Bad Battery?

System

OK everyone, please be gentle with me. I have a system that is less than a month old and I am having problems with my battery specific gravities. My system is off-grid and professionally installed:

*Outback VFX 3648
*Mate
*8--6V Surrette/Rolls 530Ah lead acid batteries in series
*8kw Northern Lights diesel generator with auto-start.

The low voltage cut-off is 48 volts, or approx 75% charge, before the generator is to start and charge.

When the batteries were first installed, I equalized them. 3 hrs after my specific gravities were around 1.265 + or - 0.02, except for battery number 7 (lucky, ha!) which was 1.225 after equalization. The ambient temps are approx 60 degrees.
So, I think I have a bad battery and have told the company that I purchased them from. They suggested that I equalize again. After a couple of cycles of using less than 50 Ah before my batteries were back down to 48V, I equalized again last night. 3 hours after equalizing (requiring 20aac X 9 hrs), my batteries are all around 1.230 except lucky number 7 which is 1.190. The voltmeter reads 6.43 on this battery and about 6.48 on all others. This seems to me to be a classic case of the good batteries reducing their capacity because of a bad battery.

I am going to talk to my solar supplier again tomorrow, but I would like a consensus from you wonderful and learned group of folks. Is this a bad battery? Is there anything I am missing?



Thank you
Salmonberry

crewzer

Re: Bad Battery?

my batteries are all around 1.230 except lucky number 7 which is 1.190. The voltmeter reads 6.43 on this battery and about 6.48 on all others.

Salmonberry,

This doesn’t quite make sense. According to both Rolls (aka Surrette) and Trojan, an SG of ~1.19 = ~ 6.1 V. not 6.43, and an SG of ~1.23 = ~6.2 V, not 6.48. I wonder about your voltmeter, some sort of contaminant on the battery terminals and/or if the hydrometer is temperature compensated.

Or, maybe I'm tired and mis-read the charts.

Also, you probably know this, but, since you didn’t mention it, you need to fully charge the batteries (full bulk and absorption charges) before EQ’ing them.

Here are some links to technical info and specs on correct charging, operation and maintenance for your batteries:

http://www.rollsbattery.com/Bulletins/507.htm
http://www.rollsbattery.com/Bulletins/509.htm
http://www.rollsbattery.com/Bulletins/605.htm
http://www.rollsbattery.com/Bulletins/606.htm
http://www.trojanbattery.com/Tech-Support/BatteryMaintenance.aspx

For reference, use the “Series 4000” instructions for your S-530 batteries. Also, make sure you mix the electrolyte in each battery cell before recording a cell SG and a battery voltage. The way to do this is to fill the hydrometer and then drain the electrolyte back into the cell three of four times before taking a sample for test purposes.

HTH,
Jim / crewzer

System2

Re: Bad Battery?

crewzer,

Thank you for answering.  I understand that the voltage and spec grav look like two separate sets of batteries.  That has confused me, but I was wondering if it was a surface charge (load was only a toyo stove and the inverter last night) or a "false high voltage" (see bulletin 605 on your links).  Surrette repeats that the spec grav is the gold standard for checking state of charge.

My hydrometer is not temp corrected.  By adding .03 to my readings, I see that they are all around full charge except #7, which is still lagging.

:oops: :oops: :oops:
I did not know that I was supposed to bulk+absorb+eq.  I thought just starting eq would do it.  Can I wait till next month, or should I do it now?


My main question now is--if my battery bank is not so bad, why do I have to recharge so often?
I guess I forgot to mention that I'm only using maybe 60Ah before I have to recharge (discharging 75-80%).  That seems to be less than what I should have.  20% is 106 Ah. I realize that I will lose some because of temp and some because they are new, but 46 Ah seems excessive. What am I missing?

Please help again,
Salmonberry

crewzer

Re: Bad Battery?

SB,

I've got a busy work and travel schedule today. I'll mull this over a bit on the plane and then get back to you tomorrow morning.

A couple of questions for you:

1) Can you tell us more about your system? For example, how do you charge the battey bank, and what are the absorption- and float voltage settings? How long is the absorption setting?
2) Do you have a remote battery temp sensor plugged into your charger?
3) Anything else we should know?

Hang in there...

