I did some more research. The fuse is referenced in the service manual as a "CAL3 starter fuse" integrated into the positive cable from the battery to the starter *and* the generator. It cannot be replaced, the cable must be replaced in its entirety if it blows, and the wiring diagram schematics rate it at 150 amps.

 

(Referring back to this old post while I'm planning to perform another parasitic draw test and just refreshing myself on the wiring).

The wiring diagram shown above indicates a 150A fusible link between the battery, and the starter and alternator/generator. On most cars, the connection between the battery and the alternator is fused, but not between the battery and the starter. So this looks different. Usually it's a direct connection between the battery and the starter with no circuit protection, probably to avoid nuisance disconnects with spikey starter draws.

I know that fusible links are slow-blow, but I'm still surprised that this starter fuse is only 150A. I would have thought the LR2 starter draws a lot more current than that when cranking. Especially since our batteries are rated heavy duty around 800 CCA.

Thoughts?

 

CCA is defined as the number of amps produced by a charged battery over 30 seconds at zero degrees Fahrenheit without dropping below 7.2 volts.

The key phrase in your message is "slow-blow". A fusible link is not like a normal fuse in that fuses are designed for low voltage circuits and will blow instantly when their rated amperage is exceeded. The fusible link takes more time to fail because what is intended is to let the higher amperage draw pass momentarily (in this case, to operate the starter) but fail if the load is maintained for a longer period of time. Essentially, you don't want to operate your starter continuously for 30 seconds, for example. If you do that, the fusible link will fail. But it will tolerate a high amperage for the second or two that it takes to start the engine.

 

That makes sense.

To make troubleshooting easier, I would have preferred that the starter and alternator each have their own fusible link and not share one. LR/Volvo probably saved a dollar or two for this sin.

 

The fusible link on the battery's positive terminal is not shared with the alternator. If your alternator ever puts out 150 amps something will be smoking.

 

Your post above on 3/23/2021 shows the fusible link before the starter and alternator/generator. Am I reading it wrong?

 

Ok, my answer was not accurate. The generator does not sit between the battery and the starter, they connect in parallel to the battery, but are not in use at the same time. When the starter is being used to start the car the generator is not running. Once the car starts the incoming current to the battery from the generator will never be anywhere close to 150 amps unless something is seriously wrong, and some other fuse(s) will have blown long before that.

 

Sounds right. But I don't like this design at all. If the fusible link opens up (which happened to the OP), then you're left wondering if the starter was pulling too much current, or the generator was pushing too much current. So you'd have to test both for shorts to really get a handle on what happened. And then after replacing one or the other component, you have to replace the whole cable assembly with fusible link. On other vehicles, this is a much simpler swap out of a fuse, and it's typically only on the generator side. End of rant.

 

It is what it is. The starter is dirt simple to test.