Battery voltage drop under load

bikemechanic53bikemechanic53 bikemechanicPosts: 7Registered Users
I have just completed the install of my RV's solar electrical system.

I've got 6 used 6Volt Crown industrial batteries. Each is rated at 325AH. That should be a total of 975AH for the 12 volt system.

They are all charged up to 1.225 or higher SG and measure about 12.4 volts for each set.

However, when I turn on the lights and am running a 225 watt load, the voltage drops to 11.9 volts.

If I try to run a 1000 watt load, the voltage drops to 10.5 volts.

My guess is that the batteries are sulfated and can't supply much output.

Does this make sense? Or am I missing something?

Tom

Comments

  • mike95490mike95490 Title:User Posts: 6,203Solar Expert ✭✭✭
    Re: Battery voltage drop under load

    sulfated is a good guess. Try a couple deep discharges (down about 60%) and recharges, see if that will knock off some of the sulphate. How old are they ?
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • nielniel Solar Shotgun Posts: 10,309Solar Expert ✭✭
    Re: Battery voltage drop under load

    allow the battery to get fully charged. the voltage will appear well over 14v on its way to a full charge.
  • WindsunWindsun Solar Shogun Posts: 1,164Solar Expert admin
    Re: Battery voltage drop under load

    One of the biggest problems we see with used batteries (even if they are "new") is that they sat around for a long time partically charged. That nearly always causes some sulfation, which sounds like the problem you are having.

    Someplace on the batteries there should be a date code that will tell you when they were actually manufactured.
  • blackswan555blackswan555 New User Posts: 246Solar Expert ✭✭✭✭
    Re: Battery voltage drop under load
    They are all charged up to 1.225 or higher SG

    Check you manufactures recommendation, but 1.225 is not charged in my book, 1.255 >1.275 would be more like it.

    Have a good one
    Tim
  • bikemechanic53bikemechanic53 bikemechanic Posts: 7Registered Users
    Re: Battery voltage drop under load

    These were made in 2007 and 2008.

    So can sulfation be reversed?


    Tom
  • solarvicsolarvic New User Posts: 954Solar Expert
    Re: Battery voltage drop under load
    Windsun wrote: »
    One of the biggest problems we see with used batteries (even if they are "new") is that they sat around for a long time partically charged. That nearly always causes some sulfation, which sounds like the problem you are having.

    Someplace on the batteries there should be a date code that will tell you when they were actually manufactured.
    If you are going to buy batterys, should you ask about the manufacture date? How old of a manufacture date should you accept ? I see in your store you recomend the Crown batterys. I have 2 distributors in the 80 to 90 mile distance from me. Are the trojans any better? I can,t see how they could be since the crown has thicker plates and is lots cheaper to buy. Since I live in Pa the freight from az. would eat me up if I bought from your co. Or do you sell them and I would pick up at the distributor close by me? S8)larvic
  • nielniel Solar Shotgun Posts: 10,309Solar Expert ✭✭
    Re: Battery voltage drop under load

    it is hard to say just how much sulfation may or may not be there, but without putting a full charge on the batteries you are going to windup with junk for batteries for sure. some say it can be reversed, but don't count on it as that is not proven technology. a good rough guess would be about 14.5v, but here is the page for charging crown batteries,
    http://www.crownbattery.com/?page=support_chargingprocedures

    solarvic,
    they usually don't answer sales questions on the forum. you could call them up and have them answer any concerns you may have with the differences between buying from them and a local guy.
  • blackswan555blackswan555 New User Posts: 246Solar Expert ✭✭✭✭
    Re: Battery voltage drop under load
    Can sulfation be reversed,
    A cut from a rolls manual, But as I said before, I do not think you have had your batteries fully charged (which you need to do before EQ) I would start with a good normal charge , watching the sg`s until they stop rising, then do an EQ till the SG`s stop rising, that should also give a better idea of battery condition before attempting corrective EQ
    Have a good one
    Tim

