Hybrid grid-tie / off-grid system: Victron

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  • NorthGuyNorthGuy Posts: 1,925Solar Expert
    Re: Hybrid grid-tie / off-grid system: Victron
    AceNZ wrote: »
    I decided I should make a diagram for this, since it's confusing enough that it's easy to forget the details. Copy attached.

    It all makes sense now. When the grid is connected, they do not want the shifted frequency on inverter/charger's Out to affect the GT inverter. Otherwise, it could disconnect when batteries are full. When the grid fails, they connect the GT inverter to the inverter/charger to form an off-grid system.
  • AceNZAceNZ Posts: 104Solar Expert ✭✭✭✭
    Re: Hybrid grid-tie / off-grid system: Victron
    NorthGuy wrote: »
    When the grid is connected, they do not want the shifted frequency on inverter/charger's Out to affect the GT inverter. Otherwise, it could disconnect when batteries are full.

    Ah, good point. Hadn't thought about that aspect.

    Hopefully that won't be a problem in self-consumption mode. I know they changed the frequency-shift algorithm from being simply based on battery voltage to something else -- this might be why.
  • AceNZAceNZ Posts: 104Solar Expert ✭✭✭✭
    Re: Hybrid grid-tie / off-grid system: Victron

    My installer just pointed out to me that I can move the solar inverter to the inverter/charger's AC-out port by disabling the ATS and switching it over manually.

    Ugh.

    I'm surprised that the inverter/charger is considered to provide sufficient isolation from the grid during a mains failure -- but that's actually how it's wired now, and the power company has already come out to measure and certify it.
  • NorthGuyNorthGuy Posts: 1,925Solar Expert
    Re: Hybrid grid-tie / off-grid system: Victron
    AceNZ wrote: »
    My installer just pointed out to me that I can move the solar inverter to the inverter/charger's AC-out port by disabling the ATS and switching it over manually.

    It is a good thing to figure out how to do in case you need it.
  • AceNZAceNZ Posts: 104Solar Expert ✭✭✭✭
    Re: Hybrid grid-tie / off-grid system: Victron
    NorthGuy wrote: »
    It is a good thing to figure out how to do in case you need it.

    Pushing the "Test" button on the ATS did the trick -- it doesn't time-out and go back to "regular" mode, even after a power failure.

    I reloaded the new firmware earlier today and re-enabled self-consumption mode. So far, so good!

    It's completed the first day-to-night transition correctly. Now on batteries only, off-grid. If it goes back on-grid tomorrow on its own, I should be set, with the possible exception of a little tuning.

    Now if I could just get some details from Trojan about the batteries. Here are my questions:

    1. One version of the brochure for the IND17-6V says C/20 capacity is 897 AH, and another (newer) one says 925 AH. Was this just a correction to the specs, or did the batteries change? If the batteries changed, how can I tell which ones I have?
    2. Is it better to end absorption based on time, or on current? If current, how much?
    3. For relatively new batteries, what is the usual/typical SOC at the end of bulk charging? Since it changes over time, is there an easy way to measure it?
    4. What is the expected charge efficiency? Since it changes over time, is there an easy way to measure it?
    5. When the batteries have been in float for an extended period, how often should they go into absorption again, and for how long?
    6. Victron's equalization algorithm works as follows: one out of every 8 repeated absorption phases becomes an equalization phase; once charge current reaches 10% of the maximum bulk charge, it's kept at that level until either absorption ends or the voltage reaches a 2.83vpc limit (68V). Since this is above the recommended 2.58vpc limit, should I use this equalization charging approach (is absorption likely to complete first?), or is it OK to rely on periodic absorption charges while the battery is in float for electrolyte mixing?
    7. What are the tradeoffs in choosing an absorption voltage from within the recommended range other than time-to-charge? Does a lower voltage help improve battery life?
    8. What is the best maximum charge current to use to maximize battery life?
    9. In periodic charge/discharge cycles, where the batteries aren't normally charged to 100% every day, how often should they be forced to full charge to maximize battery life? (I read at least once every 3 charge throughputs, so at 20% DOD average per day, that would be every 15 days, right?)

