Battery Balancing

Caveman
Caveman Solar Expert Posts: 83 ✭✭✭✭
in Off Grid Solar & Battery Systems #1
There was a really good article that I thought I read on this forum about battery balancing. I can't seem to find it, but it explained the many different ways to connect battery banks for the best longevity/output. It had diagrams and such.

Anyone know where I can find this, or something like it?
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #2
    Re: Battery Balancing

    Cave ..

    If you are looking for info on the best way to connect paralleled battery strings, this may help:

    http://www.smartgauge.co.uk/batt_con.html

    FWIW. Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #3
    Re: Battery Balancing
    If you are looking for info on the best way to connect paralleled battery strings, this may help:
    http://www.smartgauge.co.uk/batt_con.html

    And if you are looking for info on why not to parallel battery strings, this may help:
    http://forum.solar-electric.com/showthread.php?14674

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Caveman
    Caveman Solar Expert Posts: 83 ✭✭✭✭
    #4
    Re: Battery Balancing

    Thanks Vic! That's the one... and thanks vtmaps! A good read, although some of it went over my head.

    Looks like I'll only need 1 string hooked up like that last drawing in the article shows.

    Here's what I got:

    - 2 panels (12V 140 watt each) -- I guess I hook these up in series for 12V

    - 4 golf cart batteries

    Morning star Pro star 30 controller

    Inverter:Exceltech DC 12V (sys) 171 A @ 13.8V (nom) AC 117V 17.1 A 60 Hz
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: Battery Balancing
    Caveman wrote: »
    Thanks Vic! That's the one... and thanks vtmaps! A good read, although some of it went over my head.

    Looks like I'll only need 1 string hooked up like that last drawing in the article shows.

    Here's what I got:

    - 2 panels (12V 140 watt each) -- I guess I hook these up in series for 12V

    - 4 golf cart batteries

    Morning star Pro star 30 controller

    Inverter:Exceltech DC 12V (sys) 171 A @ 13.8V (nom) AC 117V 17.1 A 60 Hz

    Four GC2's @ 220 Amp hours = 440 Amp hours @ 12 Volts. These can be wired as per the Smart Gauge method #2.

    Two 140 Watt panels will be insufficient to charge them, however. That's only about 16 Amps, or 3.6%.

    Get more panels, or use half the battery. Even at half it will be a close thing.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #6
    Re: Battery Balancing
    Caveman wrote: »
    - 2 panels (12V 140 watt each) -- I guess I hook these up in series for 12V

    Morning star Pro star 30 controller

    No. With a PWM controller your panels should be parallel.

    Caveman wrote: »
    Looks like I'll only need 1 string hooked up like that last drawing in the article shows.
    - 4 golf cart batteries

    No. The last drawing on that smartgauge site is for 4 parallel batteries. They don't show an explicit picture of what you need to do. You need to have two batteries in series to make 12 volts. Since you have four batteries you need two parallel strings of batteries, where each of the two strings is itself two batteries in series.

    As Cariboocoot mentioned you don't have enough panels for your batteries.

    Here is a diagram of how your batteries should be set up:
    Attachment not found.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Caveman
    Caveman Solar Expert Posts: 83 ✭✭✭✭
    #7
    Re: Battery Balancing

    Thank you very much for the drawing. I always get parallel and series mixed up....

    What are the problems created by not having enough panels for these batteries? The system is likely to sit idle for most of the time as it is at a seldom used hunting cabin. Can't the panels just slowly charge them and eventually be sufficient? I also have a battery charger wired back to my generator for bulk charging when necessary.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
    Re: Battery Balancing

    It depends on how slowly the panels charge the batteries back up from what depth of discharge.

    There was a time when systems had a lot of battery and a little panel because panels were expensive and batteries were cheap. The result of this "recharge over enough time" strategy was having to replace batteries sooner rather than later.

    The reason why is that the longer a battery is at a lower SOC the more rapidly sulphation (permanent loss of capacity) occurs. That is why it is best to have enough panel capacity to recharge the battery from 75% SOC in one good sunny day. With no loads on this amounts to a peak charge current rate of 5% (as recommended by most manufacturers).

