How to Check An 8D

[JCTex]

I've decided to go with 6V AGM's (Lifeline 6CT) ILO LithiumIronPhosphate. After doing the numbers, I can get 450Ah at 50% DOD with AGM for $5.41/Ah. I can get the same Ah in a LFP package for $9.18/Ah. Although the weight savings would be 186 lbs vs 540 lbs, I just can't justify the extra cost TODAY. Now, if I consider the AGM's loosing10-15% Ah storage er year over the next 4 yrs vs about 3-5%/yr for the LithiumIronPhosphate, then I probably should go lithium. However, it is still in uncertain territory whether the lithium swill hold capacity that well. So, I'm going with stuff I know.

 

My problem is I have not started boondocking yet, and don't really know my daily Ah need. I've done it in great detail on paper; but not in real life. On paper, I may use ~160Ah per day. I can get 300 300Ah @ 50% DOD with 2air, and 450Ah @ 50% DOD WITH 3 pair. I don't want to buy wo testing use first.

 

I have 2 8's that are OE 6 1/2 years old but seem to,work fine when shore power is off. "Fine" is defined, however, as without the res refer wired into the inverter panel, yet. Coach has 39k mi and was part-timed in mostly on hookups by PO's. I'd like to use my OE to start boondocking to test my actual needs.

 

MY QUESTION is whether there is a way to check how good or bad these old batteries are?

 

Jerry

[Yarome]

MY QUESTION is whether there is a way to check how good or bad these old batteries are?

 

Sure. Charge them completely, put on a known load (X amps), then measure specific gravity ever hour until it hits a target soc percentage (80, 75, 50... whatever). That should give you enough info to approximate the current ah capacity. Compare that to the rated ah on the battery to get a fairly down and dirty idea of the overall health of the battery.

[Yarome]

As far as the LFP's go.. I'm still on the fence as well. They DO have some clear advantages, and even at a higher ah/$ value, they actually still about break even, cost wise, with decent AGM's. You're not really loosing any money that way, but you may have other equipment that may need to be upgraded, and then there is the learning curve and care.

 

All things aside it is a little tempting since you actually gain a significant amount of "available" ah's on tap, weight/footprint reduction, and performance advantages.

 

I'll probably ride out my AGM's to get my money back out of those before I make the jump, but straight $ to ah comparisons don't give a very clear picture. When I was dinking around with some numbers I was calculating "available" ah's over the expected lifespan of each. It was pretty much a wash between my AGM's (lifelines) and LFP cells. LFP's DO sting a bit more initially though don't they.

[Jack Mayer]

Bear in mind that the residential fridge is going to use about 100-120 Ah DC per 24 hours. So factor that in.

 

On the LFP bank, you do have the capacity decline to consider, and it is perhaps a lot more than you might expect in MOST installations. That is because the LFPs are very finicky about a temperate environment. It seems that they maintain best capacity when handled like a delicate human. No temperature extremes at all. If you are comfortable, then they are comfortable. Otherwise, the capacity decline can be more significant than the AGMs.

[Daveh]

Jack have you recieved more feedback on lifepo4? I suspect you are correct but I was thinking at this point it was only a suspicion, more likely than not

[Smitty77_7]

If you have he headroom, I found that four Lifeline L16's fit in the same footprint as two 8D's. This gives us 800AH, so 400AH at 50% SOC. This is in an 04 CC Allure.

 

We are not on an energy diet, and 5 months ago added the Samsung residential. With a 100% SOC at say 5:00-6:00PM, we will sometimes see just below 80% SOC when I get up to turn on the coffee pot. This will dip us down to 75-76% SOC while it is brewing, but back up to 78-79% SOC within 10 mins of turning the coffee pot off. At night, we use about 4 hours of TV with the Receiver on, and the related Direct TV box too. Hydro Hot for maybe 20 mins, while washing dishes, then off for the night. Run lots of lights, but the ones we run our LED. Two computers and two phones charged overnight too. (In cold areas, we use a Heat Buddy for supplemental heat.) DW usually will run the Microwave for say up to 10-15 mins at night for dinner prep. If we need the convection, we fire up the generator, which then also adds a bit more charge to the battery bank.

 

We have 1200W 48V High Efficiency Solar Panels, feeding a MidNite Classic. It usually has back to 100% SOC by 11:00AM, sometimes Noon. And that is with AM usage, including the DW's hair curler.