    Maybe I'll try calling their tech support folks next week.
  • NorthGuyNorthGuy Posts: 1,925Solar Expert
    Re: Hybrid grid-tie / off-grid system: Victron
    AceNZ wrote: »
    1. One version of the brochure for the IND17-6V says C/20 capacity is 897 AH, and another (newer) one says 925 AH. Was this just a correction to the specs, or did the batteries change? If the batteries changed, how can I tell which ones I have?

    They had a press release saying that their batteries have more capacity than the rating. My guess is they just adjusted the ratings. The difference is negligible for all practical purposes.
    AceNZ wrote: »
    2. Is it better to end absorption based on time, or on current? If current, how much?

    I used SG. The spec is 1.260. They say to equalize when it's below 1.230. So, I though an acceptable absorption would need to move SG above 1.230, say to 1.240. One time I charged at 64V with 2.5% terminating current. This worked. With 59V, the current goes relatively quickly to about 0.3-0.5% and stays there. I didn't do it for that long, but by my estimate to get a decent SG it would take 30 to 40 hours at 59V. Otherwise, 59V absorption only elevates SG to 1.180-1.220 (depending on previous discharges). After very shallow discharges, it may go to 1.240 within 5-6 hours at 59V.

    That's what I found with mine. You have a different discharge pattern, and also it is possible that my batteries are somehow defective. So, the best thing to do is to monitor SG.
    AceNZ wrote: »
    3. For relatively new batteries, what is the usual/typical SOC at the end of bulk charging? Since it changes over time, is there an easy way to measure it?

    Depends a lot of previous discharges. I can only tell about mine (1 year 4 months old now). After 50% discharge may be as high as 90%. After deep discharge, somewhere around 80%. After a week of cycling without absorptions may bew as low as 70%.

    The best way to measure is with battery monitor. Vicrton makes good ones.
    AceNZ wrote: »
    4. What is the expected charge efficiency? Since it changes over time, is there an easy way to measure it?

    Yes, divide discharge voltage to charge voltage. Say, discharge at 48, charge at 55 means 87% efficiency. The deeper you cycle the more the efficiency.

    It is also an overhead related to absorptions. An absorption will require 5 to 15% of capacity extra, again depending on previous discharge. You probably need to count this into efficiency numbers too.
    AceNZ wrote: »
    5. When the batteries have been in float for an extended period, how often should they go into absorption again, and for how long?

    I don't think floating batteries need absorptions. I would measure SG and equalize if it is below 1.230 or cells differ by 0.050 or more. That's what Trojan recommends. Shouldn't be very often.
    AceNZ wrote: »
    6. Victron's equalization algorithm works as follows: one out of every 8 repeated absorption phases becomes an equalization phase; once charge current reaches 10% of the maximum bulk charge, it's kept at that level until either absorption ends or the voltage reaches a 2.83vpc limit (68V). Since this is above the recommended 2.58vpc limit, should I use this equalization charging approach (is absorption likely to complete first?), or is it OK to rely on periodic absorption charges while the battery is in float for electrolyte mixing?

    It shouldn't be any stratification when batteries are on float, so theoretically you don't need this. But, if you notice that SG is dwindling down, then doing what Victron does will help to keep SG high.
    AceNZ wrote: »
    7. What are the tradeoffs in choosing an absorption voltage from within the recommended range other than time-to-charge? Does a lower voltage help improve battery life?

    I don't know. Lower voltages mean longer durations, which may not be good for battery life neither. I had to go way above the recommended range - to 64V - to keep absorption duration in check. But it is only applicable if you discharge deep. If you don't, electrolyte stratifies much less and you need much less effort to mix it. Again, it is a chance that my batteries are somehow defective.
    AceNZ wrote: »
    8. What is the best maximum charge current to use to maximize battery life?

    During bulk stage, they recommend 10-13%. Higher rates may cause overheating. I guess, if not for overheating, higher rates may be used, but honestly I don't know. During absorption/float it is limited by voltage.
    AceNZ wrote: »
    9. In periodic charge/discharge cycles, where the batteries aren't normally charged to 100% every day, how often should they be forced to full charge to maximize battery life? (I read at least once every 3 charge throughputs, so at 20% DOD average per day, that would be every 15 days, right?)

