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Questions about my DIY bussbars

toolguy

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Mar 13, 2021
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Hello,
I am new to the DIY solar game and have learned a lot from all the experts on this forum. I am building a 8s LiFePo battery with Eve 280 ah cells. This is a fun project to run my garage on solar only, even though there is grid power there now and the loads on my inverter can be varied at will if need be. I am going to use a 4k low frequency inverter, with an estimated constant load of around 1800 watts (mini split a/c heater, freezer, refrigerator, lights) with occasional periodic power tool loads such as a drill, air compressor, table saw, etc.
Assuming I high side my normal load as 2,000 watts, and a voltage of 26.4 volts feeding my inverter, I calculate 75.75 amp draw. I am using 1/0 cable to power my inverter which should be rated for 150 amps so that should be more than enough.
If I use a 4,000 watt load (inverter size) at 26.4 volts, I calculate a potential draw of 151.5 amps which would only be for brief periods of time, so my 1/0 cable should still be fine.
My wire should still handle even a momentary surge above 4,000 watts for a motor start.

My bussbar sizing is where I am unsure. I believe I have over engineered them, but I would like some experts to weigh in please.
From what I could find online, the formula to calculate capacity of a copper bar is ' 1.2 x width(mm) x thickness(mm) = ampacity'.
Since I want to size the potential draw to equal the inverter size, a 1" x 3/16" works out to 1.2 x 25.4mm x 4.7643mm = 145 amps which is a little small according to my calculation. A 1" x 1/4" bar works out to 1.2 x 25.4mm x 6.35mm = 193.5 amps. Using this figure as a continuous load (which would never happen) I should be capable of pulling 5,108.4 watts at 26.4 volts.

My questions for the experts here are:
Are my formulas and calculations correct?
Have I gone overboard or is this how you would size the bussbars?
Is my 1/0 inverter wiring sufficient?
I am planning to use a 150 amp ANL fuse to match the 1/0 cable. This could potentially be a problem on a motor start surge, depending on how quick those fuses blow. Never done this before. Should I be looking at a breaker instead of a fuse? If so, what do you recommend?
Any other expert suggestions or critics me are welcome! Thank you in advance for any responses.
 
Not sure about the bus bar calculation method. I just use cross section vs. awg charts

1" = 25.4mm
3/16" = 4.7mm

4.7 * 25.4 = 121mm^2

4/0 cable is 120mm^2, so your 3/16 x 1" bus bars have more cross section than 4/0 cable.

4/0 cable with 90°C insulation is rated for 260A. Without insulation, they can carry a boatload more.

2000W/25.6V/85% = 92A

1/0 w/90°C insulation can handle 170A

Consider a class T fuse.
 
I use this resource and open the charts and purchase based off ampacity.


If this helps, I use the BlueSea fuse charts and Blue Sea fuses:

DA5B2E22-2DD3-4EA9-963D-35D30EA69009.jpeg
 
Not sure about the bus bar calculation method. I just use cross section vs. awg charts

1" = 25.4mm
3/16" = 4.7mm

4.7 * 25.4 = 121mm^2

4/0 cable is 120mm^2, so your 3/16 x 1" bus bars have more cross section than 4/0 cable.

4/0 cable with 90°C insulation is rated for 260A. Without insulation, they can carry a boatload more.

2000W/25.6V/85% = 92A

1/0 w/90°C insulation can handle 170A

Consider a class T fuse.
I had a feeling what I was coming up with was way overkill, but I'm no electrical engineer and was using what I could find.
I don't know what the difference is or advantage to a T-1 fuse, I will try to research it. I'm not so much worried about a few more bucks if I can get a safer or more reliable product. The last thing I want is a fire because of an inferior component.
 
I use this resource and open the charts and purchase based off ampacity.


If this helps, I use the BlueSea fuse charts and Blue Sea fuses:

View attachment 76338
Oh, thank you for the bussbar chart! This a so much better info and makes a lot more sense. The more I dig, it does appear that Blue Sea is the place to go.
Would it make sense to use a 150 amp Blue Sea breaker instead of the T-1 or ANL fuse with a separate on/off switch? I'm thinking out loud here, I could eliminate the need for a switch by using the breaker as circuit protection and have the ability to switch the breaker off if needed?
Thanks for all the feedback, guys!
 
Oh, thank you for the bussbar chart! This a so much better info and makes a lot more sense. The more I dig, it does appear that Blue Sea is the place to go.
Would it make sense to use a 150 amp Blue Sea breaker instead of the T-1 or ANL fuse with a separate on/off switch? I'm thinking out loud here, I could eliminate the need for a switch by using the breaker as circuit protection and have the ability to switch the breaker off if needed?
Thanks for all the feedback, guys!
I believe I found the answer to my own question. No, I don't want to use a breaker instead of the fuse and a separate on/off switch.
Yes, I do need a Class T fuse because of the extremely high AIC rating required for the LiFePo battery and a separate master switch.
 
Yes to the Class T fuse and master switch. Circuit breakers can be used in other places - be sure they are true DC rated breakers though.

I would be careful about the surge from the air compressor and the table saw.

I didn't catch which BMS you plan to use.

Where are these DIY bus bars used? Is it between the battery cells? Or, is it for a common bus bar where the various components will all connect?
 
Yes to the Class T fuse and master switch. Circuit breakers can be used in other places - be sure they are true DC rated breakers though.

I would be careful about the surge from the air compressor and the table saw.

I didn't catch which BMS you plan to use.

Where are these DIY bus bars used? Is it between the battery cells? Or, is it for a common bus bar where the various components will all connect?
I am using a Daly 250 amp BMS.
I do plan to test the start and run loads on those tools, and like I said before, I can always continue to run any loads off grid power if need be. My off grid project is being built with separate circuits and outlets. At some point my plan would be to shut off the grid power once I see if everything can be powered by solar. The plan at some point is to build another identical battery to run parallel for more capacity.
I should have made myself more clear. Yes, the bussbars in question are the cell connectors. There will be a 1/0 cable from the battery to the inverter about 3' long with another fuse or breaker near the inverter.
 
Would it make sense to use a 150 amp Blue Sea breaker instead of the T-1 or ANL fuse with a separate on/off switch?
I have not found a good DC circuit breaker in the Amperage I wanted to use on a battery because of AIC. The AIC means that if your breaker, say 50 amps trips, the current between the tripped poles will not arc across the closed circuit. Lithiums can push a lot of amps, more than lead and it becomes a factor.
 
I have not found a good DC circuit breaker in the Amperage I wanted to use on a battery because of AIC. The AIC means that if your breaker, say 50 amps trips, the current between the tripped poles will not arc across the closed circuit. Lithiums can push a lot of amps, more than lead and it becomes a factor.
Thank you, chrisski. I had not heard of AIC before posing this post on the forum. It's amazing how the more I learn, the more I realize I don't kinow. I am guessing as long as I have a good Class T fuse at the battery for ultimate protection that I could put a good quality breaker downstream near the inverter.
 

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