Virtue of the dual battery solar charger with ACR's?

[Cutwater28GG]

following on my ACR questions, I have a seperate question regarding the solar controllers the boats ship with. (even if just to collect my thoughts 😉 )

The boats come with the morningstar sunsaver duo which can direct 50/50 or 90/10 charging at the house and engine batteries. most owners I believe set this to 90 to the house and top the engine up with the 10.

With the ACR's also installed, Is this really necessary? with the volts above 13V the ACR will combine the batteries.

If a solar charger is used that only outputs to one battery bank (lets say its connected only to the house batteries) and exceeds the combine voltage on the ACR (which a solar charge voltage will do - i.e. above 13v for 90 seconds or 13.6 for 30 sec) , the ACR should combine the batteries into a single battery bank.
As a result all 4 batteries (in a cutwater28) at this point will look like one battery and all get the solar charge.

what Im getting at is, I don't see any issues with swapping my morningstar PWM sunsaver duo for the morningstar sunsaver MPPT single battery solar charger. as it will charge all batteries anyway.
(the reason for choosing this model is it takes the same physical footprint as the PWM and it uses the same RM1 remote display)

what am I missing?

 

[Osprey]

Cutwater28GG
My view is that you are missing nothing. I have two solar panels connected to separate MPPT controllers. The output of both controllers connects to the house bank. Now why two MPPT controllers? Well, one panel is rated at 135 watts and the other at 200 watts. Since the two panels have different maximum output current, the most efficient overall efficiency is to use separate controllers. Had I had two identical panels and the controller were able to handle the total maximum current, then one controller would suffice (parallel connection.)

 

[Osprey]

Having written as displayed above (Osprey) I might add why do I think the factory installs PMW Sunsaver Duo controllers on Ranger and Cutwater boats. Using the common rating scale of “Good, Better and Best” I would rate PMW as “Good” and MPPT as “Best”. However, the PWM controller is cheaper than the MPPT controller. So, there is a tradeoff between performance and cost.
The dual battery connection feature of the PMW Sunsaver Duo controller does enable one to separately monitor, on the RM-1 remote, the charge status of both the house and the engine batteries. Using the Morningstar MPPT controller one can only display data for the house battery.

 

[Red Raven]

Gavin,

I don’t think it would be a problem. The only issue would be in very low solar conditions you may not have enough solar voltage with the standard panels to close the ACRs. You won’t get much charge under those conditions anyway and there should be little to no drain on the engine and thruster batteries while at anchor so really no need to charge. The real advantage of an MPPT controller, however, is that you can use higher voltage panels which ensure you will have better charging in low solar conditions. If you have two of the 12 volt panels you could wire them in series and still get this benefit.

Curt

 

[Osprey]

One caution I would add to Red Ravin’s comment on connecting two panels in series. Series will work well if the panels have the same maximum current rating. If unlike, the current output from the series pair can be no greater that the maximum current rating of the lower rated panel. This is why I use separate MPPT controllers for my 135 watt and 200 watt panels.