Need a charge controller that feeds the load first and charges battery when no load

[Dtmeagle]

I power small vent fans for my cold frames. Set up is panel to buck boost board to temperature controller. Works great but I want to be able to charge a small 12v LI battery
when the temp controller is not calling for power. Is there a charge controller that will do that? Thank

[Ampster]

I power small vent fans for my cold frames. Set up is panel to buck boost board to temperature controller. Works great but I want to be able to charge a small 12v LI battery
when the temp controller is not calling for power. Is there a charge controller that will do that? Thank

Most charge controllers only have one output. I once had a morningstar controller that had a lighting output but that would not work. It may be easier to let voltage or current be the arbitor of power output from a controller. Can you adjust the output voltage of the controller to match your desired battery charging voltage, A voltage programmable relay may be another option. Is there an issue with the battery and fan just sharing the current? The great thing about Lithium batteries is that they do not have to be fully charged every day. They can go days at lower SOC with no damage.

[Dtmeagle]

I could charge the battery when the fan is running but on cold sunny days the fan doesn’t run. The fan is set to come on at 80°F. We had some really hard freezes late and
I provided heat with a 5 gal bucket of water with an aquarium heater. I had to run a cord from the house. They make 12v dc aquarium heaters that I would like to power
from a battery at night mostly and as needed.

[Ampster]

.......... We had some really hard freezes late and
I provided heat with a 5 gal bucket of water with an aquarium heater. I had to run a cord from the house. ....

Are you in Southern hemisphere or in a high altitude? It is summer here in California.

[Dtmeagle]

Idaho. The hard frosts occurred in May, later than the historical last killing frost dates.

[solaarone]

You could wire in an appropriate solenoid that is normally closed and when power fails from the fan off, the connection would be made to charge?

[Ampster]

You could wire in an appropriate solenoid that is normally closed and when power fails from the fan off, the connection would be made to charge?

Yes I think that is the way to approach the issue. Current is not fed to devices it is drawn to loads. Control the loads and the current will flow where directed.

[Dtmeagle]

Thanks solaaron, pretty sure that will work.

[solaarone]

NP, But let me also thank you, for I was looking for verification that I could use a Buck to directly feed a 12v water heater element load.