Battery Fuse Protection

[steveg]

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)

Ray - I've really enjoyed the thoroughness of the way all of us have explored this topic!

 

[RAC68]

Hi John,

There are a number of modern battery protection setups which extend from one battery cable and fuse connection to a number of fused branches mounted on the batter post. The simplest was on my Son's 2011 Kia Soul which I had just replaced an over-charging alternator. This was a 200A setup similar to the one I had pictured but with a cover incasing the fuse and connectors.

I was thinking of your comment and how we could take advantage of having multiple cables coming from the battery. For example, what if we ran 2 cables from the battery terminal (#1 cable to a convenient operational power distribution point, #2 larger cable to the starter/solenoid) with #1 fused at around 40A and #2 fused at what ever is required by the installed starter (i.e. 450 amps-original or 250 amps gear reduction). I would expect this would work as long as we severed the connection between solenoid and voltage regulator and the #1 cable provides a sufficient path and fusing level for the generator/alternator to carry max power to the battery.

Although this would be doable and does provide fault protections from/to the battery, both paths remain separately active. This would differ from the use of a remote start solenoid approach (pictured earlier) in that after startup, the single cable path would be governed by the operational fuse (40A or what is required for generator/alternator charging) and the high amperage startup fuse switched out of the circuit. If a short happened on the main (larger) cable at any time, the 2-cable system would blow after exceeding the starter fuse amperage (450A/250A), however, this short would only need to exceed the much lower operational fuse when using the remote relay approach. As a result, it is more potential to have more damage as a result of cable dead shorting after engine startup in the multi-cable (2) approach then in a remote solenoid implementation.

John, just my thoughts,
Ray(64BJ8P1)

 

[roscoe]

As long as were talking battery fires, I have this. Years ago a co-worker loaded a company pick-up with a bunch of stuff which included 4 Optima 12V batteries and an aluminum step ladder. See where I'm going with this?. I was along for the freeway ride and paid no attention to the load until a frantic driver of the car next to us honked and pointed at the huge flames in the back of the truck. Ladder had shifted and managed to connect some battery terminals. There was quite a bit of flamable (inflamable if you prefer) stuff in the bed and we got off the road tout suite. 70 mph dumpster fire. By the time we got out of the truck we were afraid we were going to have to run, as the only fire extinguisher was pretty much in the pile that was on fire. There was a 8 foot chain link fence between our freeway pull off spot and the frontage road. As we stood there, not yet thinking how two aircraft mechanics could be in this situation ( you know...."safety is job #1), a guy in a Cadallic Escalade pulls over on the frontage road, gets out, opens the back and pulls out a 10 lb ABC fire extinguisher and tosses it over the fence to us. We got the fire out, took a quick breath or two and went back to the fence to return the now empty extinguisher. Without a word being exchanged, before we could toss it back and offer to pay, the guy flashed us the OK sign got into his car and drove off. It was probably a $60 extinguisher. If any of you were this guy next to interstate 80 in Vacaville, CA that day.....thanks!

 

[John Turney]

I'll have to say this discussion has resulted in some interesting mental exercise. When googling related topics, I came across this electrical engineering discussion: https://electronics.stackexchange.com/questions/355936/why-arent-starter-circuits-protected. Some of the reasons include:

• There isn't enough difference between operating current (the current required to operate the starter and the fault current) to ensure that the fuse won't blow in normal operation, and will blow under fault conditions.
• Having a power fuse blow on the circuit that is going to the engine starter can result in a serious safety issue. Having the fuse blow will kill entire electrical system including hazard lights, headlights etc.
• From a person who worked in automotive electronics: 'From a safety point of view, you are not trying to "protect the vehicle", you are trying to "protect the person".' He discussed this scenario with Volvo engineers. One of their criteria was that the car needed to keep moving even if slowly because one can freeze to death in 2 hours in a Scandinavian winter (not a hazard in a Healey, but a significant viewpoint).
• Battery voltage, and hence current, may drop faster than the battery cable can heat up to melting.

 

[Keoke]

HI John:

This is realistic consideration and resolves the other concerns if it happens>

" Battery voltage, and hence current, may drop faster than the battery cable can heat up to melting.​

:"

Similarly : the fuse approach suffers the similar conern , that fuse is trying its darndest to heat up N Blow , while that big heatsink, the cable connected to it is sucking heat out of it.
,
Course now them Volvo engineers knew better N to put the battery in the boot --LOL

 

[RAC68]

Hi John,

You make a very good point. I can see where separating lines for run-rate car operations from engine starter operations could potentially maintain the critical functions you bring up. However, I would expect that should a main cable or battery short be encountered, the battery would continue functioning properly and cause the second cable fuse to blow as well. As I see it, should there be a cable short, it would interrupt all electrical operations. As Keoke indicated, battery in the boot, LOL.

Ray(64BJ8P1)

 

[TimK]

I accidentally dead-shorted the battery in my motorcycle. There was no spectacular result — the battery died in seconds. No smoke, no explosion. The short was directly from the seat frame to the positive post.

 

[Keoke]

I accidentally dead-shorted the battery in my motorcycle. There was no spectacular result — the battery died in seconds. No smoke, no explosion. The short was directly from the seat frame to the positive post.

