Sizing coach battery for my style of B use B

[ptourin]

I think there was a thread or three over on Sprinter-Source that discussed the 2nd alternator approach. Things covered:
* 2nd alternator is dedicated to house batteries; lots of available charging current.
* The issue of whether running a Sprinter at idle is bad (the high idle issue).
* Expense - it's expensive like a solar installation is.
* Type of usage - solar is handy for keeping batteries charged when RV is sitting unused; 2nd alternator is handy for people who don't park at a campground for days at a time but drive more often.

Sorry, no links at the moment - just a quick summary.

[cargovanconversion]

Originally Posted by booster

The lifecycle thing is one of the areas of all this that is the hardest to get a handle on, I think. Between all the different operating conditions and claims, I don't know if anyone really knows what will happen in the real world.

One thing to remember when you do your life predictions (guesses) is that the number of cycles you would get based on the chart is really an integration of the depth of discharge cycles, not just based on your worst case discharge. If 80% down gives 500 cycles and 10% down gives 5000 cycles and you did half of each, you would be midway between them on the chart, approximately. Maybe 1200 cycles. 50% down average would give 1000 cycles, and considerably more if that was the worst case, with others all better. Many times with a single battery, you come out better costwise by adding a second one, if you have room for it, due to more cyclelife. Plus you have some emergency capacity if you need it.

Of course all of this is based on ideal conditions, and the premise that none of us are human. It is highly unlikely that any of us will ever wear out our batteries without doing something stupid to them along the way, which will shorten their life by varying degrees. Equipment glitches can also do the same.

One thing that is unknown at this point is how well the lithiums will handle abuse. It may be that the BMS is more important than the batteries themselves, as well as the charging systems. Some manufacturers claim you can use 100% of the capacity of lithium, while others say to leave 10% on each end if you want durability. Similar issues with cold charging. All of this stuff will probably be resolved in the real world as time goes by, but now is relatively unknown.

The thing that hasn't come up here, and may not be on topic, exactly, is if some other technology can negate or modify some of the thoughts on battery bank sizing. If you can get by on a single 100ah battery, you don't use a whole lot of power, so solar could be an addition that could keep you from needing more battery capacity. The lower the usage, the more effective solar is, in general. If you look at davydd's case, his 420 watts doesn't do much because of his 200ah/day use. We have 300 watts and use less than 50ah/day and can normally have surplus power. Others without compressor frigs like we have, are using in the 20-25ah/day range and do well with 100ah battery and 100 watts of solar.

The other option that might apply would be increased engine charging capacity, if you drive some, or are in areas that idling is OK (and OK with you). A 100ah lithium, or even a Lifeline AGM will accept 200 amps of charging easily, so you can recover capacity in a hurry when you need it, so you can have smaller battery capacity, and stay away from deep discharges (and get longer cyclelife).

Lots of options for everyone, based on how they use things, and what they really need have to do those things. This discussion is showing that the understanding of all this stuff is expanding quickly, and I think that is a really good thing because as folks understand more, the manufacturers are going to be pushed to cover all the stuff we have talked about here and that will make for much better equipment being available for all of us.

Nice summary, Booster!

Van Williams

[booster]

Avanti and I will wind up with many of the same components when ours is finished. I am currently about 1/3 of the way through our install. The functions will be somewhat different, but the goal for both of us is the same, good charging without overcharging, as well as increased off grid time and convenience. We also eliminated our generator as we will not need it. Our install is more complicated as I am squeezing all the charging stuff in the area originally used in our Roadtrek 190, so it tight and with homemade frames and panels. The batteries will go where the generator used to be, behind the differential.

Ours will be:

440ah of Lifeline GC2 six volt batteries.

Magnum MS2000 inverter/charger with battery monitor kit and ARC50 remote. It will be able to do return amp charging for charge accuracy.

Blue Sky 2512 solar controller that will also do return amp charging. 300 watts of solar.

