This post is about starting a discussion on what you are using for fuses or DC breakers and what your thoughts are on watt loss.
Victron recommends the Lynx Distributor for inverters using Mega fuses.
Victron also recommends the Lynx Class-T Power In for connecting Lithium batterys. (because a higher interrupting capacity is required for lithium batteries)
Other people are using EF3 fuses from Adler. These fuses are compatible with Mega fuses if used with the Victron Distributor. They offer a more cost-effective option compared to using the Lynx Class-T Power In, with the more expensive Class-T fuses.
Of course, some users prefer using a DC breaker.
I calculated (based on what I have read and from PDFs) the typical power loss for a 200A amp fuse:
Mega fuse: 10.4 W
Class-T fuse: 12 W
EF3 fuse: 27.5 W
DC breaker: 75 W
There is a huge difference in power loss if using DC Breakers over Fuses. Also the T Class fuses seem to do a little bit better than the EF3 in the long run on efficiency.
Are you guys going for system efficiency or price and what are your thoughts?
Since you referenced the DIYSolarForum.com site, I’ll say that in general on that forum we recommend a fuse over a breaker because fuses typically have less resistance than a breaker. AIC comes into play also. Between my 48 volt 280 Ah battery and my Quattro 48/3000 there are no breakers, just fuses. Class T at the battery, CNN at the Lynx Shunt and MEGA in the Lynx Distributor. I have quite a few breakers in other (lower amperage) areas of the system. Every solar charge controller has breakers on both sides. I put breakers in when I know that the circuit is one that I’ll need to isolate (turn off) for one reason or another, and I just have to suck up the voltage loss.
You wrote “Also the Little fuses seem to do a little bit better.” Did you mean little fuses or Littelfuses. Littelfuse is a brand of fuse and the one I typically go with. Not all fuses commonly found on Internet retail sites will work on a 48 volt system. Littelfuse has the right fuses to work with voltages above 48 volts.
It would be nice to measure resistance of representative samples of quality MEGA, Class T, EF3, and DC breakers of the same rating. I have a good microohm meter and access to MEGA and Class T fuses. A good quality DC breaker of several hundred amps is very expensive (which is why use Class T fuses) and I don’t have any of these. I have never been able to find a source for EF3 fuses in the USA and the couple of German companies I found won’t ship them to me, otherwise I’d be happy to measure them.
That said, good quality, high current DC breakers are very expensive so we use Class T fuses on the battery side and MEGA fuses inside the Lynx Distributors. The MEGA fuses are often the device with the highest temperature when we do load testing so the internal resistance must be relatively high.
Jim thanks for your respone. I changed little fuse to T Clas fuse. (This is what i meant. I use)
The purpose of this post is to have people talk about which fuses they are using and the power loss. I mainly use the Mega Fuses from Victron. And the T Class fuses from Little Fuse.
Unit-T UT620A It’s accurate enough for our purposes. I bought it to test new installers and DIYers crimps and show them that just because they can’t pull the lug off the cable, it doesn’t mean they made a proper cold welded termination.
Yes, I see their press release from 19-June-2025 announcing a US office. Thank you for the heads up on this! I’m going to reach out to them right now and ask for samples or a place to purchase. I’d gladly replace MEGA fuses for inverters and large MPPTs if I could source them.
There is a current and active thread over at DIYSolarForum.com where @ricardocello (also on the Victron Community) is looking at resistance from end to end, not just at the fuses.
An MRBF fuse and holder should be added to your fuse/breaker list. The MRBF is being used more and more. My gripe about the MRBF is that the rating doesn’t go below 30 amps. It’s a handy fuse to throw into a circuit, often without having to do any additional work on the cable (you can keep the cable lug that was already there).
IMO, MRBF is good for batteries at 12V, ok at 24V, not acceptable at 48V. AIC is too low at 48v. I don’t have any suggestions whether or not to use them for branch circuit protection since we don’t use them for that. Good call adding it to the list.
I may a bit of a purist but for me, a Class T fuse immediately downstream of the battery is the way to go. The AIC is the main reason. After that, it’s whatever works for that position. I am using MRBF fuses for select circuits, like low amperage 48 volt loads (with MRBF fuses rated for that voltage). The MRBF is more convenient than other fuses because I can (easily) bolt it right to a stud on a busbar. Most other fuses would require a cable from the busbar to the fuse holder, which introduces more resistance and failure points.
The jump from 10 W (Mega fuse) to ~75 W (breaker) is eye-opening. Also good points raised about AIC requirements, especially with lithium battery systems you can’t just pick based on price.