Think I need new battery bank...help!

AliZeus · January 2013

My husband and I recently bought an off grid property in Arizona. Solar and wind are our only source of power, with a back-up generator. We are extremely new to this, but have come to the conclusion that we need a new bank of batteries. Here is what we have:
Inverter: Xantrex Sine Wave Plus 5548 (48v input, 5500W)
Panels: 8 Kyocera KC125G panels (125W) with Suntracker
Turbine: Whisper 500 (3000W @24 mph, 48v)
Charge Controller: Outback MV MPPT, Model MX60
Battery bank: 32 6v golf cart batteries (4 banks of 8 ). They are Interstate batteries and I believe them to be about 5-6 years old.

We have good sun almost every day for about 7 hours and alot of wind. I have the inverter set to shut down at 44 VDC and 58 VDC and it shuts off every day shortly after the sun goes down, forcing us to use the generator daily. When there is little wind overnight, we are losing power at about 4 a.m. Essentially, after a good charge, we are losing power after about 3-5 hours. During the day we use a computer, fridge and sometimes the t.v. We are very conservative with light and unplug evrything when not being used.

I have come to the conclusion that the batteries are not holding a charge and need to be replaced. However, I am new to this and am wondering if maybe it is something else. Maybe I am not generating enough power with my equipment or do not have enough batteries? Any kind of input would be greatly appreciated. I am so happy to have found this forum!

Also - if I am going to replace my battery bank, what do you all suggest replacing it with?

westbranch · January 2013

Re: Think I need new battery bank...help!

have to go but you only have 1000W of solar vs a bank that is ~ 4(banks) x 250Ah== 1000 Ah At 48v = 48000W total capacity. 24000W recommended use.

You did not list daily use, that is the rest of the puzzle.

hth

Cariboocoot · January 2013

Re: Think I need new battery bank...help!

Welcome to the forum.

I think you're right; you need new batteries.

Moreover, you need a power usage re-assessment so that you can make some changes to avoid some built-in mistakes you've got there.

For instance, four parallel strings of batteries. Bad idea. It makes current sharing among the batteries difficult, meaning some will do more work and others will do less ironically leading to all going bad quicker than they should. Yet you got 5 years from them anyway.

Another thing is you've only got 1000 Watts of array. Even with the tracker and the wind turbine (don't expect too much from that) it's a pretty small amount of panel to recharge what is roughly 880 Amp hours of 48 Volt battery. If you really need that much battery (first thing to check) you'd be better off with a much larger array. Like about 4X the size.

So what you need to do first is get a hydrometer and measure the specific gravity of every cell of every battery. Then re-arrange them so that you have one string made up of the eight best. Charge it fully. Do an equalization charge afterwards. Try to get all the SG readings up above 1.265 and consistent. Then try the same thing with each of the other three strings in turn.

Really 220 Amp hours @ 48 Volts (one string of the batteries) represents about 4.8 kW hours stored power. That's why you should evaluate your power usage and see how much you really need to have on hand. There's no sense buying more batteries than you need nor more than you can properly recharge.

My opinion here is that the batteries have been chronically undercharged and are now sulphated, probably beyond hope.

Photowhit · January 2013

Re: Think I need new battery bank...help!

I suspect you have come to the correct conclusion, Golf cart batteries usually last 3-5 years so they are in the right ball park age wise. You might get 7-8 out of Trojans, and I have head of as many as 10 years.

4 strings is more than most people would recomend, I would suggest going with a larger celled battery like an L16 or switch to a forklift/traction battery.

Photowhit · January 2013

Re: Think I need new battery bank...help!

After seeing 'Coot's response I was reminded that you are new to renewables and perhaps you haven't gotten a grip on battery maintenance and handling. There is information in the battery FAQs that should help;

Battery FAQ link.

As others have suggested you might be undercharging, unless your in a particukarly good spot for wind and have you wind genny on a tall tower.
On a tracker and in a great area for solar your array represents as much generation as 2x the fixed array where I am. but currently solar panels are inexpensive so you might look at adding to your array, particularly if you do so before 2016 as there is a 30% tax credit (this should apply toward your batteries also! check with your tax professional)

Blackcherry04 · January 2013

Re: Think I need new battery bank...help!

I pretty much agree with whats been said. You know your life style and your use and we don't know the previous owner and their thinking. Doing the right maintenance on the batteries will go a long way. Educating yourself will give long term payback.

