Irrigation

Howlitzerbob

I have 2 300 watt panels charging 4 1100 cca semi struck batteries.  Im running a 2000watt continuous inverter. I have a half HP jet pump with an expansion tank. Batteries are full. My inverter keeps kicking off. Sometimes I can run for an hour. Other times 2 minutes. Sometimes not at all. Any help would be appreciated. 

mike95490

Is your inverter a pure sine wave, or modified sine wave ?

A 1/2 hp motor will consume about 1,000 watts running, more to start.  And the power factor on a motor is bad, and may be causing the shutdown. 

BB.

CCA is not a good number for us to use here... Normally, we are looking for battery voltage (12v or something else) and the 20 hour discharge rate (guessing your batteries are 105 AH or so).

Also looking for the battery configuration--Is this a 12 volt or 24 volt battery bus/AC inverter?

The recommended charging energy would be something like 5% to 13%+ rate of charge. 5% can work for a summer weekend cabin, etc... 10%+ recommended for full time off grid usage. Assuming a 12 volt battery bank:

• 420 AH battery bank * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 395 Watt Array minimum
• 420 AH battery bank * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 791 Watt array nominal
• 420 AH battery bank * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 1,028 Watt array typical cost effective maximum

So, your 600 Watt array is OK--But it does depend on how much energy per day you are expecting (summer/winter/etc.)...

For example, a fixed array, facing south in St Paul Mn would see:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Saint Paul
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 45° angle:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
3.39	4.08	4.36	4.76	4.96	5.19
Jul	Aug	Sep	Oct	Nov	Dec
5.40	5.20	4.76	4.08	3.15	2.77

So, for June, you would harvest roughly:

• 600 Watt array * 0.52 off grid AC system eff * 5.19 average hours of sun per day for June = 1,619 WH per day (long term average for June)

And for a 420 AH @ 12 volt battery bank, suggest that the maximum AC inverter (reliable over time, state of charge, etc.) would be:

• 420 AH (at 12 volts) * 250 Watt inverter (at 12 volts)/100 AH = 1,050 Watt AC inverter suggested maximum

Note that 12 volts @ 420 AH vs 24 volts @ 210 AH battery banks store the same amount of energy--But for larger/higher power systems, higher battery bus voltages let you use smaller AWG copper wiring on the DC side (and other advantages).

And, regarding your issues... Things I would check:

• Check electrolyte levels, refill with distilled water as needed (never let plates get exposed)
• Check wiring connections. Clean, tight. Don't use alligator clamps/jumper cables for battery to inverter wiring (very poor electrical connections)
• Check wiring AWG and length from battery to inverter (short/heavy cable, especially for 12 volt banks, really needed).
• Check specific gravity (state of charge) of battery's cells
• What is the resting voltage of the bank (if 4x 12 volt batteries in parallel, you have to disconnect batteries to measure per battery resting voltage).
• Check the battery bus voltage (at the battery, and at the DC input to the battery and AC inverter DC input). For 12 volt inveters, they typically shutdown when battery bus is at 10.5 volts or lower.

Your AC inverter takes something like 100 Amps @ 1,000 Watt load (assuming 12 volt battery bus)... So short/heavy/bolted/clean/tight connections are required.

• 1,000 Watt AC load * 1/0.85 AC inverter eff * 1/10.5 cutoff voltage = 112 Amps

And obviuosly at 2,000 Watts, ~224 Amp DC wiring current.

-Bill

Howlitzerbob

A lot of helpful information.  Its currently a 12v bank. Im going to switch it to 24v to feed my inverter.  Im dropping to that 10.5v mark when the pump is running. Im certain the 24v configuration will fix my problem. Ill let you know. Thanks guys.

BB.

You will need a new inverter too(?). The 12 vdc input inverter will generally fry on a 24 vdc battery bank.

For large loads, you need a large (AH @ xx volts) battery bank to support those loads. And a large battery bank (and large loads) usually need a large(r) solar array too.

-Bill

Howlitzerbob

So without buying another inverter my only option is shorter heavy Guage wires correct?

BB.

You generally want a maximum of 0.5 volt drop from Battery to AC inverter DC input. You need short/heavy wiring to do that--Of course, I do not know what your setup is at this point. For example, say you are using 5 feet (one way run for this calcuator) of 2 AWG cable with 150 Amps of current flow (rough estimates/guesses about your system) at 12 volts:

https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=0.5127&voltage=12&phase=dc&noofconductor=1&distance=5&distanceunit=feet&amperes=150&x=0&y=0

Result

Voltage drop: 0.23
Voltage drop percentage: 1.95%
Voltage at the end: 11.77

How does that match up to your system? What is the wiring drop for your system? Is there excessive voltage drop, or are the batteries not able to output >11.5 volts when your load is applied.

