Battery Fuse

[markz]

Do I fuse the entire pack, or if going parallel first then series would it be better to fuse each grouping of parallel packs?
What rating of fuse am I suppose to use, given a certain expected peak amperage level?
Is it crucial not to parallel fuses, or is that for more picky circuits?

I bought 9 of these
https://www.be-electronics.com/ProductDetails.asp?ProductCode=BK/AGC30

BUSS 1/4"X1-1/4" FAST-BLOW GLASS 32V FUSE *ROHS* BK/AGC30 30A/30AMP

 

[riba2233]

You should fuse entire pack, fuse positioned as close as possible to pack main positive pole. Your fuse should protect cables, so you pick a fuse that will burn before cable does.

 

[dmwahl]

Like riba said, fuse the entire pack. Doesn't matter if you do it at the positive or negative terminal unless your pack is not isolated from ground or your frame. Fuses will have an AC rating and a DC rating, or sometimes only be rated for AC. Choose a fuse where the DC rating is greater than your maximum current and voltage. If you search ebay for "ferraz shawmut fuse" you'll find a bunch of high voltage fuses. The ones you bought are under-rated for the pack mentioned in your signature.

Personally I use an 18S LiFePO4 pack with 150A fusible links between cells 6-7 and 12-13, and a 60A 500VDC rated main fuse. The fusible links are just a backup in case something goes wrong with the main fuse or I drop a wrench across the pack, etc. I had them sitting around so I used them.

 

[markz]

Would this be good, or do I need a higher amperage rating for my 18fet 65A controller?
http://www.solarwholesaler.ca/shop/din-rail-circuit-breakers-63a-150vdc-pv-array-breaker/
http://www.be-electronics.com/product_p/ecsr60.htm

 

[dmwahl]

Depends on how long the breaker or fuse will allow the rated current before opening, check the datasheet. Many fuses will operate at their rated current for a decent amount of time, maybe even a minute or two before opening. All depends on how fast the element heats up and melts.

 

[markz]

Found this one
https://www.acklandsgrainger.com/AGIPortalWeb/WebSource/ProductDisplay/globalProductDetailDisplay.do?item_code=WWG13M228&searchClick=true
with these specs
http://www1.cooperbussmann.com/pdf/ca7bf020-a650-47b5-b830-2a2759eb6716.pdf

Found this site useful.
http://forum.allaboutcircuits.com/threads/sizing-fuses-for-6-to-36-volt-storage-battery-test-supply.76730/

So for a 20Ah, 60-72Vdc, for battery protection, if shorted the amps would be huge. So a fuse thats dc voltage rated to my battery (or close, or maybe just dc rated as long as its higher then battery voltage), and 1.25x the 65A controller limit and placed within 12" on the positive wire?

Heres a search done
https://endless-sphere.com/forums/viewtopic.php?f=35&t=73145&p=1104966&hilit=100A+fuse#p1104966

should have added that the 100amp fuse is what I use on an 8s battery pack designed for a max speed of 25mph. You start tickling the specs when you push towards 30mph and beyond.

A rough "rule of thumb" is to size your fuse 13% higher than the maximum spec of what you are trying to protect.

and
https://endless-sphere.com/forums/viewtopic.php?f=9&t=73623&p=1110987&hilit=100A+fuse#p1110987

- - 12/10awg quality silicone wire, 4mm bullets, anderson 45a connect quick parallel/series connection secured in mountable chassis, inline 100a fuse, XT150 for batt>ESC connector. Tested up to 85a battery>ESC output.

 

[dmwahl]

So for a 20Ah, 60-72Vdc, for battery protection, if shorted the amps would be huge.

That's right. It will depending on the internal resistance of the cells you're using as well as any resistance due to wires, cell interconnects, etc. You can get a rough idea by watching voltage drop vs amps. For example... on my pack at 80A of draw the voltage at the controller drops by about 15V, 15V/80A = 0.19ohm. I know from other testing that the cells themselves are responsible for about half of that drop, so I assume my total pack internal resistance is about 0.1ohm. Since the maximum voltage is about 66V hot off the charger, I figure a short circuit would produce around 66V/0.1ohm = 660A, well within the interrupt rating of the fuse.

So a fuse thats dc voltage rated to my battery (or close, or maybe just dc rated as long as its higher then battery voltage), and 1.25x the 65A controller limit and placed within 12" on the positive wire?

Heres a search done
https://endless-sphere.com/forums/viewtopic.php?f=35&t=73145&p=1104966&hilit=100A+fuse#p1104966

should have added that the 100amp fuse is what I use on an 8s battery pack designed for a max speed of 25mph. You start tickling the specs when you push towards 30mph and beyond.

A rough "rule of thumb" is to size your fuse 13% higher than the maximum spec of what you are trying to protect.

and
https://endless-sphere.com/forums/viewtopic.php?f=9&t=73623&p=1110987&hilit=100A+fuse#p1110987

- - 12/10awg quality silicone wire, 4mm bullets, anderson 45a connect quick parallel/series connection secured in mountable chassis, inline 100a fuse, XT150 for batt>ESC connector. Tested up to 85a battery>ESC output.

Be careful with rules of thumb like 1.25x controller current or 13% higher, there are so many types of fuses that there's no one guideline that will work for every application. I use a 60A main fuse, but see peaks of 80-90A. It's fine because even at 90A, it takes a minute or so to blow. You really need to go off of the melting time vs current graph in the datasheet. Based on the datasheet you linked to, the 60A fuse will take a long time to actually blow at 60A. It also looks to be AC rated only.

 

[markz]

Thanks, I tried to read the specifications sheet but couldnt understand it. Theres a 60A for the same price, but the 70A is double the price.

How long would the 60A fuse hold up before it breaks, at 80+A?
Would my 65A 18fet controller spit out more before it fries?

 

[dmwahl]

Thanks, I tried to read the specifications sheet but couldnt understand it. Theres a 60A for the same price, but the 70A is double the price.

How long would the 60A fuse hold up before it breaks, at 80+A?
Would my 65A 18fet controller spit out more before it fries?

Find the line for the particular fuse you're evaluating, then draw a vertical line from the current you want to draw and find where it intersects the fuse's line. Then draw a horizontal line over to the time axis from that point and you have your approximate time before the fuse blows. At 80A it looks like the 60A part will take a few minutes at least, if if ever opens.