DC Power Engineering 250 amp alternator that is the only alternator, not a dedicated one like Avanti has. There were a couple of reasons for me to choose doing it this way. The alternator always will have the starting battery connected, so it will have a 12v reference and not go wild if the coach batteries are disconnected. The entire system can run either way for charging the starting battery. Downside is the loss of a bit of output to run the engine

I don't use a smart regulator on the alternator. The alternator runs at 14.0-14.5 volts and has a Denso style internal regulator that monitors output and regulates based on the output. Temps, loads, etc determine the voltage, and it works quite well that way. The overcharging issue is taken care of by having an ammeter for the batteries on the dash that I can see while driving. When it hits the return amps, or close to, I just shut of the manual charge relay to the coach and let the solar top the batteries to return amps. If using a smart regulator, it wouldn't be on a shunt, so loads in the coach could fool it into messing up sometimes, I think. Avanti couldn't do it with a shutoff switch because he would lose the 12v reference to the alternator and could spike voltage with full shutoff, so he needed the regulator.

Avanti will get more amps at idle than we will as his alternator is a bit larger 270 vs 250 amps, and they appear to spin it at a higher % of engine speed. Ours runs pretty slowly, which I am fine with from a durability standpoint, but we will be somewhere around 125-150 amps at idle, I think, but it might be more. We idle at 545rpm with alternator at 1800rpm. Normally alternators are rated at 2200-2400rpm.

All three of the charging sources will be controlled by return amps, and will not interfere with each other at all, so charging should be extremely accurate.

We tend to like to sit in one place longer than many folks here, less "tourey" I guess, so we are set that most of the time the solar will cover sitting as long as we want. If we got horrible sun conditions, we should still be at over 5 days with no solar input. A half hour of driving or idling would give us 1-2 days of capacity back. We use less power than Avanti at under 50ah per day, though.

[Crank]

Thanks for the quick reply, link and other info, Avanti: another good solution to keep in mind.

[Crank]

I finally found a comprehensive solution to my charging problem which will cover a wide variety of other situations.


I looked high and low for a satisfactory replacement for my van’s obsolete 32 amp 1-step, weakly-charging Magnatek converter/charger. My definition of “satisfactory” is a unit that will fully charge, maintain and protect my two 12v 100ah Lifeline AGM batteries, which require 14.2-14.4v for Bulk/Absorb, and 13.2-13.4v for float, with equalization only on demand. (I could use Trojan which charge at 14.7v.)



Many people expressed satisfaction with 3-step replacement charger-converters (not surprising after a 1-step unit), but are they getting a full charge, do they avoid overheating and avoid shortening battery life? Impossible to know without adding a monitor. The 3-stage units I have studied specify charging voltages which don’t match my batteries. None permit control of voltage or charge duration. Most equalize every cycle and lack temperature compensation.


A hint from Booster caused me to look at Magnum, who only make inverters. I was surprised, because I never thought of converting DC to AC. (I use no AC appliances while boondocking) and I don’t have solar.)

When contacted, Magnum recommended the 70a 1200W Magnum Dimensions MM1212 Inverter/Charger, the smallest of its line. I learned that shore or generator AC may be run directly to the coach to meet its AC needs, with a branch to the inverter/charger. Alternatively, AC can be wired entirely into the inverter/charger, in which case the unit allows AC for the coach to pass through unmodified, but when boondocking provides modified sine wave 120v AC – great for those with solar and lots of batteries. Installation does not look difficult, but upsizing DC wiring must always be considered.


The MM1212 at 70 amps is overkill for me: I can’t see ever drawing more than 45 amps from it (during rapid battery charging). But it does everything I desire, and I can't find anything comparable that is smaller.



I can’t be surprised that such a sophisticated system costs $719 + ~$200 for a monitor/controller. (I can consider the cost of whatever other inadequate unit I might have chosen, plus the saving from premature battery failure, maybe $600: the premium over that seems well worth it.)


The specifications and user/installation guides are at Magnum Dimensions; the most important specifications come with the controller, either the RC-50 or MRC-50 – I can’t tell how to choose one over the other.




I will appreciate comments on this choice, and suggestions for a less costly unit that would do as good a job. Thanks for all the help and knowledge in this thread: it has been an education!

