Battery Bank Fuse Plan

KamalaKamala Solar Expert Posts: 452 ✭✭
Attached is a diagram of my battery bank fuse plan. All cable is #1 AWG. Is this a good plan?

K
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Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Bank Fuse Plan

    There's really no need to fuse between batteries in series; they act together as one larger battery.

    Some people would prefer to see a separate fuse on each parallel bank, but your set up is small enough that this probably isn't a problem. Some people may disagree with me. :D

    You should do the diagonal connection to the bank: inverter (+) & (-) and charge controller (+) & (-) on diagonally opposite poles.

    Yes?
  • KamalaKamala Solar Expert Posts: 452 ✭✭
    Re: Battery Bank Fuse Plan
    ... You should do the diagonal connection to the bank: inverter (+) & (-) and charge controller (+) & (-) on diagonally opposite poles. ...

    Uh.... think I did that. Or am I more bleary eyed than you? :roll:

    The + and - leads are form diagonally opposite posts. Look again.

    The series fuses are there (I think) to protect the bank in case a cell fails due to a short. I researched some threads and this method seemed to come up often.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Bank Fuse Plan
    Kamala wrote: »
    Uh.... think I did that. Or am I more bleary eyed than you? :roll:

    The + and - leads are form diagonally opposite posts. Look again.

    Well I am looking ... but on a 7" netbook screen so ...

    But I still only see one lead coming off (+) and one lead coming off (-) of the bank.

    One (+) post should go to the inverter, the other to the charge controller (and vice versa for the negative side).
    Or is your charge controller built in to the inverter?

    Edit: the fuses between batteries in series don't matter, because any current flow goes through the main fuse. This is why some recommend separate fuses per bank. In other words, if you're going to put two fuses in anyway put them from the (+) posts to a common (+) point for the inverter & charge controller.
  • KamalaKamala Solar Expert Posts: 452 ✭✭
    Re: Battery Bank Fuse Plan
    ... One (+) post should go to the inverter, the other to the charge controller (and vice versa for the negative side).
    Or is your charge controller built in to the inverter? ...

    This is contrary to everything I have learned here. :confused:

    The + goes to a disconnect (marine switch) and then to a buss bar and on to distribution fuse block.

    The - goes to the shunt and then to a buss bar.

    Tapping off any other pos/neg point will unbalance the charge/discharge.

    Or maybe the cosmic axis shifted?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Bank Fuse Plan
    Kamala wrote: »
    This is contrary to everything I have learned here. :confused:

    The + goes to a disconnect (marine switch) and then to a buss bar and on to distribution fuse block.

    The - goes to the shunt and then to a buss bar.

    Tapping off any other pos/neg point will unbalance the charge/discharge.

    Or maybe the cosmic axis shifted?

    Uh, nope. Maybe I'm just not explaining it well.

    When you have only two parallel banks:

    (-) BATT 'A' (+) --- (-) BATT 'B' (+)
    (-) BATT 'C' (+) --- (-) BATT 'D' (+)

    Inverter connected to Batt 'A' (-) and Batt 'D' (+)
    Charger controller connected to Batt 'C' (-) and Batt 'B' (+)

    That's the standard 'diagonal' connection. There would be one fuse at the charge controller to handle the charging circuit and another at Batt 'D' (+) to handle the higher load to the inverter. But this sort of set up is small enough to put two fuses on the (+) terminals to feed the inverter & connect the charge controller too; there simply isn't that much wire involved to throw the current balance off.
  • KamalaKamala Solar Expert Posts: 452 ✭✭
    Re: Battery Bank Fuse Plan

    Well Marc, I disagree. Everything into and out of my bank (however small it may be) is taken from or provided to the same opposing connections.

    My inverter does not have a solar charge controller, but it does have a charger. So you suggest that I solar charge from one set of posts and grid/gen charge and discharge from the other pair of posts.

