Battery Terminal Fusing

Bigwooo · June 2010

I just got most of my solar up and running, however somehow in the process I missed that each battery positive terminal should be fused. I've been reading about this subject for several days now and I need to remedy my error.

I'm running 14 Concorde 2012 batteries in parallel and I'm using 4/0 interconnect cable with terminals on each end.

I'm looking for a source for fuses, preferably a fuse holder that bolts to the battery terminal at one end, and has a bolt on terminal on the other side to connect the interconnect cable to. Does such a thing exist? I'd hate to have to cut the interconnect wires to splice in the fuse using clamp type connectors. Given most of my cables are arched from battery to battery, I'm not sure if a fuse could splice into the cable given the curve. I'd hate to have to replace all the positive cables ($$) to accommodate fuses, but if I have too....

Any suggestions on the best method to go about fusing the battery + terminals?

Anyone have pictures on how they did this?

Gracias.

BB. · June 2010

Re: Battery Terminal Fusing

From Blue Sea, Fuse Terminal Blocks (one and two fuse holders--mfg. site, may be available from West Marine and other marine stores--Perhaps NAWS can special order):

Otherwise, the standard T fuse and holders (not cheap either):

wind-sun_2106_33406228

-Bill

icarus · June 2010

Re: Battery Terminal Fusing

Blue Sea is available from nearly any good marine store, as well as on line,, I'm sure NAWS carries them. A very elegant solution for a thorny problem.

Tony

Bigwooo · June 2010

Re: Battery Terminal Fusing

Thank you for the information. I've checked a few sites for the Blue Sea blocks. They seem to run about $22.00 a piece, much less expensive than the T-Fuse and holder. I just emailed NAWS to see if they carry them. Didn't show up on their website. They look like the least expensive option.

Bigwooo · June 2010

Re: Battery Terminal Fusing

One more question: If I read correctly, the fuse is sized for the cable, in my case 4/0.

If I've got this correct, the amp rating for 4/0 cable is 230amps; then multiply by 1.25 to get 287.5 amps. Should I go up to 300 amps for the fuses, or use 250 amps, or am I way off on how to calculate the fuse size?

icarus · June 2010

Re: Battery Terminal Fusing

I would fuse them for the load,, but at least as big as the smallest wire in the circuit. If for example your expected load was ~100 amps, but the wire would carry 200 amps, I might fuse it for ~125 amps.

Does that make sense?

Tony

PS West Marine carries them.

BB. · June 2010

Re: Battery Terminal Fusing

If your cable/insulation/usage/temperature is rated for 230 Amps, then, round up to the 250 amp fuse. The maximum sustained current through the wiring is 0.80 (or 1/1.25) of the fuse/wire rating:

250 amps * 1/1.25 = 200 amps maximum rated load
250 amps * 0.80 = 200 amp maximum rated load

Normally, you only want to run at 80% of the fuse/breaker rating--above that level, you may experience false trips.

-Bill

System2 · June 2010

Re: Battery Terminal Fusing

Bigwooo wrote: »

I just got most of my solar up and running, however somehow in the process I missed that each battery positive terminal should be fused. I've been reading about this subject for several days now and I need to remedy my error.

I'm running 14 Concorde 2012 batteries in parallel and I'm using 4/0 interconnect cable with terminals on each end.

I'm looking for a source for fuses, preferably a fuse holder that bolts to the battery terminal at one end, and has a bolt on terminal on the other side to connect the interconnect cable to. Does such a thing exist? I'd hate to have to cut the interconnect wires to splice in the fuse using clamp type connectors. Given most of my cables are arched from battery to battery, I'm not sure if a fuse could splice into the cable given the curve. I'd hate to have to replace all the positive cables ($$) to accommodate fuses, but if I have too....

Any suggestions on the best method to go about fusing the battery + terminals?

Anyone have pictures on how they did this?

Gracias.

Hi there. I am a new guy and have the SAME exact situation and question. Any help would be great!

EDIT:
Didn't realize the thread read backwards!

So I saw all the answers. Great Info!

So just to clarify, it is best to fuse EVERY positive terminal off of every battery?

Before I buy 8 terminal fuse blocks and 8 fuses for them, I want to make sure.

