Battery capacity for boondocking

[HB Phil]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by KU9L:
When I go back to read Bruce's original post I only see two Trojan T-105's listed, so he only has about 230 amp-hours at 12 volts nominal available. So he has about 1/2 the 400 amp-hour storage needed to follow Phil's example which either means running the generator more often or adding another couple T-105's.

Dave </div></BLOCKQUOTE>

I still think Bruce and Jenna will be fine with 200 Amp Hours.

If they are using between 50-to-100 amp hours day/night, they should be OK. Running a 60 Amp charger for 1.5-2 hours a day should bring them back up to about 80-90%.

It's best for battery life to cycle batteries staying above 75%, but just as long as they are above 50% they won't do any damage and will still be within "normal" limits.

Giving them an extra long charge/blast once a week, maybe a 3-to-4 hour run on the gennie, with that 60 amp charger and you will help to keep them equalized.

Once they get hooked up again the Charge Wizard will take cae of them, fully charging them, just fine.

A full charge could take up to 17 hours. That last 10% is very time intensive. Many folks who do extended boondocking say that it is impractical to use the gennnie to do a full, charge and try to top off to 90% as often as possible.

In general while boondocking the more that you can keep them charged up, the better.

[ChiefJohn]

Bruce,
One of HDT brothers has an outstanding web site Jack Mayer that may be helpful.

[KU9L]

Bruce will be fine, except he'll just have to replace his set of batteries a little more than about twice as often, which ironically would be about the same as if he had four batteries to start with. Since weight is an issue, having four or more batteries isn't often possible in some setups. Then main luxury being that when one battery fails you can stil limp on just one string until they can be replaced as opposed to being totally without stored battery power as happens to a single set of golf cart batteries when one gives up finally. One set is fine, especially if one has an accumulating amp-hour meter to accurately know just have many amp-hours are left in bank, whereas just a voltmeter itself is a general guess without letting it rest for a period of time to gauge it accurately from there.

Dave

[HB Phil]

The below link is a great source for battery info.

http://www.windsun.com/Batteries/Bat...of%20Batteries

This vendor, Arizona Wind and Sun, sponsors a forum for solar power users.

http://www.wind-sun.com/ForumVB/index.php

The main contributors to this forum are electrical engineers who are serious alternate energy users and/or hobbysist, very well-versed in deep cycle battery usage and maintenance. They are not affiliated with the host vendor, nor, do they sell their own advice or services. They are very gracious with excellent, expert, advice that is in compliance with NEC safety codes and practices.

They are many, many discussions of rv battery charging applications so feel free to join right in or to ask a question. Many times the reply will include mathematical equations and the laymen's translation to go with them.

Here is a excerpt from the Wind & Sun battery page about charge cycles vs battery life:

Cycles vs Life

A battery "cycle" is one complete discharge and recharge cycle. It is usually considered to be discharging from 100% to 20%, and then back to 100%. However, there are often ratings for other depth of discharge (DOD) cycles, the most common ones are 10%, 20%, and 50%. You have to be careful when looking at ratings that list how many cycles a battery is rated for unless it also states how far down it is being discharged. For example, one of the widely advertised telephone type (float service) batteries have been advertised as having a 20-year life. If you look at the fine print, it has that rating only at 5% DOD - it is much less when used in an application where they are cycled deeper on a regular basis. Those same batteries are rated at less than 5 years if cycled to 50%. For example, most golf cart batteries are rated for about 550 cycles to 50% discharge - which equates to about 2 years.

Battery life is directly related to how deep the battery is cycled each time. If a battery is discharged to 50% every day, it will last about twice as long as if it is cycled to 80% DOD. If cycled only 10% DOD, it will last about 5 times as long as one cycled to 50%. Obviously, there are some practical limitations on this - you don't usually want to have a 5 ton pile of batteries sitting there just to reduce the DOD. The most practical number to use is 50% DOD on a regular basis. This does NOT mean you cannot go to 80% once in a while. It's just that when designing a system when you have some idea of the loads, you should figure on an average DOD of around 50% for the best storage vs cost factor. Also, there is an upper limit - a battery that is continually cycled 5% or less will usually not last as long as one cycled down 10%. This happens because at very shallow cycles, the Lead Dioxide tends to build up in clumps on the the positive plates rather in an even film. The graph above shows how lifespan is affected by depth of discharge. The chart is for a Concorde Lifeline battery, but all lead-acid batteries will be similar in the shape of the curve, although the number of cycles will vary.

[BryanL]

All the numbers and specs and such are nice for geeks and for considering a new setup, but they really don't solve the problem all that well.

How you use batteries is very hard to calculate and very much dependent upon personal habits. That means your experience is going to be your best guide.

