Marine battery switch for equalization

706jim706jim Solar Expert Posts: 251 ✭✭✭
I'm thinking of connecting two strings of 4 L16's using a marine battery switch such as made by Guest.

These typically have settings for bank 1 bank 2 or both as well as off.

Would seem to be a simple solution to reduce the amount of current needed to periodically equalize these fairly large batteries with the limited amount of panels I have at the moment.

As my inverter is only 1500 watts at 24 volts, current should never exceed 80 amps or so. These switches are rated at about 400 amps continuous 600 amps momentary.

Thoughts?
Island cottage solar system with 2400 watts of panels, 1kw facing southeast 1kw facing southwest 400watt ancient Arco's facing south.Trace DR1524 MSW inverter, Trace C40 PWM controller 8 Trojan L16's. Insignia 11.5 cubic foot electric fridge. My 27th year.

Comments

  • gww1gww1 Solar Expert Posts: 963 ✭✭
    Re: Marine battery switch for equalization

    My opinion is that the equalize is not what takes the current, mine hardly take any at all, it is bulk that takes the current.
    I would never have two banks if I could have just one. I would only do so if they were in two differrent locations. There may be other reasons that this might work, like charging batteries that are not in paralel. I think it would just add even more to keep track of. Also if you can't charge two to gether you probly can't charge two seperatly. These are just my toughts and intuition and I have no real sience behind it.

    Good luck
    gww
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Marine battery switch for equalization
    706jim wrote: »
    I'm thinking of connecting two strings of 4 L16's using a marine battery switch such as made by Guest.

    These typically have settings for bank 1 bank 2 or both as well as off.

    Would seem to be a simple solution to reduce the amount of current needed to periodically equalize these fairly large batteries with the limited amount of panels I have at the moment.

    As my inverter is only 1500 watts at 24 volts, current should never exceed 80 amps or so. These switches are rated at about 400 amps continuous 600 amps momentary.

    Thoughts?
    I would be very careful about connecting two battery banks in parallel through the switch when the two banks might be at different states of charge. With the wide voltage range of lead acid batteries and the low internal resistance the current flow between the two banks could easily damage either the switch or the wiring. Not a good idea.
    You could put in a mechanical stop to prevent putting the switch in the BOTH position, at least requiring a deliberate removal of the lockout is you know the strings are balanced well enough.
    SMA SB 3000, old BP panels.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Marine battery switch for equalization
    gww1 wrote: »
    My opinion is that the equalize is not what takes the current, mine hardly take any at all, it is bulk that takes the current.

    It's not just your opinion... it's a fact.

    However, it is a good idea to separate the banks and equalize them one at a time... not because of the high current, but because the two banks will usually need different amounts of equalization. No sense in over equalizing one bank while you equalize the other.
    inetdog wrote: »
    I would be very careful about connecting two battery banks in parallel through the switch when the two banks might be at different states of charge.

    A wise precaution. Switches come in "make before break" or "break before make". When you switch from one bank to the other, you want a "break before make" switch. If you break before make, the inverter will probably not appreciate the momentary interruption, so be sure to disconnect all loads (turn off the inverter) before making the switch. If you make before break, the inverter will not see a momentary interruption, but inetdog's warning should not be ignored.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • 706jim706jim Solar Expert Posts: 251 ✭✭✭
    Re: Marine battery switch for equalization

    Here's one thought regarding possible high current during switching:

    For several years, I used a float voltage of 27.0 on my C40. The bank would drop to this voltage after reaching the upper charge voltage limit of 28.0 for two hours.

    It has been my observation that the 27.0 volt reading is transitory, that is, the slightest load would quickly bring the bank down to 24.8 volts which I would consider nearly full charged.

    Assuming that each string of 4 L16's was equalized, my thought is that any slight voltage variation between the two would quickly balance out assuming that all 8 batteries are in decent condition.

