Sizing coach battery for my style of B use B - Page 2

ptourin · 10-22-2015, 04:20 PM

Yeah, it's pause to think... You have a battery that they rate at 400 cycles @80% - mine are rated 2000 cycles and I can certainly go down to 80% - but I paid $1300 for each battery - so if you paid less than $260 US, maybe you were the smart one <g>...

Of course, it's never a smooth comparison. I'll bet that 400 cycles @80% means 400 cycles before the capacity goes down to 50% of rated capacity - that seems to be the life cycle rating protocol for the standard and AGM batteries. The LiFePO4 life cycle rating protocol gives the number of cycles until the battery reaches 80% of its rated capacity. That's another advantage of the lith phosphate batteries. But I still feel like I'm off in outer space trying to figure out how to best handle the lith batteries - would have been a lot easier to drop in a good AGM...

Crank · 10-22-2015, 05:55 PM

@ Ptourin: Yes, I'm looking hard at the PD4645. It is not temperature compensating, unfortunately, so Lifeline's correct charge rate is met only at 70 deg F, falling short of Lifeline's requirement below that. The charge and float voltage requirements go up from 14.41v @70F as temperature decreases, which is a problem. (Lifeline wants 14.4v @ 70F, but 14.9 @ 40F, hence the range I mentioned). Lack of temp compensation is a significant problem and I'll have to decide if Lifeline and I can live with it. (On warm days charge at night and when it's colder charge at noon).

I have not found an alternative to the PD with temperature compensation, but maybe there is something suitable out there.

I would like to know if one can use a stand-alone charger with compensation like Ridenfun did, and integrate it with the rest of the RV converter, which I suppose is 120v switching and protection equipment. I don't have a grasp of how the two parts of the unit work together.

Maybe it is possible to install a heater on the batteries to keep them at 70F during charging at cooler temperatures. Has anyone tried that??? (I can't avoid undercharge at higher temps.)

Anybody out there who knows how to install a potentiometer to compensate for temperature that roughly matches the Lifeline curve? I have no clue about electronics.

Crank · 10-22-2015, 06:43 PM

Re battery cycles vs DoD and Li cost: I think you come out well, Ptourin.

Lifeline says that when regularly discharged to 50%, their AGM batteries provide nearly 1000 life cycles (that means that if you want a 100 Ah bank, you need two 200 Ah in batteries for optimum life ($600). I have read elsewhere that you can discharge to 80% without harm on occasion (which is very useful - it obviates the cost of a larger bank for occasional, unexpected, longer intervals without recharge). Regular discharge to 80% about halves the number of cycles; improper charging will reduce life a whole lot more: conditions to be avoided!

Although costly, Lithium can be deeply discharged (85%+) on a regular basis, so only one (slightly larger) battery is needed to match the AGM case. Li is generally much more tolerant of conditions, and so less easily damaged. They cannot be damaged by undercharging, in contrast to AGMs; their charging demand and output are temperature independent. Their energy density is much greater (>3x) so they are much smaller and lighter.

Avoiding overcharging is critical, much like AGMs.

Here is a comparison which has the Li coming out well ahead in lifetime cost. Lifetime - 1900 cycles in 5.5 yr): http://www.powertechsystems.eu/home/...ry-advantages/

A problem is that if we don't use it heavily (which means cycling it daily for 5.5 yr, or less frequently for longer) we probably won't recover its residual value if the RV is sold.

Anyway, most do not choose AGMs or Lithium over Flooded wet cell to save money, but for convenience, particularly minimal maintenance, for greater storage capacity if space is limited and for robustness and dependability.

Ptourin: "But I still feel like I'm off in outer space trying to figure out how to best handle the lith batteries [how come your charger does not just shut does at full charge?] - would have been a lot easier to drop in a good AGM..."

Ptourin, I thought the whole discussion was about how it's not so easy to drop in a AGM! I looked at Li to see if they might make life simpler, but learned I don't expect to RV long or often enough to come close to amortizing the cost, so forget that!

Davydd · 10-22-2015, 08:20 PM

My experience with an AGM battery is if you have just one or two you can easily totally discharge your battery by simply forgetting to switch the DC on an absorption refrigerator when parked. Too many slips like that and you can forget the cycle ratings.

