diy solar

diy solar

Fusing and busbars

I don't feel like I have enough low-amp devices to justify an entire fuse block. And I need more disconnects, sooooooo...

Surface-mount breakers it is! A 30-amp on each SCC and a 70-amp on the charger. Additional plain battery disconnect switches on the battery (between fuse and busbar) and the rooftop solar panel line coming in to the MPPT SCC.

In your voltage range and for those amperages, Square-D QO breakers have suitable DC rating.
Although, with a steel box it might be more weight than you want.
They have boxes with slots for 2 single-pole breakers, 6, 8, 12, maybe other sizes in between.

DIN rail breakers are another option. I have some in a a couple PV combiner boxs for DC, others in parts of my AC system.
Once you mount a DIN rail, it is a convenient place for breakers, fuse holders, relays, connector blocks, and more.
 
OK I AM DONE!

Finally ordered all these pieces/parts. Had to just stop trying to nail down certain details, give up on some perfectionism, and click on the 'complete your order' button. Parts will be arriving next Thursday in an RV park in New Mexico. I'll be there about two days before.

Incredible weight off my shoulders to just *decide* - which is ridiculous. And yet that's how it feels.

Might stay off any solar-related forum for a week or so. LOL
 
Remember Rule Number One. Fuses protect wires. That means size the fuse to the wire AWG and insulation rating.
My opinion. Only use dc breakers on the branch circuits were you might use ST blade type fuses. . Use fuses on the main higher ampere circuits, and charging circuits. Except for catastrophic fuse at positive LiFePo, a Class-T 300A. I use MRBF on the positive BusBar for all the main circuits.
 
That means size the fuse to the wire AWG and insulation rating.
I agree with the sentiment, but I look at it as "Size the wire to the fuse".

1) Figure out the max continuous current.
2) Multiply max Current by 1.25 to determine fuse size that will be placed at the current source.
3) Pick wire that is rated for the fuse size.

1.25 x Max Current < Fuse < wire rating
 
Still short some ring terminals. Local Harbor Freight has some! Their welding department is a lifesaver. #2 and #4 AWG ring terminals in 1-2 different ring sizes. Copper.

Have SO. MANY. CABLES. to cut and strip and crimp. Will be adding 2 disconnects, 3 surface mount breakers, one ground bar and two busbars. Hope I can fit all this on my existing backing board! Will have three days before we have to skedaddle. Fun?
 
I do get quite a few things at HF. Some aren't half bad.


Is there as little meat left around the hole as picture shows?

"Extra Long Barrels with Flared Ends Attach Easily to Welding Cables"

Sure doesn't look flared to me.

At least it is copper.
I bought "Copper" jumper cables at Big 5 to replace mine after an automotive burglary (hatch window cost me way more to replace.)
Turned out they were "Copper (CCA)" which means "Aluminum"
 
I do get quite a few things at HF. Some aren't half bad.
HF is great in a limited way. For certain categories they have functional items at good prices. Good for getting started on a budget, or for something you won't use every day. They are also located in more medium-sized cities too small for Home Depot or Lowes, which is nice when you camp in the middle of nowhere...
Is there as little meat left around the hole as picture shows?
It seems more substantial in person, probably since it is nicely thick height-wise.
"Extra Long Barrels with Flared Ends Attach Easily to Welding Cables"

Sure doesn't look flared to me.
I guess that's an old picture, because they are actually flared.
 
Still short some ring terminals. Local Harbor Freight has some! Their welding department is a lifesaver. #2 and #4 AWG ring terminals in 1-2 different ring sizes. Copper.

Have SO. MANY. CABLES. to cut and strip and crimp. Will be adding 2 disconnects, 3 surface mount breakers, one ground bar and two busbars. Hope I can fit all this on my existing backing board! Will have three days before we have to skedaddle. Fun?
I prefer marine grade tinned terminals on cables. Usually from Windy Nation. https://www.windynation.com/Cable-L...able-Lug-Ring-Terminals-End/-/4277?p=YzE9MjQ=

3 days? Wish you luck......
 
Sorry FilterGuy, you are wrong. Start with the device's required maximum amperes. Size the cables for required minimal voltage drop in that circuit. Then size the fuse for the ampacity of that cable.
 
Sorry FilterGuy, you are wrong. Start with the device's required maximum amperes. Size the cables for required minimal voltage drop in that circuit. Then size the fuse for the ampacity of that cable.
However it is done, this equation needs to be true for the end result.

1.25 x Max Current < Fuse < wire rating

If the fuse rating is not greater than (or equal to) the max current, there will be nuisance trips
If the wire rating is not greater than (or equal to) the fuse rating, there is a fire danger.

If the wire size is picked first, it will usually but not always be possible to find a fuse that fits between the wire rating and max current.... if a fuse is not available that fits between the two, one larger than the selected wire size is picked. Then the wire size has to be bumped to match the fuse. Because of this, I always figure out the fuse size first.
 
