Problem with my setup or normal (24V charging)

SkykoSkyko ✭✭✭✭✭Solar Expert Posts: 121 ✭✭✭✭✭
Hi,

I have just wired up a battery/inverter/equalizer system in my camper and have noticed a difference in the absorption charging voltage across each battery (two 12V AGM in series). Both batteries were around 90% charged, I ran the 1050 watt input 700 watt output microwave for a couple of minutes drawing 24V at 58 amps (made a very nice boiling cup of water). The battery voltage was around 24V at the inverter during the high current draw but climbed quickly back up to 25.4V after the microwave turned off. I then connected shore power and the inverter flipped to absorption charging, outputting 29V at 11 to 14 amps (it is cooler here and I have a BTS which may be why it is above the stated 28.6V absorption voltage for AGM1 setting (Lifeline) at 77 degrees (it is about 69 degrees).

The issue is I measured the individual voltage across each series 12V battery while in absorption charge mode and one was getting around 13.6V while the other 15.4V (their initial rest state voltage before all of this had been 12.85V and 12.89V). I did not let the absorption charge go for very long before shutting down the charger because I was worried that this imbalance might damage the Lifeline AGMs. I do have a Vanner battery equalizer connected to them which keeps them within 0.05V of each other during discharge (but evidently not during charge). I disconnected this and still saw the same difference in absorption charge voltage so it is not doing anything funky.

Problem or am I just a worrywart? Both Lifeline 125AH GPL31XT 12V AGM were purchased a few months ago new from the same batch. Both measured 13.01 to 13.02V when purchased.

The equipment I am using:

Magnum MSH4024M hybrid 4000 watt 24V input inverter
Vanner 65-60 battery equalizer (to provide a 12V tap and keep batteries equal during 12V draw)
Lifeline GPL31XT 12V AGM connected in series (two total batteries)

Comments

  • inetdoginetdog ✭✭✭✭ Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Problem with my setup or normal (24V charging)

    Very interesting!

    Two (OK, three or four....) possibilities come to mind immediately:
    1. The two batteries have seriously different internal resistance when at or near full charge, and this allows the voltage difference that you see.
    Note that 15.4V on an AGM should lead to severe gassing and subsequent venting with permanent loss of electrolyte. The resulting electrolyte starvation will make the problem worse and the situation will rapidly spin out of control.
    When equalize charging batteries in series, you really have to monitor voltage at the battery or cell level.
    2. One of the batteries has lost capacity and so is reaching a high terminal voltage before the other does. The only way to deal with that in an AGM situation, other than using a controller very low equalize current, is to take the low battery out of the circuit and charge it separately with a 12V charger.
    3. It is possible that the high battery has just one bad cell. The end result is still equally bad, and if that cell is not damaged, then a slow (low current) equalization will be the only way to recover, if recovery is possible at this stage.
    4. I do not feel very good about battery equalizers unless you are trying to pull 12V loads from the lower battery. A rigid conformity to equal charge voltages on both batteries can easily mask problems (such as the one you are reporting) until they are so far gone as to be unrecoverable.

    PS: Was reminded by a post by ZoneBlue in another thread that you can weigh your AGMs to get a rough indication of whether you have been venting.
    SMA SB 3000, old BP panels.
  • vtmapsvtmaps ✭✭✭✭ Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Problem with my setup or normal (24V charging)
    Skyko wrote: »
    I do have a Vanner battery equalizer connected to them which keeps them within 0.05V of each other during discharge (but evidently not during charge). I disconnected this and still saw the same difference in absorption charge voltage so it is not doing anything funky.

    One reason you may see voltage imbalance during charging is if the batteries are not at the same SOC. Perhaps the Vanner is discharging one battery more than the other... in that case (even with the Vanner subsequently disconnected) the charging would be unequal.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • inetdoginetdog ✭✭✭✭ Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Problem with my setup or normal (24V charging)
    vtmaps wrote: »
    One reason you may see voltage imbalance during charging is if the batteries are not at the same SOC. Perhaps the Vanner is discharging one battery more than the other... in that case (even with the Vanner subsequently disconnected) the charging would be unequal.

    --vtMaps
    A good point, and it also emphasizes that the specified equalize voltage should be the maximum applied to any one battery in the string. Just multiplying by N and applying that voltage to the string without monitoring individual batteries is asking for trouble.