Jim / crewzer

System2

Re: Bad Battery?

Here goes,

*I charge the batteries with my 8Kw generator at 19aac. I guess 20aac is the max, so the installers put it at 19. Hopefully we'll be putting in pv this next year.

*I believe the absorb voltage is 58.4 and is set to run for 2.5 hours.

*I've been told to not let it float because we charge with the generator.

*Yes, there is a remote battery sensor (Outback). So far the charging and eq have not stopped because of temp.

*I can't think of anything else. It seems like a fairly straight-forward system. Hope you have some ideas.

Thank you again,
Salmonberry

mike95490

Re: Bad Battery?

Salmonberry wrote:

Is there anything I am missing?

*I charge the batteries with my 8Kw generator at 19aac. I guess 20aac is the max, so the installers put it at 19. Hopefully we'll be putting in pv this next year.

From your list of equipment, it seems you have no solar charging, you just have batteries, controller/inverter and and ICE genset ? I guess you need either more batteries, or more conservation effort, which do you want to spend $$ on?

Do you have wind, hydro or solar ?
is it charging ?
What is " aac " - I'm not familiar with that term?

Genset should kick in only when a series of cloudy, windless days cause batteries get to about 50% (or whatever your "pucker factor" is on battery life.
Save the genset for bulk charge, let the solar/wind do the absorption and float, at those lower rates, the genset is just making noise and burning fuel.
My 5 cents worth.

niel

Re: Bad Battery?

my guess would be amps alternating current.

crewzer

Re: Bad Battery?

SB,

Thanks for the additional info. I was able to make some notes on the plane yesterday evening, but, upon arrival in LA last night, I found I have a earlier schedule than originally planned. I'll have to get back to you later today or tomorrow AM.

In the meantime, can you check you batteries' manufacturer dates? I wonder if #7 is substantially different from the rest. :?

aac does indeed stand for "Amps AC". The FX inverter's battery charger output current (= 45 ADC max for the 3648) can be limited by setting the AC input current to the charger. This limit usually only applies to the bulk charging stage, as charge current is limited during the absorption, float and EQ stages.

45 ADC is just right for the 400 Ah battery bank, BTW. Leave your FX' battery charger current setting at 20 aac, and do not confuse this with the other AC1 (grid) and AC2 (generator) limit settings.

The formula looks something like this: DC charge current = AC input current X (VAC in / VDC out) X charger efficiency.

More later,
Jim / crewzer

System2

Re: Bad Battery?

Sorry everyone,

There was a disconnect between my brain and my fingers. I was supposed to add to the original message that we started out with just the gen and batts with the outback and mate for the winter and will add an additional bank of rolls batteries and solar panels with the mx60 (outback) in the spring. We had to separate the purchase for cash flow reasons. By the way, we live in Alaska and will never be 100% solar.

I can accept that I have a lot less storage than I thought, but I still think that I'm not getting what I should out of these batts. How can I determine how many Ah I should be able to use before recharging taking into consideration the temp, their newness, etc . . ? Also, isn't it suspicious that that one battery is consistently lower than the rest? I keep reading that one bad battery will take down the whole bank to its level.

crewzer: Thank you for taking time out of your obviously busy schedule. I will check manufacturer dates when I go back out tomorrow. Good thought. I had read somewhere that Rolls batts were not so sensitive to being of a slightly different age, but who knows, maybe they slipped a really old one in there. If the date is different, do you think it should be changed. It's hard for me to believe that a battery that will charge is not better than this one.

Thanks Everyone
Salmonberry

--Salmonberry's Halloween costume.

crewzer

Re: Bad Battery?

SB,

OK. Let’s look at several related but different issues.

Inspection and Testing.

Rolls / Surrette batteries have an excellent reputation for quality, performance and longevity. It sounds like seven of your eight batteries are functioning nominally, but that one may be compromised. Items to check right away are inter-battery connections (minimal but consistent voltage drop from battery to battery), battery dates (should be very close, if not the same), physical damage (any sign that battery may have been dropped or suffered shipping damage?), correct electrolyte level in all cells (8 batteries x 3 cells per battery = 24 cells!), SG variations between cells in each battery (i.e., for battery #7, is there an SG problem in all three cells or just one cell?).

Charging.

