Best battery choices for generator only charging?

Audiomaker

Hi all,
Browsing the net this morning, my head once again started spinning while trying to make battery choices.
At the moment I am recharging using only a generator (solar coming but I want to optimize the generator system before adding it).

I know this is a newbie question, but I came across this chart:

Average Life Cycle Chart

Depth of Discharge Cycle Life Cycle Life Cycle Life
% of AH capacity Group 27/31 Group 8D Group GC2

10 1000 1500 3800
50 320 480 1100
80 200 300 675
100 150 225 550

Now I have been discharging my (crappy) grp27 200ah FLA 48v string (12v 4 series x 2 parallel) to 50% (well 47.9v).

Looking at this chart between the 50% and 80% discharge lines, I notice that 50% is 62% of 80%, and that 200 cycles is also 62% of o 320 cycles.
So Im sitting here wondering, if I only take my bank to 50%, I get more cycles, but if I discharge to 80%, I get less cycles per day?


My math might be wrong, but isn't that a wash?

Put another way (as I always do), what is the real world wisdom on less cycles to a deeper discharge? Once again, this chart is throwing me off because it looks like it would take about 40% *longer* between cycles at 80% discharge...netting less cycles in lifespan, but also less cycles/day?

Next question...

AGM's...
Lots of websites indicated a much faster recharge rate over FLA's (some say 5x (or 1/5th the time).
While this might be less consequential in a solar system or grid backup system, with a generator it seems that cost in fuel could be huge (running the generator 1/5th, or say 1/4th as long).
Currently it takes my little bank about 2 hours to float. Does this mean I could potentially charge an AGM bank to float in less than half an hour? (Man, that would be awesome).

I'm battery shopping, so if this were even close to being true, I'd abandon any searches for FLAs (I had considered Trojan T105's...etc).

If that chart doesn't read right, the page I got it from is here: http://www.chargingchargers.com/tutorials/batteries.html

BB.

Re: Best battery choices for generator only charging?

Regarding cycle life of batteries... As long as you are cycling between 80% to 20% state of charge (from "full"), very roughly, yes--2x the AH Battery Bank will last ~2x longer.

The "improvement in cycle life" is that the bank can age/lose more capacity before you need to replace it (i.e., a dead battery bank may have lost 40% of capacity... 2x larger battery bank can lose 80% of capacity and still work for you.

However, the larger bank is also "at risk" from early death. Meaning that if somebody does murder the bank, you it will have been a greater cost/loss.

Regarding charging--Yes, AGMs can take higher charging currents... And do not need the higher voltage charging during absorb. So, instead of the 80-90% battery efficiency for Flooded Cell, you get ~90-98% charging efficiency for AGM.

Do AGM still need 2-4-6 hours of Absorb at ~14.4 volts--I am not sure--But I would think it is helpful. The still are lead acid batteries.

One thing that seems to be true for AGMs is for the same price/quality AGM vs Flooded Cell--What I have read is that AGMs are still going to going to die a couple years before the same "quality" Flooded Cell. It may be part of the cost of earlier death is the eventual "wearing out" of the noble metal catalyst in the battery used to recombine the hydrogen and oxygen. The catalyst has a limited life--And the more (light) gassing of the AGM, the shorter the life will be. Once the catalyst is gone, the batteries will vent and eventually dry out.

Some batteries, you can get replacement catalyst caps--But they are not cheap.

One interesting thing I read from one company that monitors/services battery bank (telecom/industrial) was they monitor the float/absorb/ending charge current. When the current exceeds ~2% of battery AH capacity, the batteries should be replaced before "major problems" occur. Given that AGMs may typically end charging current at ~0.1% or less of AH capacity--I see this as a good way an off gridder can "monitor" the health of their battery bank--The flat tail of the end charging current. When it starts to rise significantly (~10x "normal"), the battery bank is probably ready for recycling.

-Bill

Audiomaker

Re: Best battery choices for generator only charging?

Thanks Bill. I think I'm still not understanding, or I didn't phrase my question correctly...

In the chart it equates something like this...

(I'm using the grp27's as the example, but I think the others follow)

At a 80% DOD the battery lasts 200 cycles

At a 50% DOD the battery lasts 320 cycles

At first glance, this is a good argument to set your AGS to kick on a 50% DOD, and when being charged by solar, or by the grid, where cycling might be less frequent, I can see the logic.

