I apologize in advance for the wall of text.
I'm having a hard time understanding something about charge controlling and haven't managed to get a clear answer to it so I thought I'd try here where I've lurked forever.
For hypothetical purposes, assume a fully electric boat. The numbers don't matter, but say I have 1kw of solar panels, going into a charge controller that charges 1kw of batteries, to a 1kw electric motor. That's all the inputs and outputs to the system. Solar panels charge the batteries and the motor pulls from the batteries to spin.
As I understand it, you can charge and apply load simultaneously. If my motor is using 500w and 1000w are going into the batteries then the system will both charge the batteries and cover all the power needs of the motor. If I'm using 1000w on the motor and only 500w are going into the batteries, then the batteries will be drawn from and the batteries will be discharging 500w to make up the shortfall. Assume there are zero inefficiencies or waste.
Here's where I get confused. If I have, say, a MPPT charge controller than can cover the incoming solar energy, transform it to the appropriate volts for my batter bank (150v solar panel string going to a 48v battery bank), it increases current while matching voltage for the bank. So I'm going along with my boat, batteries charging while I'm motoring, and various speeds draw different amount of energy from the bank.
I want to maximize my power usage. Assuming 24/7 usage, I want to decrease my draw at night to, say, 20w, so I may have a lighter load and draw from the battery bank. During the day when there is peak energy production from the panels I want to draw as much as possible while the batteries charge.
Does the charge controller interfere with that? If I match the charge controller to my bank, and my bank is made up of batteries that can't fast charge, where I have to charge at a C/20 or c/10 rate, won't this impact my usage of full available power? My panels may produce 1 kw, and I may want to use 750 w, but if the controller is past bulk charging and in float, won't the controller be decreasing the power going into the bank, and leaving power on the table I can't use?
I'm not sure what a heavy draw from the batteries will do with the charge controller's algorithms and analysis system. Will it start sending full power to the batteries to account for the load while some power still charges the batteries? Will it be in float mode, but I can't maximize my motor because it would draw almost all energy from batteries and the solar panel output just goes no where except the trickle charge current the controller allows to go to the batteries since it is assuming it must send a lower current for the batter chemistry?
What are standard ways around this? Am I completely off base as to how the panels->controller-.bank relationship works and the controllers energy drop during different charge stages?
Posted by: clamk123@yahoo.com
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