    I do 2.5 throughputs if with generator, which translates to about 9 days for me. I don't think I could do 3 because SoC where bulk switches to absorption is getting close to 70%, and I don't want it to go below that. I also have a critera that they cannot stay below 70% SoC for longer than 3 days.
    AceNZ wrote: »
    Maybe I'll try calling their tech support folks next week.

    Good luck with that.
  • AceNZAceNZ Posts: 104Solar Expert ✭✭✭✭
    Re: Hybrid grid-tie / off-grid system: Victron

    Good info, thanks.

    Also on my list for this week is to get a hydrometer and measure SG. (the type I need isn't carried in-stock near me -- requires a special order).
  • NorthGuyNorthGuy Posts: 1,925Solar Expert
    Re: Hybrid grid-tie / off-grid system: Victron
    AceNZ wrote: »
    Also on my list for this week is to get a hydrometer and measure SG. (the type I need isn't carried in-stock near me -- requires a special order).

    You will need a longer nozzle because the testing well is rather deep.
  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: Hybrid grid-tie / off-grid system: Victron
    NorthGuy wrote: »
    I don't think floating batteries need absorptions.
    <snip>
    It shouldn't be any stratification when batteries are on float

    I feel like you ought to be correct, but I am not sure you are. I have seen references to the need for periodic absorption/equilization of floating batteries. I have not seen any data that specifically addresses the issue, so I really don't know.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Hybrid grid-tie / off-grid system: Victron
    vtmaps wrote: »
    I feel like you ought to be correct, but I am not sure you are. I have seen references to the need for periodic absorption/equilization of floating batteries. I have not seen any data that specifically addresses the issue, so I really don't know.

    --vtMaps

    If a battery is "floating" it is not being discharged, therefor it does not need to be recharged. Absorption is part of recharging.

    Batteries self-discharge over time no matter what. They will also sulphate and corrode and suffer plate erosion whether used or not. So as far as equalization is concerned you should check them periodically to see if the SG is dropping on any/all cells and do a correcting EQ as needed.

    This is also why some batteries, such as those used in the telecom industry or other UPS applications, are designed to be in float constantly with only occasional discharges. That's why they don't work that well in an RE application.
  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: Hybrid grid-tie / off-grid system: Victron
    If a battery is "floating" it is not being discharged, therefor it does not need to be recharged. Absorption is part of recharging.

    I think the issue is not that the battery needs to be recharged, but that a floating battery may develop stratification. The references I've seen to periodic absorption of floating batteries seem to suggest that a periodic absorption is needed to stir up the electrolyte.

    I am agnostic on the issue. I don't understand as much about stratification as I would like to.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Hybrid grid-tie / off-grid system: Victron
    vtmaps wrote: »
    I think the issue is not that the battery needs to be recharged, but that a floating battery may develop stratification. The references I've seen to periodic absorption of floating batteries seem to suggest that a periodic absorption is needed to stir up the electrolyte.

    I am agnostic on the issue. I don't understand as much about stratification as I would like to.

    --vtMaps

    You can't get stratification without altering the electrolyte density, which requires discharging. It is a chemical solution, not a suspension, so it will not alter just by sitting. Except for the self-discharging factor of course.

    Keep in mind also that "Float" Voltage is always above resting Voltage, so the battery is held in a state of negative discharge.
  • AceNZAceNZ Posts: 104Solar Expert ✭✭✭✭
    Re: Hybrid grid-tie / off-grid system: Victron

    Here's some info I've paraphrased from a publication by Victron, "Energy Unlimited":

    The acid that's produced as the battery is being charged has a higher density than water, and so tends to settle downwards. Once absorption voltage is reached, the resulting gas generation tends to stir and mix the electrolyte, helping it to become more uniform. Bigger/taller batteries tend to need more gas generation than smaller ones.

