Battery Basics 101

[NoGas]

Am starting this thread because it seems few really understand the heart of their coach - the batteries. There are many threads out there including my favorite "The 12 Volt Side of Life". If you haven't read that yet, do so now and come back. However, few are tailored to our coaches. So here's a first installment and I hope others contribute...

Steps in charging a generic AGM or lead acid battery - the 3 Phases + 1 more (in my case 3-4D Lifelines)

In all coaches except those with lithiums, the following steps happen all the time and to some as if by magic. Understanding the steps it takes to charge your batteries and then setting up each to happen according to your battery manufacturers specifications is critical (and can be expensive if you don't follow those guidelines). If you have a brand of battery other than Lifelines obtain the specific settings from them and use those:

Bulk - everything your charger can give until the battery pack reaches a specified voltage. That desired voltage varies depending on the battery temperature and according to manufacturer. For Lifelines, at 77 degrees that voltage is 14.3 volts but it varies based on the battery temperature (not ambient temperature). Once that voltage is reached the next phase starts...

Absorption - holding that desired pack voltage until the current being added (AMPS) to hold it drops below 0.5% of the battery pack's rated capacity (for a 600 Ah pack that would be 3 AMPs). The duration of this stage is NOT based on a set amount of TIME and the amount of time spent in this phase will vary depending on several factors including depth of discharge, input current, battery temperature, pack age/condition and the size of the pack. Once the current necessary to hold that voltage drops to the specified amount, the battery pack is considered fully 100% charged and the next phase starts...

Float - reducing current to a lower voltage that will hold the pack at a 100% charge state without overcharging it. The voltage of this fully charged phase is also specified by Lifeline and it too varies based on the same factors (see tables in attachments below).

Equalization - Lifeline calls this a Conditioning Charge and contrary to what most believe, their AGMs can be "Conditioned". See the Lifeline excerpts below for details on how to accomplish this procedure.

Note - as you can see from the above, it is critical that the battery temperature sensor be connected directly to one of the battery terminals. BB had installed mine outside the plastic battery case which resulted it it measuring ambient NOT battery temperature! Battery temperature will also change during charging due to the heat generated by the act of charging so make sure that sensor is connected properly.
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[gcyeaw]

Van,
Thanks for the explanation. The issue I and others have is the use of a 12 volt fan on the generator. These fans draw around 20 amps (some more some less). The charger varies the output based on the voltage level, and that is directly the result of the current entering the battery bank. However, the additional load of the fan adds 20 amps to the required charger output to achieve the correct input to the batteries. The end result is the charger current will never really drop to the proper level to enter float based on current draw.

The current entering the battery bank, however, will drop to the proper level, but the charger will not "know" that.

If your gennie battery is isolated from the main bank (usually when there is a separate charging system like an alternator on the generator) then this issue becomes moot.

I have considered adding a properly sized 12 volt converter running off the 110 to supply the fan directly and eliminate the issue.

[NoGas]

Gardner

You are exactly right. However, your converter solution would definitely work.

The M380's PowerTech generator has it's own completely separate battery & charger, so this is not an issue. Older charger/inverters may not have this Absorb to Float sensing option. That's just one reason I upgraded to a Magnum MS2812. In that manual it says: "During Absorb charge mode, as the battery charges the current required by the battery decreases. When the return amps decreases below the Absorb Done Amps setting for two minutes, the charger transfers from the Absorption charge cycle to the final charge stage (Float)". However it then warns: "If DC loads are connected directly to the batteries and a Magnum battery monitor is not installed, the Absorb Done Amps setting should not be used. To charge the batteries, plus run the DC loads - the charger must increase the current delivered to the battery bank. This may result in overcharging the batteries since the return amps reading will be skewed by the DC loads." On the Magnum (and I assume other newer Xantrex inverter/chargers) there are three ways to sense when the transition from Absorption to Float should be made - Absorb Done Amps, SOC and Time.

[MrPutz]

That's all good information. Just to add a little more..

when you charge your batteries from the generator you never reach full charge anyway unless you run your generator for extremely long times. Most only run a couple of hours in the morning and a couple in the evening so the fully charged float condition typically is never reached. They are relying on bulk and absorption to get the batteries back to something above 85% typically.

[isp2952]

Originally Posted by rtpn60

That's all good information. Just to add a little more..

when you charge your batteries from the generator you never reach full charge anyway unless you run your generator for extremely long times. Most only run a couple of hours in the morning and a couple in the evening so the fully charged float condition typically is never reached. They are relying on bulk and absorption to get the batteries back to something above 85% typically.

So, because I really don't understand most of this stuff, I may be asking a dumb question. Given your statement above, is this where a solar system would help get your batteries up to the best possible state? Just trying to figure out if the expense of solar helps to get offset by extending your battery life? Batteries are expensive and if they last longer, because of a solar system, then the cost of a solar system is even more justified?