However, if running completely off of a generator where fuel, runtime, noise, maintenance are involved, it becomes less clear...

Here's why (rough math)...

My generator runs about 5-8 times a day to recharge the bank from 50% DOD. That's 5-8 cycles per day from the expected number of 320

80% DOD vs 50% DOD equates to more inverter time between charges, and therefore less charge cycles per day.

I don't know what the actual *time* numbers are, but if it were linear...

80% DOD is about 40% more time between cycles. So in a day, if I take an "average" number of charge cycles via generator, (I'll say "6")...

Roughly the cycles per day also decreases by 37.5% (50% DOD is 62.5% of 80% --- 200 cycles is 62.5% of 320 cycles) 37.5% is the difference between 62.5 and 100%

6 cycles per day x .375 = 2.25 so 6 - 2.25 = 3.75 cycles per day. Nearly half as many cycles (well 62.5% as many cycles). Yes, you only get 200 cycles according to the chart, but that 200 cycles is spread over many more days.

I understand this math is a little washy, but the concept is clear. Less cycle life from your bank @ 80% DOD, but less cycles per day, so why not set the AGS to kick at 80% DOD and save the fuel and noise?

Audiomaker

Re: Best battery choices for generator only charging?

I'm also going to add (instead of editing) that...

@ 6 cycles/day @ 50% DOD my bank is only projected to last 53 days (is this possible?)

@ 3.75 cycles @ 80% DOD per day the bank would also last 53 days.

Same thing (according to the chart), but how real world is this idea and how real world is 53 days before bank death?

gww1

Re: Best battery choices for generator only charging?

I frequent feildlines forum quite often. I remember it being put forward there that based on a study that doing most of your cycleing of battery between 80% full and 50% dod gave the most kwh from most batteries. Charging the top level to full took a lot of extra watts and going low took life. I would think with a generator it would still be the same equation of how many watts was put in compared to how many watt where taken out. If you got rid of the noise and hassel factor the above would still seem to be true. If the generator cost to gal of gas to run and the batteries give the most efficiant watts out, that would seem to be best.
gww

Audiomaker

Re: Best battery choices for generator only charging?

gww1 wrote: »

I frequent feildlines forum quite often. I remember it being put forward there that based on a study that doing most of your cycleing of battery between 80% full and 50% dod gave the most kwh from most batteries. Charging the top level to full took a lot of extra watts and going low took life. I would think with a generator it would still be the same equation of how many watts was put in compared to how many watt where taken out. If you got rid of the noise and hassel factor the above would still seem to be true. If the generator cost to gal of gas to run and the batteries give the most efficiant watts out, that would seem to be best.
gww

Seems to be the consensus. I think the chart is wrong.

In the chart I posted, there was a linear decrease in cycles to DOD.

If the chart fell off radically (ie... 320 cycles @ 50% DOD and 150 cycles @ 80% DOD), I'd be less impressed.

It's that the chart shows 320 cycles @ 50% and 200 cycles @ 80% which basically is the same thing (or hypothetically putting out the same kWh per lifespan in a 24/7 cycling situation).

If this is true, or if the ratio is only slightly different (say 5% more or less), then it would be more beneficial to run the generator for a fewer number of (longer) cycles while staying in buik longer and keeping the generator in its efficiency range (25-50% load) longer....etc. Even if that netted 190, or 170 cycles from the bank vs 200.

A generator is a bit less efficient when it's cold, and a bit less efficient at low end loads (because the ratio to fuel being used to power itself vs output increases). It just seems like keeping it in a medium load warm state for longer would be ideal.
The (now famous) chart is accounting for battery life (err...battery damage) at the greater DOD. It accounts for this as # of cycles, but doesn't account capacity..etc. That might matter.

One number that is elusive is if discharging to 80% nets 37.5% more kWh during that cycle? I suppose it would. My math once again is based on 50% being 62.5% of 80%...leaving 37.5%

Audiomaker

Re: Best battery choices for generator only charging?

I really feel like I'm missing something here.

Let's take a look at the chart (yes..again). I'll only use the first column which is for grp27/31 batt's.

DOD = 10% = 1000 cycles

DOD = 50% = 320 cycles

DOD = 80% = 200 cycles

Ok, so is a 50% DOD equal to 5X the kwh output as 10% DOD?

