Battery Diagnosis

unklekevunklekev Registered Users Posts: 1
Why would a 'never used', brand new, 12 volt, AGM, 125ah solar charge tank, go into 're-conditioning'(stage 6) on a 7-stage smart charger? Is this just normal procedure for these chargers?


  • BB.BB. Super Moderators Posts: 26,768 admin
    How old is the battery and how has been stored? A typical AGM battery if stored more than ~6 months without recharging (if put away at 100% full charge) would start to sulfate.

    It is also possible that the charge controller would go through its seven stages when first connected to the battery--Then use a combination of timers (i.e., "equalize" once a month) and things (how deeply discharged, etc.) to decide when to run the various stages.

    Note--AGM batteries require lower charging voltages than flooded cell, and no high voltage equalization (some battery mfg. recommend extended absorb time a few times a year to "equalize" AGMs). Does the charge controller have an AGM setting?

    Flooded cell batteries can be charged at ~14.75 volts normally, and over 15.0 volts for equalization. AGMs should usually never be charged over ~14.4 volts in normal operation (and at ~room temperature). Both battery types should be "floated" at ~13.6 volts +/- (see manual) when connected to a charger and no loads/cycling is taking place (note that battery voltages are also temperature dependent, as temperature falls, chargers will jack up the charging voltage set points a bit).

    Have you taken a good quality volt meter and monitored the charging voltage(s) vs the battery manual recommendations?

    As long as the battery is not being "over charged/over voltaged" (or under charged), there is usually nothing to worry about some chargers with their 7 stages of charging.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inetdoginetdog Solar Expert Posts: 3,121 ✭✭✭✭
    But you might want to do at least a crude capacity test to confirm that your batteries did not sultate beyond recovery while sitting on the shelf.
    SMA SB 3000, old BP panels.
  • JamesJames Solar Expert Posts: 245 ✭✭
    regarding battery capacity test, can anyone outline a straightforward, crude test to follow?
  • JoshKJoshK Solar Expert Posts: 232 ✭✭
    Hi James. If I'm not mistaken, the 125ah means it should run a 6.25 amp load for 20 hours. If you find a 6 amp bulb and run it until it starts to dim, it should take 20 hours.
    I'm not sure you want to though, it's a bit rough on a battery to run it that low.
  • JamesJames Solar Expert Posts: 245 ✭✭
    I kind of hijacked the thread with my own battery question since it sort of pertained to the battery load question.
    my battery bank is quite a bit larger ah capacity.

    is there a rule of thumb, like test with a certain percentage load for 20 hours and then take voltage reading after load removed and battery at rest?
    What percentage?
  • froggersixfroggersix Solar Expert Posts: 35
    no because bulbs are watts not amps the resistance is the same so the amps goes up as battery drops volts. you can't do this unless you can have steady current which means the resistance has to chnge so the current is always the same.
  • BB.BB. Super Moderators Posts: 26,768 admin
    It is interesting that filament lamps do have a variable resistance. A Hot filament has higher resistance vs a cooler filament. Filament Lamps have been used in times past at a "rough" constant current regulator in electronic circuits (vacuum type type).

    Regarding a standard load test... You can go with the old put a heavy current on a battery for 30 seconds and measure the final voltage:

    More or less, they test the battery's ability to start a car motor. A "standardized" functional test.

    You could do the same thing with an off grid battery bank--It will measure the battery bank's ability to supply some level of surge current. Certainly if a battery does not have the ability to supply short term / large amounts of current, it may not have enough capacity to supply lower amounts of current for longer periods of time (sulfation, damaged plates, etc.).

    But--If you are expecting something different (say 10 hours of backup power at ABC Watts)--Then your only accurate method to asses the battery bank ability to supply power would be to run your loads and see what happens.

    For example, if you have a 200 AH @ 12 volt battery bank and expect it to supply 10 amps for 10 hours to 50% state of charge--Then you would put a 120 Watt load on your AC inverter and run the system for 10 hours. If the system is still running OK after 10 hours (battery bank voltage has not fallen below ~11.5 volts under load as an example), then the battery bank is "good for your needs". Of course, you can discharge for 11 hours (to 40% state of charge) to have a safety factor.Then recharge the battery bank.

