Introduction: Solar Powered Bilge Pump

Picture of Solar Powered Bilge Pump

I've had water seep through my basement window quite a few times in the past two years. While I've done what I can to prevent this (clean gutters, divert downspouts) water stills builds up within my basement window well occasionally, and eventually seeps into the basement - wrecking havoc on my day.

Last year, I added a bilge pump to the window well which was powered by a couple of 6V lantern batteries. This worked - until the batteries died.

So - I decided to up my power source to an AGM (absorbed glass mat) Lead Acid battery which gets charged via a solar cell.

DISCLAIMER: Be careful when using tools - protect your eyes - think twice before doing anything. With batteries, you can't unplug them - they're always 'hot' - watch where you put your tools - avoid possibly shorting out the terminals. Keep the protective terminal covers on the battery until you actually connect it to your circuit, and when you do, make sure a fuse is the first thing to get connected. Batteries can be dangerous - they can explode - leak acid.

Step 1: The Bilge Pump

I purchased the bilge pump and float switch at a wally world - I think it was for around $35-50. Sorry for the lack of detail here - did this at 3am after cleaning out my basement all night :(.

The bilge pump is designed for small boats to expel water within their hauls and keep them afloat, it's not an industrial pump by any means. The accompanying switch is a small float switch which closes the circuit once the water level is at a certain height.

Step 2: Mounting the Bilge Pump

Picture of Mounting the Bilge Pump

So you've purchased your bilge pump / switch - now you have to mount it to something. I used a plastic paint roller tray because it's what I had on hand.

I attached a small piece of plywood onto the bottom for added weight / stability.

I drilled a few holes into the bottom to allow the water to seep into the tray.

You'll want to test your placement of the pump / switch. You don't want the switch to be triggered on when / if the pump can't quite pump out the water. You might consider mounting the switch just a bit higher than the pump to avoid this.

Step 3: The Battery

The battery I chose for this is an AGM (Absorbed Glass Mat) Lead Acid type - 12V(volts) 7ah (amp hour). It's a maintenance free deep cycle battery that's designed to be used periodically. You'll find them in security systems, computer battery backups, etc.

A word (or two) about this kind of battery.
12V is perfect for this - the pump is designed for 12V.
It's not spillable - can be mounted in all positions.
Can put up with quite a range of temperatures.
Packs a punch - could run "safely" for a few hours at 1 amp drain - we only need this for a few mins here and there.
Small & cheap (~$26).

I could have gone with a slightly smaller size - 12V 3ah - but this was just a few dollars more.

Step 4: The Solar Panel

I found a solar panel at Harbor Freight for about $20. It's rated at 1.5 W. Let's talk about that for a minute.

In the DC (direct current) world, the math is simple. Wattage (power) = voltage * current. So, 1.5 Watts at 12 Volts should be...

1.5 / 12 = Current == 0.125 Amps

(the specs that came with the panel mention 0.120 amp maximum output, so 1.5 W is probably a bit off)

Although this is a very small current, it's probably more than enough for this application. It's a trickle charge - just a bit to keep the battery topped off. Over time, it could recharge a battery from a lesser state, but we're talking about days in the sun.

My point being - don't go overboard with this. If you get a large panel, you're wasting your money (in this application). If you DO get a large panel, you'll also need a charge controller to keep the battery in a healthy state of charge. We can get away without one here since it's only in the sun a few hours a day AND it's such a small panel.

Step 5: Misc Wiring

You'll need some misc wiring, a fuse, some terminal connectors, electrical tape.

I used 1/4' (i think) blade connectors - male and female. I don't care for the crimp on variety, but the solder adverse will probably prefer them.

18 AWG wire should be large enough - you could go a little bigger I suppose.

15 A fuse - blade type - the blade connectors can be used with it easily.

You should pick up a cheap VOM (volt ohm meter) if you don't have one already - I keep one in the battery box - it was $3 at harbor freight.

My parents gave me an old extension cord (the orange in the photos) which had broken - I ripped a lot of wire from it - and used it to connect the battery box to the pump.

Step 6: Wiring Diagram

Picture of Wiring Diagram

Wiring diagram. Never hurts to white board everything just to make sure you've got a good handle on what's needed.

Note that the solar panel was made to be plugged into the cigarette lighter of a vehicle. I took apart this adapter - found the positive / negative connections on the circuit board and soldered new wire to them - used that to connect to the battery.

I didn't want to bypass the small circuitry - wasn't sure of it's significance. Does it prevent the panel from draining the battery? Does it aid in the charging of the battery? Just to be safe, I kept it intact.

If I were to purchase a small solar charge controller, I would have bypassed the circuit completely - just wired right to the panel.

Step 7: Putting Everything Together

Picture of Putting Everything Together

At this point, I'm just focusing on the battery box - I had already put together the bilge and switch about a year ago.