    Even if the inverter did not grid charge, it would be rare indeed when my discharge rate was identical to my recharge rate. For example, discharging at a high rate from one pair of posts while recharging at a more moderate rate on the other pair of posts. Again, unless my corpus callosum has sprung, I see this as a path to unbalance.

    I'm pretty confident in this part of the set up. My real question is about the series fuses in case of cell failure.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Bank Fuse Plan

    It's not about having the same charge and discharge rates - that never happens. It's about keep the charge or discharge rates even through all batteries. To really see the effect you need more than two parallel banks; with just two you won't see much difference no matter how you wire it. It takes more than a few inches of wire to add up to significant enough resistance to throw the balance off.

    The diagonal idea is that current must cross between the (+) and (-) terminals of all parallel banks. If the charge current comes in to the (+) on one bank and the (-) on the other, then current must flow through both parallel connectors. Without it, the current can flow in to one bank and the other bank just "hangs on"; there's no absolute current path through the other bank.

    I still think if your going to have two fuses anywhere you should have them on the (+) terminals of each bank to a common inverter point. Your design has three fuses (plus, I presume, one more for the charge controller) which means extra parts and extra connections.

    BTW, don't expect much protection from fuses over cell failure. I had a short develop in one cell last year; it made no difference to a 200 Amp inverter fuse. All it really did was mess up the charge on the second battery in the series. Not really a big problem.
  • KamalaKamala Solar Expert Posts: 452 ✭✭
    Re: Battery Bank Fuse Plan

    Maybe it's a nitpick, but when I say "bank" I mean all batteries (whatever their number or connection scheme. As in a place to keep your precious.) What you call a bank, I call a string of series connected batteries (or more generically, elements. Could be PVs or even loads.)

    I'm sure you're aware of the recommendation that when PV strings (series) are paralleled, each string should be individually fused. (Combiner boxes?) Why should batteries be different?

    I remember your posts about battery failure. How was that 200A inverter fuse implemented? Just in the inverter supply? Or in the series connections of your battery bank? If only in your inverter circuit it could not possibly have protected your batteries.

    As I see it, the purpose of the series battery fuse is to protect other batteries in the string (and ultimately the entire bank.) If a cell in a battery in a string shorts, the current from that string will rise blowing the fuse. Don't shorts always result in increased current?

    Regarding the battery configuration. An alternate diagram is attached. Electrically equivalent. Original post diagram is two series strings in parallel. Alternate is one string of two batts in parallel.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Bank Fuse Plan

    That's an interesting idea there, Craig. I'll think about it for a few months and see if I find any flaws, okay? :p It takes me that long to analyze things sometimes!

    No, like I say; with two in parallel it usually isn't trouble to connect them either the way you had in plan 'A' or my confusing method. Add up a bunch in parallel and you start to get problems.

    Yes, two fuses is a good idea. But usually they don't go between the batteries in series. To tell you the truth, though, I think you're on to something there. The fuses could protect against over current and serve as interconnects. Right now I don't see a down side. You wouldn't need the addition bank-to-inverter fuse.

    The trouble I had is that when a cell shorts it doesn't take out the whole cell; only a couple of plates. The resulting increase in current is not outside of operating range and any fuse that would blow under such circumstances would pop easily any time the inverter tried to supply higher Wattages.

    So now I'm thinking theoretically: if your inter-connects were fuses at 1/2 the full expected maximum current for the whole bank would they correctly protect the whole circuit in case of a short? It's an interesting idea all right!

    Or maybe it's just too late in the day for clear thinking. At least for me. :p
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Battery Bank Fuse Plan

    kamala,
    your battery arrangement is flawed imo as it will have more inequities because as i see it you just piggybacked more batteries. the upper right and lower left batteries will receive and give the most power and will fail first. a simple correction that may help this is to take the blue wire from the lower right + to the - of the upper left battery. or you can have the main power taps for the battery bank at the + of the upper left battery and the - at the lower right battery.
  • BB.BB. Super Moderators, Administrators Posts: 32,608 admin
    Re: Battery Bank Fuse Plan

    Sorry,

    I think I am losing my way in this thread... Kamala's first post shows two fuses in the middle of two series strings. The location of the fuse (negative, middle, or + final string terminal probably does not matter unless there are some design issues that we cannot see.