    Of course, discharging the battery to 50% or less SOC is hard on the battery bank (will slightly reduce battery life). And you have to recharge the battery bank quickly to avoid damage (sulfation).

    Otherwise, another way to monitor the health of your battery bank is to setup a standard test condition (say you use a 1,000 Watt space heater)--Turn on the space heater for 20 minutes and measure/log the voltage of teach battery. And use a DC current clamp to log the current through each parallel string of batteries (if you have 2 or more parallel strings). Also log temperature corrected specific gravity for each cell ~once a month too (if flooded cell).

    Do this when the bank is new and 1 to X times per year to get a base line. Now--when a battery begins to fail, you will see the early indications of failure (one or more batteries behave "differently" than your baseline)--And you will have an early indication of battery failure or other problems (bad electrical connection, charger problems, etc.).

    My own suggestion is to keep it simple--If it is too complex to perform the testing--Then I would never do it anyway--And I would just react to something wrong (and, I guess, run the genset/reduce power usage until the problem is fixed).

    You could also skip the 1,000 watt heater and simply do the testing under normal loads (or even normal charging) and, again, look for differences from "baseline" (voltage, current, specific gravity).

    To a degree--Your testing standard would be based on your risk tolerance... If you have a battery failure, is it the "end of the world" (single string of batteries, 200 miles from nowhere) or is it just an annoyance (two or more parallel strings, reduction of loads until fixed, use genset more until you get the parts). Do you "keep a spare" (such as an extra Honda eu2000i genset and some extra fuel) instead of a major, every three months, testing/qualification procedure. I cannot say.

    Kind of goes back to the old saying of "Two is one, one is none." idea of backup... If your system is critical to your needs, you should have three alternative sources of power/spares... I.e., a Battery bank + main backup genset + second (smaller?) backup genset if loss of power is something you cannot have. And if you never test your backup power sources=-You don't know if one of them has failed in storage/since last use.

    Complicated answer to a simple question (or, I made it an overly complicated answer :blush:).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • JamesJames Solar Expert Posts: 245 ✭✭
    Thanks Bill,
    Your answer does help. Since I do have grid power, I can afford to perform the load test whatever way i wish without any loss of critical circuits. i can run those circuit off of grid power in order to do a controlled test. Although my batteries were new. not in service, they sat in a warehouse for 6-8 months.
    I did confirm they were on a float charger while awaiting installation. I bought my set thru a telecom auction.
    I kept the bank on a float charger "most" of the time awaiting installation at my home. So I know the bank my have been compromised right from the start. To add insult to injury, my existing PV array was most likely starving the batteries in the winters.
    I got the batteries for so low of a price that I was willing to take a chance with them. I have been running them for 7 years and 6 winters. They have never let me down.
  • BB.BB. Super Moderators Posts: 26,768 admin
    I have moved this thread to the Old Tech Battery discussion forum...

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    unklekev wrote: »
    Why would a 'never used', brand new, 12 volt, AGM, 125ah solar charge tank, go into 're-conditioning'(stage 6) on a 7-stage smart charger? Is this just normal procedure for these chargers?

    Ah, you must be talking about the VMAXTANKS agm's, and their own line of smart-chargers which also happen to be designed to work with flooded. I checked the manual for their chargers.

    Problem is, the smart charger mis-identified your agm as a deeply discharged flooded, and automatically applied an EQ/Reconditioning stage (16v, 0.6a for 4 hours) to it. Most agm's, especially the type that are not pure lead, won't stand for this. You may want to ask the people at VMAX if they approve of such a high voltage EQ to their agm's when their charger manual states that the reconditioning mode is for flooded.

    But you aren't the first one. I had a similar Schumacher "smart" charger ruin my brand new Deka agm the same way by going into a high-voltage eq right after bulk. Unfortunately, I didn't have a display or led to inform me that it did. I had previously capacity tested it and charged it with other chargers no problem, but this one got too smart for it's own good. I suspect the charger here did much the same.

    My suggestion is to dump that charger, and pick up an IOTA.

    Barring that, another great choice especially if you are just wanting to commission an agm, have it detect problems, constantly test, yada yada, the Tecmate / Optimate 6 is worth a look. I do solar, but I have 4 different versions of these chargers now mainly for the testing and results without having to use lab equipment to do so.

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