Recommended current for external breadboard power supply

Question

I want to buy an external power supply for my breadboard (this one). It says that the input should be between 6.5V and 9V, which is easy enough to understand. To power the supply, I planed on buying a wall plug with a barrel jack as an output. There are plenty of wall plugs which supply 9V. However, I found that they differ in the amount of current they output (i.e. ranging from 1A to 2A while both supplying 9V). My question now is, which one is suitable to power the breadboard, and what the benefit of one other the other is.

Cheers!

Answer 1

I suggest you buy a 5V regulated adapter for your ~1A requirements. A standard adapter (or power bank if you want battery power) and use the USB socket rather than the barrel jack.

Similar (but not interchangeable) boards with the same part number are available with a mini or micro USB socket to match standard power supplies as used with Raspberry Pi, cell phones etc. Make sure the two are compatible, there are a number of combinations. The USB power connections are connected directly to the +5/0V and nothing else.

This will avoid excessive dissipation on the board, and help prevent oopsies that can destroy your parts.

You can use the power supply module you linked to create a 3.3V bus if you need it. The 5V from the USB socket is passed along directly when switched on. See my answer here for the schematic of a similar product sold with the same part number.

Note that the one you've linked does not include a resettable fuse, which I would consider at least an advantage if not a 'must'.

As another detail, it would be nice if the polarity of output matched the color of markings on your breadboard (red = +, blue = GND), but most seem to be reversed.

Answer 2

The current capability of your input power supply doesn't matter as long as it's enough to run the circuit. This PSU that you link to is a linear power supply, which means that its input current will be equal to its output current (plus a negligible amount for powering the power supply itself). That said, with a 9 V input, a linear power supply outputting 5 volts will dissipate \$4\ \mathrm V · I_{out}\$ in heat, which can be quite a lot, so you do need to consider this. And 3.3 V output will be even worse, at \$5.7\ \mathrm V · I_{out}\$.

This type of power supply is not good for providing high current, and generally shouldn't be used for anything involving motors or solenoids--simply put, don't use this PSU for your relays or pump. It's fine to power electronics, but the high current draw of a pump or several low-coil-voltage relays will be a problem for it. It will be less of a problem if you power it with a lower-voltage input, since the power dissipation (the limiting factor) is proportional to the difference between input and output, but I would still recommend looking for a switching power supply module, such as this one or this one.