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Old 02-02-2017, 03:31 PM   #1
Mini-Skoolie
 
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Batteries

Hey guys!

I will be using about 400 amps per hour (3600 watts per day) and trying to figure the best types of batteries...

1) get 4 100ah 12Volt deep cycle batteries
OR
2) get 2 220ah 12Volt deep cycle batteries

Also what brands do you like?

I'm sure these are simple questions for some of you but I appreciate you helping me out!

Thanks!


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Old 02-02-2017, 03:44 PM   #2
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Originally Posted by TheRoanBus View Post
I will be using about 400 amps per hour (3600 watts per day) and trying to figure the best types of batteries...
I think you mistyped something? Or your math is off? I don't understand how you could have a 400 amp per hour current draw that turns into a 3,600 watt per day usage.

400 amps at 12v means you would be using 4,800 watts each hour, which I don't think is what you mean, given that you say your daily consumption is 3,600.

What are you powering?
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Old 02-02-2017, 04:00 PM   #3
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If your 3,600 watts of daily consumption is correct, then that translates to:
3,600 watt hours / 12v = 300 amp hours

But, keep in mind that you cannot access all the amp hours that a standard lead acid battery is rated for. If you even come close, you can damage the battery and you will shorten its operating life.

If you need to pull 300 amp hours from your storage batteries before recharging them, then your battery bank needs to be at least twice that size. This is referred to as depth of discharge (DoD) when discussing battery bank sizing. You don't want any lower than 50% DoD for a standard lead acid battery bank - less, if possible, since a shallower depth of discharge will result in longer life for your batteries, but 50% is a generally accepted bottom line to avoid immediate damage.

So, to safely pull 300 amps, you would need a 600 amp battery bank.

My suggestion would be to build a bank using six 6v golf cart batteries. Each will contain 200 to 220 amp hours. You'd wire them in pairs, and then hook the three pairs together in parallel, producing a total battery bank with about 600 to 660 amp hours.

That's assuming you can recharge it daily. If you need to go more than one day between recharges, then of course you'll need more batteries.

I suggest golf cart batteries on the basis that they tend to be cheaper and more heavily built than commonly available 12v so-called "deep cycle" batteries.
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Old 02-04-2017, 04:12 PM   #4
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Sorry, I meant to say 300amps.
Ok that makes sense, I knew about how you can drain it totally down but I didn't realize you practically need to double your amps in batteries!

These are the items I'll be using:

Laptop (100-240 AC) x 3A. 360Wx4 hrs 1440 watts
Phones (2) 3A- 4 hrs 36 watts
Lights LED - 4W-4 hrs 16 watts
Stove eyelet (900 watts) - 15 amps - 30 min 450 watts
Toaster Oven (15 amps)- 30 min 100 watts
Electric fridge (64 watts, but probably 100 watts) - 1 amp- 329 kwh 1536 watts
Eccotemp propane water heater (1.5gpm. 3 volt D-cell batteries.
Flojet Water pump 2.9gpm 50 psi. 10 amps 12V - 10min 20 watts

Total: 3600 watts per day=300 amps

BATTERIES: 6 Crown 6v 220aph golf cart batteries (www.solar-electric.com/cr225am6vode.html)

Can you explain a MPPT and how to use it, where to put it and how many amps it should be? I know basically what it is, doesn't it efficiently match the amount of energy being outputted from the panels to the batteries?


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Old 02-04-2017, 05:05 PM   #5
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Can you explain a MPPT and how to use it, where to put it and how many amps it should be? I know basically what it is, doesn't it efficiently match the amount of energy being outputted from the panels to the batteries?
That's the basic idea. Your solar charge controller sits between your solar panels and your batteries. As long as it is built with MPPT (Multiple Power Point Tracking) technology, is able to convert the power coming in from the solar panels to the correct charging voltage for your battery bank. This is what lets you connect a 24 or 30+ volt set of solar panels to a 12v battery bank. Or, I suppose in theory, a 12v solar panel to a 24v battery bank, but that would be weird, and you tend to lose more power from up-converting the voltage than you do from down-converting it.

There are also PWM (Pulse Width Modulation) controllers, but they can only drop voltage, not increase it, and they become increasingly inefficient the greater the difference between your battery voltage and panel voltage becomes.