Another possible issue? Is the pump starting against backpressure sometimes (bad check valve) and stalling, and other times starting sucessfully against no backpressure?

And I guessed about your battery AH ratings... It would seem that your bank is "on the small side" (AH wise) for this pump.

Given that your system worked sometimes for 1 hour, and other times it failed... It could be your batteries are not getting fully charged? Or the batteries are starting to fail (truck batteries are not really deep cycle batteries, and they could be simply failing from deep cycling)?

You might look at "golf cart" batteries (6 volt @ 200 AH typical). They store (probably) the same amount of energy as a 12 volt @ 100 AH battery--But are usually cheaper (high volume) and designed for deep cycling.

Also, when you put them in series, you get 12 volts @ 200 AH. It would be nicer to series/parallel these 6 volt batteries. Each string is 200 AH, so you only need 1/2 the number of parallel strings vs using 12 volt batteries (for a 12 volt bus). And you can use your volt meter to check the voltage of each 6 volt battery (rest, charging, discharging) and quickly check if there are any poor performers.

Also, when paralleling batteries, this website has a quick explanation on how to do it "correctly" so that they balance current flow.

http://www.smartgauge.co.uk/batt_con.html

Personally, I do not like/suggest paralleling more than 3 strings of batteries if you can avoid it... Lots more cells to check electrolyte levels, more cabling, etc. I would suggest getting larger batteries (higher AH) to keep the number of parallel strings to 3 or less.

There are "solar friendly" pumps (low/no surge current, more efficient than Jet Pumps, etc.)--But they are not cheap. Also, using a "slow pump" in well to pump to a cistern/non-pressurized tank, then use an "RV DC pump" (12 or 24 volt) to pressurize the house/cabin.

Usually it takes several sets of "paper designs" to see what would be more cost effective for your needs.

-Bill

Howlitzerbob

Ok so I'm using the 12v converter. I have it configured in method 4 for 4 12v batteries. It helped switching to method 4 but eventually my volts dropped. All the batteries are brand new. Im running 4 awg wire less than 24 inches each. I just don't think my bank is big enough for the draw. Also my panels are only 120 watt. Im rather going to need more batteries or a 24v converter. Unless a 24v-12v step down is an option?

mike95490

>   . Unless a 24v-12v step down is an option?

nope, they cant handle as much power as your pump consumes.  If you decide to bite the bullet and get a new inverter, consider just going all the way to 48V.   Once you leave 12V land, the cost difference between 24V & 48V gear for the same power rating, is about the same.

BB.

What is the battery bank voltage? Generally, for FLA batteries you want to see something like 14.75 volts (absorb stage) held for ~2-6 hours (2 hours for slightly discharged, 6 hours for deeply discharge--Numbers are very approximate).

Resting (after the bank has sat for a few hours, no load, no charging), you want to see something like a minimum of 12.7 or 12.8 volts for 100% State of Charge.

It sounds like the battery bank may not be getting a "good charge". At a 5% rate of charge, that will take 2-3 sunny days (at least) to get charged from 50% SoC (again, very rough numbers).

Checking the charging voltage setpoint(s), checking the charging current, checking the battery charging voltage (also double check the voltage at the charge controller battery connections, you really should have at most, something like 0.05 to 0.10 volt drop maximum--Higher voltage drops can dramatically slow down your battery charging--The controller thinks the battery is "fuller" than it really is).

And confirming Mike's answer--There are no (reasonbly priced/available) high current 24 to 12 volt down converter. Most are in the 20 amp or less range, and you need >100 or even >200 amps @ 12 volts.

-Bill 

Howlitzerbob

Bill you are a rock star.  Im only running the system for max 2 hours a day. I need bigger panels and I'm switching to a 24v converter. 

BB.

HBob,

I hope we are helping... I highly suggest that you do several paper designs. The first one, is like I did above. You figure out your loads, and what is needed to support them (loads->battery bank voltage and AH; Battery bank->solar panels, and loads+hours of sun per day->solar panels too).

Once you have a "simple" definition of your solar power system--Now you go look for batteries/hardware/etc. that support your needs, and figure out how to configure them to run together nicely (for example, MPPT controllers can take different combinations of series/parallel solar panels and different size solar panels, but whatever you pick must also meet the basic input requirements for the MPPT controller).

We do not try to throw you in the "deep end of the pool" at this point--Please continue to ask questions.

And regarding terminology--A "converter" generally converts from one DC voltage to another DC voltage (24 VDC to 12 VDC, etc.). An Inverter (or AC Inverter) converts XX  Volts DC to XXX Volts AC. (not that I am great with technical terms).

Good luck!
-Bill