    Note also that Skyko stated that the resting voltages of the two batteries were very close to equal. If the same resting voltage corresponds to a very different SOC on two sealed batteries, you are already in trouble that equalization cannot cure.
    My only concern with that diagnosis would be to confirm that the resting voltages were still equal with the Vanner disconnected for at least four hours.
    SMA SB 3000, old BP panels.
  • SkykoSkyko ✭✭✭✭✭ Solar Expert Posts: 121 ✭✭✭✭✭
    Re: Problem with my setup or normal (24V charging)

    I stopped the absorption charge rather soon so as to not damage the batteries if 15.4V on one was bad.

    I managed to swap the characteristics by discharging the other battery with a small load for a few minutes until it was about 0.05V below the other. Now when I turned on the charger and it went to absorption mode, the opposite battery was getting about 15.3V and the other 13.7V.

    This has me believing the SoC on these is super critical and the internal resistance must be very low. Both batteries seem to easily be able to deliver current without much voltage sag which makes me think the batteries are ok.

    I now limited the absorption mode to 0.5 hours (Magnum recommends 1 hour for 200ah to 300ah and I only have 125ah).

    When the batteries switched to float mode and the float voltage from the charger dropped to 26.4V, the individual battery voltages measured were 13.15 and 13.25...of course the current had dropped to 1.5 amps.

    Might be ok? How bad is 30 min of 15.4V at 4 amps going to be to a 125AH AGM?
  • Marc KurthMarc Kurth ✭✭✭✭ Solar Expert Posts: 536 ✭✭✭✭
    Re: Problem with my setup or normal (24V charging)

    You didn't hurt the batteries at 15.4v for a short while. In fact that's in range for equalization if need to do it in the future. For the absorption time, you didn't indicate your charging capacity and what you have it set for as max. How much charging capacity do you have available?

    Important: You need to cycle new Lifeline's a few times to break them in. I do not mean that you must deep cycle them, just bring them down a bit, then charge them up again. In other words, use them normally for about a dozen cycles. Then you can expect to see "normal" voltages readings.

    Was on the higher voltage battery always on the "negative" (-) end of the string?

    Marc

    (Edit: just looked it up, you have a 110 amp charger)
    I always have more questions than answers. That's the nature of life.
  • SkykoSkyko ✭✭✭✭✭ Solar Expert Posts: 121 ✭✭✭✭✭
    Re: Problem with my setup or normal (24V charging)
    Marc Kurth wrote: »
    You didn't hurt the batteries at 15.4v for a short while. In fact that's in range for equalization if need to do it in the future. For the absorption time, you didn't indicate your charging capacity and what you have it set for as max. How much charging capacity do you have available?

    Important: You need to cycle new Lifeline's a few times to break them in. I do not mean that you must deep cycle them, just bring them down a bit, then charge them up again. In other words, use them normally for about a dozen cycles. Then you can expect to see "normal" voltages readings.

    Was on the higher voltage battery always on the "negative" (-) end of the string?

    Marc

    (Edit: just looked it up, you have a 110 amp charger)

    Yes, it is a honking charger but I lowered the digital setting for shore power input to 15 amps instead of 30 to match my generator so I would guess 29V at 60 amps or so is going to be the maximum bulk charge rate.

    I think I do need to cycle the batteries a few times. I have just now read that in Lifeline doc and you confirm it.

    The higher voltage battery was just whichever battery had 0.05 more rest voltage before I turned on the charger. This is what makes me think this whole thing is a non issue.
  • Marc KurthMarc Kurth ✭✭✭✭ Solar Expert Posts: 536 ✭✭✭✭
    Re: Problem with my setup or normal (24V charging)

    60 amps is a good setting for that bank because I'm forecasting that you will be dragging them way down with such a huge inverter-to-battery ratio.

    See what happens after cycling a few times. Whoever sold you the batteries should have told about cycling them........
    I always have more questions than answers. That's the nature of life.
  • SkykoSkyko ✭✭✭✭✭ Solar Expert Posts: 121 ✭✭✭✭✭
    Re: Problem with my setup or normal (24V charging)

    After a few more cycles I am noticing more capacity from the Lifelines, but the Vanner equalizer is definitely keeping one battery about 50millivolts above the other which seems to cause them to charge unequal. Now in absorption they are charging at 13.9V and 15.1V respectively. I guess Vanner thought 50 millivolts was not significant but for these Lifelines it seems to represent a significant difference in state of charge.

