Battery String Fusing??? Anyone want to tackle this one??? :)

[ligwyd]

Hello there,
Hoping to find some help here with my current project.

I have 12 - 12 volt FLA batteries hooked up in 3 strings of 4 batteries each and then paralleled to get 48 volt battery bank.
Below are the batteries I am using.

https://discoverbattery.com/en/product-search/view/12VRE-3000TF-L

I am searching for the best fusing option and install for each of the 3 strings of batteries in my battery bank.
I have found a number of different products but am not sure as to the best way to go and so I am here.....

I have read that fuses should be no more than 7" from the battery string being fused. Is this necessary or just best practice?

Can the fuse on each string be anywhere in between each of the four batteries in each of the three strings?

I found these buss bars which seem just fine for positive/ negative bus bars? Is this the best choice for bus bars or is this overkill?
https://www.bluesea.com/products/2104/PowerBar_600A_BusBar_-_Four_3_8in-16_Studs

Or would these be fine?

https://www.amazon.com/dp/B078VGH8DW/ref=twister_B078VX4Q5W?_encoding=UTF8&psc=1

I read in my charge controller manual page 2-22 in the event of a Ground Fault and the fuse in the Charge controller blows that the aux. output of the charge controller and battery cable connections can be subject to high voltage and as such should be rated for min. 300V (AC rating I am assuming)
https://41j5tc3akbrn3uezx5av0jj1bgm-wpengine.netdna-ssl.com/wp-content/uploads/2018/01/ML201711_Conext-MPPT-60-150-Installation-and-Owners-Guide-975-0400-01-01_Rev-H_ENG.pdf

It is for this reason that I am wondering if all my battery connections and fuses be rated for min 300V as well?

I have some of these fuse holders/ fuses and they should work fine but they are so big and bulky and would require 2 more battery lugs and two more special length 4/0 cables for each fuse installed, even before the cable gets to a bus bar? Maybe this is the best bet just not sure? I would think there may be a better solution out there that I am not aware of yet?
http://www.deltecco.com/fuseblocks.html

I found this Blue Sea product that seems to both act as a bus bar and fuses each of my 3 battery strings in one shot. Perfect I thought, until I see that it is only rated for 58VDC max. It is possible that I will equalize at 64 VDC and the fact that my charge controller manual is calling for min 300V rating, will this product not be the best for this application or is in fine?
https://www.bluesea.com/products/5196/MRBF_Surface_Mount_Fuse_Block_-_Common_Source

Then I find that it is best to keep the battery string fuses within 7 wire inches from the battery string so once again I am thinking this product will not be the best?

So I find these types of fuses:
https://www.go2marine.com/product/202660F/blue-sea-systems-terminal-fuse-block-1-terminal-stud.html

but the bolt for the cable lug is 5/16" and not 3/8" like I need?

Also, what is the best method to use for calculating fuse size for each battery string? I am told 200 amp fuse will be fine but want to be sure.

I am using a Schneider XW+ 6848 than can surge up to 12000watts for 30 secs. I am using 4/0 cable everywhere - for battery inter-connects and right back to the inverter.

Sorry to ask so much in one post.
Thanks in advance for help and support.

[Vic]

Hi John,

To me,   battery string fusing is a topic that is filled with imprecision,   and is very application-specific,   but an important thing to do.   If Insurance companies might be involved,   proper fusing is probably essential.

Was going to suggest that you post your query on the Wind-Sun Forum,   went there,   and,   using the search term,  "   fusing battery strings   ",   your thread was the first hit.

That is a great resource,   over a broader range of topics than are generally covered here.

If you can avoid using Class T fuses (they are very,  very expensive),   that would be a good target,   especially if you bump into nuisance fuse-popping events.

IMO,   those Blue Sea  fusing devices look very good,   and they are a good company,   BUT,  agree that the 58V max limit is simply not high enough for FLA batteries.

Will defer to the comments that you find on the Wind-Sun Forum.

Good luck,   Vic

[mike90045]

I'd prefer to  see larger batteries & fewer parallel strings. 

Perhaps using a breaker, with some lugs pig-tailed onto it, would be workable,
http://www.midnitesolar.com/productPhoto.php?product_ID=202&productCatName=Breakers&productCat_ID=16&sortOrder=15&act=p
175A and you never have to worry about a fuse to replace.  (midnight max fuse is 30A, that I found)

I think it's better to have a breaker fly-wired, than to have nothing.   