[MrPutz]

Originally Posted by isp2952

So, because I really don't understand most of this stuff, I may be asking a dumb question. Given your statement above, is this where a solar system would help get your batteries up to the best possible state? Just trying to figure out if the expense of solar helps to get offset by extending your battery life? Batteries are expensive and if they last longer, because of a solar system, then the cost of a solar system is even more justified?

Exactly!

Now you're getting it. Not only does solar help you off grid to be self sufficient it can also increase your battery life because it will take care of your batteries automatically. Charging with the generator can also do the same job BUT you'd have to run it many more hours and it's just not cost effective to run a 12.5kw generator long enough to achieve a truly 100% charged battery to float.

Other side affects of solar;

1) You don't irritate your neighbors with generator noise
2) You're generator lasts longer
3) You save all that fuel running the generator
4) You shouldn't run a generator unless it's properly loaded (>70%)
5) Battery life is extended

Believe me, I was never a real big advocate on solar but the last few years of research and testing and now I'm a big advocate for high voltage home systems with MPPT controllers. I'm still not sold yet on solar for my house though.

[NoGas]

All lead acid battery packs last longer IF they are NOT repeatedly DEEPLY discharged & IF if they are NOT allowed to sit too long in a discharged state. One advantage of solar is every day the battery pack is recharged to a 100% SOC and that increases the lifespan of batteries. While I doubt the savings of that extend lifespan would completely offset the cost of solar, it helps.

Details - Lead batteries, whether they be AGM's or old style wet golf cart T105's like Putz's are not a good match for our big generators. That's due to the way lead acid batteries charge. In the first Bulk phase, your pack accepts all the amps your charger can give so pack voltage rises quickly. But then the constant voltage Absorption mode kicks in and begins progressively reducing the charging amps to the pack. Initially the Absorption charge rate is as high as Bulk, but as the battery pack "fills up" charging amps steadily goes down. At Q the last several years using just the generator I'd only need 5-10 minutes of Bulk charging followed by a couple hours of generator supplied Absorption charging both morning and night, to reach a 85-90% State of Charge (SOC). In each charging session it might have taken an additional 2 hours to reach 95% and then 3 more to reach 100%. The whole time that big generator would have been loafing and consuming diesel. So getting that last 10% SOC is an extremely inefficient process when on generator. However if you are spending the night at an RV park with shore power available, your charger has the time it needs to eek out that last 10% SOC without consuming several gallons of diesel. The same is true with solar charging during the rest of the day. It feeds amps at that progressively reduced Absorption rate over hours and for free as long as the sun is shining, which results in a 100% SOC for "free".

A big advantage of lithiums over lead acid batteries is they can accept a very high amp charge rate throughout their one Bulk charging phase, all the way up to 100% SOC. This makes generator charging of them faster and much more efficient.

[MrPutz]

Exactly, well said.

[MrPutz]

Just another tid-bit of info about your battery sizing.

While on generator you shut down at quiet time (10pm) and start up at 6am. You just went an entire 8 hours using only your house deep cycle battery bank. Now the question, what was your battery voltage at 6am before the generator was turned on? The absolute lowest is 12.0v (50% charge), anything less is not good. So, if you're above 12.0 consistently your bank is sized right for your needs. If however you find them below 12.0 then you need a larger bank, it's that simple.

Now, you want to go solar.

Here's your new obstacle, you lose sun power at 5pm (winter in AZ) and you get it back just after 8am so now you have to go 15 hours without a charge! Compare that to the 8 hours with the generator, you almost double your charging & battery needs!

Now you see why I always say "GO BIG". You'll have a good 5 hrs (winter in AZ) to replenish that bank but what is your voltage now at 7:30am before the sun comes up? I found mine was under 12.0 with my home refrigerator, heaters, CPAP, and normal parasitic draws of the bus with my old 4x 6v battery bank. So I added another set of 6v deep cycles to my coach to bring the total house bank from 440ah to 660ah. I find this is just enough for my needs in the winter (design for worse case) so I'm good now.

BTW, it's hard to have too much battery as long as you can charge them 100% during the day light hours you have. Check your area to see what your total solar day is. Arizona is in "zone-2" so we get 5.78hrs winter and 7.3hrs summer. To give you an idea of how little sun hours you may need to design with; Michigan and North Eastern states are zone-5 which only has 2.7hrs of sun hours in the winter! So if you have a 660ah house bank that is down you'll have to charge that back up in less than 3hrs!

[Jim Brookshire]

Mike, what you are saying is right on and certainly correct. However anyone who is smart enough to have a Bird should be smart enough to not try to run a Bird with solar in Michigan in the winter.