    I assume the two fuses are in the middle of the string because they are easy to access/service there.

    Single fuse in the bus + output really depends on the size of the output limit and the number of parallel strings... If you have two 75 amp fuses and 150 amp protection is needed on the output--it may be redundant to add a 150 amp on the bus output...

    However, if you had 4 parallel strings each with 75 fuses, then you would need the 150 amp fuse on the common + bus output.

    For house wring, there is the concept that a circuit is "de-energized when a fuse/breaker opens.

    Placing a fuse in the middle of a string means that there is at least one battery potential that is not equal to zero if the fuse pops.

    The last drawing by Kamala with the "Z" battery wiring--I think, if one want to put a fuse per string--that last wiring diagram makes that very difficult as there are no discrete wires anywhere where "each parallel" string current flows uniquely...

    I have seen suggestions where, for example two heavy current sources/loads (such as battery charger and inverter) can connect "diagonally" from each other...

    Other than possibly easier to make the physical connections (maximum length of studs limit stacking of wire lugs)--I do not really see any advantage. And, it can make the balancing a bit complex to figure out (is charging balanced but discharging unbalanced)--And where do you add the next load(s).

    I like the concept of a common "bus bar / bus lug" there you can connect anything to equal potential/resistance with respect to the battery bank.

    Please let me know if I am completely missing the point of the discussion--that may very well be happening here.

    -Bill

    PS: Looking at the last drawing--I don't think that is a balanced setup... The lower left/upper right batteries have a lower resistance path to the loads. The Upper Left/lower right have two "extra lengths" of wire for current to flow through.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • KamalaKamala Solar Expert Posts: 452 ✭✭
    Re: Battery Bank Fuse Plan

    OMG, this is incredible.

    The battery arrangement is consistent with what I have often here offered from SmartGauge.

    Neil, please see the first post with original diagram. AGAIN, the question I have is about the series battery fuses.

    This is a good forum. But as Marc & I have bantered, my OP has become buried. And few, myself included, read more than the most recent posts. My question was about fusing series strings.

    It is possible that my time on this forum in the past year has been in vain. (Not true by any stretch.) That is, I learned wrong. If so, I remain to still learn.

    Reattached is the original diagram.
  • BB.BB. Super Moderators, Administrators Posts: 32,608 admin
    Re: Battery Bank Fuse Plan

    This repost of the diagram from #1 is still fine with me.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Bank Fuse Plan

    Don't fret, Big K! :D

    You didn't learn wrong. But remember that when we have just two PV parallel connections individual fuses usually aren't used; not really necessary. Same with just two battery parallels.

    But if you've got three or four PV's or batteries in parallel then yes there should be a separate fuse on each. That's also where you need to get picky about even wire lengths and using buss bars to try and keep current flow even across all batteries.

    I like our original plan best. There could be a "shortest current path" problem with design 'B' (I think Neil was pointing at that) using the one center connector. But with the first one ... the notion of putting two "half current" fuses as connectors is either brilliant or else none of us has seen the flaw in it! Could we all be daft? Well, yes I suppose so ... :p

    But with that design you wouldn't need the additional (+) line fuse. In other words, two 50 Amp fuses as the series connectors between batteries would take the place of one 100 Amp fuse on the inverter line. Even so, it won't protect against the slight current increase caused by typical a case of plate shorting (roughly a 1/6 maximum current on one bank).

    Ideally the connection between inverter (I) and two batteries would be like this:

    (+)---(I+)---(+)

    (-)---(I-)---(-)

    In other words, equal length wires from batteries to inverter & charge controller. Still, not a big issue on this size set up.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Battery Bank Fuse Plan

    sorry for the side posting on what you had shown in post #9 as that is not consistent with smartgauge, but that in post #1 is consistent with smartgauge. the fuse arrangement looks fine to me in your last diagram. the fuse arrangement works only if there is balance between the strings otherwise 75a fuses may blow at times due to string inequities.
  • KamalaKamala Solar Expert Posts: 452 ✭✭
    Re: Battery Bank Fuse Plan

    Thanks and nighty night.

