80% is as low as you should ever go if you want the batteries to last. Therefore unless you have a sophisticated means of battery monitoring you should shoot for 50% which is a better number for a long battery life. 500 cycles at 80% DOD is very optimistic.
Keep the voltage above 12.0 volts unless you are discharging heavily then it is OK to go a little lower.
The confusion over 20% or 80% comes from the ads for the SCS150 in solar application. They talk about using it for a remote house off the grid and running it down from 100 % SOC to 80% SOC each day and how many years the battery will last doing that. They call that a 20% discharge cycle.
The problem IMO, is that is not what you do in typical RVing using deeper cycles. The OP's camping style might make it work, don't know enough about his ah numbers, but his solar recharging plan and operating in the 80-100 SOC looks somewhat dubious IMO. Those who have solar can comment better on what the OP needs there.
The ads also confuse the 100ah capacity Trojan gives it, as being 110ah or even 111ah.
I'd like a reference to that chart that says 80% DOD with 500 cycles - that is at the extreme edge, I think. The definition of 'cycle' is rather 'pure' in these specs so they can't be easily applied to typical RV service. Also note that very few RVers are going to cycle a battery more than a 100 times or so in the expected 5 year life of a typical lead acid battery.
Usually there are quiet periods in your power cycle when the battery isn't charging from the sun or other source and you aren't running any significant loads. If you measure the voltage after a half hour or so of a quiet period, you can get a very good measure of the current charge status of your battery bank. I'd suggest the 50% DoD to be your target or keeping the battery bank above 12.0v after a half hour or so of quiet.
If you never run your batteries below about 12.4 volts then you have too much battery and they don't get exercised properly. If you find them below 12.0v a lot then it is likely you don't have enough battery.
Perhaps the biggest drain on the life of a battery bank is not getting them fully charged. Serious full-timers often handle this by using a genset in the morning to get the bank up to absorption levels then a solar system to finish the charging during the day. For the weekenders, the primary battery killer is storage - batteries need a good maintainer and charger on them when not in use to keep the charge up and sulfation down.
One of most misunderstood task is how to measure battery voltage. Battery surface charge can easily fool one into believing the battery is full when it's not. Surface charge will accumulate (even with a near dead battery) and give the wrong message.
The 'official' method to measure battery voltage is to load the battery with 25A for 3 minutes, let the battery sit for 5 minutes unloaded and then measure the voltage. It's understandable not many people will do this.
I've found (as others also mentioned) true battery voltage can be measured by simply measuring the voltage when the battery is loaded with ~3 A (a couple of lights on). Measure after the voltage settles. If you have solar, disable it or wait till it's dark to make this test.
Like others, I keep the battery voltage above 12.0V.
BTW, hygrometer measurements aren't that accurate either (in determining SOC). Unless you shake up the battery real good (to get an even mixture of electrolyte) the measurement will be incorrect. The hygrometer is best used to determine if individual cells are bad.
Sal
bryanl wrote:
Usually there are quiet periods in your power cycle when the battery isn't charging from the sun or other source and you aren't running any significant loads. If you measure the voltage after a half hour or so of a quiet period, you can get a very good measure of the current charge status of your battery bank. I'd suggest the 50% DoD to be your target or keeping the battery bank above 12.0v after a half hour or so of quiet.
bryanl wrote: I'd like a reference to that chart that says 80% DOD with 500 cycles - that is at the extreme edge, I think. The definition of 'cycle' is rather 'pure' in these specs so they can't be easily applied to typical RV service. Also note that very few RVers are going to cycle a battery more than a 100 times or so in the expected 5 year life of a typical lead acid battery.
I posted a chart above. I agree that under part time use cycling more than 50% will not shorten the life as much as many would have you believe. US Battery says going beyond 80% discharge is what really hurts. IMO what shortens the life more than hard usage is not getting back to 100% periodically or letting the battery run down while in storage.
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Quote: One of most misunderstood task is how to measure battery voltage. Battery surface charge can easily fool one into believing the battery is full when it's not. Surface charge will accumulate (even with a near dead battery) and give the wrong message.
and near everything else battery! - what I see is folks trying to re-establish laboratory conditions and then failing to consider the underlying accuracy of the measures. Very precise but not very accurate because batteries can vary by 20% or more from cycle to cycle and also by a large number of variables.
