Possible over voltage/ over charging or charge controller error

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Nila
Nila Solar Expert Posts: 173 ✭✭
in Solar Beginners Corner #1
Hi All,

I have recently setup a solar panel system at my home with help /advices from this forum.

Quick info here about my setup.

12v batteries * 4 in series, 200AH at 48v.
3.5kw inverter which has inbuilt charging .
8 250w panels , 30.x VMP panels wired in 4 strings of 2 array. (Please note : this VMP may not be accurate.,could be like 30.5 or little higher )

This post has LOTS of small questions from me, basically reason is I have always been a battery illiterate , and all of the battery related voltage stuff is 100% new to me.
If i am sounding like an idiot, please do yell at me. I'm trying to learn this stuff as quickly as possible before I murder my bank.
Before I setup solar, ONLY thing i know about my batteries is to water them and I trusted on my UPS to take 100% care of that and never cared about voltage ,etc .


ok now here is the situation , during our morning and noon, It looks like the batteries are reaching 60v on a daily basis.
When i check the voltages on individual batteries they are like 15v and I see close to 59.9 to 60.1 on the series .

At my temperatures of over 32 degrees celcius, I think this very bad? :(.

Batteries will be charged and will be 100% by the time its morning by our UPS then I shut the utility to let the solar charge batteries and utilize that power.

Another problem , My charge controller voltage readings are like off by 2.5v to 3v.

When i check the battery voltage on my voltmeter it shows 60.1 and my UPS would report the same but charge controller will report it being 57-58, is this the reason why it is keeping the battery voltage at 60v and sometimes at 61v instead of 57 or something?

Is it normal for the battery voltage ( or the voltage in the battery terminals ) to reach and be there at 60v range daily ( not at equalization)

More questions here .. at an average temperature of 31 degrees, what would be the max voltage for the stages of bulk/absorb/float for a deep discharge 12v lead-acid batteries?

My inverter / ups charger seems to keep them only at 53 v at the float. I didn't measure its other voltages yet.
53/4 = 13.25 which is not bad? but 60.3v/4 =15.1 from the charge controller looks bad from what i see on websites ?


My inverter usually thinks 54.5v is already a battery that is 100% ( may be adjusted to indian conditions) ? or may be its under charging but we dont have to worry as I have another source now to charge the batteries.

My charge controller doesn't really bring them back to float range at all, I think its killing the battery? what happens when a battery is brought to 60v for like 2 hours a day daily?

What would be the best advice here?

I can replace it with an Tristar 45 MPPT within 1 month when some of my client is returning to India from US. ( I dont think its good idea to pay like 100$ in shipping )

And i was constantly told at this forum that VMP is too little to charge my battery bank, with these voltages and battery getting full daily ( and even more than what it bargained for ) I think that's no longer a concern or it still could be?

Is there any online calculator which has battery voltage chart charge adjusted to the temperatures?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: Possible over voltage/ over charging or charge controller error

    60 Volts is actually a normal charging Voltage for a 48 Volt system, but at 32C it shouldn't b showing up. I'm going to guess there's no remote temperature sensor on your batteries telling the inverter and/or charge controller to adjust the Voltage readings to compensate for battery temperature. Don't know what controller or inverter you've got so there is an question of if temp compensation is even possible.

    The Voltage discrepancy could be a result of undersized wiring. If so, this will be at its worst during Bulk charging or any time the current flow is high. At Float the two Voltage readings should be closer. You should check the batteries with a known good DMM at this point. Some charge controllers (like Outback) can have their Voltage readings adjusted internally. Morningstar's units have separate Voltage sense wiring which solves the problem of variations caused by current draw: essentially they have their own meter probe leads to read the battery Voltage independently of the Voltage on the current carrying wires.

    2000 Watts of panel certainly ought to be able to recharge 200 Amp hours @ 48 Volts, without the need of input from the utility grid. As such the first thing to do is check the circumstances of the Voltage discrepancies which would require info on the components used and the size/length of wiring. The second thing to do would be determine the cause of the problem, which may be the lack of temperature compensation or may be a wiring fault.

