As for me, I have another point.. I can get a pair of six volt golf cart batteries for around 120-150 dollars at Costco, these are top quality batteries (Well, not Trojan's but as good as my Interstates) Or even cheaper at Sams (But I question the quality there, Sams and Costco have different suppliers)
To do the same with 12 volt pairs would run me over 200 bucks, AGM's around 300 bucks. So, cost is the final factor.
The reason is they make a LOT of golf cart batteries so the economy of scale cuts the cost.
I called Costco today.....their 6V golf cart batts are $78 each (plus a core charge I beleive). I got a discount on the Interstate U220 for $95 each delivered. $205 with tax. Everyone is telling me "Lead has gone through the roof thanks to the war" Plus I would have to drive 120 miles one way to get to the Costco that stocks the GC batt...
The other thing I don't see mentioned here much is that batteries in parallel "feed off of each"- meaning that since none of the cells produce the exact amount of power the neighboring cells & collectively the weaker battery, feeds off of the stronger neighboring cell/battery, slowly destroying each other. Batteries wired in series are not subject to this phenomenon.
"The other thing I don't see mentioned here much is that batteries in parallel "feed off of each"- meaning that since none of the cells produce the exact amount of power the neighboring cells & collectively the weaker battery, feeds off of the stronger neighboring cell/battery, slowly destroying each other. Batteries wired in series are not subject to this phenomenon."
- I'd like to see some solid lab data proving this can/does happen.
- Anyone using more than a single series set of 6V CG batteries (i.e. 4 each 6V or 6 each 6V batteries in series/parallel combinations) to make large capacity coach banks can (see the wiring error below) wind up having the above problem (..if it exists) between their parallel/series sets of 6V batteries, too.
- I wonder if some/all of those who claim to have any first hand field knowledge of the "feed off of each" problem with 12V parallel banks didn't have them wired wrong -> with the positive and negative feeds coming off the same battery of the parallel 12V set? This is NOT correct for perfect parallel battery load and charge balancing. (I see this error a LOT in battery wiring articles written by the experts.)
Quote: - I wonder if some/all of those who claim to have any first hand field knowledge of the "feed off of each" problem with 12V parallel banks didn't have them wired wrong -> with the positive and negative feeds coming off the same battery of the parallel 12V set? This is NOT correct for perfect parallel battery load and charge balancing. (I see this error a LOT in battery wiring articles written by the experts.)
The wiring might help a little but the big problem is keeping the battery connections clean. If the battery connections are in good shape and a reasonable wire size is used it makes very little if any noticeable difference.
However it is still the correct way to do it but it does not protect against a bad battery connection which will cause the other battery to do most of the work and fail prematurely. So clean those connections at least once a year...parallel or series connection.
pnichols wrote: - I wonder if some/all of those who claim to have any first hand field knowledge of the "feed off of each" problem with 12V parallel banks didn't have them wired wrong -> with the positive and negative feeds coming off the same battery of the parallel 12V set? This is NOT correct for perfect parallel battery load and charge balancing. (I see this error a LOT in battery wiring articles written by the experts.)
I've seen the "feed off" problem multiple times when there was a shorted cell in one battery. But that's it - never a problem when the batteries were still functional on all 6 cells.
That hardly qualifies as an endorsement of 6 volt batteries since that only happens when the batteries are essentailly completely worn out.
smithrock wrote: Does spacing 2 6v have anything to do with anything? In my set up I can run 2 batteries, one in each compartment on each side of the generator. if I chosse to go with 2 6v and run them in a series the spacing shouldn't matter, right?
Wow lots of stuff I agree with the posts by John, Robert and Dick.
Phil I have some field experience with series/parallel battery connections and how they cross feed, or don't. I've used parallel batteries in RVs and boats for 30 years and just blindly followed guidelines provided by the battery folks until the last ten years when battery monitors became available and I could observe what was happening during discharge and charge; which validated the previous recommendations.
The recommendations for parallel conections was that the batteries should be of the same make/size/type and age, sorta like the two tires in a dual setup. A battery has internal resistance (which varies depending on SOC) and to a charging source is just a load like a light bulb, connect two light bulbs in parallel and the one with the lowest resistance will hog all of the currrent. Identical batteries will have the same resistance and voltage at all state of charge levels so all will accept charging current and deliver current the same. They will also reach full charge at the same voltage and accept maintanance voltage the same. The phone companies have large rooms full of deep cycle batteries connected in series/parallel for power backup and use them for years/decades without problems.
