In Line Fuse for Positive Lead from Battery Bank?

[straightshooter]

I have been reviewing YouTube Videos from "Explorist" to assist in my solar install. He had 2 videos on how to fuse your system and one of the things he brought up was the need to place an inline fuse on the positive lead in close proximity to your battery bank. I've checked out the wiring on my GD23LDE and I don't see a fuse on the positive anywhere near the battery. Anyone with experience on this and if they placed an inline just near the battery, how did they determine the wire size? Was it in relation to the gauge of the wire, which in my case appears to be only 10 gauge.

 

[TimtheToolMan]

What you are describing may not be uncommon with many TT and 5th wheels, at least. Adding the right size fuse for the various battery capacities and types LFP/LA with in 6" or battery would be a hassle and add cost or dealer for manufacture but is the right thing to do.

Adding an MRBF on the positive battery post is an easy fuse option, and a very good one for LFP also. LFP could produce 3,200 A with a 320Ah battery (one calculation from another forum) if short circuited! LA acid with higher resistance is nowhere near this.

Wire size vs current. It is common to take maximum current driven by total of anything going in or out of battery and multiply by 1.25 for fuse size.

 

[Steven@147]

Something like this? Queston? I am interested as well.
Eaton says the interrupt rating is
10,000 AMP at 14VDC
5,000 AMP at 32VDC
2,000 AMP at 58VDC

The fuse in the picture is 300 amp but they have them from 30 - 300. Blue Sea. I also read the following;
For two 100 amp lithium batteries, a 100 ampMRBF fuse would be the appropriate size, as you should choose a fuse rating that matches the maximum current draw of your battery system, which in this case is 100 amps per battery.

Key points about MRBF fuses:

• Marine Rated Battery Fuse:
  MRBF stands for Marine Rated Battery Fuse, designed for high current applications in marine environments and suitable for lithium batteries.
  
  
• Amperage Rating:
  Select an MRBF fuse with an amperage rating equal to or slightly higher than the maximum current your battery system can draw.
  
  
• Important Consideration:
  When dealing with multiple batteries, consider the combined current draw, not just the individual battery rating

 

[Riverbug]

It sounds to me like you are talking about your stock setup, not upgraded lithium batteries or anything. If that's the case then you are correct that there is not a fuse near the battery, however, there is a 30A auto reset breaker mounted on the frame at the front. If you follow the positive lead from the battery down to the frame you'll see it leads to the breaker. You really don't need to do anything to change that setup if you are just going to keep a 12V lead acid battery up there.

If you upgrade to LFP, then it is certainly beneficial to add fuse protection at each battery. Many people do not. But you'll definitely need to understand the proper fusing for that system; T-class type or similar next to a proper cutoff switch, along with other things...

 

[TimtheToolMan]

Something like this? Queston? I am interested as well.
Eaton says the interrupt rating is
10,000 AMP at 14VDC
5,000 AMP at 32VDC
2,000 AMP at 58VDC

The fuse in the picture is 300 amp but they have them from 30 - 300. Blue Sea. I also read the following;
For two 100 amp lithium batteries, a 100 ampMRBF fuse would be the appropriate size, as you should choose a fuse rating that matches the maximum current draw of your battery system, which in this case is 100 amps per battery.

Key points about MRBF fuses:

• Marine Rated Battery Fuse:
  MRBF stands for Marine Rated Battery Fuse, designed for high current applications in marine environments and suitable for lithium batteries.
  
  
• Amperage Rating:
  Select an MRBF fuse with an amperage rating equal to or slightly higher than the maximum current your battery system can draw.
  
  
• Important Consideration:
  When dealing with multiple batteries, consider the combined current draw, not just the individual battery rating

Agreeing with you. From the Blue Sea curves, it appears that there is a cushion (125%?) above fuse rating built in so multiplying actual current by 1.25 does not appear appropriate.

Consider:
--MRBF fuses mounted on each positive battery post (AIC 10,000) and
--Class T (as Riverbug said) fuse with proper enclosure where multiple batteries combine (AIC 20,000)
--Purchase only from quality name brand manufactures like Eaton Hussman, Blue Sea (rebranded), ... What is going on from many others is scary!
--Solid interrupt ratings AIC (numerous fuses have no AIC rating)
--UL approved or other well-known certification
--Fast trip (most circuit breakers are too slow and resistance too high)
--Proper shut-off switch (Riverbug)

The BMS helps in above but can possibly fail closed.

Powerwerx has favorable pricing on MRBF even with shipping, depending on what is purchased.

The AIC calculation used 8-10 times battery Ah and then a cushion like 1.25x(?). This has not been verified though testing so more cushion could be used? Information from a solar related forum for DIY.

 

[straightshooter]

It sounds to me like you are talking about your stock setup, not upgraded lithium batteries or anything. If that's the case then you are correct that there is not a fuse near the battery, however, there is a 30A auto reset breaker mounted on the frame at the front. If you follow the positive lead from the battery down to the frame you'll see it leads to the breaker. You really don't need to do anything to change that setup if you are just going to keep a 12V lead acid battery up there.

If you upgrade to LFP, then it is certainly beneficial to add fuse protection at each battery. Many people do not. But you'll definitely need to understand the proper fusing for that system; T-class type or similar next to a proper cutoff switch, along with other things...

Thanks for the info. I'm actually in the process of installing 2 LiTime 100AH Lithium Batteries so I'll probably look into MRBF fuses at the terminals.

 

[Riverbug]

Thanks for the info. I'm actually in the process of installing 2 LiTime 100AH Lithium Batteries so I'll probably look into MRBF fuses at the terminals.

