Battery suggestion needed please

[contaucreek]

Frequent power outages while we are not home have dictated that we need to build a 12v battery backup for my sump pump. It only has to run for maybe 8 hrs intermittently so this is what I have in mind.

-existing 1/3 hp 5a 120v pump.
-1000w inverter
-battery ?
-transfer switch

I would run the transfer switch at the closest receptacle and utilize a maintainer to  keep the battery charged and ready.

What battery based on this size and how long would it work at say 35% duty cycle. Do I go deep cycle or regular lead acid and what capacity ?

I also don't know much about the small transfer switch I would need. Do they make them to just plug into a standard 120v receptacle ?

Edit- something like this  http://www.ebay.ca/itm/110VAC-15AMP-AC-LINE-VOLTAGE-TO-POWER-INVERTER-BACKUP-AUTOMATIC-TRANSFER-SWITCH-/190978420289?pt=LH_DefaultDomain_0&hash=item2c77336e41

Thanks guys

[mike90045]

group size 24 battery    12V 85ah   =  1020 watt hours total.   for emergency usage, 10 times a year, you can go 80% discharge. 
 However Peukerts law will create voltage sag and the inverter will shut down from under-voltage long before then with one battery.
   http://en.wikipedia.org/wiki/Peukert%27s_law

for a critical item like a sump pump, 5a x 120v = 600watts running at 100% efficiency, and the inverter has to supply at least 5x that to start it.  So you need about 3,000w surge (for 5 seconds) and then about 800watts (SWAG at actual running power - not watts).   If you are gone for 48 hours, [38,400wh] at 35% duty cycle, that's 13,440 watt hours to keep your basement dry.  that could be contained in 13 batteries (with no reserve)   Ouch.   What happens if it floods ?

Or did I drop a decimal in the math somewhere ?

[ronmar]

You have a sump pump that clocks 8 hours of run time in every 24 hours?

How many GPM is your current pump?  How much head/how high must you pump the water?

What I am angling at here is you are going to have quite a few losses going battery/inverter. You will also need an inverter with some wave shape, modified sine or pure sine.  Induction motors like on your described pump are horribly innefficient on a non sine wave inverter.  And as mentioned, the starting load will be several KW over running load.   

If this were me, I would look at installing a second DC pump.  You could set the float switch to lag behind the AC pump, IE: if the ac pump fails to run, the water will rise above it's float switch start point and trip the DC pump switch at a slightly higher level.  The off point can be at the same point. It could be tied into the existing plumbing with just an additional check valve.  This has several advantages IMO:
1. No complicated transfer switch or wiring, just a plug in charger, battery bank, float switch and pump.
2. No inverter and motor efficiency hits.
3. In important applications, "two is one, one is none"
If the pump is that important to prevent flooding, how long would it take you to recover from a pump failure? Do you have a high water alarm? Would you have to roll in a gas pump to dewater the basement to get the water low enough to swap a pump?   A redundant parallel system really shows it's value when one fails...  After the cost of good inverter large enough to do the job and a transfer sw, the DC route might be significantly less expensive.

As always my .02

[xyzer]

I would probably follow ronmars path. A lot to be said for redundancy! With a DC system you could probably save some real money plus increase your battery bank.
.02 cents more.........

[contaucreek]

There is no room in the sump hole for a second pump. Start on the pump is 9amp. This setup only has to provide power until I can get home tostart the lister. I work 2 hours away. We receive notice of schedualed outages and I can guess when a bad storm is coming and prepare so the likelyhood of an 8 hour run is low. I for sure am not buying 13 batteries lol. My basement is finished, laminate flooring etc over concrete pad. Water HAS got to the subfloor but not high enough to effect the flooring. That was an extreme situation. At "that time" of the year we are very vigilant.

[BruceM]

Hammer drill and chipper hammer away!  (At least if it's limestone not granite.)

I would go with Ronmar's suggested DC pump route also.  A backup for the AC pump sounds wise.

[Hugh Conway]

Also think the DC pump would be a better option. There are quite a few types available for small boats that do not have a large draw and are fairly inexpensive.

Something like this may do:
  http://www.ebay.com/itm/New-12V-Submersible-1100-GPH-Marine-Boat-Bilge-Pump-with-Float-Switch-/331028664158?pt=Boat_Parts_Accessories_Gear&hash=item4d12d88f5e&vxp=mtr

They're cheap, get two!

Cheers,
Hugh

[veggie]

You may not like the idea of 8 to 13 batteries but energy-is-energy and you are going to have to get it from somewhere if not from the batteries.
Consider the cost against the possible damage if you cannot get home in the two hours that it normally takes.
I wonder if this would work...

- A small air cooled diesel generator using the chinese diesels from princess auto.
- A small acreage jet pump (say 5gpm or throttled to the same flow rate as your sump pump).
- Auto start module (McPerson Controls) http://www.mcphersoncontrols.com/details.cfm?ECU-05-12-Volts&cat_main=1&cat_sub=4&id=84

Place the jet pump beside the sump with the suction hanging into the sump.
Tee the jet pump discharge into the sump pump discharge line (after the check valve) and also use a check on the discharge of the jet pump.
Run the 120 VAC line from the pump to the generator.

Place a High Level float switch in the sump (at a level just above the sump pump cut-in) and wire the level switch to the auto start module on the small diesel generator.

When the level rises, the float switch starts the generator--->Pump.

I did not give this a lot of thought so it's just a starting point for discussion.
When you add it all up, it may cost the same as 10 batteries and an inverter LOL   

veggie