 

If you feel you will be doing enough boon docking, having excess AH capacity gives you some peace of mind. Also be sure to check our charger. Many have an AGM setting, but Lifeline has a different set of parameters, so look to see if yours has a Lifeline setting, or is customizable to set up the Lifeline parameters. (We changed over the MS2800 PSW and related components, with the battery bank update.)

 

Ours is a good size bank, but for sure you can go larger. One CC Intrigue owner has 5 Lifeline 8D's tucked into his battery bay, along with one wet cell 8D for the chassis. Only one of the AGM's is on it's side. (Pictures over on the Yahoo User Group for CC, believe his name is Dallas.)

 

Best of luck to you, have fun:)!

Smitty

[reed and elaine]

We have noted no noticeable decline in our LFP bank in two years. The maximum outside temperatures have been -20 F (-29 C) and 110 F (45 C). Battery voltage is limited by the BMS to 3.4 V per cell.

 

It is to be noted that we merely left the rig at son's place at 7800' in northern NM when we flew to Guatemala and Honduras for 12 weeks a year ago. The batteries did charge/discharge at the low temperatures but it was at low charge rates. We have sufficient energy storage (180 amp hours at 48 V nominal = 780 amp-hours at 12 V nominal = 8600 W-hr = 7k-W hr usable power at 20% SOC) to run a couple of 50 watt bulbs in the front bay overnight to keep the battery suite above 0 C. We have done this on cold nights in the main bay to keep the pipes from freezing. We would insulate the front bay if we were to camp in very cold weather. We leave the doors of front bay open during day in summer to permit cooling by the fans that are integral to the batteries.

 

We have always run the Dometic fridge on solar during the day and 24 hours a day if we know there will be a sunny day following since we wind up with a -3.5 kW-hr deficit the following morning. Right now there is sufficient insolation that we are turning the hot water onto AC in the morning (we do not turn on hot water normally until we need it) and it takes about 1.7 kW to heat the water (and then cycles). We are using between 7 and 8 kW-hr daily. When the weather or terrain changes, our power management procedure changes. We lasted 6 days in the rain forest of the Olympic Peninsula and were only down to 50% SOC. We ran everything on propane, turned off the inverter when not in use but still used the microwave and watched our Mystery Theater DVDs each night. The monitor showed we were obtaining 300 W-hr through the trees but we were still losing 1 kW-hr a day.

 

We went with LFP for several reasons

1. Previous rig was destroyed in 70 vehicle pileup in fog between Vera Cruz and Puebla, Mexico (we had been quite happy with glass mats)

2. The weight differential as Pebbledropper noted. Our weight difference would be our 254 pounds versus 700 to 800 pounds. This is important in a lightweight 5th wheel but not as important with a coach. An extra 500 to 600 pounds would overstress the front bay and push rear axle weight of dualie near maximum. Right now we are 800 pounds or so below max weight of rear axle (weigh with 80 gallons of fuel in pickup, six x 6 gallon Jerrycan of water, 81 gallons of freshwater and 2 to 4 weeks of foodstuffs)

3. Our son is in the business and designed/fabricated as family project and charged the parts at contractor rates. He is following the Tesla battery closely

 

We are Goldilockers as in "not to hot and not to cold" and go north and/or up in elevation when it gets to hot and reverse when it gets to cold. We do not overstress ourselves or the battery bank.

 

If satisfied with lead acid and do not have weight concerns, then I would stay with lead-acid. Like everything else, it is choice of life styles and we are 95% dry camping/boondocking (dry camping for us is mootchdocking in kids' backyards and BLM/Forest Service CGs and boondocking is "dispersed camping" on public lands)

 

Reed and Elaine

[reed and elaine]

Peukert's Law and Peukert Disadvantage cae mean a lot of things and it gets reasonably technical fast but understood at high school physics leve.. The reality of LFP is

 

Much lighter weight

Much higher electrical efficiency

Much longer working/cycle life

Faster recharge

 

Lighter weight is mentioned above

 

Ripped the below off an Aussie forum. Aussie caravaners are far ahead of US in use of solar and lithium than the US. A much higher percentage are boondockers with quite small rigs and fairly low power requirements. (http://www.camperscircle.com/12555/lithium-iron-phosphate-batteries-for-camping/)

 

"... Lead acid batteries are typically 70% - 85% charge efficient LiFeTech lithium batteries are approx 98% charge efficient.