Ok, got it. Then yes, it's best to fuse each battery. It gets challenging because there isn't an RV standard like there is for marine and automobiles. So most often if one wanted to follow a standard they refer to the marine ABCY standards. In that case, every DC positive conductor requires protection.

 

[TimtheToolMan]

Ok, got it. Then yes, it's best to fuse each battery. It gets challenging because there isn't an RV standard like there is for marine and automobiles. So most often if one wanted to follow a standard they refer to the marine ABCY standards. In that case, every DC positive conductor requires protection.

If you plan on removing batteries when in storage/not in use the Anderson SB50 are sweet and can be ordered with cable if desired. There are various AWG options. BatteryCablesUSA make it very easy to customize order using a note form when ordering.

 

[Riverbug]

If you plan on removing batteries when in storage/not in use the Anderson SB50 are sweet and can be ordered with cable if desired. There are various AWG options. BatteryCablesUSA make it very easy to customize order using a note form when ordering.

Thanks, that's not a bad idea. But looks like the largest cables are 1/0. I don't find it too difficult to unbolt them when I need to.

 

[TimtheToolMan]

Sorry Chad and thanks for being so kind to my error. I had @straightshooter in mind and made wrong selection.

4x280 (1,120)Ah and everything cool that you have would need way more than basic cables (buss bars...), and I doubt that you remove the batteries for storage. What a system that you have built!

 

[Riverbug]

Sorry Chad and thanks for being so kind to my error. I had @straightshooter in mind and made wrong selection.

4x280 (1,120)Ah and everything cool that you have would need way more than basic cables (buss bars...), and I doubt that you remove the batteries for storage. What a system that you have built!

No problem at all, I assumed you were just trying to help out and there's nothing wrong with that! We've had mild winters lately in MN so I have not removed them the last few years. But when we get back to normal winters and -20 spells, I will pull them out just to be safe. So far our lowest is -7 starting tonight. It has been a fun to use the system I built and finding that it actually works even! We love being able to use everything as if plugged into shore power while on the road or boondocking.

 

[Scott'n'Wendy]

Something like this? Queston? I am interested as well.
Eaton says the interrupt rating is
10,000 AMP at 14VDC
5,000 AMP at 32VDC
2,000 AMP at 58VDC

First time I've ever seen anyone mention the IR of a fuse on an RV forum. If you are concerned about IR you need to determine your total available fault current. IE max your batteries could supply in the event of a solid short to ground.

 

[JPS350]

Concerning fuse size, it’s determined by the current capacity of the wiring you’re trying to protect. For the 10awg wiring mentioned that would be a 60a MRBF fuse. See chart in the link.

Part 2: Select a Fuse and Fuse Holder For Your DC Product Installation - Blue Sea Systems

Engineering high quality marine electrical components for safety, reliability and performance

www.bluesea.com

 

[TimtheToolMan]

First time I've ever seen anyone mention the IR of a fuse on an RV forum. If you are concerned about IR you need to determine your total available fault current. IE max your batteries could supply in the event of a solid short to ground.

I have not been able to find any test data or verified calculations for total available fault current for LFP batteries and codes that specifically deal with LFP fuse design calculations. My post #6 mentions 8-10 times Ah as an unproven calculation (not mine).

If you know where one can obtain IE max for LFP from a proven source, that would be very helpful in proper design.

It appears that proper related codes and data are very slow in catching up with high amp low resistance low voltage (12-48V) batteries. AGM are lower resistance than standard LA but related changes, at least that I have been able to find, are rarely and imprecisely mentioned.

Many of us have been falsely assuming that if a fuse worked fine for my previous LA/AGM at 12V and driving the same equipment, surely a different battery type would not matter.

 

[Scott'n'Wendy]

The only place any accurate data for that would have to come from the manufacturer of the batteries themselves. Sooo you probably aren't going to get that data if they haven't published it already.
For myself I would guess about 1000 amps per battery - that also needs to include a BMS failure. So 10Ka is lots imo.
FYI, 10Ka @ 14v is the MRBF std. If it doesn't state IR, doesn't matter it's still 10Ka@14v

 

[TimtheToolMan]

Here is a reasonably short publication with current related test data that includes some smaller LFP, not just large EV batteries. One graph shows over 80A for a very small 8Ah LPF and over 1000A for 160Ah. Is there a correlation of 7-10 times Ah capacity for maximum dead short current and is the ratio somewhat less for those very large LFP?

Added: Popular ANL fuses are rated at 6000 AIC so may not be sufficient for medium/large Ah systems?

 

[straightshooter]

Agreeing with you. From the Blue Sea curves, it appears that there is a cushion (125%?) above fuse rating built in so multiplying actual current by 1.25 does not appear appropriate.

Consider:
--MRBF fuses mounted on each positive battery post (AIC 10,000) and
--Class T (as Riverbug said) fuse with proper enclosure where multiple batteries combine (AIC 20,000)
--Purchase only from quality name brand manufactures like Eaton Hussman, Blue Sea (rebranded), ... What is going on from many others is scary!
--Solid interrupt ratings AIC (numerous fuses have no AIC rating)
--UL approved or other well-known certification
--Fast trip (most circuit breakers are too slow and resistance too high)
--Proper shut-off switch (Riverbug)

The BMS helps in above but can possibly fail closed.

Powerwerx has favorable pricing on MRBF even with shipping, depending on what is purchased.

The AIC calculation used 8-10 times battery Ah and then a cushion like 1.25x(?). This has not been verified though testing so more cushion could be used? Information from a solar related forum for DIY.

Powerwerx was very helpful in the selection of the proper sized MRBF fuse and fuse block. Thanks for the lead on a great supplier.