ANother minimum battery bank question

[vtoffgrid]

I want to be able to start my 240 vac 400' deep well pump without a 120/240 transformer (once a day) and charge a battery bank with my existing 240 vac 8000w generator. I am expecting to exercise the crap out of these batteries and not get the longest of life out of them.

How under sized would 4 6v (420AH) interstate L16HC batteries be when used with a Magnum ms4024 with a 240 vac 8000 watt generator to charge? Am I going the wrong way down a one way road?

[Sunking]

Huh? No way to do this without an Inverter. Batteries are DC, you motor is AC.

[sensij]

That Magnum part number is an inverter, not a generator.

How many HP is that deep well pump?

[vtoffgrid]

Not sure on the HP rating for the deep well pump. I was going to see if my clamp on meter will catch the starting surge...any other ways to verify HP? Previous owner has no clue and I can't find a sticker anywhere for the pump.

[Wy_White_Wolf]

Are you planning on running the well pump only while the generator is running? Once a day sounds like your filling a cistern to supply the rest of the day.

If so, then it has very little effect on the batteries. You can limit the amps that the inverter/charger put back into the batteries so they are not too over ampped by the genny. How big are the rest of your loads?

WWW

[vtoffgrid]

The rest of our loads are small...5 10watt lights (LED) , laptop charger, two phone chargers, modem, maybe a radio or tv if things get crazy. Refrigerator, stove, and hot water are propane. Wood stove for main heat. Im planning on running washer and dryer while batteries are charging.

We have an 80 gallon pressure tank that seems to supply us enough water for a day and runs well pump 5-7 mins to fill. I was hoping to be able to run the well pump off the inverter and bank but can run when bank is recharging.

I was hoping to be able to discharge these batteries consistently to 50% over a day or two days before recharging with the generator. Will I be able to load that generator with the magnum charger and that size battery bank or will I find that the bank will not except that much?

I really just need to get an accurate load for the well pump...will a clamp on ct and meter pick up the starting surge?

[Mike90250]

...I really just need to get an accurate load for the well pump...will a clamp on ct and meter pick up the starting surge?

A clamp on meter will give you the running power. You can figure the starting power is at least 5x that. Is your pump above ground ? Can you compare motor size to other motors at the well store, and come up with a guess ?

Peak reading meters start at about $300, some electricians have them, might have to pay for an hour of time.

[thastinger]

What size is the circuit breaker which the well pump presently runs off of?

They sell 4" DC in well water pumps, they aren't cheap.

[vtoffgrid]

Currently the well pump runs off a 240v 20amp breaker and is about 350'-400' deep. I will use the 5x applied to my running amps for a good estimation for starting load.

[sensij]

The original post suggested the pump be running *without* a 120/240 transformer. The Magnum inverter outputs 120 Vac, and the pump requires 240 Vac. The transformer is required if you want to run the pump from the batteries (through the inverter), otherwise, the pump will only run from the generator directly.

If you actually meant to say *with* a 120/240 V transformer, then more discussion of the pump's power requirements with respect to the inverter and batteries is worthwhile.

Does the startup surge matter much for battery sizing? Lots of power, but for such a short amount of time that there isn't much energy discharged. As long as the inverter is big enough to handle to spike, the running current should be more important for battery sizing. 8000 W generator should be able to handle the spike from at least 2 HP, maybe bigger. If the pump is too big for the inverter, you could still start the pump up on the generator, and then switch to batteries when it is running.

To see if the pump is too big to start on the inverter, first, let's look at the running current. A 1.5 HP motor might draw 6.6 A at 240 V. On the 120 side of the transformer, that is slightly more than 13.2 A. 13.2A * 120 V = 1584 VA, which is well within the 4000 VA capability of the inverter.

The surge capability of the inverter is 120 A for 1 ms, 72 A for 100 ms, and 5800 W for 5 sec. An AC motor might have a surge current of 10X to 20X for maybe 100 ms, then drop down to 4X-8X for a few seconds. You can see that the surge current for a 1.5 HP motor would probably exceed what your inverter can supply. Without spending the money for a meter, could could probably just charge the batteries, hook the pump up to the inverter, and see if you can start it. The inverter should protect itself and cut out if the motor is pulling too much. In that case, instead of trying to start the pump line to line, you could look into a soft starter that would reduce the peak current required.

Back to the original question, those are flooded lead acid batteries, and should be charged between C/8 and C/10. That means something like 42-52 A. At 24 V, that is 1000 - 1260 W, although actual charge voltage will be somewhat higher. So yeah, although the generator is capable of charging a much bigger bank, and the charge controller in the Magnum inverter could probably handle a battery double the size (it is capable of putting out 105 A). There shouldn't be any problem charging your smaller battery correctly.

[vtoffgrid]

I was looking at the split phase magnum (MS-4024PAE) I like the idea of not having the extra transformer to run the well pump and the ability of feeding the inverter/charger 240v from the generator. After looking around it sounds as though this magnum inverter can handle its advertised surge ratings no problem as long as the bank is there to support it.

I was leaning towards the L16-HC 6v batteries from interstate (FLA) because of price and correct me if I'm wrong they are more geared for consistently being discharged to around 50% before getting a full recharge, because they are for floor maintenance machines.

After I get the running load nailed down for the well pump I may find that this Magnum ms-4024PAE is way to big and I will have to use a smaller inverter with an auto-transformer.

[Mike90250]

Xantrex / Schneider have a line, Conext XW inverters, with native split phase (standard USA 240V) output. The also have good surge capacity and generator inputs for recharging via inverter circuit too. 24V and 48V models.

The battery bank & wire has to be able to support the starting surge for 1 second, if the resistance is too high, the any inverter will choke on low voltage.

If you use a 120 - 240 transformer, it has to be large enough to handle the starting surge, or it too will choke.

Any pump larger than 1hp, will likely need to be driven by a beefy inverter or a generator, the transformer size gets prohibitively large

[Amy@altE]

My off-gridders love the Magnum for well pumps, it handles the surge well. As thastinger mentioned, it may be less expensive to switch over to a DC well pump like the SunRotor or SunPump, depending on the head, and just pump when the sun is shining to a cistern. Easier to store water than power. Then just size a much smaller off-grid system for your small loads.

[SunEagle]

My off-gridders love the Magnum for well pumps, it handles the surge well. As thastinger mentioned, it may be less expensive to switch over to a DC well pump like the SunRotor or SunPump, depending on the head, and just pump when the sun is shining to a cistern. Easier to store water than power. Then just size a much smaller off-grid system for your small loads.

Sounds like a great idea going with a DC pump but what if he needs water every or every other day and gets 5 days of clouds. Then his battery better be able to handle that DC pump.

[Amy@altE]

Sounds like a great idea going with a DC pump but what if he needs water every or every other day and gets 5 days of clouds. Then his battery better be able to handle that DC pump.

Or a big enough cistern to hold 5 days of water. Another small DC pump like the Shurflo 2088 can be run off battery to pressurize the house, again allowing the pump to bypass the inverter. Done all the time.