Main power protection

[Redstang69]

As I've read over the build threads, something has caught my eye with many of the cobra builds, not just FFRs and I'd like to draw some attention to it and ask about it.
Considering the fact that the battery is located in the rear and the main positive power wire is ran all the way up the frame rail to the front, I see very few people putting a main fuse or breaker on this wire right off the battery. This is a pretty serious thing IMO. For those that might not understand the severity, I will attempt to explain.
If for any reason, the positive battery cable's insulation would get rubbed/cut/damaged and allow the bare spot in the wire to touch the frame and make a connection, you would have a dead short to ground, and all the energy from the battery will be able to flow through this spot to ground. This would be large amounts of current, more than the battery cable can handle, thus melting the cable and potentially causing a fire.
Some may argue that they clamp the cable and may even put additional insulation around the cable, but what if you would get into an accident and that cable would get pinched/cut (a scenario nearly impossible to predict)?
You might argue that you put the battery dissconnect switch in and could shut it off, however if the fault would occur between the switch and battery, you would still have the same cable melt down issue.
I don't have my car yet, so I don't have the manual or wiring or anything so I could be off on this, but 95% of the builds I've looked at on here and on hurricanes sure I don't see anyone mention installing a fuse or breaker or some sort of protection for this cable.
I also don't want to start something or offend anyone, as an electrical engineer I take wire size and protection into account almost daily and this has bothered me about these cars since I started looking into them. If I'm off base on this I will be glad to gain wisdom and understanding from someone who may have already been down this road and would offer up a different opinion.

Also, if I were to do a breeze front mount I wouldn't worry about this issue since it'd be like 99.9% of cars on the road and the positive battery cable run very short.

[nucjd19]

Well crap.You just gave me something to worry about and another project. My battery cut off switch is under the dash with a long run between the battery to this point. Going to need to look into wiring a fuse into the power cable near the battery. Oh well, tweaking these rigs are part of the process.

[narly1]

This is the cleanest high current fuse at the battery post solution I've seen. The fuse element itself is in the form of a small cube under the bolt head. Littlefuse FHZ00855-BX.

FHZ-series_DSL.jpg

[frankeeski]

2005 Dodge Magnum-Battery in the back, battery cable running all the way to the engine compartment-No overcurrent or short circuit protection.
2007 Chevy HHR-Battery in back, battery cable running all the way to the engine compartment-No overcurrent or short circuit protection.

Those are just two of the cars we currently own. Bet there are plenty more cars out there similar.

[TMartinLVNV]

It is interesting that you brought this up. I've run 4 to 8 gauge wire from a battery in the engine compartment back to the trunk for amplifiers in several regular production cars. I've always put a fuse at the battery for this very concern. I've never even considered it with a battery in the trunk running all the way forward. But it makes just as much sense as you have a fat battery cable running the length of the car with only an insulation wrap keeping the electrons in.

In my case, it is not an issue as I used the Breeze setup. As an EE, what amperage would you recommend?

[Alan_C]

An example size would be the 250A mega fuse that is supplied with the Coyote Controls Pack. Sizing would depend on what your starter draws when cranking plus a margin. I had a guy use a clamp type Ammeter to determine what the starter draws when starting a Coyote powered car, that was about 175 Amps.
I have my battery in the trunk. I actually have two 12V positive runs in the car. A primary #1 AWG cable directly to the starter fused at 250A. I have a second run #6 AWG going to the Coyote power distribution box and then the American Autowire harness for the rest of the car. This second run is fused at 100 A. The second run was added so the controls pack does not see the full voltage drop seen at the starter. Ford wants you to keep the distance to the PCM within 10 feet, where my run is 13 ft. The second positive run will see a minimal voltage drop beyond what is seen at the battery itself.

Frank, the two examples of production vehicles not fusing the run from a trunk mounted battery shows a common auto industry practice, but that does not make it safe. The automotive engineers in Detroit are as much bean counters as they are engineers. A few dollars per car in reduced production cost improves the bottom line by millions over a production run. With my build being a vintage Mustang, myself and others with their builds will want to exceed the standard practices of our friends in Detroit. For us, fusing the positive cable from the trunk is not a big cost. I will sleep better at night knowing the fuse is there.

