• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Battery Fuse Protection

Share this page

Marine V8 engines have geared starters and are often protected by a 90 or 120 amp block fuse, I fitted a similar fuse of 100amp to my battery terminal running a hi torque starter on my BJ8 a couple of years ago with no issues. However I do keep a torch with hazard flasher and spanner to bypass the fuse just in case!
 
Very interesting:

Take a good look at Johns current test table and note that the current continuously decreases in the cable as he makes repeated tests.

What is happening here is the cable is beginning to heat up which causes its resistance to also increase. in so doing , the current will decrease as shown



"Repeated tests"" as used here refers to the 1/2 second intervals between readings
 
Last edited:
Keoke said:
Very interesting:

Take a good look at Johns current test table and note that the current continuously decreases in the cable as he makes repeated tests.

What is happening here is the cable is beginning to heat up which causes its resistance to also increase. in so doing , the current will decrease as shown
Click to expand...
What?? If you are writing about the table a few posts up, there was only one test. Readings were recorded at ~500 millisecond (1/2 second) intervals. The initial current reading, 319 A, was near the initial inrush current of when the starter had not started to turn. The readings of 271 A - 276 A were when the starter was turning. As motors turn, they produce "reverse EMF" which reduces the potential between the battery and motor, decreasing the current. The cable didn't heat a significant (enough to feel) amount.
 
1B563F9B-D102-48BD-83B3-02F25AC329CB.jpegFound these an easy fix available up to 300 amp
f2cc0401-b0fd-473d-b869-64e5a1558db7
 
Last edited:
Found these an easy fix available up to 300 amp
​
newreply.php
Click to expand...

Thank you for the find.

I am very much interested (and have been for years) to complete my electrical circle of protection by addressing the last link (battery and cable to the starter solenoid). However, I have and wish to continue to use my original starter and, when first starting this thread, admit that I forgot to consider the extremely high initial amperage draw (
when compared to a gear reduction model). Since starter gear lockup amperage is listed as around 450-480 amps, and hopping for further verification of initial starter draw when John has a chance to do actual measurement, understanding what fuse size and type (i.e. time delay), for me, is still an open issue.

Also, Keoke and others have brought up further concerns about the potential of a shorted cable to act as a heat sink and not raise sufficient the necessary conditions to blow a sufficiently sized fuse. As I have never worked with or have knowledge to understand how this condition should be handled, I must rely on others and, as yet have not come to understand what is required to address his concerning indication.

As a result of all this, I am at the point of waiting for a knowledge breakthrough and have also considered dropping back to an earlier proposal (reposted in this thread) that would use a Ford Remote Starter Solenoid placed in the boot to allow unfused initial starting with a drop back after starting to a 40 amp fuse injection. This does not provide short protection during the actual short time high amperage starting of the car but does provide fused protection during the car's much longer ongoing operation.

Thanks all, and I look forward to a complete solution being identified,
Ray(64BJ8P1)
​
 
Electrical code fuse design is based on full load operating current (FLA). The codes assume continuous running. As I’m sure you all know, early autos didn’t have electric starters. Main reason seems to have been that wire current ratings were insufficient to carry the required starter current. For example, my battery cable is 4AWG. According to ABYC code, I would need 0AWG to carry the starter current of 275 A. When someone finally figured out that if one limits the starter operating time to 5 sec, or so, smaller wires could be used, and electric starters became practical.

The electric codes say say for DC motors the fuse rating should be 150% of the FLA or the next larger standard fuse size. 150% of 275 A is 412 A. The next standard fuse size is 500 A, which is too great to protect the wire per the codes.

Bluesea.com has a Circuit Wizard which can be used to calculate wire and fuse sizes, which is where I got the wire size. NEC would require size 400 kcmil cable.
 
RAC68 said:
Thank you for the find.

