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Old 01-07-2019, 03:16 AM   #1
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Battery Draw limits in Series & Parallel?

Quick query guys. No matter what my battery setup is, 6v, 12v in any combination of Series or Parallel or both, with a Charge Controller in place I'm still stuck at 50% max draw before the system has to charge back up again correct?

I was thinking of putting two 6v 450ah batteries in Series and Parallel (I haven't seen any documentation for just two 6v's in that duel config but I assume it's doable?) for a 12v 900ah setup but then remembered the 50% guide & assumed i'd only be drawing max 450ah before it would have to charge back up again.

Same for if I went ahead & had 6v 325ah batteries in Series & Parallel for a total of 650ah's, if that's only going to draw max 325ah before the Controller cuts it off? Am I correct in calculating this? Perhaps I'm missing something.

Since I'll have a hungry 240w laptop (at max draw) among other things I was hoping 3 x 350W solar panels would be enough on a MPPT Controller at 60amps. but it's the roughly 50% draw limit that's making me wonder about the most efficient battery setup & if my assumptions are actually correct or not.

any knowledge on the battery draw/limit would be helpful.

Thanks!
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Old 01-07-2019, 06:06 AM   #2
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It's not a B&W hard line, just a guideline, try not to go below 50% too often - applies to all lead chemistries.

The deeper your average discharge

and the longer not at 100% Full, as per endAmps,

the quicker you'll need to replace the bank.

The bigger the bank, the more you need a BM to ensure

you take out each day only 80-90% of what you'll be able, to replace.

No matter how many amps your charge current, with lead's long tail it takes 6-7hrs to reach endAmps.

Best to have just one big House bank, and must be quality brand and true deep cycling.

Everything at this site wrt DC electric well worth reading
https://marinehowto.com/what-is-a-deep-cycle-battery/

Firefly Oasis is exceptionally robust, both for deeper discharge and resisting PSOC damage.

LFP eliminates all this but costs 5-7x more, pretty risky.
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Old 01-07-2019, 08:18 AM   #3
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Quote:
Originally Posted by john61ct View Post
It's not a B&W hard line, just a guideline, try not to go below 50% too often - applies to all lead chemistries.

The deeper your average discharge

and the longer not at 100% Full, as per endAmps,

the quicker you'll need to replace the bank.

The bigger the bank, the more you need a BM to ensure

you take out each day only 80-90% of what you'll be able, to replace.

No matter how many amps your charge current, with lead's long tail it takes 6-7hrs to reach endAmps.

Best to have just one big House bank, and must be quality brand and true deep cycling.

Everything at this site wrt DC electric well worth reading
https://marinehowto.com/what-is-a-deep-cycle-battery/

Firefly Oasis is exceptionally robust, both for deeper discharge and resisting PSOC damage.

LFP eliminates all this but costs 5-7x more, pretty risky.

Hey thanks for the reply, ya Lithium batteries are probably too much of a splurge for me.

I had a quick look into it but doesn't seem like any carbon foam batteries are available here in Australia unfortunately. They do look like a good choice though.

Good to know I'm on the right track then, just a matter of doing as much research as I can before I purchase anything & that it all shakes out in the as efficient & affectedly as possible. At this stage I've been in front of the computer on & off for the last 14 hours or so, so I'm practically brain dead at this stage. Thanks for the info, I jump into the link tomorrow before I head out into town
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Old 01-07-2019, 10:31 AM   #4
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Batteries in series will add voltage with the amp hours being the same as a single battery. Batteries in parallel will add amp hours but will have the same voltage as a single battery. For a 12v 900 ah bank you will need 4 6v 450 ah batteries in a combination of series and parallel.

Ted
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Old 01-07-2019, 12:57 PM   #5
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Yes Australia is a completely different battery market.

Tap into local forums for brand advice.

Full River is OK if you need AGM, dunno if Lifeline or Odyssey are sold there.
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Old 01-07-2019, 01:10 PM   #6
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Quote:
Originally Posted by TalesFromTheBelgarad View Post
No matter what my battery setup is, 6v, 12v in any combination of Series or Parallel or both, with a Charge Controller in place I'm still stuck at 50% max draw. before the system has to charge back up again correct?
Voltage, battery bank configuration, and method of charging have nothing to do with the acceptable level of discharge for a lead-acid battery bank. 50% discharge is the maximum 'tolerable' discharge for lead-acid battery. Less is even better.

Quote:
Originally Posted by TalesFromTheBelgarad View Post
I was thinking of putting two 6v 450ah batteries in Series and Parallel (I haven't seen any documentation for just two 6v's in that duel config but I assume it's doable?)
No, it's not doable. Two batteries can be connected in exactly one way - either series or parallel.

Quote:
Originally Posted by TalesFromTheBelgarad View Post
Same for if I went ahead & had 6v 325ah batteries in Series & Parallel for a total of 650ah's, if that's only going to draw max 325ah before the Controller cuts it off? Am I correct in calculating this?
Four 325 AH 6VDC batteries connected in series/parallel will result in a 650 AH 12VDC battery bank. From that bank, 325 AH are theoretically available for use (ideal condition and all that).

What controller? In a typical RV scenario/system, there is nothing that prevents an owner/operator from drawing a lead-acid battery bank below 50% SOC and damaging the batteries. Well... wait. The exception would be an auto start generator. I think those are based on voltage. If so, that is not ideal but certainly better than nothing. Btw, I don't think there is an automatic generator shut down but could be wrong (certainly possible to engineer something though - NOT based on voltage.)

Quote:
Originally Posted by TalesFromTheBelgarad View Post
Since I'll have a hungry 240w laptop (at max draw) among other things I was hoping 3 x 350W solar panels would be enough on a MPPT Controller at 60amps.
I don't understand your statement. Your hoping that 1050 watts of panels will put out 60 amps?? What voltage? If charging a 12VDC battery, then something around 14 VDC and yes, under absolutely ideal conditions (which very rarely occur).

Put a Kill-A-Watt meter on that power supply and I think you'll find that it does not draw a constant 240 watts. It may if the laptop battery is nearly depleted but likely drops to somewhere around 40 watts when the laptop battery is 100% SOC (or near 100%).
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Old 01-07-2019, 03:23 PM   #7
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If you expect reasonable live from your batteries you need to be able to charge them at a minimum rate of C/12 to avoid sulfating the batteries leading to an early death.

If you have a 12volt/900 amp hour battery bank then you will need a charge controller and panels that will support 12 volts at 75 amps MINIMUM.

It just occurred to me that a 12v/900ah battery bank will weigh 300 kilo's... And cost $2-4k....

Considering system losses the minimum array I would consider would be around 1800 watts.

OR.....

You may consider showing us your energy audit and see if perhaps you could meet your needs with a bit smaller system.
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Old 01-07-2019, 04:14 PM   #8
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For 900AH, a 120A charge would be a lot better.

1 kW of panel might average 300AH in good weather, would need more if actually using 400+ AH per day, or when weather's not ideal.
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Old 01-07-2019, 05:45 PM   #9
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Wow, this is super overwhelming! That's a lot to chew through! So I've been looking into electrical systems & solar setups for my Bus for about 3 days now & wow can it be a complex en-devour. I'm basics 101 atm but I'm absolutely appreciating everything everyone's said so thank you all, I'm taking it all on board.

I'll be back with many more questions I think later on! There's so much to figure!!! But learning heaps, thanks everyone! This is all invaluable information.
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Old 01-08-2019, 06:20 PM   #10
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Take a look at: https://www.solarpaneltalk.com/forum...battery-design

And take a look a the stickies on that forum. LOTS of good solar information.
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