using 12v dc appliances during the day

73 Posts
May 24, 2008 09:01 pm
using 12v dc appliances during the day

The small system I have for a computer:

low end laptop draws 20watts
20 watt 12v solar panel (PowerUp BSP-2012)
morningstar sungaurd 4 charge controller
12v 32ah agm battery
female DC adapter hooked to battery

when I am powering the laptop using DC power during the day when the solar panel is producing electricity, is the solar panel providing most of the DC power and the load on the battery is minimal?

Does this then "extend" the use time I can have with the laptop during the day?

I am trying to only cycle the 32ah battery down about 20%. Since the battery capacity in watts is 384watts and my laptop draws 20watts per hour, this would mean that I can get roughly 3.5 hours of use off the battery alone without the solar panel. So does using the computer while the solar panel is generating electricity, extend this use time significantly?

would love to hear some comments on this please.

J
 
73 Posts
Sep 1, 2008 09:48 am
Re: using 12v dc appliances during the day

Got to answer my own question yesterday. Now that I have my system up and running. The laptop pulls 1.6 amps. I have 60watts of solar making 3.4amps+/- of power during the day.

I turned on the computer hooked up via DC only.(no inverter) at 10:30am and was able to run a very intensive application that kept the computer draw at max 1.5 amps continuously.

The day was full sun and I was able to run the computer non-stop till 4:30pm in the afternoon without pulling amps from the battery. The charge controller kept flipping back and forth from "charging" to "charged" state for the battery about every minute or so, keeping the battery fully charged all day. After 4:30pm I disconnected the computer and allowed the system to run normally with the battery showing "charged" on the "Trimetric" meter.

So....running 12v DC appliances during the day greatly extends run-time, as long as the load amps are less than the array amps, you never really touch the battery bank.

This reminds me of an article from Home Power Magazine, where the off-grid couple had a massive array for their daytime use and only needed a 650ah bank that they cycled only about 30% deep.

This is sort of the reverse way of designing a system, in that you see sun as "the battery" and concentrate on maximum direct "solar power" for daytime use and size the bank for just simple night-time use-age. Since I'll be using the studio only during daylight hours, this scenario works perfectly.
 
462 Posts
Sep 5, 2008 02:12 pm
Re: using 12v dc appliances during the day

James, you got it, use the sun as the sun shines. Same priciple applies to solar hot water and heating......
 

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