If so, let's just put the cycle @ 1 "unit" of power for the sake of simplicity.

10% DOD = 1000 cycles @ 1 unit = 1000 units

50% DOD = 320 cycles @ 1 unit x 5 = 1600 units

80% DOD = 200 cycles @ 1 unit x 8 = 1600 unit (the same as 50% DOD)

100% DOD = 150 cycles @ 1 unit x 10 = 1500 units (What !???)

Darn it, gonna see if any of my friends have extra Prozac

gww1

Re: Best battery choices for generator only charging?

audio

I don't pretend to do the math and don't try very hard. Math was my best subject in school so this just shows how lacking I am all around. I don't think the study they were refering to had much to do with life of battery. It was reconized that a 20% discharged battery lived longer then a 50% one. I think the sole purpose was to show the sweet spot of getting the most posible kwh out of a battery even if they lived shorter lives. You mention the ineffeint cold start but on the opossite side is the heating of a battery with bringing it from so low of a discharge rate. I, by the way did not read the study but just took the presenters on faith. It sound to me like most of one has a counter cause to the other and therefore is about a wash. I do believe reading every chart I ever read that the battery makers all pick 50% and even the forktruck charts have anything below the 40% mark in yellow in there little color coded charts. I will now read the link you posted as I enjoy comparing and find all kinds of conflicting info even on the battery makers own sites. I guess in the end it is buyer beware and maybe common sense.
gww

Audiomaker

Re: Best battery choices for generator only charging?

gww,

Yeah... copy that.

There is some misleading info' out there when people or companies talk about "lifespan". Kwh over the life of the battery is probably a more useful number than "cycles", and of course it gets even more complicated when filling that kWh isn't from the power grid. Battery companies after all aren't advertising how long they make your generator last right?

The type of study you mention is probably the closest, but I'll betcha still accounts for the kwh "input" from the grid...which is cheap and doesn't require oil...etc.

In fact, the rudimentary chart I linked to agrees that discharging to 80% shortens the battery life, but as a matter of cycles, not kWh produced, and if you were to look at a solar system, there is no penalty in saying that your bank will last longer if you only discharge to 10% DOD (um...as long as you have enough battery to get you through until the next sunlight).

Being off grid on generator however is sort of like having a deep cycle battery and a generator in a boat powering a trolling motor. Lifespan has to be looked at in miles, not months. You sit there and run that generator in the boat every 15 minutes so you don't over drain the battery, and at some point you are kind of thinking "man, I should have just bought a 120vac trolling motor"...lol.

What I'm sort of gathering is that deep cycle batt's can be taken down to 20% and survive at a rate not *wildly* different than 50%. Different yes, optimum for the battery no, something you would do "on grid", no, but perhaps the smarter choice when a $5000+ generator is paying to optimize those extra cycles the battery company wants to sell ya?

westbranch

Re: Best battery choices for generator only charging?

AM, there is a slight anomaly in that a true 100% discharge will only happen once. After that the battery will be unrecoverable for any type of normal use. So it should read 1 cycle. Expensive...

gww1

Re: Best battery choices for generator only charging?

Audio....
But in the end it still seems that getting the most kwh out for the fewest kwh in would still be the best deal. Therefore it would in my mind be adding enough batteries that allow a 50% to 80% cycle over the time needed with the ability to get to 100% every 10 to 14 days. So if you want a 12 hour run time on gen and a 12 hour run time on batteries, how many batteries would it take to run those times at a 50% to 80% cycling.

Then if the report hold merrit, you would have did the best posible with your batteries as to what you put in and what you got out. You can move any of the numbers around, like only running the generator for 8 hours and batteries for 16 hours. At some point you can't move the generator time down cause batteries take time to charge. To me, If I took the study on faith, I would hit a 50 to 80 percent charge cycle cause then I get the most from the money I spent on batteries and I get the most I spent on fuel. If I wanted to compare the rest, it wouldn't be the batteries charging I looked at but how much the storage cost compare to running pure generator. If the fuel and wear and tear on the generator was cheaper with out batteries then with, I would take the money I was going to spend on batteries and buy a backup generator. If however I was going to get solar are biodesel or even wind and the generator was untill I got those things I would buy batteries. Why even have batteries if it is generators that will really be running your stuff. Just get generators and put your battery money toward infrastructure to quiet the generator and maby recycle the heat it produces.