[booster]

I think you have to go up to the MR50 to get the ability to run the BMK monitor kit, which you need to have if you want to do return amp charging. Without the return amp charging, you have a timed unit that is not a lot better than many much less expensive units. One step more to the ARC50 remote gives some shortcut keys and convenience stuff, but not a lot of improved charging function. The 1212 looks like a very nice unit for the money, even with the extra cost of the remote and monitor kit (the monitor kit is about the same as a Trimetric, so that is about a break even). No matter what charger you have a monitor is good idea to have. We wound up going to a Magnum MS2000, but only because we needed a bigger inverter.

IMO, the smaller the battery bank, the more important it is to have a charger that gets you totally full, and a monitor to let you know where you are at. I think you are on your way to a very nice setup.

[Crank]

I forgot to mention the BMK monitoring kit: I thought it was included - perhaps not - but yes it is a must-have. Thanks for the pointers on the controller.

A small battery bank needs to be fully charged not only to provide maximal power storage in a limited system, but also because continual undercharging is bad for battery life. So I thing the same quality equipment and precautions are needed for larger banks too where more is at stake, even if excess power is available.

What is striking to me is how long consumers have tolerated (perhaps unwittingly) inadequate charging systems, partly because they are uneducated on the technically complex subject (as I was a month ago) and partly because they may not want to hear that an adequate system costs much more than they are used to, especially if they have only one or two wet cells, and use them only a few times a year.

It is possible to devise a less expensive system for small battery banks (lower power rating, only the essential charging settings, optionally with no inverter, without loss of essential functionality). This is an open market niche with growth potential, I think, both for upgrades, and for units sold with new, small, quality RVs so cost can be amortized over the life of the vehicle, especially as solar becomes more ubiquitous.

[booster]

Originally Posted by Crank

A small battery bank needs to be fully charged not only to provide maximal power storage in a limited system, but also because continual undercharging is bad for battery life. So I thing the same quality equipment and precautions are needed for larger banks too where more is at stake, even if excess power is available.

Good observation, and I totally agree. The whole dynamic of small and bigger battery banks is an interesting study, for sure. In a small bank of 100-200ah, if you are charging only to 80%, you are leaving a lot of usable power on the table where you can't get it, and you are shortening your battery life. The deep discharges just make all that much worse. The good part is that the battery cost risks are lower than with a big bank, but that doesn't mean much if you run out of power.

On a big bank, you can be in the same situation as a small bank if you are a big power user, so all the same stuff applies except the cost risks are higher. You can also be in the area of the big bank mainly just reducing your depth of discharge, and to hold voltage better for big loads. In this case getting the batteries fully charged at least every 5-7 cycles is to make them survive longer and reduce replacement costs.

Either way, getting a good charge all the time is a very good thing, most folks don't understand that idea.

As the systems in our B have evolved over the last 3-4 years, I have been amazed at how little the RV community, dealers, and vendors really now about battery charging systems, even if they sell or make them. I think the class B forum is about the only place you will find any detailed information on how the stuff works, or doesn't, in many cases/

The marine folks are way ahead of us RVers in that respect, although many of them are also stuck in the past. The do get all the cool products though!

[Crank]

Well Said!

I have seen some very sour posts from characters who understand the electric side very well; they talk about dealers who are ignorant or just don't care, or who even appear to give bad advice that guarantees failure and more sales, e.g. "if your batteries don't last long enough, you need more of them, better ones, or more solar" when the problem is undercharging commonly due to undersized wiring, or very long runs, etc. Don't try to kid me these salesmen and dealers who have been in the business a while don't KNOW this basic stuff! (They are probably not interested in promoting better charging systems, either).

Look for HandyBob's Blog.

Lesson: seek out the advice of someone knowledgeable with no axe to grind, or a known honest dealer. This is why ClassBForum is so valuable.

[booster]

Look for HandyBob's Blog.