    I am thinking of rewiring the Vanner equalizer to be a DC-DC converter. This is possible according to the manual, you just remove the 12V tap to the batteries and disconnect your 12V equipment from the batteries then wire it directly to the Vanner 12V terminal. It isn't ground isolated but then again it wasn't ground isolated before. I am not seeing an advantage to an equalizer if it cannot keep them closer to equal. Maybe with a different type of battery it would work as intended.
  • SkykoSkyko ✭✭✭✭✭ Solar Expert Posts: 121 ✭✭✭✭✭
    Re: Problem with my setup or normal (24V charging)

    Ok, so this morning after running the house lights and fridge yesterday and overnight the batteries were at 12.5V and 12.55V (the difference being the Vanner equalizer not quite equalizing the charge).

    I disconnected the equalizer and started the magnum, which flipped to absorption after a couple seconds in bulk and was delivering 30 amps to the batteries with the 12.5v battery getting 13.9V and the 12.55V battery getting 15.1V. I turned off the charger and left the equalizer off, then applied a 5 amp 12V load to the 12.55V battery for about 40 minutes, dropping it to 12.45V. Now with the equalizer still off, the absorption charge when started back up was delivering almost exactly the opposite 15.2V to the 12.45V battery and 13.8V to the 12.5V battery. Since now the upper battery was getting 15.2V, I flipped on the equalizer and it caused the charge rate for both batteries to be exactly 14.5V (it is cooler this morning so charging a bit more than 14.4V at 77 degrees standard).

    So, a few things I have learned.

    1) 50 millivolts is huge in Lifeline AGMs

    2) The Vanner equalizer is useless if the lower 12V battery is higher than the upper but works quite well to equalize during charging if the upper battery is getting a much higher voltage than the lower.

    3) It would probably be better if I didn't own a multimeter and just remained ignorant to all of this, treating the battery as one big 24V cell.
  • Marc KurthMarc Kurth ✭✭✭✭ Solar Expert Posts: 536 ✭✭✭✭
    Re: Problem with my setup or normal (24V charging)

    I have requested additional info from Concorde about this, because you have me curious now! Will let you what they say.

    Marc
    I always have more questions than answers. That's the nature of life.
  • vtmapsvtmaps ✭✭✭✭ Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Problem with my setup or normal (24V charging)
    Skyko wrote: »
    It would probably be better if I didn't own a multimeter and just remained ignorant to all of this, treating the battery as one big 24V cell.

    I don't agree about the multimeter. I very strongly agree with treating it as a 24 volt battery. A real 24 volt battery would have just a plus and a minus terminal and you couldn't use that Vanner equalizer thing. When you tap the middle of a 24 volt battery, you don't have a 24 volt battery... you have two 12 volt batteries.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • SkykoSkyko ✭✭✭✭✭ Solar Expert Posts: 121 ✭✭✭✭✭
    Re: Problem with my setup or normal (24V charging)

    Thanks Marc.

    A little reading this morning has determined that you can't use the 65-60 as a 12V power source because for safety reasons the 12V terminal will not supply current without sensing a ~12V battery connected to it. Thus evidently you cannot simply connect the 12V terminal to your 12V accessories and leave the midpoint tap on the batteries disconnected (you could do this on family 1 and 2 series). You *could* have a very small battery connected to the 12V terminal and trick the Vanner into supplying 12V out of it's 12V terminal (this would be considered a house battery, even if it was a 7 amp motorcycle type AGM).

    I wish there was an adjustment to the Vanner to allow you to vary the equalize voltage triggers. I think what is happening is the lower battery of the 24V string (which is supplying 12V loads) is getting too much juice from the upper battery during medium or high current draw. This leaves the upper battery a few millivolts lower than the lower battery which for Lifeline AGM is a big difference in capacity (maybe 10%). Theoretically the lower battery should actually be the one which doesn't get charged as much but this is not the case with the Vanner.