    At any rate, we need some more information about the system to work with.
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  • Nila
    Nila Solar Expert Posts: 173 ✭✭
    #3
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    Re: Possible over voltage/ over charging or charge controller error
    Cariboocoot wrote: »
    60 Volts is actually a normal charging Voltage for a 48 Volt system, but at 32C it shouldn't b showing up. I'm going to guess there's no remote temperature sensor on your batteries telling the inverter and/or charge controller to adjust the Voltage readings to compensate for battery temperature. Don't know what controller or inverter you've got so there is an question of if temp compensation is even possible.

    The Voltage discrepancy could be a result of undersized wiring. If so, this will be at its worst during Bulk charging or any time the current flow is high. At Float the two Voltage readings should be closer. You should check the batteries with a known good DMM at this point. Some charge controllers (like Outback) can have their Voltage readings adjusted internally. Morningstar's units have separate Voltage sense wiring which solves the problem of variations caused by current draw: essentially they have their own meter probe leads to read the battery Voltage independently of the Voltage on the current carrying wires.

    2000 Watts of panel certainly ought to be able to recharge 200 Amp hours @ 48 Volts, without the need of input from the utility grid. As such the first thing to do is check the circumstances of the Voltage discrepancies which would require info on the components used and the size/length of wiring. The second thing to do would be determine the cause of the problem, which may be the lack of temperature compensation or may be a wiring fault.

    At any rate, we need some more information about the system to work with.

    Mine is a chinese charge controller, sort of no-name 48v ;/ 50A / PWM and an Inverter is again a simple home UPS kind of inverter from a company called su-kaam

    not sure if they are actually famous/known http://www.su-kam.com/Power-Solutions/OEM-Solutions/Inverters/Fusion-Series/57/6

    There is a temperature sensor with my charge controller which is sticking to my battery.

    My wiring is certainly heavy enough for this setup I believe (16mm2 ) which I use for both panels to cc and then cc to the batteries. I used several online wire size estimators to find which one to go

    The 60V is showing up only when there is no / little load on the inverter it drops to like 54 or 55 when I use my computers which would draw some 300/400 watts easily.


    Regarding 2000Watts is enough for the 200AH at 48v, I think since I use 2 computers with 2 monitors each at the night, with/without utliity power, I would easily eat up half of this bank. Since my night usage is more, I think even if i have it full by evening, one power cut for 2 hours after sunset would spend a lot of battery then my ups charger has to charge it .

    It is guaranteed that I wont have at-least 4-5 hours of power shutdowns between 6pm to 6am. I am sure UPS charger has to rescue me during the nights.

    Anyways is this like very big problem to attend this immediately or just I need to be cautious and keep monitoring the voltage/temps of battery,etc?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
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    Re: Possible over voltage/ over charging or charge controller error

    Okay, so first the accuracy of both the charge controller and inverter are called into question. Nothing can be done about that, but I would not rely on the readings of either; stick with your actual DMM Voltage readings at the batteries for accuracy.

    The temperature sensor is good, providing it's actually working. You can check this by disconnecting it and seeing if there is any change in Voltage as a result. In hot conditions with it removed the Voltage reading on the controller should go down (usually they compensate the 'read Voltage' not the charging set points).

    16mm2 wire is approximately 6 AWG which should be large enough for the 50 Amps max from the controller providing the runs aren't too long (up to 35' total with 48 Volts @ 50 Amps). That should be good.

    400 Watts on a 48 Volt system is only 8 Amps or so. You should not see any Voltage drop from that. However, 60 Volts would not be a normal Float Voltage on a 48 Volt system, whereas 55 would be. So we have to wonder what charge stage is it at when you see 60 dropping to 55? It would be a pain, but you may have to let the system run a full day without any loads on it to see how it performs and then compare that to running with loads to see if there is any drastic difference in charging performance.

    Overnight power usage: 400 Watts? For how many hours? Your 200 Amp hour battery bank should be able to supply roughly 4 kW hours AC before reaching 50% SOC, which is about 400 Watts for 10 hours. This is where you start to suspect that the inverter is inefficient in its conversion and has a high self-consumption rate. The web site you linked to didn't show that info anywhere I could find.

    Also check the battery Specific Gravity (if they're not sealed) as this will be most important. That's the only way to really know if they are charged or not. And again the wires from batteries to inverter, although it's hard to imagine there's a size problem there.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #5
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    Re: Possible over voltage/ over charging or charge controller error

    It sounds like the batteries are being charged at a bit too high of voltage. Assuming you want 59 volts charging at 25C:

    59 volts + (-0.005 volts per cell per degree C * 24 cells * (32C - 25C standard temp)) = 59 volts - 0.84 volts = 58.16 volts

    How are the batteries doing? Are they bubbling pretty hard after a couple of hours at 60+ volts?

