DIY Home Improvement, Remodeling & Repair Forum > DIY Home Improvement > Electrical and Wiring > battery backup for sump pump?

Help Support House Repair Talk by donating using the link above.
Thread Tools Search this Thread
Old 09-12-2010, 09:37 PM  
Senior Member
Join Date: Jun 2009
Posts: 171
Liked 11 Times on 11 Posts
Likes Given: 67

Default battery backup for sump pump?

We are not quite ready to install a generator, so in case we lose power the most important piece of equipment that we might want to keep working is the sump pump. Can I buy a battery backup for it? How do I determine how long this backup will last? In other words, if I have specs for my pump, how do I calculate what type of backup I need for the pump to operate, say, for 24 hours?


ilyaz is offline  
Reply With Quote
Old 09-12-2010, 11:34 PM  
Emperor Penguin
Nestor_Kelebay's Avatar
Join Date: Mar 2009
Location: Winnipeg, Manitoba
Posts: 1,844
Liked 2 Times on 2 Posts


I think the answer to your question boils down to recognizing that: 1 watt (AC) = 1 watt (DC) = 1 volt X 1 amp

Find out how much amperage your sump pump draws.
Multiply that by 120 volts to get the wattage of your pump.

The amperage rating of your pump is "real" power, but your sump pump get's it's power from an electric motor, which has a high inductive reactance, meaning that a lot of the power just goes into creating magnetic fields (which doesn't actually pump any water). So, boost the wattage of your pump by a guestimated 35% to account for power factor.

Multiply that by 24 hours to know how many Watt-hours you need to run your pump off batteries.

Multiply that number by two because you don't want to drain your batteries down by more than 50%.

If you're using 12 volt deep cycle batteries, then divide the above number by 12 to get the amp-hours of battery life you need.

Deep cycle batteries are rated according to the number of amp-hours they can deliver at different rates of discharge; typically over 8 hours, 20 hours and 100 hours. Use the 20 hour rate cuz it's closest to 24 hours.

So, let's say you work out that you need 800 amp hours of battery power, and your 12 volt deep cycle battery delivers 200 amp-hours when discharged over 20 hours.

Then you'd need FOUR 12 volt deep cycle batteries wired in parallel to meet your needs.

And, besides the four batteries (probably costing about $100 each) you also have to buy an inverter to convert the 12 volts DC into 120 volts AC so your pump can use that power.

For $500 (guessing) for the battery back-up system, you could buy a gasoline powered generator to keep the sump pump running.

That is, the cost of a battery back-up system to tie you over until you buy a generator would cost you darn near as much as the generator.

You'd be better off buying the generator.

Last edited by Nestor_Kelebay; 09-13-2010 at 01:02 AM.
Nestor_Kelebay is offline  
Reply With Quote
Old 09-13-2010, 01:11 AM  
triple D
Senior Member
Join Date: Jan 2008
Posts: 296
Liked 1 Times on 1 Posts

Default use a marine pump....

Depending on how much water you need to move, and how fast, you could put a bildge pump in there. Then cut the float switch off and wire to a standard sump float. Use two deep cycle batteries, and go to that one store that has everything, and get a small solar battery charge pad. This can maybe get you through extended outages. Providing the pump runs for 45 seconds, every 20 minutes or so. This is just a thought from my tired head after midnight, good luck..
See my work-Check out my album. "Git 'Er Done":D
triple D is offline  
Reply With Quote
Old 09-13-2010, 05:25 AM  
Senior Member
Join Date: Nov 2007
Location: Grand Blanc, MI
Posts: 2,724
Liked 241 Times on 204 Posts
Likes Given: 113


I don't think you calculations would need to be based on the pump running constantly for 24hrs. Like Triple D says, 45 secs. every 20 mins. However, if your not on a well that would require power to deliver water to the home, you could consider installing a water powered sump pump. These basically harness the power of city water to run and impeller on a unit to evacuate the sump crock.
kok328 is offline  
Reply With Quote

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Similar Threads
Thread Thread Starter DIY Home Repair Forum Replies Last Post
A new sump pump? Jonn Plumbing Forum 11 09-11-2010 01:22 PM
lift pump or sump pump mikey9626 Plumbing Forum 2 05-18-2009 05:37 PM
Need a Water Pump (Sump pump?) Innis74 Plumbing Forum 13 05-05-2009 08:36 PM
Best sump pump? juryduty Plumbing Forum 6 05-01-2009 06:55 AM
Guardian Battery Backup for Sump cheesefood General Home Improvement Discussion 1 08-25-2007 03:30 PM