Confused about calculating proper size of wire

MaxHeadRoom

Joined Jul 18, 2013
28,619
Have you looked at a recent alternator? The new ones are nothing like the ones from ~15 years ago. The wire in the coils are much bigger now, and the diode/bridge technology has changed a lot.
I would be interested to see some empirical testing at 150amps, I am using some 150a rectifiers at present and the majority are large stud mount, mine have a 3/8"NF mounting with 6awg leads .
Max.
 

crutschow

Joined Mar 14, 2008
34,285
Much has been said about charging a dead battery with the alternator and how that is not the thing to do....For the record, I only want to maintain the charge in my boat battery while towing. I would like to leave my refrigerator in the boat on so that I can continue to use the boat as my 'Boaterhome' while traveling to the next cruise location. Sometimes that takes days, so it's just easier to keep the battery charged as I go rather than using a generator once I get to an overnight spot (Walmart frowns on the usage of generators in their parking lots :D).
If the battery is always pretty well charged, and you are mainly keeping it topped off then I seen no problem with using 12AWG or 14AWG wire unless the fridge requires a lot of current.
How much current does it take?
 

bwilliams60

Joined Nov 18, 2012
1,442
Much has been said about charging a dead battery with the alternator and how that is not the thing to do....For the record, I only want to maintain the charge in my boat battery while towing. I would like to leave my refrigerator in the boat on so that I can continue to use the boat as my 'Boaterhome' while traveling to the next cruise location. Sometimes that takes days, so it's just easier to keep the battery charged as I go rather than using a generator once I get to an overnight spot (Walmart frowns on the usage of generators in their parking lots :D).

Thanks for all your input.
If this is the case, you can charge it at a low rate and circuit protect the wiring so that it does not exceed the rating of the wiring you are using. For the record, I used to use a continuous duty magnetic switch hooked up to the ignition and when the vehicle was running, the second battery would charge. When shut off, the second battery was on it's own.
 

shortbus

Joined Sep 30, 2009
10,045

MaxHeadRoom

Joined Jul 18, 2013
28,619
What that says to me is essentially an alternator is capable of supplying the rated current at 6000 rpm, it does not state for what period of time this is valid for, I still would like to see an empirical test for a specific period at this rating, the size of alternators has not really changed over the years so I am very suspicious of some of the ratings claimed.
Max.
 

shortbus

Joined Sep 30, 2009
10,045
Couldn't find that kind of data online. The 6000 and 2000 RPM though doesn't mean that engine needs to turn that fast. They are alternator shaft RPM ratings. An Alternator is running at ~3:1 of engine speed.

I do know though that the 130A one I replaced was about half again bigger than the 100A one that was also listed for the vehicle. 130A with A/C and 100A without. Plus the windings were way bigger diameter than the old Delco 10S and 12S alternators had.

As far as diodes for the rectifier, couldn't they be using 'synchronous rectification'? Didn't have time to tear the old one apart to look inside.
 
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