AGM House Battery Charge/Discharge

[truk4u]

While at Marathon yesterday getting the ole Genmate Auto Gen working, I had a good conversation with the tech who specializes on electronics and we discussed the famous battery percentage of discharge. Marathon for many years has setup a default for inverters/chargers and auto-gens to run the batteries down to 11.4/22.8 and then charge back to 13.3/26.6. He explained that Marathon/Concord/Trace have worked in harmony many years and this method is time tested. So, we setup my auto-start for those numbers. After running the batteries down to 11.4/22.8, the auto-start ran the gen for exactly 5 hours, then shut down with batteries topped at 13.3/26.6. With these settings, the amount of time you can go between charge cycles with the inverters is fantastic.

So, the anal in me (sorry Jon) just couldn't except the fact that Concord insists the magic number is 12.2 and that being 50% discharged. This gives you great battery life, but pretty whimpy usage tiimes with the inverters. I called Concord tech and here is the skinny...

The AGM's are 100% discharged at 10.5/21.0. It is OK to run the batteries down any level above the 100% discharge rate without hurting the batteries. The deciding factor is number of cycles (1 cycle = 1 discharge/charge). What you get is a trade off of battery life vs inverter time. Here's an example based on discharge rates:

10.5/21.0 will give you 450 cycles
11.4/22.8 will give you 650 cycles
12.0/24.0 will give you 1000 cycles

The AGM state of charge follows:

100% 12.80
75% 12.55
50% 12.20
25% 11.75
0% 10.50

So all this time I've been yacking about not going below 12.2 and now I have to change my tune. I'm sticking with the 11.4/22.8 discharge as Marathon suggested and that should equate to 650 cylcles (my batteries are almost new) and if I used 50 cycles a year dry camping, I'm good for about 12 years. Of course we know we're lucky to get 5 years since were always plugging, unplugging, running the gen, etc. and not always taking the batteries down with a full cycle. I think that's what kills the batteries over a shorter time.

One note, Concord told me Marathons logic works, the guy said he's been there 10 years and only remembers 2 battery warranty issues with Marathon.

OK, there's my latest story and I'm sticking with it.....

PS - I ran two A/C's, fridge, tv and a few lights for over 3 hours on the inverters as a test for the auto gen startup. 2, 4000 watt inverters and 6 AGM 4'd's.

[dalej]

Great post Tom, I personally like what you said. I have never had auto start on our 4, 8D's AGM
batteries. I usually run them until I see them hit 11 volts and then charge. Our gauge isn't digital
so its not a exact science. Knock on wood, our batteries were bought in 1999. I was told by the
lifeline salesman that I’m pushing the end.

[jello_jeep]

Nice post Tom! Makes sense.. I will have to reporgram mine when I see it again..:rolleyes:

[Just Plain Jeff]

Your overview is interesting.

Could you possibly provide some details?:D

[jack14r]

Tom,I have been thinking about this low voltage set point and I knew my Marathon was below 12 volts.I was almost at the point of changing the auto gen on to 12,thanks for taking the time to research and get the facts.Marathons electrical system seems to be superior to me to some others because of the 2-4000watt inverters that lets me not run the generator for hours,but still run AC or heat without running the generator.I have recently noticed that other converters have increased the size of their inverters and batteries.I wish Marathon had 8 batteries rather than 6 like Vantari.
Jack

[Jon Wehrenberg]

Tom,

The logic as explained is very clear. Rather than dig through my research previously my reason for not allowing the batteries to discharge as deeply as the autostart allows was predicated on different numbers (such as 5000 cycles at about 12.3 or 12.4 volts versus a quarter of those cycles at the lower voltage) but conceptually your information and mine agrees.

I have a second reason, and it is a seasonal issue. The Webasto likes higher voltages. I would rather manually start my generator prematurely than have to deal with a funky acting Webasto. But further, I am a generator slob. I bought it and by golly I intend to use the damn thing. I want to wear it out. I want to be able sit in my coach with every light on, the AC's running, and the toe space heaters all at once.

I started using our old coach by conserving our battery power. It did not have auto start so I would sit in the damn dark so the batteries would last all night. Not any more. I like the smell of generator diesel exhaust and I intend to get as much as I can.

[truk4u]

Good point about the webasco Jon. On the way down to FL we parked at my sisters house with no power and had to let the webasco run all night. In the morning I still had 12+ volts and it ran fine. In those situations and when needing A/C, I would let the gen run, run, run and not depend on the inverters and auto-start.