    I'm considering this battery switch after reading several posts in these forums which have suggested that equalization will require a greater current than the 15 odd amps my modest array can provide. My Trace 1524 will function as a bulk battery charger providing up to 37 amps which should be in the ballpark for 4 L16's if not 8. And if I read gww's post correctly, it sounds like it will be ok if the inverter charger drops the current as the voltage rises to 28.0

    Just doing some armchair designing before I can get back to my island cottage in May.
    Island cottage solar system with 2400 watts of panels, 1kw facing southeast 1kw facing southwest 400watt ancient Arco's facing south.Trace DR1524 MSW inverter, Trace C40 PWM controller 8 Trojan L16's. Insignia 11.5 cubic foot electric fridge. My 27th year.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Marine battery switch for equalization
    706jim wrote: »
    Here's one thought regarding possible high current during switching:

    Then you go on to talk about Voltage. The two are not the same thing and you need to understand the difference between them.
  • gww1gww1 Solar Expert Posts: 963 ✭✭
    Re: Marine battery switch for equalization

    706jim
    And if I read gww's post correctly, it sounds like it will be ok if the inverter charger drops the current as the voltage rises to 28.0

    My point is if you eq at 28 volts. Getting to the 28 volts takes alot and after you reach the 28 volts you need very little current. What I do when the eq last longer then the sun, or if I don't want it to take forever. I will drop loads use solar imput and the grid and inverter chargerer and put them together to get the battery recomended max charging amps to get the battery charged as fast as possible so that when I start the eq I will be using very little juice to keep them at that level for as long as I need. I understand vtmaps position that you can take care of parelel batteries better by eq independently cause during normal use they due to being in parelel may be off from each other during normal charging.

    I am no expert. I am pretty lazy and figure everything is a compermize. I would not personally wan't to seperate my bank due to the extra oversite it would take,in my mind. Things like when I put them back together are they in the same state of charge so there is no great influx of current rushing from one bank to the other due to different states of charge. Which one need what?

    I am not saying what you should do but what I would do. If I had your solar and your batteries, I would either reconize that I need more or I would reconize I am going to have to use grid/generator alot for charging. I would pay real attention to my cable lenths and try to get it perfect as possible and then watch the banks as I go and if I get imbalances, try to figure out why and or rotate the batteries every so often (not easy either).

    The one benifit of being able to seperate you bank would be if you had a battery go bad you could just use half of you batteries while you addressed it.

    When Chris olsen was doing parelel batteries he put cheap voltage meters on each so he could se imbalances as early as possible while the batteries were still in use.

    Did you get the point that caraboohoot was making?

    My oppinion is, If you seperate your banks and use them that way, you lose what your banks could provide too loads and have to remember which is charged. If you charge them seperatly and then combine them you have to make sure they are at the same charged stage before putting them together, which means you have to take both out of service to charge.

    I may not know what I am talking about either.
    gww
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Marine battery switch for equalization
    gww1 wrote: »
    When Chris Olsen was doing parallel batteries he put cheap voltage meters on each so he could see imbalances as early as possible while the batteries were still in use.

    All batteries in parallel will have the same voltage, but the current may be be different in each string. A voltmeter may be used to monitor battery banks, but you need a meter for each battery in the string. You might find, for example, that a string of four 6 volt batteries has a voltage of 24.0 volts, but three of the batteries are 6.1 volts and the other battery is 5.7 volts. That would be an indication that there is a problem in the string.

    If you have multiple parallel strings, you would need voltmeters on each battery in each string.

    As a practical matter, if you have parallel batteries, a reasonable monitoring protocol is to use a current clamp meter periodically to see that the current in each parallel string is the same. When you find different currents in each string... that's a good time to resolve that your next bank will not have parallel batteries.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • gww1gww1 Solar Expert Posts: 963 ✭✭
    Re: Marine battery switch for equalization

    vtmaps
    All batteries in parallel will have the same voltage, but the current may be be different in each string. A voltmeter may be used to monitor battery banks, but you need a meter for each battery in the string. You might find, for example, that a string of four 6 volt batteries has a voltage of 24.0 volts, but three of the batteries are 6.1 volts and the other battery is 5.7 volts. That would be an indication that there is a problem in the string.

