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12 to 6 v battery switchout |
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offgrid 
Senior Member 
Joined: 23 Jul 2018 Online Status: Offline Posts: 5290 |
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 Topic: 12 to 6 v battery switchoutPosted: 04 Jan 2023 at 6:01pm |
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Whups, I had a math error in my previous post, (corrected). One DIY 12V (actually 13.2V) LiPO battery is the equivalent of four 6V GC2 batteries, not 2. So LiPO can now be as cheap as low cost golf cart batteries. Not to mention the longevity (4x or more), efficiency (around 10% better) and weight (1/5) advantages. And they don't emit dangerous or noxious gasses either, so you can keep them inside the cabin if you want to. And that solves the only real issue with them which is keeping them warm in sub freezing weather. Other advantages: negligible self discharge and no multi stage charge protocol like lead acid has.
The weight factor is critical if you want a high power system to run a/cs or other big loads. As an example, right now I'm planning a 48V 280ah system for my new to me RV, that's the equivalent of 16 GC2 batteries but will weight in under 200lbs vs half a ton of lead acid batts, which would of course be impossible.
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1994 Chinook Concourse
1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
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StephenH
podders Helping podders - pHp
Joined: 29 Nov 2015 Location: Wake Forest, NC Online Status: Offline Posts: 6288 |
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Posted: 04 Jan 2023 at 1:11pm |
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Not to mention the life should be much, much longer than the GC2 batteries. In the long run, the LiFePO4 batteries should be much less expensive although the up-front cost is higher.
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StephenH
Happy is the man that findeth wisdom,... ouR escaPOD mods Former RPod 179 Current Cherokee Grey Wolf 24 JS |
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offgrid
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Joined: 23 Jul 2018 Online Status: Offline Posts: 5290 |
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Posted: 04 Jan 2023 at 12:23pm |
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Check out some of the Li battery tear down videos on YouTube. What's in there is just bunch of Li cells and a BMS. So you can just buy the Li cells and a BMS and make your own. Pretty easy, plus you get Bluetooth access to the BMS setpoints and datal if you want to track or change anything. If you do it that was the cost is around $700 for a 280ah, 12V battery.
Being lithium about 80% of that capacity is useable so 280ah is roughly equivalent to 2 series (edit) x 2 parallel 220ah golf cart batteries used down to 50% SOC, which will set you back about (edit) $600-700. So lithium batteries are really now (edit) about the same cost as low cost flooded lead acid. Not (edit) even considering all the benefits.
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1994 Chinook Concourse
1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
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StephenH
podders Helping podders - pHp
Joined: 29 Nov 2015 Location: Wake Forest, NC Online Status: Offline Posts: 6288 |
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Posted: 04 Jan 2023 at 10:19am |
The price has dropped tremendously if you don't go for the big names such as the one that has two of the letter B in its name. Even it has come down below $900 but it is still on the high end for 100Ah LiFePO4 batteries. |
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StephenH
Happy is the man that findeth wisdom,... ouR escaPOD mods Former RPod 179 Current Cherokee Grey Wolf 24 JS |
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offgrid
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Posted: 04 Jan 2023 at 7:03am |
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I think there are a few things related the Jato's truly exceptional battery life vs typical golf cart deep cycle lifetimes. Most people get 3 to 5 years from golf cart batteries.
1) SLI and dual use "marine" batteries have a different chemistries from deep cycle lead acid batteries. IIRC the deep cycle batteries use a lead antimony alloy which makes the plates more phyically robust (so they can handle the mechanical effects of deep cycling which consumes and redeposits the lead on the plates). But the antimony makes for higher self discharge rates. Also deep cycle batteries usually use higher specific gravity sulfuric acid (so that there is more acid there to be consumed during discharge). Both those chemistry differences increase deep cycle battery internal corrosion rates vs SLIs so shorten their shelf life. 2) There is a rule of thumb chemists use to assess the effect of temperature on reaction rates. That is roughly, to assume a doubling of reaction rate for every 10C temp rise. Internal corrosion in a battery is just another chemical reaction so if a battery in Michigan is 10C colder than a battery in FL it should last twice as long everything else being equal. And looking at annual average temp is misleading because the doubling corrosion rate factor is an exponential function, meaning that the extreme temps high and low will tend to dominate lifetime, not the averages. 3, jato is clearly an expert on how to manage batteries from his long experience with golf cart maintenance, plus he is very careful in monitoring hus battery system state of charge. 4) And yes he has a shorter use season than EchoGale does. So he is able to extract more life from his batteries than pretty much anyone. Including me, I'm not anywhere near as careful as jato is and live in a warmer climate, and run deep cycle golf cart batteries not SLIs or "marine" batts. So I've always hitting the 4 or 5 year lifetimes too. The way I look at it golf cart batteries are kind of an insurance policy for those of us who aren't going to be perfect in our battery management techniques and will wind up deep cycling them more than we'd like from time to time. Of course Li batteries blow away PbA's in all these areas and theyre so cheap now that for those of us who are a bit electrically handy they have become a almost a compelling upgrade. And since it's mandatory that Li's have a BMS for safety, you do t need to be a super conscientious operator as much with them. The BMS provides that last line of defense fircyou automatically. |
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1994 Chinook Concourse
1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
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StephenH
podders Helping podders - pHp
Joined: 29 Nov 2015 Location: Wake Forest, NC Online Status: Offline Posts: 6288 |
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Posted: 03 Jan 2023 at 12:03pm |
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Could the difference be the consistent use in Florida as opposed to the periods of non-use in Michigan?