I grabbed a small project / tool box at Fry's for a few dollars - just big enough to fit everything. I did a couple of test fits to make sure there was plenty of room. It's important that this box is vented in some manner - a hole or two in the top will do fine. I had a hole in the side - and two more where the handle was snapped into the top. You don't want water in there - so you may want to add some cover of sorts to prevent water from seeping in, yet allowing hydrogen to escape. (batteries often create hydrogen / oxygen when charging - though this is a sealed type - it can happen - you don't want an exploding box)

The first thing you should wire is the fuse to the battery. In this manner, if you screw up anything (short out the battery) you just blew a fuse - you didn't melt any wire or let the smoke out of anything.

Start wiring up your items - referring to the wiring diagram as needed. Note that all positives connect together, as well as all negatives. This includes the battery to the solar panel. It never hurts to double check using your voltmeter before connecting.

Many people use wire nuts to connect multiple wires - I chose a small terminal strip because I had it laying around. It's probably a little too industrial for this application - nice if you want to add items down the road. (like what I don't know)

Step 8: Done - Epilogue

Picture of Done - Epilogue

I've got the system installed now - and just last night we had a lot of rain - but no water in the basement!!!!

You'll want to point your solar panel south (if you're in the US) - but even just a few hours of sun (even cloudy) will keep this battery charged up.

I have been going out everyday and checking the voltage on the battery - left a cheap meter in the box. This battery should have around 13 V +. If the voltage starts creeping above 13.5 - and once it gets warmer outside - I might consider some sort of charging controller.

I would also like to add some way of knowing when / how long the bilge pump ran. I might take an old tape recorder and use it to trigger a movement when the pump runs... that would at least tell me it ran. Perhaps a microcontroller is the answer - I've got a PIC16F84A laying around I haven't used for anything.


JoeInventor2 (author)2009-11-15

Great idea, I'm building something similar and wonder if you might know how/what could be used to turn on/off your pump at 1-2-3-4 designated times 7 days a week. This switch must be battery operated, economical/cheep and no bigger then a common paperback book?????
Any answers out there?????

84westywolf (author)JoeInventor22010-02-23

joeinventor2 : Just buy an automatic bilge pump that runs whenever water is detected. Would you still need a switch for this? You could still add a SPDT switch, one that has "On/Auto/Off" positions (the center position is Auto). OR, buy an (expensive, about $80 ) DC timer . Those have lots of settings.

I just installed a solar powered 100ah battery system to run my 12 volt sump pump (we often get a LOT of rain). It is a Rule 360 GPH (gallons per hour) 12 volt bilge pump, requiring 2 amps at 12.3 to 13.6 volts, assembled basically as jedi27's is. The solar panels provide about 3 amps per hour unless it is raining (which is where the battery comes in!!).  If the pump runs about 3/4 of the time, it's using 1.5 amps per hour. 100 ah / 2 (max. recommended discharge) = 50 ah. 50 / 1.5 = 33 hrs. In other words, if it rains for 1 day and a half, the sump pump probably will run the battery too low to do much pumping. Add to that: the solar controller has a disconnect setiing of 12.2 so you just won't get even that far! I have been forced to connect a 2 amp battery charger to the battery pack at times to keep the voltage up.

Next task for me is to find the user manual for the controller to see if the LVD is user adjustable.

I hope this is all of some use. I'm a new guy, liking this forum very much.

jedi27 (author)JoeInventor22009-11-15

The battery operated portion makes it more complex, otherwise I'd say grab a timer from big blue and have done with it...

You COULD look up a 555 timer based circuit - have a small counter circuit - calc that out to run every so many hours - have it activate a relay for so many sec /.mins - which would then power your pump.

This would be better suited for a micro controller... a lot of folks use the arduino (look them up in instructables) - it's a great hobby level pic that would allow some interfacing to things such as a relay - low power consumption, small, $35ish?  depends on model...  this would allow a lot of flexibility.  You could modify the logic to only run if moisture detected within the allotted periods - perhaps warn if low battery - log run times, etc... 

(I'm curious how this will be used... the requirements are a bit off kilter...)

Good luck!!!! 

baudeagle (author)2009-02-12

I have heard that if you do not add a diode into your circuit the battery will discharge through the solar panel at night. I am not that familiar with this but maybe someone else can enlighten me.

jedi27 (author)baudeagle2009-02-13

I suppose the panel could do that, but I left the original solar panel circuit intact - which is (probably) designed to disallow that type of discharging. I didn't poke around the circuit too much - looks like it's just a cap, resistor, LED, plus another diode (the LED is a diode too!). Keep in mind that my cheapo panel was designed to trickle charge a car battery - even noted in the manual that it wouldn't drain the battery at night - so I'm putting some faith into that! (i believe) The purpose of the diode is prevent current from flowing the wrong way - in that case, from the battery to the panel.

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