As for sizing, you just need to make sure that the charge controller (whether MPPT or PWM) matches a few key ratings. It must be rated up to the highest voltage your solar panels are able to produce, preferably with a little cushion for safety. Meaning, hooking a 24v panel up to a charge controller rated at a max of 24v would probably break something because there would be no margin for error. It must also be able to output at the appropriate voltage levels for your battery bank - a label rating of 12v in your case, though the actual charge output will be more like thirteen to fourteen something because the controller has to run a bit higher than the nominal ratings in order to work.

Finally, the controller needs to be rated for the amps that it outputs to the batteries. To properly charge your bank, a good rule of thumb is aiming for a charge output of 10% of your total battery capacity.

If you have a 600 amp hour battery bank, then you would want a charge controller capable of running at 60 amps of 12v DC output power in order to make sure your system is actually capable of fully charging your batteries. Figuring back, that means your solar array needs to provide at least 720 watts of power. That actually works out passably well, by coincidence, since a theoretical 5 hours of full sunlight would give you the 3,600 watt hours of power that you'll be using throughout the day.

Keep in mind, these are all off the cuff tolerances and ballpark guidelines, and they don't figure in inefficiency. You always lose power when it is converted, stored, and then pulled back out. This could mean you will need a solar array able to generate anywhere from 20-30% more power than you actually intend to use. This would be to compensate for the fact that a charge controller may only be 90% efficient at converting power from the array voltage to the battery voltage, while the batteries themselves may be only 80% efficient at charging and releasing power.
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Old 02-04-2017, 06:33 PM   #6
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You said you used two MPPT charge controllers, why two? What does the 60amp mean?
So if I'm only using 300aph I'll need 600aph worth in batteries=3 6v 220amp batteries.
How do I run the batteries if I want them to equal 12v, but add up all the amps? Series adds up all the volts and parallel adds up the amps.
Is this the way to run things: Solar panels to charge controller to solar inverter to batteries?


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Old 02-04-2017, 07:27 PM   #7
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I didn't say anything about two controllers.

The 60 amp rating refers to the power that your single charge controller would have to be capable of carrying between your panels and your batteries.

Regarding your question of how the batteries would be hooked up, this site has an illustration of series and parallel connections: SERIES AND PARALLEL BATTERY CONNECTIONS (Simple calculations...)

I've attached the most relevant bit - a picture showing three pairs of batteries attached in parallel. This is more or less what your application would look like. Three series strings connected in parallel.

Overall, you'd have:
Solar Panels >>> Charge Controller >>> Batteries

That's your setup for getting power in. All your 12v DC loads can just run straight from the battery connections. If you have 110v AC loads, then you would need an inverter to make that AC power.
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Old 02-04-2017, 10:28 PM   #8
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So if I'm only using 300aph I'll need 600aph worth in batteries=3 6v 220amp batteries.
You'd have to use your 6 volt batteries in pairs (2 or 4 batteries) to get 12 volts. Cable two 6 volt batts together in series to make 12 volts then cable the two 6 volt pairs together in parallel to double the amps. Your 4 6v cabled together series/parallel gives you 12 volts at 450 amps.

Cable two in parallel (+ to + and - to -) to double amps at the same volts.
Cable two in series (+ to -) to double volts at the same amps.

So two 6v 225 amp batteries cabled in series in effect gives you one 12v 225 amp battery.

The same pair cabled in parallel in effect gives you a 6v 450 amp battery.
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Old 04-04-2018, 04:06 PM   #9
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What does the ratings mean

I'm completely new at this especially electricity so the 600amp rating is how many amps/hr it can put out??🤔🤔🤔
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Old 04-04-2018, 06:23 PM   #10
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I'm completely new at this especially electricity so the 600amp rating is how many amps/hr it can put out??🤔🤔🤔
600 amps is the total capacity of the proposed battery bank, but as Lucasd posted, for good battery life only half of that can be used before recharging. A deep cycle battery can only be deep cycled so many times before the battery dies. If a battery is rated for say, 150 deep cycles you can get many times that number by discharging only 50%. Basically, the less a battery is discharged before recharging the longer the life.
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