24v charger/inverter

Wuggs

I have 12 Duracell 6v golf cart batteries that I am going to wire in 3 strings of 4 for a 24v system with each battery being 235ah for a total of 705ah.  Looking for recommendations on a charger/inverter of 2000-3000W for my system which is off-grid and will be tied to a 3000W gennie.  I have four 235W panels that I will eventually tie into the system but I need to get the battery bank up and running first. I've calculated a daily draw of 3000 watt hours with a propane fridge, no A/C, occasional circular saw or vacuum cleaner use, a 1550 microwave and a soft start Grundfos 1/2hp shallow water well pump.  Please go easy on me for any stupidity you see in my setup as I'm about as noob as one gets.  Thanks

westbranch

welcome, please tell us the general location of this off grid site, that can have a large bearing on comments...
first, before you get the panels and even after they are up, run your pump, vacuum and saw when the gen is running, so you are not drawing the batteries down... those ~1000w of panels should be increased a bit too, maybe to 1500W or so based on use...
next do a more detailed analysis of those loads, they seem a fair bit high... 
when looking at recharge you should figure on 110% of the use is needed to replace that use due to losses in the system...

hth

Wuggs

westbranch, thanks for your reply.  Location is N. WI and I plan to run microwave, circular saw etc  with generator running.  The panels I have already will be all I'm able to afford at present.  I know my generator will be running most days we are here; it's a remote cabin and not a full time residence.  When you say "more detailed analysis of those loads" are you referring to my estimate of 3000 watt hours per day?  I anticipate my draw will be closer to 2000-2300 but I don't want to short change myself if we need to draw a little more on occasion.  I have a EP Solar Tracer series 40A MPPT charge controller that will connected to the panels and then to my charger/inverter.     If I buy a Samlex EVO 2224 will that be a good match for my system?  Thanks

westbranch

For those loads that are less than 1000w you can use a Kill-a-Watt meter to get a good handle of what they are over a day.  Also a fridge as the surge at startup is not enough to upset the meter....  mine did Not like the microwave surge!...  hth


ADD:don't know about that Samlex 2224, first I have heard about it..... compare to the Outback inverter chargers first... tried and true...

BB.

3,000 Watt*Hours per day is a fairly large system... Especially if you are not running a refrigerator. Unless you are doing  a lot of water pumping (irrigation, etc.). Also, a 705 AH battery bank is pretty large--You might want to think about going 48 volt (fewer batteries in parallel, less voltage drop at high inverter current levels). If this is a cabin (part time, weekend), a large solar power system may not be the best investment at this time. A smaller system (run lights at night, power small stuff for "quiet time") and use a nice (quiet) genset (Honda eu2000i or similar) for moderate loads--And for big shop loads/construction, run a 5+ kWatt genset when needed.

But, anyway, using our rules of thumb for an off grid cabin/home and 3,000 WH per day. Battery is sized for 1-3 days of storage (2 days nominal) and 50% maximum discharge (longer battery life):

• 3,000 WH per day * 1/0.85 inverter eff * 1/24 volts * 2 days storage * 1/0.50 max discharge = 588 AH @ 24 volt

And to charge such a battery bank, between 5% to 13% rate of charge (solar)--5% for weekend/seasonal use, 10%+ for full time (9 months or more) off grid living:

• 588 AH * 29.0 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 1,107 Watt array minimum
  
• 588 AH * 29.0 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 2,215 Watt array nominal
  
• 588 AH * 29.0 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 2,879 Watt arary "cost effective" maximum
  

So--As you see, the larger the battery bank, the larger array you need (regardless of loads). Note that many battery mfg. recommend 10% minimum rate of charge for their flooded cell lead acid deep cycle storage batteries. 5% is the smallest I would suggest.

And there is sizing the array based on your energy usage. Assuming a fixed array
http://solarelectricityhandbook.com/solar-irradiance.html

Wausau
Average Solar Insolation figures

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

Jan	Feb	Mar	Apr	May	Jun
3.24	4.11	4.55	4.73	4.97	4.98
Jul	Aug	Sep	Oct	Nov	Dec
5.04	4.83	4.27	3.55	2.74	2.56

Toss the bottom three months (assume generator/not present):
3,000 WH per day * 1/0.52 off grid system eff * 1/3.55 hours sun (October) = 1,625 Watt array minimum (break even month)

If your usage is much closer to 2,000 WH per day--I would down size the system to the level--Assuming part time use. And use the genset more (when needed) for heavy loads (temporary, construction, etc.).

If/when going full time, then you could go with a larger battery bank/solar array/ac inverter. Yes--It is difficult and expensive to expand a solar power system (you cannot "expand" a VW bug into a 1 ton Pickup "easily"). Also, depending on the area, you may have to worry about theft too (small, fixed solar power system, inexpensive/easy to move back home genset). Possibly even figuring out how to secure your well pump too (in California, even well pumps have been stolen).

If you currently use the well pump for pressurization--You might think about filling a cistern and use a smaller R/V type pump to pressurize for sinks/shower.

-Bill

Wuggs

westbranch/BB, thanks for your responses.  I'll look into the OB inverter/chargers.  Propane fridge but I'd like to run microwave off the battery bank if possible.  The panel on the back says 1550W but there's a label on the inside of the door that says 1100W so I'm using the higher figure.  
Our cabin gets more use than our "primary" residence.  We spend approx 12 days/month at the cabin and am looking at nearlt full time  this summer and in 5-6 years when I retire.  My wife and I both have healthcare machines that run 8 hours/night.  Hers says 2.5A @110V and mine says 1.43. Those numbers are driving the size of my battery bank to a large degree.  I seriously doubt either actually draws that much so I'm going to put a kill-o-watt meter on them and see what they're actually drawing. In addition, we have the usual TV, phone charging and a few lights for a few hours/day.  We currently run our gas gennie all night so you can see the need for alternative energy.  
The well pump is a 240v 1/2hp soft start and I believe the installer said I could power it with a 1000W inverter but I'm going to have to confirm the specs with him.  The pressure tank gives us 21 gal between the 60 and 40 psi settings and we use little water, although that will change when I finish the plumbing.  The cistern is a nice suggestion as I've thought of capturing rain water from the roof and running it into a cistern also.
I plan to add panels beyond the four 235W panels I currently possess but that will have to wait.  In the interim I plan to run the generator daily or every other day to make up for my solar shortfall.  Thanks.