I am an EE too and have been said to over think things a bit. Safety in our cars is important as these projects can kill you if done poorly.

[edwardb]

While I'll agree our Detroit (and everywhere else...) automotive engineers are heavily driven by the accounting department, they are also heavily driven by safety standards, government regulations, etc. Read about some of the safety recalls and how much it costs them. Fusing the main battery link is not common practice, period. Frank gave two examples. Most are the same. I would also add there's more to consider. A single point of failure that would cause a vehicle to be completely incapacitated is its own kind of safety concern. So that has to be factored in as well. Very different kind of discussion than for add-on cables like amps, accessories, etc.

A properly insulated and installed battery cable shouldn't move enough to wear through. That needs to be the main focus. On top of that, often whatever it's next to isn't a ground source. Including in our cars where usually the frame is coated in some manner. I'd also add that a front battery mod is very common in these builds. Reducing the exposure even more. If it helps you sleep at night, by all means add the battery fuse. But I always get a little concerned when safety is thrown out there and the perhaps amateur and inexperienced builders take it as gospel. Often, as in this case, there's more to the story.

[Redstang69]

All great points brought up here and that was why I wanted to bring it up because obviously others have thought about this and taken different approaches.
In regards to what size, I haven't yet put a meter on any of my vehicles but would agree with Alan_C's approach. Painless also makes one that you can put different size fuses in https://www.summitracing.com/parts/prf-80000
This came about because of an experience I had related to what TMartin said. In my younger days I had an amp in the trunk for a sound system and did not have the power feed fused for some unknown reason. I went around a turn one day and something in the trunk slid, hit the amp dislodging the power cable from the amp and I think the power wire grounded out on the amp case. I saw smoke start rolling up in the rear view mirror and pulled over and got it all under control, but it made me realize how quickly something unexpected could happen.
Paul is right also, there is a lot to consider here and I'm not a fan of fuses because once they're blown you better have a replacement or you're dead. However I see people going above and beyond Detroit by putting driveshaft loops on, using scatter shield bell housings, stainless steel brake lines, etc.
I don't want this to be a "you must do this" topic, but more of a "hey, just something to consider in case you never gave it a thought" kind of thing.

[ggunter]

Your concerns are legitamate. I work in the truck word and rubbed through cables are a regular thing from vibration and abrasion on cables and the resulting fires usually burn the truck to the ground before any fire equipment is able to put it out. Multiply the amperage times four batteries and you can do some serious welding with 2000 amps of current shorting to the frame. In recent years they have started installing 200 amp circuit breakers on the ground side of the battery box circuit to reduce this hazard. 200 amps is only on the accessory side of the circuits because 200 amps won't come close to cranking over a 13 liter engine. So a fuse or breaker of some sort would certainly help on our cars. When I went to FFR and looked at a car on display and saw how the hot cable was run from the rear forward I didn't care for how it was tightly bundled with the rear harness and that made the decision to go with the forward battery box mainly because that rear mounted battery looks like a bear to change out when needed and all that cable running forward left too many abrasion points in my mind. Now I know there is always diferent opinions of nothing ever happening so it's up to the individual building his own car to choose the direction he wants to take. If you get a dead short under the trans tunnel there is no way get that current shut down unless you cut off switch is located at the rear of the trans tunnel. Then your at the mercy of the quality of the Indian made cut off switch in hoping the contacts don't weld themselves together under a dead short situation.But there again well supported wiring with ample insulated clamps and protective loom as added protection will usually make the install trouble free. There is an online class the OEM manufacturer has I have taken on routing and clipping which shows the proper procedure on how to run wiring and plumbing. It's pretty interesting.

[narly1]

The Z case fuses used in the battery post mounted solution I posted are also available in different amperage ratings.

This is what the fuses look like on their own:

Littelfuse-Fuses-APS-ZCASE.jpg

I think if I was going to use this set-up I would probably keep a spare fuse in my go-bag.

