Sizing coach battery for my style of B use B

[Ridenfun]

Very interesting and educational tread at least for me. I couldn't/wouldn't justify the expense of lithium for my casual type of use, so went with the best AGM I could source locally (and quickly as I needed it in a day or 2 as I had no usable battery) and didn't want the hassle of wet cells and need to physically isolate and vent them as well as top them up).
But I have little DC loads in my intended usage and older B van, and if needed I'll just top up with generator and/or solar and just "manage" to get by. If I shorten battery life by overly discharging, so be it I guess. If we really use it lots and find the lack of capacity disruptive, I'll consider a 2nd battery, but that takes space up which is already limited. Only time will tell.
I sure do understand however how someone with need to run inverter constantly and other loads mentioned would find a successful cost vs benefit in going with higher costs for lithium and the charging systems need to optimize their benefit.
Thanks all for your insight, very educational to say the least.

[booster]

Originally Posted by Ridenfun

Very interesting and educational tread at least for me. I couldn't/wouldn't justify the expense of lithium for my casual type of use, so went with the best AGM I could source locally (and quickly as I needed it in a day or 2 as I had no usable battery) and didn't want the hassle of wet cells and need to physically isolate and vent them as well as top them up).
But I have little DC loads in my intended usage and older B van, and if needed I'll just top up with generator and/or solar and just "manage" to get by. If I shorten battery life by overly discharging, so be it I guess. If we really use it lots and find the lack of capacity disruptive, I'll consider a 2nd battery, but that takes space up which is already limited. Only time will tell.
I sure do understand however how someone with need to run inverter constantly and other loads mentioned would find a successful cost vs benefit in going with higher costs for lithium and the charging systems need to optimize their benefit.
Thanks all for your insight, very educational to say the least.

Making sure you get your battery, no matter how small, totally charged to full is one of the easiest ways to gain capacity. Many chargers don't get the batteries full, so a battery monitor is very good investment. Another benefit is that getting totally full when you recharge can go a long ways in reducing the bad affects of deep discharges.

[booster]

Originally Posted by Scottbaldassari

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'..

We hear all the time about the "no compromise" setup davydd has, but in reality, he can not go as long without some kind of auxiliary charging as many of the rest of us can with much more modest systems. 3 days of not much sun, or maybe 4 with sun seems to be where he would hit the wall (unless he compromised and conserved power) and either have to drive, idle, or plug in. To me, that is certainly a compromise, but davydd would say he planned it that way. Those of us with more modest use, can go pretty much forever without auxiliary charging if it is sunny, and a week or more if it is not. The no compromises thing can be totally manipulated by how you set the rules. One solution certainly does not suit all, and a huge cost setup is not something that many folks, need, want, or can afford.

[Davydd]

It was not too long ago when conversation centered around AGM batteries or multiple batteries as being too expensive or not necessary. Just sayin'.

[Scottbaldassari]

Originally Posted by Davydd

It was not too long ago when conversation centered around AGM batteries or multiple batteries as being too expensive or not necessary. Just sayin'.

That's exactly right! Multiple AGM's ARE too expensive, and not necessary for many. There are still thousands of RV's on the road with one single wet cell battery that are doing just fine. That was kind of my point. Just sayin'.
(and just playin with you Davyd)

[Crank]

Originally Posted by Scottbaldassari

...There are still thousands of RV's on the road with one single wet cell battery that are doing just fine. That was kind of my point. Just sayin'.
...

How do you know they are doing just fine, Scott? I'll bet 70+% of those "just fine" people are hauling batteries bought this year.

If they have no means of determining when their battery is fully charged (AGM) or use wet cells and don't bother with specific gravity checks during charging (know anyone who does?), (and perhaps have only a one-step charger,) they must put their trust in the camper idiot lights for lack of a better alternative. Consequently, they will overcharge or undercharge, and especially with one battery, probably over-discharge repeatedly; so they will have to replace their battery about every year. I know, I was one of them.

_Technically_ that is not "just fine" (and they may discover that after a few days on last year's battery). Moreover they are not getting value out of the battery

They may _feel_ 'just fine" if they are happy to buy a new battery each season and forget about the waste.

