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Question about Bus Bar needs, & suggested alternatives to Victron Bus-Bars?

coreyzev

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I am building a 48v 300Ah system, planning to get a 3000W or 3500W Inverter/charger, and have about max 70A of solar charging ability. Running an off-grid RV, including 1 inefficient AC, 1 desktop PC, and other basic RV things both 12v & 120V.

I am pretty sure I dont need a 1000A bus-bar, and would like to not pay for that if I dont need it. But I'm a bit confused on how to find an alternative. For what it is, the Lynx Power In or Distributor really arent that badly priced, but I'm curious if there's a better option for me.

So, by my calculations, I technically shouldn't really be hitting anything over 120A (inverter does about 5500W peak), so do I only need a 150A bus bar? Or do I need to consider more things? Possible different loads at the same time?

I've been looking for comparable bus bars and have found these so far, they have much lower load ratings than Victron's, but also cost less, but possibly not enough less?:
Is 300A enough for me?

That's a lot of questions, thank you for reading.

Corey

EDIT: Does it matter if it's MEGA or other types of fuses? I will research this more tomorrow, but I need to sleep now.
 
Treat bus bars just like wire. A bus bar should be able to handle as many amps as the biggest wire connected to it. Another way to look at it is that the bus bar must be able to handle more amps than the biggest fuse on the wires connected to the bus bar. The fuses/breaker MUST ALWAYS be the weakest link. The wire and bus bars MUST ALWAYS handle more amps than the fuses/breakers.

With 5500W at 48V you will likely end up with 1AWG wire and a fuse around 175A - 200A*. Given this you should be able to use a 250A bus bar. Of course, like wire, you can go bigger. It would be fine to use a bus bar that can handle 300A, 500A, even 1000A. But 250A is likely enough. However, work out your whole system first to be sure. Nail down every wire and their gauge, every fuse/breaker and their size, then you can determine the final size needed for the bus bars.

* 5500W / 48V / 0.85 efficiency = 135A for the wire. 135A * 1.25 = 170A for the fuse. The 1AWG can handle a max of 250A fuse under the right conditions.
 
I have used this type of busbar on a system that occasionally sees 200a, and regularly sees 100a.

I use this type of fuse/disconnect. You can get a 300amp version, it is physically larger.
 

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Follow up question, I see lots of bus bars rated for only 12V or 24V, I was going to do a 48V system. What decides the voltage limits for a bus bar?
 
Generally speaking, amp ratings are determined by the current carrying capability of the conductor, and the voltage rating is determined by the insulation level, or the ability to prevent the current from jumping from one conductor to another, whether that's positive to negative, or just to ground. A higher voltage rating would indicate either thicker insulation, or insulation with a higher dielectric value.
 
The busbar voltage limit is probably because for human safety, access to voltages above 48V (like battery being charged) is supposed to be restricted.

Compute IR drop of wires based on maximum surge current.
If that is only seconds not minutes, ampacity (self-heating limit) can be sized according to continuous rather than surge current.

3500W continuous / 42V low-voltage disconnect / 90% efficient x 1.25 to avoid nuisance trips x 1.12 ripple factor = 130A

So I would say fuse should be at least 130A, and wire ampacity equal or greater to fuse.

"Ripple Factor" is my contribution you won't find anywhere else.
The capacitors in an inverter are only big enough to smooth out high frequency switching; they can't absorb 60 Hz cycles of current (as AC voltage goes between zero and +/-170Vpeak.)
Current in battery cable will be a rectified sine wave, at full-load of inverter dropping to zero and cycling to peak.
Power delivered to inverter is battery voltage x "mean" average current.
Power dissipated in wires is "rms" current ^2 x resistance.
RMS current is 12% higher than mean, so I multiply by 1.12 to size wire & fuse.

(funny how close to your 120A figure I got, by a rather different method.)
 
Also, how does a inverter/charger work in an off grid system?
It's a little hard to take your opinion/rec seriously with this question.

A) it takes the DC power and turns it into AC power.
B) it takes Shore or GenSet AC Power, and turns it into DC Power for charging or powering.

Would you care to explain why you think 48V is too high?
 
Update, 48V is the only way to get the amount of power I need in a system as small as I have.
 
The voltage limit on a bus bar doesn't make sense to me. There's nothing mechanical or electronic about a bus bar. A circuit breaker? Yeah, I can see voltage being an issue there.

My opinion on bus bars is that if it satisfies the amp rating the next most important requirement is the number of studs. I have four studs on mine and wish I had six. I'm using common bus bars rated at 250 amps.

I run 12v in my toy hauler with 1280 watts of PV. I don't yet have a big enough inverter to run the air conditioner and microwave. But when I upgrade in the future, I will continue with a 12v system and don't expect any major issues. 24v would be a bit more efficient, but I see no need at all for 48v in my scenario.
 
but I see no need at all for 48v in my scenario.
Tho i really dont want to derail this thread, it's because I plan on putting nearly 3kW of solar on my roof. I can now do it with a 70A or 85A SCC, and much smaller wires. Going down to even 24V means I'm putting 112A Impp thru the solar wires.

Hopefully that's the end of that. (I realize you're likely talking specifically about your own, but I wanted to further clarify).
 
Going down to even 24V means I'm putting 112A Impp thru the solar wires.

Through SCC wires to battery, not through PV wires.

How big a battery? Make sure 3kW of charging doesn't exceed its specs.
Even if it is happy with that much while at nominal temperatures around 25 degrees C, if lithium the max charge current reduces at lower (or higher) temperatures. That could be as low as 0.05C down under 10 degrees C, but above freezing.

I would suggest setting a low-temperature charge disconnect, and maximum charge current, which together protect battery.

Ideally, SCC delivers enough current to charge battery at appropriate current, plus current for loads present at the moment.
That can be accomplished several ways. But a dumb SCC not talking to anything else doesn't know where the current is going.
 
Through SCC wires to battery, not through PV wires.
Through PV wires too.
Hmm... you're right. Back when I made that decision I didnt understand Impp vs Isc well yet. That said. I already bought a 150/85 SCC.

battery is 48v 300ah, using the battery hookup 3.3v 100ah cells. Only 1 BMS. 16s 100A. Will definitely be setting those protections in both the battery BMS, and the Inverter/charger.

Likely doing victron for everything, so they'll be talking.

1633631374162.png1633631430244.png

and this is what we're looking at when it comes to my current build.
 
Roughly 14.4 kW of battery, so 3000W is 0.21 charge rate.
You might just set a minimum charge temperature where that is acceptable.
If not documented for your cells, use spec for brands that do give current vs. temperature.


If your panels are tilted rather than flat, using multiple orientations can reduce peak current and extend hours of production.
(All panels in series need same orientation. Multiple strings need to be same number of panels in series, but each string can be of different orientation.)

With Victron, you can connect a battery shunt and some sort of Victron monitor, which will command SCC to adjust its current.
But not necessarily required, depending on available current and low-temperature cutout.
If you have other sources of charging (e.g. shore power), you could still get too much current if PV active at same time.
 
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