Scottbaldassari · 10-22-2015, 10:52 PM

Always reading about these "life cycles"... I don't have much real experience with RV power systems. Years ago I had a Sportsmobile with just one battery, it performed well with a few lights, a laptop, and a printer. I plugged in to shore power pretty often, and drove nearly every day, so it was constantly getting charged, but in about 5 years of ownership, I don't ever remember replacing the battery.. I might have, once. 1000 battery cycles mean you could run the battery down EVERY SINGLE DAY of the year for three YEARS before you killed your battery, correct? Are you guys living in these things without plugging in all year long? Hell, run the battery down 1000 times, and then replace it. The way I plan to camp, it would last more than a decade.
My point is, does the "casual" user really NEED all this boondocking power? I can understand (someone like you Davydd) who seems to spend a good part of the year on the road and has an all electric rig, but how many are actually doing this? fulltiming I mean... REALLY fulltiming and boondocking, for months at a time, with no campgrounds/shore power.. Don't you have to empty tanks? fill water? etc etc, seems like a campground or some hookups are inevitable pretty often with a class B.
I lived in a solar powered home, when my batteries got too low, I started the generator, my batteries lasted almost 20 YEARS, and that was every day use (household use), LOTS of use, with 5 people, 365 days a year.
Crank, if you really do boondock 5 days in a row, how OFTEN do you actually do that in a years time? If its only a few times, doesn't it make more sense to just conserve power and/or run the generator a few times A YEAR when needed? Yeah yeah, I know everybody hates generators, BUT, it seems like there is an awful lot of "over building" going on in the Class B RV world for the very few times that extended use of battery power is needed.
I'm not trying to ruffle anyones feathers, I'm just asking a question. Maybe I'm missing something, but If we have reasonable power demands, and propane, solar, the engine alternator, shore power, AND generators, do we really NEED these huge battery systems?

ptourin · 10-22-2015, 11:10 PM

That's a serious question to be asked about cost vs. life cycles with LiFePO4 batteries. If you can cycle over 2000 times and still have 80% of the rated capacity, it will indeed be years even if you're a full-timer. I doubt I'll live long enough to do 2000 cycles on mine!

But I haven't had your kind of luck with flooded cell batteries. Haven't lived off grid solar, but I've used them in lots of vehicles, and replaced them lots of times, often after not many years of use. I suspect that deep cycle batteries in a well-designed solar setting are nowhere as roughly used as vehicle batteries. And they're often much better quality batteries than run of the mill vehicle batteries.

But you sure can get crazy over-thinking what your RV battery needs and wants are <g>...

booster · 10-22-2015, 11:56 PM

I will admit to not reading each of the replies to the intimate details, but I think some things should be considered from all sides.

Normally, the ratings for AGM life are number of cycles to get down to 80% drawndown capacity, not 50% or totally dead. I would also say that the number of cycles for the lithium is still in the "predicted" area, as there is not enough history to know yet for sure.

IMO, there is no current real option in charging other than return amp termination of absorption, it you want to get 100% full without overcharging. This may sound harsh and unyielding, but I do think it is true. All the different chargers that have lots of fancy algorithms are still just guessing at what the battery needs based on bank size and instantaneous voltage, when all they need to do is look at the charging amps to determine what is really going on. There seems to be a huge resistance to checking charging amps in RV systems, much less resistance in marine applications. Bottom line is that if a charger doesn't control off a battery current shunt, it is not very accurate.

Skipping all the things that the different charger folks will tell you, there are only a few chargers that will give you accurate charging based on amps to the battery. The one I am the most familiar with is Magnum. Their chargers, when paired with one of the higher end remotes, will give you true return amp charging. No guesses, no algorithms, just plain amps, actually measured, and totally repeatable. If your read the Lifeline information, they plainly state that return amps is the premier way to tell if the battery is charged. The best of the lithium research says the same for lithium. I will repeat what I said earlier, there is essentially no way to tell from voltage if your battery is full charged, or what SOC it is at, with any amount of accuracy, that is needed.

As for interactions between the charging sources. If the sources all use return amps to control the charging, there should be no bad interactions between them, because all they are looking at is the battery charging amps, not any load or other "noise" from other sources. In a perfect world, they will all terminate absorption at the same time, in a less than prefect world they will terminate absorption very near the same time, but not enough to make any real world difference.

I don't want to sound like I am bashing PD chargers, because I think they do a better job than most, but if you want the best in charging you have to run them manually, or get a different charger. Again, as I mentioned before, the 4 hour absorption is either going to be too much or too little as it doesn't consider bank size or SOC when starting, but you can look at your Trimetric and see amps and control manually based on return amps, so then the PD is good. For lithium, I think that PD has missed the boat, as almost all of the best references say not to put full charge voltage on full lithium batteries, which PD does. Other constant current/constant voltage chargers give you the option of full shutoff at absorption end, which IMO is what you would want to do for lithium.