I am very much interested (and have been for years) to complete my electrical circle of protection by addressing the last link (battery and cable to the starter solenoid). However, I have and wish to continue to use my original starter and, when first starting this thread, admit that I forgot to consider the extremely high initial amperage draw (
when compared to a gear reduction model). Since starter gear lockup amperage is listed as around 450-480 amps, and hopping for further verification of initial starter draw when John has a chance to do actual measurement, understanding what fuse size and type (i.e. time delay), for me, is still an open issue.

Also, Keoke and others have brought up further concerns about the potential of a shorted cable to act as a heat sink and not raise sufficient the necessary conditions to blow a sufficiently sized fuse. As I have never worked with or have knowledge to understand how this condition should be handled, I must rely on others and, as yet have not come to understand what is required to address his concerning indication.

As a result of all this, I am at the point of waiting for a knowledge breakthrough and have also considered dropping back to an earlier proposal (reposted in this thread) that would use a Ford Remote Starter Solenoid placed in the boot to allow unfused initial starting with a drop back after starting to a 40 amp fuse injection. This does not provide short protection during the actual short time high amperage starting of the car but does provide fused protection during the car's much longer ongoing operation.

Thanks all, and I look forward to a complete solution being identified,
Ray(64BJ8P1)
​
Click to expand...

Ray--

With respect, I think you may be chasing a chimera.

Yes, even assuming you go down the "alternative starting circuit with a solenoid" path, no matter what you do there is always the chance (however slight) that a small short drawing significantly less than a protective fuse's value could develop and potentially lead to trouble. But if you use good wiring, connectors, heat-shrink and harnessing and pick a route that is not likely to be chafed, etc. the odds are slim that such a scenario will develop.

You are not flying at 30,000 feet or going offshore and if you run your wires so that they are relatively accessible you can do periodic or spot-check inspections whenever you feel the need.
 
Hi Michael,

Well, it is difficult to argue with your points and finding a way to protect the original path from battery to starter solenoid at the time of starting the engine with an original starter does seem like a close to unreasonable path to follow. The reason to use the remote starter is not to start the car but to allow a non-fused circuit when starting the car but then switching to a protected circuit once it has started...so to only switch out an in a fuse. Before the key is turned and after the key has been released, a 40 amp fuse would be in the circuit. Also, if an issue should develop and be recognized when the key is turned, by releasing the key the 40 amp fuse would be switched in and blow if a cable short is present. So, as I see it, it would be a very short time that the circuit is not fuse connected and you have the power to imediatly switch in the fuse when and if you feel it is needed.

As far as rerouting the battery cable to a more protected location, yes that is another alternative. However, I believe a small box housing the remote solenoid can be placed next to and above the battery that will not take much room. A normal wire between the key and this box can be easily routed next to the transmission and enter the boot through the small opening at the corner of teh boot bulkhead. I believe the most difficult thing in the installation will be severing a small section from the cable and fixing 2 connectors that would allow connection to the added Ford remote starter solenoid.

My thought is to just add the Ford Remote Starter Solenoid and leave the original starter solenoid in place. Yes, that means when yu are turning the key, you will have 2 solenoids responding to the switch. However, although you can eliminate the original and rely on the Ford Remote Starter Solenoid, you will loos the ability of conveniently turning the engine with the original's button … something I use during annual maintenance.

Well, sorry for being so verbose but you have probably come to expect it,
Ray(64BJ8P1)
 
Naw Ray

Jest find U a good Volvo engineer.

OR

Install a hand crank'
 
Keoke-

I was a bit puzzled by your reference to Volvo and then I came across this (see answer #5):

https://electronics.stackexchange.com/questions/355936/why-arent-starter-circuits-protected

As an aside, on my old boat I had a single Caterpillar 3306-T engine with four Surette 230AH 8-D batteries, two of which were wired solely for engine starting and two for ship's service, with provision to bring the house batteries into parallel for emergency starting via some remotely switchable extremely heavy duty solenoids that had circuit breakers built into them. The solenoids were about the size of #10 cans and the sound of their closing was similar to that of a baseball coming off of a wooden bat.
 