BB. · June 2010

Re: Battery Terminal Fusing

The normal requirement is to fuse each string (one 12 volt battery, 2x 6 volt batteries in series, 8x 6 volt batteries for a 48 volt bank, etc.) should have one fuse to limit the maximum current to that of the rating of the wire (if your cable is rated for 250 amps, then you should have a 250 amp fuse/breaker).

You do not need a series fuse on each battery in a series string--Just one at the + end of each string (assuming Negative Ground).

[FONT=Fixedsys]                string fuse   Batt   Batt
                 /====o~o====+|-====+|-====\
Positive ==0~0==/                           \==== Negative
        master  \                           /
       fuse or   \[/FONT][FONT=Fixedsys]====o~o====+|-====+|-====/
       breaker[/FONT]

And you need a master fuse/breaker if you have two or more parallel strings to limit the total current from all the strings added together.

The string fuse(s) (or circuit breakers) are rated for the battery interconnect cable ratings.

The Master fuse/breaker is rated for the main cable leaving the battery bank to the bus/common connection (if different gauge than the battery interconnect fuses.

It is probably a good idea to have at least one high current switch or breaker on the output of your battery bank that you can turn off in an emergency or for servicing.

-Bill

System2 · June 2010

Re: Battery Terminal Fusing

BB. wrote: »
The normal requirement is to fuse each string (one 12 volt battery, 2x 6 volt batteries in series, 8x 6 volt batteries for a 48 volt bank, etc.) should have one fuse to limit the maximum current to that of the rating of the wire (if your cable is rated for 250 amps, then you should have a 250 amp fuse/breaker).

You do not need a series fuse on each battery in a series string--Just one at the + end of each string (assuming Negative Ground).
[FONT=Fixedsys]                string fuse   Batt   Batt
                 /====o~o====+|-====+|-====\
Positive ==0~0==/                           \==== Negative
        master  \                           /
       fuse or   \[/FONT][FONT=Fixedsys]====o~o====+|-====+|-====/
       breaker[/FONT]
And you need a master fuse/breaker if you have two or more parallel strings to limit the total current from all the strings added together.

The string fuse(s) (or circuit breakers) are rated for the battery interconnect cable ratings.

The Master fuse/breaker is rated for the main cable leaving the battery bank to the bus/common connection (if different gauge than the battery interconnect fuses.

It is probably a good idea to have at least one high current switch or breaker on the output of your battery bank that you can turn off in an emergency or for servicing.

-Bill

I have 8x T-105's for 48 volts and about 225 AH. So put on terminal fuse on the Negative end with the wire going to the inverter and another on the opposite positive end which goes to the inverter?

I only have one string.

So you are also suggestion I put in basically a breaker in between the positive lead to the inverter and the battery bank? Just so I can cut off the supply just in case?

So I need to find a switch that can handle AT LEAST my ah of my bank, which in this case would be 250 ah?

BB. · June 2010

Re: Battery Terminal Fusing

You may have multiple connections to your battery bank... Inverter, charger, small 48 volt loads, etc... Each wire/cable that "leaves the positive battery common bus point" should have its own protection.

In your case, I assume the wiring to the battery bank and to the inverter is probably the same gauge--so you could use one protective device from the battery to the bus common point.

If the inverter wiring is smaller, then you should have a separate fuse/breaker for that smaller line leaving the bus common point (yes, this is expensive and kind of a pain because everything is big, stiff, and has lots of expensive copper in it).

Normally, we do not Fuse/Breaker the negative side of the battery bus... The idea is if you blow a fuse--you want it to be in the positive lead--if the fuse blows, then that circuit is dead. If you have a second fuse in the negative/return line--you could blow the negative fuse instead--and now you your positive lead and return leads may still be hot with respect to ground. If you touch a tool to that positive lead to any ground in the system--you will have an arc and other issues too.

The assumption is all negative/return leads are at zero volts and therefore are reasonably safe to touch.

Some other suggestions for fuses/breakers/switches:

Blue Sea Battery Switch 1-2-OFF 350 Amp

Blue Sea 9001e 350 Amp Battery Switch Make-before-break contact design allows switching between battery...

High current fuses/fuse holders...

Midnite Solar Breakers and Boxes

Outback DC Power Products

Midnite Solar specializes in high current DC wiring for solar power systems (among other things) at reasonable prices... Take a good look through there.

-Bill

Battery Terminal Fusing

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