    Replacing "used Amp hours" is not a linear thing; you don't get 20 Amp hours back by applying 10 Amps for two hours. In this case if you used 25% of the capacity - 110 Amp hours - and you have only 16 coming from the panels at peak sun even if it were linear you'd need 7 hours of recharge time. So two days of good sun might bring them back up.

    But what is more likely is that you'd use 110 Amp hours * 12 Volts or 1320 Watt hours and need three days to recover it due to losses in efficiency (you'd get a bit more than 400 Watt hours per day from 200 Watts of panel - terrible, isn't it?).

    Low charge rate is not always effective at charging either. Down around 3% is right at "maintenance" level, where the charging can just stay ahead of the self-discharge (depending on the particular battery). As we used to say in the analog days: "doesn't even wiggle the needle."

    No one ever regretted getting more panel, but so many have regretted not getting enough.
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  • Caveman
    Caveman Solar Expert Posts: 83 ✭✭✭✭
    #9
    Re: Battery Balancing

    Thanks for that explanation cariboo.
    In looking at this drawing, where should I put my shunt? Which cable (+ or -), and how close to the battery? I am guessing the "load" in the drawing is the inverter in this case....
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #10
    Re: Battery Balancing

    The shunt goes between the last Battery - and the - Battery Bus.

    You want ALL battery current (charging and discharging) going through the shunt. And you want to shunt on the negative (grounded) side of the battery to reduce the chances of a short circuit in the current sense leads causing a fire (shorting a shunt wire to ground means virtually zero current flow).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #11
    Re: Battery Balancing

    Shunt for battery monitor? Normally on the negative battery cable, between the battery (or batteries) and everything else. It has to keep track of all current going in or out.
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  • Caveman
    Caveman Solar Expert Posts: 83 ✭✭✭✭
    #12
    Re: Battery Balancing

    Well that makes sense, thanks. So I guess I would put my 200A inline fuse downstream of the shunt as well, but between my buss.

    Battery
    Shunt
    Fuse
    Buss(which I would hook my controller and charger to)

    Is this a good buss to use?

    http://www.solar-electric.com/mnsbb.html
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #13
    Re: Battery Balancing

    Fuses/breakers usually go on the positive cable (wiring convention).

    What you use for a bus depends on what connections you need to make. If that one has enough connectors for handling the right size wires it will work.
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  • Caveman
    Caveman Solar Expert Posts: 83 ✭✭✭✭
    #14
    Re: Battery Balancing

    And I'm guessing my fuse goes between the battery and the positive buss.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #15
    Re: Battery Balancing
    Caveman wrote: »
    And I'm guessing my fuse goes between the battery and the positive buss.

    Correct. As close to the battery as possible so that the maximum amount of wire is protected (you don't want any significant length of "always energized" positive cable waving about).
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  • Caveman
    Caveman Solar Expert Posts: 83 ✭✭✭✭
    #16
    Re: Battery Balancing

    How do I ground this system? Do I ground the negative cable or what?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #17
    Re: Battery Balancing
    Caveman wrote: »
    How do I ground this system? Do I ground the negative cable or what?

    That question is bigger than it appears. :D

    As a rule, you ground the AC output ground, which needs to be tied to the AC output neutral in one place only. If the inverter already has an N-G bond inside it you don't make another one outside it. If it is an MSW inverter you don't make this N-G bond. Always check the manual carefully.

    On the DC side you ground the negative battery pole. Same ground rod as the AC. Unless it is MSW in which case such grounding may cause trouble too. Check the manual.

    Metal cases of components and metal conduit for wires needs to be connected to the ground rod. Usually it "flows through" and thus is.

    Metal frames and mounts of solar panels should be grounded. Exactly how is subject of much debate. In fact a lot of ground wiring is, because how it is done often depends on the particular installation.

    And then there's the NEC rules and how strictly you have to follow them. For example they now require DC ground fault interruption, which means the negative isn't grounded directly. It's complicated, and potentially troublesome. They also require grounding from the panels come in to the house and connect to the AC ground rod there which many of us feel is a bad idea as it can introduce high Voltage from nearby lightning to the interior.

    I could draw a dozen different diagrams showing grounding needs and methods and I still miss some out that would apply to a particular situation. I guess this is why I haven't done it. That and being lazy. :p

    If you understand the why of grounding you can usually figure out the how. It can actually help if this is an inspected install because ultimately the AHJ has to tell you exactly what is required to pass inspection. Not that they necessarily understand it.

