Battery Fuse

Scottg4001
Scottg4001 Solar Expert Posts: 47 ✭
in Solar Beginners Corner #1
Excuse me for being dumb, but when wiring a inline fuse between the battery positive and charge controller, which end is considered the "load" side of the fuse and which side is considered the "line"? Its confusing because I know I have current flowing both ways to and from the battery. Does it go: from battery to load side of fuse and line to cc, or the other way around? Thanks in advance.
· Share on Twitter

Comments

  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #2
    Re: Battery Fuse

    there is no right or wrong way for a fuse.. but there is for some DC circuit breakers.
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,637 admin
    #3
    Re: Battery Fuse

    In general, the battery is the current source, and everything else is the load... What you are protecting against is short circuit current. And that 1,000 of amperes will come from the battery bank--not from your charge controllers or other sources (charge controllers are naturally limited current sources).

    If you are fusing parallel connected batteries (or solar panels)--Typically, the common bus is the source of excessive current that the fuse/breaker is protecting against.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • Scottg4001
    Scottg4001 Solar Expert Posts: 47 ✭
    #4
    Re: Battery Fuse
    BB. wrote: »
    In general, the battery is the current source, and everything else is the load... What you are protecting against is short circuit current. And that 1,000 of amperes will come from the battery bank--not from your charge controllers or other sources (charge controllers are naturally limited current sources).

    If you are fusing parallel connected batteries (or solar panels)--Typically, the common bus is the source of excessive current that the fuse/breaker is protecting against.

    -Bill

    I am fusing a battery bank with four battieries in series. So from what you said, the battery positive will connect on the fuse "line" side and the charge controller will connect to the "load" side of the fuse.
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,637 admin
    #5
    Re: Battery Fuse

    That is what I would do... Note that you should avoid turning off the DC Breaker when the charge controller is actively pushing current to the battery bank. The polarity of the current may make internal arcs last longer and could damage the breaker.

    One of the methods to kill and arc is to put a string magnet next to the contacts so it "blows" the arc away from the contacts. With reverse current flow, it may not work correctly.

    Also note the orientation of the breaker--They probably have a "this side up" installation requirement.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • Caneman
    Caneman Solar Expert Posts: 71 ✭✭✭✭
    #6
    Re: Battery Fuse
    BB. wrote: »
    That is what I would do... Note that you should avoid turning off the DC Breaker when the charge controller is actively pushing current to the battery bank. The polarity of the current may make internal arcs last longer and could damage the breaker.

    One of the methods to kill and arc is to put a string magnet next to the contacts so it "blows" the arc away from the contacts. With reverse current flow, it may not work correctly.

    Also note the orientation of the breaker--They probably have a "this side up" installation requirement.

    -Bill

    ^^^ BB, what is the correct sequence to shutdown a PV system? do you start with the inverter and work your way back to the pv?

    disconnect load --> open battery disconnect --> open cc disconnect --> flip open combiner box breakers

    like this?
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,637 admin
    #7
    Re: Battery Fuse

    You have to check with the manual... But my generic answer would be to turn off the solar array first, then turn off/disconnect the batter power to the charge controller.

    To restart, connect battery bank/turn on controller, then reconnect solar array.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #8
    Re: Battery Fuse

    BB you are talking about breakers he is asking about a "fuse". Or is his "fuse" a breaker?
    I agree its a bit pointless putting a fuse or breaker as protection between the charge controller and batteries. I would be putting a shunt there , for other reasons. but thats another story.
    · Share on Twitter
  • Scottg4001
    Scottg4001 Solar Expert Posts: 47 ✭
    #9
    Re: Battery Fuse
    john p wrote: »
    BB you are talking about breakers he is asking about a "fuse". Or is his "fuse" a breaker?
    I agree its a bit pointless putting a fuse or breaker as protection between the charge controller and batteries. I would be putting a shunt there , for other reasons. but thats another story.

    Most wiring diagrams I have seen illustrate a 25amp fuse between the battery positive and charge controller.
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,637 admin
    #10
    Re: Battery Fuse

    Scott type about Line and Load size of the fuse... There are many fuse designs and I don't know if "line" vs "load" really matters (sometimes it is an issue of exposed metal when changing a fuse, etc.). But even "line" does not address the issue of + or - for DC current flow.

