calculating a vehicles amperage needs

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calculating a vehicles amperage needs

Post #1 by sdiesel » Mon Nov 05, 2018 12:15 pm

how do we calculate these numbers to get an alternator output that corresponds to the need?
the simple answer is to just overkill.
yea, thats cool, go with a 3G and have done with the issue.

here is the gambit. i want to use a hitachi alternator for its hydraulic pump attachment. this pump will be dedicated to running a hydraulic cooling fan-eliminating another need for electricity, wiring, failure and so on.

i can manipulate pulley size to get greater amp charge at idle. but total need must be factored to be sure my alt can keep up.
the Hitachi is an 70 amp model and cannot be modified for greater output.

Also will going to dual batteries increases amperage or just amperage capacity. going to a 4d dozer battery will that help also?
the answer to this is yes. larger capacity allows a longer discharge to empty, A plodding steady low amp alternator will catch up the amp draw in time,during run time.
Another consideration is the heat factor. Higher amp alternators will have a shorter life span, if worked hard to restore charge to small capacity reservoirs. they have a duty cycle which is less than that of a 70 amp alternator. they generate more heat thus are at risk of failure sooner. the smaller alts, will keep charging through thick and thin.

our 6 cylinder engines do not help this by locating the alt directly above the exhaust manifold.
cooling must be considered in the build up of a charging system.

so the upshot seems to be according to my research
A small amp reliable alternator is just as useful, and in many cases more useful than a high amp output alternator IF, you have the capacity to store the charge.
small capacity?, bigger alternator. as the discharge will get ahead of the alternators charging capacity when there is heavy draw on the system.
A smaller capacity alternator also is less parasitic draw on the system.
Heat needs to be mitigated.

What size wire??
hmmmm dunno.
Voltage drop and correctly wired electrical systems will relieve pressure on the charging system also.
many comments on how the headlights perked up when the alternator was upgraded. this is likely due to the alt pushing higher charge through substandard wiring. open up that conduit and even the earlier alternator would likely have sufficiently brightened the headlights.
Remember car makers build a car to make a profit, they dont have to drive the damn thing on a rainy night...

imagine on this work truck: 5 aux lights at about 6 amps each, 2 headlights, heater, winch, ignition (HEI, duraspark TFI coil). which needs 12v all the time.

this disjointed verse, is my discoverie at the time, on the subject. Can anyone with more knowledge help me out here and correct me or add to this (or take away if im wrong).?

a long love affair with the 300 six.
my lastest and final fling is a fresh 300 in an 88 ford f350 dually 4X flatbed

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Re: calculating a vehicles amperage needs

Post #2 by pmuller9 » Sat Nov 17, 2018 1:21 am

A larger alternator has less internal resistance than a smaller output alternator and thereby generates less heat for a given load current.
Technically speaking the larger alternator has less "I squared R" loss.

The second problem occurs when a large capacity battery system is allowed to discharge to a low level and the charging system now has to handle very large charging rates.
The smaller alternator will run hotter.

I had a case where I changed the wire from the alternator to the two large batteries in the rear of the vehicle to a 6 gauge cable.
He never had problem with the charging system until the one day the batteries were low and after the car was jumped started there was that wonderful smell of hot insulation.

Some 300 sixes had the alternator mounted on the drivers side.

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