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You do not need a BMS for a 4S system. Would be complete waste of money as is using lithium in your application.

 

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Two strings give redundancy without buying a spare cell

Who cares and why pay up for it? EV is different, loose a cell in a single string, and you are stranded. Loose a cell in a RV house battery is no big deal.

 

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I can see the logic in not using a BMS in a 4S system but it would be easy and ensure pack stays balanced. A BMS that small is cheap.

The BMS will never turn on, last thing you want to do is fully charge a Lithium battery which is required for a BMS to even turn itself on. Just float them at 13.8 volts. and set your Inverter to trip off-line at 11.5 volts.

I respectfully disagree that lithium is a waste of money for a RV house battery. To get the same 400AH capacity, you would need almost 800Ah in FLA and deal with the off gassing, maintenance and smell. I won't even get into the space required for a 800AH FLA 12v system.

I have no clue where you came up with that? A good higher end FLA like a Trojan Industrial or a Rolls 4000 or 5000 series has the exact same usable capacity of 80% capacity. However will live a lot longer than any Lithium battery. You would have to be pretty gullible to think otherwise. CALB, Winston, GBS if you could get a Chi-Com manufacture to honor a 1 year warranty tells you how long they will last. Trojan Industrial has a 10 year warranty with first 3 years full replacement plus 7 years prorated for 10 year total. Rolls 4000 and 5000 same 10 year warranty Trojan offers. Either cost 1/3 what Lithium cost and will last 5 times longer.

In the last 8 years I have done about 100 Off-Grid Solar Solar Systems where the client insisted on using CALB and GBS batteries in 24 and 48 volt configurations up to 1000 AH. All have been replaced with Lead Acid because the Chi-Com cells just do not last. None of them over discharged or over charged. They just loose capacity and internal resistance goes way up in a year or less. That is why DIY EV guys no longer use Chi-Coms.

 

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You disagree that FLA's have off-gassing, maintenance and smells?

It your batteries are gassing excesively would tell you the voltage is set too high

You can't argue that discharging past 50% will shorten the life of a FLA.

I never said anything otherwise now did I? What I said is both have the same usable capacity at 80% DOD. At 80% DOD, which would be a very rare event unless the owner is DIY and clueless, Trojan Industrial line still has twice the cycle and calendar life than Chi-Com LiFeP04.


I have designed around 50 RV systems for Tree Huggers that want to use solar, and some who listen and use other means of recharging. You size the battery for 3-day run time which is easy.This gives you 2-day Run Time with no sun or driving to recharge. Only a fool would size their battery for 1-day Run time. FWIW a fixed off-grid system uses 5 day reserve capacity to get that 20% DOD for maximum cycle life. Yes I get questioned about only using a 3-day reserve on RV's, but here is the deal, it is no big deal. A home system is used every stinking day, but not an RV which is part time use, and the batteries will last longer than stationary systems.



As for charging, well that is easy. Yep some people think solar will work, wrong. How many people are stupid enough to park their RV where in full sun with no shade issues from sun rise to sunset? Seen lots of folks spend a few thousand dollars on solar to charge their batteries with solar only to find out they still need a generator or shore power. Smart money is use a small wattage solar system as supplement, but rely on a $75 Electronic Battery Isolator and use the engine alternator to do the heavy lifting and charging. If they are parked more then two days will use a generator and charger.

I just saw the Rolls have a 7 year warranty, that is very impressive. I haven't heard of them till now. I have experience in traditional Trojan 12v FLA and they only provide ~3 years service in golf carts.

Rolls is to Rail Road and Marine as Trojan is to Golf Cart and Floor Sweeper machines. They have been around a long long time. The 5000 series carries 10 year warranty. Both Trojan and Rolls are 100% made in the USA.


You are right golf cart batteries last about 3 years as designed. Golf courses do not own golf carts, they lease them with 3 year contracts. But you are talking Trojan entry level Signature Series, not the Premium or Industrial lines.

