What do I need?

Re: What do I need?

If you have reliable domestic water supply (i.e., not a well pump on utility AC), you can also find various water powered sump pumps (here is one--don't know anything about it or the vendor).

If I had one of those, I would have saved my hole in the ground central heater too when the float on my old/cheap sump pump stuck.

But, I got a better (and more efficient) furnace now (95% or so) and I put in a less cheap pump and float assembly (dual floats plus pump fail alarm).

Still have not gone the extra measure of a backup electric/water powered pump yet--probably not needed as long as I know the sump is filling (takes weeks to over flow).

-Bill

Re: What do I need?

You talked about a 12 VDC inverter--I was not clear if you where looking for a second 12 VDC pump or just use your inverter for power.

A 12 VDC pump will probably be much more efficient.

750 Amp cold cranking rating still does not tell us much about the battery. Marine batteries do not make great deep cycle batteries--but for light usage, it may be the best bank for the buck for your application.

Assuming your battery is 100 AH at 12 volts, and we recommend 5% to 13% rate of charge, then a good choice would be a 10% rate of charge and assume 77% panel+charger derating:

• 100 AH * 14.5 volts charging * 1/0.77 derating * 0.10 rate of charge = 188 Watt solar array

Or, if you only need a minimum 5% rated panel, then:

• 100 AH * 14.5 volts charging * 1/0.77 derating * 0.05 rate of charge = 94 Watt solar array

The amount of AH a 94 watt array can output is very dependent on your local sun conditions... Let's assume ~2 hours of sun per day (deep in winter):

• 94 watts * 1/12 volts * 0.62 system derating * 2 hours = 9.7 AH per day

So, the next question is how much power will the pump pull and how long per day will it run.

A "inexpensive" higher end bilge pump will do:

Continuous Duty. Submersible with 6' Tinned Wire Assembly. Removable Cartridge. Tough Nylon Housing. Exclusive Quick Snap Swivel Base. Ignition Protected. ISO 8849.
12 volts, 3.2 amps.
Dimensions 4.5" X 3"
Footprint 2 3/8" Round [86mm]
Flow @ 0' 1000 GPH - Flow @ 3' 840 GPH - Flow @ 6' 650 GPH
Port Size 1 3/8" Fuse Size 6.0 A

Besides battery, will also operate from a solar panel that can supply about 3.2 amps or more

So, a 3.2 amp motor pumping 6' of water at 650 GPH will run around:

• 9.7 AH per day in December * 1/3.2 amps = 3 hours per day with 94 watt panel charging your battery bank

Is this helping?

-Bill

PS: A 100 AH battery will run around:

• 100 AH battery bank * 0.80 useful capacity / 3.2 A pump = 25 hours

So, without sun, your battery would supply around 25 hours of pumping (with 80% capacity factor).

Re: What do I need?

IF your battery is rated for 100 AH and was deep cycle (Marine batteries are not deep cycle batteries and if they get deep cycled, will not last very long), then yes, about 25 hours (20 Hour Rate is what we use around here for most solar applications). The 80% is assuming the battery can lose 20% of it capacity (aging/sulfating) before you recycle for a new one.

So, assuming 4 minutes per hour, 80 AH usable capacity, 3 amps, then you would be looking at:

• 4 min per hour / 60 min per hour = 0.067 hours per hour of operation
• 80 AH * 1/3 amps * 1/0.067 Hours run time per Hour = 398 Hours
• 398 Hours / 24 hours per day = 16.6 days without sun

Note, letting the battery set for days/weeks at less than full charge will cause accelerated sulfation... But that may be OK ($100 battery vs $10,000 worth of damage for a once a decade power failure).

Solar panel wise, you would need (assuming 2 hours of sun per day, 0.62 eff, 3 amps with a 0.067 duty cycle:

• 3 amps * 14.5 volts charging * 24 hours per day * 0.067 duty cycle * 1/0.62 sys eff * 1/2 hours per day sun = 56 watt solar panel

So, roughly a 56 watt panel would keep up with your "typical load".

Battery wise, a 56 watt panel with 5% to 13% rate of charge, and picking 10% rate of charge as a good number:

• 56 watts 1/14.5 volts * 0.77 derating * 1/0.10 rate of charge = 30 AH @ 12 volt battery bank.

Obviously, a 30AH battery is about 1/3rd the size of your 80-100AH battery, so it would only power the pump for ~5 days without sun vs 16+ days with the larger battery.

However, you can use a smaller solar panel and still keep the battery well charged.

More or less up to you what is important in your situation (15+ days of battery only pumping or 5 days).

Charge controllers... For smaller panels (that have Vmp~17.5 volts), any good quality PWM controller should be fine.

If you want to spend a bit more money, you want a 3+ stage controller with "Float" (which cuts the charging voltage from 14.5 volts to 13.5 volts or so). Batteries will use less water and may last longer, especially in your case, when using a float charge stage (less "boiling" of the electrolyte).

Simple charger (no float)

SunGuard 4.5 amp solar charge controller

This guy below has a "sealed" battery setting (sets to 14.1 volts--better for longer term service in your case with flooded cell and rarely used):

SunSaver 6 amp solar charge controller

And this one has a true Float Stage (not real cheap):

ProStar 15 solar charge controller

For an AC backup (or primary) charger, a Battery Minder brand unit is pretty nice (I use one on a car that does not get driven very often and it works well).

I got this Battery Minder and it seems to work well (usual disclaimer--sample of one on in-laws' car).

At some point, to be cost effective, a solar panel + charge controller + small battery (plus a small charger) vs a Battery Minder + larger battery and no solar backup is a tough call.

On thing you will need too is a way to monitor/test your system. You don't want to find out 4 years down the road you find the the backup pumping system because of a failed charge controller, pump, or battery...

-Bill