    If you can't adjust the Vanner, then one solution might be to leave a small 12V load on while charging, like the LED lights. In this way the lower battery will have a drain and the upper battery will get a couple more amps causing them both to gain an equal charge. Or just swap the battery positions every few months. Or ???
  • SkykoSkyko ✭✭✭✭✭ Solar Expert Posts: 121 ✭✭✭✭✭
    Re: Problem with my setup or normal (24V charging)
    vtmaps wrote: »
    I don't agree about the multimeter. I very strongly agree with treating it as a 24 volt battery. A real 24 volt battery would have just a plus and a minus terminal and you couldn't use that Vanner equalizer thing. When you tap the middle of a 24 volt battery, you don't have a 24 volt battery... you have two 12 volt batteries.

    --vtMaps

    Well, the equalizer was supposed to be a rugged, tried and true solution used by the bus conversion people, military and marine applications...
  • vtmapsvtmaps ✭✭✭✭ Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Problem with my setup or normal (24V charging)
    Skyko wrote: »
    Well, the equalizer was supposed to be a rugged, tried and true solution used by the bus conversion people, military and marine applications...

    I prefer to use a 24 v DC to 12 v DC converter... it's very easy to know if it's working, and it can't possibly unbalance your batteries. Also the 12 volt output is not subject to variation like a battery's voltage during its charge/discharge cycle.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CariboocootCariboocoot ✭✭ Banned Posts: 17,615 ✭✭
    Re: Problem with my setup or normal (24V charging)
    Skyko wrote: »
    Well, the equalizer was supposed to be a rugged, tried and true solution used by the bus conversion people, military and marine applications...

    A solution to a problem which in your case doesn't exist.
    Many of those applications mentioned use 24 Volt starting & charging with a 12 Volt 'tap' to run common lights and accessories, thus a built-in load imbalance which needs to be compensated for.
    A standard battery of 6 or 12 Volts is multiple 2 Volt cells connected in series. There's no need for an equalizer with them, nor with putting multiples of such batteries in series to create higher Voltage: it's all just 2 V cells strung together.
  • SkykoSkyko ✭✭✭✭✭ Solar Expert Posts: 121 ✭✭✭✭✭
    Re: Problem with my setup or normal (24V charging)
    A solution to a problem which in your case doesn't exist.
    Many of those applications mentioned use 24 Volt starting & charging with a 12 Volt 'tap' to run common lights and accessories, thus a built-in load imbalance which needs to be compensated for.
    A standard battery of 6 or 12 Volts is multiple 2 Volt cells connected in series. There's no need for an equalizer with them, nor with putting multiples of such batteries in series to create higher Voltage: it's all just 2 V cells strung together.

    No, you are misinformed. I definitely do have a problem. I need 12V for a number of loads (led lights, 12V outlets, 12V water pump, 12V furnace fan, 12V water heater control board, 12V vent fans).

    The inverter runs on 24V as does the refrigerator.

    The possible solutions were a 12V house battery fed with separate charger, a DC-DC converter capable of 40 amp loads (if everything was on), or something like the Vanner equalizer which allows you to tap off the center of a 24V bank. I didn't have room for another 12V battery so chose the equalizer over the DC-DC converter.
  • CariboocootCariboocoot ✭✭ Banned Posts: 17,615 ✭✭
    Re: Problem with my setup or normal (24V charging)
    Skyko wrote: »
    No, you are misinformed. I definitely do have a problem. I need 12V for a number of loads (led lights, 12V outlets, 12V water pump, 12V furnace fan, 12V water heater control board, 12V vent fans).

    The inverter runs on 24V as does the refrigerator.

    The possible solutions were a 12V house battery fed with separate charger, a DC-DC converter capable of 40 amp loads (if everything was on), or something like the Vanner equalizer which allows you to tap off the center of a 24V bank. I didn't have room for another 12V battery so chose the equalizer over the DC-DC converter.

    And the equalizer is meant to take 24 Volt input and distribute it equally to two 12 Volt batteries in series. Only it doesn't. Not much difference in wire resistance is required to throw this off, especially with AGM's which have very low internal resistance to begin with. You've discovered this.

    You would have been better off using the converter method as it evens the draw between batteries instead of trying to compensate for uneven discharge with uneven charging.

    If the over-all current demand is too much for one converter, multiple appropriately sized converters can be used. Each of which will present its own cost to the battery bank, another downside.

