Charging and discharging at the same time in a simple system

[drabina]

I read some threads regarding charging and discharging the battery at the same time but I am still a bit confused. In a super simple setup with 100W solar panel, PWM controller, battery and a load (i.e. LED lights), can the solar panel charge at the same time when the LED lights are connected and on?

I am still trying to figure out a solution for my refrigerator in the car problem. I need a setup that during the day will allow me to run the refrigerator while the solar panel is charging the battery to which the refrigerator is connected to. I do have a power station but according to the manufacturer, this particular model cannot be charged via solar and used at the same time.

Posting here in the noob section as this is probably something easy and obvious to you guys but I am fairly new to the solar power.

 

[BentleyJ]

I read some threads regarding charging and discharging the battery at the same time but I am still a bit confused. In a super simple setup with 100W solar panel, PWM controller, battery and a load (i.e. LED lights), can the solar panel charge at the same time when the LED lights are connected and on?

Yes. In your example the solar panel and PWM charge controller are separate devices that will take sunlight and convert it to the proper voltage regardless of what else is connected to the batteries such as LED lights and/or an inverter. Whether the battery charges is dependent on the amount of power being produced compared to power being consumed. If there is 75Watts coming in from the PWM controller on a sunny day and the LED lights draw 25W, the 50W remainder is available for charging the battery but may or may or may not be entirely used depending on how full the battery already is.

The power station you mentioned has a different layout with all the electrical components on a single PCB where some circuits are probably shared as a cost saving measure. As such the power station can only do one thing at a time.

EDIT: @RCinFLA would be a good source on the forum to look up old posts regarding hardware designs.

 

[drabina]

Thank you for the explanation. All makes sense now.

 

[MichaelK]

I read some threads regarding charging and discharging the battery at the same time but I am still a bit confused. In a super simple setup with 100W solar panel, PWM controller, battery and a load (i.e. LED lights), can the solar panel charge at the same time when the LED lights are connected and on?

I am still trying to figure out a solution for my refrigerator in the car problem. I need a setup that during the day will allow me to run the refrigerator while the solar panel is charging the battery to which the refrigerator is connected to.

Let's be clear here. The little system with a single 100W panel is not likely to be able to power even the smallest dorm-size refrigerator. Is the panel going to be mounted flat on the roof of your car? If yes, derate the power to maybe 60W. You will also be hobbling yourself with the selection of a PWM controller instead of MPPT.

If you want this project to be a success, first look on the back of your frig and find how many watts it consumes. Is this going to be a DC RV-style frig? If it's standard AC, then you need an inverter to. A little 100W panel is not likely to run even just an inverter by itself, let alone a refrigerator on the inverter.

Get some real-world numbers for us first before you go out and spend money on stuff that will not work.

 

[mikefitz]

If you use a 12v compressor fridge / coolbox, not a thermoelectric type, the power needed is around 3 amps when running, with a 30% to 50% duty cycle depending on conditions.

Example,

https://www.amazon.com/DOMETIC-9600013931-Coolbox-33-litre/dp/B086LZDNPW/ref=sr_1_1?crid=3RTBY1U3TX4BG&keywords=Dometic%2Bcoolbox&qid=1684485785&sprefix=dometic%2Bcoolbox%2Caps%2C228&sr=8-1&th=1

Iñ practice a 100 Ah battery and a 100 watt panel with good solar conditions will be OK with a small compressor fridge.

A method of charging from the vehicle alternator would be helpful. Consider a MPPT type controller for solar, this will produce up to 30% more than PWM, some types have integrated vehicle charging, example Renogy DCC30

DCC30S 12V 30A Dual Input DC-DC On-Board Battery Charger with MPPT

Designed to give you options, the Renogy 30A Dual-Input DC-to-DC MPPT On-Board Battery Charger can charge a service battery in two different ways. The multi-stage charger can utilize connected solar panels or an alternator linked to a starting battery. While your vehicle's alternator prioritizes...

www.renogy.com

Mike

 

[drabina]

The fridge is a 12V portable one. When on, it draws about 46W of power. My current power station has about 50Ah capacity and works fine. The reason for the solar panel is (if I can charge and discharge at the same time) that the panel will maintain the battery and the time I can use the fridge will be extended. I usually cool all the stuff before at home but still if I need to leave for the whole day, the battery at the end of the day is down to 30% or so. If I can stay above 50% with the solar panel, I will be happy as the fridge will keep going overnight.

 

[12VoltInstalls]

100W panel is not likely to be able to power even the smallest dorm-size refrigerator.

Iñ practice a 100 Ah battery and a 100 watt panel with good solar conditions will be OK with a small compressor fridge

I tested this for five or six weeks a few years back with ~80Ah of usable storage and 200W of panels with a dorm fridge, P30L controller.
That just barely worked until a rainy day and it shut down mid morning on low voltage.

 

[mikefitz]

I am talking about a high efficiency compressor 12v low volume fridge/ coolbox with a MPPT controller

 

[drabina]

I have a fridge similar to the Dometic mentioned by Mike.

The idea of a controller that can take input from solar as well as car's alternator is great. It is just the price that holds me back. I was initially looking for an inexpensive one panel system and now I am adding/upgrading to the fancier gear and the price is rising up. But I think using both charging systems would definitely be the way to go since I can only fit one panel on the roof.