Nice write up Brandon.
In
this post I discuss the sizing of the charging wire and did a crude fusible link test. Around 26 seconds the load gets up to around 150 amps and the fusible link does not start smoking until around 1:00 minute. I did not go to complete destruction because I wanted to save the fusible link, but it did make it to about 1:30. My intention was trying to put around 150 amps through the stock 80 fusible link to see what would happen.
Exactly.
And that test represents a worst case scenario - a straight short to battery. Something like a front quarter collision where body panels puncture into the factory wiring somewhere behind the links . In fact the puncture would have to be precisely between the batt post and the first fuse box more or less. I'd be curious to see the current level on the B+ wire with a 150A alt, the truck idling, at speed, with all acc. on and again with them off.
And not to ramble endlessly, but to ramble endlessly...
An alternator only responds with current in the presence of demand for current. Put another way, alternators aren't constant-max-current devices. Unless the battery shorts internally, the average resistance within a battery will keep the current flow on that B+ wire within specs for nearly all applications, throughout its working voltage range.
If you wire all accessories off the battery post (as should be done, w/appropriate fusing/breaker'ing), the truck itself will demand no more current than it ever has before and that's all the fuse links protect - the factory wiring harness.
A winch for example doesn't draw its current from the trucks wiring (behind the links). It is (normally) wired directly to the battery posts. The links never 'see' (facilitate the conduction of) the current demanded by those accessories. And when you're using the winch, it is the battery providing the lions share of that current. Not the alternator. Tho the alternator is there and responding to the demand for current that it sees from the battery, but it's some exponent less than the direct current demand of the winch in operation. (assuming you're also consuming fuel to run the truck at the same time)
Plus consider the use cases.
How often are all the accessories running when the truck is? And is the truck idling or at speed?
How many devices are high-current short duration and used when the truck is running?
How many devices are low-current/long duration and used when the truck is running?
I'm just suggesting that simply upping an alternator output *capacity* doesn't demand that OEM wiring be changed also (see para #2) It probably does no harm to upgrade them IF the upgrade is performed correctly (good cable/great crimps/hard to do w/o proper equipment). It's just not a 1:1 mandate in many cases. Especially if you have a second battery and feed it straight from the B+ post on the alt. This allows the max current capacity (should it ever be demanded) to be split across two B+ wires, lowering the amount of current each wire sees to well within current specs.
As
@Cruzerman touched on above - and what I've suggested too - with sufficient storage the 90A OEM jobbies are more than enough to provide the amounts of current to keep that storage topped off by and large. Then let the storage provide all the current you need for the accessories.
@Photoman - I have recently come into possession of your bracket and a 130A alternator (came with something else I bought). And while the alt came with a 4-wire connector containing a 3-wire pigtail, I did not get the 3-wire conversion bit.
Do you sell them separately? Yes I could splice, but I'd like to preserve the factory 90A'er connector. That is what your conversion piece does, yeah? (the connectors of the 130A and 90A alts look very similar admittedly. perhaps no conversion needed? Haven't looked too closely yet)
My vintage 90A with fresh brushes is giving me no issues charging 500Ahr+ storage and I do not expect to see much of a diff in performance after the upgrade. Just doing it to have the extra capacity should it ever be needed.
LOVE the bracket and having the option to upgrade. Big shoutout to
@Photoman for providing it to the Cruiser world!
Anyhoo, just thought some quantification was in order after reading some posts indicating some confusion about the whole thing.
Happy Trails!
Of course all that can be replaced and made new.