Well Tim:

The C rating of a ​

battery

is the power capacity of a ​

battery

. Typically this is shown by a number (C100, C20, C10 or C5) indicating the number of hours this power must be spread over.

So the capacity of your battery is probably in the low C range , which prolly may not get one home when off a long distance on ah dark night ,but may save the bike, battery and the bikes rider??.​

Well Tim:

 

[Legal Bill]

I find this discussion very interesting. A lot of thought has gone into this. While I do not agree with the original poster's sense of need for such protection, I heartily endorse his research into the subject. My BJ8 has new leaf springs and battery cables and the roads I take it on are all in good repair. I have not bottomed out my exhaust yet and i see no reasonable degree of risk that I need to mitigate, but others may certainly have a different situation. Further, if there were a fast, and easy way to install such protection in a fashion that makes the vehicle safer over-all and does not require any irreversible modification, I may adopt it anyway. However, I am concerned that the fuse may, itself, present new grounding points that can cause the very problem we seek to avoid. As stated by others above, I believe the greater threat resides in the trunk itself where metal objects can contact and ground the positive terminal if not adequately protected. Could the solution make this risk worse? For example, now you will have the battery post, plus the connection to the fuse in an area where the hot side could ground to the body. I rely on a tidy trunk with everything well bagged or tied down to avoid that problem.

My lingering question, and forgive me if I missed this in the discussion above, is why we are not considering battery circuit breakers rather than fuses? This is now tried and true technology in the marine world where batteries are called upon to start very large diesel engines, so I don't see the Healey drawing more amps than a Cummins diesel. The circuit breaker gives you a second chance to start the vehicle. Why would anyone want a fuse instead? Perhaps it has to do with the positive ground configuration? I have not researched the sensitivity of the circuit breakers to polarity.

 

[Keoke]

Legal Bill

Just depends on how much current the short produces, for hard short the circuit breaker will trip each time you reset it, that is good.

Contrastingly: for a soft short it may set there and let the wire melt.

These type circuits introduce a very nasty thermal problem.

 

[Bob_Spidell]

I got curious:

https://store.solarhomestead.com/products-page/dc-fuses/400-amp-dc-class-t-fuse/

Still think you'd want a 'slow blow' variety.

 

[Keoke]

I got curious:

https://store.solarhomestead.com/products-page/dc-fuses/400-amp-dc-class-t-fuse/

Still think you'd want a 'slow blow' variety.

HI Bob:

The slow blow fuse was specifically designed to handle Inductive circuits , most of which contain a motor.
They address the normal transient associated with these type loads which generally have very high peak voltage but very short time constants-Not much energy in the transient.

Utilizing one here for short circuit protection may work, but the entire car may shut down without additional circuit changes .

 

[Michael Oritt]

If you are going to circuit breakers the best ones are magnetic/hydraulic. Thermal breakers tend to lose their value after repeated tripping.
See: https://www.atcadvance.com/vs.html

 

[John Turney]

Time (h:m:s:ms)	Current, Amps
13:34:51:498	9, ignition only, no fuel pump
13:34:51:997	319, starter & ignition
13:34:52:496	274
13:34:52:991	274
13:34:53:496	275
13:34:53:996	275
13:34:54:497	276
13:34:54:996	272
13:34:55:495	271
13:34:55:997	7, starter off

Ok, I have some data to add.

• Temperature 58F.
• Cold 3000 engine.
• Fuel pump off so it won't actually start.
• Gear reduction starter.
• Measurements on negative battery cable using DC clamp-on ammeter and recorded at 1/2 sec. intervals.

Maybe next Saturday, I can get current readings on an original starter.

 

[Legal Bill]

Legal Bill

Just depends on how much current the short produces, for hard short the circuit breaker will trip each time you reset it, that is good.

Contrastingly: for a soft short it may set there and let the wire melt.

These type circuits introduce a very nasty thermal problem.

I wonder how the entire boat industry does it??

 

[Novamonte]

I have a 5.5 liter 6 cylinder diesel in my boat. There are two 12 volt batteries in parallell connected to the starter solenoid (and two more for all other electrics onboard). The starter motor is about four times bigger than that on the Healey and the cable is equally thicker, so I assume that the current it carries is many times higher (which makes sense, given the high compression and the larger cylinder capacity). There is no fuse or circuit breaker between the starter batteries and the solenoid, but the battery box is located just in front of the engine. The cable is quite short and safely routed, so the risk for a short is much smaller than having a long cable running under the car with low ground clearance.

The anchor winch and the bow thruster also draw much current when used, altough much less than the starter. There is a 355 amp. fuse for the bow thruster and a 100 amp. fuse for the winch.

 

[RAC68]

John,

Have you had a chance to check the amperage operating profile of the original starter?

Ray(64BJ8P1)

 

[Keoke]

Musta been Volvo Engineers:

" but the battery box is located just in front of the engine."

That all was good engineering IMOP>---Thanks Novamonte​

 

[Novamonte]

Correct-It's a Volvo Penta engine.

 

[John Turney]

John,

Have you had a chance to check the amperage operating profile of the original starter?

Ray(64BJ8P1)

Hi Ray,

I was going to check today at our tech session, but all the startable cars had gear reduction starters. If there are none next Saturday (Board Meeting), the next opportunity will be April 7th, for the season opener.

John