For electronics designers, the decision about how to power the project is a necessary part of the design.
- Plug in?
- Then is it AC or wall-wart or USB?
The issue with batteries is that the voltage drops over time, which has to be factored in.
- Disposable or rechargeable?
But there’s another option that’s available, and is especially useful when the project also uses Ethernet: Power over Ethernet (PoE). The problem with PoE is that the cable delivers around 48V—which is great for a reasonable amount of power, therefore current, but unfortunate since the project now needs a down-converter, as well as having to abide by the IEE802.3af (and later) PoE standards.
Silvertel make a range of PoE module voltage converters, to supply 3, 5, 12 or 24V to the project. Their smallest module has two different form-factors: the through-hole ‑LP “low profile” series, which gives slightly less current and doesn’t have thermal protection; and the surface-mount ‑M and ‑MT series—the latter has thermal protection. Although it only requires a minimal number of external components, for EMI/EMC reasons more components are recommended.
So I’ve started playing around with these modules, and have a number of projects with them in mind. Not all the projects will have Ethernet—I’m just using it for the raw power.
The first is a project to power a curtain motor. It needs 12V at 0.833 amps, which is perfect for PoE. The problem is that the motor is controlled by a 433 MHz “garage door opener”, so the EMI coming from the module needs to be carefully suppressed.