While FLA are proven technology, I'd much rather prefer a sealed battery in my camper. I see Trojan has high capacity 250Ah 12v AGM's but they only have a 1 year warranty. Any thoughts on a quality AGM with at least 250Ah size and a great warranty? I could parallel two for a 500Ah pack in the future.

AGM has its place, a niche application place you really need to justify for the added expense. AGM cost twice as much and only last half as long as FLA. So in the end you are talking 400% higher cost. You would be better off using a decent LFP battery. AGM is great for locations:


1. Unusual installation orientation like on their side.
2. Where very high charge and discharge rates will be encountered.
3. Spills cannot be tolerate like aircraft for which AGM was invented for.
4. Extreme cold of -40 and lower.


Sounds like you might be stuck inside a 12 volt toy box. Last thing in the world you want to do is install Pb batteries in parallel. Guaranteed to cut cycle life in half. That is why battery manufactures suggest parallel installations. Smart money is if you need 500 AH, then buy 500 AH batteries. They will not be 12 volts, they will be 6 or 4 volt batteries wired in series. Say a pair of Rolls S-550 or Trojan SIND-06-610. Both Trojan and Rolls have had their batteries tested by 3rd party testing agency and put through IEC 61427 an real world cycle life test very few manufactures would ever make available to the public because it would make them look very bad. IEC61427 on Trojan Industrial Line-Up is 17 year cycle life and Rolls 5000 series to be at 15 years.

 

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Not quite $0.85 per amp hour but the cells we have are about $0.875 per amp hour now on eBay:

Completely meaningless.You do NOT PRICE BATTERIES based on AH because it tells you NOTHING. Your base battery cost on Watt Hour Capacity.

Which battery cost less?

1. LFP 100 AH cell = $125
2. LMO 100 AH cell = $140

By your logic the LFP cell is less expensive and is dead wrong. The LMO cell is less expensive.

Battery Watt Hour Capacity = Nominal Voltage x Amp Hours

100 AH LFP = 3.2 volts x 100 AH = 320 Watt Hours for 39-cents per WH.
100 AH LMO = 3.8 volts x 100 AH = 380 Watt Hours for 37-cents per WH.

 

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unfortunately that's how LFP cells are usually priced to compare them...

If you are comparing LFP to LFP with the same nominal voltage, then you can compare Amp Hour cost.

 

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I have considered the idea of a higher-voltage RV battery, but specifically to make 120 V AC integration better in a motorhome:

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.

 

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In fixed solar installations, sure, but in an RV?

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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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.

Well you would be surprised how many folks use Solar as their primary power source. As long as you keep panel wattages to less than 1000 watts which is the vast majority, 12 volts works just fine. Kicker is and this is the big kicker, if you have an Electronic Battery Isolator and drive at least every 3-days, then solar is just a wasted expense. Most setups I recommend and design only use Solar as a Supplement in the 200 to 400 watt range into a pair of 6-volt batteries wired for 12 volts. If truth be known Solar in that case is just show and tell and actually does not do much. You see this type of setup a lot in RV Rentals and Factor designs.



Then you have that crowd of tree-huggers who hate anything that uses gas or diesel. They will require a huge system in excess of 1000 watts, and that requires 24 volts or higher. Funny thing is if truth be told off-grid solar is not only 5 to 10 more expensive than buying power, but is also a very heavy polluter and Li batteries make that even worse because they require so much energy to make you never get an EROI. However I could care less, just pay me.

 

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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.

Brian I think you are overlooking some things. 24 and 48 volt super high efficiency air conditioners like Truckers, Off-Griders and Telecom use. I agree with your POV. If all you need is lighting, some entertainment like a TV/Radio/AV and low power devices 12 volts is just fine. But you have people who insist on electric cooking, refrigeration, and the impossible air conditioning requires a lot of power that a 12 volts is just not capable of doing safely, efficiently, and economically. How many 12 volt EV's do you see. Only a DIY would be that foolish. If the owner refuses to consider using propane for high energy requirements, you have limited your options and have to get creative.