(Of course there will be a minority who have learned how to conserve their batteries for years.)

Just sayin'.

I used to do 4-5 10-day boondocking trips annually. I bought 2 batteries rated for several years, and was pretty angry to find they lasted a year (50 days' service), sometimes two. Of course, I just didn't know how to care of them very well, and nor did the charger.

NOT fine with me! When the battery died in my recently acquired van, I discovered I had a 1-step charger and I started to read. The confusion I found lead me to start this thread: it has turned out to be a most rewarding education.


I'll respond to some of the other excellent recent comments when I have more time to think about them and am feeling less snarky

[Scottbaldassari]

Well Crank,
Sorry if I've offended you somehow. I thought you were "open to advice on choice of a battery system".. I was just trying to make the point that MORE isn't always the answer. As I said, I think its "smart to study all the ins and outs of charging etc".
Sorry your batteries didn't last, I've never had that experience..
..carry on..

[ptourin]

I've sure had Crank's experience. Up till a few years ago I knew a bit about batteries and was somewhat careful with them - but there were always those times - phantom loads on the motorcycles, and the battery was dead after sitting for a month, cars I didn't drive over the winter and the battery was dead in the spring, etc. So I'm pretty much there now - I want to understand at least enough so that I have a pretty good sense where all my various batteries are at. With RV's and camper vans, my personal experience is that batteries and fridges are the 2 most constant sources of irritation.

I would say I've seen 2 camps on the RV forums - one is, "they're big and expensive and it makes sense to buy really good ones, know exactly where they're at and try to make them last for lots of cycles - the other is, "there a lots of cheap batteries, get a reasonable brand, put them in, use them up and replace them". I'm in the first camp - I got tired of buying cheap-to-medium batteries, treating them OK most of the time and replacing them every few years. But I'm sure I could find deals on cheap batteries so that over the life of my current RV I could replace them 3 or 4 times and not come up to the cost of my lithiums. I've tried to compare both camps so that I understood the relative costs before mortgaging my soul for expensive batteries that I don't yet know how to charge well <lol>...

[Crank]

@ Scottbalddassari:

No offence: this is an open discussion. You are right: "more" (if you mean generation or storage capacity) is not necessarily required: but it partly depends on the type of trip. Adequate charging control technology IS necessary: but it is hard to find.

Whether multiple AGMs are "too expensive" depends on their performance and the needs and the purse of the purchaser.

In my case, if you had read my earlier posts, you would know that I am considering AGMs and a remote monitor because I'm getting too old to struggle with disassembling the bed every time I need a specific gravity reading during charging, and lifting the batteries out annually has become too much for me. If it were not for age, and the poor wet cell longevity I have experienced, I would have had no reason to consider change.

I'm just trying to get a 20-year-old van's battery system to operate properly and to meet my requirements, which include boondocking (although not for as long as I might wish due to unrelated factors). That's not an unreasonable goal. Cost is an issue, so no Li batteries for me! But I'm going to do it right and cut no corners!

Davydd wanted extended shore power independence on his terms, and could afford his enormous battery bank which affords peace of mind and flexibility, and is using it. I'm glad for him because he has given so much to this Forum of his time and experience, his wisdom, DIY solutions and good advice (2,700+ posts)! He deserves his dream van!

Two very different examples of why something very basic is insufficient.

MY point was simply that one cannot assume that the people who use a single wet cells do so trouble free or economically. (We don't know if they are boondocking, and have a generator tucked away, which makes a big difference). It is in fact common for people to increase storage capacity to compensate for inability to fully charge their batteries and other inefficiencies.

Sometimes they discover that one battery holds insufficient power for such events as keeping the propane heater fan going in the face of a freak storm, in which case the camper freezes up (yes that happened to me).

So saying "bigger is unnecessary" based on some people using a single battery with assumed success is an argument without basis.

There is a place and a need for every kind of imaginable set-up in the RV community.


Please can we now return to the central topic of this thread?

