Fuses protect wires, not equipment - a discussion

[WorldwideDave]

I think that is what I have heard a few times in these forums.
I was told that mega and ANL fuses were not as good as t-class fuses.
Was curious to know why the Victron Lynx distributor uses MEGA fuses.
Guess it depends on what you are trying to protect or prevent?

I am doing a t-class fuse on the positive conductor between my positive bus bar and my battery kill switch. Is this okay, or should it be between the battery itself and the kill switch (other side of the kill switch so to speak)?
I am doing MTBF between MPPT #1 positive conductor and positive bus bar.
I am doing MTBF between MPPT #2 positive conductor and positive bus bar.
I am doing MTBF between inverter positive conductor and positive bus bar.

What else am I missing with regards to fusing?

I think my system at 2000 w uses about the same as Will was doing in his early videos and his off grid solar book, and yet, he wasn't using this gear back then. This is in no way a dig at Will, but it might just be he didn't know or couldn't afford it back then when living off grid in his own RV. Mad respect for you, Will. What a long way you've journeyed.

It is clear that there are full time and retired electricians on this forum - so thankful for your comments and feedback and suggestions. Sometimes I get conflicting information, though. Grateful either way.

 

[HRTKD]

Fuse should be as close to the battery as possible. Definitely not downstream of the switch.

Why are MEGA fuses seen so much in Victron gear? Because it's a European thing. That's what I was told when I asked that exact question of one of the bigger U.S. distributors.

MTBF? Do you mean MRBF? Marine Rated Battery Fuse.

I prefer a breaker between the solar charge controller and the common busbar. This allows me to turn off and isolate the solar charge controller completely.

 

[robbob2112]

My 2 cents -

Mega - because they started making that when lead acid was the thing and 12v or maybe 24v was what you could do. They are perfectly capable of those. They have been updated to 80v, but we're originally 32v and for use on 12v and 24v systems.

MRBF - marine rated battery fuse - they are designed as an ignition protected fuse for use on terminals in a vented battery hold that might have hydrogen gas from charging the lead acid battery bank present. Same thing, originally used for 12v or 24v...they max out at 32v 58v

Victron Lynx - designed around the 60v version of the Mega fuse ... they have released a Lynx that uses class T fuses.

Why Mega? Who knows...

 

[HRTKD]

MRBF - marine rated battery fuse - they are designed as an ignition protected fuse for use on terminals in a vented battery hold that might have hydrogen gas from charging the lead acid battery bank present. Same thing, originally used for 12v or 24v...they max out at 32v.

58v MRBF is available.

https://www.waytekwire.com/product/eaton-s-bussmann-series-mrbf-60-marine?srsltid=AfmBOoqnZJG2CsBwdy0cAksgfvc5gbjktjP0uujHCuJ0rHGs23iNntNl

 

[ricardocello]

If I could figure out how to make or build a fuse holder for AMH fuses, I would throw out all of my Class T and MEGA fuses.
They are superior in every way. Including price, $12-16 at mouser (not all values in stock).
The 20 kA AIC @125VDC is unbeatable.

Thread 'Eaton AMX and AMH Fuses alternative to Class T'
https://diysolarforum.com/threads/eaton-amx-and-amh-fuses-alternative-to-class-t.60804/

High-Power Automotive Bolt-Down Fuses - AMX(L)/AMH Series

Eaton-Bussmann's AMX and AMH series bolt-down fuses provide power density with 350 A and 500 A nominal current ratings.

www.digikey.com

 

[WorldwideDave]

Just to be clear...

The stuff I just bought on your recommendations will work for the 12v setup, but I'll be replacing it for 48v setup?
Yes, MRBF - I said that wrong.
I'll check the items I bought to see if they go to 58V. Nope - MRBF all say 30A on them. That sucks.
The t-class fuse does say 160V DC max.
I don't have a use case to disconnect a MPPT, but if I did, I can unscrew from the bus bar.
Almost every setup I've seen with a kill switch has the fuse between it and the bus bar.
We all agree I should move that now to the opposite side (battery-->t-class-->kill switch --> bus bar)?

 

[ricardocello]

Just to be clear...