I have built a many RV systems with both Solar and w/o Solar. Even rented several RV, and the factory units I have rented that have Air Conditioning all have a generator built-in using 24 volt batteries, and a 24 volt heat pump like Truckers use to cool their sleeper cabin. To do that demands higher voltage if solar is used. a 80-amp MPPT controller can only input 1000 watts and that is not enough power for heavy loads.

Besides anyone who is truly off-grid solar stationary requires a generator to perform routine maintenance and cover their your butt for cloudy spells. Otherwise you spend a lot of days in the dark and destroy your batteries prematurely.

I agree 12 volts makes the most sense sense for most applications. But when you throw electric cooking, electric refrigeration, and air conditioning into the mix, 12 volts is not going to cut it on solar. 250 MCM and larger copper wire is not practical or cheap. Let alone the experience and tooling to terminate such large cables and compound that with 1-hole Terminals or stabs expecting to have no issues loose connections and burning up with 200 to 400 amps flowing.

Do you wanna talk food trucks now? That is 240/120 territory and higher.

 

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in the US market, stick to Lifeline, Odyssey and Lifeline.

All good batteries, but there are more of equal quality and better. You mentioned Lifeline made by Concorde but they make even a better AGM in a much wider range of capacities and voltages called Sun Extender. All those mentioned are on the same boat as lithium with a worthless 1 year warranty. Another manufacture of high quality AGM batteries is Fullriver and carry a 7-year warranty. You can hammer them with 80% DOD with no problems in an RV application.

 

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1. Voltage sag under load falsely hitting low voltage cutoff on inverter reducing house battery usage, even with a fully charged battery. Especially apparent if running microwave or aircon. This wouldn't happen using LFP pack as lithium doesn't experience voltage sag nearly as bad.

Well you can wait for guesses or calculate it yourself pretty easily. Most of the AGM batteries you are interested in specify Internal Resistance. For example a Fullriver DC400-6; a 6-volt 400 AH AGM specifies Ri = .0016 Ohms. It would take 2 in series for 12 volts thus total Ri = 2 x .0016 Ohms = .0032 Ohms.

From there is simple Ohm's Law Voltage = Amps x Resistance. So at say C/4 or 100 amps x .0032 Ohms = .32 volts sag or on a 12 volt system is 2.7% loss. Add another 2 to 3% for cable and connectors and you met a reasonable 5% or less loss.

FWIW broaden your horizons. Go look at one of the 400 AH LFP cells. Just about all of them will list Ri. For 12 volts you would need 4 in series. So multiply the Ri by 4 and tell me if it is higher or lower than the 400 AH AGM. What you are going to gain from that will surprise you because it will be exact opposite of what you are expecting. It will tell you which battery has the higher Specific Power which is expressed as Watts / Kilogram. Put another way how high a C-Rate the battery is capable of. So go see what you find, and tell me what you think.

Last part of your question regarding FLA. A 6-volt 400 AH battery Ri= will be higher than AGM by about 50% or around .002 Ohms. So they will not have quite a high as a C-Rate. Here is what trips up people. Lithium Batteries C-Rate is a THERMAL LIMIT, not a Performance Specification like all other batteries are measured by. So when you see a CALB rated at say 3C continuous and 10C Burst is a Thermal Limit. At those levels voltage sag will be extreme . Now that you looked up a 400 AH Lithium, do the math at 3C. On the AGM is 1200 amps x .0032 = 3.84 volts.

 

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sportecoupe one more design tip. Be real careful with On-Line Wire Size Calculators. They will get you in trouble real quick. Most have a serious FLAW. They only calculate the Resistance required to meet a voltage drop. What they do not do is check their answer to see if it meets any listing agency thermal limits. The Flaw is it will give you too small of aa wire on short distances of 15 to 20 feet or less. Example say you have a 300- amp fuse and want 2% at 10 loop feet, and you will get an answer of 2/0 AWG copper which is too small fine for an EV because that is peak for a few seconds, but not on Power Wiring like an Inverter where loads are continuous.