    Equalization - Corrective

    Corrective equalization needs to be performed if symptoms arise such as a constantly running generator (low capacity) or the battery bank will “not hold a charge”. These symptoms are typical of a heavily sulfated battery. If a battery is not being fully charged on a regular basis or limited equalization is performed using a generator (see Bulletin 611, Generators, Inverters and Equalization) sulfation will occur from “deficit” cycling. This undercharge condition can take months before it becomes a major and noticeable problem. This under charge condition is caused when batteries are deficit cycled. The bank receives less of a charge each cycle and starts to sulfate. Eventually the sulfate will cause a resistance to charge and a “false high voltage” reading will occur. The “false high voltage” is measured by the charge controller, which further lowers the charging current to maintain the voltage set point. This further increases the undercharge condition. This is one reason why specific gravity measurements are so important as “false high voltage” readings can be misleading. See Bulletin 609, Voltage, SG and State of Charge for information on how to correctly interpret voltage readings.

    Amperage hour meters can compound the problem and cause people to believe they are returning the correct amount of energy back into the batteries to maintain a good state of charge. Amp-hr meters should be thought of as simply a fuel gauge that does not measure state of charge directly but indirectly. The state of charge is determined by using an equation (peukert's equation). Sometimes there can be fundamental errors with factors used in these calculations. You should always confirm, at least initially, state of charge by taking a specific gravity measurement of one cell when it is thought the bank is fully charged.
    Corrective Equalization - Method

    Corrective Equalization can take a very long time depending on the degree of sulfation. It is not recommended to equalize with a generator as some generators produce low grade AC that is not properly filtered by the inverter. This is especially true at higher voltages.

    1. If you have hydrocaps remove during equalization.
    2. Set charging controls to the highest voltage allowable by the charge controller (inverter). If the bank is severely sulfated or available current is very limited, charge control can be removed or by-passed. Temperature should be monitored very, very closely and keep below 125ºF.
    3. Charge at a low DC current (5 A per 100 AH of battery capacity). If grid power is not available use solar panels or a good DC source when possible. At high voltages, charging with generator can be difficult and hard on the inverter.
    4. Once an hour, measure and record the specific gravity and temperature of a test cell. If the temperature rises above 115ºF (46ºC) and approaches 125ºF (52ºC) remove the batteries from charge. (For temperature measurement choose a center cell, if applicable).
    5. If severely sulfated, it may take many hours for the specific gravity to rise.
    6. Once the specific gravity begins to rise the bank voltage will most likely drop or the charging current will increase. The charging current may need to be lowered if temperature approaches 125ºF (46ºC). If the charge controller was by passed, it should now be used or put back in line.
    7. Continue measuring the specific gravity until 1.265 is reached.
    8. Charge for another 3 hours. Add water to maintain the electrolyte above the plates.
    9. Allow bank to cool and check and record the specific gravity of each cell. The gravities should be 1.265 ± 0.005 or lower. Check the cell electrolyte levels and add water IF necessary.

    To avoid this situation it is recommended that a specific gravity reading of one pilot cell is measured and recorded on a regular basis when it is thought that the bank is fully charged. The measurement should be compared to previous readings. If the measurement is lower than the previous reading a longer absorption time and higher voltage setting should be used. Note as stated above, the longer the absorption time and the higher the bulk voltage, the more water will be consumed but less equalization will be required. Note: the specific gravity should rise as the cells use water. Look for trends in the specific gravity over a period of time and make very small adjustments as necessary.

    Caution: If you have HYDROCAPS, remove during equalization.
  • westbranchwestbranch Not So New User Posts: 4,024Solar Expert ✭✭✭
    Re: Battery voltage drop under load

    What kind/brand of charger are you using ? what is its amp rating?

    EJ
     
    CL 647 asleep  24V 900Ah C&D AGM
    CL 4592  175A E-Panel WBjr, 2 x 4s 140W to 24V 900Ah C&D AGM + 4s 140W 
    Linksys Wet54g WiFi Bridge ,  ASUS RTN10 router, Hughes Sat Modem
    Omnicharge 3024, Cotek ST1500W 24V Inverter,
    1680W & E-Panel/WBjr to come, Eu3000i & 1000i Gens,
    West Chilcotin, BC, Canada




  • WindsunWindsun Solar Shogun Posts: 1,164Solar Expert admin
    Re: Battery voltage drop under load
    These were made in 2007 and 2008.