    Water usage, are you having to refill the cells ever month or more often? Then probably need to figure out how to back the voltage down a bit. If you only need to add water every 2-6 months--Then the charging cycle would seem to be OK

    If these were AGM batteries (sealed type--sorry, don't remember if yours are flooded cell or not), then this would be a problem that needs immediate fixing. Sealed batteries when over charged would vent--costing you electrolyte that cannot be replaced.

    Over charging flooded cell batteries is hard on them, but they are a bit more forgiving.

    There are variation in battery construction/chemistry that can cause them to need charging in the 62-63 volt range (calacium added to plates)--Have you checked the temperature corrected specific gravity yet? Once the specific gravity stop rising between readings (when checked every 30-60 minutes), then the batteries are full and additional charging is useless (or worse).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #6
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    Re: Possible over voltage/ over charging or charge controller error

    With the charge controller readings being off by 2.5 to 3 volts--That could be a big issue--It would sound like the controller is not properly calibrated and that is a big amount to be off by... Which is it doing reading high or low?

    Also--There could be the issue of accuracy with your volt meter (don't think so)--It would not hurt to confirm that it is working OK by checking a car battery with the engine running (should be around 14.2-14.4 volts, although, it could be as low as 13.8 volts too) or borrowing a second meter to confirm (old saying, a person with one meter knows what the voltage is. A person with two meters does not).

    What you have going for you is that you are only charging during daylight--So this is not as bad as if these were batteries "cooking" on an AC powered battery charger 24x7.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Nila
    Nila Solar Expert Posts: 173 ✭✭
    #7
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    Re: Possible over voltage/ over charging or charge controller error
    Cariboocoot wrote: »
    Okay, so first the accuracy of both the charge controller and inverter are called into question. Nothing can be done about that, but I would not rely on the readings of either; stick with your actual DMM Voltage readings at the batteries for accuracy.

    The temperature sensor is good, providing it's actually working. You can check this by disconnecting it and seeing if there is any change in Voltage as a result. In hot conditions with it removed the Voltage reading on the controller should go down (usually they compensate the 'read Voltage' not the charging set points).

    16mm2 wire is approximately 6 AWG which should be large enough for the 50 Amps max from the controller providing the runs aren't too long (up to 35' total with 48 Volts @ 50 Amps). That should be good.

    400 Watts on a 48 Volt system is only 8 Amps or so. You should not see any Voltage drop from that. However, 60 Volts would not be a normal Float Voltage on a 48 Volt system, whereas 55 would be. So we have to wonder what charge stage is it at when you see 60 dropping to 55? It would be a pain, but you may have to let the system run a full day without any loads on it to see how it performs and then compare that to running with loads to see if there is any drastic difference in charging performance.

    Overnight power usage: 400 Watts? For how many hours? Your 200 Amp hour battery bank should be able to supply roughly 4 kW hours AC before reaching 50% SOC, which is about 400 Watts for 10 hours. This is where you start to suspect that the inverter is inefficient in its conversion and has a high self-consumption rate. The web site you linked to didn't show that info anywhere I could find.

    Also check the battery Specific Gravity (if they're not sealed) as this will be most important. That's the only way to really know if they are charged or not. And again the wires from batteries to inverter, although it's hard to imagine there's a size problem there.


    Hey, thanks for reply

    I tried to pull out the charge controller sensor and it didnt make any difference in the reading.

    Volt meter and the UPS/Inverter shows the same reading so I believe only charge controller is wrong here.

    53.7v at DMM shows as 50.9 at the controller.. so a difference of 2.8v


    400 Watts at my night usage was just PC I guess, my total usage with 4 fans + 3 lights + 2 computers would be close to 1000-1200 watts or so
    I am buying a Kill a watt meter to check this and waiting for it to arrive soon.

    That would probably give me only few hours at this load. I guess inverter used to alarm me after 3-4 hours .

