Hi all - I am planning my camper electrics by going over various other schematics online and cant help notice the amount of people that combine switches and resettable fuses. Can someone explain to me why you'd use both as i always understoof resettable fuses provided a switch function. Thanks!
Circuit breakers are fast acting and respond quicker to over current and have close tolerances, where as fuses are slower acting so a bit more tolerant to over-current transitions/spikes so fuses are less likely to blow with very fast current transitions, may not want the circuit to disconnect on these current transitions, only continuous over-current.
Given the above possible scenario - Current transitions/spikes can occur during state changes e.g. Multiplus switching between charger and inverter. Although this may only be an instant current spike you wouldn't want a circuit breaker tripping every time this happened - where a fuse would be more tolerant of these spikes and less likely to blow. Other places you may want fast disconnect on over-current where spikes/transitions less likely to occur
I use both in my camper electrics.
hope this helps
When you say you use both in your electrics do you mind letting me know where you do use the thermal breakers? I'll have to finish up my initial design and post on here to hopefully get some feedback, but would be great to know. Thanks!
Van Electrics i use Mega fuses as main circuit protection and between battery and MultiPlus for the same reason above. Charge circuits and DC system (Lights, USB Chargers, TV etc), i use breakers as these are lower current circuit protection devices .
See Attached
That black thing is a thermal circuit breaker. Horrible devices. They get hot and trip early. I mean so hot they can burn you. Some come with little rubber covers for the terminals that I reckon are for your protection from getting burnt!
Not the sort of thing to use on a main battery cable. Terminals usually too small anyway. I don't think Victron provide them in a ~1000 item product list, fusing gets the preference, all the way to the Lynx integrated system.
They may have their place in some people's systems. Indeed I revived a 100 Amper from the trash bin to isolate a 5A circuit, and a 150A to isolate my main 12V fuse system (maybe 10-20A at most).
Google up the Victron fusing range. Even if you buy another brand from your local auto store.
Some people substitute a circuit breaker where a fuse would make sense just so they don't have to carry spare fuses and wrenches to change the fuses. That's usually why you would see a breaker followed by a switch. Either they were following someone else's diagram, or it's a last-minute substitution in a design.
Fuses have fewer problems than breakers though, so excessive use of breakers is actually a way to increase the failure rate of your system.
The circuit extract above you have to consider the direction of current flow. The circuit breakers are to protect the charge circuits/MPPTs/DC-DC and the cabling from them, to stop the battery/inverter/DC Load or a fault, trying to draw too much current, avoid damaging the devices and the cable, which may be a much smaller gauge and support far fewer amps than the main bus.
Remember current can flow in two directions - from the battery to the loads or from the charge devices to the battery.
Yes, it's redundant. Most people would consider it a design flaw to have a resettable breaker and a switch, however this is not the first time that I've seen it. I was just explaining how people back into this design choice not recommending that you follow it.
A fuse and a switch are usually the most robust choice. A single resettable breaker would be acceptable in most situations, but some codes require an actual switch. This is because breakers fail much more often either switches or fuses.
