diy solar

diy solar

Power Draw

Virginia

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Nov 25, 2020
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I have a very tiny set-up for an off grid cabin. 4-100w panels, an MPPT charge controller, 1-12v200aH battery with shunt and monitor, 1000w inverter charger connected to a breaker box. 5 breakers 15amps each. An electrician did the cabin wiring and panel box. I use this to run 9w LED bulbs, typically one at a time, the occasional vent fan and charge a laptop or cell phone, not every day(and mostly around mid-day when the solar battery is fully charged.) I recently installed the battery monitor so I could keep track more easily the voltage on the battery, fearful of draining it to low. When nothing is running, there are small pulses of current through the inverter/charger until a load is detected. These pulses show up on the battery monitor and are no cause for concern. What I do not understand is this: When a single 9w .13amp bulb is turned on, the battery monitor shows around 3.5amps/45w being used. If I turn on a second bulb it increases by approximately 10w (ok) and amps rise to 4.3(a .8 increase for a .13amp bulb?). Why does the initial bulb draw such a high wattage or amperage? No matter what I plug in and turn on, the initial draw for a device is around 3.5amps.
 
Probably no-load power consumption of the inverter. That's why it has a standby mode.
Maybe you can get yourself a more efficient 12V LED light, not needing the 45W inverter draw.
Just make sure there is a way to automatically disconnect all loads if battery gets discharged to some appropriate cutoff point.
 
So the inverter with no load is drawing enough power to drain the battery that quickly? What can I do to disconnect the inverter when not needed? Is there a DC photo eye I can put between the battery and inverter? I'm using a photo eye on the lights.

Also not sure if it has a standby mode is or if its working. It goes into alarm, but neve seems to re-charge the battery.
 
I have a very tiny set-up for an off grid cabin. 4-100w panels, an MPPT charge controller, 1-12v200aH battery with shunt and monitor, 1000w inverter charger connected to a breaker box. 5 breakers 15amps each. An electrician did the cabin wiring and panel box. I use this to run 9w LED bulbs, typically one at a time, the occasional vent fan and charge a laptop or cell phone, not every day(and mostly around mid-day when the solar battery is fully charged.) I recently installed the battery monitor so I could keep track more easily the voltage on the battery, fearful of draining it to low. When nothing is running, there are small pulses of current through the inverter/charger until a load is detected. These pulses show up on the battery monitor and are no cause for concern. What I do not understand is this: When a single 9w .13amp bulb is turned on, the battery monitor shows around 3.5amps/45w being used. If I turn on a second bulb it increases by approximately 10w (ok) and amps rise to 4.3(a .8 increase for a .13amp bulb?). Why does the initial bulb draw such a high wattage or amperage? No matter what I plug in and turn on, the initial draw for a device is around 3.5amps.

Own power draw of the inverter. Running the LED bulbs and charging the laptop with DC would have been much better.
I have very bright Toshiba 40W-36V LED lights that are fed with a step-up DC Buck converter with 97% efficiency, and I can dim them down al gusto down to 1W...
Many laptops are charged with 19V, some will be just happy with the 13v of the battery, for the others, a step-up converter 12V-19V does the job.
Pretty every AC power supply labelled 100v-240V AC input will work just fine with 70V-90V DC from a step-up charger as well.

Inverting to low frequency AC, just to rectify the signal to DC and re-chopping inside the power supply to high frequency AC which is transformed and rectified again to DC is a waste of the scarce PV energy.
 
So the inverter with no load is drawing enough power to drain the battery that quickly? What can I do to disconnect the inverter when not needed? Is there a DC photo eye I can put between the battery and inverter? I'm using a photo eye on the lights.

Also not sure if it has a standby mode is or if its working. It goes into alarm, but neve seems to re-charge the battery.
Inverters tend to draw 10W to 150W with no load.
Some have an idle mode where they wake up occasionally to check for loads, but that won't do well for motion sensor or a light beam that is to be interrupted.

You could get a completely DC motion sensor and light system. Or power the motion sensor with DC, have it switch a remote input of the inverter. Switching battery power to inverter would take something like the starter solenoid from a car.
 
Own power draw of the inverter. Running the LED bulbs and charging the laptop with DC would have been much better.
I have very bright Toshiba 40W-36V LED lights that are fed with a step-up DC Buck converter with 97% efficiency, and I can dim them down al gusto down to 1W...
Many laptops are charged with 19V, some will be just happy with the 13v of the battery, for the others, a step-up converter 12V-19V does the job.
Pretty every AC power supply labelled 100v-240V AC input will work just fine with 70V-90V DC from a step-up charger as well.

Inverting to low frequency AC, just to rectify the signal to DC and re-chopping inside the power supply to high frequency AC which is transformed and rectified again to DC is a waste of the scarce PV energy.
Can you please clarify what component inverts to low frequency AC, what component then just rectifies the signal to DC, what power supply re chopps to high frequency AC, what component transforms and rectifies again to DC... ? Please. I have a nice powerful boost converter I want to use and will wire it up if it can help me to reduce energy withdrawal by not having to use my inverter to charge my Dell and Macbook.
 
Most notebooks are charged with something around 19V DC (look at the power supply), internally in the laptop, this voltage is converted to the different voltages required.
So if you supply 19V from boost converter instead of your laptop power supply, it will be much more efficient that using an inverter to make AC, followed by a switching power supply to make 19V DC.
 
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