HOWEVER, breakers are not explosive atmosphere rated, so if your battery area is not well vented, this may not be for you...
same caution applies to fuses, if they are near batteries, and are not hermetically sealed

[ligwyd]

Thanks Mike and Vic,

Will keep on moving forward and will post what I end up going with. I do agree that bigger batteries in ONE string is ideal and will be what I would like to do in the future. It came down to this is what I had to work with and was more economical with the 12 volt batteries, possibly due MASS production. One guy can move them around too. 142 lbs each. Much heavier than that and you need lifting equip.

I always wonder what the best FLA are for off grid but it seems everyone has their own opinion and budget to work with. In a perfect world 24 - 2v Rolls. What your guys favorite battery or is that way too broad a question?

John

[ligwyd]

I am not sure where I seen it, but has anyone ever heard of a T-class style ignition protected 600V 200 amp fuse that has structural integrity so that is can be directly attached to a battery terminal and  have battery cable attached to the other end of the fuse?

Can the fuse be anywhere in line of batteries that are in series or does it have to be after the last positive battery terminal only?

I'll ask the NAWS guys as well. More info the better
John

[mike90045]

.....I always wonder what the best FLA are for off grid but it seems everyone has their own opinion and budget to work with. In a perfect world 24 - 2v Rolls. What your guys favorite battery or is that way too broad a question?   

If this is a weekend only camp in the woods, it's hard to beat the price point of a pair of 6V golf cart batteries,
for about $200, you get 12V @ 200ah, that should last 3-5 years of weekend use, float charged between weekends. 

A house you live in, depends if 8 of them will be enough (wired in series for a 48V system) to debug the system for a year, and then buy the proper $ize, after all the kinks are worked out.

[Vic]

I am not sure where I seen it, but has anyone ever heard of a T-class style ignition protected 600V 200 amp fuse that has structural integrity so that is can be directly attached to a battery terminal and  have battery cable attached to the other end of the fuse?

Can the fuse be anywhere in line of batteries that are in series or does it have to be after the last positive battery terminal only?

I'll ask the NAWS guys as well. More info the better
John

Hi John,

Regarding a Class-T fuse that has enough structural integrity to  tolerate  mounting on a battery terminal,   and have a battery cable attached to the free end (NO Fuse Mount),    have not seen such a fuse.   AND,   would expect that the uncertainty of what might be the torqueing of the fuse might make most fuse manufacturers  wince at the thought (IMO).

In theory,   in a single string of batteries,   for ignition protected fuses, the fuse could be anywhere in that string.   It might be acceptable to Inspectors that that Class-T fuse be mounted in its holder,   but  supported only be the 4/0 battery cables ...   perhaps not.   Would suggest using the correct holder for the fuse used.

And,   mike90..,  this is the approximate system configuration,
"   ...   I am using 2 Schneider 150's charge controllers in each separate solar system. Each system has 18 - 260 watt Jinko solar panels totaling 4680 watts on each array  ..."   Plus,   IIRC,   a Schneider conext XW+ 6848 (or similar number) inverter,   for each of the two separate systems.   So,  the Ah Capacity of the batteries that John currently possesses   is in the correct ballpark.

YES,   have always  tried to spec a single string of batteries that have sufficient Capacity to do the job intended.   But,  John  owns  all of this hardware,   and is trying to make it work,  in the absence of the original designer/installer.

John,   I  DO like Surrette batteries. All of the battery banks here are (Rolls) Surrette,   and all have been in service for about 12.8 years,   and are doing well.   Agree that 2V batteries would be superior to batteries with more than one-cell per.   13+ years ago,  when we were designing this system,   there were many fewer 2V batteries from Surrette available. The two main banks here are 4V cells,  but the cells are bolted together,  and are removable as single cells,   and  replaceable individually.

FWIW,   more opinions,    Vic

[ligwyd]

Yah I guess it all comes down to budget, knowledge and experience level and of course size of battery bank required and preference of product,...thus many choices of batteries
I guess a guy could call a few local Rolls dealers and ask them what is their most popular battery that is flying off the shelf for off grid and start you investigation there since there might be real good reason why the market is consuming that particular product.
Thanks guys.
Have a great night.
John

[Resthome]

I believe the 7" requirement is a Marine requirement. Don't have the exact regs in front of me. But if your installation is not marine then this does not apply.

[ligwyd]

Good point. I'll check Canadian Code and I'll call my local inspector to involve his knowledge base in the decision.
Thanks.
John