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diy solar

Dealing with charging appliances greater than 12vdc (Using buck boost)

ThePest

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Joined
Mar 1, 2021
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2
Hi,
Sorry I'm told I tend to be too verbose. [I prefer overly clear, hehe]

In starting my adventures into building a solar camper I ran into a somewhat trivial concern but i thought it an interesting topic/puzzle [I love puzzles]
The situation: Charging items such as laptops and other devices that use greater that 12vdc.
Anyone who understands the basic laws of conservation and dabbles in thermodynamics is aware that whenever you change an energy source from one form to another, there are always losses, usually thermal, that create efficiency issues. Convert gasoline to mechanical [vehicles] is terribly inefficient, AC power to heat {microwave, electric coffee maker] pretty good, but high power consumption. Solar to DC battery to AC inverter, reasonably good, but still, huge heat-sinks and cooling fans, so quite a bit of loss.
The puzzle?
Solar to 12vdc to 120VAC inverter to 19.5 and 20vdc adapters to charge 2 laptops make for some serious loses. Solar panels work better when cool but the IR from the sun lowers efficiency as they heat up, LiFePo4 batteries become more efficient at higher temps, high loads on 12vdc-120vac inverters [say 3000W] have huge heat-sinks and fans, [all of these items generate a lot of heat, panels aside, in a tiny camper] potentially making the environment inside uncomfortable in warmer climates, so why add to the problem by converting from light, to DC to AC and back again for the small amount of voltage needed to charge the laptop? the wall wart charging adapter isn't terribly inefficient [and we carelessly use many wall warts for phones, and countless other gadgets leaving them plugged in 24/7 because it's convenient and in a house [grid power being pretty cheap and readily available] allows us to accept such waste.

in a mobile solar system particularly where you don't have space for 400w+ of panels on a small roof, if every milliwatt counts, specially when you can have more than 4 or more days of rain/clouds in a row. [unless youre in AZ, NV, NM etc.]
While HP makes a 12vdc charge adapter for their laptops, [rather expensive "from them"] to plug into a cigarette lighter [prolly the worst/lousy electrical connection going (check how warm the socket gets charging your phone sometime] remember, bad connections generate heat/and loss efficiency [not good on a tight power budget]
So my thought was use a 'mostly solid state' adjustable buck boost converter to crank up the voltage to 19.5/20VDC avoiding the DC-AC- back to DC thermal loss while I'm building the whole system. Adding dedicated 19.5 and 20vdc receptacles for my two laptops.
Note: both of my laptops have 9cell Ninja battery packs for 12 hrs of run time. they take quite a long time to charge when nearly flat and even the house wall wart gets pretty warm doing so. [I haven't put a wattmeter on them yet but I suspect they're not all that efficient thermally.

The idea was to use two of these: https://www.amazon.com/dp/B07VNDGFT6/ref=emc_b_5_t for my two dedicated receptacles making a simple power cord with std DC coaxial plugs on each end [the kind typically found on wall warts]that tend to make far better electrical contact than a cheesy cig lighter. [no more clumsy/tangled'tywraped wall warts with piles of wires, as well]
Am I making sense here? Over thinking? being too persnickety/nitpicking a 45-90w AC adapter?

Cheers,
Brian

PS: Will, Kudos on your site, YT channels, books etc. I'm ever grateful for what you do. I was very skeptical about building LiFePo4 batteries until watching almost all of your vids and reading your posts/replies. Thanks stacks ? and serious congrats on conquering your illness,! [I'm perm disabled with a collapsed spine] multiple myeloma free after 3 yrs of chemo so I appreciate your situ. [tight budgets are a way of life]

Suggestion: add a glossary of acronyms somewhere. i'm still unclear about 1C, 3C, S3 and what a few others are. I'm guessing 'states of charge' and 'cell quantities' respectively.
 
