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77 Hornet, 10si to 12si |
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amcfool1
AMC Addicted Joined: Jun/18/2011 Location: roanoke va Status: Offline Points: 1071 |
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Posted: Jul/22/2017 at 8:44am |
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hi, seems alternator questions are in vogue lately, so, here is mine. I have 77 Hornet AMX, 258/T5, WITH AC, currently has a newish factory type 10si. 63 amps, afaik. I am considering , not today, but in the mid future, going to electric fans, ie the Ford Contour type. I have a 12si on the shelf, from a mid 80s Eagle, that I rebuilt myself. 78 amps, afaik.
Is it a good idea to swap in the 12si? Will it be enough/too much? Will wiring need to be upgraded? Or, just go directly to the modern CS130, 105amp? Too much? Related question, anybody make a new/better harness for the Hornets? mine is ok, but OLD! ps, I have an 84 Eagle, with the stock 12si/78amp alternator. I put in a relay headlight set. When headlights turn on, idle speeds up a bit, must mean the Sol-Vac is working as it should. Life is good! thank you, gz
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george z
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Lyle
AMC Addicted Joined: Jul/17/2014 Location: None Status: Offline Points: 772 |
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You can likely determine this yourself as you have not given enough information to do a load calculation.
Your new fans will draw 10 to 12 running amps and 25 start inrush. Usually you don't include the inrush current as the battery will supply this load. If you have a kick rump stereo and amp, this could be a 40 amp load all by itself, big alternator and extra battery. If you have normal accessories including air, with the headlights on, your looking at approximately 40 to 50 amps to run them and charge the battery so 63 amps should be fine. Look at all your loads - not breakers or fuses as these are sized for the inrush current, and calculate your running amps and add 10 amps for battery charging. Changing to LED tail and side marker lights will save you about 5 amps running if you are getting close. |
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amcfool1
AMC Addicted Joined: Jun/18/2011 Location: roanoke va Status: Offline Points: 1071 |
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thank you for your response, where in Ontario are you? I'm from North Bay, but grew up/went to McMaster in Hamilton. Still have a brother in Sudbury, another in Kingston, and a sister in Kitchener.
I did change the rear side markers to LED, may go to the fronts as well, though I believe those little 94 lamps in led are polarity sensitive. From what I've read/researched so far, including the writings of our own and esteemed billd, I think the 12si may be good idea, cools better, bolts in, etc. Radio is stock, but rebuilt with modern guts, ie 45watt x 4, internal amp, basic 4 speakers, so, nothing crazy. except, ahem, the bluetooth, voice activated, USB port, thumb drive, etc. :) thanks again, gz
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george z
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James73
AMC Fan Joined: Jul/19/2017 Location: vero beach Status: Offline Points: 2 |
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bigbad69
Supporter of TheAMCForum Joined: Jul/02/2007 Location: Ottawa, Ont. Status: Offline Points: 6614 |
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Bear in mind, if your 63 Amp alternator is adequate, a 78 Amp replacement gains you nothing. The alternator only supplies the current required to charge the battery and no more. You might find the initial inrush is a little higher, or the charge rate at idle is a bit more, but that is more dependent upon the design of the alternator than the rating.
How big the wire needs to be from alternator to battery depends on the charge current which is roughly equal to the load from the car's electrical systems. The ampacity of a conductor is generally determined by the heat rise due to current flow. |
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69 Javelin SST BBO 390 T10
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James73
AMC Fan Joined: Jul/19/2017 Location: vero beach Status: Offline Points: 2 |
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Thank you for the response.
My 73 it is petty plain and I just ad LED tail lights, so I do't think my car is pulling a bigger load from the alternator but if is any way to check that I would like to learn. Also I can find the fuse box but I see a lot of inline fuses in this car so I assume that these jeeps don't use fuse box? thanx
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Lyle
AMC Addicted Joined: Jul/17/2014 Location: None Status: Offline Points: 772 |
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Hi amcfool1, I,m from Ingersoll Ontario. It looks like your 63 AMP alternator will be fine and as far as wire gauge sizes, just look up "automotive wire gauge chart" and you will get some good results. The length of the conductor is a large factor in picking your wire size. Also short term use wires, e.g. starter don't follow these charts.
As for the Jeep I believe you will need the TSM to find all the fusable links, etc but the starter cable will be 2 or 1/0 gauge I believe. You can use welding cable here as it is likely to be easier to find or just go to a wrecker and pillage.
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