    And people wonder why we so often recommend just powering an inverter and using all 120 VAC loads. This is one reason why; balancing out different Voltage loads can be a real nightmare and the "greater efficiency" of LVDC often isn't actually there.
  • zonebluezoneblue ✭✭✭✭ Solar Expert Posts: 1,218 ✭✭✭✭
    Re: Problem with my setup or normal (24V charging)
    Skyko wrote: »
    I need 12V for a number of loads (led lights, 12V outlets, 12V water pump, 12V furnace fan, 12V water heater control board, 12V vent fans). The inverter runs on 24V as does the refrigerator.

    Check the LEDs, many will run at 24v. Replace the shurflo with a 24v model. What little remains put on the dc dc converter.

    Our motorhome is 100% 24v, both house and SLI. Wasnt hard.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • Marc KurthMarc Kurth ✭✭✭✭ Solar Expert Posts: 536 ✭✭✭✭
    Re: Problem with my setup or normal (24V charging)
    A solution to a problem which in your case doesn't exist.
    Many of those applications mentioned use 24 Volt starting & charging with a 12 Volt 'tap' to run common lights and accessories, thus a built-in load imbalance which needs to be compensated for.
    A standard battery of 6 or 12 Volts is multiple 2 Volt cells connected in series. There's no need for an equalizer with them, nor with putting multiples of such batteries in series to create higher Voltage: it's all just 2 V cells strung together.

    Yep. This is the answer that I've always gotten from Concorde. Sometimes their answer is posed as a question back at me:

    "OK Marc, what is the voltage variation between the (12) two volt cells in one of our 24v batteries, or the (6) cells in a big 12v? If you could measure it, you would see the same thing... They will equalize to each other when they reach float for even a short time."

    I'm still not comfortable with some of the details behind this answer, so I've kicked it up the ladder for a more detailed answer from the top of the engineering food chain.

    Marc
    I always have more questions than answers. That's the nature of life.
  • vtmapsvtmaps ✭✭✭✭ Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Problem with my setup or normal (24V charging)
    Marc Kurth wrote: »
    Yep. This is the answer that I've always gotten from Concorde. Sometimes their answer is posed as a question back at me:

    "OK Marc, what is the voltage variation between the (12) two volt cells in one of our 24v batteries, or the (6) cells in a big 12v? If you could measure it, you would see the same thing... They will equalize to each other when they reach float for even a short time."

    I think their approach works when the batteries are used normally... that is, when they are discharged evenly. Your batteries appear to be discharged unevenly because of that vanner thing.

    My advice: get a 12 volt charger and separate your batteries and charge them individually.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • SkykoSkyko ✭✭✭✭✭ Solar Expert Posts: 121 ✭✭✭✭✭
    Re: Problem with my setup or normal (24V charging)

    I thought about the Vanner equalizer some more, and have an idea to trick it into being a DC-DC converter. If it needs to see 12V on the 12V terminal before it will supply current out of that terminal, I could just hang a resistor voltage divider between 24V and ground, connecting the center tap to the Vanner 12V terminal. Assuming that the Vanner does not need more than a signal level current of a few milliamps at most, I could use high value resistors like 5K ohm in the divider. The parasitic draw would then be 26V/10K = 2.6 milliamps for a fully charged battery bank. 2.6 milliamps is probably much less than the natural charge decay in a AGM (it would be about 1.8 amp-hr per month drain).

    If I size the divider slightly off balance where the voltage drop across the resistor between the 12V Vanner terminal and ground is greater than 1/2 of the whole battery bank voltage, then the Vanner equalizer will remain off until a 12V load is applied from the various things I have which use 12V.
  • SkykoSkyko ✭✭✭✭✭ Solar Expert Posts: 121 ✭✭✭✭✭
    Re: Problem with my setup or normal (24V charging)

    Three more shallow charge discharge cycles (about 20% DoD) with the Vanner totally disconnected and I am becoming convinced it is just a feature of the Lifeline batteries that they charge wacky when in series.

    Charge 1: Battery A: 12.66V Battery B: 12.64V Absorption charge readings: Battery A: 15.05V Battery B: 13.95V

    Charge 2: Battery A: 12.59V Battery B: 12.60V Absorption charge readings: Battery A: 14.02V Battery B: 14.97V

    Charge 3: Battery A: 12.65V Battery B: 12.62V Absorption charge readings: Battery A 15.11V Battery B: 13.91V
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