On 02/04/2019 08:30 PM, arlen holder wrote:
> On Mon, 4 Feb 2019 16:45:34 -0500, Tom Del Rosso wrote:
>
>> If you turn over an engine periodically to keep it charged, how long do
>> you run it to make up for the charge lost in starting?
>>
>> In this case it's my neighbor's 87 Buick Regal while he's in the
>> hospital.
>
> 72 seconds
>
> Having said that, here's how I arrived at 72 seconds, bearing in mind
> there's a complexity to your question which, outside of the engineering
> specs of both the battery & engine (and parasitics), we can only help you
> guess at it mathematically, where empirical results would seem to be more
> accurate than our guestimates.
>
> Starting with the basics, a quick search for a Buick Regal Alternator nets
> <https://www.partsgeek.com/catalog/1987/buick/regal/engine_electrical/alternator.html>
> which says the alternator outputs 100 amps at idle (if needed) and 150 amps
> output at max rpm (again, if needed as alternators adjust output based on
> "B" sensing).
>
> Running a direct search for the power needed to start an 87 Buick Regal,
> it's easy to find the vehicle, but hard to find the power needed to start
> the engine:
> <https://en.wikipedia.org/wiki/Buick_Regal#Grand_National,_Turbo-T,_T-Type,_and_GNX>
>
> We're kind of stuck with the "generic" stuff, such as this:
> o How Many Amps Does It Take to Start a Car?
> <https://www.reference.com/vehicles/many-amps-start-car-e35b6f3d4d8bf426>
> Which says an average car needs 400 to 500 amps but doesn't say how long.
>
> Let's assume it takes five to ten seconds to start it, at 500 amps, where
> the maximum power would be 10 seconds times 500 amps, which means you
> sucked out 5,000 Coulombs (i.e., 5000 amp seconds) if the math is right.
>
> If I did the math right, that's less than 1.5 amp hours, and since we
> guessed high, I'd say the amount used is roughly about 1 amp hour to 1.5
> amp hours, but since we want to "be safe" and have "easy math", I'd use 2
> amp hours as the amount to add back.
>
> If you put back two amp hours (to cover for inherent losses, mostly in
> heat), you're back to where you started, where we have to "assume" that the
> battery sense circuit allows the alternator to output enough current to
> charge the battery after just one start.
>
> At idle, if we assume the battery sense allows you to get those 100 amps we
> saw in the spec, to generate 2 amp hours would take only about 0.02 hours,
> or about 72 seconds (if I did the quick math right) - which -
> coincidentally - is about how long it took to run the quick math.
>
> If that 72 second answer is wrong, I welcome someone who can tell us how to
> arrive at the better answer.
>

<https://www.jstor.org/stable/44611429?seq=1#page_scan_tab_contents>

It's behind a pay-wall but I can probably get my hands on a copy