How long to charge a battery bank?

[Jedon]

Okay I have 16 Trojan L16H 6V 420AH batteries, 2 strings of 8 for 48V. 420Ah @ 6V = 210AH @ 12V, 105AH @ 24V , 52.5AH @ 48V, 21AH @ 120V * 16 = 336AH for the whole bank at 120V optimally. They are probably 6 years old and might have been abused. So maybe 200AH?
I charge them with two Xantrex SW+ 5548 inverter/chargers fed from a 5400W Lima head on a Lister SR2 12HP.
The chargers are 3 stage, bulk, float and silent. They bulk charge at 57V and float at 55V and equalize at 60.2V.
So right now I run the setup around 10 hours per day, 5 in the morning and 5 in the evening.
In the morning the bank is usually around 46.4V to 47.6V which I am not too happy with.
My main draws at night are the fridge ( 1.2KWh/day so 8 hours at night should be 400W/Hr , maybe 4AH) then the freezer, about the same, another 4AH. A few other drains like routers etc call it another 4AH. So 12AH used and I should have 200AH but the batteries are nearly dead in the morning?
I let the inverters take 22A each to charge so 100+A DC total
When I go to turn off the generator after 5 hours the batteries are floating at 55V or so.
The batteries do bubble and use water.
Am I doing something wrong? Not running the generator long enough to really charge them up? Battery/ies bad?
Thanks!
http://picasaweb.google.com/lh/photo/wqxtpBns72ddelW3WtSHJA?feat=directlink

[mobile_bob]

if they are bubbling some that is good, if violently that is bad

do you have a hydrometer? if not get a good one because you will need one along with
a log book to track the conditions of each cell.

i get beaten up when i say this, but here goes

Voltage is not a good way of determining the condition of a flooded lead acid battery, yes it will give you a general
idea, but no where near as accurate as you need for long life.

the exception to this rule is a bank of telecom batteries that are predominately just sitting there in float and hardly
used to any depth of discharge,

get the hydrometer, check with the manufacture for what a fully charged  cell should have for specific gravity
and check all your cells the first time an log them in your chart, the cells that are weaker will need special attention
to get them back up to as high as you can get them (an equalization charge per spec from the manufacture) and then
once it is at its max level, log it in your chart.

then each month thereafter take new readings and compare against your chart of cells, if things are staying pretty well in balance
there is no need to intercede, if however you have a weaker cell, take it out of the string and equalize it if necessary.

apart from that, the bank should be topped up periodically (once a week or so at least) and then the hydrometer will tell you if you are truely
fully charged.

bob g

[Jedon]

I do have a hydrometer but it's a cheap one, I had a better one but it broke.
I looked into the pentametric meter which seems perfect but I don't have $500 to drop on it right now.  http://www.bogartengineering.com/pentametric.htm
I thought I read to get good hydrometer readings you need to wait 2 hours after charging with no load on them? If so that wouldn't work since I use them.
I do have 8 golf cart batteries to play around with and a 12V Trace inverter/charger.
Sounds like I need to add water more frequently!
I found this on the net:

Next look at the maximum DC charging amperage of your inverter(s) and if it is less than 20% of your battery bank's amp-hour capacity (at the 20 hour rate) then you should consider using an inverter with a more powerful charger or go with multiple inverters (or separate chargers) to increase your charging rate. To determine how many hours of generator run time will be required to fully charge the battery bank from its deepest depth of discharge you should divide your battery bank's 20 hour amp-hour capacity by 2 (to account for a 50% depth of discharge which is the lowest point we recommend you discharge your battery bank) and then divide that by half of your inverters' maximum DC charging rate. The reason for using only half of your inverter's maximum charging rate is because inverters don't charge at their maximum rate over the entire charging cycle. Reducing the charging rate to half of its maximum value will give you a more realistic estimate of your generator run time.

So battery bank capacity at 48V DV is 840AH, 20% of that is 168A. Half battery bank AH is 420 then half the DC charging rate of 100 = 50. 420/50 = 8.4 hours. I am using power when the generator is on, say an average of 4A @120V so 10A @ 48V DC, now 90/2 - 45 and 420/45 = 9.3 hours. About what I'm running the generator for.

[mobile_bob]

add another 10-15% to cover charging inefficiencies

you really need to rest the batteries overnight after a equalization before you test the specific gravity of each cell
that is to get a very accurate reading

you can however get a relative idea by checking them after a charge, not accurate in determining the cells being fully charged
but will show if you have a weak sister in the group that needs more attention.

you mention two strings of 8 batteries, maybe split the pair once a month so that it can be equalized and tested without load
and alternate to the other next month?

or find a way to do without power for a few hours at least to let the batteries settle a bit, then test them
you ought to be able to do this at least once a month?

bob g

[mike90045]

Start Shopping.

Fully charged, a 48V battery bank is 50.8V
  http://www.windsun.com/Batteries/Battery_FAQ.htm

Try a charge cycle, remove all loads, and let sit a couple hours, and then you can measure voltage.  Measure EACH battery, and likely, you will find one is 2V lower than the others, that dead cell in the battery, has destroyed your bank.    6 years for Trojan is about average.

