Typical charging rate of a car battery (from alternator)

Toward the end of determining how many "external" car batteries can I put in parallel with the car battery, without over-loading the alternator??
I know the charging current draw would depend on the degree of discharge of the batts, so figger 50% discharge. Or even total discharge, ie, a dead battery.
I figger that if no lights, defrosters, etc are being used, the alternator could handle two extra batteries, charge-wise.
Have I figgered right?
Is there such a thing as a "current limiter", so that the alternator would never "short out", from too many loads?
--
EA



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On Wed, 31 Oct 2012 23:39:12 -0400, "Existential Angst"

Depends on what alternator you have and how fast you want to charge the batteries. Some of the small GM high output alternators cannot put out high current for a long time without failing. The large-frame old Mopar units could put out full rated power (I believe theat was as high as 114 amps) day in and day out. The big Lecce Nevilles used in ambulances and busses were good for full output steadily as well. Many of the lightweight high amperage units in current use can handle charging one dead battery with no problem - 2 big ones might be hard on them.
I know guys who have a switch/relay to disconnect the "coach battery" and only connect it when the main battery is up to charge to prevent overloading the alternator. There are kits to beef up the little GM alternators with a better rear case for better cooling and a stronger bearing.
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wrote:

That's what I plan on doing. The main car batt will never be discharged, so really the only extra load will be the one or two "carriage" batts in the back. If I have to charge them one at a time, so be it. Hopefully I won't learn anything the hard way.
Speaking of learning the hard way, if I do try to charge two farily discharged batts at once, what might be an indication that it is tough on the alternator? A low charging voltage? What would approx acceptable limits be?
fwiw, the two vehicles at hand would be an 04 Nissan Frontier, 07 Honder Shit, I mean, Fit -- ackshooly a good car, so far. I'd sure hate to have to change out alternators, tho....
--
EA


There are kits to beef up the little GM
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Your car alternator is probably capable of generating about 40 amps, which basically means that it will re-charge a fully dead 40 amp-hour battery in about one hour.
An average car battery holds ~ 40 ~50 amp-hours, do the math.
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On Wed, 31 Oct 2012 22:38:07 -0700, "PrecisionmachinisT"

the law -" When the reading lights get left on and the battery is dead, charge it up enough to get it here and let it sit on the big charger for an hour". It seems that after about 1985 factory alternators are only capable of maintaining the battery, not charging it from flat.
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snipped-for-privacy@rogers.com wrote:

Not like the old 83A model on my stepvan. They cut weight every place they can to try to meet the gas mileage requirements.
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On 11/1/2012 8:49 PM, Michael A. Terrell wrote:

I don't really think that's it--I just went and looked at replacement alternators listed for Chevy Lumina -- of 10 or so the amp ratings ranged from one at 85 to 140 w/ the bulk at 100-105A. I've never had any problem in any vehicle of recharging a _good_ battery from discharged condition as long as there wasn't something else wrong (like a bad regulator, etc.)
Any one vehicle may be built w/ the lower amp-output, of course, but these days w/ the advent of A/C and all the other electrical accessories as standard equipment more often than not the alternator is far larger than on vehicles of yore (say '60s/early '70s and earlier, particularly).
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dpb wrote:

But they don't put those bigger models in on basic vehicles with no AC, do they?
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On 11/2/2012 9:46 AM, Michael A. Terrell wrote: ...

How many vehicles are sold in the US _w/o_ AC these days? Very small percentage, I'd wager...
But the 85A was the _smallest_ in the list of compatible for the vehicle class mentioned (out of nearly 20 choices) and there was only one of them in the first 10 or so of the list (ordered by price) that I actually paged through that was under 100A. That indicates that anything under the 80-some A class is pretty limited to me...
I'm sure you can still find 50 and 60A ratings but even they shouldn't have any problem charging a battery as long as the rest of the system (and the battery) is in good shape.
IOW, I suspect something else was the underlying culprit in the preceding comment of killing alternators...
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A bad battery will do it - REAL QUICK.
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Those 100 to 140 amp units are only good for that kind of output for a VERY short time - untill they get hot, and die.
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snipped-for-privacy@snyder.on.ca wrote:

Those old alternators were designed & rated for continuous service. Today's 100 amp is an old 37 amp with Schottky diodes instead of Silicon diodes. They have a lower forward drop, and can handle more current in the same size package.
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On Fri, 02 Nov 2012 14:29:28 -0400, snipped-for-privacy@snyder.on.ca wrote:

I worked as a engineering tech with Autolite in the mid 1960. They originated the commercial automotive alternator for Chrysler. I can honestly tell you that if an alternator was rated at 60 amps at 14.2 volts it will put that out, for about the first 5 seconds of testing, thereafter degrading quickly because of heat and in most cases were not capable of continues max um output for longer that 1/2 or 1 hour without sever over heating.
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You can guess how to improve MPG, or you can measure it: http://www.scangauge.com/products/scangaugee/
jsw
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I have one of the original scangauges. That was the basis for my disconnecting the alternator Q, so I could see what the diff would be. I mentioned somewhere that when the alt on my ole mazda 929S went, that my mpg's seemed to jump. Ahm still tryna figger out how to disable the alternator.... :(
But, THIS Q is for sumpn diff: I'll be adding "carriage batts" for an inverter setup, and am curious about the extra loading of the alt by extra batts.. I'm hoping johnB is right -- he's saying the max output of an alternator IS current limited, iow, you *cannot* short out an alternator?? That would be nice!
--
EA




> jsw
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put

?
ge

I

Solar Panels...
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On 11/1/2012 6:08 AM, Existential Angst wrote:

I've lost the logic of this. If your objective is to have emergency power at home, why do you want to haul around hundreds of pounds of batteries that don't need charging?
Put the batteries adjacent to the inverter. You want the long cables from the alternator to the battery at 40 amps instead of between the battery and inverter at hundreds of amps. Put a smart trickle charger on the batteries. Hook up the car in an emergency to charge 'em when the grid is down. I haven't done measurements in decades. It would be interesting to know the car engine RPM required to get 40A out of an alternator.
The primary result of putting the batteries in the vehicle is to reduce gas mileage and wear out your brakes faster.
Or you could buy a $89 Harbor Freight generator that will give you more reliable power for longer and cost less than the inverter and be portable.
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rec.crafts.metalworking the following:

    If one insists on having 12 volt batteries, one can wire the batteries into a "charging station" which charges them off main power, till the power goes out. Add a genset of some sort to recharge them when the main power is out.     I understand that Coors (of all people) is doing some interesting work in ceramic batteries, with such an idea in mind. -- pyotr Go not to the Net for answers, for it will tell you Yes and no. And you are a bloody fool, only an ignorant cretin would even ask the question, forty two, 47, the second door, and how many blonde lawyers does it take to change a lightbulb.
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snipped-for-privacy@mindspring.com says...

FWIW, CoorsTek, a major ceramics company, is a different company from Coors Brewing. They used to be under the same parent company and the ceramic business derived a large percentage of its income from support services for the brewery but they separated in 1986. I remember back in high school in the late '60s thinking it humorous that the crucibles we used in the chemistry lab were labelled "Coors".
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"J. Clarke" wrote:

The 1" Sony VTRs we used at Ch. 55 (WACX), a Christian TV station in Orlando, Fl. were bought from Coors marketing unit where they produced their commercials.
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