That is quite the manifesto, isn't it? There was a fairly lengthy discussion here on the forum pretty early on in our quest for better charging that included a lot of Handybob's information. At that point, I only new that the original Tripplite in our Roadtrek did not, and would not, get our batteries full, but driving could get them too full. Like many others, all I had heard was that "multistep chargers take good care of your batteries" and driving was a good way to charge.

Looking back at what Handybob believed and said, it is very interesting with all that we have learned since then. He was dealing in mostly solar, but understood that most shore chargers didn't get batteries charged correctly. On the solar, he came up with ways to make his system work well, but now looking back, he tended to apply what he did to all systems as a good thing, which I think was only partly true. Things like using the high end voltage for Trojan wet cells is a good thing, but you need to have the charge capacity match the bank size and usage if you use a single stage charger or controller like he did. One of the things he did was reduce the bank size by 1/2 so he could get the batteries full every day, which kind of makes sense because the big bank was always charging at the lower charge efficiency near full end of the cycle, and would also have larger parasitic loss with twice as many wet cells. His blanket statement of not using more water when charging at 14.7v was true for his system, but it would not apply for a shore charger with no good shutoff control when full, for instance.

That said, Handybob's writings got a lot of us to look closer at all this stuff, and to try understand what really goes on. His distrust of manufacturers and dealers was necessary for all of us to hear, I think, and it was entertaining besides.

I very much enjoyed reading his stuff, and especially his no holds barred attitude. I wonder if he has evolved into the more sophisticated charge controllers that can accurately take care of the batteries without the very careful matching he had.

[Crank]

I rather expected you would be familiar with HandyBob's writing, Booster. I ran across him and a couple of other skeptics rather early on in my quest, and they made me wary.

I admire the extent to which he freely helped others, revealing the prevalence of unnecessary, human-created problems, and his mission to educate us on these matters and their fixes.

What shocked me was that Bob ran into the same fundamental installation mistakes time after time, which made it pretty clear owners were (and are) being exploited by the industry.

I also found it interesting that some owners with problems were closed-minded to Bob's rather obvious logic (not to mention technicians who should have known better). Inability to solve a problem means either inadequate or faulty knowledge or thinking, so it is necessary to examine one's assumptions; it makes no sense to reject a novel solution out of hand, unless it violates a law of physics.

I think that is part of the reason why the low end of the RV industry is stuck with inefficient 3-stage, fixed voltage chargers: they have become a fixture due to unthinking people.

Another reason is that cheap, crude chargers attract return business - repairs/upgrades, keep prices down, and help sell RVs to the majority who don't know the requirements for proper battery charging. And why should they? After all, all a lot of auto owners know is that they put money in one end and get miles out of the other RVs are another whole learning curve which unfortunately often does not begin before acquisition.

If a salesman is going to suggest an upgrade, it is going to be something sexy like a cool electric slide-out or an electric deploying bed, not a balanced charging system upon which both depend! So if you are in the boonies and your bed won't deploy for lack of power, tough noogies!

I wouldn't know about the high-end market, but solar has clearly begun to force some welcome rethinking of system integration including the productive use of inverters.

It blows my mind that Roadtreks can now sell for $125,000: One hopes that they incorporate state-of-the-art charging technology for that price! My '95 originally retailed for $45,000 with nothing special installed except for the 1-step Magnatek, and 20 years later is only worth $9-10K by the book. It's turned out to be more like a boat than a van (a boat is a hole in the water into which you throw money, as you doubtless know; an RV is a similar hole in the sand or mud. Money thrown in is never seen again). Mine turned out to be a bigger hole than I had budgeted for, so I'm not as enthusiastic as I might seem about upgrading the power system.

I've had the van for 16 months, but because of unplanned, but necessary projects on it and unrelated interruptions, I have made only a maiden voyage to the Albuquerque Balloon Festival RT Rally, which ended in fiasco on day 2 when a rusted freeze plug blew out downtown at 5.00pm on Friday night. A good friend in town bailed me out, and we were running again, (homeward) on Sunday Thought I'd learn something about Roadtreks at the Rally, but not what I got So my cruising has been on the internet. I'm putting off a real road trip until the spring (again).

... Just Saturday night reminiscing ...