    Modern flooded batteries with low antimony content don't gas very much, though. They require being in float for an extended period (possibly weeks) before the electrolyte is well mixed. Such batteries can have a low hydrometer reading, even though they are fully charged.

    Modern batteries aren't designed to be in float beyond a few days or weeks at most. In the 2.3vpc range (55.2V), the positive grids corrode more quickly, which will shorten battery life. By dropping the charge to 2.15 to 2.20vpc (51.6 to 52.8V) after 24 hrs, aging and gassing will be under control, but a regular refresh charge in absorption mode is needed to maintain the fully charged state. The cells will also need to have water added less frequently that way.
  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: Hybrid grid-tie / off-grid system: Victron
    AceNZ wrote: »
    Here's some info I've paraphrased from a publication by Victron, "Energy Unlimited":

    The acid that's produced as the battery is being charged has a higher density than water, and so tends to settle downwards.
    <snip>
    By dropping the charge to 2.15 to 2.20vpc (51.6 to 52.8V) after 24 hrs, aging and gassing will be under control, but a regular refresh charge in absorption mode is needed to maintain the fully charged state.

    They explicitly mention that stratification occurs during charging. They don't mention explicitly that discharging also causes stratification. They also are clear that a battery held in float for some time needs an absorption, but they don't say explicitly that stratification develops during float.

    Several other brands of battery chargers also have an automatic absorb or equalization that occurs after a number of days of float. Here is a quote from the Iota battery charger manual:
    FLOAT STAGE - This charge state holds the batteries at Constant Voltage for a period not longer than seven days. During this state, the charger not only floats the batteries, but it can also provide load current up its maximum rating for other loads without depleting the battery capacity. The FLOAT STAGE will end when either the battery voltage drops below the “Low Trigger” point or at the end of seven days when the IQ4 initiates an equalization stage to remove sulfate layers from the battery plates. In either situation, the unit exits the FLOAT STAGE and enters the BULK STAGE.

    Still no explicit statement that stratification occurs during float, but what other reason could there be for so many battery charger manufacturers to run an absorb after several days of float?

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • AceNZAceNZ Posts: 104Solar Expert ✭✭✭✭
    Re: Hybrid grid-tie / off-grid system: Victron
    vtmaps wrote: »
    They explicitly mention that stratification occurs during charging. They don't mention explicitly that discharging also causes stratification.

    Yes, but it clearly does; it's the same process, just running in reverse.
    vtmaps wrote: »
    They also are clear that a battery held in float for some time needs an absorption, but they don't say explicitly that stratification develops during float.

    What they're saying is that modern low-antimony flooded batteries will only come to full charge, peak SG and destratified, after an extended period in float.
    vtmaps wrote: »
    Still no explicit statement that stratification occurs during float, but what other reason could there be for so many battery charger manufacturers to run an absorb after several days of float?

    My understanding is that a high float voltage will reduce stratification and increase SG until the battery is fully charged. But the price you pay for allowing that process to go on for longer than about 24 hours is an increase in the oxidation rate of the positive electrode, which reduces battery life.

    The alternative is to lower float voltage slightly after 24 hrs. This doesn't provide the slight ongoing mixing that the higher float does, so it also doesn't bring the battery all the way up to full charge, or even hold it there -- hence the need for periodic absorption charges, which mix the electrolyte, raise SG, and bring the battery back up to (close to) full charge.
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Hybrid grid-tie / off-grid system: Victron

    During discharge the electrolyte density changes consistently throughout as sulphur separates from the mixture and adheres to the plates. It does not stratify.

    During charging the sulphur is forced off the plates and recombines with the water in the immediate area, forming a dense mixture which sinks below the lower density mixture; stratification. The Absorb stage causes stirring which returns the mixture throughout the battery to an even consistency. When it doesn't from cell to cell Equalization is used to correct the inconsistent distribution of sulphor (as indicated by SG level).

    This is why tall case batteries suffer from it more so than short case batteries; because there is literally more physical depth for the varying density mixtures to separate in.
  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: Hybrid grid-tie / off-grid system: Victron
    During discharge the electrolyte density changes consistently throughout as sulphur separates from the mixture and adheres to the plates. It does not stratify.