Marathon owners with Trace inverters can go back to the factory settings by pushing and holding the reset botton for a few seconds. The trace has a chip in it with the Marathon settings. The only other thing you have to do is manually change the power cord size as needed for 30 or 50 amp.

[Just Plain Jeff]

As I begin to approach middle-age, there seem to be some things I don't recall the way I used to.

Isn't there something about battery 'memory?' That is, that batteries, if left below certain levels won't return to a full charge?

Maybe that's just for certain kinds of batteries?

We were told once that it was a good idea from time to time to fully cycle the batteries from low to full charge. Maybe that was hogwash?

[jack14r]

I believe you are thinking about nicad batteries that do have memory.

[Joe Cannarozzi]

Ya know, we can go to all the technical sites out there and read up on the subject and god knows I've been to plenty myself.

Only here are we able to get "the rest of the story" :rolleyes:

Tom GREAT POST!

Imre, great link!

Jon, I once heard the best humor always contains a little bit of truth:D

[MangoMike]

Truckman,

Great post and you didn't even have to buy the guy a beer.;)

mm

[kmuller]

We have a fairly comprehensive tech article regarding batteries on our website. On the home page, click on Assured Service, then down the left side you will see ZMI LINKS, under that click on Tech Articles. It's about the 5th or 6th article down - intitled AGM Batteries.

[kmuller]

Here is some more food for thought relative to the Marathon discussion at the top of the thread...

Comments from our VP of Operations...

"This flies in the face of both the common wisdom in the marine industry as well as my research and anecdotal experience. I've been selling, installing, servicing (and replacing) AGMs for nearly the entire time I've worked here at ZMI. We wrote an entire article about AGM batteries and why they fail (posted on the website). I would most definitely take with a large grain of salt anything battery manufacturers have to say on the subject of life cycles, they all exaggerate, it’s an accepted fact. I had a number of conversations with two representatives from Concorde/Lifeline and got conflicting info, the engineer was more frank than the front office guy (big surprise). In the marine industry, we use 50% discharge cycles and experience and testing shows this gives a good balance between cycles and longevity and, this is important, the key metric being amp hours delivered over the life of the battery. I wouldn't discharge an AGM below 12.2 (technically, this voltage has to be measured at rest, that is with no load on the battery for 24 hours, so some interpolation is often necessary). If the batteries are at 11.8 or 12 under a load, they may come up to 12.2 or 12.4 when the load has been removed for some time. Additionally, running batteries this low produces unwanted side effects for any motor loads. As the voltage falls, amperage rises on these inductive loads, which causes the motors to run hotter and die sooner, not to mention tripping circuit breakers. Simply put, working a battery, and the motors attached to it, this hard, regardless of battery chemistry, will, in my opinion, dramatically shorten its life as well as the life of motors, fans, pumps etc. 50% discharge has been accepted for quite some time as a standard in the marine business. 13.3, by the way, is the float voltage, the voltage at which a battery is maintained. The charging voltage is typically much higher, on the order of 14.7, depending on temperature, if the charge source is temperature compensated, AND IT SHOULD BE, particularly for AGMs. The leading cause of their failure is positive grid corrosion, which results from floating at too high a voltage."

Hope this adds to the discussion,

[Joe Cannarozzi]

Karl seems to me that where the gen. kicks in and the inverter starts charging "under load" would be important to the relationship between the inverter and batteries.

Well if we run our 12s down to 11.4 under load as Toms are set I'm wondering were that would put them if you shut everything down at that point and check them later, resting?

Let me rephrase.

What is the under load voltage you can go down to and still have the batteries come back to 12.2 resting without recharging?

I'm thinking that both posts just about corolate. Marathon is streatching it but just a little?

[truk4u]

Karl,

Thanks for the posting, this is the stuff we need. It's difficult to sort out the correct way to go with regard to the magic discharge number and the 12.2 still makes the most sense to me, but I'm going to stick with Marathons recommendation and see how it goes.

One of the problems I had using 12.2 was the short amount of time for inverter use. As an example, at float of 13.3 and resting, as soon as I turn on the master light switch with all house lights on (all 24v) the voltage goes to 12.8, but will hold there a long time. We seldom use all the house lights and usually have the 120v lights on.

What I found was I could go from about 9 or 10 pm with normal 120v usage, fridge, tv, lights, webasco and still be good until 8am with 12.2 or better on the gauges. I guess this a pretty acceptable amount of time, but if it was during the day and using the microwave, coffee pot, etc., the time would be much shorter.