    So can sulfation be reversed?
    Tom
    2007 would make them 3-4 years old. If they were kept charged up, they could still be good - but what often happens is that some business or person will buy extra batteries for whatever reason and then just store them with no maintenance - and that is the major cause of sulfation.

    It can sometimes be partly reversed by fully charging them and then keeping them peaked up with a trickle charge. But that might take weeks, if ever. Some people have had limited success with desulfators, but how well those work depends a lot on what is really going on internally, and unless you disect the battery you often cannot really tell.
  • BB.BB. Just some guy Posts: 24,203Super Moderators admin
    Re: Battery voltage drop under load

    Also, check the cabling and connections for voltage drop. A 1,000 watt load is nearly a 100 amp load on a 12 volt battery bank.

    Bad cables, bad connections, too long of cables, etc. can all cause voltage drop.=

    I like to use d DVM set to 2 volt full scale and check each connection and length of wire an make sure that all voltage drops are small. Also, you can compare current flow between the different paralleled strings. You might find that 3 of your banks are supplying a lot of current and one bank not supplying any--that bank may have an electrical connection problem or one of the batteries has an open cell.

    Under heavy load (or under heavy charge)--check the voltage of each battery and see that the are all the same. One too high or two low can indicate where problems may be.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bikemechanic53bikemechanic53 bikemechanic Posts: 7Registered Users
    Re: Battery voltage drop under load

    Thanks for the good info.

    The RV has a Progressive Dynamics charge controller. It has been charging the batteries at 13.75V for the past month. Which has brought only 1 of the 3 12V pairs of batteries up to full SG of 1.275.

    Based on the info you guys sent, I've set the charger to manual, 14.5V mode, on only 1 pair of batteries. I'll monitor the SG ( currently at 1.225) and hopefully it will come up to full charge. Then I'll switch to the 2nd pair to try to bring that up to full SG.

    Does that sound like a reasonable plan?


    Tom
  • bikemechanic53bikemechanic53 bikemechanic Posts: 7Registered Users
    Re: Battery voltage drop under load

    I checked the voltage at the batteries and at the converter. Only a .1V difference between the two. So I assume the connections and cables are OK.

    It's quite possible that the 'good' pair are supplying most of the current. I'll check that today.

    Thanks again for the ideas.


    Tom
  • icarusicarus Super Moderator Posts: 5,070Super Moderators
    Re: Battery voltage drop under load

    Is it possible that you are putting the cart before the horse?

    Get them fully charged, run a EQ charge to them, top up the water, and then do a load test. It is possible that given the original state of charge, they couldn't carry the load, but when fully charged they might,,, or might come close(r).

    Tony
  • bryanlbryanl New User Posts: 175Solar Expert ✭✭✭✭
    Re: Battery voltage drop under load

    re: "The RV has a Progressive Dynamics charge controller." - I understand that this is an RV converter you are talking about. Does this have the charge wizard thingy with it? If it does and if it has been on and maintaining the battery, you have about as good a battery maintainer as you can get.

    A charge wizard controlled Progressive Dynamics converter will hold a 13.2 volt float with a bump to 14.4v every 14 hours for a few minutes. You have to hit the button for manual over-ride to set a particular voltage (intended to allow boondockers to more quickly recharge batteries at bulk when they know their charge time is short).

    Voltage drops are due to resistance. I agree that battery sulfation is a primary suspect and wiring next. A bad cell is also possible but its drop curve is usually kneed rather than logarithmic.
  • bikemechanic53bikemechanic53 bikemechanic Posts: 7Registered Users
    Re: Battery voltage drop under load

    The Progressive Dynamics 4600 has the charge wizard, which allows me to set it to 14.4 volts. But not higher. So I don't have any bubbles coming up.

    After 5 hours, the SG on the 2 batteries has come up from 1.225 to around 1.235. So it may take another 20 hours to get this pair up to .275?

    Tom
  • bikemechanic53bikemechanic53 bikemechanic Posts: 7Registered Users
    Re: Battery voltage drop under load

    Hmmm. I've been checking the cells and the electrolyte level is at the bottom of the vent wells.