    The purpose of electrical safety ground is to prevent people from coming into contact with energized surfaces in the event of a fault and to cause the current to go high enough to trigger circuit protection and shut down the power. That's the why.

    The how has been a matter of discussion of many engineers over many years and they still don't always agree. So the default is to follow wiring conventions aka industry standards. It only needs to work when something else fails. :roll:
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  • Caveman
    Caveman Solar Expert Posts: 83 ✭✭✭✭
    #18
    Re: Battery Balancing

    Thanks for that explanation. So I guess it's okay that the cabin is grounded separately? Or can it have 2 ground rods, one at the cabin, the other at the dog house 100' away, with the AC output being grounded at both ends? Hope I am making sense....
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #19
    Re: Battery Balancing

    The standard answer (and complies with code) is to put one Neutral to Earth/safety/ground rod connection at the Cabin... And "float" the Neutral grounds everywhere else.

    The "I think the best grounding" for a distributed power system that is in a lighting prone area...

    I am tending towards grounding the cabin as above, and driving a separate ground rod at the dog house (call it >20 feet away from main building) and tie the Neutral (White) wire to the doghouse ground and tie the "local" green wire ground to the same Dog House ground rod.

    What, I think, we don't want is two grounds, two neutral to ground rod grounds, added with a green wire connection from the dog house to the main home/cabin.

    You do not want the White Wire (Neutral) and the Green wire (safety ground) to be sharing the current flow... So to avoid that with multiple Neutral to Earth bonds, you would not bring a green wire ground between the two rods (and that would include a buried 6 awg cable between the two widely spaced ground rods).

    You could skip the Neutral to Earth Bond in the dog house--But then I would very much recommend installing a Midnite 120/240 VAC surge suppressor at the dog house.

    Using surge suppressors at the remote sites and not bonding Neutral+Earth would seem to be a good alternative (and you can still tie all the green wire + ground rods in the system together).

    And you should probably use surge suppressors even if you Neutral+Earth Bond. You still have the hot wires that need lightning control/suppression.

    I am welcoming discussions on this grounding issue (widely distributed AC power and generation) in lighting prone areas. It would be nice to have a clear and detailed grounding strategy that would work for everyone--But it may be that this is not possible. :confused:

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #20
    Re: Battery Balancing

    imo you can have the separate ground rods at each location, but only one neutral to ground connection being at the cabin. the reason is ground loops that can be generated with more than one tie point. the use of an spd at the dog house would be able to tie directly to ground there and handle the surge from that far end. you may want them at the cabin too being it is a 100ft spance.
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  • Caveman
    Caveman Solar Expert Posts: 83 ✭✭✭✭
    #21
    Re: Battery Balancing

    Okay I think I might be getting it haha...

    I drew a little schematic, correct me if I'm wrong, but I don't want to ground my AC charger (for bulk charging with the generator) to the negative buss for the reasons you gave, right? See question marks in diagram, where do I put the charger ground wire?
    Attachment not found.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #22
    Re: Battery Balancing

    OK, some things to double check (at least on my side).

    What AC inverter will you be using? A TSW that supports a ground bonded neutral or a MSW inverter which (typically) does not support a ground bonded neutral?

    Second, you show three AC wires from the inverter to the house... Is that Hot+Neutral+Safety Ground? Or is that Hot+Hot+Neutral (120/240 VAC split phase)?

    Is the generator Neutral grounded to the generator frame+Green wire?

    Will you have a transfer switch so you can run Generator AC directly to the Home (when servicing the DC system and/or as emergency backup if DC system fails)?

    Are you planning on Bonding the AC neutral at the house main panel?

    The battery negative bus, if bonded to all of the sheet metal electrical boxes and conduit is also your Green Wire Safety Ground for all equipment in the shed. Your Generator+AC Battery Charger safety grounds should go to the "master ground" too.