Lot of options depending on your long term goals. If a generator I what you are always going to use why have the losses assotiated with batteries?
Good luck
gww

gww1

Re: Best battery choices for generator only charging?

Bill

One interesting thing I read from one company that monitors/services battery bank (telecom/industrial) was they monitor the float/absorb/ending charge current. When the current exceeds ~2% of battery AH capacity, the batteries should be replaced before "major problems" occur. Given that AGMs may typically end charging current at ~0.1% or less of AH capacity--I see this as a good way an off gridder can "monitor" the health of their battery bank--The flat tail of the end charging current. When it starts to rise significantly (~10x "normal"), the battery bank is probably ready for recycling.

I found this a very interesting statement, I had been stressing that my battery sg was not rising till it had been at 1% for some times. I had knew that many were setting their end amps at 2% on there charge controllers. I was thinking maby something was wrong but maby something is not wrong untill the sg starts raising to full with a 2% end amp charge. My battery will get close to the 1% before sg quits rising.
gww

Audiomaker

Re: Best battery choices for generator only charging?

Don't get me wrong gww, I need batteries and an inverter. I wasn't really pondering a genset only solution.

What I'm saying is that optimum battery life seems to be a 2 dimensional equation.

You state "But in the end it still seems that getting the most kwh out for the fewest kwh in would still be the best deal."

I agree except that noise and maintenance issues do come into play on the generator.

The divergence from optimal is the number that isn't often seen, and its effects.

I'll make up an example...which is exaggerated only to demonstrate a point.

Let's say that the bank is the most efficient with the generator running ever other hour (1 hour on generator, 1 hour silent).

Now lets say that we diverge from that extremely (12 hours generator, 12hrs silent)

The question becomes not that we moved away from optimum, but by what percentage penalty we pay.

In the chart, 80% DOD @ 200 cycles vs 50% DOD @ 320 cycles is pretty much the same in *hypothetical kWh output* but I think we can assume that it's even worse by some percentage (ie...80% DOD shortens the life more, or in other ways), but by how much? 1% 10% 30%?

Maybe it's better to look at it long term...

Let's say we have a battery bank that will last for 10 years if treated optimally...

Examining the idea that shortened cycle life doesn't often mention increased cycle *time*, we perhaps are just looking at a kWh deficit of some percentage over those 10 years.

Maybe it's 20%? I don't know, but let's use that...

Because of the nature of the world, that 20% hit you take on lifespan kWh from your bank might allow you to do less oil changes, perhaps less rebuilds, and enjoy silence for longer periods (especially important ones like overnight), perhaps get you into the next solar period without having to start your genset at all...etc.

Generators are a lot like batteries. They are expensive, require maintenance, and have optimum run practices to extend *their* lifespan. Mine gets $30 oil changes every couple weeks just for this reason... in 10 weeks that's enough to buy a nice battery (or 5 Trojan T105's/year)... just oil.

It's too bad the study you're referring to didn't give a kwh lifespan with percentage of deviance (ie... "subtract 1% kWh per point of DOD"...etc").

I wonder if I joined the generator-electric.com forum, if they're over there going "But you'll see a 20% increase between rebuilds if you if only start/stop your generator 2 times a day vs 5, and avoid cold starts". Right??

As of this writing I've changed my AGS settings to start my 48v bank @ 46.6v (I had it at 47.6v). Wow...all this for a volt! Amazing that this is so far almost doubling my time between generator starts.
I'll let you know how it goes.

Westbranch... Yes, I was looking at that too. 100 cycles at 100% discharge. Maybe that chart is for the birds.

gww1

Re: Best battery choices for generator only charging?

Audio

I agree except that noise and maintenance issues do come into play on the generator.

I say this with respect.but the point you seem to be missing is, You can not get one kwh out of a battery that you didn't put in.

It would not mater if it was done with solar, the grid or a generator. All the rest of the talk is simatics, If it cost such and such from each sorce to provide the kwh, that could be dicussed. If you can only get what you put in back out then it would seem to matter what the effiency of the watts going in is compared to what comes out. If you charge to 100% then you lose watts to heat and get fewer watts out. If you discharge to 80% dod you lose watts you could have gotten from the battery. If I was running a generator then I would want to size it where it was most efficiently loaded fuel wise, wear and tear wise to match a 50 to 80% charging pattern cause I would know every watt made was putting wear and tear and eating fuel so making the fewest watts I could would be best.

