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 > Parallel 12volt, more capacity then AH rating? 2.7 x's more!

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lawrosa

Horry County

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Posted: 02/11/18 10:56pm Link  |  Quote  |  Print  |  Notify Moderator

Just to throw another wrench in the works.

Per my other posts on 12v vs 6 volt I found some vids that seem interesting

It seems this guy tested parallel 12 volters. Nothing about voltage drop but about capacity.

If you watch these two vids it seems batts in parallel get 2.7 times more then their rated AH ratings opposed to one. ( His test anyway but seems plausible)

So is my one 12 volt 75 AH battery actually about 202 AH's when paralleled?

Interesting.. Also he has a whole thing that peukert's law dont work but I haven't watched them yet...

I only wish he did it with series 6 volt batts...

Parallel Batteries Don't Add part1: When 1+1 = 2.7

Parallel Batteries Don't Add part2: When 1+1 = 2.7


Mike L ... N.J.

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Tom_M

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Posted: 02/12/18 04:32am Link  |  Quote  |  Print  |  Notify Moderator

The video is simply a demonstration of Peukert's law. As the rate of discharge increases, the battery's available capacity decreases.


Tom
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valhalla360

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Posted: 02/12/18 04:50am Link  |  Quote  |  Print  |  Notify Moderator

Tom_M wrote:

The video is simply a demonstration of Peukert's law. As the rate of discharge increases, the battery's available capacity decreases.


Yep, 6v or 12v shouldn't matter as long as they hold the same number of watt-hours at the same rated discharge and are both deep cycle designs (not labeled but actual design).


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red31

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Posted: 02/12/18 05:35am Link  |  Quote  |  Print  |  Notify Moderator

if ya compare a discharge rate to 1/2 discharge rate (2xbatt) ya might find a 10% increase based on this 2004 JCI spread sheet.

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SoundGuy

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Posted: 02/12/18 07:02am Link  |  Quote  |  Print  |  Notify Moderator

lawrosa wrote:

I only wish he did it with series 6 volt batts...


You're reading way too much into this ... yes, using 2 paralleled 12 volters of the same type, age, etc will yield a multiplying effect but it won't be any different than using 4 similar 6 volters in series / parallel as that's all those four 6 volters represent electrically - two 12 volt battery supplies in parallel. Secondly, in practical terms few of us are going to buy high end industrial grade batteries as used in this test so there's no chance you're going to find 1+1=2.7 as this YouTuber claims - more like 2.2 for garden variety batteries most of us buy. There are so many other variables that will affect this multiplying effect as well, with those batteries with lower internal resistance better able to withstand heavy loads with less voltage drop. Think about it - while this may be an interesting test no RVr in his / her right mind is going to intentionally draw any deep cycle battery 100% to 10.5 volts when most consider ~ 50% draw down the most you'd want to do on any regular basis if you expect to get reasonable use out of those batteries. Yes, the bottom line is there will be a multiplying effect if using multiple batteries but it's fantasy to believe it will be anywhere near 2.7 for a pair in any practical application. [emoticon]

wa8yxm

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Posted: 02/12/18 07:53am Link  |  Quote  |  Print  |  Notify Moderator

Ok, there is an effect I can never recall the proper spelling of which says THE FASTER you discharge a battery the faster^2 it runs down

So a battery that holds 220 amp hours at the 20 hour rate (11 amps) may only hold 150 at say 20 amps. or 300 at 5 amps.

This is why a Group 24 battery ( roughly 75 AH at teh 20 hour rate) has over 100 amps at the "one amp" rate.. (Wal*mart) they slowed the discharge so as to make the battery LOOK better on the spec sheet.. We who research are not fooled.

So I am assuming the person pushing parallel. Did not double the load else his result would be different.

I have the bandwidth today (And tomorrow) so let me research...

Explanation better than mine at Battle Born Batteries dot com

Peukert's law Wikipedia

I can spell it well when I'm looking at the above URL [emoticon].


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BFL13

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Posted: 02/12/18 08:12am Link  |  Quote  |  Print  |  Notify Moderator

Nothing new. For years we have been telling folks on here to not use one battery and then use the second one. Instead use both together and get more than twice the AH running the same load.


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pianotuna

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Posted: 02/12/18 08:24am Link  |  Quote  |  Print  |  Notify Moderator

The smartgauge site has a downloadable Peukert spreadsheet.


Regards, Don
Full Time in a 28 foot Class C, 256 watts solar, 556 amp hours of AGM in two battery banks 12 volt batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

wnjj

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Posted: 02/12/18 09:26am Link  |  Quote  |  Print  |  Notify Moderator

valhalla360 wrote:

Tom_M wrote:

The video is simply a demonstration of Peukert's law. As the rate of discharge increases, the battery's available capacity decreases.


Yep, 6v or 12v shouldn't matter as long as they hold the same number of watt-hours at the same rated discharge and are both deep cycle designs (not labeled but actual design).


12 versus 6 matters if both are sped’d at the same discharge rate because a pair of 12’s will be drawing down at half the rate in the same system. The parallel 12’s will get the 10 percent bonus capacity that the series 6’s won’t. That never seems to come up in the “just add the amp hours” 12 versus 6 comparison threads.

SoundGuy

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Posted: 02/12/18 09:49am Link  |  Quote  |  Print  |  Notify Moderator

BFL13 wrote:

Nothing new. For years we have been telling folks on here to not use one battery and then use the second one. Instead use both together and get more than twice the AH running the same load.


I don't disagree in the theory but it's all too easy to recommend 2 batts when you're not the one paying for them. [emoticon] I'm in this situation myself - I have no choice but to replace my 10 yr old G27 Interstate battery this spring, it's gone to battery heaven, no amount of resuscitation helped. [emoticon] We normally camp on electric sites and based on that alone a simple G24 sitting on the tongue would serve the purpose. However, because we lose campsite power for one reason or another at least 2 or 3 times each season I installed a 1000w PSW inverter in the front pass through storage compartment so we can still use a couple of 120 vac fans and make coffee & toast the same way we always do. Although the 6' run to the tongue mounted battery with 4 gauge cable met specifications for the max 60 amp load I would ever draw voltage drop was still problematic with just one G27 as the source. Obviously the solution was to invest in 2 new batteries but I wasn't about to do that until my existing G27 announced it's entry through the pearly gates. In the meantime I found that if on the few occasions I actually needed to run my toaster or coffee maker using the inverter that load supporting the trailer battery with the truck solved the problem of excessive inverter voltage drop nicely. That was then, this is now, and I need a new battery. I had considered inexpensive flooded dual GC-2s on the tongue but even those would be problematic with the space I have available and no way would dual G31s fit. My solution is to instead go with a single G31 AGM battery that can sit in the front pass through storage compartment, which in turn means I can connect the battery to the inverter with short 18" 1 gauge starter cable that will measurably reduce voltage drop due to cable length & gauge. So - why not 2 batteries in parallel? ... COST. Here in Canada a G31 AGM can easily run well north of $400 Cdn, $800 for a pair, even much more for premium brands. Then there's the issue of recharging them ... my WFCO won't do a proper 14.4 volt bulk charge, the CTEK I have will but it's not really the appropriate choice for recharging dual G31 Deka AGMs I'm considering that require temperature compensation. Third, because we'd only be running on battery power just a few times each season having 2 would be a total waste the rest of the time. Bottom line - it's easy to say go with dual batteries but not a universally applicable recommendation for everyone. [emoticon]

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