    Apparently it does stratify during discharge... the water that forms during discharge floats, just as the acid that forms during charging sinks.

    Of course, I don't know this from personal observation/experimentation, but I did provide credible references recently in another thread.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Hybrid grid-tie / off-grid system: Victron
    vtmaps wrote: »
    Apparently it does stratify during discharge... the water that forms during discharge floats, just as the acid that forms during charging sinks.

    Of course, I don't know this from personal observation/experimentation, but I did provide credible references recently in another thread.

    --vtMaps

    I shouldn't think so. This is going to be one of those "lab vs. real world" things where the practical effect of stratification during discharge is not observable.

    The reason for this being that the discharge activity is consistent across the plates (until hard sulphation starts to take its toll) and so there is enough activity to keep the electrolyte mixed as the battery goes down.

    Bulk charging occurs at a fairly rapid rate, allowing the varying density of mixtures to form more quickly than they can be assimilated. As such a very high rate of discharge may induce the same effect, but at the normal usage rates there would be none to speak of.

    In my own experience I have only ever noticed the problem in limited cases, hence my suspicion that for the most part it is not a serious enough condition to be concerned with.
  • AceNZAceNZ Posts: 104Solar Expert ✭✭✭✭
    Re: Hybrid grid-tie / off-grid system: Victron

    I finally got a hydrometer and did some measurements after absorption finished: SG was 1.225, which Trojan says is about 80% SOC.

    Not quite sure yet where to go from here with that...

    It was a short absorption, though, so I'm not convinced the electrolyte was well-mixed. After the standard charge program finished, current in low-float (52.8V) was 12A. So, I set the charger to run for a few minutes at high-float (55.2V), then at absorption voltage (57.6V). It started out drawing 46A, and had dropped to 30A about 20 minutes later, before the charger flipped it back to float. (10% of C/20 is 90A for these batteries; I have bulk configured to an 80A maximum).

    I have to say that the hydrometer I have is an awful, terrible device. Hard to use, hard to read -- not to mention dripping and splattering acid; a good burn is only a matter of time, even with gloves and protective clothing.

    I think I'm going to get a reflectometer, and see if it's easier (and safer).
  • stephendvstephendv Posts: 1,571Solar Expert
    Re: Hybrid grid-tie / off-grid system: Victron

    IMO, High float vs. low float are not going to make much of a difference to the charge of your batteries, unless you leave them running for multiple days on end without any discharge in the battery. If the battery was discharged and you want to recharge, then you should lengthen absorb time. If they're 900Ah batteries and the charger stopped absorb at 30A, that's 3% and they were clearly not charged yet. If you can, set absorb time to 10 hours then go through a typical discharge and watch the current during absorb every half hour. When the current stops dropping, and remains fairly constant, then that indicates that the batts are charged and that'll be your typical absorb time for that depth of discharge.

    Some say the end current should be 2A for every 100Ah capacity, but mine are still charging at that rate and only reach fully charged at about 0.5A for every 100Ah capacity. By watching the rate of change of the current you'll get a better idea of when the batts are finally charged.

    Regarding hydrometers, don't know if someone has mentioned this one already: http://prismsolar.co.uk/shop/index.php?_a=product&product_id=86 it ticks all the right boxes.
  • AceNZAceNZ Posts: 104Solar Expert ✭✭✭✭
    Re: Hybrid grid-tie / off-grid system: Victron
    stephendv wrote: »
    IMO, High float vs. low float are not going to make much of a difference to the charge of your batteries, unless you leave them running for multiple days on end without any discharge in the battery.

    Sure. I was just fooling with them to see the effect on charge current. If the batteries were fully charged, I would have expected the change to be small in going from low-float to high-float. In a normal GT scenario, the charger's firmware goes into high-float for 24 hrs after absorption ends, and then to low-float (aka "storage") after that, if they haven't been discharged.
    stephendv wrote: »
    If the battery was discharged and you want to recharge, then you should lengthen absorb time. If they're 900Ah batteries and the charger stopped absorb at 30A, that's 3% and they were clearly not charged yet. If you can, set absorb time to 10 hours then go through a typical discharge and watch the current during absorb every half hour. When the current stops dropping, and remains fairly constant, then that indicates that the batts are charged and that'll be your typical absorb time for that depth of discharge.