Bottom line, IMO, is that you will not get the best in charging and battery life with anything less than return amp charging on all you sources (usually shore, solar, alternator). If any one of them is not that style, you have lost a lot of the benefit of the others that are that style. I know that MANY folks will disagree with this, and that is fine. That is what opinions are for. I just say, look at the available literature from folks other than those trying to sell you something, and then decide for yourself, and be aware that there is a lot of biased, to outright inaccurate, information out there.

I would encourage all to question this and ask for explanations, and I will try to clarify to the best of my ability. Much of it does not make a lot of logical sense, until the entire picture is seen, and much of the conversation is being directed by the charger manufacturers to highlight how they do things, and to their benefit.

I do think that the B forum has been far and away on the leading edge of the higher tech charging discussion, and you will find very little of this level of discussion elsewhere. I also think that in a few years the standards will change and the stuff we are now talking about as being "new" will be the standard, and probably applied to lithium.

Crank · 10-22-2015, 11:57 PM

Davydd, that is a useful reminder. The fridge is one of the most troublesome things to manage correctly. Turn on 24 hr. before leaving, park only on level spots, or level the vehicle EVERY time, turn from gas to electric and back before and after driving EVERY TIME, remember to lock-latch the door....sigh.

As you said, leave it on electric at your peril when parked for any length of time. (Leave ANYTHING on that draws much power at your peril, especially fans).

My 20' Roadtrek has no solar, officially room for one 80 Ah battery, grudgingly considering uprading to two 100 Ah, which I'm leaning towards, although I'm griping about giving up valuable storage space. No automatic switching available for my old refrigerator, as far as I know. 2 AGMs will provide a little more mental block leeway.

I'll just have to rely on my wife nagging me - she never forgets anything

Did you have a solution in mind?

eric1514 · 10-23-2015, 12:06 AM

Quote:

Originally Posted by Crank

Davydd, that is a useful reminder. The fridge is one of the most troublesome things to manage correctly. Turn on 24 hr. before leaving, park only on level spots, or level the vehicle EVERY time, turn from gas to electric and back before and after driving EVERY TIME, remember to lock-latch the door....sigh.

As you said, leave it on electric at your peril when parked for any length of time. (Leave ANYTHING on that draws much power at your peril, especially fans).

My 20' Roadtrek has no solar, officially room for one 80 Ah battery, grudgingly considering uprading to two 100 Ah, which I'm leaning towards, although I'm griping about giving up valuable storage space. No automatic switching available for my old refrigerator, as far as I know. 2 AGMs will provide a little more mental block leeway.

I'll just have to rely on my wife nagging me - she never forgets anything

Did you have a solution in mind?

Don't ever run it in 12v mode. Simple.

booster · 10-23-2015, 12:14 AM

Crank, don't want to speak for Davydd, but there are several ways you can go. The frig thing and killing the batteries is real, and happens all the time. One solution is to make the 12v source only hot when the engine is running, with an alarm lamp to remind you to turn on the propane.

You may be able to find some space under the van for an extra battery or two. With AGM, you don't need to be accessible, so that makes it much easier than when they made your van. Any solar would help, or course.

The other often ignored thing is that if you are only getting charged to 80%, which is pretty common, you can get an instant 25% increase in capacity just by improving charging.

The balance of power use and power source is a constant issue for all of us.

Davydd · 10-23-2015, 12:58 AM

Big battery banks needed? I've crossed the Rubicon and will never go back. I have the 800ah lithium ion battery bank and I never have to think about shore power. Right now I am parked on a Queens, New York City very inner city neighborhood street for two nights and still have 100% electrical functionality of our B. I could go five days this way as I dare not give up our precious parking spot on the street. Until you experience the electrical freedom it might be a hard concept to understand. I see it as transparent use and a bit of travel freedom.

The lithium ion battery bank I have has low discharge and over charge protection. It also has low temperature protection and I have constant temperature and voltage monitoring of all individual cells. I don't know of any converter providing anything but over charge protection on AGM batteries which is pretty new within the last 10 years.

booster · 10-23-2015, 01:16 AM

But, you have to remember that lots of folks could do the same times on 200ah of battery without issue, some with 100ah. It is all a matter of balance and needs.

