400AH lithium cells? Best price per AH? $0.85/ AH?
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Normal RV practice for capacities larger than is practical with a single battery is to use two 6V batteries in series, most commonly of the GC2 size simply because deep-cycle batteries in this size are readily and economically available. Yes, some parallel 12V two-battery installations are used (I have one in a trailer), usually to be able to use cheap "RV/marine dual purpose" 12V batteries.
For capacity beyond about 200 Ah @ 12V, the typical practice is to use four 6 V GC2 batteries. While just two large 6V batteries in series would be ideal, most builders, owners, and maintainers don't want to deal with the weight of a battery large enough to handle half of this total capacity in a single box; that Trojan SIND-06-610 weighs 100 kg. Three 4V batteries in series is a rational way to handle this, but it's hard to find a 4V battery as small as 500 Ah, and even if you find one it's going to be at least 50 kg.
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Dont overthink this.
1. Lithium batteries freeze easily and are expensive
2. Lead chemistry batteries are HEAVY about 400 pounds.
If you plan to use this battery when the weather drops below 40F you are pretty much stuck with FLA or AGM
If weight is the main issue , you need lithium.
Personally I would go with a higher voltage battery running a DC to DC convertor so I could put a bunch of small cells in series.
You can buy a 24 Volt , 200 AH battery pack with a steel case and built in charger (Standard battery pack for electric pallet jacks) for about $2000 if you go with lead
If you decide on lithium , a 48 volt pack with 100 AH cells would provide the same power and it's easier to find 100AH cells.
1. Lithium batteries freeze easily and are expensive
2. Lead chemistry batteries are HEAVY about 400 pounds.
If you plan to use this battery when the weather drops below 40F you are pretty much stuck with FLA or AGM
If weight is the main issue , you need lithium.
Personally I would go with a higher voltage battery running a DC to DC convertor so I could put a bunch of small cells in series.
You can buy a 24 Volt , 200 AH battery pack with a steel case and built in charger (Standard battery pack for electric pallet jacks) for about $2000 if you go with lead
If you decide on lithium , a 48 volt pack with 100 AH cells would provide the same power and it's easier to find 100AH cells.
This is one way to reduce problems of paralleling, but if you're building a pack from individual cells is that really a problem? Production EVs normally parallel at least two cells at the lowest level, and those using tiny 18650 cells parallel dozens of them at the lowest level.
The DC to DC converter would provide a nicely regulated output voltage, but it would also add conversion loss. A similar problem would exist on the charging side, with none of the usual RV charging sources able to charge the battery without the cost and efficiency loss of a voltage conversion step.
I have considered the idea of a higher-voltage RV battery, but specifically to make 120 V AC integration better in a motorhome: with a nominal battery voltage over the peak-to-peak voltage of 120 VRMS, the inverter could be very simple and efficient, the raw 3-phase output of a typical "inverter" type generator could be used by a rectifying charge controller without an unnecessary 60 Hz step, and a regenerative braking system could produce several kilowatts without excessively high current. All of this is probably viable only with substantial custom component construction.
Nope.
Cannot **charge** (much) below freezing,
nothing to do with "freezing"
but discharge is fine down to far below
Storage often even lower no problem.
See the spec sheets for Winston, CALB etc
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If you are comparing LFP to LFP with the same nominal voltage, then you can compare Amp Hour cost.
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Well I am hear to tell you is it is common practice to run at 24 volts, and a few 48 volt systems. But be warned going to a higher voltage eliminates your prime power source, the 12 volt alternator to recharge your batteries whenever engine is running. Pretty much means you would need a generator.
In fixed solar installations, sure, but in an RV? There are lots of 24 V vehicles (mostly military), but I've never heard of anyone doing that in an RV - do you have links to any RV which comes this way, or a company converting them? I wonder what they use for conversion from battery voltage down to 12 V (nominal).
In a quick search I only found a single example of a 24 V RV system (DIY RV Solar), and that was a poor choice driven only by availability of a cheap inverter/charger.
I already identified the issue with charging from the engine, which could be done with a DC-to-DC charger.
I considered 48 V, but I don't think I would bother with 24 V or 48 V, which for an RV doesn't seem high enough to provide much benefit to offset the hassles of being at anything other than 12 V.
Yes, true.
Savings in wire gauge rarely offsets cost of voltage conversion gadgetry.
But for those with some good reason I can't imagine, 24V and even 48V alternators do exist, can be custom wound.
Maybe on a boat using electric propulsion or very big winches, bow thrusters etc
Savings in wire gauge rarely offsets cost of voltage conversion gadgetry.
But for those with some good reason I can't imagine, 24V and even 48V alternators do exist, can be custom wound.
Maybe on a boat using electric propulsion or very big winches, bow thrusters etc
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Sure, but you got caught in a 12 volt box. There are two applications that demand 24 volts and once in a while 48 volts.
Any solar application with 1000 watts or more require 24 volts. IMO anything above 500 watts. That has to do with economics, efficiency, space, and safety. The largest practical Charge Controllers you can find today are 80 amps. At 12 volt battery input limit is 1000 watts. Any higher requires two expensive controllers. At 24 volts only requires a 40-Amp Controller. A good 80 amp controller will cost you $600 and up. A good 40 to 45 amp controller can be had around $300 to $400. Savings continue to wiring because you use smaller wiring.
The second application is perhaps something you have over looked. Class A Motor Homes/RV with diesel engines and 24 volt electrical systems. Like a Tour Bus Conversion with all the Bells and Whistles.