[narly1]

On the subject of separate cable runs from the battery in the trunk to the starter and to the rest of the electrics, the post mounted solution I mentioned earlier also comes in 2 and 3 circuit versions.

https://www.littelfuse.com/media?res...-bmz-datasheet

[Redstang69]

On the subject of separate cable runs from the battery in the trunk to the starter and to the rest of the electrics, the post mounted solution I posted up earlier comes in multi circuit versions.

https://www.littelfuse.com/media?res...-bmz-datasheet

That is a really cool piece of equipment. We use Littelfuse brand stuff a lot in the industry I work in, I would trust it in an application like this.

[J R Jones]

Some aft battery, fwd engine examples are better than others, and if successful, the details are transparent. I have had Jaguar and BMW cars with remote battery, and no problems to 200K+ miles.
EV cars have more of a challenge in this regard, and I know not of what their safety methods are. Tesla might be worth looking into.
USAF interceptors basic DC was 28 volts and it went everywhere. The radar/weapons voltages were AC & DC at staggering levels of volts and amps. Design and execution resolve the danger.
Considering duty cycle diversity, helicopters are probably worse.
jim

[FF33rod]

I added a 250A main fuse at the battery in my '33 build. Perhaps OEM vehicles don't do this but I'm not going to pretend that my build has all the same installation and safety practices of an OEM build. So for me it gives peace of mind. This is a somewhat similar discussion to the crimp vs solder discussion. Perhaps in the professional world, a crimp is as good as as a solder joint and is standard practice for a certain industry, but they also use expensive specific purpose crimping tools that the average amateur doesn't use. That said, I do crimp end terminals but solder the wire splices. JMO

Steve

[bobl]

When I was building my car the main positive cable unbeknownst to me grounded on the frame. When I turned the power switch on it got ugly. I immediately flipped it back off but it did no good. The saving grace was the lead battery terminal melted off and killed the circuit. You would think an overcurrent would cause the power cut off switch to fail in an open position, but nope it welded the contacts solid. So, I installed a much better cut off switch and a high current fuse right at the battery. I also installed a fuse on the alternator charge lead just slightly larger than the current rating on the alternator. I'm slow, but I do learn from my mistakes!

[TriPower]

My first job as an ME was with a tractor company. I heard of an incident in the field that burned a farmer. We had to replicate this in the lab. We put a pin hole leak in the transmission hose and used a 12 GLOW plug in the stream of oil. This produced a flame 6 to 8 feet long. The point is, it does not take a spark to start some fires if some fuel or oil is around.

Lee

[CraigS]

I haven't worried about this at all. But maybe I should have. Having worked as a Lexus tech for 20+ years I have seen how OEMs keep their cars pretty safe including the hybrids. Basically they enclose the battery to starter/fuse relay box power leads in heavy duty plastic sheathing specifically molded for the car. If I were building again I'd look at the grey pvc conduit available at HD and L. Search pvc electrical conduit. I see the straight rigid stuff all the time and there is also another type that is flexible enough that it comes in coils. There are many, many types of joints, boxes etc to go with it. The stuff is cheap to buy and the medium grey color would be easy to live with in an FFR.

[narly1]

Basically they enclose the battery to starter/fuse relay box power leads in heavy duty plastic sheathing specifically molded for the car.

Split flex wire loom seems to be the automotive standard based on all of the newer cars I've ever owned.

Earl

[CraigS]

Here is an example of both. The black hard plastic piece is what I was thinking of and the orange and black loom is what narly1 is thinking of.
https://www.bing.com/images/search?v...t=0&ajaxserp=0
When I moved my battery to the front I used a double layer of the flexible loom for the + cable going to the starter. I got a diameter that was a good fit on the cable and then got a diameter that fit over the first one. I also indexed the split so they were opposite each other.
https://www.autozone.com/starting-ch...eVehicle=false

[narly1]

There are probably a few places in the build where this type of high temperature sleeving might not hurt either:

unnamed.jpg

[CraigS]

The heat insulation tube is also available in several sizes split and held together w/ velcro. This is fantastic for after the fact install since you don't need to take anything apart to install it.
https://www.summitracing.com/parts/the-14030