 

The lithium battery will charge better/faster than a lead acid battery and this can be particularly important where only limited charging methods are available such as from solar panels... "

 

Our experience has been that the charge rate is linear. We get to float and everything is fully charged by 11 am (unless we start the day at -3.5 kW-hrs or more and we are running hot water and fridge on AC). Float/Absorb stage takes less than an hour.

 

Our experience with our glass mats was that it got up to 90% SOC fairly rapidly and then took forever to get to 100%.

 

Reed and Elaine

[Jack Mayer]

What Reed posted above is pretty much my opinion as well.

 

I do have AGM batteries (6xL16 Fullriver for a total of 1200 Ah), but only because I don't mind the weight. And did not want to incur the expense on a coach that will likely be sold within 2 years.

 

I'll point out, though, that those using LFPs that are carefully measuring ARE finding a capacity decline over time. In some cases I've seen reported the decline is pretty significant from a cost per storage unit measure. But I don't personally have an LFP bank, so I'll limit my comments to that. It certainly would not stop me from going that route, and I may be in the somewhat near future in a small motorhome where the weight issue will be significant.

[reed and elaine]

Have not heard of significant decline in carrying capacity. Liberty Coaches which fabricates high end Prevost coaches uses LFP in their Liberty Ladies ($1.8 M and up) and claim that they have run their LFP banks through 2000 full cycles with little degradation and expect 10 years or more life span. I noted this on a forum and a Liberty Lady owner wrote that the 2000 full cycles was old news and that Liberty Coaches had gone through a lot more cycles since the 2000 level full-cycle was reached. Liberty Coaches has given reasons for going with LFP on their web-site. They have the usual:

 

less weight, supposedly 1000#

much better charging rate etc

 

and then there is the kicker for the really rich who trade in their Liberty Ladies every two years or so, and this is that they will not have to trade out their battery suites upon trade-in.

 

From "A Comparitive of Lithium-Ion Batteries

http://www-scf.usc.edu/~rzhao/LFP_study.pdf;

 

LiFePO cells experience a slower rate of capacity loss (aka greater calendar-life) than lithium-ion battery chemistries such as LiCoO
cobalt or LiMn₂O₄manganese spinel lithium-ion polymer batteries or lithium-ion batteries.^] After one year on the shelf, a LiFePO
cell typically has approximately the same energy density as a LiCoO₂ Li-ion cell, because of LFP's slower decline of energy density. Thereafter, LiFePO likely has a higher energy density.

 

 

 

From the EETV Motor Verks (a vendor) http://evtv.me/2012/06/battery-jump-shift/

One of the disadvantages of LiFePo4 cells compared to other lithium chemistries is a rather sorry performance in cold weather. While not nearly as debilitating as it was in the old lead acid battery era, the decrease in capacity of LiFePo4 cells is very much a factor.

At a temperature of -20C, and a discharge rate of 0.3C, the SE series of cells will provide 71.9% of capacity. Your 100Ah cell will provide a discouraging 72 amp-hours at that temperature. This is of course even worse at higher discharge rates.

The CA series cells provide a dramatic improvement in cold weather performance with 87.49 % of the original capacity. Your 100 Ah cell now provides a little better than 87 Ah at -20C or -4 degrees Fahrenheit at a 0.3C discharge rate.

CYCLE LIFE

One of the most important advantages of LiFePo4 cells compared to other lithium chemistries and certainly with Pb chemistry cells is their very long life. We measure this life in the number of expected charge/discharge cycles to 80% discharge and until the cell exhibits 80% of its original capacity..

This is projected by doing several hundred charge/discharge cycles at 1C and to 100% depth of discharge and extrapolating the data to the point where the cell exhibits 80% of its original capacity. This calculation is also improved by assuming an 80% depth of discharge instead of the tested 100%.

At 290 cycles to 100% at 1C,(1 C is discharging total charge in one hour) the SE series cells show about 85% of original capacity. The CA series has upped that to about 91%. This represents a huge increase in cycle life for the CA series cell.

Assuming that this had extrapolated to a 2000 cycle life at 80% DOD, the new cells would imply 3300 cycles. For 3000 cycles at 70% DOD, the CA cells should see 5000 cycles

Chinese Aviation Lithium Batteries (CALB) are CA batteries and are what we use.