I'm concerned about all of this because I spent a pile of Lew bucks on new batteries and want to get the most out of them. I could sure live with shorter inverter time if the batteries would last longer. I'm going to follow up with Trace and see what their take is on all of this.

[merle&louise]

I have a question about the auto start feature on the generators.

After the generator starts up and runs until the batteries are fully charged up, does it shut the generator down or does the operator have to do that?

[Jon Wehrenberg]

Tom,

This is a perfect example of how confusing some of these issues are.

I admit to being too conservative with my batteries. I justify that position by saying there is no downside to using the generator, so I rarely ever have the auto-start switch on.

If we look at the two points of view (doing a deep discharge versus charging the batteries at some higher level such as 50%) to me the choice is obvious.

There is no downside to limiting the amount of discharge on the batteries. There is absolutely no disagreement about the fact that the batteries suffer no ill effects by doing this. A deep discharge may have an adverse impact on battery life, and as Karl points out there may also be some additional considerations.

For someone who must leave the coach for an extended time period occasionally it seems the deep discharge and use of auto-start is acceptable, but other than that type of situation it seems to me that running the generator for extended periods (or often) does no harm, and may possibly be beneficial.

[Joe Cannarozzi]

Tuga It will shut itself down as well. You can also hook an A/C thermostat into it to keep cabin temps. down and program it for timed sequences, daily or weekly or whatever. We had to replace ours and picked one up for 159 bucks. Never did install it however because the low voltage limit is 12.0 at the high end Ind I thought that was too low. After reading the posts in this thread I've decided to install it afterall. When I dig it out of the basement I'll give you a web adress. The big boys units have other options as well like kicking on when park power is insufficiant and probably other things as well but the up front cost of the one we got is uncomparable.

[Jon Wehrenberg]

Imre,

When I talk about being a generator slob, maybe I need to be more specific.

If my batteries are at an acceptable voltage and I have no loads beyond maybe a light or two, my refigerator and the TV I agree and typically do not run the generator, but, as soon as I ramp up loads such as running a lot of lights at night even if I am not running toe space heaters or the AC I crank it up until I go to bed.

It borders on insanity to worry about the fuel a lightly loaded generator consumes, or how heavily it is loaded while we are sitting in an RV that is typically on the extreme high end of the expense curve. I'll go so far as to bet nobody on either of these forums has run a generator to death. These things are good for 30,000 hours or more if maintained and if there are any out there with even 3000 hours I gurantee you that will be rare.

There is only one time when I don't want the generator running and that is when I go to bed, so by running it often I don't have to try to keep track of battery condition or wonder if the available battery power will make it until morning with the refrigerator and Webasto and whatever else is running.

[Jon Wehrenberg]

I can't speak for others on Power PUlse, but for me...no.

[MangoMike]

Liberty WatchDog,

Is factory set to start the generator at 11.15 volts. I asked one of the Liberty's techs, and this setting is unchangeable.

Mike

[merle&louise]

Imre,

I have installed 4 of the PowerPulse units on the AGMs in my coach. The batteries are only 1 year old, so it is premature to report on their life.

I have spoken with other owners who have installed PowerPulse and they love it. The installation is simple, takes about 10 minutes.

With batteries costing upwards of $3,000, PowerPulse seems like a good investment to me. Mine were about $80 each X 4 = $320 (10%). I'll pay 10% if the battery life is doubled.

[Jon Wehrenberg]

Mike,

On the Liberty Watchdog you can alter the start voltage.

The wire that carries the voltage the Watchdog sees as the starting voltage passes through a fuse located on a fuse strip in the electric bay. I think it is a 1 amp fuse.

To make the watchdog start at a higher voltage, all that is required is to add a small resistance in that circuit so when the house voltage is at your target voltage the Watchdog sees its programmed start voltage. I'm sure a few minutes with a soldering iron would get the job done.

[truk4u]

Hmm, seems that Liberty and Marathon are pretty close in their battery discharge scenerio's for auto start.:rolleyes:

[Jon Wehrenberg]

I think Liberty and Marathon have both done a great job of analyzing the entire concept of battery charging and have probably both concluded the small trade off in potential loss of battery life due to deeper discharging is offset by the reduced number of autostart cycles and length of time between those cycles.

While I resist relying on the autostart I can understand why it was set up that way and the success of the concept has certainly been proven.

It sounds like the only difference between the two converters is one has a fixed voltage level and the other offers an opportunity to adjust the starting voltage level.