I had one boat with six Trojan T-125s and two 8D gels, plus a Link 20 to monitor both banks. I often charged both banks in parallel with two chargers and it was interesting to observe how each bank took charge differently and how the chargers responded. Two things happened: the gels have low internal resistance and when both banks were at the same SOC the gels hogged the charge current, but if the GCs were significantly lower SOC they would take more charge current. If one bank had a higher SOC than the other and I connected them in parallel the higher SOC bank would discharge into the other until they had equalized their voltages. Gels are suseptable to damage from overvoltage
so I only interconnected the two banks during bulk charging (well sometimes a little into absorb). They were always finish charged and maintained with their respective chargers.
My experience, and the practices of the phone companies, validates the make/size/type/age rule, but there are ways to optimize the charging of different battery types.
pnichols wrote: wonder if some/all of those who claim to have any first hand field knowledge of the "feed off of each" problem with 12V parallel banks didn't have them wired wrong -> with the positive and negative feeds coming off the same battery of the parallel 12V set? This is NOT correct for perfect parallel battery load and charge balancing.
Having RVs and boats for decades, it's happened to me more than once. They were wired quite correctly. Each time, I considered it my own fault. Any parallel banks that were not isolated automatically got a manual switch like a Perko OFF/1/2/BOTH. I installed these switches to control charge and discharge and to isolate the banks when idle. I've had bad batteries drag down and kill their parallel partners when I neglectfully left the switches in the BOTH position. Keep in mind that this is only two or three times with probably a hundred plus batteries, but I don't know how many I would have wasted without switches. Now, of course, reliable isolators help in the MH, but I still run the switches on the boats.
Quote: Consider how abused golf cart batteries are in a daily life. Thick plates stand up to abuse. Not many batteries are rated for an 80% discharge without damage.
No lead acid battery will last long if cycled down that far! The studies I have seen indicate optimum longevity is at about the 50% point (batteryuniversity.com). The Az WindSun FAQ notes that traction batteries are often used this deep but doesn't tell you the whole story. You have to read that FAQ carefully because it covers a much broader range of batteries that you will find in any RV service.
If you start dissecting batteries, you will find that there is very little difference in plate design these days for batteries used in RV's. They are not solid plates of lead anymore. The AGM and the Firefly project batteries are in another class.
And, again, define 'golf cart' battery or 'deep cycle' in a way that I can see it in typical battery specifications. They are marketing terms and otherwise meaningless. Look at how much "Having RVs and boats for decades" there is and how little factual information and think about it. Anecdotes and personal experience are fine but are no substitute for properly qualified measures.
Quote: A battery has internal resistance (which varies depending on SOC) and to a charging source is just a load like a light bulb, connect two light bulbs in parallel and the one with the lowest resistance will hog all of the currrent
The thing is that battery resistance can change depending upon its state of charge. It has a voltage that depends upon state of charge and the existing current draw that makes it a completely different animal than a load like a light bulb. That is why you can charge both your house battery and your engine battery in parallel when going down the road as most RV's do.
Batteries connected in parallel will quickly reach an equilibrium voltage after which they will share in current (in or out) proportionate to their capacity and condition. That is a fundamental behavior that modern chargers depend upon as well.
What often gets missing in the parallel batteries bashing is the Peukert effect. The Smartgauge website has a good rundown on this and why there can be significant advantages to running batteries in parallel.
No matter what the components of your battery bank, proper wiring, use, and maintenance are necessary for optimum performance and life. If you have bad batteries you have a bad bank and need to correct the situation. Using low probability failure modes out of context is not a good rationale for supporting a point of view IMHO.
I see a lot of citing popularity as if it were a substantive argument. What is missing is the rationale behind this popularity and its actual measure. For good decisions, you should really get beyond what those in a specific self selected circle seem to be concluding, You need to know the why and you need to know the characteristics of the group. Your RV is not a golf cart and it isn't an alternative energy home site, either. Learn from the differences and also from the similarities.
But then, its a lot easier to just follow the lemmings off the cliff! ;-)
Offline