Crank · 10-23-2015, 01:41 AM

Thank you for your second long contribution, Booster. The refrigerator post kind of took the spotlight off it, and is somewhat secondary to the goal of this thread, which started off as how to size the battery bank in a van, but quickly became the much more important question of how to fully charge AGM batteries (AGM precisely because accessibility is unimportant). This latter question you have addressed very helpfully.

When talking about battery drawdown, there is room for confusion between "drawdown to 80% of full capacity", and "drawdown of 80% from full to 20% remaining". (I may have been inadvertantly ambiguous on this, but I meant AGM can be occasionally drawn don to 80% of full capacity without harm). Certainly the lifetime cycles of Li are still in the theoretical zone and writers tend to forget to mention this, but it appears that empirical results remain on the theoretical curve so far.

The concept of "return amp termination of absorption" as a measure of "Fully Charged" is new to me and I have not grasped what it means and how it is measured. If a Trimetric measures it, I will be satisfied with that (except that one has to sit and watch it), and just apply the result. I will check out Magnum, and hope it is temperature compensated (PD is not).

Thank you and Davydd for the refrigerator tips. The topic is a good reminder of how little latitude we often have, especially when batteries are regularly not getting fully charged (apparently a common occurrence, although difficult to recognize).

I think this second post of yours has touched on a means of determining "fully charged" that should attract some useful discussion from others more knowlegeable than I. (If not, the question defaults to "please elucidate").

Davydd · 10-23-2015, 02:21 AM

Quote:

Originally Posted by booster

But, you have to remember that lots of folks could do the same times on 200ah of battery without issue, some with 100ah. It is all a matter of balance and needs.

There I disagree. I've had the 200ah battery bank and I have stretched five days boondocking with it. Note I said transparent and 100% electrical functionality. That means I can travel with inverter always on with microwave, Keurig coffee pot , induction cooktop and 120vac outlets always on and I can use them. I also have a lot of things always active like two wifi routers, cell phone booster, Trik-L-Charger active-more than most Bs. As I said it matters not to be plugged into shore power and it requires no active electrical conservation or monitoring. Transparent means I can behave the same way in a Walmart parking lot as I do plugged into shore power at a campground and indefinitely. As I said I've crossed the Rubicon. With over 140 days on the road this year I could cite numerous travel examples that would not have happened without this capability especially traveling this time of year with most campgrounds closed in the north. Most peoples' mind sets are traditional in expectations with an RV. I can't accept that anymore.

ptourin · 10-23-2015, 02:58 AM

Crank, about the terminology for the amount of drawdown - I'm being a bit of a word geek here, but if you're concerned about stating it clearly...

If you talk in terms of State of Charge, you can say things like, "you get twice as much usable capacity if you draw down to 20% SOC then if you draw down only to 60% SOC, but it's rougher on battery life."

There are several ways of using Depth of Discharge - if you use percent, it's the complement of SOC. You can say things like, "you get twice as much usable capacity if you draw down to 80% DOD then if you draw down only to 40% DOD, but it's rougher on battery life."

I think that's what you were trying to get at in your earlier post. If you put it in terms of SOC or DOD, it's clear to everybody what's being discussed. In this case, DOD is a bit clearer - 80% DOD gives you double the amp hours as 40% DOD.

You don't need to talk about DOD in percent - for example, I have a 200 Ah battery bank, and I could say, "you get twice as much usable capacity if you draw down to 160 Ah DOD then if you draw down only to 80 Ah DOD, but it's rougher on battery life."

booster · 10-23-2015, 01:03 PM

Crank, the return amp charging is really not hard to understand or complicated, but it is misunderstood and usually badmouthed by charger manufacturers because they can't do it with their chargers.

It is very basic. You put a shunt in the negative battery lead right next to the battery so it measures current in and out of the battery on the Trimetric or with a monitor built into the charger. You charge at absorption voltage until the amps to the battery quit going lower, and you are done. Go to float.

The current the batteries will get to varies, with Lifeline saying .5% of capacity in ah, up to wet cells that will say 1-3%. You can check what your batteries will be easily just be holding the charger in absorption until the amps stop dropping. If you are doing the manual thing with a Trimetric you repeat that each cycle (a PITA sometimes) or if you have a charger that does return amp charging, you program it to transition just at just a bit higher amps than you tested and forget about it.

You may be a candidate for a Magnum charger, as they do have temp compensation, and will also do return amp charging option with the right remotes. With those remotes, you also get a built in battery monitor so you don't need the Trimetric any more if you don't want to.