Try to get enough battery in your rig so you can go a weekend in mild temperatures (3 days, 2 nights, occasional furnace) without the batteries going below 12 volts measured after they have been resting for a half hour or so. Either get more battery or figure out how to be more 'green' on energy use to get to this point.

Get a 3 stage charger that can provide 20 amps for each 100 ah of battery (at system voltage) you have for good charging. As Phil notes, the PD with Charge Wizard is a good option for this and will also do an excellent job of storage maintenance.

I remain skeptical about the importance many put on discharge cycles as a limiting factor - from what I see, the primary cause of death of RV batteries is not there but in poor use and management practice. I know we have a lot of full timers here but how many actually run their batteries down to 50% SOC more than a few dozen times a year? (maybe a good topic for a forum poll?)

Do run your batteries down at least 10% but no more than 50% between charges. (start charging below 12.3v resting and don't let batteries get below 12.0v resting - 12.2v is 50% SOC)

Do not let your batteries sit around without a full charge on them.

Use a maintenance charger that features desulfation or equalizing (like the PD+CW or Battery Minder) if you are not using your batteries for more than a couple of weeks.

Your batteries should last 5 - 7 years if properly maintained and used in nominal conditions of the typical RV experience. (Trojan or SOB, 6v or 12v, makes no dif as long as they are 'deep cycle' or RV/Marine rated)

If you find you need to add water to your batteries more than once or twice a year, re-consider your charging and maintenance practice. (especially if they are AGM's or other SLA's! ;-) )

Another good site for understanding how batteries behave is smartgauge technical - Az Wind Sun is also top notch in my experience.

[JavaJelly]

When my batteries go bad, and I do maintain them, I am going w/Dr. Peter's solution, AGMs. I know they are expensive but, having to adjust my RVing experience for battery maintenance seems to make it worth it.

I'm the worst user of wet cell batteries for RV's. I use the RV in relatively short spurts w/heavy use due to long travel times w/dry camping and a family of 4. I also live in the Buffalo area where there is extreme cold and I store for long periods.

I'm not saying it is for everyone, just all this maintenance and learning is a lot to have to worry about when you are not a full timer or near full timer.

[Bruce and Jenna]

After reviewing the accumulated wisdom here and on web pages, I've come up with these calculations (Bruce's motto – if it ain't in a spreadsheet, ignore it.)

12v draws amps * hours = amp-hours
Refrig burner 1.2 * 8 = 9.6
Misc background 1 * 24 = 24
Propane furnace 5 * 4 = 20
lights 6 * 5 = 30
Water pump 6 * 0.5 = 3
Computers 3 * 4 = 12
No draw when charging at night
-22.2 * 1.5 = -33.3
Total 55.7

Battery capacity in amp hours
2 T105 6v batteries 447 mins at 25amps 186.3
With 50% reserve 93.1

[Sorry for the poor formatting, but this site ignores spaces and tabs]

Questions:
&gt;Where does one get an accumulating amp-hour meter?
&gt;If a guy spends most of his time with shore power, should he cut that cord occasionally to deplete the batteries a bit? Or would the PD Charge Wizard or other smart charger take care of this?

One more CW dig – I searched for "accumulating amp-hour meter"�. Number one hit – washer-dryer. Number three hit – Coleman plush pet toys.

[HB Phil]

Looks to me like you estimate that you'll be consuming about 95 Amp Hours/Day. Your T-105's have 225 AH's, combined. So you are under 50% DOD with some wiggle room. You'll be fine if you plan on charging 1.5-to-2 hours per day, to 80-90% charge.

If you plan on frequently boondocking and do not like to run the gennie, you may consider adding 2 more batteries. Then, if you still consume about 100 AH's per day, you would only have to run the generator every other day to stay above 50% DOD, and so on... But I would still advise running it every day. That way you could stay above 75% which is better for the batteries. Once a week give them a good 3-4 hours of the gennie charge - a solid 90% charge.

If you do not plan on frequently boondocking, and do not mind running the generator everyday, I would keep my battery banks and associated gear and accouterments, to a minimum. Those T-105's that you have are very robust batteries and they will give you many years of service. Some guys claim 6-7+ years. Also if you boondock in the summer w/o using the furnace, your electrical consumption will drop and you might get by with 3-4 days w/o risking a 50% DOD. It's when folks get inverters and run microwaves and heavy load appliances that requires big, expensive, battery banks and, by virtue of the heavy electrical loads and expense, they need more sophisticated means to ensure they are optimizing their battery life.

One thing that is nearly universally agreed upon is that your Progressive Dynamics 9260 (a 60 amp charger) with Charge Wizard is very, very good at maintaining batteries, even when in prolonged storage.