Advice please: solar panel triggers shore power fan

[LiftyK]

Hi, when I connect my portable solar panel to my service battery, it sometimes causes the shore power unit (not connected to mains at the time) to run its fan. May I ask for your advice:
a) is this causing any harm, apart from losing energy to the fan?
b) how might I prevent the fan running?

The setup
- two 12V Lead acid batteries
- all-in-one shore power and multi stage battery charger for both batteries, Dolphin I think, professionally fitted many years ago
- NASA BM1 battery monitor, fitted by me, only to service battery, following all instructions and works fine
- new portable 120W solar panel with built in PWM charge controller, connected to the load side of the NASA BM1 shunt. The main purpose of the panel is to enable a compressor fridge to run continually while out and about
- the solar panel is only connected when we don't have shore power

What happens
The solar panel is new. Last weekend I had my head in the cockpit locker where the all-in-one shore power and charger is fitted. To my surprise, I could hear the Dolphin cooling fan running even though we were not connected to mains shore power. The solar panel was connected. It was sunny and warm. Later in the day the fan stopped, perhaps related to reduced power coming from the solar panels. Apart from this strange behaviour, the solar panel appears to work fine.

What next
Clearly having the shore power/charger fan running, powered by the solar panel, is not a good setup. What modification would you advise please? I will try to see exactly how the shore power/charger is wired in next time I can get on the boat.

 

[matt1]

I have a dolphin charger supplied by merlin as part of their then "intermediate" complete system, Installed in 2006. I also have a deck mounted solar panel, with the same issue you describe. When I questioned why the fan operated when not connected to shore power Merlin explained that the dolphin charger wasn't sophisticated enough to determine when to deploy the fan so it simply ran when the voltage reached a certain level (apologies I can't recall the voltage) since that would likely be when the fan was needed. I wasn't overly happy as I felt it would limit the fan life....like I said... That was back in 2006. Over the last 12 years I have come to quite like the fan running as it gives me an audible warning my batteries are pretty much charged. Still on the original fan too with no signs of wear. Hope this helps

 

[William_H]

The (12v) fan on or off obviously depends on a type of voltage sensing relay effectively sensing output voltage of the charger/shore power 12v supply, which is also battery voltage. Presumably it also runs when engine charging is operating. But you can't hear it over the engine. Only option is to turn off (disconnect from battery) the shore power unit or fit a relay to disconnect from battery when shore power is connected. But mostly just accept it as the battery probably draws little current and will last a long time. olewill

 

[LiftyK]

Many thanks Matt and Olewill. I now understand what is happening, why it is happening and know that it is nothing to worry about. Lucky me that Matt already had this experience with his Dolphin charger. I particularly like the suggestion of learning to enjoy the gentle fan noise as a sign that all is well and batteries and panel are both healthy. Much better outcome than expected, bringing peace and tranquillity on sunny days. Cheers!