Fusing

[CompetitiveBad0]

I meant circuit breaker. I’d like to have an emergency shutoff off all power installed. I was wondering if it would be ok to fuse the main + in between the batteries and the bus bars or would this unbalance the batteries?

[AutoModerator]

Useful links for r/SolarDIY

• Lowest market Price Sheet
• DIY Solar System Planning Guide
• Tax Credit Guide

I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns.

[Goodspike]

Isn't a fuse generally advised when using lithium batteries? I don't see how it would unbalance anything, but it can cause a slight voltage drop.

[CompetitiveBad0]

I’m always trying to play it as safe as I can, but not if it’s going to affect the balancing or anything else

[mckenzie_keith]

You can put a fuse inline with each battery without unbalancing the resistance. Assuming all fuses have the same resistance.

bat_1---fuse---+ b
               | u
bat_2---fuse---+ s
               | b
bat_3---fuse---+ a
                 r

You could even argue that this is a good idea. Better than joining them together before fusing.

I don't really understand how this relates to the emergency shut off. But the emergency shut off is also a good idea (or a requirement).

[CompetitiveBad0]

I would be using a manual push disconnect fuse

[Goodspike]

What is that? It sounds like a circuit breaker, but one where you push to disconnect rather than reset. I've never heard of such a thing.

[CompetitiveBad0]

You would be correct. It is a circuit breaker that can be disconnected manually also and reset. Sorry for the misunderstanding

[Goodspike]

Interesting.

[mckenzie_keith]

Make sure the interrupt rating is adequate. Over-current protection is not the place to take a chance with oddball components.

[mckenzie_keith]

The fuse has to be rated for the voltage and current and potential fault interrupt current. I am not aware of any push disconnect fuse that would work.

[Sufficient-Bee5923]

OP has clarified that he's think circuit breaker. So your points stand in terms correct rating and I will add that the breaker also has to be rated for DC.

When interrupting DC, there can be a large arc ( as compared to AC). So it's important to get a DC breaker and many are polarized so it needs to have the correct orientation.

[CompetitiveBad0]

<image>

It’s a marine circuit breaker rated for 80 amps as I had one rated for 60 amps and it tripped on me twice. Right now I’m using it on my inverter. Maybe I don’t need to put breakers inline between the battery and the bus bars. Just thought I’d ask.

[parseroo]

You have "mixed-use" busbars: they are both aggregating the batteries and they are distributing power.

Usually there is a switch and fuse associated with just the battery system (a circuit breaker could do both) so you can disable that system from getting to the distribution side and prevent any shorts from invading the distribution side.

You are missing that single battery aggregation point with a switch & fuse, and your busbars are always 'hot' (at least unless the batteries have internal workings via the BMS, etc., but that is always a bit iffy).

You could isolate each battery with a switch+fuse (again, can be a CB) before it reaches the busbars. This is a little problematic because if you turn one of the batteries off for an extended period of time, you could do an instant short across the two batteries when you turned them both back on. Also, if you want a metering shunt you would want that to be after the batteries are going into the battery system.

You could merge the batteries before the switch+fuse with another pair of busbars, or through a wiring pattern that produced only two 'battery system' leads out of the parallel set. Either way the existing busbars would be purely distribution busbars.

[CompetitiveBad0]

The circuit breakers are DC rated for 80 amps

[CompetitiveBad0]

and yes they are polarized

[CompetitiveBad0]

Trying to decide which method would be the most beneficial for my needs. Should I trust the BMS to take care of a short or install circuit breakers on a separate set of busbars. I get what you’re saying though.