[Daveh]

It does seem clear that some who have carefully monitored lithiums have noticed a decline. It also seems clear that some, in the boating world specifically, that have monitored carefully found no decline. In the RV world, neither Reed nor Bill Joyce have noted decline, although technomadia has measured decline. Some accounts I have read state that the cells are above spec new so even with decline they remain in spec. I have not seen any report of someone using lithiums that experienced decline and consequently stopped using the batteries or had anything else negative to say. The reviews are very positive. I have read that temperature extremes cause decline but I have also read this slow decline takes place on batteries being charged and simply held for sale at room temperature (the decline occurs regardless of temperature or cycles used). What also seems clear is that we are dealing with batteries from various overseas manufacturers that are evolving and the batteries themselves can be difficult to source. There appears to be variance amongst the manufacturers. From all of this it is hard to draw any firm conclusions except that if you want all of the significant benefits of LiFePO4 it may be wise to size your bank a little larger in anticipation of some decline and take measures to avoid extreme temperatures. Other than that people seem happy with LiFeP04 and the evidence re decline remains anedotal.

[reed and elaine]

Cherie and Chris (Technomadia) and Ron Jones were among the first with LFP for RV use. Their battery suites are 3 to 4 years old LFP formulations are changing every year and technology has undoubtedly gone past what we have been using for two yea.rs. Have been in e-mail conversation with Ron and Cherie/Chris of and on for two years. It is still a small coterie of LFP users

 

Agree with Daveh that it is best to oversize bank - but then one decides to increase solar panels - and then....

Just like Cracker Jacks "the more you eat, the more you want."

[Rich Stiner]

First of all... there is some fantastic detail on the aspects of battery choices here. Kudos to all who contributed. I'm absorbing the material, as I am in "the electron biz", but I am not yet at the point to pull the Buck$Zooka trigger on anything.

 

However, I spotted something in the conversation that triggered an autonomic response from me: Consumption reduction. We live in a fantastic time for reducing power consumption, and the technology is coming at us so fast, be barely have the opportunity to shift mental gears - jettisoning "old-think". LEDs put the boon in boondocking, but there's more that can be done for very little money. I just bought four 12V 24" monitors for $139 each (Acer) at Costco (for a project at work). They also have a 12V 28" for $179 right now.

 

In reading the material here, I'm sure many of you already know this - but it must be said for any newbies that click on the thread title: Every conversion from one power type to another experiences a significant loss of efficiency. Going from DC to AC with an inverter is good for warming the power management compartment, but not so good for making optimal use of available battery capacity.

 

I saw the word "DVD" above, and I'd like to point out that you can store a lot of DVDs or a few Blu-Rays on SDs, micro SDs, SSDs, or even thumb drives. I have copied my audio library to a large hard drive for backup, and I have 128G solid-state cards for transferring from the hard drive, CDs, Blu-Rays and DVDs when on power. This would leave me with several days worth of video/audio entertainment using no moving parts (spinning disks are a waste of power). Many LED screens use 12 volts now, and have USB ports. A 128G thumb drive plugged into your modern TV will use very low amperage - with no need to turn the inverter on for entertainment purposes... unless you want to fire up the surround sound with a subwoofer.

 

For those with high-speed internet while boondocking, the Ultraviolet feature with modern movies is another inverter-free alternative.

[reed and elaine]

OCD2AT

 

Your thoughts are extremely good. Power management is very important and the inefficiency of inverter usage to go from DC to AC is fairly high.

 

1. 12 V LED screens. But the cheapie 120 V works

2. Residential fridges that run on 12 or 24 V. But the Dometic works and a residential is expensive

3. Split-level air conditioners that run on 12, 24, or 48 V. But we try to avoid places where it is hot

 

Should love to do all of these three, especially the modern LED screen.

 

May someday put our DVDs onto solid state cards as you suggest. We do have a large stack of BBC Mystery Theater (Inspector Lewis, Inspector Morse, Poirot, Holmes, etc) and it would be nice to have these on a card instead of taking up so much space.

 

We often have no internet when we boondock otherwise we would look into that Ultraviolet feature. But we do have sufficient solar/battery suite that we are now running Dometic fridge on AC 24 hours a day and running the water heater on AC during the day as well. This comes under power management and we can do this in New Mexico, Colorado, and Wyoming from April to October depending on weather. It is back to propane on overcast and rainy days. If boondocking with shade for a major portion of the day, we are back to propane for water and fridge. Sometimes we intentionally site rig so that we have solar in morning with shade in mid-afternoon. Try to set rig so that the awning is to the east.

