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Old 10-08-2016, 11:56 AM   #31
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Originally Posted by rossfree View Post
If you're using all of those solar watts to power a couple of 6k btu air conditioners during the day as well as charge your batteries I can understand that. Anything approaching 50% depletion on your battery bank between recharges will kill your batteries in 1-2 years.
This. I've been making a living off the solar industry for almost two years now and I really believe solar has progressed to the point where cooling via solar might be possible. Additionally i will have a half sized fridge which could drain 3-4aH alone. I do not want to have to be frugal. We are boondocking and full timing.



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Originally Posted by jazty
But you want to make sure that your solar panels and charge controller are able to properly charge the battery bank

Can you post your source on all that info? It'll come in handy should I choose to go the middle ground like rossfree said and leave room for expansion in the future. I haven't found any reading info on sizing panels /charger for maximum output into battery bank.
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Old 10-08-2016, 12:00 PM   #32
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Can yours your source on all that info? It'll come in handy should I choose to go the middle ground like rossfree said and leave room for expansion in the future. I haven't found any reading info on sizing panels /charger for maximum output into battery bank.
It's pretty standard. 10% of the battery bank's C/20Ah. You can be certain by looking at the spec sheet for your batteries. I'm using several US Battery XC2s: http://usbattery.com/wp-content/uplo...t_2015_web.pdf

Look at the bulk charge rate. That's the max you want to put in.
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Old 10-15-2016, 11:14 AM   #33
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But you want to make sure that your solar panels and charge controller are able to properly charge the battery bank. If you have a huge battery bank and an underpowered means of charging them then you'll be trickle charging. This is far from ideal. You want to get your charge rate somewhere around 10% of the C/20Ah of the battery bank for bulk charging. If all you do is trickle charge then you'll end up with stratification of the water and acid in the batteries.
On the same note, you don't want to dump huge amperage into a small battery bank or you'll boil the batteries.

There is a perfect ratio for charge rate and battery bank size. For my 12v battery bank of 455Ah the ideal rate is 45A for bulk charge. I'm putting in 35-40A most days, which is close enough for now. One more mini panel would get me right where I need to be.
Can we get a couple basic figures up here for the layman? Wattage to battery bank size in terms of usage and efficient charging? Ie 400 or 600 or 800 watts of solar power = x aH in battery bank...
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Old 10-15-2016, 08:50 PM   #34
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I have enjoyed this thread. I am cautious with giving information on solar because I have only been running solar on my bus for a few months. I do however have electronics knowledge and what I believe is a fairly thorough understanding of solar and and charging.

First thing to keep in mind is how much power you can take from your battery bank without over stressing your batteries. Taking 20% of the available battery power and then recharging will give you years of service. Taking 50% will kill your batteries in a couple of years (of regular use).

When discussing a 455 Ah battery bank, 20% is roughly 91 Ah's (at 20 Ah rate). 91 Ah times 12 volts = 1100 watts for one hour or 100 watts for eleven hours.

Keep in mind that power usage from your battery bank is NOT linear. When you take more power than the 20 Ah rate you will get less total Ah's.

A good battery monitor knows this and will do the necessary calculations in real time to give you a reasonably good estimate of the state of charge in your batteries. The battery monitor will have a shunt mounted within inches of your battery bank. Voltage readings will be taken across the battery bank. You cannot read voltage anywhere else and get reliable estimates of state of charge.

So go back two paragraphs.

1100 watts of power usage equates to less than four hours of 300 watts per hour of charge from your solar panels. It is not more complicated than that.

My 480 watt panel has never given my batteries 480 watts of charge. But on a sunny day I regularly see over 300 watts of charge for five or so hours... more than enough to recharge my batteries. I have seen as high as 440 watts of charge from my panels. It was very sunny and about 1:00pm in the afternoon. I see 300 watts regularly. So I am comfortable giving you these numbers.

Batteries can give you more than 20% but it shortens their useful life. Leaving them at this depleted charge for extended periods of time is also hard on the batteries... thus it is important to recharge them quickly if it is possible to do so. Having more solar can help in this but 500 watts of solar is a good balance for 450Ah's of battery bank.

I believe jazty's 10% of Ah capacity is overstated when you are using your batteries in the top 20% of their available power. I can easily top off my battery bank with 480 watts of solar in a single afternoon. 20 amps of charge current is not a "trickle charge" on a 440 Ah battery bank.

I think jazzy is ultimately charging two battery banks with 1000 watts of solar per bank. So he is getting roughly double the charging current that I am using (40 amps). That means it takes half the time to recharge his batteries. The extra solar energy is a bonus. Once the battery bank is charged he has solar to help power his air conditioning and whatever else he wants to power while the sun shines. When the sun goes down he's back to that comfortable 20% of available charge from his battery bank.

I hope this helps you size your system. 455 Ah's is not a lot if you plan to use energy like you would plugged into shore power. If you wish to boondock as I do small savings in power usage will go a long way. Four batteries are manageable and won't break the bank. Even at today's prices you are looking at $1700 for the system I have when you add in panels, charge controller, batteries, cables, mounts, plugs and a good battery monitor. Not cheap.

It is so cool to go out and work on my bus, plugging in to 110vac power created by solar to run my tools, air compressor, lights and music system. Every day I go back out it's all charged up again from sunlight. Damn... I love it!

Big wire, MPPT charge controller, 6 volt flooded lead acid batteries, 500 watts of solar, no shadows... you get the picture!