    I can force the charger to do something like that as a one-time thing if I need to. In the normal "adaptive" operation mode, absorb time is set based on how long it was in bulk, rather than a fixed time.

    One challenge I used to have is that my daily DOD was usually around 12%, so bulk didn't last very long -- which means absorb didn't either.
    stephendv wrote: »
    Some say the end current should be 2A for every 100Ah capacity, but mine are still charging at that rate and only reach fully charged at about 0.5A for every 100Ah capacity. By watching the rate of change of the current you'll get a better idea of when the batts are finally charged.

    The limited documentation for the firmware option I've recently starting using (self-consumption) says the charger does not normally go into absorption, except once every 28 days, when it forces a full recharge, even if it requires using the grid to do so -- although I have seen it go into float.

    The firmware provides two options for ending absorption: either based on time, or on current. I have it set to time -- which is now a fixed period, unlike before -- but from what you're saying, it sounds like current might be better, in that would adapt to different DOD levels. The default setting for the current option is 1.25A / 100A, which is in the range of what you've described.
    stephendv wrote: »
    Regarding hydrometers, don't know if someone has mentioned this one already: http://prismsolar.co.uk/shop/index.php?_a=product&product_id=86 it ticks all the right boxes.

    Looks much nicer than the piece of junk I have now! Thanks. Any idea how it compares to a reflectometer in terms of ease of use, mess and accuracy?
  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: Hybrid grid-tie / off-grid system: Victron
    AceNZ wrote: »
    I have to say that the hydrometer I have is an awful, terrible device. Hard to use, hard to read -- not to mention dripping and splattering acid; a good burn is only a matter of time, even with gloves and protective clothing.

    I think I'm going to get a reflectometer, and see if it's easier (and safer).

    I used to feel that way about hydrometers, and was about to buy a refractometer, but then I bought the hydroVolt hydrometer that Blackcherry04 linked to. I purchased mine from Midnite solar.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • AceNZAceNZ Posts: 104Solar Expert ✭✭✭✭
    Re: Hybrid grid-tie / off-grid system: Victron
    vtmaps wrote: »
    I used to feel that way about hydrometers, and was about to buy a refractometer, but then I bought the hydroVolt hydrometer that Blackcherry04 linked to. I purchased mine from Midnite solar.

    How long is that little pipette on those hydrometers? The Trojan Industrial batteries have a fairly deep well.

    I think I can buy a refractometer for less, BTW.
  • Blackcherry04Blackcherry04 Posts: 2,486Solar Expert ✭✭✭
    Re: Hybrid grid-tie / off-grid system: Victron
    AceNZ wrote: »
    How long is that little pipette on those hydrometers? The Trojan Industrial batteries have a fairly deep well.

    I think I can buy a refractometer for less, BTW.
    It has a piece of 1/8 " plastic tubing that should be long enough ( 5-6 " ), but could be replaced with a longer piece is necessary.

    Remember the 3 variable's of Battery charging, Voltage, Time and Current. Raise the Voltage, Lower the Time. Raise the Time, lower the Voltage. The Current will take care of itself. I'd raise the Bulk / Absorb 1 volt for a week and see what the trend is on your bank. North Guy has already told you what he has to do the get his SG's up to level.
  • AceNZAceNZ Posts: 104Solar Expert ✭✭✭✭
    Re: Hybrid grid-tie / off-grid system: Victron
    stephendv wrote: »
    If you can, set absorb time to 10 hours then go through a typical discharge and watch the current during absorb every half hour. When the current stops dropping, and remains fairly constant, then that indicates that the batts are charged and that'll be your typical absorb time for that depth of discharge.

    Some say the end current should be 2A for every 100Ah capacity, but mine are still charging at that rate and only reach fully charged at about 0.5A for every 100Ah capacity. By watching the rate of change of the current you'll get a better idea of when the batts are finally charged.