[Ridenfun]

Crank, your reasons above are exactly mine, not wanting to check electrolyte SG readings, nad removing batteries annually etc. I'm not really sure how much capacity I'll need, as I'm as yet not sure how I'll use it so for now I'll go simple, ie 1 AGM with as much as I can find.
I've learned a lot in this thread, but biggest being the inability to properly fully charge the AGM up. My converter only puts out about 13.7 vdc according to a separate meter, which I guess was (maybe) OK in 2000 when it was new.
What are you considering (or have already done) to get the charging up to full on your older unit. I'd like to at least start from as full as possible.

[ptourin]

To keep from confusion and correct an earlier error of mine - Booster's right about my 10/22 post - the life cycle calculations on the Lifeline AGM's assume that end of life is when the capacity is down to 80%, not 50%. Check out the bottom line on the graph, all the way to the right.....

http://www.lifelinebatteries.com/ima...LIFECYCLES.jpg

That make the financial comparison even more interesting. Looking at that graph, I can get 500 cycles out of a 100 Ah Lifeline discharging to 80% DOD. I can get 2000 cycles out of one of my 100Ah lith phosphate batteries discharging to around 80%. I just did a quick search and I can buy a Lifeline GPL-31T for $325, vs. $1300 for my SmartBattery.

I am, of course, ignoring all the other reasons to buy one or the other battery type, and just talking dollars.

How do you like that? Pretty identical cost over lifetime, and I may die before I cycle my SmartBattery bank 2000 times <g>... That makes it pretty tempting to install AGM's and use them hard in order to gain the extra usable capacity. How many years will it take you to cycle your batteries 500 times? I don't know, but I'm not retired yet, so it'll take me quite a long time...

[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.

[avanti]

Originally Posted by booster

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).

As a case in point of the above, here is some real-life data collected on a recent trip showing the performance of our 270amp second engine alternator charging 440Ah of AGM:

--We started out one morning at 61% SOC, charging at about 230 amps.
--After 1 hour driving, our Trimetric showed 94% and 40 amps.
--After 2 hours, 97%, 8 amps.
--After 3 hours, 98%, 3.8 amps.

So, basically, if we drive or idle for an hour or so every day, the solar will typically top up the battery and we could continue on indefinitely without hookups.

Given that we are more "tourers" than "campers", this works very well for us.

[booster]

Originally Posted by avanti

As a case in point of the above, here is some real-life data collected on a recent trip showing the performance of our 270amp second engine alternator charging 440Ah of AGM:

--We started out one morning at 61% SOC, charging at about 230 amps.
--After 1 hour driving, our Trimetric showed 94% and 40 amps.
--After 2 hours, 97%, 8 amps.
--After 3 hours, 98%, 3.8 amps.

So, basically, if we drive or idle for an hour or so every day, the solar will typically top up the battery and we could continue on indefinitely without hookups.

Given that we are more "tourers" than "campers", this works very well for us.

Odd question, but how did you wind up down 170ah?

[ptourin]

So you replaced about 145 Ah in that first hour - that's pretty tempting alright! We're not retired yet, so a lot of our trips are more touring than camping, and I've started thinking about alternators vs panels. Don't know what it'll be like once we retire...

Booster, I've also started wondering about the lith abuse factor. I went to SmartBattery's site as I was putting together my last post, and I noticed that they now say "Use 100% of rated capacity". Perhaps they're figuring that it's OK to take the battery "all the way down" because their BPS will disconnect it at 8V and protect it from destruction.

I also notice that they're now advertising "3000-5000 cycles". Back into the gray area - but if you use 3000 instead of 2000, the numbers come out nicer for the lith batteries - though their chart still says 2000 cycles @80% capacity.

[avanti]

Originally Posted by booster

Odd question, but how did you wind up down 170ah?

Dry camping with large compressor fridge, evening of watching TV, cold night running heat, several cups of Keurig coffee, and (especially) using electric rather than diesel to heat water for morning shower.

[booster]

Originally Posted by avanti

Dry camping with large compressor fridge, evening of watching TV, cold night running heat, several cups of Keurig coffee, and (especially) using electric rather than diesel to heat water for morning shower.

That would do it! Pretty soon you will catch up with davydd.

[wincrasher]

Originally Posted by ptourin

So you replaced about 145 Ah in that first hour - that's pretty tempting alright! We're not retired yet, so a lot of our trips are more touring than camping, and I've started thinking about alternators vs panels. Don't know what it'll be like once we retire...

