batteries and inverters

Ok all I have a question about batteries and inverters.

I have a 1/3 hp sump pump that runs at 120v at 5.8 amps. So if I multiply the volts and the amps I get the watts which is 696.

Now I want to create a backup power source for my pump so that if the power goes out while I am at work it will still run.

I can buy an inverter/charger and hook the batteries and pump up to this and that could solve my problem. The pump would plug into the inverter/charger unit. The unit is then plugged into the regular house power source (outlet) and the battery (ies) are hooked up to the inverter/charger unit. When the power goes off, the batteries would take over and keep the pump running.

From everything I have read, I need to factor in roughly 15% for the inverter draw. So 15% of 696 watts is 104 watts making a total draw of 800 watts. to get the amp per hour draw I need to divide the watts by the volts so 800 watts/120v is 6.67 amps.

If I wanted to run the pump say 5 hours continuously (which I know it does not do in reality) I would then need a battery that could handle this.

5 hours * 6.67 amps = 33.5 amp/hours at 120 v or 335 amp/hour at 12v.

What would be the best battery (ies) for me to look at for something like this?

I would like to use a maintenance free type if at all possible. Are my assumptions correct or am I missing something?

Any feed back would be welcomed.

First thing, triple the startup wattage, so your 696 watt pump on startup better be able to get ahold of 2100 watts (120V@17.4=2088watts). Secondly the inverter if pulled from 12.6V DC, will need 2088/12.6=165.71Amps draw for startup and 700/12.6=55.55Amps continuously (these are assuming no loss in the inverter or cables, so actually it will take more). For this to work for 5 hours, you would need:

At least 1340AH (55.55*1.2Eff*20Hours_rated_AH_factor@80%SOC) of battery bank this will provide you (safely) with the 55Amps continuously for 5 hours. You don't want to keep discharging your batteries past 80%SOC, it will put them in the grave faster.
And at least 70Amps (55.55*1.2Eff) of charge current if solar or 17.5Amps if a 24Hour/day source is available.

The other option is to look into getting a second DC pump, some of them can be a lot more efficient than the AC models (slower pumping, but it gets the job done with less panels and batteries).

Loup Garou

Russa:

Good start of the questions.

But we need to address your readings [assuming you verified using a meter].
One HorsePower is ~750W. So 1/3 = ~250W.

re 5.8Amps:
- Your pump Info Plate is either lying or your just read this and took it as the gospel.
- You need to get a new one.

Now let's add.
1. The motor will surge 2-5 time Run Power on startup, so you'll need at least a 1200W inverter.
2. Batteries really hate being discharged beyond 50%, so you'll need to double the rated capacity.
3. You will need a charge controller or intergrated system to do it conviently.

I know of some folks who use big UPS [battery backups] and hook marine deep cycle batteries to them. The only issue is if the battery is deeply drained the UPS will not be able to recharge the battery - just slap a car charge on and go. I call that "Packrat Engineering". The older APC inverters will turn ON even if their is no line power. Many of the newer units will just complain and not power up - TEST them in the store before you buy [assuming they have reasonable charge].


Edited to add: I agree with Lou, a DC sump pump would be less work.
Also, please do a search on TB for "solar panel fridge" we have many rambles that you should explian in more detail.
here some examples
http://70.97.123.22/vb/showthread.php?t=34624
http://70.97.123.22/vb/showthread.php?t=122340
http://70.97.123.22/vb/showthread.php?t=170864

Lou, thanks for the info. in regards to the dc pump, i am already looking into that as an alternative.

Ozfuzzy. Yes the numbers I stated on my sump pump came right off the plate attached to it.

The inverter/charger unit I was looking into getting was a Tripplite PowerVerter APS Inverter/Charger this has 12V DC input; 120V AC output; 2 outlets , 1250 watts continuous output (1440 watts bypass output), 3-stage, built-in battery charger
(here is the link if you interested: http://www.tripplite.com/products/product.cfm?productID=2939)

In reality the pump runs for about 10 minutes each 30 to 60 minutes in the really wet seasons like spring or right now (which is kind of strange here in new england when it should be cold). It depends on how fast the hole fills back up with water.