    Mine are flooded, lead acid, I will learn how to check the specific gravity and check this to be sure if battery is healthy.
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  • Nila
    Nila Solar Expert Posts: 173 ✭✭
    #8
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    Re: Possible over voltage/ over charging or charge controller error
    BB. wrote: »
    It sounds like the batteries are being charged at a bit too high of voltage. Assuming you want 59 volts charging at 25C:

    59 volts + (-0.005 volts per cell per degree C * 24 cells * (32C - 25C standard temp)) = 59 volts - 0.84 volts = 58.16 volts

    How are the batteries doing? Are they bubbling pretty hard after a couple of hours at 60+ volts?

    Water usage, are you having to refill the cells ever month or more often? Then probably need to figure out how to back the voltage down a bit. If you only need to add water every 2-6 months--Then the charging cycle would seem to be OK

    If these were AGM batteries (sealed type--sorry, don't remember if yours are flooded cell or not), then this would be a problem that needs immediate fixing. Sealed batteries when over charged would vent--costing you electrolyte that cannot be replaced.

    Over charging flooded cell batteries is hard on them, but they are a bit more forgiving.

    There are variation in battery construction/chemistry that can cause them to need charging in the 62-63 volt range (calacium added to plates)--Have you checked the temperature corrected specific gravity yet? Once the specific gravity stop rising between readings (when checked every 30-60 minutes), then the batteries are full and additional charging is useless (or worse).

    -Bill

    Batteries are not bubbling hard ,, i hear a rare bubble/sound but not like it is noticeable.

    With just inverter/ charger I would refill only once in 5-6 months. I am monitoring the water levels daily and i dont think any celll needs watering anyone.

    Mine is a flooded cell /LA and not sealed.

    I am waiting for my specific gravity testing tool to arrive, I will update when I have it.

    Thanks for the numbers for temperature compensation, I was looking hard for that :).
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  • Nila
    Nila Solar Expert Posts: 173 ✭✭
    #9
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    Re: Possible over voltage/ over charging or charge controller error
    BB. wrote: »
    With the charge controller readings being off by 2.5 to 3 volts--That could be a big issue--It would sound like the controller is not properly calibrated and that is a big amount to be off by... Which is it doing reading high or low?

    Also--There could be the issue of accuracy with your volt meter (don't think so)--It would not hurt to confirm that it is working OK by checking a car battery with the engine running (should be around 14.2-14.4 volts, although, it could be as low as 13.8 volts too) or borrowing a second meter to confirm (old saying, a person with one meter knows what the voltage is. A person with two meters does not).

    What you have going for you is that you are only charging during daylight--So this is not as bad as if these were batteries "cooking" on an AC powered battery charger 24x7.

    -Bill

    Its reading low .. 55 at battery would seem like 53.2 at charge controller

    and volt meter accuracy is not a problem, I have 2 of them already ;)

    Also I have an option to choose 12AMPS or 16AMPS to charge the batteries from the Inbuilt charger of inverter, I kept it to 12A,should i change it to 16? and as you already know, morning to night I would just switch off the grid so Inverter's charger does not kicking.

    Since I am using around 1200Watts at the night , what is the better choice with this?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
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    Re: Possible over voltage/ over charging or charge controller error
    paimpozhil wrote: »
    Also I have an option to choose 12AMPS or 16AMPS to charge the batteries from the Inbuilt charger of inverter, I kept it to 12A,should i change it to 16? and as you already know, morning to night I would just switch off the grid so Inverter's charger does not kicking.

    I would, as 200 Amp hours of battery can take 20 Amps peak current without any trouble. Bringing them up through Bulk quickly so they can spend more time in Absorb may help if they are not getting enough over-all charge time now (which we don't know). Not sure what charge profile your UPS unit has. Let's hope it's okay for deep cycle batteries and not just "Bulk/Float" like some are.
    Since I am using around 1200Watts at the night , what is the better choice with this?

    Watts is one thing, Watt hours another. 1200 Watts for one hours is 1200 Watt hours. Your battery capacity has up to 100 Amp hours @ 48 Volts available, or 4800 Watt hours, before reaching 50% SOC. 1200 Watt hours would be 25% of this capacity, so you could run that 1200 Watt load a maximum of 4 hours before reaching 50% capacity. You don't want to do this, as in reality the conversion and other losses mean you really will hit 50% sooner than that.

    It sounds like your charge controller should be replaced with a better one.
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