What would be recommended in MRBF for house batteries? Interested in knowing what others are using in a similar OEM setup. I recently bought two Group 31 AGM Duracell Platinums and need advice for simple fusing. It's a stock harness setup for two batteries. I'm not looking for major modifications or anything over the top in configuration (I'm electrically challenged). Blue Sea seems mentioned a lot for a easy, clean single post/fuse installation. How many is necessary and what amp fuse is needed?
Thanks!
Ref: 2001 Concourse V10
new installed...
Progressive Dynamics PD4645 converter/charger
Hardwired Progressive Industries EMS
SmartPlug cordset/outlet
SurePower battery separator
SunForce (aka: Coleman) 30 amp digital solar controller
Duracell Platinum AGM group 31 (two house)
MRBF for house battery bank
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HoosierB
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MRBF for house battery bank
Last edited by HoosierB on October 14th, 2018, 5:09 am, edited 1 time in total.
"Wanda" – '01 Chinook Concourse XL V10
Re: MRBF for house battery bank
There are a few things that determine fusing. The MRBF is a good choice for many battery banks. The two specific reasons not to use them would be 1) You don't have the height; or 2) Your battery bank requires a fuse with a higher AIC rating.
So, let's assume for now you have the height (at any rate that's easy for you to measure). What is the AIC rating and why do you care? Well, the AIC (ampere interrupt capacity) rating is basically a way to rate how heavy duty the body of the fuse holder or fuse are. This is regardless of the fuse size you put in it. It's about whether the fuse "style" itself - or the fuse holder - will or will not just melt or blow apart (thus rendering the fuse useless as a safety item).
The MRBF has an AIC rating of 10,000 amps. So is that enough for you? Well you can check to see if your battery mfgr. gives a short circuit amp rating. For the sake of discussion now (or if they don't), let's look at the Lifeline specs (which they do publish). If you have just "normal" Group 31 AGM batteries, then if they were Lifelines they'd have a short circuit amperage rating (in other words, how many amps could come flying out in a short circuit situation) of 3,564 amps each. So if you have two batteries, that's 7,128 amps. Therefore, the MRBF with its 10,000 amp AIC rating is fine for the job. As a counter example, I have three Group 31 "+" sized Lifelines. Each one is rated at 4,257 amps, so three times that is 12,771 amps. Therefore an MRBF is not rated highly enough so I had to go with a Class T fuse (rated at 20,000 AIC). The MRBF is less expensive, less costly, and takes up less space (also the spares you will want to carry are smaller and cheaper). So if you have the height, good deal!
The next thing to consider is what size fuse you will want to put into the fuse holder. The fuse is sized to protect the wire. The number you are looking for is the "ampacity" of the wire (more on that below). So you size the fuse to protect the wire size that is coming off the battery, and then any time that wire joins to a smaller wire, you fuse again there (smaller fuse size to protect the smaller wire), and then again on down the line. Those "down the line" fuses don't have to have the big AIC rating because you have the "big one" at the battery and that covers the rest for AIC rating.
To find out the ampacity of the wire, you need to know a few things:
1) The gauge of the wire (for example, 6AWG, 12AWG, and so on).
2) The heat rating of the wire (printed on the wire jacket). This will be 105ºC for "good" wire, but some wires can be 90ºC or even 75ºC. IIRC all of the stock Chinook wires were 105ºC, but of course double check.
3) Whether or not the wire is "alone," in conduit, or in a bundle of wires (if in a bundle, how many wires in a bundle; this is heat related).
4) Is the wire in an engine space or not along its run (again, heat related).
One you have all that, you look on an ampacity chart. So let's say you have the stock Chinook 8AWG wire leading to/from the brown box from the battery (at least that's what mine had).
1) 8AWG
2) 105ºC
3) in a bundle of around 15 or so (when passing above window).
4) Not in an engine space.
So, I'm going to start by leaving out #3. If the wire were "alone" then it would have an ampacity of 80 amps. A big bundle causes de-rating. In a bundle 7-24 wires, the ampacity is multiplied by .714, so that's 57 amps.