My advice to you and anyone interested is use this Table. Find your Fuse or Breaker size, find the Distance. This Table is for Marine which exceeds SAE and NEC standards which means you can sleep at night. Note 300 Amps is not listed. For 300-Aamp Fuse requires a minimum 4/0 AWG Copper at 10-feet loop distance.



Note wire size is not based on Load Current. Minimum wire requirement is sized to the Fuse or Breaker size feeding the wire. A 3000 watt 12 volt Inverter requires a 300 amp circuit. Good luck with that and 4/0.

 

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LFP Ri is double some AGM batteries. I didn't expect that.

I tried to tell you that in PM's but you were not having any part of AGM out performing LFP. Amp Hour per Amp Hour, AGM out performs Lithium with respect to high current. I had to have you discover it for yourself. The math does not lie.

I will be real honest with you, From what you have stated in this thread, you have not justified an Inverter greater than 1000 watts, 1500 watts is over kill.

If you buy a quality Inverter/charger/ATS of say 1000 watts is continuous power, 2000 peak. So I know 1000 makes you nervous, then go with 1500/3000 which is way more than enough. You wil be able to drop conductor sizes down to 4 or 2 AWG. Remember you are using continuous currents for power and lighting. Not burst currents used in an EV. Different rules and practices for different applications.

For RV's I use Marine Standards because they exceed NEC and SAE codes. SAE and NEC do not take voltage sag into consideration. Additionally all marine cables are rated for 105 degrees C, wet/ damp, and if you buy Marine Battery Cable you get oil and gas resistance on top of high temp insulation. Marine Battery Cable is Class "I" stranding (super-flex) tinned copper. As good as you can get.

 

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If LiPo, how can they be made to work at 12V for a House bank?

They cannot and is of no concern for scum bag spammer. LiPo is the last thing you want for a house battery or any application requiring long life as LiPo only have roughly 100 cycles in them. LiPo's are used in RC aircraft where C-Rates run 20C or greater continuous. Extremely dangerous lithium batteries notorious for catching fire.



They do have a application in EV used as Drag Racers where you can put a very small battery in, just enough for 1 or 2 runs. Some of the new ones claim 100C-Rate for 10 seconds which is all you need for a drag race. A 20 pound battery vs a 1000 pound battery.

 

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Wire size calculations in aircraft get even crazier.

Stricter yes like NEC, and for good reason. Easy to hop out of an RV or EV on fire. Not so easy on a plane or boat.

What many on-line calculators fail to take into consideration is SHORT distances. They assume lengths of 15 feet or longer will be used. Many do not put a Fail - Safe check built-in to see if the wire can safely handle the current or not.

For example enter in 2-feet, 50 amps, and 3% loss and many sites will come back with 12 or 10 AWG. If you have experience in electrical power know immediately that is dangerous. Sure a 2-feet run of 12 AWG will have the resistance low enough so that the wire only losses .36 volts with 50 amps flowing. Trouble is it becomes a Space Heater and burns the insulation off the wire. You would know instinctively and from experience the minimum safe wire size for 50 amps using 105 degree Insulation is 6 AWG.


Now some on-line sites are aware of this and have put in the Sanity Check. Some learned the hard way when they got sued and had to replace someones home because they are incompetent pretending to be experts. I know this for fact because it happened on a Forum I moderate. Yes this forum can be sued giving inaccurate or false information.

So remember this. Wire size is based on the OCPD (Over Current Protection Device like a fuse or breaker) feeding the wire. If you have a 20-amp circuit, the minimum wire size must be 14 AWG or larger. Does not matter if the circuit only caries 1 amp. A OCPD only has one purpose and one purpose only, and that is to protect the wire connected to the LOAD side. It has no other purpose. They are not there or capable of preventing electrical shock or protect the utilization equipment. Only the wire and nothing else. That 3000 watt Inverter at 12 volts requires a 300 amp fuse and a minimum 250 MCM (aka 4/0) copper cable. Voltage drop of a short 10 feet is of no concern operating at 12 volts. On the same lines anything over say 15 feet because a huge concern using toy voltages like 12 and 24 volts. You could find yourself needing multiple parallel pairs of 750 MCM. Use a higher voltage and all that goes away or a lot further out before it becomes a problem.