Here’s the charging algorithm I suggest based on Rolls’ specs:

Absorb Voltage ref 77 F (25 C) battery temp: 57.8 V for 2 hours
Float Voltage ref 77 F (25 C) battery temp: 53.2 V

The FX’s charger will adjust these voltages to compensate for battery temperature if the BTS is attached to the battery bank and plugged into the FX. A typical correction factor for a 48 V battery bank is -0.12 V / C. So, at ~59 F (15 C), the absorption and float voltages should be automatically increased by (15 – 25) x (-0.12) = 1.2 V.

System Understanding and Operation.

I think there may be some misunderstanding about the system data and how the systeml operates. As mentioned previously, only EQ the batteries after they’ve run through a complete recharge cycle (bulk and absorb). Follow Roll’s and/or Trojan’s recommendation for equalizing and for safety.

Battery voltage measurements is a complex issue. The presence of charging sources and/or loads typically results in skewed battery voltage readings. Accordingly, the battery should be at rest and disconnected from all charging sources and loads for at least three hours before measuring the voltage to determine SOC.

Your series string of eight S-530 batteries is rated for 48 V x 400 Ah at the 20 hour rate (20 A discharge current for 20 hours). Allowing for a 1% / degree C capacity reduction, the nominal capacity will be ~360 Ah at 59 F (15 C). 20% of that is 72 Ah. However, the battery voltage under load will be lower than the ~49.8 V (open circuit) you’d expect to see from the battery at rest (see above).

The suggestion to not use the generator to float the batteries is generally sound, as float current is low and the generator operates inefficiently. However, you might want to consider running high-power loads when the charger is limiting charge current while in absorb or float mode. The generator is running anyway, and this strategy will (probably) increase generator efficiency while it’s running, reduce daily loads on the battery, and, by reducing bulk stage time, also reduce generator run-time.

A 48 V gen start setting may be too low, as the batteries are likely discharged by over 50% at that point.

Finally, take a look at the FX’ input current settings, as it’s possible for them to conflict. For example, if the AC2/gen input current limit is to low, then the FX will reduce battery charging current while AC loads are connected to its AC output.

That’s it for now… I’ve got more meetings today, and I fly home tomorrow. I've no doubt missed a few things, but we'll catch up on those later.

Good luck!
Jim / crewzer

Patman3

Re: Bad Battery?

I check each battery in a series  pack with a 6V 15 amp Schumacher battery charger and digital voltmeter.  My EV has 20 6v batts in series.  1 bad one can ruin your day.  After the batteries are mostly charged (bulked) I put the charger and voltmeter on a battery and see how it takes the charge.  If it takes 15 amps or so and the voltage only slowly rises, it's taking a charge good and has capacity.  If the voltage rises quickly past 7.5v, it has low capacity and is probably making gas.  Also check the voltage after sitting idle for 2-3 hours if possible.  Weaker batteries will be like 6.35V and better ones will be closer to 6.45V.  You need a good digital voltmeter that can measure two decimal places, I hate messing with SG and acid, although there is much to be said for checking it.  You can also check each battery WHILE it is charing on your genset and measure each battery voltage - they should all be within .02V (HA ha).  After charging note which ones are weaker and give them extra from the 6v charger as above.  If it's voltage rises quickly maybe replace that one.  If more than one is bad you must replace the WHOLE pack as Niel would suggest.  This is just what I have learned so far and I know I have much more to learn.  Hope this helps.

PS. One other fact I learned is the most negative battery in a chain gets the hottest because all the electrons going into it (or out?) are already warm from the other btteries. Having a larger cable on the neg post can help sink the heat away from the battery.

BB.

Re: Bad Battery?

Since all of your batteries are in series... Then they should all behave exactly the same. Any that is significantly different that the rest is a weak cell/battery.

By the way, can you measure the individual cell voltages for each battery, or just the 6 volt battery overall? Also, are the SG levels in battery #7 all off, or is just one cell off?

Generally, if a battery begins an early life failure, it should be the result of just one cell failing first--indicated by SG problems and/or low individual cell voltage (during discharge)... If one battery/cell of a new bank is low during discharge (under load), I would suspects a bad battery and have them replace it--or at least, explain why you should not be worried.