H Michael:

You must not have read Novamonte post earlier it is similar to what you just posted , so I just kibitz about the Volvo engineers,--See Ya Later
 
Keoke--

OK, I think I now understand what you meant--I think....

In any case, to his point: properly sized, made-up, located, harnessed and maintained wiring goes a long way in providing circuit protection.
 
Keoke/Michael,

You may be on to something.

When again reviewing the post by "4tecdog" of the Volvo fusing philosophy, it struck me that the reason so many new cars have multiple fuses directly connected to the positive battery pole is to separate the networks early at their power source.

Since the connection of power between the battery and all other parts of the Healey has its first stop at the starter solenoid connection, we are cataclysmically vulnerable to a failure of the cable or, to some extent, the starter. As a result, any short in this area will likely cause all power to be severed and vehicle operation and lighting terminated. However, if the battery terminal is made to support 2 independent power distribution networks (i.e. Starter Circuit, Operations Circuit) and one circuit experiences a short circuit, it is very possible that the second circuit may not be totally disrupted and can continue to perform … even if it is at a diminished capacity … as in the Volvo philosophy

If we had 2 circuits coming directly off our Healey's battery terminal. #1 (Starter Circuit) going from battery terminal to the starter solenoid as original and #2 (Operational Circuit) originally connected between the starter solenoid and "B" terminal on the regulator but now connecting the battery terminal to the "B". As I see it, we would have something that could represent the Volvo philosophy.

Further, if we install a 2 fuse connector at the battery terminal (as some modern cars) 1. (Starter Circuit) Large enough to support starter amperage (i.e. 200-500 amps) 2. (Operation Circuit) Sufficient to handle car operations (i.e. 20-40 amps). The separation of the circuits would be further protected. However, this assumes a short circuit of the starter circuit would blow the larger fuse fast enough to sever connectivity prior to bringing down the Operation Circuit.

However, by installing a cabin resident second path from the battery as an operations power path, I think we could move our Healey's closer to what "4tecdog" had so astutely provided for our review with a minimum of change.

What do you think,
Ray(64BJ8P1)
 
Ray,
IMO your 2-circuit idea has merit.
Comments:
--It makes sense to place a new solenoid in the trunk at the end of a 12" cable from the battery. Protecting all connections from shorts.
--Do not fuse the starter cable because it's only energized during starting and the fuse represents a point of failure.
--For the fused ops circuit, run the wire directly to the B terminal on the voltage reg, bypassing the stock solenoid.
--metal armor for starter cable and ops wire with raceway or flex conduit. Or at least provide sleeving and a protected route for the ops wire.
--figure out a way to energize the trunk solenoid in order to energize the cable for the "bump" feature on the stock solenoid - plenty of issues here.

Alternative: lose the stock solenoid with bump feature.
--Run starter cable directly to starter from trunk solenoid
--run ops cable directly to B terminal on voltage reg.
--run alternator charge wire back to battery - not sure whether this could just connect to the ops wire.
--suppose you could use a stock solenoid in the trunk and run the bump feature from there - IMO not practical

Having written the above...with respect, I'm not really buying it.

IMO the chances of such a cataclysmic failure and the need for the Volvo scenario (in a collector car, yet) are vanishingly small.

Important: by making such radical changes, we may be in fact decreasing the reliability of a known-reliable system which has worked well for generations.

What is easy to do here in order to prevent damage to the starter cable, is to armor it with metal conduit against scrapes. If correctly executed, this adds no potential for failure into an already-reliable system.

I'm more likely to run over a rock or other road obstruction than to get stuck in a life-threatening situation such as a Scandinavian winter.

Nevertheless, a very worthwhile discussion! :smile:

My 2 cents.
 
Last edited:
Back
Top