The stuff I just bought on your recommendations will work for the 12v setup, but I'll be replacing it for 48v setup?

The higher the DC voltage, the harder it is to kill the arc.
12V? not that bad
48V (meaning up to 60V actual), much harder.

It can be really challenging to find decent fuses and holders rated up to 60VDC.
Plenty of threads on here about that.

 

[Mike8061]

Protect the wires is maybe an over simplification from people trying to explain certain concepts. Say the 14 awg wire in your house has a 15 amp fuse. The fuse is matched to the wire. If a device plugged into the wall need protection at 2 amps then it needs it's own 2 amp fuse. The 15 amp in the panel is sized to stop the wire overheating. Not necessarily to protect what's plugged in.

In the case of inverters or solar chargers it may combine both. Say your inverter says run a certain wire and fuse. Even if you run a bigger wire you should still run the fuse it called for.

If the inverter has its own fuse then you can decide to fuse to the wire size you run from the buss bar or run a wire that can handle the rating of the fuse on your battery and have it protected by that.

The t class fuse is not necessarily "better". It is rated to break higher amps than the other ones you listed. If your running batteries that can deliver those amps then it would be more appropriate.

Matching the voltage has already been mentioned. It's basically the same theory. The fuse should be rated to handle the volts and amps it may be required to stop.

 

[HRTKD]

We all agree I should move that now to the opposite side (battery-->t-class-->kill switch --> bus bar)?

Yes, that is the correct order.

Not all components that work on 12 and 24 volt systems will work on a 48 volt system. It's very important that the rating of the components match the system voltage.

 

[robbob2112]

If I could figure out how to make or build a fuse holder for AMH fuses, I would throw out all of my Class T and MEGA fuses.
They are superior in every way. Including price, $12-16 at mouser (not all values in stock).
The 20 kA AIC @125VDC is unbeatable.

Thread 'Eaton AMX and AMH Fuses alternative to Class T'
https://diysolarforum.com/threads/eaton-amx-and-amh-fuses-alternative-to-class-t.60804/

High-Power Automotive Bolt-Down Fuses - AMX(L)/AMH Series

Eaton-Bussmann's AMX and AMH series bolt-down fuses provide power density with 350 A and 500 A nominal current ratings.

www.digikey.com

View attachment 258896

https://www.mouser.com/ProductDetail/Bussmann-Eaton/C5268-5?qs=sv12qe8ZWxOYh0DphappVw%3D%3D&mgh=1&utm_id=17222215321&gad_source=1&gclid=Cj0KCQiAgJa6BhCOARIsAMiL7V8_8qsYFGFKU53q51MZcOcH_Of0EyJr-3oZFLI9xXQ73VbtCifBGqkaAm9zEALw_wcB

 

[ricardocello]

https://www.mouser.com/ProductDetail/Bussmann-Eaton/C5268-5?qs=sv12qe8ZWxOYh0DphappVw%3D%3D&mgh=1&utm_id=17222215321&gad_source=1&gclid=Cj0KCQiAgJa6BhCOARIsAMiL7V8_8qsYFGFKU53q51MZcOcH_Of0EyJr-3oZFLI9xXQ73VbtCifBGqkaAm9zEALw_wcB

Yeah, those will certainly work, and I’m not opposed to making a bank of them hanging off of a busbar if I ever get free time.
Concerned about the 100A rating, I wonder why that is?
Thanks

 

[WorldwideDave]

Wait a minute… Can the voltage of the fuse, like the 200 amp class T fuse I have, which is rated for 160 V, still protect a 12 V system? Similarly, can the 125 amp MRBF terminal fuse I bought that is rated for 32 V work for the 12 V system? I understand I will now be ordering some 60 V MRBF fuses.

 

[ricardocello]

Wait a minute… Can the voltage of the fuse, like the 200 amp class T fuse I have, which is rated for 160 V, still protect a 12 V system? Similarly, can the 125 amp MRBF terminal fuse I bought that is rated for 32 V work for the 12 V system? I understand I will now be ordering some 60 V MRBF fuses.

Yes, absolutely!
The voltage ratings are maximum values.