    In any case, one should pay close attention to ratings for fuses and breakers--The AC vs DC ratings can be very different for the same device.

    I use fuse/breaker to talk about over current protective devices...

    More or less, I use fuses to protect wiring. And as such, there should be a fuse/breaker between the battery bank and the charge controller. If the charge controller has an internal short (bolt/wire fails, etc.), I would still want a protective device installed near the battery bank.

    I understand you like to use Shunts as fuses--and you make a very good practical case for that (based on your testing).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • SolaRevolution
    SolaRevolution Solar Expert Posts: 410 ✭✭
    #11
    Re: Battery Fuse

    It is more likely for the fuse holder to have a line and a load side.

    Some fuse holders are labled with line and load. If it isn't labled it shouldn't matter. If the "holder" is part of a switch assembly, the line side will be disconnected from the fuse when the switch is open (turned off) so the fuse can be de-energized if you need to remove it. If there is a current source on either end of the fuse holder, the line side should be on the side with the most potential. (usually the battery)

    Alex
    · Share on Twitter
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #12
    Re: Battery Fuse
    john p wrote: »
    BB you are talking about breakers he is asking about a "fuse". Or is his "fuse" a breaker?
    I agree its a bit pointless putting a fuse or breaker as protection between the charge controller and batteries. I would be putting a shunt there , for other reasons. but thats another story.

    I don't think its pointless. When charge controllers fail they may present a short circuit to the batteries. I think a fuse/breaker between controller and battery is one of the most important fuses/breakers in the system.
    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
    · Share on Twitter
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #13
    Re: Battery Fuse
    vtmaps wrote: »
    I don't think its pointless. When charge controllers fail they may present a short circuit to the batteries. I think a fuse/breaker between controller and battery is one of the most important fuses/breakers in the system.
    --vtMaps

    And there have been several times when I've needed or wanted to restart my controllers, both the MX-60 and the TS MPPT-60. So easy to shut off the breaker from the panels, then the breaker between the controller and the batteries, wait 15 seconds, then restart and all is well again. And then there's isolating the controllers for maintenance etc.
    I wouldn't want mine any other way.
    · Share on Twitter
  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #14
    Re: Battery Fuse

    Most wiring diagrams I have seen illustrate a 25amp fuse between the battery positive and charge controller. That would only be valid if the charge controller was rated at 20a. Not so good for a 80a controller.For that you would need a 100a breaker/fuse.
    After testing and overload destroying literally hundreds of charge controllers over the last few years have never had one go short circuit on the output. I believe the reason being when oveloaded the input section fails and lets the small amount of smoke each manufacture puts in each ic out. then no output.:grr
    100a quality breakers are expensive, fuses are a cheaper option and usually less chance of "arcover"
    · Share on Twitter
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #15
    Re: Battery Fuse

    i am in favor of some protection at the battery as well. regardless if the cc shorts the wires can short accidentally.
    · Share on Twitter
  • Scottg4001
    Scottg4001 Solar Expert Posts: 47 ✭
    #16
    Re: Battery Fuse
    john p wrote: »
    Most wiring diagrams I have seen illustrate a 25amp fuse between the battery positive and charge controller. That would only be valid if the charge controller was rated at 20a. Not so good for a 80a controller.For that you would need a 100a breaker/fuse.
    After testing and overload destroying literally hundreds of charge controllers over the last few years have never had one go short circuit on the output. I believe the reason being when oveloaded the input section fails and lets the small amount of smoke each manufacture puts in each ic out. then no output.:grr
    100a quality breakers are expensive, fuses are a cheaper option and usually less chance of "arcover"

    I am using a 15 Amp charge controller with a DC load that can pull 6 amps max.
    · Share on Twitter
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #17
    Re: Battery Fuse

    Further to fuses in circuits with extended times handling heavy current. I would, from personal experience ONLY recommend bolt on fuses, if fuses are to be used. Twice I've had automotive type fuses develop enough resistance where the fuse plugs into the socket, that both one end of the fuse leg and the holder receiving clip melted, arced and welded together, before the plug in leg of the fuse burned off. In both cases, if the assembly had not been in a metal box, a fire could very easily have resulted! One was a "Heavy Duty" 30 amp fuse package handling 15 amps pretty much 24/7. The other, an 80 Amp Maxi-fuse handling roughly 50 amps for hours at a time. It took several months before the problems developed, but develop it did! So watch it!
    · Share on Twitter
  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #18
    Re: Battery Fuse

    I am using a 15 Amp charge controller with a DC load that can pull 6 amps max. ???? you mean the solar panel puts out a max of 6a? if that is the case then a 10a fuse would be more suitable.. As the original question was about a fuse between the controller and battery..