If it were my money I'd scrap that bank and buy two new strings of 8 ( 16 ) new GC-2, golf cart batteries from Sam's Club or Cosco. They are about $85. 00 each. You already have the cabling in place. If after a few days you find it's not enough you can add another string. 4 strings is to many to maintain for most people, it can be done , but takes a lot of manipulation. This is your first set and they are cheap enough to learn on. $1,300 is a heck of a lot better than spending $6,000 and having the same issues.

You need to do a proper Commissioning of the bank and let it rock and roll. Your going to be surprised what a new bank that has 100 % capacity is like.

westbranch · January 2013

Re: Think I need new battery bank...help!

I'm back, in addition to all that has been said, it would help in knowing just when you took over from the previous owner and what his usage pattern may have been as that may fill in a few holes.

Just for info, not too long ago,( ~ 2-3 years, PV panels were as much as 5 times as pricey as they are now, also when batteries were relatively not as expensive as PV panels) the 'old way' of setting a system up was to go light on the panels because, if the system was for weekend use 'it will 'fill' the batteries while no one is there. This is called DEFICIT charging and is a sure way to shorten the life of any battery.

Also before replacing the bank, you can experiment with trying to recover those cells. Most here consider the first battery bank as sacrificial as most owners kill the first set... not deliberately but by inexperience. Get to know your battery like you know you dog, intimately.

hth

AliZeus · February 2013

Re: Think I need new battery bank...help!

Because of financial constraints, I took your advice and purchased 16 Energizer golf cart batteries at Sam's Club. We installed them last weekend and are not having the best of luck. First off, I have a meter that shows how many Volts DC I have at any given time. With the old batteries, this meter showed up to 58VDC when they were being fully charged. Now, this meter only goes up to 54 VCD, never any higher. I don't know exactly what this means. Could someone explain the "Volts DC" and what it means, exactly? Since we got the new batteries, we have had great weather - lots of sun and very windy. However, we are still losing power at night. This happens even when we are gone all day and the only thing running is the fridge. The power just disappears over night. I really need to pinpoint whether it is my array or my batteries. Thank you for your continued suggestions!

BB. · February 2013

Re: Think I need new battery bank...help!

Need to know the current too...

Old batteries may have lower capacity as they "die"... So, it is not uncommon for older battery banks to "charge very quickly". And new batteries to be less than full charge--So it can take a while to fully charge (especially with a smaller array--which could have caused the older batteries to die too soon).

But, it is also possible that cabling was broken or poor/loose connections were caused by the battery bank change out. It is also possible that the charge controller has been confused (most controllers should be connected to the bank first, then the solar panels.

Anyway--Take voltage readings with a good volt meter through the entire chain... Battery posts/bus common. At the battery connection to the charge controller, at the solar panel connection to the controller, etc... Note the current, how sunny it is (i.e., noon time on a clear day, vs late evening/overcast, etc.).

-Bill

Blackcherry04 · February 2013

Re: Think I need new battery bank...help!

AliZeus wrote: »

Because of financial constraints, I took your advice and purchased 16 Energizer golf cart batteries at Sam's Club. We installed them last weekend and are not having the best of luck. First off, I have a meter that shows how many Volts DC I have at any given time. With the old batteries, this meter showed up to 58VDC when they were being fully charged. Now, this meter only goes up to 54 VCD, never any higher. I don't know exactly what this means. Could someone explain the "Volts DC" and what it means, exactly? Since we got the new batteries, we have had great weather - lots of sun and very windy. However, we are still losing power at night. This happens even when we are gone all day and the only thing running is the fridge. The power just disappears over night. I really need to pinpoint whether it is my array or my batteries. Thank you for your continued suggestions!

A short guess and answer is that you are in a Deficit situation and are not able to catch up. You should start your Generator and see how high you can push them and do a full charge. If you just installed the batteries and didn't commission them, then they are what they are. They should be reaching at least 58 volts or so. You really need to get someone to look at your system and explain it to you.

BB. · February 2013

Re: Think I need new battery bank...help!

Do you have a digital voltmeter? I would suggest a DC current clamp meter like this one--Not too expensive, full "DMM" functions (digital multi meter), and good enough for working on an off grid power system. The DC Current Clamp makes current measurements much easier and safer.

-Bill

Cariboocoot · February 2013

Re: Think I need new battery bank...help!

