, bridge rectifiers and voltage regulators. I thought about it, but it was easier to just jumper it and strip a few wires for outputs.

I’ve done this quite a bit over the years, recycling old weak power supplies to lower load applications like the Arduino.

I’m planning to make a higher current phone charger with it sometime in the future. It’s not very hard. Put 5V on the right pins, and a resistor between the others. Voila, a phone charger capable of (theoretically) 25A. The phones will only draw 2 or 3A, so I could charge a dozen if I wanted. :slight_smile: It’d be better than the questionable quality chargers that you’d normally use.

If you plan to do analog circuits, steer clear of switch mode supplies, the noise/hash is too high
for many situations. Standard (linearly regulated) bench supply is what you need to start with,
go for a second hand unit (eBay?) with analog meters if at all possible, digital meters are annoying to
work with(*).

(*) The typical scenario with testing a new circuit with a bench supply is:

  1. set the current limit to something low enough to prevent damage
  2. crank up the voltage while watching both voltage and current meters, ready to wind back
    instantly if the current is higher than expected - watching two meters at once is vastly easier with
    analog meters than digital. Analog meters react instantly if there's a sudden change, and
    you can make sense of varying load currents (with digital you get effectively a random stream
    of numbers which is uninformative).

I use one of these.
Get one when they are back in stock:

http://www.mpja.com/Variable-Dual-0-30V-3A-and-Fixed-5V-3A-Benchtop-Supply/productinfo/29623+PS/

.