    From my past notes, there was an absorption charge that ended like this:

    9:22a, 58.04V, 21.3A
    10:32a, 58.07V, 8.5A
    11:32a, 58.06V, 5.64A
    12:37p, 58.04V, 4.06A

    I don't know when it started, which means I don't know how long it ran -- but the knee in the curve seems to be around 10A. My bank is about 900AH, so that's a little over 1A / 100Ah.

    Sound about right?
  • AceNZAceNZ Posts: 104Solar Expert ✭✭✭✭
    Re: Hybrid grid-tie / off-grid system: Victron
    It has a piece of 1/8 " plastic tubing that should be long enough ( 5-6 " ), but could be replaced with a longer piece is necessary.

    Thanks.
    Remember the 3 variable's of Battery charging, Voltage, Time and Current. Raise the Voltage, Lower the Time. Raise the Time, lower the Voltage. The Current will take care of itself. I'd raise the Bulk / Absorb 1 volt for a week and see what the trend is on your bank. North Guy has already told you what he has to do the get his SG's up to level.

    North Guy doesn't have the luxury of a long absorb time like I do.

    I'm thinking of configuring the charger to end absorb based on current instead of time -- that would let it run as long as it needs to, but without excessive gassing. Also, the charger only goes into absorb once every 15 days now, although I can temporarily change it to every day to force a full charge sooner rather than later.

    If that doesn't do the trick on the SG side, then yes, a higher absorb voltage would be a logical next step.
  • Blackcherry04Blackcherry04 Posts: 2,486Solar Expert ✭✭✭
    Re: Hybrid grid-tie / off-grid system: Victron
    AceNZ wrote: »
    Thanks.



    North Guy doesn't have the luxury of a long absorb time like I do.

    I'm thinking of configuring the charger to end absorb based on current instead of time -- that would let it run as long as it needs to, but without excessive gassing. Also, the charger only goes into absorb once every 15 days now, although I can temporarily change it to every day to force a full charge sooner rather than later.

    If that doesn't do the trick on the SG side, then yes, a higher absorb voltage would be a logical next step.
    Yeah thats true, I think he has grid and has cut it off. You do have forklift batteries in smaller cases, those 1/4' + plates do take a lot of juice to keep the SG's up. I came so close to buying a set a couple months ago, I was just afraid I couldn't keep up with them. I ended up with a set of Rolls S-1725's, I hope they are a little easier, so far they have been all over the place and have very few cycles on them, I have them shut down for the winter here.
  • AceNZAceNZ Posts: 104Solar Expert ✭✭✭✭
    Re: Hybrid grid-tie / off-grid system: Victron

    I heard back from Trojan. I'm including their answers below, in case others might be interested.
    AceNZ wrote: »
    1. One version of the brochure for the IND17-6V says C/20 capacity is 897 AH, and another (newer) one says 925 AH. Was this just a correction to the specs, or did the batteries change? If the batteries changed, how can I tell which ones I have?

    Just a change to the specs; the batteries didn't change.
    AceNZ wrote: »
    2. Is it better to end absorption based on time, or on current? If current, how much?

    Either method is fine. Current is probably a better indicator that the batteries are becoming fully charged.

    For the current approach, something around 2% of the bank’s 20-hour rating would be appropriate. When the current drops to this low level, it indicates the batteries are nearing 100% charged.
    AceNZ wrote: »
    3. For relatively new batteries, what is the usual/typical SOC at the end of bulk charging?

    Between 80 and 90%.
    AceNZ wrote: »
    4. What is the expected charge efficiency?

    Flooded batteries are approximately 91% efficient in their recharge as about 110% overcharge is required for full charge.
    AceNZ wrote: »
    5. When the batteries have been in float for an extended period, how often should they go into absorption again, and for how long?