Therefore, you'd likely choose a 50 amp fuse. BUT, maybe that's too close for comfort if you have a 50 amp charger (because the stock wiring uses the same wire for charging and loads). Well then you can decide to fuse larger, just knowing what's behind your own personal decision.
On the other hand, we know from previous calculations that that super long, skinny (for this use) wire has a bunch of voltage drop (very undesirable). So some folks have run say, a 6AWG wire along the wall behind the water tank (then that 8AWG wire can be re-purposed to the TV area or the floor by the driver pillar). So if that wire was 6AWG, not bundled, 105ºC, no engine room, then it has an ampacity of 120 amps, just for example.
So that's the wire that goes to the brown box. Then there is the wire that goes to the start battery. That one will want to be fused separately (it's a different size). They make dual MRBFs or you can use two singles, depending on your setup. But the stock wire, at least in my rig, was 4AWG and that is problematic. Reason is that the starter will blow a 175 amp fuse (buddy tried since he only had 2AWG wire). A 200 amp fuse will do the job, but the ampacity of 4AWG wire in an engine space (it runs across the top of the engine area) is only 136 amps. I believe that's why Chinook did not fuse the wire at all (that's a safety risk, but any fuse that would meaningfully protect the wire would just blow constantly).
What I did there was replace the wire with larger wire gauge. Now I could fuse it safely, and also side bonus of less voltage drop for combining (charging). And I can self jump start without blowing the fuse. In my case that meant coming off my Class T fuse on the house bank, and then putting an MRBF on the start bank (which is just one battery so the AIC rating of an MRBF is just fine. I can say that an MRBF can sit on top of the Group 65 battery and clear the hood (had to test that one before adding it!).
The original solar wire also went right to the battery with skinny 12AWG wire and only a wee inline fuse. obviously with a tiny AIC rating. Some people say the whole wire will just vaporize if there is a short so that's okay. I avoided having to decide that by running the solar in to the rest of the system "downstream" of the big fuse protecting the main line.
Does that help? If you have any specific questions or want me to look up any particular wire size just holler.
So, let's assume for now you have the height (at any rate that's easy for you to measure). What is the AIC rating and why do you care? Well, the AIC (ampere interrupt capacity) rating is basically a way to rate how heavy duty the body of the fuse holder or fuse are. This is regardless of the fuse size you put in it. It's about whether the fuse "style" itself - or the fuse holder - will or will not just melt or blow apart (thus rendering the fuse useless as a safety item).
The MRBF has an AIC rating of 10,000 amps. So is that enough for you? Well you can check to see if your battery mfgr. gives a short circuit amp rating. For the sake of discussion now (or if they don't), let's look at the Lifeline specs (which they do publish). If you have just "normal" Group 31 AGM batteries, then if they were Lifelines they'd have a short circuit amperage rating (in other words, how many amps could come flying out in a short circuit situation) of 3,564 amps each. So if you have two batteries, that's 7,128 amps. Therefore, the MRBF with its 10,000 amp AIC rating is fine for the job. As a counter example, I have three Group 31 "+" sized Lifelines. Each one is rated at 4,257 amps, so three times that is 12,771 amps. Therefore an MRBF is not rated highly enough so I had to go with a Class T fuse (rated at 20,000 AIC). The MRBF is less expensive, less costly, and takes up less space (also the spares you will want to carry are smaller and cheaper). So if you have the height, good deal!
The next thing to consider is what size fuse you will want to put into the fuse holder. The fuse is sized to protect the wire. The number you are looking for is the "ampacity" of the wire (more on that below). So you size the fuse to protect the wire size that is coming off the battery, and then any time that wire joins to a smaller wire, you fuse again there (smaller fuse size to protect the smaller wire), and then again on down the line. Those "down the line" fuses don't have to have the big AIC rating because you have the "big one" at the battery and that covers the rest for AIC rating.
