How stupid is this?

[offgrid-curious]

I am not saying you're wrong, but it doesn't make sense to me that 2 busbars clamped together create resistance, but individual copper strands which are not clamped together don't.

My point is that everything has resistance. The reason you want to minimize the number of connections in your system is because every time you are connecting something together you are adding more resistance to the system. The reason you might use 2/0 gauge copper wire instead of 20 gauge copper wire to connect your battery to your inverter is because the resistance of the 20 gauge wire is too high. It's also why we are using copper wires instead of say, rubber wires; because they have lower resistance.

A similar example is the JK-BMS ships with 2 connect wires instead of 1 for its connections, presumably to lower costs because 2 thinner wires is cheaper than 1 thick one with the same cross-sectional area. Would you advise JK to use only a single thinner wire, because adding a 2nd creates resistance? Again, not saying you're wrong, I just genuinely don't understand your logic.

I think that with the JK BMS there are two wires instead not just because it's cheaper, but it also allows more flexibility. They also use silicon wires that can withstand higher temperatures, so they handle more current. There's nothing wrong with two wires on the JK BMS, because like you said it works out to the same cross-sectional area of an equivalent single wire. You can also terminate both of the wires into a single lug instead of using two separate lugs.

 

[kolek]

You can also terminate both of the wires into a single lug instead of using two separate lugs.

That's also a really good point I didn't think of.

 

[Q-Dog]

Hey @Q-Dog thanks a LOT for the picture, I'm no expert but that is beautiful work. When you say the bars on the disconnect were doubled, do you just mean where they visibly overlap in the picture, or you actually stacked busbars to gain a thicker connection?

I stacked 2 bars to get enough mass for 300 amps.

edit to add, Blue Sea and BEP make link bars and joiner bars that are a little more substantial than battery bus bars, and are made precisely for what you want to do. Here's a link.

Link Bars

 

[kolek]

I stacked 2 bars to get enough mass for 300 amps.

edit to add, Blue Sea and BEP make link bars and joiner bars that are a little more substantial than battery bus bars, and are made precisely for what you want to do. Here's a link.

Link Bars

But according to @offgrid-curious, by stacking them you actually are increasing resistance. What's your thinking on that?

 

[offgrid-curious]

But according to @offgrid-curious, by stacking them you actually are increasing resistance. What's your thinking on that?

Don't read too much into this. It can be increasing resistance, but it may not be significant assuming you're doing it right. For example, do you know why you want to properly torque your connections? Because if you have loose connections that increases the resistance between the connection, which is what leads to heat and potentially fire. But if you've properly torqued your connections the resistance will be minimal.

 

[kolek]

Don't read too much into this. It can be increasing resistance, but it may not be significant assuming you're doing it right. For example, do you know why you want to properly torque your connections? Because if you have loose connections that increases the resistance between the connection, which is what leads to heat and potentially fire. But if you've properly torqued your connections the resistance will be minimal.

lol offgrid-curious, you're turning my mind into a pretzel. 1 busbar is better, 2 are better, now I have no idea which is better.

 

[kolek]

For example, do you know why you want to properly torque your connections?

No actually I was gonna just kinda lay the nuts on top of the lugs gently without actually tightening them, and put a tortilla between the 2 busbars.

 

[wpns]

But according to @offgrid-curious, by stacking them you actually are increasing resistance. What's your thinking on that?

You are increasing the resistance at the ENDS of the busbars, just like individual copper strands it's the ends that matter.

 

[offgrid-curious]

No actually I was gonna just kinda lay the nuts on top of the lugs gently without actually tightening them, and put a tortilla between the 2 busbars.

You laugh but look at the number of posts in the Up in smoke section that are caused by bad connections!

 

[Checkthisout]

Or just switch to cables and then you can orient the breaker up/down, place it wherever you want and use the standard connections on the power-in as well as not having to shrink wrap and bend the bus bars or use spacers so the height between the breaker connections and power-in match.

You'll know you're setup is successful if you CAN'T brown a tortilla at the connections when the system is under full load.

 

[kolek]

You'll know you're setup is successful if you CAN'T brown a tortilla at the connections when the system is under full load.

lol. Gracias amigo for putting this in terms that even my small Mexican brain can understand.

 

[Hedges]

But according to @offgrid-curious, by stacking them you actually are increasing resistance. What's your thinking on that?

Stacked busbar is in parallel, decreases resistance.
The second busbar has contact resistance in series, so maybe:

0.0001 ohm busbar || 0.00005 contact + 0.0001 bus + 0.00005 contact = 0.0000667 ohms

(those numbers don't even qualify as SWAG, only placeholders.)
Because path through stacked busbar is greater, current doesn't split evenly. At current so high both are needed, too much current through lower one overheats it.

In theory. Because these are bare, they will dissipate heat to air well.
If these were cables, I'd stack A on top of B at one end, B on top of A at the other. Busbars, can't change order.

Various jumpers for lithium cells were offered, some solid, some several sheets stacked similar to yours.

 

[wpns]

Because these are bare, they will dissipate heat to air well.

The OP has promised to cover them for safety. 8*)

I like the concept of bus bars, but I like the flexibility of cables better for this application.

 

[kolek]

Stacked busbar is in parallel, decreases resistance.
The second busbar has contact resistance in series, so maybe:

0.0001 ohm busbar || 0.00005 contact + 0.0001 bus + 0.00005 contact = 0.0000667 ohms

(those numbers don't even qualify as SWAG, only placeholders.)
Because path through stacked busbar is greater, current doesn't split evenly. At current so high both are needed, too much current through lower one overheats it.

In theory. Because these are bare, they will dissipate heat to air well.
If these were cables, I'd stack A on top of B at one end, B on top of A at the other. Busbars, can't change order.

Various jumpers for lithium cells were offered, some solid, some several sheets stacked similar to yours.

Thank you @Hedges This actually makes sense to me.

 

[bolhuijo]

If these were cables, I'd stack A on top of B at one end, B on top of A at the other. Busbars, can't change order.

You're not trying hard enough.

 

[wpns]

How about making your own out of copper pipe? 8*)

 

[Checkthisout]

How about making your own out of copper pipe? 8*)

Or just make cables.

 

[Q-Dog]

But according to @offgrid-curious, by stacking them you actually are increasing resistance. What's your thinking on that?

The manufacturer recommends stacking them for more capacity.

 

[Q-Dog]

Stacked busbar is in parallel, decreases resistance.
The second busbar has contact resistance in series, so maybe:

0.0001 ohm busbar || 0.00005 contact + 0.0001 bus + 0.00005 contact = 0.0000667 ohms

(those numbers don't even qualify as SWAG, only placeholders.)
Because path through stacked busbar is greater, current doesn't split evenly. At current so high both are needed, too much current through lower one overheats it.

In theory. Because these are bare, they will dissipate heat to air well.
If these were cables, I'd stack A on top of B at one end, B on top of A at the other. Busbars, can't change order.

Various jumpers for lithium cells were offered, some solid, some several sheets stacked similar to yours.

I think you guys are overthinking this.

 

[timselectric]

Busbars, can't change order.

In this case, they actually do.
Look at the picture again.