[truk4u]

Another interesting point just to drive everyone more crazy, is the Webasco and pumps are designed to operate at a range of 10 - 14 VDC. So if that is the case, then our flame throwers should have no problem running at the Liberty/Marathon discharge rates of 11.15 and 11.40.:eek:

This should get Mango deep into the technical manual for Webasco!:D

[Jon Wehrenberg]

IMRE,

You need to learn more about Liberty.

When we drive down the road our bus OTR AC keeps us so cool if we did not adjust the knob upwards they would have to thaw us out so we could register in a campground. Our bus AC system does a great job and for my wife and I it is a necessity. Others prefer differnt systems and that is fine.

When we stop and hook up or rely on our generator we use our Cruise Airs.

End of story.

[Jon Wehrenberg]

When I am in a campground that cannot supply me with the 50 amp power I am connected to, I have no problem whatsoever running my generator as long and as much as required.

I admit my coach is not set up to run AC units from inverters, but I never can envision wanting to do that anyway. If I need AC I intend to be plugged in or to run my generator. Others may have a different opinion.

[truk4u]

Imre,

You don't run the cruisairs all day on inverter, there good for a few hours as needed in between stops or whatever. One good example is stopping to eat or take a break, it's great to just let 1 or even 2 A/C's run off the inverters and then the house is charged back up while driving. I look at it as a temporary short term option instead of running the gen for an hour or two. While driving I can run 2 A/C's indefinately, but I haven't had to do that, my dash air freezes my knee off. Western desert in the summer probably has everyone using the cruisairs while driving. That's one big plus for OTR like Jon has.

If I need A/C long term and there's no shore power, the ole gen will run 24/7 if needed. Mine is so quiet and exhausting out the roof that I doubt it would piss anyone off. Besides, if I'm in a campground paying for 50 amp and it's whimpy causing low voltage to the cruisairs, I'll be on the gen making smoke all night if need be.

[kmuller]

This has been a great thread.....our last comment!

AGM's do fail and they do wear out, especially if you discharge them 75% or if they are not properly charged. Servicing hundreds of installations over the years, on average, we’re seeing about 4-5 years life expectancy of an AGM. Gels and good lead acid battery last longer. The primary advantage of AGMs is quick charge time and no maintenance. Don’t get me wrong, they have revolutionized the charging business, but they are not a panacea. Hook them up to a standard charger or, worse, an alternator designed to charge a truck/bus starting battery and you’ll see just how quickly they fail. Although fairly new to the coach business (I think Newell said they have used them for three years now), these batteries have been in widespread use in the marine and other industries for a decade now.

Proper discharge levels and keeping the batteries at a proper, temperature compensated float voltage is the key to longevity. The telecom industry pioneered the use of AGM's and knows more about them than most businesses, and they stress proper float voltage as the critical variable. Sulfation occurs when a battery is allowed to remain discharged for extended periods of time, it’s combated by proper float voltage. The most common cause of failure in AGMs, by the way, isn’t sulfation, that’s more of an issue for flooded batteries, it’s chronic overcharging or high float voltage, which occurs when AGMs are charged w/out the benefit of temperature compensation.

[merle&louise]

I have 6 - 8D AGM batteries connected in parallel in my coach. When I am dry camping and the Link System inside is set on amp hours when should I start the generator to recharge the batteries? The only accessories that run off of my inverter are refrigerator/freezer, TV, Aqua Hot, & lights. My basement ACs do not run off of the inverter.

Someone at POG II (I think that it was Peter vS) told me that each battery had 300 amp hours. Therefore, I assume that 1800 amp hours would be completely discharged. So would I then start the generator @ 600 amp hours of discharge if I wanted to not allow the batteries to go below 50%?

Also, what is the difference between a 4D and an 8D battery?:eek:

[jack14r]

Jon,Liberty has seen the light,their newest coaches just off the production line now have 2-4000 watt inverters.They still have otr bus air,but you can now run 2 ac units off the inverters.My 2001 Marathon has the same setup and it works great.the people at Marathon always question me when I talk about bus air,they basically stopped putting in bus air years before mine was built.They were so unfamilar with bus air they failed to reinstall the fan rheostat in their dash,wired it to the wrong batteries,and installed a 12 volt relay where a 24 volt should have been.I am the 3rd owner and the others must have run the generator as they traveled in order to run the ac.I got help from prevost on the rheostat wiring,and marathon warrantied all of the rest.It now works great.Does anyone know what type batteries(gel-agm) Marathon would have installed in 2001?