Reed and Elaine

[Jack Mayer]

I think Dave (Daveh) summarized it very well. Some have reported decline and some have not. Most who report decline have seen the batteries in somewhat challenging environments. Some of the decline may be attributed to older battery technology. As I said, none of this would sway me from buying LFPs. I also am a firm believer in having "more than you need" within some limits. Because you do not want to be caught short and have to run the bank below acceptable performance levels. Also, bear in mind the decline (if even reported) is over a long period of time - years. If I put in an LFP bank I'd probably want to make sure that it was in relatively moderate environment. That just seems like a wise move considering some of the reports. And is relatively easy to do.

 

The reduced power demands that are pretty easy to achieve with modern technology also is a big consideration. When designing a rig I believe an effort in that direction pays big dividends and is pretty easy to do. Even with my residential fridge, I find this coach takes very little power to live an easy lifestyle. Now if I could just get DTV to make a DVR that did not consume scads of power we would be better off. It is pitiful when your sat receiver uses 30-50% of the power of your refrigerator.

[Daveh]

Thanks OCD2AT for some thought provoking comments.

 

One last thing Pebbledropper is your cost estimate on LiFePO4. $9.18/Ah is way above today's street cost. That cost must be based on one of those premade drop in replacement package but that cost almost double what you need to pay. If you look at the site Reed quoted http://store.evtv.me/proddetail.php?prod=ca100fi you will see the newer CALB CA100FI 100Ah LiFePo4 Cell for $139.00 per cell and assuming a 70% dod for a per Ah price of $7.94 or if you want to take a chance on their liquidation sale for batteries without warranty you could get the CALB SE100AHA 100Ah for $95 per cell and assuming a 70% dod for a per Ah price of 5.40. This is a straight cost comparison before considering LFP longer cycle life, weight reduction, faster charging and lack of power fade.

[reed and elaine]

I read Chris Dunphy's discussion on LFP battery capacity decline on his website (http://www.technomadia.com/2015/02/living-the-lithium-lifestyle-3-5-year-lithium-rv-battery-update/) and he candidly admits to mistakes that will occur to the DIY pioneer in this field.

 

Temperature: They were having their bus worked on in Arizona where the ambient temperature was above 110 F.(43 C). Their vehicle was parked in the sun on blacktop. Their battery suite was in the same small enclosed compartment as their inverter so the temperature was probably far greater than 110 F. Our battery suite is in the front bay and is shaded by the front end of the 5th wheel (does this structure have a name) and we leave the front hatch open when operating on warm days (never been over 100 F (38 C). We also open the side hatch (propane tank access) on shady side for cross ventilation. We may put in a 12 V fan in future in consideration of this potential problem. Extreme cold can be a problem in charging. We left our rig one winter at son's place where it go to -20 F (-29 C) without disconnecting battery suite; however, the charge state was fairly high and the rate of charge was minimal. We would install a 50 W bulb in the bay and insulate the if we expected to live in rig at very cold levels (and that is not something we would choose to do). A 50 W heating pad on each set (2 batteries) would do the same.

 

To high a voltage for floatation: They may have been hooked up to line power for months at a time (when rig was being worked on) so that they were always at float. Their float level is the now recommended 3.4 V per cell. We have not hooked into line power but once in two years so our SOC will go between 100% (at 3.4 V per cell) and 60% daily if we are profligate with energy. So being hooked into line power for a long time may not be a good idea.

 

Lack of Balance / Laggard Cell. Their Energy Management System (EMS) of 4 years ago did not do the job that more modern Battery Management Systems (BMS) do. The following is quoted from Chris' excellent discourse "...This means that we don’t have the granularity to monitor each of the 20 individual cells – so if we have a laggard cell bringing down the whole bank it is very hard to isolate the troublemaker

The sense boards are also designed to put a slight balance load on the cells to keep them all in sync with each other – but the balance boards 3.5 years ago did not trigger a balance load until the cell voltage reached 3.7V. This is actually slightly above the over-voltage cutoff on the EMS, meaning that our cells effectively never benefit from being auto-balanced..."