To find out the ampacity of the wire, you need to know a few things:
1) The gauge of the wire (for example, 6AWG, 12AWG, and so on).
2) The heat rating of the wire (printed on the wire jacket). This will be 105ºC for "good" wire, but some wires can be 90ºC or even 75ºC. IIRC all of the stock Chinook wires were 105ºC, but of course double check.
3) Whether or not the wire is "alone," in conduit, or in a bundle of wires (if in a bundle, how many wires in a bundle; this is heat related).
4) Is the wire in an engine space or not along its run (again, heat related).
One you have all that, you look on an ampacity chart. So let's say you have the stock Chinook 8AWG wire leading to/from the brown box from the battery (at least that's what mine had).
1) 8AWG
2) 105ºC
3) in a bundle of around 15 or so (when passing above window).
4) Not in an engine space.
So, I'm going to start by leaving out #3. If the wire were "alone" then it would have an ampacity of 80 amps. A big bundle causes de-rating. In a bundle 7-24 wires, the ampacity is multiplied by .714, so that's 57 amps.
Therefore, you'd likely choose a 50 amp fuse. BUT, maybe that's too close for comfort if you have a 50 amp charger (because the stock wiring uses the same wire for charging and loads). Well then you can decide to fuse larger, just knowing what's behind your own personal decision.
On the other hand, we know from previous calculations that that super long, skinny (for this use) wire has a bunch of voltage drop (very undesirable). So some folks have run say, a 6AWG wire along the wall behind the water tank (then that 8AWG wire can be re-purposed to the TV area or the floor by the driver pillar). So if that wire was 6AWG, not bundled, 105ºC, no engine room, then it has an ampacity of 120 amps, just for example.
So that's the wire that goes to the brown box. Then there is the wire that goes to the start battery. That one will want to be fused separately (it's a different size). They make dual MRBFs or you can use two singles, depending on your setup. But the stock wire, at least in my rig, was 4AWG and that is problematic. Reason is that the starter will blow a 175 amp fuse (buddy tried since he only had 2AWG wire). A 200 amp fuse will do the job, but the ampacity of 4AWG wire in an engine space (it runs across the top of the engine area) is only 136 amps. I believe that's why Chinook did not fuse the wire at all (that's a safety risk, but any fuse that would meaningfully protect the wire would just blow constantly).
What I did there was replace the wire with larger wire gauge. Now I could fuse it safely, and also side bonus of less voltage drop for combining (charging). And I can self jump start without blowing the fuse. In my case that meant coming off my Class T fuse on the house bank, and then putting an MRBF on the start bank (which is just one battery so the AIC rating of an MRBF is just fine. I can say that an MRBF can sit on top of the Group 65 battery and clear the hood (had to test that one before adding it!).
The original solar wire also went right to the battery with skinny 12AWG wire and only a wee inline fuse. obviously with a tiny AIC rating. Some people say the whole wire will just vaporize if there is a short so that's okay. I avoided having to decide that by running the solar in to the rest of the system "downstream" of the big fuse protecting the main line.
Does that help? If you have any specific questions or want me to look up any particular wire size just holler.
1999 Concourse
Re: MRBF for house battery bank
Wow, all I ever wanted to know about electricity in one post!
And believe it or not, I read the whole thing!
Which leads me to the conclusion that I will hire someone to do my dirty work for me lol! (Metaphor).
My batteries are fine right now, but I have given some thought as to what I will get next when the inevitable happens.
Thanks Blue, for helping me think about what to do next with batteries, solar and controller. I would love to have more solar up top so I can boondock eventually.
And believe it or not, I read the whole thing!
Which leads me to the conclusion that I will hire someone to do my dirty work for me lol! (Metaphor).
My batteries are fine right now, but I have given some thought as to what I will get next when the inevitable happens.
Thanks Blue, for helping me think about what to do next with batteries, solar and controller. I would love to have more solar up top so I can boondock eventually.
2000 Ford E-350 415CI/6.8L V-10 Triton Superduty 4X4 Chinook Concourse XL Club Lounge