This only works if you believe the study, which I mostly do. The rest is what is the math to make that happen. If generator run time is important, then get the battery that accepts the charge the fastest and a bigger generator. That of course is the same as taking batteries down to 80% dod as those batteries may not last as long and are higher priced to begin with.

I would probly just buy more of the flooded and then the only time the long charge rate would bother me would be the every 10 to 14 days I had to get to full charge. They would take a high rate of charge from 50% to 80% and for the same money you would have more cappasity which would get the long run time you want by taking the agm down to 80% dod.

I do not say I am right, there may be things I don't understand. I have never used a generator and only read what others have done.

Good luck
gww

Audiomaker

Re: Best battery choices for generator only charging?

gww1 wrote: »

Audio

It would not mater if it was done with solar, the grid or a generator.
gww

To the battery, no. To your wallet and ears...yes.

The best example I have so far is the one I posted below, which is that perhaps by *damaging* your battery bank to a small degree, you might be able to make it until the sun reaches your PV's and skip starting the generator altogether that day. Generator power in cost per kw is many times more than the grid or solar...especially when you factor in maintenance and replacement.

If running your batteries at less than optimum DOD"s costs you some percentage in longevity, it might be balanced out by savings on the generator end (both in fuel and maintenance).

Generators also have their own set of conditions for optimum efficiency and longevity. One example is that in my case, my XW6048 waits 5 minutes for the generator to warm up before it transfers power. That's 5 minutes of fuel being used with zero charging being done. 6 times per day = 30min/day just in prep' time with no kw being utilized.

That is just one of many examples of how the efficiency of one system has to be weighed against the efficiency of the other. It's not as simple as kWh-in vs kWh out.

These loses are in the low percentages yes... maybe a few percent, but the longevity losses of the batteries might also be in the low percentages at one DOD vs another (when looking at it in the kWh/life regard).

We might gather from the study you read that 80 to 50 is the best DOD, but what we don't know is how much less % in lifetime kWh we might get from say... 80 to 30. If it's low, it might be better to run it that way?

westbranch

Re: Best battery choices for generator only charging?

AM, I meant that 100% = dead for FLA's and a bit higher for AGM, however what if you use 80% as the bottom and add LiFePo4 to the question, I think from what we know at this time, longevity is still a major and unanswered question, and make a 10 year life span assumption, the answer might fall towards the Li battery.

I reference Reefbum's comparison table here...http://forum.solar-electric.com/showthread.php?26203-Battery-Cost-Compare&highlight=battery

gww1

Re: Best battery choices for generator only charging?

Audio...

Generator power in cost per kw is many times more than the grid or solar...especially when you factor in maintenance and replacement.

This aurgument has no merit. The fact is you are using a generator and the cost are there. In the end if you use 10 kwh overnight, that 10 kwh has to be replaced and whether it is grid or generator it is still 10 kwhs.

If running your batteries at less than optimum DOD"s costs you some percentage in longevity, it might be balanced out by savings on the generator end (both in fuel and maintenance).

10 kwhs is 10 kwhs

Generators also have their own set of conditions for optimum efficiency and longevity. One example is that in my case, my XW6048 waits 5 minutes for the generator to warm up before it transfers power. That's 5 minutes of fuel being used with zero charging being done. 6 times per day = 30min/day just in prep' time with no kw being utilized.

This has some merit, however, buying more expencive batteries that already have a shorter lifespan and then discharging the in a way that shortens life even further leaves lot of money toward buying flooded batteries at a higher capasity and running them optimized and comeing out with the same runtime of your abused batteries with a much longer life and therefor a better price point to put your expencive fuel in.

If this is true, or if the ratio is only slightly different (say 5% more or less), then it would be more beneficial to run the generator for a fewer number of (longer) cycles while staying in buik longer and keeping the generator in its efficiency range (25-50% load) longer....etc. Even if that netted 190, or 170 cycles from the bank vs 200.

Or a differrent battery with more capasity for the same cost that gives the same runtime and last 1500 cycles.

