Save your basement: The Sump Pump Emergency Kit

The basement sump pump is an inexpensive solution that keeps your basement dry but it will fail one day. It's good to have a pump kit ready to go in case there is a problem. You can also lend this kit to friend who is in trouble.

An emergency backup soltion that will always work

No matter how many pumps and backups you installed there is always a risk that something does not work at the moment when you need it most. Power outages are a particular challenge.

Those emergency situations don't happen often. You might need the emergency backup only every 5 or 10 years. The shelf life of generators or dedicated spare batteries is just not long enough. There is a good chance that the generator will not start or the spare battery has expired when you are trying to use it.

The backup solution presented here is designed with this in mind. It will work when you need it and it can be stored for decades without going bad.

We need some source of power and for this we will use your car battery. You maintain your car battery for other reasons. It will be in working condition when you need it to keep your basement dry. This is different from a battery sitting on the shelf and going bad without anybody noticing it.

The plan

We buy a 12V pump on ebay and build our own control electronics. It's great fun and we save some money compared to a read made kit. As an added benefit you will be familiar with your kit and you will remember how to use it when you need it.

The main components are:

12V pump
check valve
sensor and control electronics
a flexible corrugated hose

Let's build it

You want a pump that can do at least 1000 Gal per hour at a delivery height of 2m. Some pumps come with detailed specs but for others you might have to guess. Sometimes you can find a tiny bilge pump for boats specified at 1500 Gal per hour. You can be sure that this is only possible if the pump does not have to pump any height. In any case, you want to verify that the pump you bought can do the job by testing it with a hose and a bucket of water.

I found 2 pumps that are suitable for this project. One is a larger bilge pump (yellow pump in the below pictures. It came with a datasheet.) and the other one is a general utility pump for farmers (orange pump in the below pictures). Both pumps run on 12V DC. The small yellow bilge pump is specified for a pump height of 4m (chart shows 6m) but it was not able to lift the water up more than 2.5m. My tests show that it is suitable for a shallow basement where you have to lift the water up to chest hight. The bigger orange farmer pump is specified for up to a height of 8m and I had no problems to achieve 3m. It should be OK for most basements.

All these pumps have 1inch outlets. Most sump pump hoses and connectors are 1-1/4inch. You can find 1-inch bilge hoses at Canadian Tire or at marine supply stores. You can use such a hose to attach to an adapter that takes a 1-inch hose on one side and has 1 1/4inch thread on the other end.

1 1/4 hose to 1 1/4 thread and 1 inch hose to 1 1/4 thread

50W pump adapted to 1 1/4inch threaded connector

125W pump adapted to 1 1/4inch threaded connector

It is very important to have a check valve. It's a little flap that prevents the water from returning after the sump pump has stopped. Sump pumps do not pump continously because there is a finite volume of water in the sump pump pit. Without the check valve all the water that is still in the hose would come back down immediately. The pump would have to do a lot of double work without the check valve. Most check valves are not entirely stopping the water from coming back done. The flaps in the valves are always leaking a tiny bit but that is OK as long as most of the water is still in the hose at the start of the next pump cycle. Using a small adapter piece we can make the check valve fit onto the 1 1/4inch threaded connector that is now at the end of our two pumps.

check valve version 2, it has a bleed-hole which needs to be closed for our use case

Now we have the pump ready for the job and it can easily connect a 1 1/4inch sump pump hose.

The next thing we need is a float switch and control electronics. It's good to have a little buzzer that tells you how the pump is doing. The buzzer can be switched on and off and if it is on it will simply buzz when the float switch indicates high water level. If everything is working as expected then you will hear a short buzz once in a while. If the buzz is continous then something is wrong and the water does not get pumped out properly. There is as well a push-button for manual activation without float switch. When you see that flooding of your basement is imminent than you just get your car battery, connect the hose and you push that button. Once all the water has been pumped out, new water fills the pump pit only slowly. This gives you time to install the float switch without any stress. You install it and you adjust it to automate the pump cycles.

To simplify things I use just one float switch that senses the high water mark. There is no mechanical hysteresis that would need to be adjusted. Instead you can change how long the pump continues to pump after the float switch activated. This simplifies the installation significanty. Put the float switch at the high water mark and approximately adjust the timing, done.

circuit diagram, click on the image to download it as PDF

The circuit is designed with water in mind. I recommend to spray the circuit after complete assembly with some clear coat for protection but even without that it should not malfunction if little bit of water got onto the circuit. How long the pump should continue to run can be set via some jumpers. The max time is about 40sec. I set the jumper between the 33K resistor and GND. This results in a time-off delay of about 7sec which is what I need for my pump and sump pump pit size. The jumper at 100K is about 15sec and you can combine it with the jumper at 200K for in-between values. The jumper at 200K alone is about 30sec. It's not a problem if the pump runs a few seconds longer than needed.

float switch with a bracket to attach it to a pipe or pole

float switch with a bracket to attached to a pipe

Any float switch will work. The best ones are using a reed contact as shown in the pictures above. It's a magnetic switch protected inside a tiny tube and the magnet is attached to the floater. Two versions of those switches exist and our control circuit can work with either of them:

Normally connected: the switch is closed while the float is not in the water. It opens as the water level rises. All the switches shown in the pictures above are such NC-float switches.
Normally open: the switch is open while the float is not in the water. It closes as the water level rises.