    No right or wrong answer here (at least not yet :p)--The details matter.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Caveman
    Caveman Solar Expert Posts: 83 ✭✭✭✭
    #23
    Re: Battery Balancing

    Inverter: Exeltech XPX 2000 True Sine Wave with N-G bond

    Wires to cabin are hot-neutral-safety ground

    Generator says "neutral is bonded to frame"

    Yes, transfer switch installed

    I believe I already bonded AC neutral please see
    http://forum.solar-electric.com/showthread.php?19988-Instalation-devolpment-help
    the last page

    When you say master ground, I'm guessing you mean back at the cabin, but it's 100 feet away. How would I ground AC charger then?
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  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    #24
    Re: Battery Balancing
    Caveman wrote: »
    Okay I think I might be getting it haha...

    While working on this, you need to remember that you have bonded invertors Neural to the Ground inside the transfer switch. There was another thread about a month ago.
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  • Caveman
    Caveman Solar Expert Posts: 83 ✭✭✭✭
    #25
    Re: Battery Balancing
    NorthGuy wrote: »
    While working on this, you need to remember that you have bonded invertors Neural to the Ground inside the transfer switch. There was another thread about a month ago.

    Yes I remember, so does that mean I don't need to bond it in the inverter?
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  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    #26
    Re: Battery Balancing
    Caveman wrote: »
    Yes I remember, so does that mean I don't need to bond it in the inverter?

    It has to be no more than one bond.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #27
    Re: Battery Balancing
    Caveman wrote: »
    Inverter: Exeltech XPX 2000 True Sine Wave with N-G bond

    From my current thinking--You can have multiple N-G bonds in an AC distribution system--But you have to basically not carry the Green Wire safety ground from building to building. That "breaks" the ground loop and, appears to, still give you good lightning ground protection.

    What you don't want is the Neutral and Earth/Safety Ground wiring to be in parallel--then you can have circulating current--and if your DC side is mixed in there (with upwards of 5-10x as large DC currents vs AC currents), the DC current could fry the AC safety ground wires (typically green wire AC grounds are on 15-30 amp rated circuits--DC circuits in larger off grid systems are 100-200+ amp rated).
    Wires to cabin are hot-neutral-safety ground

    If you choose to AC G-N bonding at both the AC inverter and the house--Then I would not carry a green wire (and connect) the two grounding systems together. Just Hot+White wires.
    Generator says "neutral is bonded to frame"

    What type of AC transfer switch did you get and where exactly did you wire it?

    An AC transfer switch can be (in 120 VAC case) just one contact for Hot switching or two contacts (Hot+Neutral) to switch both.

    If you choose to Earth Ground Neutral at the house and in the "dog house" (and not carry the green wire from house to power shed), your generator can be of issue. Especially if the generator has a GFCI outlet on-board... Having two neutral bondings (one in the genset before the generator GFCI) and a second N-G bonding (power shed and/or house), will kick off the GFCI outlet at the generator.

    You should (pretty much for sure) disconnect the N-G bond in the generator. Bring the H+N+G from the genset and wire into the power shed as normal.

    And second, I would wire the power from the generator to the power shed without the GFCI outlet in the middle (remove GFCI or wire around it).
    Yes, transfer switch installed

    Where and H or H+N, or what?
    When you say master ground, I'm guessing you mean back at the cabin, but it's 100 feet away. How would I ground AC charger then?

    I was referring to the Ground Bus Bar in the power shed--Where "everything" power shed related is being bonded: DC negative Battery Bus, various AC and DC equipment "green wire grounds". Conduit and other AC safety grounds. And the power shed Earth Ground Rod. There are no "separate" grounding points in your power shed system. And, from what I can "see"--That is fine.

    People can argue the N-G bond to earth--House only + green wire to shed, or House+Shed N-G bond to earth and no green wire to Shed. NEC Code would suggest the first. And lightning grounding/distributed power would suggest the second.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Caveman
    Caveman Solar Expert Posts: 83 ✭✭✭✭
    #28
    Re: Battery Balancing
    BB. wrote: »
    From my current thinking--You can have multiple N-G bonds in an AC distribution system--But you have to basically not carry the Green Wire safety ground from building to building. That "breaks" the ground loop and, appears to, still give you good lightning ground protection.