So I was trying to figure out if this idea was do able. I did take into consideration that startup of the motor in regards to it's draw in regards to the inverter. That initial startup would only last a few seconds I would believe.

Loup's numbers are good. Don't pay much attention to HP/kWh theoretic conversion, just use the current on the plate. (There is a pump AND a motor on one shaft, each has its own efficiency and so you can't use the theoretic conversion number.)

Basically:
Motor voltage x motor current x motor effeciency x pump efficiency x power factor of motor = pump output rating 1/3 HP. (253 W)

By the time you have the 253 Watts converted back to input current, you probably have what's on the plate.

The things you DON'T know: efficiency of motor, efficiency of pump, power factor of motor... So just believe the plate!

The inverter and battery have to provide the start current without going DC undervoltage (and cutoff)

Actually I am surprised that it is only 700 watts, the pump I have for my well is at 180 feet but the water level is usually at 40 feet. When the water level is up at 40, it only takes 12.3Amps startup and 4.8Amps constant at 240VAC (2952Wstart/1152Wcontinuous), however, when the level dropped to 70 feet, the power requirements went to 19.2Amps startup and 6.7Amps continuous (4608Wstart/1608continuous). It is a full 1HP pump that is good for the full 180 foot lift and still give me 4.something gallons per minute, and almost 14GPM when the water level is at 40 feet, both with at least 40PSI. Overkill for most houses, but I have to play the role of fire department if something happens, so the 10+GPM could save a few things if a fire breaks out (will make a pond later). My backup pump is a DC slow pump Dankoff TSP1000F, sitting at around 160 feet and it takes a miserly 380Watts (48Volts@7.9Amps into the pump controller) to get me to the surface with 4.something gallons per minute flow. The problem is that it has no pressure behind it, so a shower is pathetic. I have to have to fill a large poly tank with it and use a second "house pressure" pump to bring it up to the PSI needed for a good shower. So for backup purposes, I have water, but have to take baths instead of showers. It does have enough pressure to run it through the first set of filters and I do use it for filling the waterbuckets in the pens, just to keep it tested and used every once and a while.

If you get a DC pump, make sure of two things, first get one that is user repairable and stainless steel, and second, make sure that you have at least three sets of backup parts (impellers/diaphrams, brushes, valves, and other consumables). You might also want to get an extra controller if it is a brushless unit, or if it needs a boost controller/linear current booster.

Shurflo makes a nice model 9300 that will pump from up to 230 feet and still get almost a gallon per minute, using a miniscule 107 watts (26Volts@4.1Amps). Plus it is user repairable and not very expensive. Perfect for backup use to fill tanks, I don't know if I would use it for day in/day out use though. If you want a heavier duty one that runs about the same wattage, but would work for 24/7/365.25 type of use, Dankoff makes a slowpump (model 1300 and 1500) that are almost the same specs but a whole lot heavier duty (the price is much higher as well).

Shurflo also makes one that takes under 4Amps@13Volts that can lift water from 50 feet. Good survival pump, for under $100, don't expect to get a good shower though.

Loup Garou

Ok Loup that makes sense. Now I undertsnad what your talking about. The pump I have is not for drinking water. I am not sure if I was clear. This is a sump pump that I use in my basement sunk in a hole about 18" deep. It only goes on when the float is lifted to a predetermined level and pumps the water out away from the house. It helps keep my basement from having water problems. I have decided to go with something like this:

http://www.secamerica.com/pump_sentry.html This will serve the needs that I have. I already have one marine battery and I will just get another one and hook them in parallel to this. It will cover the time I am at work if the power should go out.

Ok, that clears things up a bit then. Actually both Lowe's and Home Depot here in town sell battery backup sump pumps. They also started selling 10Watt solar panels that can be used to help keep them charged (over in the attic vent section).

Loup Garou