That is just one of many examples of how the efficiency of one system has to be weighed against the efficiency of the other. It's not as simple as kWh-in vs kWh out.

You are right, it is not just the kwh in to kwhs out. It is the cost for kwhs in to kwhs out. If cost didn't matter then how much it cost to run or fix a generator would not be mentioned. I don't get your discussion points at all. I could only see one reason to consider what you are considering. That is if I just had room for so many batteries and had to lay them on their sides to fit there and it was worth it to have them and cost was no object.

I hope you take my comments in the spirit of descussion and an honest heart and not just me trying to be mean, I am being truthful that I don't see your points as having merit. I am not judgmental no matter what you end up with. I have wind turbines in a zone 2 wind area if you want something to giggle about of me.
gww

westbranch

Re: Best battery choices for generator only charging?

A lot of the basic manuals for a lot of battery brands will state something like it takes 110 KwHrs to replace 100Kwhrs as a rule of thumb to account for a lot of the inefficiencies of a solar system and a battery... just saying so this additional cost does not get glossed over...

gww1

Re: Best battery choices for generator only charging?

Westbranch
You last post is why I mentioned earlier that if generator was the only charging source planed, why use batteries at all cause they all have losses. There is something to be said in a mobil system that quiet time while sleeping is worth something.
gww

westbranch

Re: Best battery choices for generator only charging?

quiet time while sleeping is worth something.

100% on the money GWW

softdown

Re: Best battery choices for generator only charging?

There are so many problems here that I can't even try to correct them. Hopefully one of the mods will digest this mess and get you pointed in the proper direction. Sure, we have a lot of knowledgeable users here but the mods generally have more plentiful experience in correcting "solar gone wrong."

Audiomaker

Re: Best battery choices for generator only charging?

softdown wrote: »

There are so many problems here that I can't even try to correct them. Hopefully one of the mods will digest this mess and get you pointed in the proper direction. Sure, we have a lot of knowledgeable users here but the mods generally have more plentiful experience in correcting "solar gone wrong."

Lol! We're just talkin'.

BB.

Re: Best battery choices for generator only charging?

Best I can say is don't obsess about fuel saving strategies... It appears that the optimum is going to be cycling between 50- and 80% state of charge for ~6 days a week and on the 7th, charge to >90% state of charge.

Run 10% to 20% rate of charge 6 days a week... On on the 7th, once you get around 80-90% state of charge, you will see the battery charging current drop. Once that value falls much below ~50% rate of charge, you may wish to use a smaller genset+charger to run out the absorb time at 5% rate of charge for the 2-4 hours or so needed to bring the batteries >90% state of charge.

Once vendor (Rolls/Surrette?) to one poster here suggested the >90% (or 100%?) SoC only need to happen once every 28 days.

From what I have read here, that will optimize fuel usage (flooded cell lead acid batteries are much more efficient charging below 80% state of charge). And if these batteries are true deep cycle, they should do OK cycling between 50% and 80% State of charge daily with an over 90% SoC once a week. And a possible 100% Soc/Light Equalize once a month (again with a smaller genset).

If you do not cycle the batteries for a day or more (going away for a few days or longer), recharge the battery bank >75% State of Charge--Do not let the batteries set below 75% SoC for days/weeks/months on end--That will accelerate sulfation.

Keep battery bank on the small/optimum side (do not get a bunch more battery than you need). Keeps any failures in operation (spouse, kids, guests, oops)--If they happen to take your battery bank "dead"--Keeps the replacement costs lower.

Make or get something to monitor voltage... ~50% SoC, start the genset. If drops below 50% SoC call you for help, get backup genset+charger going, check loads, etc. Below 12.0 volts resting (no loads) or below ~11.5 volts (12 volt bank) for minutes+ with some loads for warning voltage. Not real accurate, but will give you a quick and easy warning.

A few folks here have suggested this meter from Midnite as a good backup/simple to use meter for monitoring battery bank charging--And the >1 week warning between full charges works nice with the 1 full charge per 7 days of operation I suggested above:

http://www.solar-electric.com/batteries-meters-accessories/metersmonitors/mnbcm.html

A true battery monitor would also be very nice (one with a battery shunt to measure actual battery usage)--But they can also mislead the user if they do not watch overall battery voltage/specific gravity/etc.

