XPost: alt.home.repair
From: NONONOmisc07@fmguy.com
In alt.home.repair, on 7 Jan 2023 17:19:31 -0000, kludge@panix.com
(Scott Dorsey) wrote:
>Mark Olson wrote:
>>In rec.autos.tech Smoke Signals wrote:
>>>
>>> I have a charger for my Lenovo laptop that plugs into 12 V cigarette
>>> lighter socket, so theoretically less losses than converting to AC and
>>> back to DC.
>>
>>That car charger will certainly be more efficient than plugging
>>the laptop's mains power brick into a 12VDC to 120VAC inverter,
>>but it is still converting the 12VDC to an AC current internally,
>>as a necessary step in the 12V->20V DC->DC boost conversion.
>
>Yes, and such devices are also more convenient, and they are available
>from most laptop manufacturers or worst-case from a third party.
>
>If you have a moderately-sized laptop pulling 50 watts and you have a
>car battery able to put out 40Ah or so before dying, then you have a
>continuous battery load of 4 amps and can run the laptop for about 10
>hours.
I may have been wrong when I said 2 hours. I was in a rental car and
had no tools and didn't want to run the battery down using the computer
and listening to the radio in the middle of a March night, then try to
start it to get warm again and find the battery dead. So I was being
very cautious.
>
>Car batteries are starting batteries and they are designed for high
>peak currents rather than the ability to be discharged very far. They
>usually have very thin plates in order to get more plates with more
>surface area for the high starting current, so they are prone to issues
>with the plates warping when discharged a lot. So don't discharge the
>car battery down too far. 40Ah is not out of the question but don't
>treat it like a telco battery.
>--scott
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