 

[robbob2112]

https://www.mouser.com/ProductDetail/Eaton-Electronics/HMX-111?qs=rQFj71Wb1eWVrlnsuUuwhg%3D%3D

 

[dougbert]

58v MRBF fuse

https://www.amazon.com/gp/product/B0C6LDZH5Y/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

 

[ricardocello]

https://www.mouser.com/ProductDetail/Eaton-Electronics/HMX-111?qs=rQFj71Wb1eWVrlnsuUuwhg%3D%3D

Note that these only have a 2 kA AIC at 58V.
Which may be ok, but with LiFePO4 I generally shoot for 10 kA breaking capacity.

 

[cs1234]

58v MRBF fuse

https://www.amazon.com/gp/product/B0C6LDZH5Y/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

They have AIC 2000A @ 58VDC . That might be good enough for a 50ah or 100ah lifepo4 battery if they break fast enough.

I'm not sure I trust BOJACK brand fuses.. but they certainly are appealing price / ease of ordering / installation wise.

 

[Rednecktek]

Was curious to know why the Victron Lynx distributor uses MEGA fuses.

Because it's blue so it's just better than you are. Do not question the almighty smurf!

 

[ricardocello]

They have AIC 2000A @ 58VDC . That might be good enough for a 50ah or 100ah lifepo4 battery if they break fast enough.

I'm not sure I trust BOJACK brand fuses.. but they certainly are appealing price / ease of ordering / installation wise.

Makes me think of LoJack…

 

[ricardocello]

Because it's blue so it's just better than you are. Do not question the almighty smurf!

I’m not sold on Victron Lynx, despite my blue heritage.
I’m more of a DIY busbar/fuse guy.

MEGA fuses are very 2020. This is 2024.
But yes, they are a nice shade of blue.

 

[Pappion]

Fuses downstream of the Class-T battery fuses do not need to have Class-T AIC.
There should be wire resistance which would limit the current.
Victron Lynx does not have the resistance. It's a buss bar that can handle hundreds of amps.

 

[Pappion]

BTW, fuses can be used to protect wires and protect against equipment fires. Electronic equipment maker would have liability if they depend on the wiring fuse.

 

[Supervstech]

Protect the wires is maybe an over simplification from people trying to explain certain concepts. Say the 14 awg wire in your house has a 15 amp fuse. The fuse is matched to the wire. If a device plugged into the wall need protection at 2 amps then it needs it's own 2 amp fuse. The 15 amp in the panel is sized to stop the wire overheating. Not necessarily to protect what's plugged in.

In the case of inverters or solar chargers it may combine both. Say your inverter says run a certain wire and fuse. Even if you run a bigger wire you should still run the fuse it called for.

If the inverter has its own fuse then you can decide to fuse to the wire size you run from the buss bar or run a wire that can handle the rating of the fuse on your battery and have it protected by that.

The t class fuse is not necessarily "better". It is rated to break higher amps than the other ones you listed. If your running batteries that can deliver those amps then it would be more appropriate.

Matching the voltage has already been mentioned. It's basically the same theory. The fuse should be rated to handle the volts and amps it may be required to stop.

Class T is BETTER because it can handle extinguishing arc flash higher voltage DC produces. Saying it handles higher amps is insuficient explanation, it handles extinguishing ARC FLASH INTURUPT up to 20,000A
See, when there is a dead short, and a failed bms, a large bank of LFP can output 10,000A easily. So your 4/0 wiring becomes a length of incandescent flame throwing wood burning, home destroying molten flash plasma...

You want the arc extinguishing voltage clamping fuse as CLOSE to the energy source battery bank as possible.

 

[WorldwideDave]

58v MRBF fuse

https://www.amazon.com/gp/product/B0C6LDZH5Y/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

Bought a Buss brand a few hours earlier, thanks. They'll be here Friday, but I'll install the smaller ones for the 12v system tomorrow morning anyway.

 

[WorldwideDave]

Note that these only have a 2 kA AIC at 58V.
Which may be ok, but with LiFePO4 I generally shoot for 10 kA breaking capacity.

All of this is LiFePO4. Are you suggesting that I bought the wrong stuff for the 3rd time in 3 days?