    Its impossible ? to buy bolt in fuse holders for fuses below 50a.. if you can I have never seen them..But they would be good if you could..
    · Share on Twitter
  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #19
    Re: Battery Fuse

    i am in favor of some protection at the battery as well. regardless if the cc shorts the wires can short accidentally. Niel I cant believe a careful person like you would need such protection on a system you were using..:D
    · Share on Twitter
  • Scottg4001
    Scottg4001 Solar Expert Posts: 47 ✭
    #20
    Re: Battery Fuse
    john p wrote: »
    I am using a 15 Amp charge controller with a DC load that can pull 6 amps max. ???? you mean the solar panel puts out a max of 6a? if that is the case then a 10a fuse would be more suitable.. As the original question was about a fuse between the controller and battery..

    Its impossible ? to buy bolt in fuse holders for fuses below 50a.. if you can I have never seen them..But they would be good if you could..

    The panels can generate up to 15 amps max. The load is 6 amps max. I currently have a Ferrat midge fuse holder and a 20 amp fuse for DIN rail mount. Not wired in yet.
    · Share on Twitter
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #21
    Re: Battery Fuse

    http://bluesea.com/productline/overview/379

    Batter terminal fuses as low as 30 amps,,,

    Tony
    · Share on Twitter
  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #22
    Re: Battery Fuse

    A 20a fuse/breaker is about right for 15a max panels and a 10a fuse/breaker is good match for 6 a max load.
    This thread hard to follow sometimes as one post its about a fuse between battery and charger next its about a load from the battery.
    a 30 a fuse is way to high for a 6a load as its wiring and internals would be long gone before the fuse blows if the device developed a fault.

    Have a look at the window of response of the blue seas fuse 30a and 200% load it has an allowable variation between 5 seconds and 80 seconds. And people tell me that a shunt wont give a predictable blow point. HA HA.
    80 seconds is way too long if you get one that just meets that spec, and you will never know what the blow point is of the fuse. There is no way to test it.

    a shunt will fail at 200% load in less than 5 seconds is the usual rating.
    I just tried a 50a one and it failed at 100a in 3.3 seconds.. about as expected
    · Share on Twitter
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #23
    Re: Battery Fuse
    john p wrote: »
    i am in favor of some protection at the battery as well. regardless if the cc shorts the wires can short accidentally. Niel I cant believe a careful person like you would need such protection on a system you were using..:D

    careful is why i have a breaker coming off of the battery bank before it goes to my epanel. stuff can happen and i wouldn't want to see what happens should 400ah of batteries short. most everybody here advocates something to protect the wires from accidental shorts and it is good practice.
    · Share on Twitter
  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    #24
    Re: Battery Fuse

    Personally I use, for a 6 panel 24V array (max current 32A):
    1. A set of car fuses between parallel strings.. of max 10A... they are rated 32V, and this is above the limit of a 24V PWM Charge Controller, so should be able to handle it. This will normally be located outside. (these are the only car type fuses I use after waynesfromnscanda's advice)
    2. For additional protection a cylindrical 40A (depending on array size) on +ve side between the solar array and the Charge Controller.
    3. Another cylindrical 40A fuse on the +ve side between the Charge Controller and Batteries.
    4. A 63A, or 80A cylindrical fuse on the +ve between the Charge Controller and the Inverter (depending on inverter maximum current of course)

    I've attached a couple of photos that show such a setup
    Attachment not found.Attachment not found.


    Ideal sequence for disconnection in my experience is:
    1. Switch of Inverter
    2. Disconnect PV array (always before disconnecting battery)
    3. Finally disconnect Charge Controller and Battery


    I was taught that the Charge Controller is always the first to be connected to the battery bank and the last to be disconnected.
    · Share on Twitter

Categories