Fuse types 12 volt selection/use

jennowhat

New member
Hi All. I'm hoping to get a little advice on what types of fuses I can/should be using for my 12v system (Anl, mega, midi, maxi...)

I will need 5 or 6 of these between 100 and 200 amps for various places (battery to inverter, isolator to battery, battery to fuse block, etc.)

I understand that ANL is the best and it's a bad idea to go for a cheap brand, but $40 for a Blue Sea ANL fuse with holder is adding up quickly.

Is there any reason I shouldn't use other types, like MIDI or MEGA? Or another brand that is still quality but less expensive? Even the Blue Sea circuit breakers are less expensive than the ANL fuses including holders.

If not... is it okay to use the cheapo fuse holders with the Blue Sea ANL fuses?

Any suggestions for keeping this budget-friendly without sacrificing quality and safety are welcome. Thank you!
 

autostaretx

Erratic Member
What year is your Sprinter?

If it's an NCV3 (2007 and newer), there are some empty fuse positions on the Sprinter battery's Power Distribution Block that's wedged in the under-floor battery box.

Where it's at: (the "PDC")



What it looks like:



If you can use those to whittle your needs down to only a couple more at the House battery, BlueSea has these:



--dick
 
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marklg

Well-known member
If you can use those to whittle your needs down to only a couple more at the House battery, BlueSea has these:



--dick
I've used those MRBF fuses described above from Blue Sea, and also some ANL fuses and a Class T fuse.

One important thing about fuses used with large wires on batteries is the Ampere Interrupting Capacity or AIC rating. The fuse may have a rating of 250A, but the fuse can blow and DC will still arc over and the current can be much higher. If you have low resistance wire and a big battery, there can be thousands of amps.

A poorly made fuse may open but arc over and the current will still flow until something else, usually bad, happens. The AIC rating is how much current the fuse will interrupt. Typically it is about 6,000A for a real ANL fuse, 10,000A for the MRBF fuses and 20,000A for a Class T fuse, which are really expensive.

I did cheap out and use generic ANL fuses on some of my house batteries because the MRBFs did not fit. However, there is one big Class T fuse in line with the inverter where all the battery current comes together.

Hope this helps.

Mark
 

avanti

2014 GWV Legend 3500 I4
One nice thing about MRBF fuses is that they are small, convenient, and cheap enough that they can be used on each battery terminal, thus protecting the cross-connects, which are often left unprotected.
 

Aqua Puttana

Poly - Thread Finder
I understand interrupting ratings. I haven't been aware of great problems with arcing over and current continuing to flow with 12 volt systems. The more common failure is that the fuse self destructs under the failure condition. That said, I may not be aware of some arcing failure modes of the compact special design fuses. If those are the problem children it sounds like a design issue.

Whatever fuses are chosen I would be certain to buy 1 ea. spare of each size to carry along. Many of the high current fuses are not readily available.

Short heavy cable runs (jumpers) are often straight through with no fuse protection needed. That is common in vehicle design. For cables sized for efficiency using voltage drop, the fusing is generally necessary for short protection, not continuous overload heating.

:cheers: vic
 
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jennowhat

New member
Thank you! I like these MRBFs...is it okay to use one of these for a 200a fuse going to my 2000w inverter? I keep hearing that a quality ANL fuse is best for this application, but is there any reason why one of these won't work just as well?

Also, is there any problem with stacking 2 of these single MRBFs on top of each other? I'd love to do one going to the inverter and the other going to my busbar (one 200a and one 300a so the dual holder would not suffice).

Thanks again!
 

marklg

Well-known member
Thank you! I like these MRBFs...is it okay to use one of these for a 200a fuse going to my 2000w inverter? I keep hearing that a quality ANL fuse is best for this application, but is there any reason why one of these won't work just as well?

Also, is there any problem with stacking 2 of these single MRBFs on top of each other? I'd love to do one going to the inverter and the other going to my busbar (one 200a and one 300a so the dual holder would not suffice).

Thanks again!
The MRBF fuses are sold separately from the holders, so I think you can put a 200 and a 300 on the dual holder. I don't have any duals though.

The MRBFs have a higher AIC rating than the ANLs, so I would not hesitate to use more of them. They are tall with the post, so there was not room to fit them in two battery holders, so I used ANLs there.

What does the inverter manufacturer recommend? My 2kW inverter has a high peak capability and they suggest a 300A fuse. The individual battery cables are sized for 250A fuses. The original installer made some big mistakes with the wiring, causing a short on the inverter 120V output to the chassis. Only because the inverter was smart enough to figure out something was wrong and shut down was I saved from a fire or electrocution.

So, I am now extra careful, probably overly so, and have a fuse on each battery so no run of cable can short and be unprotected. It does result in a little more voltage drop. The DC battery wiring was also crap. I replaced it with all AWG 1/0 wire and combine the two original house batteries into one cable to the inverter and the other two house batteries I added into another cable to the inverter, so that helps with the voltage drop.

Regards,

Mark
 

jennowhat

New member
The product description on Blue Sea's site says the dual holder can accommodate up to 300amps combined between the two. So to be safe, I was thinking of stacking two singles. Would that be okay?

The inverter manufacturer (AIMS) recommended a 200a fuse. It is 2kw with a 4kw surge capability. I am running 2/0 wires to it (short run). Does that sound right?

Glad to hear your inverter was smart enough...yikes.
 

marklg

Well-known member
The product description on Blue Sea's site says the dual holder can accommodate up to 300amps combined between the two. So to be safe, I was thinking of stacking two singles. Would that be okay?

The inverter manufacturer (AIMS) recommended a 200a fuse. It is 2kw with a 4kw surge capability. I am running 2/0 wires to it (short run). Does that sound right?

Glad to hear your inverter was smart enough...yikes.
I did not know that about the dual holders. I wonder what is the limiting factor? If it is the lug that attaches to the battery, it would seem that stacking two would be OK, but I really don't know.

The cable capacity depends on the max temp rating of the wire insulation and the heat generated in the cable compared to that. I am using welding cable rated at 105C and the manufacturer rates 1/0 at 285A and 2/0 at 325A. If you were to follow the NEC, they only list 90C wire and the ratings are 170A and 195A. The NEC is not required for conversion vans. They are more like boats where for 105C cable they are rated at 285A and 330A. So, I would think 2/0 would be OK.

The above ignores voltage drop. For 2/0 cable, 200 Amps through 10 feet will give you about .31 V drop for a 10 ft run. Here is a handy calculator:

https://www.calculator.net/voltage-...ce=10&distanceunit=feet&amperes=200&x=45&y=30

That would seem to be OK to me, depending on the dropout voltage of your inverter. My cable runs are longer, maybe 20 feet and there are effectively two 1/0s in parallel. That gives a .39 V drop, but there are other voltage drops in the fuses, connectors, etc. It seems to work fine for me. I can load up the inverter fully.

Best of luck,

Mark
 

Midwestdrifter

Engineer In Residence
I would not be concerned about the 300A limit on the dual holder. That is likely the max continuous current it can carry. Your loads will never hit that, so you need not worry about overheating the fuse holder.
 

HarryN

Well-known member
The product description on Blue Sea's site says the dual holder can accommodate up to 300amps combined between the two. So to be safe, I was thinking of stacking two singles. Would that be okay?

The inverter manufacturer (AIMS) recommended a 200a fuse. It is 2kw with a 4kw surge capability. I am running 2/0 wires to it (short run). Does that sound right?

Glad to hear your inverter was smart enough...yikes.
Might want to spend some more time researching inverter brands. example amazon, youtube, etc for user experiences.
 

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