3.7 V is a full 0.3 V above recommended float and a full .1 V above accepted absorb level of charge. Even at 3.6 V absorb, the individual cells do not get above 3.4 V.

Chris then notes what I have written earlier "...Since then cell quality and consistency has improved, and cell chemistry and construction has been enhanced..."

Chris and Cherie are the real pioneers in this technology for RVs and are free in their advice and these expensive lessons learned. We have learned much from their experiences.

 

Reed and Elaine

[JCTex]

Thanks for everyone's answers. Re my original question of how to check the health of my 4.5 yr old 8D's, the one poster who answered said to check specific gravities. My question is how? These are sealed AGM's. I wouldn't know where to begin obtaining access to the fluid. I was thinking there must be an electronic meter way to check their chargeability and total Ah holding capacity. Is there?

 

Lithium (meaning Yyridium Lithium Iron Phosphate 4):

Sorry, but I'm correct on my coster Ah. We can't just buy the cells without a super good, reliable Battery Management System to protect them. The absence of BMS's is what has held us up. The providers have spent mor money than I can imagine developing marketable BMS's they are willing to base their reputations on and have just recently accomplished that. When Chris did his suite, he pretty much built his own with a little expert help. Victron finally built a BMS appropriately sized for something other than a yacht and offered it in 2013. It costs a ka-jillion. AM Solar has been fighting this problem for at least 4 years and put one out in 2014. So did Balqon (formerly branded as Winston) late in 2014. NO manufacturer who has developed a BMS (that one of us would trust and buy) will sell it alone. ALL BMS's for the size storage we need are sold only as packaged with the cells. They also include all the fusing necessary to interface with everything down stream. Every one decided they couldn't trust us with their reputations and decided to market only a turn-key, drop-in suite. So, while the cells can be had very cheaply, that doesn't help us. We can't use them without a device proven to prevent overcharging and over-discharging, plus keeping the cells balanced. My cost per Ah was based on Balqon's 5kW package and even still, it only makes 328Ah available after 30% SOC. it costs $3,150, including 2 needed add-on's. Balqon's largest package offers 523Ah atfter 30% SOC and sells for $4,150 w adds. Neither price includes shipping. Last time I checked, AM Solar's largest package is only 400Ah (rated) and sells for more per Ah than Balqon. I'm not aware of any other companies selling lithium cells with BMS's designed specifically for,their calls.

 

AGM: I did a spread sheet comparing L16's to Lifeline 6CT's. The latter offered more storage capacity (when new) PER poumd and footprint square inch. Odd, but true. I can buy locally 6-6CT's for $2,436, including shipping to north of Dallas. They will offer (new) 900Ah, or 450Ah at 50% SOC. That should cover me for 2+ days of no sun and not driving. I figure to lose 15-20% each year. I can get these 6-6CT's in the same pull-out tray now used by 2-8D's. I think I'm limited within that space only for 4 L16's.

 

Which to buy: If I knew based on actual use the Lithiums would not deteriorate as fast as AGM's; and if I knew I'd ALWAYS keep my Lithium suite neither too hot nor cold; and if I knew Lithium BMS/cell packages will stay this expensive for the next 4 years; and if I knew for sure al you guys would chip in with a collection to,pay for my Lithium experiment if something went wrong--THEN I'd buy Lithium. Since none of those suppositions are likely, I'm going with the heavier, less efficient, harder to charge, and sooner to need replacing Lifeline 6CT AGM's. That's what Imagonndo (until one of you show me why that's a bad idea).

 

Please continue.

 

Jerry Lewis

2008 Country Coach Allure 470 38' tag

2014 JKUR

[JCTex]

Forgot to comment on the post about changing technology: Yes, yes, all true. However, as long as I want a residential refrigerator, and until they invent a compressor that will spin up using only 12 volts in the line, I, stuck with feeding a 120VAC thing 7/24/365. This means I am required to leave my inverter on when boondocking 7/24/365.

 

I've done and will keep doing everything I can to convert everything to DC; but many things (TV's, some kitchen appliances, tool battery rechargers, and space heater) I already own. If I can provide the power, they will serve me well. I'm certain more than half of the devices needing watts in this coach that run on DC evolved in the last decade from ones requiring AC. We have come a long way.

 

We only have 2 big problems left to solve, really. One is the laws of the universe are not cooperating regarding the storage of electrons; and two, the rotary design being a good try, no one seems to be able to,figure a way to get a compressor to compress a gas using only 12 volts.