(maybe run one bank while you rest & measure the other.)

[mobile_bob]

the reason i don't like voltage as an indicator of battery charge, for a flooded cell
of unknown condition and no historical record or specific gravity???

because you can take a badly sulfated battery and charge it until the voltage says 12.8 for a 12volt nominal
and apply a load only to have it fall flat on its face.

once a battery is fully charged as indicated by specific gravity, one can then for a time (a few weeks perhaps) get a good indication
of battery condition based on voltage alone, but once the specific gravity gets out of whack so will voltage as an indicator of battery condition
or state of charge.

bob g

[mike90045]

Okay I have 16 Trojan L16H 6V 420AH batteries, 2 strings of 8 for 48V. 420Ah @ 6V = 210AH @ 12V, 105AH @ 24V , 52.5AH @ 48V, 21AH @ 120V * 16 = 336AH for the whole bank at 120V optimally. They are probably 6 years old and might have been abused. So maybe 200AH?

Batteries are 420A each. 2 strings in parallel = 840A @ 48V  That's what I'll eventually have.
420AH useable  (till 50% discharged) = 420 x 48 = 20,160Wh,  which is pretty beefy

What has your water consumption been like, a little every month, a lot, one cell that needs none or a lot?

How often do you equalize?  never? monthly? 2x a year ?

Rule of thumb is to charge at 5-10% of capacity.  Taking something in the middle, 8%, your charge current should be [ 840 x .08 ] = 67A, which should be enough to EQ with. If you are running loads, you cannot count the inverter load as charge current.  Do you ever get to Absorb mode, or only bulk charge ?

[Jedon]

What has your water consumption been like, a little every month, a lot, one cell that needs none or a lot?

I would say right now they are using quite a bit of water, mostly the bank that the inverter leads come off of so maybe the two strings are not being charged and discharged at the same rate. I'll try switching the leads and see what that does.

How often do you equalize?

I equalize about once a month.

maybe run one bank while you rest & measure the other.

Oh I hadn't thought of that, good idea! I'll charge them both, then unhook one, wait two hours and measure SG.

you mention two strings of 8 batteries, maybe split the pair once a month so that it can be equalized and tested without load
and alternate to the other next month?

I like this idea but right now I'm not sure a single string would get us through the night, worth a shot though.

[BruceM]

I won't add anything to the good advice you've already gotten except that you should measure the night time load to make sure it's as low as you think; measure on the DC side, so you see if there's something fishy with your inverter or some other "sneak" load.

Since you have two strings in parallel, you can alternately disconnect one after charging and see where your dud(s) are, while keeping your system alive on the other string.

I chuckle when I read about "energy independance" as the sales pitch for PV/battery/inverter systems, as now instead of paying the power co., you are paying the lead-acid battery man instead.  

Plans for homebrew nickel-iron batteries anyone?

[Jedon]

I'm hoping that as soon as I get my hydro going the batteries won't be such a big issue, I have a spring that does 20+gpm at the end of summer in a drought year with 100 feet of head. That's my big project this Spring, should get be 270W or so 24/7 plus the 780W of solar and I'll only need to run the generator to run the well pump and equalize the batteries.

[mike90045]

If you have a spring with 100' head, what the heck are you needing a well pump for   

[Jedon]

If you have a spring with 100' head, what the heck are you needing a well pump for?

Well for one we were told it's too close to the surface so we shouldn't use it for drinking water, in retrospect that was the people who drilled our well so they had a vested interest.
The spring is a few hundred feet from the house and 50+ ft elevation downhill, the place where I could get 100' of head out of it is another few hundred feet below that and 100' elevation change of course.

[mbryner]

That's a goldmine!  270 watts 24/7 is 6.5 KWH/day.   Nothing to scoff at.   Especially if that's in summer.   You have it made.   Just use large enough wire back to the house and keep your batts charged.   I wouldn't drink from it either, but it's free irrigation water.    Man, I'm jealous.   I have a spring like that, but it's 1000 ft from the house site and it only runs in winter and spring.   The big creek is off limits to me.

[Jedon]

Yeah I'm very eager to get it up and producing power since we're spending about $360/month in diesel fuel right now.
I've been trying to figure out how to get the power back to the batteries. I just used Google Earth to measure, the spring is 400ft from the batteries, the place where the pelton wheel goes is 780ft as the crow flies, I'm sure it will be more than that due to terrain, might be easiest to run the wire back up the pipe to the spring and to the batteries from there so 550ft from the wheel to the spring, then 400 to the batteries. I guess generate AC and step it up to 480V?

[mike90045]

Build your powerhouse, with a minimal battery bank, near the generator/alternator. Use a good, high effiency sine inverter, and step it up as much as you can (480 sounds good) and then step back down at house.   

Depending on your loads, you can just run from that, and allow the remote batteries to take the surges.  Or rectify, charge a BIG battery bank at your house/loads, and use a honking big inverter to run it all.  Not as efficient, but you have power 24/7 to run the microwave, vacuum, coffeepot, that your remote little bank, could not supply via a 300W morningstar suresine.