    What you don't want is the Neutral and Earth/Safety Ground wiring to be in parallel--then you can have circulating current--and if your DC side is mixed in there (with upwards of 5-10x as large DC currents vs AC currents), the DC current could fry the AC safety ground wires (typically green wire AC grounds are on 15-30 amp rated circuits--DC circuits in larger off grid systems are 100-200+ amp rated).

    Would I be right in saying that if I tied my AC charger to to the negative buss I would be doing just that (Neutral and Earth Safety Ground in parallel)?
    What type of AC transfer switch did you get and where exactly did you wire it?

    This one: http://www.solar-electric.com/miso30amp240.html
    wired in cabin near main AC panel

    Generator outlets are GFCI protected

    The rest of what you said I'm still digesting, so I'll deal with that next....
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  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    #29
    Re: Battery Balancing
    Caveman wrote: »
    Would I be right in saying that if I tied my AC charger to to the negative buss I would be doing just that (Neutral and Earth Safety Ground in parallel)?

    If you already have a ground wires between inverter and transfer switch, and there are two bonds - at inverter and at the transfer switch, then you have them in parallel. In this case you should remove one of the bonds. It's very easy to remove the bond at the transfer switch - you just remove the short jumer wire.

    If you don't have the wire, then you need to have bonds in both places.

    I don't have an opinion on whether or not there should be a ground wire between inverter and transfer switch. Bill knows everything about this.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #30
    Re: Battery Balancing
    Caveman wrote: »
    Would I be right in saying that if I tied my AC charger to to the negative buss I would be doing just that (Neutral and Earth Safety Ground in parallel)?

    Correct--You want a short from "any hot" (AC or DC) to "safely" return to its power source (via neutral+earth bond--if short is Hot to green wire / metal ground).
    This one: http://www.solar-electric.com/miso30amp240.html
    wired in cabin near main AC panel

    What exactly is the input/output to the transfer switch (AC Inverter and AC Generator on the "inputs" and Cabin AC on the output)?
    Generator outlets are GFCI protected

    I would highly suggest you remove/connect around the AC GFCI outlets on the generator. Just buy a handful of GFCI outlets and install them where needed (outside outlets, near sinks, in bathroom, laundry, etc.).

    You should disconnect Neutral to Green Wire (frame) ground in the generator. And connect Generator Neutral to power shed neutral and Generator Green Wire to your "power shed" AC power system and "everything" ground.

    Big problem if you use both Generater GFCI and N+Frame bonding--Anytime the generator is connected to your power shed or home wiring system, their N+G bonds will trip the GFCI in the generator.

    If you either remove Generator GFCI outlet OR N-Frame ground--You have sort of worked around the problem and it will probably work. However--I would suggest doing both (in my humble opinion).

    If the generator is >~20 feet from the power shed, then we may need to treat it as a remote AC power source and then do the whole Green Wire vs Bonded Neutral discussion for it too...

    None of this is "do A+B and not C"--There are multiple "works" and "may not work" conditions and multiple options. Grounding is a huge issue with off grid power--And there are different opinions on what is best, and NEC code requirements which sometimes are not really ideal for DC and Lightning issues.
    The rest of what you said I'm still digesting, so I'll deal with that next....

    So am I--This grounding stuff is a pain. And I have changed my philosophy a bit over the last 1-2 years because of discussions here. :cry: I now am more in the camp of multiple N+G bonds for "out buildings" with local ground rods, and not bringing Green Wire safety grounds between buildings.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Caveman
    Caveman Solar Expert Posts: 83 ✭✭✭✭
    #31
    Re: Battery Balancing

    Okay this is all helping me to understand. To answer a few things...
    What exactly is the input/output to the transfer switch (AC Inverter and AC Generator on the "inputs" and Cabin AC on the output)?

    Input comes from generator and from inverter. There is a disconnect just before the transfer switch on the inverter wires, and I ran 3 wires from inverter to transfer switch.

    Generator has its own separate wires to trans switch.

    One set of output wires from inverter (via transfer switch) and one set from generator (again via trans switch) go to main AC panel that services the whole cabin just like any typical residence.

    Not sure if you were a part of this, but in this discussion I dealt with the issue of N-G bonding my transfer switch in the cabin. Not sure how that will play into the current discussion.
    http://forum.solar-electric.com/showthread.php?19988-Instalation-devolpment-help

    And thank you very much for your explanations....
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