Solar Charge Controller for Special Project on the Ocean

[dvillal]

I need a solar charge controller for a mobile platform. It will be on a small boat (less than 8 feet) in the ocean so it will rock a lot. It will have a 100W 12V solar panel and I plan to have an 80 amp load (not all the time, but it needs to be able to handle at least that much). Now I know most solar charge controllers have connections for 1) the solar panel, 2) the storage battery, and 3) the load. Is the only reason you would attach the load to the charge controller is so that you could cut-off the battery when the charge gets to low? If that's all, it would be cheaper for me to get a 10A controller and attach the load directly to the battery? Or will that cause other issues as well.

Also, what I've read is that MPPT's are worth it for higher voltage systems. Since I'm just having a single 100W panel at 12V, I'm thinking I would get a PWM module. Does this make sense with all the above?

If you can answer one or both of my questions I would be grateful for the input.

Dan

[Logan5]

Is the 80 amp load a trolling motor?

[jflorey2]

Is the only reason you would attach the load to the charge controller is so that you could cut-off the battery when the charge gets to low? If that's all, it would be cheaper for me to get a 10A controller and attach the load directly to the battery?

You should not connect the load directly to the battery without an LVD (low voltage disconnect) to protect the battery from overdischarge.

[dvillal]

Logan: Yes, it is a trolling motor. So the amp draw fluctuates depending on the speed of the motor. 80 amps would be its max speed.

Jflorey: Good point. So would it look like an 80A charge controller is my best bet? Pwm or Mppt. I only have a 12V setup but I get a few cloudy days here. I'm trying to keep the price as low as possible.

[Logan5]

Solar and keeping the price down does not fit together very well. If you are using the 9' boat on the open Ocean, I would not use a 12v trolling motor but a 24v motor instead. On open Ocean 12v could leave you stuck and as you know conditions can change almost instantly. Either way, even a short 10 to 12 min run, will require several hours to recover with 100watt 12v panel.

[SunEagle]

Logan: Yes, it is a trolling motor. So the amp draw fluctuates depending on the speed of the motor. 80 amps would be its max speed.

Jflorey: Good point. So would it look like an 80A charge controller is my best bet? Pwm or Mppt. I only have a 12V setup but I get a few cloudy days here. I'm trying to keep the price as low as possible.

Sometimes keeping the price low could put your life at risk. Running out of power to run you motor in open water without any backup would fall into that category for me.

[dvillal]

Thanks all for your responses. Let me clarify the project a little. It is an unmanned boat. I'll have a 12V 40amp hour battery to run the motor. The solar panel is just a way to recharge the battery with a day or two of good sunlight (no load from the motors) as I would like to leave it in the water (inshore only). The only thing I'm missing is the charge controller - just hoping to keep costs down.

Logan - I have already bought the 12V solar panel but I will keep the 24V in mind for the future. I think the 24V would have been a better investment for the load I'm drawing

[Mike90250]

Large PV controllers do not have load terminals. So you need a 80A rated Low Voltage Disconnect
A 40 ah battery will not support a 80A motor very long, That will need to be re-designed.
The value of adding a small 100w PV panel that will never be at optimum angle, is questionable. Put the PV on the dock and charge the battery at the dock.

[dvillal]

Thank you, Mike. I had hoped to keep the boat out on the water instead of having to come back and dock. Its really more of a research vessel. But I'll admit, I have find away to reduce my energy consumption and still be able to handle the ocean with anything more than a light breeze.

Thanks everyone for your answers.

[Mike90250]

The amount of range gain realized, with sub-optimal panel, will be minimal. Using a 90ah battery instead of a 40ah battery and a 40lb solar panel (sail) and mount will likely have you ahead of the game,