Okay what you've got now is two parallel strings of eight in series to provide about 440 Amp hours @ 48 Volts. This is still a lot of battery (about 10 kW hours worth) and is not going to be recharged properly from 1kW of panels. Again, that array may manage 16 Amps @ 48 Volts or a measly 3.6% rate. This will not recharge them. The new batteries are dying already.

Disconnect one string. Then you will have 220 Amp hours @ 48 Volts or about 5kW hours stored power.
Your Voltage was going up higher before because the batteries' actual capacity was depleted. You simply haven't got enough charging power to bring that much battery up to full power before the sun goes down and the loads drain them again.

You need to get a hydrometer and take specific gravity readings of every battery cell.
You need to definitely fully charge the batteries (this should be done before they are put in service).
You need to be able to see the current coming from the panels and the turbine (to see if it is really contributing anything).
You need to set the low Voltage disconnect to 48 Volts (don't let it go below that).
You need to check the charging parameters on the MX60 to make sure the Absorb Voltage is set to at least 58.4 and that the Absorb time is at the maximum 4 hours. You can also set the End Amps to 2% of the battery bank capacity plus loads (this is trickier) so that Absorb will end before the full time limit if possible.
And if you are using more than 5 kW hours of power a day you need to either investigate your power consumption or ramp up the solar array drastically: the battery bank you have now need about 2.7 kW of array.

icarus · February 2013

Re: Think I need new battery bank...help!

Coming late to the party, but have we defined the loads correctly?

As we oft say, all sewing considerations stem from the load calcs. Load calcs define the size of the battery bank, which in turn defines the size of the PV array etc. if you don't REALLY know what your daily loads are, total and peak the rest is shooting in the dark.

Tony

Photowhit · February 2013

Re: Think I need new battery bank...help!

AliZeus wrote: »

Because of financial constraints, I took your advice and purchased 16 Energizer golf cart batteries at Sam's Club. We installed them last weekend and are not having the best of luck. First off, I have a meter that shows how many Volts DC I have at any given time. With the old batteries, this meter showed up to 58VDC when they were being fully charged. Now, this meter only goes up to 54 VCD, never any higher. I don't know exactly what this means. Could someone explain the "Volts DC" and what it means, exactly? Since we got the new batteries, we have had great weather - lots of sun and very windy. However, we are still losing power at night. This happens even when we are gone all day and the only thing running is the fridge. The power just disappears over night. I really need to pinpoint whether it is my array or my batteries. Thank you for your continued suggestions!

A lot of this are going on right now, the reason people want more information and measurements.

Until we know more we don't know enough, lets get some information, but don't be too fearful yet. It may be that your old bank never got fully charged and your new bank is staying in 'float' all the time since you are having a lot of wind. Once you have a handle on what's going on you should be able to relax a bit.

Normal charging parameters for the MX60 are here;

The normal cycle for charging is for the batteries to bulk charge until they reach 57.6 volts then the charge controller will maintain that voltage then drop back to float 54.4 volts to maintain the charge. Since you have wind charging over night, at least at times, you could be maintaining a full charge.

You say "The power just disappears over night." This is a bit of a concern, it you have no wind, then you would normally see a fall off over night, with solar only. Indeed a 48volt battery if fully charged and not accepting charge or having a load, will be roughly 50.8-60 volts. If you have no other way of determining what your state of charge (SOC) is you could disconnect the loads and the charging and let it rest for 3-4 hours and the voltage should be in this range.

Did you get a chance to read through the battery FAQs?

So in normal operations,with solar only, a 48volt battery would far over night with reasonable use to 48.7 volts, but this is a measurment at rest, since it would be discharging/ having a load the voltage might well read lower than this.

Outside influences might well be at work here. If your not be at home during the day, you might not see the bulk charge rate and only see the system in float. You could apply a heavy load and draw down your batteries to get them to start back in bulk mode or your could disconnect eveything at the end of a sunny and windy period for 3-4 hours and see where your true SOC is.

As others have stated a hydrometer is the true test of a batteries SOC, and a clamps meter will give you some true reads of what is coming into your batteries. A shunt based meter, like the trimetric will give you some idea for the input and output as well. It may be that you wind charger has failed and you can't maintain the batteries with the solar you currently have.

Hope this helps.

Think I need new battery bank...help!

Comments

Categories