    So it appears the cells are overfilled. Apparently I overfilled them. But I thought I had not added water to any cell that was close to the bottom of the vent well.

    What should I do?

    Tom
  • BB.BB. Just some guy Posts: 24,203Super Moderators admin
    Re: Battery voltage drop under load

    Yep--if full charge SG is 1.270, then they will take that long (or longer) to charge.

    When the batteries start to bubble, then they are approaching full charge.

    Around that point, you can cut the current to 5% of bank capacity and take the specific gravity reading every 30-60 minutes. once all of the cells stabilize at some SG reading (no increases in the next 30-60 minutes)--then you have equalized the bank and hit full charge.

    Also watch the battery temperature... If they get too warm (around 100F maximum), pull the plug and let them cool awhile, then reconnect and finish charging/equalizing.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • westbranchwestbranch Not So New User Posts: 4,024Solar Expert ✭✭✭
    Re: Battery voltage drop under load

    keep charging. the increase may be due to gassing off. EQ ing will also gas off some of the excess, if any.

    HTH
    EJ
     
    CL 647 asleep  24V 900Ah C&D AGM
    CL 4592  175A E-Panel WBjr, 2 x 4s 140W to 24V 900Ah C&D AGM + 4s 140W 
    Linksys Wet54g WiFi Bridge ,  ASUS RTN10 router, Hughes Sat Modem
    Omnicharge 3024, Cotek ST1500W 24V Inverter,
    1680W & E-Panel/WBjr to come, Eu3000i & 1000i Gens,
    West Chilcotin, BC, Canada




  • BB.BB. Just some guy Posts: 24,203Super Moderators admin
    Re: Battery voltage drop under load
    Hmmm. I've been checking the cells and the electrolyte level is at the bottom of the vent wells.

    So it appears the cells are overfilled. Apparently I overfilled them. But I thought I had not added water to any cell that was close to the bottom of the vent well.

    What should I do?

    1. Stop charging and let the cells cool (if bank is hot)
    2. Don't top off electrolyte levels until done charging (make sure plates are covered with electrolyte).
    3. Get a plastic or glass cup per cell and draw of electrolyte per cell. Finish charging/equalizing, let cool, add electrolyte back to same cell.
    Is there still a "cut or slot" in the side of the fill tube? If so--you are OK. If not (level near top of cut/slot or slot is covered) you will have to pull some electrolyte to prevent the electrolyte from being pushed out the battery filler onto the battery top.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jeffkrusejeffkruse Posts: 204Solar Expert
    Re: Battery voltage drop under load

    What I noticed is that even a ¼ makes a difference in SG readings. I am supposed to fill ¼ inch below the chimney. Then the SG readings seem to get to charged (1.260 – 1.280). When I filled them to touch the chimney the SG readings were lower, maybe .010 - .020 lower.
  • bikemechanic53bikemechanic53 bikemechanic Posts: 7Registered Users
    Re: Battery voltage drop under load

    The batteries aren't hot, not even warm. So I'm OK there.

    The levels are at the bottom of the vent wells, not up the sides.

    The Crown battery site agrees with you that overfilling the cells reduces the SG.

    I'll pull some of the electrolyte out of each cell till they are at the standard level. I have a large glass SG 'reader'. But these bulbs don't appear to be very accurate. Does anyone know of a more accurate way to read SG?

    Thanks,


    Tom
  • jeffkrusejeffkruse Posts: 204Solar Expert
    Re: Battery voltage drop under load

    Why pull the electrolyte if its not going to spill. I think if you pull the electrolyte now it won't help with the SG readings. To get the electrolyte to the proper level you will just have to "boil" it off over time and full charging.
  • mike95490mike95490 Title:User Posts: 6,203Solar Expert ✭✭✭
    Re: Battery voltage drop under load

    If the electrolyte is not bubbling out the "chimney", leave it in there. Sure , if you add too much water, it will reduce the SG, but storing 24 dixie cups of acid, and getting it all back into the right cells, just seems like a accident waiting to happen. Leave it in the cells, and as it gasses off, it will recover.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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