The disclamers--I am not a battery engineer, I am not your battery engineer, I am on-grid (not off grid), and this is based on what I have read here and other places. Batteries can be surprisingly rugged, but also surprisingly easy to destroy. Do your own research and ask questions (here and other places, battery vendors, etc.).

If there are times that you will be leaving for weeks/months--I would still suggest a 1-2% minimum rate of charge solar array+charge controller. Leave the batteries fully charged (>90%) when you leave and have the solar "float" the batteries while you are gone (very cold batteries, below freezing, have much lower self discharge rates--so periods of snow on the panels are usually not a big issue).

Keep water levels (using distilled or similar water) to normal levels, don't cycle often below 50% SoC, do not ever let the bank cycle below ~20% SoC, check cabling, get a DC Current Clamp Meter to monitor shared current with battery banks that have parallel strings of batteries, etc...

And enjoy the them. Batteries start a slow death from the moment they are manufactured. And cycling does age them too... Batteries are a consumable--Just like generator fuel and electronics with a life of ~10+ years.

-Bill

Alaska Man

Re: Best battery choices for generator only charging?

Real world........... I live with just my generator and battery bank from October through March. In the depth of winter I may need to recharge twice a day. This depends on the temp outside, if I'm home to feed the woodstove or if the Toyo Heater is running full out. At -40°F the heater runs constantly.

My routine is to run the bank down 20% - 25% before I recharge. I don't always burn enough gas in my generator to float the bank. The last part of the charge from about 8%-2%, left, takes as long or longer than to go from 80% to 96%. I do float the bank every Saturday, so as not to lose any "Life". I have AGM's and can charge from 80% into the 90% in under two hours sometimes in under an hour. The fuel savings everyday or sometimes twice a day recharging, means that I'm dollars ahead not to mention huge time savings over using FLA. I don't like baby sitting the generator. I have been using these batteries hard for about 3 years now and have not noticed any decrease in the battery bank's performance. In fact I would say it is just broken in and working better now than last year.

The manufacturers recommendation and the recommendation from everyone of them I have ever read, says that running the bank down to 50% or to 12.0 (For a 12V System)will shorten the banks life by twice the amount if you only run it down 20%. I can't speak to this point yet, but I can say so far I'm happy with my AGM's. Again I don't have to baby sit them and check on them all the time. I monitor my State of Charge with my Xentrex Control Panel and with my Tri-metric. Other than that the batteries sit in their compartment doing their thing and pay them little mind.

Audiomaker

Re: Best battery choices for generator only charging?

BB. wrote: »

<snip>
And enjoy the them. Batteries start a slow death from the moment they are manufactured. And cycling does age them too... Batteries are a consumable--Just like generator fuel and electronics with a life of ~10+ years.

-Bill

Well that's just it Bill. The generator is also a consumable. Being a newbie on any kind of site temporarily grants one a unique perspective and without offending anyone, I'd suggest that a great deal of OCD'ing goes on here about battery life as if that were the overwhelming issue at hand with off grid power.

I understand that I"m a minority on this site being one who doesn't yet have solar, is completely off grid, and 100% counts on a generator.

Things go wrong with generators too... they can overheat, run low on oil, or expensive little circuit boards can fail, and every hour that they run is decreasing their lifespan. You could also include that generators don't usually fail when they aren't running.

So I would beg everyone here to acknowledge the fact that in my case, and in the case of a few others, that if my battery bank fails that I can still make a cup of coffee and type this post, but if my generator fails, it's over.

When you come from that perspective, you start looking at the batteries as a means to support your generator, not the reverse, and also as the means to have a little quiet luxury and maybe even a little fuel savings to help pay for the battery investment.

I understand that there are battery charging strategies that are optimum for the battery, less than optimum for the battery, and catastrophic.
I would also put forth that what is optimum for the battery is less than optimum for the generator in some cases, and also defeats one major purpose of having batteries (silence).

So what I'm after here is to discover how far one can move away from optimum battery life and find the crossover point for both generator longevity and peace and quiet.

I would speculate that we aren't ever going to find this point in "what the battery manufacturer recommends".

Alaska Man

Re: Best battery choices for generator only charging?

Audiomaker wrote: »

Well that's just it Bill. The generator is also a consumable. Being a newbie on any kind of site temporarily grants one a unique perspective and without offending anyone, I'd suggest that a great deal of OCD'ing goes on here about battery life as if that were the overwhelming issue at hand with off grid power.