You can find such float switches on ebay. The most common kind on ebay is the white one (see above pictures) and it is meant as fill switch for an aquarium tank. Thus it opens when the tank is full. Our control electronics can handle this inverted logic. Don't worry about getting an "NC" or "NO" sensor.

The rest of the components for this circuit are standard. You can find them in any store that sells electronic components. I installed the circuit board together with a little voltmeter module, the buzzer, the switches and the relay on a wooden board. It's much easier to grab and handle this way and you can put it on top of the car battery.

Get your basement ready

An important part of being ready for handling potential problems with the sump pump is being prepared. You might have only 5-10min to act before your basement floor starts to get wet. In other words, you have to know what to do and plan ahead. Where do you run the hose for the emergency pump? Sump pumps are often hidden in crawl spaces and there might not be a window or other opening. It is not a good idea to run a long hose up the stairs thought the house. It would diminish the efficiency of the pump. There are two options:

Add a T-section with a screw-on lid to your existing sump pump line. This allows you to attach another hose and pump.
Drill a 2-inch hole into the wall. The hole is normally closed with a rodent safe plug (e.g a metal tin) and some insulation but you can pull it out easily to run the hose from the pump to the outside.

2-inch hole in the wall to run the hose to the outside

T-section in sump pump line to attach another pump

Note that the photo of the 2-inch hole is an example of how to not do this. You should never drill the hole near or below a beam. The particular photo shows a borderline case. The hole is at the edge of the beam and it seems to hold. There is no crack and the beam did not move. Take careful measurements before you drill and drill first a small hole to check that your drill comes out at the expected location.

Make also sure that the access to the sump pump pit is easy and there is enough space. Otherwise re-model your existing sump pump pit to make room.

Pack the kit

It's a good idea to have everything ready and in one box in a convenient location. You don't want to start searching and run around in the event that you will need to use it. Here are some things that you might want to pack into that box:

pump and control electronics
float switch
hose
screwdriver for the hose clamps
spanner to take the battery out of your car
printed instructions

Have a flashlight on a shelf near the entrance of the room where the sump pump pit is. Get a flashlight that can stand on a table. You will need both of your hands and you don't want to hold a small round flashlight in your mouth. I used a normal round flashlight the first time I had to work near the sump pump pit. I placed it on box near the pump and sure enough it rolled off and fell into the sump pump pit. You want to avoid that. There are some flashlights that are meant to be installed in a closet and they are quite good for this kind of application. Here is a flashlight that I made myself after the incident with the small round flashlight.

Flashlight batteries need to be replaced every 3-5 years to make sure that the light is still in working condition.

How long does it take to get this pump kit going?

Obviously it's good to train this with the family. You could do a little drill every 2-3 years. You should have the kit in a box, ready to go. It takes me about 3-5 minutes and I think anybody can set it up in that time.

To take out this car battery you have to loosen just 4 small screws with a 10mm spanner. When taking the battery out you disconnect the ground terminal first and you re-connect it last when putting the battery back in (note: this is for safety in case the spanner hits accidentally any metal parts).

How long will the pump run on a car battery?

This depends obviously on how deep your basement is, how frequently the pump needs to run etc... but as a rule of thumb you can expect to keep your basement dry for 10 hours or more. After that you will either have to look for a second car battery or see if somebody in the neighborhood has a generator to which you can run extension cables.

In any case this provides an immediate solution and you can be sure that it will work. After that you can relax and plan further steps.

An ordinary car battery is not a deep cycle battery

It is true that a 12V backup pump should normally be connected to a special 12V deep cycle battery but a normal car battery will work as well. It could potentially reduce the lifetime of the car battery but a replacement car battery is much cheaper than renovating a basement and such an emergency might happen only every 5-10 years. I have used my car battery a few times to run the sump pump and I have never noticed any problems.

How about an inverter?

You could attach an inverter to your car battery and use it to run your ordinary 120V sump pump from it. It sounds simple but the technical reality is unfortunately rather complicated. To run a 300W sump pump you will need an inverter rated at least to 4 times the capacity (1200W). This is because motors draw rather high currents at startup. Many inverters are not true sine wave inverters. They approximate the AC waveform and that is OK for light bulbs and computers but not for motors. True sine wave inverters (sometimes called pure sine wave) exist but they are often more expensive. Finally there is the problem that inverters loose power during conversions. You loose as much as 30%.

It is an option but it costs about 10 times as much as this 12V sump pump kit and you get less run time.

I have a Dodge Journey

Some carmakers put the batties in strange locations. Check how easy it is to take the 12V battery out of your car before you start this project.

Is there a ready-made kit that I could buy?

It is actually possible to buy a solution that is very similar to what we built here. It's sold at hardware stores for permanent installation as a backup. You would just have to add clamps to connect to an ordinary car battery and you would need to add an adapter to connect to a flexible sump pump hose. It's more expensive than the kit described in this document but you spend less time assembling it.

simer 12V sump pump with 90-deg 1-1/-inch hose adapter added

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