Whats wrong?

[Rob01]

I have to 15watt solar panels and 2 12v deep cycle batteries with a 7amp charge controller. I am trying to run a 3amp bilge pump but can only get it to run for 20 minutes at the most before the batteries drop to low. I live in eastern Canada and we get a fair bit of sunny weather, about 8 hours on a good day. I unhook the pump when charging the batteries, but they never seem to last long. Any help. BTW brand name of panels is motomaster 15watt panel and batteries are nautilus 12volt marine batteries.

[Mike90250]

15w panels are not much at all, as you have found. Use a regular charger and get the batteries recharged ASAP, the longer they sit discharged, the faster they will die, if they are not dead yet.

How long do you plan or eventually running the 3 A pump. 3A x 12V = 36Watts
36Watts x 4 hr = 144watt hours

PV recharging batteries, because of losses, only gives you roughly 50% of the nameplate PV value. So your 30W of PV downrates to 15w

15w x 5 hours (only 5 really good charging sun hours in a day) = 75W replaced in 1 day.

So you see the problem, 2 days of charging to run the pump for 4 hours. or
1 day = 2 hours of run time. Less if there are clouds.

Bur recharge your batteries from a regular charger soon.

[Rob01]

So how many 15watt panels would i need to run the bilge pump for say 3 hours a day and charge the batteries for the following day.

[Mike90250]

3A bilge pump @ 12V = 36 watts x 3 hours = 108 WH / 5 hrs =
22W harvested for 5 hours.

45 w of panel should be able to maintain 3 hours of pump , as long as you have sunny days.

Be advised, the common 15W panels, are NOT well made, or of the long life type, they will quickly degrade for about 6 months, to about half their nameplate wattage, and then slowly degrade till dead. They are toys, not serious power plants. If you want serious power, get a panel with a 20year warranty, not 1 year