Using only one fuse on a battery with SCC ?

[meetyg]

Hi there.
Having seen some of Will's beginner videos and read across his site, I'm a bit confused and would appreciate your help.

For example in this video, he uses only one fuse on the battery for the load and the SCC:

I understand that you should have a fuse directly on the battery.
Is it wise to connect loads and the SCC to this one fuse?

If the load shorts for some reason, the battery will be protected.
But won't that cause damage to the SCC in some way ? If so, does it matter if its a PWM or MPPT?
Shouldn't we be putting a separate fuse to from the battery to the SCC ?
I suppose the SCC has some capacitors/FETs in it, won't these be damaged due to a short on the battery side (or at least cause a spark/arc)?
For my use case I'm talking about 12v/20Ah SCC and LifePo4 battery - does it make a difference if its a larger system (lets say 24v/48v and a few hundred amps)?

I thought about using one of those 30A reset-able circuit-breaker fuses on my battery, because it also allows me easy disconnect if I need to do some maintenance on my setup.




Would you recommend it, or should I get a proper disposable fuse?

Thanks

 

[circus]

Shouldn't we be putting a separate fuse to from the battery to the SCC ?

I did. Used a sacrificial fuse considering output from the controller is fixed.

 

[mikefitz]

Fuses or breakers are used in battery systems to protect from over current in the cables and whatever is connected on the end of the cable. The rating of the fuse/breaker will normally be rated at 125% to 150% of the current capacity rating of the cable. Best practice is to add fuses/breakers to every feed from the battery.

Many of the demonstration videos and illustrations do not show correct and safe over current protection.

Suppose your charge controller develops an internal fault that is equivalent to a short circuit within the unit, or the cable is damaged in some way that results in a similar short. Without over current protection directly on the battery, or very near to the battery, the charge controller and/or the cable will be supplied with all the current the battery can supply. For a battery without a BMS, or a failed BMS, this could be several thousand amps, Even with a working BMS the current could still be 100s of amps.
Cables and components will melt and perhaps catch fire, shrapnel from failed and melted parts could cause injury.

Fuses or breakers, unless there is a need to frequently isolate part of the system I prefer to fit fuses. Some of the lower cost breakers are unreliable.

Mike

 

[meetyg]

Thanks for the info.

I think I will put a fuse (ANL type) directly on the battery (like Will shows in a more advanced video), and then connect the breaker just for added safety and convenience.

I guess I will also fuse the SCC separately.
Just wanted to make sure that I'm understanding this. At first I was gonna go the simple way, one fuse for both load and SCC connections. But as this will a vehicle mounted system, I prefer to make it as safe as possible.

 

[Cavendish]

May I ask is it a good idea to use a bussbar to connect a Fuse to the battery main positive?
Seems safe and saves wire/lugs and distance between battery and fuse.

 

[12VoltInstalls]

May I ask is it a good idea to use a bussbar to connect a Fuse to the battery main positive?
Seems safe and saves wire/lugs and distance between battery and fuse.

Main feed cable fuse from battery should be at the battery between battery and busbar. It should be appropriate for the cable amp rating plus 20%-25%
The fuses appropriate for that connection are usually equipped with an eyed tab that is sorta its own ‘bar’ and can be bolted directly to the battery and then cable to the busbar is bolted on the protected side of the fuse.

 

[Cavendish]

Main feed cable fuse from battery should be at the battery between battery and busbar. It should be appropriate for the cable amp rating plus 20%-25%
The fuses appropriate for that connection are usually equipped with an eyed tab that is sorta its own ‘bar’ and can be bolted directly to the battery and then cable to the busbar is bolted on the protected side of the fuse.

Thank you. I can't find the fuses usually used in a high enough amp rating (300a) available nearby. Would one like in the photo attached be acceptable?

 

[12VoltInstalls]

Would one like in the photo attached be acceptable?

There’s breakers like that I’ve used on jeeps with 300-375A potential winches and as alternator cutout on high-amp output jeeps - again with winches. This stopped “Bad Things” when heavy winching that was apparently creating a lower potential on the PDC at high draw and the PDC would melt, catch fire, or both.
But they are cheap imports. I wouldn’t use them for your battery cable safety device.

Buss, BlueSea, and another brand that escapes me at the moment offer quality breakers in that style. They might all actually be made by bussman?

Even then at 300A I’d use a fuse.

Add to that’s the knowledge I gained right here a while back in a thread discussing the amp rate of LiFePo battery cables being closed to a dead short and more recently: the factor of an arc not breaking with a LiFePo dead short discharge you learn a Class T fuse is really the only suitable choice.

Not familiar with scorpion-brand but I don’t even think the bussman breaker is suitable for 10,000 gagillion amps or whatever.

 

[Cavendish]

There’s breakers like that I’ve used on jeeps with 300-375A potential winches and as alternator cutout on high-amp output jeeps - again with winches. This stopped “Bad Things” when heavy winching that was apparently creating a lower potential on the PDC at high draw and the PDC would melt, catch fire, or both.
But they are cheap imports. I wouldn’t use them for your battery cable safety device.

Buss, BlueSea, and another brand that escapes me at the moment offer quality breakers in that style. They might all actually be made by bussman?

Even then at 300A I’d use a fuse.

Add to that’s the knowledge I gained right here a while back in a thread discussing the amp rate of LiFePo battery cables being closed to a dead short and more recently: the factor of an arc not breaking with a LiFePo dead short discharge you learn a Class T fuse is really the only suitable choice.

Not familiar with scorpion-brand but I don’t even think the bussman breaker is suitable for 10,000 gagillion amps or whatever.

Thank you, very helpful ? appreciate your help/ time

 

[meetyg]

May I ask is it a good idea to use a bussbar to connect a Fuse to the battery main positive?
Seems safe and saves wire/lugs and distance between battery and fuse.

I would put the fuse as close as possible to the battery. The reason for this is to avoid any shorts that might occur from the battery leads, like while doing installation/maintenance. Other than that, using a bussbar should work just fine.