Low Voltage + High Power = Fire Hazard. Anything over 500 watts is high power for 12 volts.

 

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Looking at heating for hot water and even the van air, I may need to abandon the want for an all electric camper and add propane to the requirements list.

I was wondering how long it would take you to realize that. I would not have an RV without propane to do the cooking, heating, refrigeration, and generator. That is why many come with Propane Tanks. Batteries are for lights and entertainment.

 

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I never charge 4S LFP higher than 14V, usually 13.8V.

Under load stays around 13.1-2 cutoff at 12V.

Avoid the shoulders, gain longevity, no need to balance.

I agree with this. For 12 and 24 volt LFP systems a BMS is just a waste of time and money, and will kill your pack. I do not even use one for 32S 96 volt pack in my golf cart. All successful Solar Systems I have designed do not use any BMS.


Just Bottom Balanced the cells, charge to 13.8 volts, and LVD at 12 volts. This really works great on solar systems because you just Float Charge the batteries and never disconnect panels. With a POS BMS, you have to terminate charge and disconnect the Solar Panels which is STUPID because if the batteries are charged by noon, you disconnect the panels and go on batteries while the Sun is still up and usable. All it does is kill the batteries faster. Let them Float and all you use is power from the panels and save your batteries for night and rainy spells.

Never came across a load wasn't just fine with that, much less V sag than lead for winches, huge inverters etc.

This part I do not fully agree with. LFP are drop in replacements for Pb, and no changes are required. However Chi-Com LFP batteries do not have the high C-Rates of a good lead acid, and there is no contest against AGM will run circles around any Chi-Com LFP. A Chi-Com LFP internal resistance is 2 to 3 times higher than than a Pb battery of same AH capacity. You can take say a 55 AH Optima Red Top and put it up against a 100 AH CALB, and the Optima will outperform the LFP with respect to voltage sag by a large margin. To get really low Ri would require you to buy a quality LFP cell from reputable manufactures like A123 Systems or LG Chem, but you will pay up some 400% to get them if they were available.

 

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Most companies building Class B and C motorhomes using the ProMaster went with the gas engine from the beginning, presumably for cost savings. All manufacturers have had challenges getting diesel engines approved

That you can blame on the Employment Prevention Agency. Last thing they want in the USA is efficient diesel engines. Go to about any other country in the world, and passenger car fleets are mostly diesel engines. They get much better gas mileage. If it were not bad enough the enough the EPA make sit almost impossible to pass ever increasing emission standards no manufacture can can keep up with, Those that do pass are forced to pass those cost on to consumers. For those manufactures that do offer diesel engine options in the USA, EPA has an answer for it by making refining requirements so high making diesel significantly higher price than gasoline so no one will buy the cars because the fuel is too expensive. The Employment Prevention Agency needs to go and be replaced. EPA is Nixon's last one finger salute to America, he gave us the EPA before he resigned and laughing at us now. He made it look like a Democrat program.

 

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Partially because diesel fuel is much cheaper then petrol (gasoline) in most other countries.

Correct and the EPA made damn sure Diesel in the USA would be higher by making refineries refine diesel more than other countries. All done to discourage deisel fuel use by design. That means the EPA does not care about efficiency and want to punish the citizens.

Also EPA restrictions installed for US market diesels makes them very complicated engines and expensive to fix. Example is DEF or diesel exhaust fluid and the regen system. Run out of DEF and you cannot just add more and drive, it needs reset by the dealer to even start the engine again in some cases.

Again intentional by design to keep diesels out of the country and punish those that can get in. Want a diesel engine. By a Dodge Ram Truck. No DEF required.