    I'll try to find the threads that landed me here.
  • KamalaKamala Solar Expert Posts: 452 ✭✭
    Re: Battery Bank Fuse Plan
    niel wrote: »
    sorry for the side posting on what you had shown in post #9 as that is not consistent with smartgauge, but that in post #1 is consistent with smartgauge. the fuse arrangement looks fine to me in your last diagram. the fuse arrangement works only if there is balance between the strings otherwise 75a fuses may blow at times due to string inequities.

    So, Neil, do you agree, that in the original diagram, the series fuses play an important role? Please explain how they do or do not.

    K
  • BB.BB. Super Moderators, Administrators Posts: 32,608 admin
    Re: Battery Bank Fuse Plan

    The series fuses in #1 protect the interconnect wiring (per series string) from excessive currents (and the batteries in each string string too). A third (and more fuses as needed) would be used to protect any down stream loads that draw from the common bus (at the appropriate rating for each wire leaving the bus).

    Also, remember that you have additional current sources (solar charger, possibly an AC charger)--so you would still need a fuse/breaker per wire even if the inverter load can accept 150 amp because you still have the XX amps from the solar charger and the XX amps from the AC battery charger--so you could be >> 150 amps available once the other power sources are included.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Battery Bank Fuse Plan

    as marc said i don't think it would be mandatory for 2 battery strings to fuse protect the interconnections, but it certainly does not hurt as stuff happens. bb's last post is on the money for the general explanation on the functions those fuses play.
  • KamalaKamala Solar Expert Posts: 452 ✭✭
    Re: Battery Bank Fuse Plan
    BB. wrote: »
    The series fuses in #1 protect the interconnect wiring (per series string) from excessive currents (and the batteries in each string string too).

    Thanks Bill. That was the intent. The fuses I am considering are the Blue Sea terminal type. They are reasonably priced.
    BB. wrote: »
    A third (and more fuses as needed) would be used to protect any down stream loads that draw from the common bus (at the appropriate rating for each wire leaving the bus).
    My bold! And now my comment.

    The fuse is to protect the wiring connected to said loads. I have included this fuse.
    BB. wrote: »
    Also, remember that you have additional current sources (solar charger, possibly an AC charger)--so you would still need a fuse/breaker per wire even if the inverter load can accept 150 amp because you still have the XX amps from the solar charger and the XX amps from the AC battery charger--so you could be >> 150 amps available once the other power sources are included.

    -Bill

    I have not forgotten. So, with a 150A terminal fuse at the positive tap of the bank to the buss, the "downstream" fuses are: 125A class T fuse to the ProSine 2.0. 25A fuse to the SS-MPPT-15. 2A to the water tank level sensor. 1A to the TriMetric. Then the buss goes directly to the on board distribution panel which feeds the three house circuits through 15A fuses.

    Thanks to all. I still would like to have the following issue resolved...
    ... One (+) post should go to the inverter, the other to the charge controller (and vice versa for the negative side). ...

    This is a case of tapping the bank at more than one point. But in this case it is a current tap rather than a voltage tap. The bank is the bank is the bank! One and only one + connection and one and only one - connection!

    Thanks again. I'm good.
    Craig
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Bank Fuse Plan

    Craig, think of it as a detection thing. Blasted hard to explain in words and there's no drawing program on this toy. But if the parallel connectors between batteries suffer a partial or total failure you get a possibly unnoticed loss of current through one pair either on charge or discharge. When charge goes through the the batteries through one diagonal and discharge through the other any imbalance shows up quickly. I'll say it again: on a small bank like yours there's no point; you're way is fine. But I use the "corner connections" on mine and it works. Of course mine also has the weird adaptation of being able to connect/disconnect either battery set from the controller and/or the inverter. It won't be like that after this year; the crazy old 'coot is changing things again!