    Float ensures the batteries are maintained at a full state of charge, overcoming any natural self-discharge that occurs. There is really no requirement to go into an absorb phase, although given that the batteries are stationary, absorbing would help reduce the risks of stratification (heavy acid at the bottom of the batteries, lighter at the top). There would be no need to do the absorb phase more than once a month to mix the acid and reduce stratification.
    AceNZ wrote: »
    6. Victron's equalization algorithm works as follows: one out of every 8 repeated absorption phases becomes an equalization phase; once charge current reaches 10% of the maximum bulk charge, it's kept at that level until either absorption ends or the voltage reaches a 2.83vpc limit (68V). Since this is above the recommended 2.58vpc limit, should I use this equalization charging approach (is absorption likely to complete first?), or is it OK to rely on periodic absorption charges while the battery is in float for electrolyte mixing?

    2.83 volts per cell is high. We typically like to see around 2.58 volts per cell. I’ll need to ask some other folks here at Trojan their thoughts on this high voltage. At least the current is low.
    AceNZ wrote: »
    7. What are the tradeoffs in choosing an absorption voltage from within the recommended range other than time-to-charge? Does a lower voltage help improve battery life?

    In general, you want to use a higher voltage to ensure the batteries are fully charged. We provide a range as giving one specific set point is not realistic with all of the equipment used in the field. The biggest issue we see with PV installs is chronic undercharging of batteries. It seems everyone is so concerned with not overcharging their batteries, that most people are barely fully charging them. Chronic undercharging leads to reduced life and poor performance.
  • AceNZAceNZ Posts: 104Solar Expert ✭✭✭✭
    Re: Hybrid grid-tie / off-grid system: Victron

    After switching to a slightly higher float (55.2V) and absorb (58.5V), I let the system run for two weeks, in its normal operating pattern, thinking that the higher voltages might help normalize things.

    It was sunny for most of that time, so the system typically goes into bulk in the morning, and when bulk ends, it switches to float, then when the sun goes down, it goes off-grid and runs on the inverter -- typically 12% DOD by morning. Since solar alone was enough to keep them fully charged (100% SOC on the battery meter), the system never went into absorb during that period, as far as I can tell. It did drop down a few times to the nominal 75% SOC floor I set for maximum discharge.

    At the end of the two weeks, I measured SG again; it was about 1.205. I wasn't too concerned before at 1.220. Now I am.

    Trojan tech support suggested running an EQ (of course) at 62V and limiting max current to 2% of C/20 (18A), for two hours; then repeating for another 2 hrs if SG is still low. I finally figured out how to make my charger do the right things for EQ (it's built-in EQ mode isn't compatible with Trojan), and ran it today.

    What I did is this: near the end of Absorb, with current at 16A (1.8%), I changed the charger's Absorb voltage from 58.5 to 62V, and set the charge current limit to 18A. Charge voltage went up to 59.4V at 18A right away, and slowly increased to 60.4V over the next two hours, with current remaining at 18A -- still well below the recommended 62V. When I switched back to 58.5V, current dropped to about 10A, which caused the charger to drop out of absorb and back into float, with 55.2V at 5A.

    SG is now 1.210. Some change, but not much.

    I'm planning to repeat this tomorrow (or the next time I can get it into Absorb mode, which isn't straightforward), and let it go longer.

    In the meantime, my question is: does this seem normal? Am I risking any harm to my batteries by continuing to use them while I work on the SG?

    I think both of my battery meters are still not as close to the correct values as they could be. The external meter often has much higher SOC readings than the Quattro's internal meter, but I think both of them are reading high. Not quite sure what to do there yet. There are only three knobs on the internal meter: battery capacity, charge efficiency, and SOC at the end of bulk. The external meter replaces SOC at the end of bulk with a tail charge current plus time factor, after which it resets to 100% SOC. It also has a Peukert coefficient. The internal meter is the only one that's really important, though, since it triggers various state changes in the inverter/charger.
  • stephendvstephendv Posts: 1,571Solar Expert
    Re: Hybrid grid-tie / off-grid system: Victron

    2% of C20 is a very low charge rate, and I think is quite safe to keep charging at that rate for much much longer. I've seen spec sheets for industrial forklift batts that recommend EQ at 5% of C5 rate for 72 hours straight. I'm not suggesting you do that, just want to provide some perspective that 2% rate is quite safe and in my opinion you can safely charge at that rate for much longer than 2 hours.
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