[Jon Wehrenberg]

Jack,

I try to keep life simple. If the engine is running I use the bus OTR AC to keep me cool. If the engine is shut down I am either plugged in or I am running the generator with cruise airs running.

I can't ever envision the need to run AC units off the batteries.

That's why America is great. Everybody can do it their own way.

[Jon Wehrenberg]

BTW,

Absent in these discussions is how Thompson Coach has designed and set up their coach electrical systems. I will not go into detail, but I am extremely impressed with the logic (as in both computer logic and the designer's logic) that has been applied.

The coach to start with is totally automatic. To bring it alive you use a control unit and turn two "boxes" from red to green. From that point on, your environmental settings are maintained and based on a complex set of parameters that are built into the computer logic the electrical system is monitored and the generator starts and stops as necessary to maintain a battery charge based on a large number of factors that have been programmed into the system. The coach has more inverter power than you can get in any campground so it can function as required without any input on the owner's part.

It sheds loads as required, and generally is probably better than any system I have ever read about or seen. So far it is the only coach that I know of that asks nothing of the owner in respect to systems operation because once you bring it alive, it does not matter if you are driving, dry camping or plugged into shore power. It totally manages all systems with no intervention.

[truk4u]

Hey grumpy ole man, if Tuga has 6 8d's in parallel, he has a wopping 12V at the end does he not?:D

[jack14r]

does anyone know what the voltages should be set at for gel cell batteries?

[merle&louise]

Are you sure that your AC is not running on AC? You would have to have pretty hefty cables from the batteries to the compressor to deliver the at least 5KW of power.[/QUOTE]

imre,

I don't understand your question. My air conditioners are running on AC from shore power or generator! The air conditioners will NOT run on the inverter.

How can I check to see if my house system is 12V or 24 V? Could I test voltage at a light socket for example? Sorry, I don't understand too much about electrical systems. That's why I like this forum, guys like you can help guys like me understand the systems in the coach.

I'm learning all the time.

[garyde]

Hi Tuga. Check your dash for Voltmeter reading guages. Do they show 12volt or 24 volt guages. That is one indicator. Also, on my Liberty , I have both 12 volt and 24 volt systems. So, you may have both as well on your Newell. The engine batteries may be 12 volt and the Coach batteries may be 24 volt . Or , like mine a combination .

[merle&louise]

Gary,

I have a 12 volt system. All of my batteries are wired in parallel, not in series.

Thanks for the help.

[Jon Wehrenberg]

IMRE,

Before you criticize Thompson, you need to understand how they are set up. Specifically they have two alternators and for the technical details you need to understand how they are hooked up.

[matsprt]

Regarding my previous post, I only expressed my limited and very personal understanding of the Outback inverters. And I am looking very much forward to talking to Thompson in Tampa. I am only curious about how things work and would be delighted to learn more about their system from you or anyone else. If the post sounded critical I appologize. I find it very refreshing to see new converters using more ingenuity to get us out of the RV dinosaurs era.

And now to respond to the personal aspect of your post, I find you a great sport and I am very encouraged to know that replacing the air bags (among other things) can be done in my garage without having to deal with annoying help. I would like to place some sensors there to monitor the wheel weights from my laptop (dream on, right :) ).

They are actually already using this technology in OTR Trucks. There are several systems that allow one to "weigh" the truck axles on site thereby saving a trip to the scales and avoiding overweight tickets. I do not know the particulars as I have never been interested in it for my fleet but I have seen them, talked to several who have them and like them.

If you want to know more I'll see if I can run down one of the suppliers and get their info to you.

Michael

[Orren Zook]

Neway and Hendrickson both supply a 'scale-o-matic' device that can give you an estimated axle weight for each axle of your vehicle that has this installed, that axle weight is then displayed on a guage.

[Joe Cannarozzi]

All you need is to T off the supply line to 1 air bag per axle and run it to an air pressure guage into the cockpit. Pete or K-W actually have guages marked suspension air. Once installed you can calibrate by going to a truck scale and crossing the air pressure with the axle weight. I know that these busses wont vary as much as a semi, loaded compared to empty, but as an example when empty in a semi a bag has about 15 or 20LBS and loaded your at 60 or 65LBS. It will probably vary from axle to axle on the bus. I have a lot of friends with on board scales and they love them. a simple air pressure guage will achive the same result. If you like the idea of an onboard scale the dash moniter looks almost the same as my wireless tire pressure moniter.
729

The loaders at the quarry now have them as well so I didnt get them. Ask for 24 ton and get almost exactly 24 ton every time, SWEET.