They have now started making some smaller units that take a lot less space but still have all the features available. They are also less cost. We nearly got one of the small ones, but the inverter in it was just a bit too small to run our microwave.

booster · 10-23-2015, 01:06 PM

Quote:

Originally Posted by Davydd

There I disagree. I've had the 200ah battery bank and I have stretched five days boondocking with it. Note I said transparent and 100% electrical functionality. That means I can travel with inverter always on with microwave, Keurig coffee pot , induction cooktop and 120vac outlets always on and I can use them. I also have a lot of things always active like two wifi routers, cell phone booster, Trik-L-Charger active-more than most Bs. As I said it matters not to be plugged into shore power and it requires no active electrical conservation or monitoring. Transparent means I can behave the same way in a Walmart parking lot as I do plugged into shore power at a campground and indefinitely. As I said I've crossed the Rubicon. With over 140 days on the road this year I could cite numerous travel examples that would not have happened without this capability especially traveling this time of year with most campgrounds closed in the north. Most peoples' mind sets are traditional in expectations with an RV. I can't accept that anymore.

Yep, and if folks are setup and used to using 25-30ah per day, it will be just as transparent to them.

Scottbaldassari · 10-23-2015, 04:28 PM

Davydd: ..."Big battery banks needed? I've crossed the Rubicon and will never go back. I have the 800ah lithium ion battery bank and I never have to think about shore power. Right now I am parked on a Queens, New York City very inner city neighborhood street for two nights and still have 100% electrical functionality of our B. I could go five days..."
..."I've had the 200ah battery bank and I have stretched five days boondocking with it. Note I said transparent and 100% electrical functionality. That means I can travel with inverter always on with microwave, Keurig coffee pot , induction cooktop and 120vac outlets always on and I can use them. I also have a lot of things always active like two wifi routers, cell phone booster, Trik-L-Charger active-more than most Bs."...
..."With over 140 days on the road this year"...
Exactly my point. I think most will agree your set up and travel habits sound great, (except maybe for being on the street in inner city New York for 5 days

) but it is the exception rather than the rule. Most people don't NEED their inverter on all the time, with 100% electrical functionality. I'm not condemning it, just saying I think most can live comfortably with out it.
The OP said he "likes to boondock 3-5 days", I was trying to figure out how often that is actually done, and if it is really worth all the extra expense and work involved. I personally would like to boon dock about 250 days a year maybe, but in reality, I don't. It's interesting to fantasize about the most luxurious "transparent" system, and smart to study all the ins and outs of charging etc., but if you scan through these posts, it sounds like every single poster manages with their system from 25 amps, to 800. As Booster and others have said already, it is a matter of balance, there is definitely a point of diminishing return for the casual user. If you can afford it all, I guess the more, the better, But at some point you have to figure out just how much you need. If you already have a generator, a solar panel, and some gas appliances, you might get by happily replacing your one single battery, and getting back on the road. just sayin'..

ptourin · 10-23-2015, 04:31 PM

Booster, that explains a comment in Victron's Tail Current parameter. They default Tail Current to 4%, and they comment, "Some battery chargers stop charging when the current drops below a set threshold. The tail current must be set higher than this threshold" - or the monitor will never read 100% SOC.
Of course, my charger doesn't do this - my whole exercise is to see if I can use the monitor internal relay to control the charger.
Thanks - another piece in the puzzle makes sense now.

booster · 10-23-2015, 04:55 PM

Quote:

Originally Posted by ptourin

Booster, that explains a comment in Victron's Tail Current parameter. They default Tail Current to 4%, and they comment, "Some battery chargers stop charging when the current drops below a set threshold. The tail current must be set higher than this threshold" - or the monitor will never read 100% SOC.
Of course, my charger doesn't do this - my whole exercise is to see if I can use the monitor internal relay to control the charger.
Thanks - another piece in the puzzle makes sense now.

Yep, your charger is full out, all the time, so you certainly will be able to get to the lowest "tail current" (I wish they all would get together and call it the same thing

). Once you see what that current is, you could just set your tail current to a bit higher than that, and the meter should tell you when it gets there and light the "fully charged" or whatever they call it. What it might not do is show 100% on the meter at that point, as many of the meters require you to be discharging, and passing full battery voltage, going down, of about 12.8 volts, as that is a calibration of the meter to allow for charge and discharge efficiency. On some you can set that threshold voltage, but not all. I chased that for weeks before I figured it out, and it was driving me crazy.

You may also like: