Over the past week, I built a small nichrome based 50 watt heater that
runs from 12 VDC power supply. It currently has 5 amp fast blow AGC
fuses in both lines, but what's to stop me from using a small circuit
breakers in each line instead? I see plenty of NOS or used ones on eBay
at maybe double the price for fuses, but not always the case as I've
seen fuse packs of similar price to the breakers.

a) Ever see a fuse jam? Breakers are a risk on purely resistive loads. Nothing to stop you, however.
b) I would never purchase a critical part from eBay - no guarantee that it is as described, or even from a legitimate manufacturer.

Peter Wieck
Melrose Park, PA

On Sat, 12 Dec 2020 14:55:14 -0500, Witherspoon wrote:

Over the past week, I built a small nichrome based 50 watt heater that
runs from 12 VDC power supply. It currently has 5 amp fast blow AGC
fuses in both lines, but what's to stop me from using a small circuit
breakers in each line instead? I see plenty of NOS or used ones on eBay
at maybe double the price for fuses, but not always the case as I've
seen fuse packs of similar price to the breakers.

You should look at automotive, RV or marine hardware, where battery
operated equipment is regularly used.

Heaters may offer different hazards that simple fusing doesn't
address. Suggest you take a look at commercial units before closing
off your design. Unregulated heaters are usually limited to a specific
application.

RL