Another issue could have been somebody made a mistake filling battery #7 when new if all cells are low SG (bad acid and/or contamination)...

Another possibility would be if battery #7 was significantly at a lower level of charge when new versus the rest of the batteries in the bank... The other 7 batteries would be at full charge, while #7 was still needing more charge.

When you bulk charge/equalize, is battery #7 generating as much gas/bubbles as the rest of the batteries, or is is generating less gas--that could indicate #7 would still need further bulk charging while the other series connected batteries are full--Disconnecting #7 from the bank and individually charging it with a 6volt charger might fix the problem (just a long shot possibility).

-Bill

System2

Re: Bad Battery?

Patman3 wrote:

PS. One other fact I learned is the most negative battery in a chain gets the hottest because all the electrons going into it are already warm from the other batteries.

---

I cured that problem in my system by running the Neg cable out through the wall and along the north side of the shed for about 10 feet and back again, sort of like a heat exchanger. The batteries charge better this way too, since cooler electrons move more slowly, so have a chance to do their work, instead of just racing through the batteries.:evil:

= = = = = = These are my tracks, running for the hills, to avoid what will surely be thrown at me. LOL

Sorry guys, every so often I just have to lighten up.
Wayne

crewzer

Re: Bad Battery?

PS.  One other fact I learned is the most negative battery in a chain gets the hottest because all the electrons going into it (or out?) are already warm from the other btteries.  Having a larger cable on the  neg post can help sink the heat away from the battery.

:?

BB.

Re: Bad Battery?

A very quick and good test of your wiring is to place the battery bank under heavy load (or even a high charging current) and start feeling for warm connections. The ones that are warm are, typically, in need of terminal cleaning and/or replacement of the crimp cables/connections.

Another way is to set a DVM on millivolt scale and measure the voltage drop between the center of the battery post and the bolt-on connector, connector to wire, one wire end to the other, etc.... When you find a a connection that has higher then "normal" voltage--that is a terminal/cable that needs cleaning or replacing.

If you have a one warm/hot battery terminal (and all of the other battery terminals are good/cool), and using the DVM find no unusual voltage drop readings--then it is possible that you have a battery with one or more cracked/broken plate connections--potentially a battery that you will need to replace soon (especially if it is still under warranty).

-Bill

niel

Re: Bad Battery?

2 things here and i'll shut up.
1> an infrared thermometer is great in a case like this as you can easily map the temperature at any point instantly be it the wire, the connections, or the battery itself. i use it for air infiltration detection too in the winter.
2> keep in mind that an unnecessarily overheated terminal could affect the charge coming from a temperature compensated controller. the sensor is supposed to sense general battery temperatures and bad or undersized connections can throw a false sense of the temperature to the controller and falsely change the charge voltage levels.

System2

Re: Bad Battery?

Thank you so much,

Before going out to our new property yesterday, we were run into by a nice older man, so were not able to get out there. It will be another day before I get out there. You all have given me many things to assess. I will do so and get back to you.

By the way, my batts are a month old. Can't I get away with changing just the one battery if it turns out to be bad?

Salmonberry

BB.

Re: Bad Battery?

Yes, you can change 1 battery at any time (new, old, mixed bank)... And in your case, the batteries are all virtually new--so they will still all have the same capability and the replacement battery will be just fine.

The bigger issue is that you don't want to replace 1 battery in a (for example) 10 year old bank one month, then another 2 months later, etc... Basically, the battery bank will perform based on its weakest battery--And especially for parallel banks, the newest battery will carry the most load--therefore degrade quicker until it has the same capacity/capability as the rest. When you have an old bank, and one or two batteries begin to fail, the rest are probably not far behind.

-Bill

System2

Re: Bad Battery?

Thanks BB and everyone.

The dates of manufacture are the same on all the batteries. When I equalize, neither the batteries, the posts, nor the wires on any of it are significantly warmer to the touch. in the #7 battery, all of the cells are low spec grav.

I did get a 6v Schumacher battery charger and took #7 out of service. I charged for 3 hours (all the time I had out there) with 15 amps and my spec grav did come up. I am working all weekend but will be out on Monday to try again. This may be what it needed. If I had equalized properly in the beginning, I may not have been having this problem. I'll keep you posted.

Salmonberry