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StephenH
Happy is the man that findeth wisdom,... ouR escaPOD mods Former RPod 179 Current Cherokee Grey Wolf 24 JS |
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jato
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Joined: 23 Feb 2012 Location: Kewadin, MI Online Status: Offline Posts: 3226 |
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Posted: 03 Jan 2023 at 11:58am |
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An interesting caveat to this who discussion is how long golf cart batteries last in golf carts. Here in the north country we would be replacing batteries after three seasons, and the season lasts 7 months or a touch longer. However those exact same batteries in the same name-brand and year golf cart will easily last 4 or 5 seasons in Florida where they are basically run all year long. Or looking at it this way, in Florida those batteries will give up to 60 months of service before replacement whereas in Michigan you only get 21 months of service. Our maintenance on batteries was stellar, keeping batteries clean, keeping an eye on electrolyte levels and filling with distilled water when necessary, keeping contacts corrosion free, charging cart after every 36 holes of play. Have not been able to figure out why the difference in battery life since as has been noted, the life of the battery ought to be longer in cooler climes (as the batteries owned by me attest to) than in warmer areas such as Florida.
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God's pod
'11 model 177 '17 Ford F-150 4WD 3.5 Ecoboost Jim and Diane by beautiful Torch Lake "...and you will know the Truth and the Truth will set you free." |
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offgrid
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Joined: 23 Jul 2018 Online Status: Offline Posts: 5290 |
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Posted: 03 Jan 2023 at 2:23am |
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EchoGale, yes, deep cycle golf cart batteries will tolerate more and deeper cycles than SLI (starter, lights ignition (aka auto batteries) or dual use (aka marine) batteries. But of course tolerating the cycles isn't the same thing as liking them. So with any lead acid battery, around 50% is about as deep as you want to plan to go on a daily basis if you want to get some life out of them.
That being said, since you live in a hot climate your battery life will be relatively shorter because what's called shelf life (aka corrosion life). This is just inherent in lead acid batteries because the sufuric acid is constantly corroding the lead plates, and the hotter it is the faster the corrosion rate. So you won't get Jato's Michigan climate battery longevity in FL. Plus deep cycle batteries usually corrode faster than SLI batteries because the chemistry is optimized for cycling rather than shelf life. It's a trade off like most things in life. Probably you won't get more than about 4 years out of your golf cart batteries where you live even if you're really careful about cycle depth. Long story short, don't be afraid to cycle the batteries you have now when you need to, while avoiding going below about 50% as you can. Hope that's clear. So, don't
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1994 Chinook Concourse
1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
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jato
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Joined: 23 Feb 2012 Location: Kewadin, MI Online Status: Offline Posts: 3226 |
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Posted: 02 Jan 2023 at 9:16pm |
A single 6v battery can safely be taken down to 6.1v (50% S.O.C.) without damaging it. If you are reading the meter with both batteries hooked together than what offgrid states (12.2v) is correct. Yes, please keep an eye on the electrolyte levels, keep filled with distilled water only. My oldest 12v battery (Interstate deep cycle group size 24) will turn 12 years old in 3 months. Proper care and maintenance is key with battery life/longevity.
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God's pod
'11 model 177 '17 Ford F-150 4WD 3.5 Ecoboost Jim and Diane by beautiful Torch Lake "...and you will know the Truth and the Truth will set you free." |
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EchoGale
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Joined: 10 Mar 2019 Location: FL Online Status: Offline Posts: 461 |
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Posted: 02 Jan 2023 at 1:04pm |
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Thanks, no I don't mean complete discharge. I was, however, under the impression that the 6V golf cart batteries could be discharged down more than that though. Am I mistaken?
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Julie
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