Booster, I've also started wondering about the lith abuse factor. I went to SmartBattery's site as I was putting together my last post, and I noticed that they now say "Use 100% of rated capacity". Perhaps they're figuring that it's OK to take the battery "all the way down" because their BPS will disconnect it at 8V and protect it from destruction.

I also notice that they're now advertising "3000-5000 cycles". Back into the gray area - but if you use 3000 instead of 2000, the numbers come out nicer for the lith batteries - though their chart still says 2000 cycles @80% capacity.

Also note that the true capacity of their 100ah battery is 108 amp hours. So taking it down 100%, there is really 8% left. So I think under normal usages, you are really only taking this battery down 90%. If I'm making any sense, I think that is the basis of their statement that you can fully draw down the battery. In reality, you are not.

[Crank]

Originally Posted by avanti

As a case in point of the above, here is some real-life data collected on a recent trip showing the performance of our 270amp second engine alternator charging 440Ah of AGM:

--We started out one morning at 61% SOC, charging at about 230 amps.
--After 1 hour driving, our Trimetric showed 94% and 40 amps.
--After 2 hours, 97%, 8 amps.
--After 3 hours, 98%, 3.8 amps.

Thanks for some REAL data, Avanti. Almost recharged in 2 hr: wow!

I'm aware that people some add an extra alternator: is that what you have done? Is it exclusively dedicated to the coach? Does the original alternator have an isolator that permits an additional contribution to the coach battery charge?

Are there any special considerations for such a set-up? I think it was Booster, who earlier pointed out that if you have a FULL battery, an alternator can cause overcharge: how do you prevent that?

A very important question: were your Trimetric amp readings at idle or cruising speed?

I agree that for tourers, plenty of alternator recharge is very useful, especially if you can "top up" with solar (because an alternator does not quite put out enough volts to fully charge an AGM deep cycle battery).

For boondocking, the alternator approach first sight seems dreadfully inefficient, except in emergency. Having a second, powerful alternator may entirely change the picture by increasing efficiency of the charge and greatly reducing recharge run time). That's why I am so interested in your installation.

What does your Trimetric read when the battery is at about 61% SoC and the engine is idling? If the amps don't fall too much, it would probably be effective to charge up the batteries at idle to about 95% SoC. The charge can then be completed with solar or a small generator like my 2.8KW Onan (which by itself would take all day to recharge).

[avanti]

Originally Posted by Crank

I'm aware that people some add an extra alternator: is that what you have done? Is it exclusively dedicated to the coach?

Yes and Yes.

You can read about my install starting here:
http://www.classbforum.com/forums/f5...html#post31345

Does the original alternator have an isolator that permits an additional contribution to the coach battery charge?

No. The coach power system is now completely isolated from the chassis.

Actually, I DID leave the old isolator in place, but its only purpose is to provide a "boost" capability in case of a dead chassis battery.

Are there any special considerations for such a set-up? I think it was Booster, who earlier pointed out that if you have a FULL battery, an alternator can cause overcharge: how do you prevent that?

The Balmar regulator that comes with this system is a fully programmable 3-stage charger. It is very capable.

A very important question: were your Trimetric amp readings at idle or cruising speed?

It was cruising. At idle I see just slightly north of of 200amps.

For boondocking, the alternator approach first sight seems dreadfully inefficient, except in emergency. Having a second, powerful alternator may entirely change the picture by increasing efficiency of the charge and greatly reducing recharge run time). That's why I am so interested in your installation.

This is one of the best upgrades I have ever made.

What does your Trimetric read when the battery is at about 61% SoC and the engine is idling? If the amps don't fall too much, it would probably be effective to charge up the batteries at idle to about 95% SoC. The charge can then be completed with solar or a small generator like my 2.8KW Onan (which by itself would take all day to recharge).

Running at idle would not be very different from the numbers I reported. It can do a reliable 200amps at idle, and the charger doesn't stay above that for very long.

Note that the Balmar is perfectly capable of fully-charging the battery. It just takes a long time, but that is the battery's fault, not the charger's.