Battery Fuse Protection

[steveg]

I found this on Youtube: https://www.youtube.com/watch?v=d2nPHWNoDSA. A modern four-pot seems to draw around 100 amps, so I figure that it may be around 150 or so on a Healey. If voltage drops to 10 volts that would equate 1500 watts or around 2 hp, which seems reasonable. But again, if you put a, say, 200 amp fuse on the battery that would only protect the cable from the battery to the starter. If there is a short somewhere else in the system the cable would probably melt before the fuse blows.

Am arguing the only purpose of Ray's proposed fuse is to protect the cable between the battery and the solenoid against a dead short to the frame.

The rest of the car is relatively easily handled by the various fuses for the circuits. It would be relatively easy to add a fuse between the solenoid and brown wire that supplies the car if one was worried about that well-protected wire.

Thinking about this, the size of the fuse would be subject to experimentation. If one picked a size and it didn't blow during cranking, it would certainly blow in the case of a dead short to the frame.

Some fusible links - the biggest is 100 amps. If one installed this and it didn't blow, we'd be good to go:

 

[steveg]

If the fuse blows due to a scraped cable, you're stranded - the car's undrivable, therefor better to protect the cable from that eventuality:

 

[John Turney]

These marine fuses, https://www.westmarine.com/buy/blue...rotected-fuses--P009_273_004_004?recordNum=11 go from 35 A to 500 A. They are suitable for use near gasoline tanks. Look at the blow delay curve here: https://newcontent.westmarine.com/documents/pdfs/OwnersManuals/ELECTRICAL/ANL_Fuse.jpg. If the fuse was rated for something less than the full locked-rotor current of the starter, the starter would have almost 5 seconds to start the engine.

 

[Keoke]

Well Guys:

There is another approach to this:

Consider a relay with the same current carrying capability as the starter solenoid ,witch is wired to bypass a 60 amp fuse when ever the key is used in the start position.

 

[RAC68]

Hi All,

Thank you for all your comments and sugestions. As Steve and John have indicated, I have been concerned about the potential for a dead short in the main battery cable igniting fuel (tank / line) in close residence. Keoke's "Fault Protection Isolation" has some potential but how would we isolate the combination of high amperage electrical and fuel paths without a redesign to one or both systems.

Back in 2013 we also discussed an approach to provide fusing of the battery/cable and ran into the same high amperage starter draw issue. Back then I provided a drawing and Keoke just brought up the approach. The drawing used a remote Ford starter solenoid that switched the circuit to fuse protection once the engine was started. This allow practical fuse protection (40 amp) during operation but allowed the circuit to be unprotected during starter activation. Yes, there is some exposure during startup but reasonable protection thereafter.

The reason why I never implemented this approach is that it started to become quite complex with a potential for unintended consequence due to being first. When seeing the simplicity of a battery fuse on so many newer high electrical use cars, I had forgotten how much amperage it takes to start our cars.

Thanks again guys,
Ray(64BJ8P1)

 

[steveg]

I know two Healey owners (BJ8 & BT7) who have had trunk fires which caused minor damage because they were caught and extinguished quickly.

Both of these were caused by loose metal items shorting to ground from either the battery or the shutoff switch.

IMO the simplest method is to make sure the in-trunk connections and top of the battery are covered by insulating material. Then run the 1/2" flex conduit under the frame from rear to front.

I installed a new 8 ft cable under my car 18 years ago and have very seldom given it other than a glance. Out of sight, out of mind. If one were to armor that cable under the car with flex conduit, one would have more peace of mind because it would be, well, armored.

 

[Keoke]

" I installed a new 8 ft cable under my car 18 years ago and have very seldom given it other than a glance. Out of sight, out of mind. If one were to armor that cable under the car with flex conduit, one would have more peace of mind because it would be, well, armored:​

:

Steve I am sincerely clad this worked for you

,However,:
I do not consider it a valid electrical resolution that the forum members and guests should follow.

 

[steveg]

" I installed a new 8 ft cable under my car 18 years ago and have very seldom given it other than a glance. Out of sight, out of mind. If one were to armor that cable under the car with flex conduit, one would have more peace of mind because it would be, well, armored:
​

:

Steve I am sincerely clad this worked for you

,However,:
I do not consider it a valid electrical resolution that the forum members and guests should follow.

Keoke - have you installed the above "valid electrical resolution" on either of your Healeys?

 

[Bob_Spidell]

Inductive loads--like starters--are effectively dead shorts for a couple milliseconds until the load gets saturated and impedance builds. I think you'd want a 'slow blow' fuse (like on the ODs; solenoids are inductive loads).

Anybody think a ground fault interrupter (GFI) might be made to work in this application?

 

[Keoke]

Keoke - have you installed the above "valid electrical resolution" on either of your Healeys?