Either way just use a good Buck DC to DC Converter for 12 volt gadgets and gizmos if needed. Physically makes no difference if 12, 24, or a rare 48 volts is used in an RV. From a practice POV all the voltages are treated the same being low voltage below 50 volts. Only real issue is sacrifices you may encounter using 24 volts in a 12 volt vehicle. The RV market makes a lot of 12 volt gizmos and gadgets you may have to give up, or provide a converter for. The deal breaker IMO is loosing the engine alternator as a primary power source. However people who use solar have no fear of loosing the alternator. They just use a genny or do without for times of clouds/rain.
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OP used a/h so I used it. Sorry it offended you.
I personally would not use LMO (lithium manganese oxide) in an RV, especially at 12V, not compatible with typical alternator voltages. Also too prone to thermal runaway, especially if not managed.
That's a good example of where it would make sense. Those are a tiny fraction of the RV world (I don't think even a normal diesel Class A would be 24 volt).
Sure, but we're discussing an RV, and one that is unlikely (I would guess) to have a massive solar installation and will almost certainly have a 12 volt automotive charging system. Carrying a generator just because the system wasn't properly set up to charge from the vehicle would be silly, and doing without power is not reasonable.
48V as a House bank makes little sense to me, would need to run a separate 12V bank for normal devices, converters are crazy expensive. Maybe if you want an all-mains setup, run everything off a huge 48V inverter?
But no, silly to give up alt charging when it's already there.
Even 24V to me violates KISS. SCs are not a major expense overall, and wiring runs are one time, don't break like conversion gadgets.
From a practical economics POV, only if the alt is 24V already, or if really needed for important high-current devices, maybe say winches?
But no, silly to give up alt charging when it's already there.
Even 24V to me violates KISS. SCs are not a major expense overall, and wiring runs are one time, don't break like conversion gadgets.
From a practical economics POV, only if the alt is 24V already, or if really needed for important high-current devices, maybe say winches?
24 volt alternators are for vehicles that are 24 volt (military, maybe still some large commercial vehicles). 48 volt? Who knows... I don't know what is used on boats. I checked a random bow thruster manufacturer, and their smaller units are 12 volt while the largest are 24 volt.
Yes, LFP is the only safe non-lead chemistry for any small space / mobile House bank use case. And new big prismatics, not a science projects of cylindricals or ex-EV banks.
Completely agree AGM are poor value, use only if install space requires, or money not an issue.
Yes Rolls / Surrette is fantastic. But only FLA. Their AGM are relabeled chinese.
But that has never been an issue for me even in a tightly sealed living space, long as good controlled ventilation is in place. Put the exhaust port in the bank area.
Yes, some people are hypersensitive or dislike the smell, so box the bank up and vent to the outside, NBD.
> Chi-Com LiFeP04
Please define, and link to LFP that you consider better quality wrt longevity.
> Only a fool would size their battery for 1-day Run time
True for lead maybe, but not if ICE recharging on demand is convenient, and solar there for the long tail. LFP makes the solar redundant.
> not an RV which is part time use
millions live mobile full-time
> You are right golf cart batteries last about 3 years as designed.
Well coddled, even just-decent GCs can go 6-7 years and still be above 70% SoH.
Yes Rolls / Surrette is fantastic. But only FLA. Their AGM are relabeled chinese.
Normal usage to vendor charging specs produces some gassing.
But that has never been an issue for me even in a tightly sealed living space, long as good controlled ventilation is in place. Put the exhaust port in the bank area.
Yes, some people are hypersensitive or dislike the smell, so box the bank up and vent to the outside, NBD.
> Chi-Com LiFeP04
Please define, and link to LFP that you consider better quality wrt longevity.
> Only a fool would size their battery for 1-day Run time
True for lead maybe, but not if ICE recharging on demand is convenient, and solar there for the long tail. LFP makes the solar redundant.
> not an RV which is part time use
millions live mobile full-time
> You are right golf cart batteries last about 3 years as designed.
Well coddled, even just-decent GCs can go 6-7 years and still be above 70% SoH.
Finally!
I think
> Guaranteed to cut cycle life in half
is overstating the case though, for just a few paralleled strings.
I personally like / need two strings for redundancy, in critical and/or remote full-time use cases.
But it is indeed my understanding, that going **past 3-4 strings**
(not of single cells paralleled to get higher AH, but of multiple-unit strings)
will result in balancing issues and shorter overall cycle lifetimes.
Can you confirm that is the case? Are there other issues? Can you concisely describe **why** paralleling too many strings is bad?
Any links or cites to back it up?
Would be greatly appreciated
$400 for local pickup Deka GCs, gets more AH, and plenty left over for a top-notch 40A marine charger, panel kit and a genny.
From top-notch vendors, makers like
Systems: OceanPlanet (Lithionics), Victron, MasterVolt, Redarc (Oz specific?)
Bare cells: Winston/Thundersky/Voltronix, CALB, GBS, A123 & Sinopoly
If I have missed any sold to consumers, please let me know.
Their spec'd cycle lifetimes appear to actually be very conservative, perhaps building in some expected abuse.
Very much unlike the lead batt industry, where even perfect coddling rarely matches claimed lab performance, marketing departments have too much influence vs engineering.
But IMO, following the vendor LFP charging specs for day to day usage is IMO inherently abusive, compared to avoiding the voltage shoulders.
With the latter, looks like decades' daily use is possible, certainly 3-5x their lifetime estimates,
if well coddled, no big mistakes, and in a gentle House cycling use case. It is possible that calendar lifespan will end up being more influential than # cycles.
Kindest explanation is, longevity is not their primary goal, violent-currents military and EV usage is the assumption for their testing and research.
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