    BTW, if you fuse the output of the batteries for current protection there's no point in putting additional fuses in the series connections. One cell totally shorted will drop Voltage by about 2, and won't raise current outside of normal operating range. Any fuse that would blow under those circumstances would pop whenever the inverter drew any significant power.

    I could be totally wrong, of course, but so far everything works and I haven't burned anything up or killed myself.

    I'll keep trying! :p
  • KamalaKamala Solar Expert Posts: 452 ✭✭
    Re: Battery Bank Fuse Plan

    I have, as do most people, only one discharge sink. I have two charge sources, one of which whose path is intrinsically tied to the discharge (ProSine Inverter/'Charger.) The other charge source is the SCC.

    I stand on one way in and one way out.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Battery Bank Fuse Plan
    Don't fret, Big K! :D

    You didn't learn wrong. But remember that when we have just two PV parallel connections individual fuses usually aren't used; not really necessary. Same with just two battery parallels.

    I've seen this about not having to fuse two parallel PV strings before (although I usually fuse strings separately no matter what) and it's caused me to wonder, idly, if one could subcombine pairs of strings in a larger array without fusing at that level.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Bank Fuse Plan
    ggunn wrote: »
    I've seen this about not having to fuse two parallel PV strings before (although I usually fuse strings separately no matter what) and it's caused me to wonder, idly, if one could subcombine pairs of strings in a larger array without fusing at that level.

    As in:

    Panel 'A' paralleled to Panel 'B' ---> fuse ---> charge controller
    Panel 'C' paralleled to Panel 'D' ---> fuse ---> charge controller

    As opposed to each panel having its own fuse.

    Yes, you can. Providing the fuses and wiring are rated accordingly. You'll save two fuses and a few bits of related connections. Should you? That would probably depend on how much current is involved with the panels in question.

    Fuses on each is best, just not absolutely necessary if there's only two.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Battery Bank Fuse Plan

    if i read what you're saying rightly, i'm going to say no as the nec requires more than 2 strings to be fused and concealing those strings just by combining earlier does not circumvent the requirement.
  • BB.BB. Super Moderators, Administrators Posts: 32,608 admin
    Re: Battery Bank Fuse Plan

    For several reasons no... One, the fuses are roughly Isc*2 and running Imp*2 through the fuse is near unreliable (generally, you would want Isc*1.25 at a minimum).

    Second, unless that two to one fuse has a blocking diode at that one fuse--the short circuit current in the substring is now Isc*2 plus Ifuse--so you are now exceeding the rated "safety limits" of the panel.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    Re: Battery Bank Fuse Plan
    Blasted hard to explain in words and there's no drawing program on this toy.

    Need to get Open Office, their Draw program is good.


    This is what I think Marc is trying to say about cross connecting the chargers.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Battery Bank Fuse Plan

    On my 7" netbook screen, even "blown up" the pictures are only 2" across ... :cry:
    But in all likelihood n3qik has what I meant. Not a necessary thing; just a sort of detection when one of the cross-connects goes down thing. (Note to self: Gosh, any better explanation possible you old fool?:p)

    As for the other Q that cropped up here ....

    Neil & Bill's explanations point out what I was only hinting at; the big difference between 4 15 Watt panels used off-grid to recharge a radio battery as opposed to (more than) 4 230 Watt panels used in a GT system. I'm pretty sure that NEC reg has something to do with the power difference. As you might guess, I don't have much to do with NEC regs.
  • KamalaKamala Solar Expert Posts: 452 ✭✭
    Re: Battery Bank Fuse Plan
    n3qik wrote: »
    Need to get Open Office, their Draw program is good.


    This is what I think Marc is trying to say about cross connecting the chargers.

    I think I see (possibly) more "elegance" in this configuration. But where would I connect the 12VDC loads/distribution panel?
  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    Re: Battery Bank Fuse Plan

    Same spot as the inverter.
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