 

Now, please continue.

 

Jerry

[Sehc]

Danflos compressors work fine on 12 volts

[Jack Mayer]

Jerry, your assessment is why when I built this coach I put in Fullriver L16 AGMs instead of going to LFPs. I came up with the same issues as your did - not so much issues, I suppose, but facts that work against ME putting in the LFPs. I talked to Chris and others about it at the time, read all the yachting stuff, and did other research. I decided to spend my money on a sure thing - the AGMs. I don't have any weight or space restrictions, though.

 

On my small motorhome (28') that I'm about to purchase I "may" do the LFPs, because I: 1) don't need a big battery bank, 2) weight is a big issue, 3) I can control the environmental factors pretty well, 4) I intend to keep the MH for many years so the cost/time works out, 5) the turnkey systems have now been pretty well thought out vs. a year ago.

 

That is where I stand on the LFP decision.

[Daveh]

Page 21 of this manual has procedure for testing of AGM http://www.lifelinebatteries.com/manual.pdf. Many here use the Trimetric 2030 http://www.bogartengineering.com/content/trimetrics to keep track of Amp hours used. These are very useful to make sure you do not go below the recommended Depth of discharge for your particular battery. They are also useful to determine the actual capacity of the battery under load. You are correct that testing fluid is not an option with AGM.

 

Although I am currently testing and getting to install LiFePo4 batteries, I am knowingly taking on the risk. I am building my own pack. The battery management system can be added without much additional expense http://minibms.mybigcommerce.com/categories/HousePower-BMS/. I do think AGM makes the most sense for the moment but I want to explore this technology. I am reluctant to use the premade packs both because of cost and I want to select the type of battery management system to be used, if any. In my case I will be using a battery monitoring, with alarms, rather than battery management (that shunts current). , .

[reed and elaine]

I could say that we got a drop in system two years ago from Manzanita Micro. The BMS and monitor associated were steep but have worked superbly. Elaine thinks I am OCD (or maybe a Cod) since I do check the BMS monitor several times a day. It is amusing to watch the individual batteries and cells being balanced every couple of seconds when using high draw such as air condioning.. The only problem is that the BMS andmonitor are designed for EV world and the percentage of SOC (EV'ers call it fuel) does not work well but the deficit in W-hr is easy to follow (sometimes it shows a +200 W-hr surplus is charge/discharge rate (in amps at 48 V nominal). It is drop in but son who is a licensed master electrician with BS in Electrical Mechanical Engineering and 23 years in designing/fabricating solar systems took a few days to fine tune it.

[Daveh]

Yea, Reed, I sure wish I had a resource like your son. What you say regarding BMS is also my impression after reading various boards. These systems are mostly built for the EV world and there is a question as to their necessity with regard to RV usage. As I understand it, the BMS systems have two purposes: (1) to balance the cells (by shunting voltage from high cells to lower cells) and (2) to provide high and low voltage alarms and/or cut offs. The question is whether the active balancing is even necessary since the experience has been with the low draw of RV use the batteries tend to remain in balance. So, by avoiding the active balance you are avoiding the additional expense and, more importantly, reducing the complexity of the batteries. The argument is that each additional shunting circuit also carries the risk of failure and thus damaging the pack. If active balancing is not necessary, do not add the additional risk. I am going to start with just monitoring, and I mean very close monitoring, but if that becomes problematic I will add the shunts. Also, what you mention regarding air conditioning has me concerned about my theory since I iintend to run the AC off the batteries and am concerned that may mean I do need active battery balancing.

[reed and elaine]

Daveh

 

Just talked with son Cary (we are mootchdocking with him and family at his place at 7800' in mountains of northern NM - and hail is really coming down and Elaine is worried about panels - if they break, Cary has 5 palletloads at 480 kg each next to trailer). He and grandson spent a solid week fabricating system. He did it as family project but we did pay grandson apprentice electrician wages.

 

Actually, the only time we saw the dancing of lights in the BMS monitor was the one time we were on line power and using the air conditions (wrote that it was 103 in Spokane and we were parked in shade at an RV park). The system is designed to have all AC run off battery/inverter so the battery was being charged at 1.5 kW and being discharged at 1.7 kW.

 

Chris of Technomadia indicates that he will be going to a BMS in future.

 

Reed and Elaine