Dixonge, where in NM are you? I'n in Abq and do have a few surplus terminals and 'stuff' lying around as well as the crimping tools etc. I see you've ordered your bus bars so I'm too late there, but personally I use the ones sold by Waytek when I need fusing on the circuits. A little hard to find all the options but here's one so you can see what I'm talking about: https://www.waytekwire.com/item/46390/EATON-s-Bussmann-Series-LMI1-E-0-0-Fuse-Holder/ They're modular, available with different stud sizes, allow you to make them any length and are designed for fusing.
 
Dixonge, where in NM are you? I'n in Abq and do have a few surplus terminals and 'stuff' lying around as well as the crimping tools etc. I see you've ordered your bus bars so I'm too late there, but personally I use the ones sold by Waytek when I need fusing on the circuits. A little hard to find all the options but here's one so you can see what I'm talking about: https://www.waytekwire.com/item/46390/EATON-s-Bussmann-Series-LMI1-E-0-0-Fuse-Holder/ They're modular, available with different stud sizes, allow you to make them any length and are designed for fusing.
Currently up N of Ruidoso, but about to hightail it down to just outside Artesia to avoid the next cold front. Would rather not drive a big RV in 60-mph gusts! I think one stop at Harbor Freight and one at Home Depot will take care of most of my current needs, but thanks for the offer!
 
The wire >must< be sized to carry the amperes the device may ever need with the reasonable voltage drop required of the device. The fuse >must< protect the wire from amperage that will soften or melt the insulation. While providing this protection the fuse should be as large as possible with two objectives. One is protect the wire, the other is to have the least voltage drop in the circuit. The fuse is sized to the wire. The wire is sized to reduce voltage drop. We must start with the device. Size the wire for voltage drop. Size the fuse to protect the wire. If my device needs 2/0 cable for a 2% voltage drop, that 2/0 has ampacity of 330 amperes, I would use a 300 ampere fuse. If the device draws 150 amperes through 2/0 cable. I would still use a 300 ampere fuse.
 
If my device needs 2/0 cable for a 2% voltage drop, that 2/0 has ampacity of 330 amperes, I would use a 300 ampere fuse. If the device draws 150 amperes through 2/0 cable. I would still use a 300 ampere fuse.
You lost me on that.

Why would I ever want to put a 300A fuse on a circuit that will only run 150A? Even if I put in the 25% kicker to avoid nuisance pops I only get 188A. A 200A fuse will protect the 2/0 wire *better* than a 300A fuse. Up sizing the wire to reduce voltage drop does not require upsizing the fuse.

While providing this protection the fuse should be as large as possible with two objectives. One is protect the wire, the other is to have the least voltage drop in the circuit.
Wow! That is a new one on me. I believe the exact opposite. The fuse should be as small as possible while 1) protecting the wire and 2) avoiding nuisance trips.

Or is the argument that the larger fuse has lower resistance and therefore lower voltage drop? If that is the argument, I don't buy into it. I would much rather limit the current to just over what is needed than to try to get that tiny extra voltage difference between a 200 and 300A fuse. Allowing an extra 100A before the fuse blows is amplifying the possibility of a fire.
 
Replaced backing board, mounted main devices. Final parts arrive Thurs.
battery-bay-prep.JPG
 
I disagree. A fuse sized to protect the wire is the largest fuse with ampere rating under the wires ampacity. In our mobile, limited power, dc systems voltage drop is a very real issue that must be considered. Even across fuses as well as connection points and wire resistance. If I have a 2/0awg that can dead short over 300 amperes with out overheating there is no reason to fuse that wire at lower amperes.
 
dixonge, nice build. My inverter cautions against horizontal mounting because of ventilation fans.
 
dixonge, nice build. My inverter cautions against horizontal mounting because of ventilation fans.
Yeah, I mounted vertically so the fan is at the top away from the batteries. It also orients the heat fins vertically. Same for the SmartSolar SCC.

The fact that the charger and inverter aren't exactly parallel is bothering me though. LOL
 
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re: wire gauges - I have finally learned the big end of wire gauges and am so relieved to be rid of this confusion! 2AWG, 0AWG, 00AWG, etc. I kept seeing 2/0 and thought it was the same as 2AWG!

re: fusing - I thought that the range of possibilities was from 'possible load' on the low end to 'cable will melt and/or catch fire' on the high end. Common sense says the fuse size should be somewhere in this range. My first thought would be to size it about halfway between nuisance tripping and melting. In my case my average load is 5-10 amps DC (per battery monitior), high end would be 100 amps when running blender (900w AC, 82.8amps DC according to online calculator). So having a 125amp ANC fuse on the 2AWG cable from my battery seems fine, but if it blew a few times I'd go for 150 or 200. Sound about right?

Related note - am now officially doubtful if all my big cables are 2AWG vs. 2/0 - need to check this today!
 
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