Last edited:
Hi,
Sorry I'm told I tend to be too verbose. [I prefer overly clear, hehe]

In starting my adventures into building a solar camper I ran into a somewhat trivial concern but i thought it an interesting topic/puzzle [I love puzzles]
The situation: Charging items such as laptops and other devices that use greater that 12vdc.
Anyone who understands the basic laws of conservation and dabbles in thermodynamics is aware that whenever you change an energy source from one form to another, there are always losses, usually thermal, that create efficiency issues. Convert gasoline to mechanical [vehicles] is terribly inefficient, AC power to heat {microwave, electric coffee maker] pretty good, but high power consumption. Solar to DC battery to AC inverter, reasonably good, but still, huge heat-sinks and cooling fans, so quite a bit of loss.
The puzzle?
Solar to 12vdc to 120VAC inverter to 19.5 and 20vdc adapters to charge 2 laptops make for some serious loses. Solar panels work better when cool but the IR from the sun lowers efficiency as they heat up, LiFePo4 batteries become more efficient at higher temps, high loads on 12vdc-120vac inverters [say 3000W] have huge heat-sinks and fans, [all of these items generate a lot of heat, panels aside, in a tiny camper] potentially making the environment inside uncomfortable in warmer climates, so why add to the problem by converting from light, to DC to AC and back again for the small amount of voltage needed to charge the laptop? the wall wart charging adapter isn't terribly inefficient [and we carelessly use many wall warts for phones, and countless other gadgets leaving them plugged in 24/7 because it's convenient and in a house [grid power being pretty cheap and readily available] allows us to accept such waste.

in a mobile solar system particularly where you don't have space for 400w+ of panels on a small roof, if every milliwatt counts, specially when you can have more than 4 or more days of rain/clouds in a row. [unless youre in AZ, NV, NM etc.]
While HP makes a 12vdc charge adapter for their laptops, [rather expensive "from them"] to plug into a cigarette lighter [prolly the worst/lousy electrical connection going (check how warm the socket gets charging your phone sometime] remember, bad connections generate heat/and loss efficiency [not good on a tight power budget]
So my thought was use a 'mostly solid state' adjustable buck boost converter to crank up the voltage to 19.5/20VDC avoiding the DC-AC- back to DC thermal loss while I'm building the whole system. Adding dedicated 19.5 and 20vdc receptacles for my two laptops.
Note: both of my laptops have 9cell Ninja battery packs for 12 hrs of run time. they take quite a long time to charge when nearly flat and even the house wall wart gets pretty warm doing so. [I haven't put a wattmeter on them yet but I suspect they're not all that efficient thermally.

The idea was to use two of these: https://www.amazon.com/dp/B07VNDGFT6/ref=emc_b_5_t for my two dedicated receptacles making a simple power cord with std DC coaxial plugs on each end [the kind typically found on wall warts]that tend to make far better electrical contact than a cheesy cig lighter. [no more clumsy/tangled'tywraped wall warts with piles of wires, as well]
Am I making sense here? Over thinking? being too persnickety/nitpicking a 45-90w AC adapter?
_b_5_t for my two dedicated receptacles making a simple power cord with std DC coaxial plugs on each end [the kind typically found on wall warts]that tend to make far better electrical contact than a cheesy cig lighter.

Am I making sense here? Over thinking? being too persnickety/nitpicking a 45-90w AC adapter?


Cheers,
Brian

PS: Kudos on your site, YT channels, books etc. I'm ever grateful for what you do. I was very skeptical about building LiFePo4 batteries until watching almost all of your vids and reading your posts/replies. Thanks stacks ? and serious congrats on conquering your illness,! [I'm perm disabled with a collapsed spine] multiple myeloma free after 3 yrs of chemo so I appreciate your situ. [so tight budgets are a way of life]

Suggestion: add a glossary of acronyms somewhere. i'm still unclear about 1C, 3C, S3 and what a few others are. I'm guessing 'states of charge' and 'cell quantities' respectively.
AND as typical, the moment I post something, a whole pile of threads show up, that weren't returned while searching,, sheesh. I apologize
 
It's not you. The forum search isn't that great. If I really need to find something I use Google and tell it to look at only this site.
 
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