For most of us, we want to get an idea about our battery when we are in the field. That means the battery is in use and the question is whether we'll have heat in the morning with the furnace or to plan a charging session. The easiest way to gain this information is by a proper interpretation of the battery behavior. That is why the 'quiet period' voltage check is suggested as it is something easy to do, simple, and will usually yield sufficient information for an effective decision.
re the posted chart: it is missing so much necessary data as to be nothing more than an indication of the shape of the curve. (see batteryuniversity.com for a similar result with better provenance). My query was about a specific battery and how we could apply a specification to RV needs. I think there is a reason why you do not find life cycle ratings on commonly available spec sheets but that reason is not explicit. Instead you have to infer from warranties and comparison, for instance, of automotive SLI, RV, and commercial application warranties.
Quote: IMO what shortens the life more than hard usage is not getting back to 100% periodically or letting the battery run down while in storage.
I'd only add electrolyte stratification when in storage. That is why the PD+CW or WFCO converters or the Battery Minder Plus can be so effective in prolonging battery life.
The title subject of "battery break in" has not been beat to a pulp yet. That's a curious one as I have seen several comments from reputable sources that you need to cycle a battery a few times before you can realize its full potential. I haven't seen any measure of what this difference is or why it would be so - yet, still looking.
For most of us, we want to get an idea about our battery when we are in the field. That means the battery is in use and the question is whether we'll have heat in the morning with the furnace or to plan a charging session. The easiest way to gain this information is by a proper interpretation of the battery behavior. That is why the 'quiet period' voltage check is suggested as it is something easy to do, simple, and will usually yield sufficient information for an effective decision.
My RV is in a "quiet period" right now. The battery voltage reads 12.8V. This , of course is incorrect. By definition, the battery is 100% full at 12.6V. Anything over 12.6V is bogus. The surface charge is giving us a wrong reading. The battery may be only 75% full of charge, but it's reading 12.8V unloaded. Without loading the battery we would never be able to determine the SOC.
To each their own. However I find it unwise to measure the battery state of charge your method.
oh boy, I just love the augmentative nitpicking these things get into (pse pardon the sarcasm). Now it turns out that "quiet period" and "100% full" are being defined for me - despite what I said - it seems only in order to pick nits. Does that really help?
Quote: The battery voltage reads 12.8V. This , of course is incorrect.
If you measured the voltage then it is most likely correct unless your meter is broken. What is incorrect is how the measure is interpreted.
As I said, what you are looking for when you are out using your RV is a voltage below about 12.4v down to about 12.0v after a half hour or so when you haven't been working your battery. As I also said, looking for an excess of accuracy is a fool's errand. Whether your battery is at 75% or 80% DoD is irrelevant to the question about how urgent the need for a charge may be.
Note also that there is a difference between measuring state of charge and answering the questions an RV faces when using his battery. My focus is on the latter.
As with any measure, it is the _interpretation_ of the measure that counts. Even if you used a device to actually measure SoC it won't help you much until you interpret that measure in the context of your energy use patterns, battery bank size and type, battery age, and other matters.
For those who are not willing to use a modicum of common sense in interpreting battery behavior (or in trying to understand messages in these discussions), check out the smartgauge web site. That device has the 'smarts' built in so you don't need any. Better yet, the technical information has some easy to read information about how the device interprets its observations of battery behavior to provide its conclusions.
What I suggest may be "unwise" (I'd rather see differences of opinion rather than judgments) but it works and it is easy, in my experience, to teach the concepts to others so they can be more effective in their battery management in their RV.
"By definition, the battery is 100% full at 12.6V."
This comment is of course referring to the wet cell Trojans owned by the OP. FWIW, I have three AGM batteries in my RV's coach. Two of them rest disconnected for weeks at slightly above 12.8 volts. The third (a different model from the other two), rests disconnected for weeks at slightly above 13.0 volts.
By the way #1 - Regarding break-in of wet cell batteries, check this link:
By the way #2 - Don't use three-digit voltmeters for measuring your RV battery terminal voltages. Use a four-digit voltmeter for this so that the increased resolution will give you a reading of "12.46" volts instead of "12.5" volts.
* This post was
edited 10/01/08 10:18pm by pnichols *
From link: Assuming that your batteries have the expected Amp-hour capacity, the break-in discharge(s) will take about 20 hours. Let the discharge continue until the battery voltage reaches 10.5 Volts.
WOW. They suggest 100% discharge about five times to break in a battery. I can see 50 to 80% discharge but 100 seem like a bit much to me.
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