I understand that I"m a minority on this site being one who doesn't yet have solar, is completely off grid, and 100% counts on a generator.

Things go wrong with generators too... they can overheat, run low on oil, or expensive little circuit boards can fail, and every hour that they run is decreasing their lifespan. You could also include that generators don't usually fail when they aren't running.

So I would beg everyone here to acknowledge the fact that in my case, and in the case of a few others, that if my battery bank fails that I can still make a cup of coffee and type this post, but if my generator fails, it's over.

When you come from that perspective, you start looking at the batteries as a means to support your generator, not the reverse, and also as the means to have a little quiet luxury and maybe even a little fuel savings to help pay for the battery investment.

I understand that there are battery charging strategies that are optimum for the battery, less than optimum for the batter, and catastrophic.
I would also put forth that what is optimum for the battery is less than optimum for the generator in some cases, and also defeats one major purpose of having batteries (silence).

So what I'm after here is to discover how far one can move away from optimum battery life and find the crossover point for both generator longevity and peace and quiet.

I would speculate that we aren't ever going to find this point in "what the battery manufacturer recommends".

I agree with this for the most part, but I will add. you can buy a good generator for $500. A Good AGM battery bank starts around $2,500. So unless you have the money of the Koch Brothers getting the most life out of your bank only makes good financial sense.

I'm 100% off grid, I live it. Like you, this isn't a hobby for me. It's my life.

gww1

Re: Best battery choices for generator only charging?

Alaskaman
I personally enjoy hearing your real life experiances. You, for sure, are living in pretty extream conditions and I hope you keep us posted on you experiances good and bad. I personally never mind being wrong and learning more.
gww

Alaska Man

Re: Best battery choices for generator only charging?

gww1 wrote: »

Alaskaman
I personally enjoy hearing your real life experiances. You, for sure, are living in pretty extream conditions and I hope you keep us posted on you experiances good and bad. I personally never mind being wrong and learning more.
gww

Thank you for saying so. I hope I can help others with the experience of living like this. I also enjoy this life style very much, there is freedom not being tied to the grid.

Land is a lot cheaper too. ;-)

Audiomaker

Re: Best battery choices for generator only charging?

Alaska Man wrote: »

I agree with this for the most part, but I will add. you can buy a good generator for $500. A Good AGM battery bank starts around $2,500. So unless you have the money of the Koch Brothers getting the most life out of your bank only makes good financial sense.

I'm 100% off grid, I live it. Like you, this isn't a hobby for me. It's my life.

Well we have different systems.

True, an AGM setup for me is about $2500.

My generator however has a replacement cost of about $7500.

Engine rebuilt cost is about $1500

Alternator head cost is about $1100

For the record, it's a Powertech CD7000

Alaska Man, as one off-gridder to another, I'm amazed that you can go 100% on a $500 generator for months. That hasn't been my own experience in the past.

Audiomaker

Re: Best battery choices for generator only charging?

Let me add this...

I think one thing I'm not grasping is what people are calling "battery life".

Is this in years, cycles, capacity? Is there some formula that takes all of these into account?

Gww came in with a really interesting angle which was lifespan as kWh/lifespan.

I keep hearing how X% vs X% will shorten a battery's "life" by 50%, but I'm just missing the *runtime* factor there.

Don't be mad with me, blame that stupid chart I came across and posted here. It's numbers reduced the *cycles* of the battery in relation to DOD, but as far as I could tell increased the time of each cycle proportionately as well... again..more kWh per cycle. The percentage of cycles @ 80% DOD vs 50% DOD were linear. Newbie logic thinks this means that I'm powering this computer *longer* per cycle (62.5% longer running the bank down to 80% DOD), so why would I make more cycles if the output is more or less the same?

That's not me presenting that I'm right about anything, it's begging that you explain why that chart is wrong, or what number I left out to make this logic untrue?

Blackcherry04

Re: Best battery choices for generator only charging?

Do a test, when I moved to a fast Charge scheme of bulk charging at 25 - 30% of C below gassing level I saved enough $$$ in fuel savings in the first year and a half to pay for the whole battery bank and 3 years later they are still trucking along. I have to say, it's for batteries that are pulled to 50 % dod and have 300-400 amp hrs to be returned.