    I don't believe he was doing every battery, I think he had mutiple parelel strings and he was putting a volt meter on each 12v/24v (whatever he had) string and then he was looking for a half volt differance in the strings and then he would address the issue ie check connections, rotate, chk batteries, ect.
    As a practical matter, if you have parallel batteries, a reasonable monitoring protocol is to use a current clamp meter periodically to see that the current in each parallel string is the same. When you find different currents in each string... that's a good time to resolve that your next bank will not have parallel batteries.

    This is very good advice also.
    gww
  • 706jim706jim Solar Expert Posts: 251 ✭✭✭
    Re: Marine battery switch for equalization
    Then you go on to talk about Voltage. The two are not the same thing and you need to understand the difference between them.

    Yes, I am aware of the difference between voltage and current. My point is that when the voltages of the two 4 battery strings are similar (and at the high end after equalization) is that there is only a small amount of current required to drop the strings down to their normal "resting" voltage which is around 24.8 volts.

    So I don't anticipate a problem reconnecting the two strings together after equalization which is the only time they would be separated regardless.

    If I DO go with the switch, I'll be sure to have a face shield on when I reconnect the two strings after equalization.
    Island cottage solar system with 2400 watts of panels, 1kw facing southeast 1kw facing southwest 400watt ancient Arco's facing south.Trace DR1524 MSW inverter, Trace C40 PWM controller 8 Trojan L16's. Insignia 11.5 cubic foot electric fridge. My 27th year.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Marine battery switch for equalization
    706jim wrote: »
    My point is that when the voltages of the two 4 battery strings are similar
    If the strings are connected, the voltages are identical. If they are not connected, under what conditions are you measuring the voltages? (that is, have both batteries been disconnected from all loads and charging sources overnight?)
    706jim wrote: »
    only a small amount of current required to drop the strings down to their normal "resting" voltage which is around 24.8 volts.

    What type of L-16 batteries are these? The ones I'm familiar with have resting voltages significantly higher than that. I think it would be worthwhile to compare the voltages on each L-16 in each string.

    btw, After charging a battery, its voltage will be higher than its resting voltage because of surface charge. It can take hours for this charge to bleed off in a resting battery, but it can bleed off pretty quick with even a modest load.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • 706jim706jim Solar Expert Posts: 251 ✭✭✭
    Re: Marine battery switch for equalization
    vtmaps wrote: »


    What type of L-16 batteries are these? The ones I'm familiar with have resting voltages significantly higher than that. I think it would be worthwhile to compare the voltages on each L-16 in each string.

    btw, After charging a battery, its voltage will be higher than its resting voltage because of surface charge. It can take hours for this charge to bleed off in a resting battery, but it can bleed off pretty quick with even a modest load.

    --vtMaps

    Trojan L16's; the 370 Ah version. I have them sitting in my garage, new from the supplier and their voltages range from 6.17 to 6.20. Four in series would be pretty much be the 24.8 that I mentioned.

    My experience with surface charge would seem to agree with yours; a very small load would quickly bring the batteries down to their resting voltage. The bank I'm replacing was three strings of Dunlop GC's set up for 24 volts.
    Island cottage solar system with 2400 watts of panels, 1kw facing southeast 1kw facing southwest 400watt ancient Arco's facing south.Trace DR1524 MSW inverter, Trace C40 PWM controller 8 Trojan L16's. Insignia 11.5 cubic foot electric fridge. My 27th year.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Marine battery switch for equalization
    706jim wrote: »
    Trojan L16's; the 370 Ah version. I have them sitting in my garage, new from the supplier and their voltages range from 6.17 to 6.20. Four in series would be pretty much be the 24.8 that I mentioned.

    Hopefully your voltmeter needs calibration.... According to Trojan, your batteries should have a resting voltage of 6.37. That's 25.5 volts for a 4 battery string.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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