Small 12v solar bilge pump

[45North]

Idea for using a small solar-powered system to power a small 12v bilge pump in an open, uncovered unattended boat.
Components:

• 12v bilge pump
• small battery
• small solar panel
• inexpensive 10A solar charge controller - with load output with settings for low voltage disconnect and voltage re-connect setting
  • Note: this is a standard feature of even the simplest $20 SCC's, and, while not recommended for powering an Inverter, it should easily be able to power a small bilge pump
• small aluminum fishing boat (not included)

How it works:

• When it rains, the water builds up in the bottom of the boat until the float switch on the bilge pump kicks in
• The battery powers the bilge pump and starts lowering the water level
• The SCC protects the battery from going under-voltage and cuts out until the next sunny day
• When the skies clear, the solar panel re-charges the battery 'till it reaches the re-connect voltage
• The SCC powers the sump pump again until the lower water level is reached and the pump cuts out
• The SCC continues charging the battery until it's full and ready for the next rain storm

 

[snoobler]

Assuming you're looking for input...

Load ports on SCC have a rating, so it's important to confirm the pump will not exceed the SCC load port rating.

I would set the recovery sufficiently high to ensure you're not rapid cycling the system in marginal solar conditions.

 

[Bubba1]

If the boat doesn't leak it should work fine. You could buy or make a tarp to shed most of the rain water.

 

[45North]

If the boat doesn't leak it should work fine. You could buy or make a tarp to shed most of the rain water.

True. And thanks for the suggestion.
But the owner doesn't want to be bothered doing that. It's not worth building a superstructure for a small aluminum boat.
Also, If it's used nearly every week it's not worth the trouble putting a tarp on and off so this is the solution we've come up with.

 

[45North]

Assuming you're looking for input...

Load ports on SCC have a rating, so it's important to confirm the pump will not exceed the SCC load port rating.

I would set the recovery sufficiently high to ensure you're not rapid cycling the system in marginal solar conditions.

Agreed. And thanks for the input.
The whole thing depends on powering the pump from the controller, within its capacity, as you say.
If you hook it up directly to the battery (as he used to do before getting the controller) the pump could run too long after a heavy rainstorm and permanently kill the battery. Not good.
This way, some water may remain in the boat until the next sunny day which is fine. No harm done.

Edit: Someone may suggest just getting a bigger battery and PV panel to handle a bigger rainstorm. Possible, yes, but this would cost a lot more than the $20 for a small SCC to protect a small system.

Edit2: Someone might be thinking that relying on a cheap $20 controller is risky and not wise. True, but what's the downside? If it fails the boat will not drain and will have a bunch of water in it next time he visits the cottage. Worst case: it sinks while tied to the dock. Messy, yes, but not the end of the world.

 

[gnappi]

Having a 12 volt relay enable the float switch to turn on the pump will fix the dead battery in a rainstorm issue.

A 12v relay will likely drop out its coil at 11.8 to 11.9 volts within the safe DOD of deep cycle batteries. You would have to put any relay before the float switch to "enable" it so the float switch would only come on if the battery / solar cell can support it.

 

[45North]

That would work too!
So, I guess it comes down to which one has the lowest phantom load, the relay or the controller.
And I think he'd still want to have a controller to protect the battery anyway.

 

[gnappi]

That would work too!
So, I guess it comes down to which one has the lowest phantom load, the relay or the controller.
And I think he'd still want to have a controller to protect the battery anyway.

A CC for sure!

 

[deeuubee]

Can you define small pump, panel, battery for us?

A small 50 Watt (24" square roughly) will give you 2-3 amps if your lucky.
A 100 Watt panel is almost 4 ft long, and then maybe 6 amps.
A small bilge pump 500 gph is about 3 amps.
A small 50Ah battery will get you maybe 8-9 hour before it goes dead.
So, if it rains all night your battery is dead in the morning and will take 2 days of full sun to charge up.
You also have to keep in mind a waterproof container for the solar charger.

Been there, tried that. Crackhead stole my battery.
Now I just pull it on shore before I leave

 

[Bubba1]

I'm a boat guy. A bilge pump runs maybe ten minutes an hour in downpour. 50w panel should be plenty. If there's a chance of waves the bow needs to be facing out towards the waves. Waves will swamp the boat if the stern is facing the waves. Personally if I had a camp and boat I would make or buy a lift to keep it out of the water.

 

[45North]

OK, thanks for your input guys.
Keep in mind this is just an old, small open-top aluminum runabout. Worth just a few hundred bucks total, including the motor, so he's not wanting to spend a lot on covering it or lifting it etc.
If he's gonna be away for a while or expecting an extended run of windy, wet weather then sure he could run it up on shore.
And for "security" the battery and controller are small enough to fit under the seat - dry and out of sight.

 

[JoeHam]

When you need it most you won’t have solar power.

Just sayin

 

[45North]

When you need it most you won’t have solar power.

Just sayin

True. And that's where the battery comes in.
Pumps 'till it quits then waits for a sunny day.
But it's a dedicated system. Only supposed to do one thing.
You're not counting on the power to run anything else, just the pump. And if you have to wait a few days, that's OK too.

And if you need to take it out for a spin that's OK too:

• in a pinch, you could bail it out manually
• or, it might be "self-bailing" where you pull out the plug once you get goin (it's not my boat, I forget)

 

[JoeHam]

True. And that's where the battery comes in.
Pumps 'till it quits then waits for a sunny day.

Agreed. But what if it keeps raining for a day or two (no sunny days) after the battery dies and you aren’t around.

Thats the situation I’m talking about.

 

[45North]

Agreed. But what if it keeps raining for a day or two (no sunny days) after the battery dies and you aren’t around.

Thats the situation I’m talking about.

Granted. It's not ideal.
But he's prepared to live with the possibility that there could be some water in his boat for a few extra days and he'll deal with it when he next visits the cottage.
Worst case: it sinks tied to the dock in shallow water.

The improvement here was the addition of the SCC to protect the battery with the low voltage cutoff and keep it from destroying itself. Yes, having water remain in the boat 'till the next sunny day (whenever that is) is not ideal: but it's waaay better than a having the sump run and run until you have a permanently dead battery, which was what he had before the addition of the SCC.

 

[JoeHam]

Good enough, been there done that years ago. More than once.

I boat in fresh water but if it sinks just pull out the spark plugs, turn the motor over to burp out the water and life goes on.

With a 2 stroke just check for milky oil in the lower unit. 4 stroke check the crank oil. Change as needed.

While I’m sure it didn’t extend the life of the outboard it still lasted for as many years as we beat on it in a misspent youth.