Regards!

Ross
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Old 10-16-2016, 08:59 AM   #35
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most mppt charge controllers max out at 800 watts for a 12 volt system. i have 3 260 watt panels, 4 l-16 batteries, a battery life saver, 60 amp charge controller 2000 watt inverter/charger and a trimetric battery monitor. i live off this full time. i run my 10 cf fridge during the day and unplug at night. on most days it takes 3.0 to 3.7 kw to top my batteries off and run the fridge. when living off solar you waist nothing. you want your batteries as full as possible. mine are around 85% in the morning, they are 7 years old now. my advise is to get a morningstar 60 amp charge controller, everything else you can add to later. good luck
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Old 10-16-2016, 12:14 PM   #36
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most mppt charge controllers max out at 800 watts for a 12 volt system. i have 3 260 watt panels, 4 l-16 batteries, a battery life saver, 60 amp charge controller 2000 watt inverter/charger and a trimetric battery monitor. i live off this full time. i run my 10 cf fridge during the day and unplug at night. on most days it takes 3.0 to 3.7 kw to top my batteries off and run the fridge. when living off solar you waist nothing. you want your batteries as full as possible. mine are around 85% in the morning, they are 7 years old now. my advise is to get a morningstar 60 amp charge controller, everything else you can add to later. good luck
I am thinking 4 x 305w (1220w) 24v panels, the Morningstar Tristar MPPT 60 amp charge controller, and approximately six Crown 390aH 6 volt batteries (parallel and series for 12v at 1170aH. Are my figures close to correct? I am basically matching watts to aH here. Is this going to trickle charge?
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Old 10-16-2016, 07:47 PM   #37
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Using a very rough rule of thumb:

10% of 1170 c20/Ah is 117. You want 117 amps to max out your bulk charge rate.
The percentage could be higher. You'll need to find a spec sheet to know, or call Crown.

1220 watts @ 12v is ~100 amps.
Charge voltages are always higher than 12 volts, so the amps will be lower, but this is a simple highball estimate.

That all seems pretty good to me!
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Old 10-16-2016, 07:59 PM   #38
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on a 12 volt system, 800 watts of panels is maxing it out. you would need 2 controllers to run 1200 watts of panels
https://www.altestore.com/store/char...troller-p7728/
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Old 10-16-2016, 08:48 PM   #39
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Sounds good with the two charge controllers and add the battery monitor. Without it you will always wonder... like taping over the fuel gage in your car and driving to work after the kids used it over the weekend.

Remember to use big cables when putting it together. Especially between the batteries and inverter. You will likely want to purchase a hydraulic crimper to make your own cables. I would use nothing less. Every cable end must be crimped solidly. You're looking at about twelve cables just between the batteries and also between the battery bank to the inverter. The cables from solar to the charge controller must be large enough to carry the current you expect to see. Likely four gage or thereabouts. And you have cables between the charge controller and batteries. And you should also have power disconnects between the batteries and the inverter and between the solar and charge controller. Lots of big wire cables. It adds up. Get a good hydraulic wire crimper that will do a bunch of different sizes of wire ends. Oh and a good pair of cable cutters.

The list of stuff goes on and on. My 480 watt system probably ran more like $2000 with all the stuff mentioned above. That's after getting my two 240 watt panels for $240 each. Keep your cable runs short and use BIG WIRE.

Solar rocks!

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Old 10-17-2016, 12:28 AM   #40
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I'm struggling with hearing the need to have a 2 kilowatt solar array to charge four 6volt, 220 Ah batteries. If you need that much solar wattage you must be depleting the crap out of your batteries between charges which will kill your battery bank in no time. 2000 watts in an hour of sun will turn on 20 100 watt bulbs for an hour in perfect conditions. Who uses that kind of power from a four battery bank? If I use 30% of my 440 Ah's I can easily top that off with a nice day on 480 watts of solar.

If you're using all of those solar watts to power a couple of 6k btu air conditioners during the day as well as charge your batteries I can understand that. Anything approaching 50% depletion on your battery bank between recharges will kill your batteries in 1-2 years.

500 watts of solar, big wire, 4 battery bank of 6v deep cells, good MPPT charge controller, a GOOD BATTERY MONITOR and a bit of frugality will take you a very long way. Overkill is always nice but a 500 watt system will run your lights, power your pumps, turn your fans, heat your coffee and charge your laptops no problem with room to spare. Add a small catalytic propane heater and stove top and you're good to go!

Just my two cents.

Ross
You got it wrong! Each group of four grid-tie panels charges four (eventually) golfcart batteries at about a 13% charge rate. That's eight batteries in total, about 900 aH total capacity, in two separate systems running in parallel. If I want to use L-16 batteries instead, then I'll still be able to keep them correctly charged. It really isn't that much power for full-timing. My intention is to normally not discharge the batteries more than 20% each day, and to have three day's self-sufficiency if the sun's not shining before I reach 50% SOC, at which point I'll use my emergencies-only generator to bulk-charge the batteries back to 80% full. My system will need to run everything I have, and do so reliably all year round, even when the sun's not strong in the winter or it's overcast. It will power the fridger, maybe also a small freezer, a 12K mini-split A/C, my Splendide washer/dryer, microwave oven, induction cooktops, maybe the water heater as an opportunity load if I have excess power available, my power tools and 120 VAC air compressor, and anything else I want.

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