No Steve:

I would have used a plastic conduit thereby adding an additional layer of electrical insulation over the cable as well as providing additional mechanical protection from external abrasion''

Using a metal conduit virtually wraps the cable in a physically close ,potential electrical short circuiting case, but does not add any electrical insulation over the cable.

 

[Keoke]

Inductive loads--like starters--are effectively dead shorts for a couple milliseconds until the load gets saturated and impedance builds. I think you'd want a 'slow blow' fuse (like on the ODs; solenoids are inductive loads).

Anybody think a ground fault interrupter (GFI) might be made to work in this application?

No Bob:

But there is another rather simple approach to this:

Simply replace the existing cable with welding cable ,they have been designed to resist physical abrasion and have significantly lower resistance /FT because they use more stranded conductors to meet their flexibility requirements..

 

[steveg]

Looking at Ray's drawing, would it be possible to simplify it slightly by using the Ford solenoid to start the car, eliminating the stock solenoid up front?

Still simpler to armor the big cable (agree re welding cable above), uprate the insulation of the trunk connections and figure out a fuse for the battery side.

 

[steveg]

No Steve:

I would have used a plastic conduit thereby adding an additional layer of electrical insulation over the cable as well as providing additional mechanical protection from external abrasion''

Using a metal conduit virtually wraps the cable in a physically close ,potential electrical short circuiting case, but does not add any electrical insulation over the cable.

No Keoke - Rigid plastic tubing sounds sort of ok, but metal conduit would give better protection in the advent of a scrape. Conduit's not there to add insulation. We'd be using it for the same reason they use it in buildings - as armor to prevent damage to the wiring. The insulation on the cable can take care of itself inside of a grounded metal tube. Just like your garage wiring.

 

[Keoke]

Steve:

Garage / House wiring conduit adds add contiuity to the
electrical ground system in addition to the current 3rd green wire and isolates your wooden structures from potential electrically generated fires.

However :
Unfortunately this is not universal in USA.

 

[John Turney]

.... Anybody think a ground fault interrupter (GFI) might be made to work in this application?

In theory, one could measure the current in the cable at the battery and at the starter solenoid, and if different, open a breaker. In practice, it would probably be difficult.

 

[RAC68]

Hi All,

Although I would like a complete solution to a grounded battery cable, keep in mind that the issue of high amperage lasts only for the duration time the starter is active and a much lower fuse (i.e. 40 amps) can be implemented after the car is started. Yes, there is still a risk during the start time period, however, it should be for a small percentage of the overall time the car is in operation and a high amperage fuse implemented during starter operation could be implemented during that time to cut that risk down further​

​

Keoke: The plastic conduit encasing cable would provide additional protection against an abrasive-caused dead short and should not take substantial space in the run under the car.​

​

Steve: Your simplification with the elimination of the original starter solenoid should work fine but would require modification at both ends of the cable. The approach I outlined would allow all changes to be placed in a box under the battery or in some convenient location in the boot. However, it would require that the starter switch, maintains its original connections and with the addition of a separate line to the Remote Ford Starter. Return to the concourse arrangement would be achieved by unplugging the box and reinstallation of the original cable terminal to the battery post. I would favor your changes if return to concourse were not of interest.​

​

Bob: A GFI is an interesting approach but I don't know how a DC GFI would work but have not, as yet, come across any examples of this approach in an automotive circuit as we are addressing. My next thought is to contact one of the companies in this market to see how, and what they have, to address this issue. Maybe a company that are in the area of marine electrics. Do you have any ideas?​

​

Thanks guys,​

​

Ray(64BJ8P1)​

​

 

[Bob_Spidell]

"Do you have any ideas?"

That's all I got. I just make sure my battery->starter cable isn't hanging below the chassis rail when I get under the cars, and don't lose much sleep about a short.

 

[steveg]

Idea: anecdotally, a fire is more likely to start in the boot, rather than under the frame rail, so beef up the defenses in the boot.

 

[RAC68]

Steve,
I don't disagree and I have isolated the battery and connections as well as I could in a battery box. However, as you know as well as I, both the battery and cabel could, if shorted, create substantial heat to easily set its surroundings ablaze, including nearby stored fuel. My objective is to reduce the risk of this happening in an accident or unseen abrasion by finding and installing the most effective reasonable solution I can find. This is not an obsession and I am learning quit a bit in the search from all.

Again, thank for all the suggestions,
Ray(64BJ8P1)

 

[John Turney]

Hi All,

..., I am reconsidering the installation a battery terminal fuse, installed in most modern cars, to protect against a catastrophic short in the direct battery circuit (battery and its main line power lead). ...

Back to the beginning of this thread. I looked at our "modern" cars, the newest is 2009, and they have two cables coming form the positive battery post. One goes to the starter solenoid and is not fused. The other, smaller one, goes to everything else and is fused. Do newer cars really have a fuse in the cable to the starter? If so, what amperage do they use?