Cable size/fusing

skoobus

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Hi all, I've got my main components picked out and now I'm getting all the smaller doodads and cabling.

I've got 6 of the ECI power 12v 100ah batteries going in to a 24v battery bank, as far as I can tell 2 AWG wire is recommended by my inverter (Growatt 24v 3000 watt AIO) but the manual is pretty hard to understand, all the info I can find is pretty conflicting.

1. Will 2 AWG work well in this case for both the batteries and to the inverter AIO?
2. How exactly do I size a disconnect switch for my bank?
3. How do I size the fuse?

Thanks in advance
 

Rednecktek

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The fuse will be 120% of max draw, so (3000w/24v)*1.2= 150a breaker for that setup. The breaker is also your disconnect.

Yes, 2AWG will give you a rating of 130a so you should be good as long as the insulation is the 90c rated. The colder rated stuff (70c or 60c) have less capacity.

It sounds like your batteries are in a 2s/3p config so if you're taking the batteries to a bus bar and then to the inverter you can use smaller wire because each bank of batteries will be providing 34% of the amperage, or 50a which would be 6AWG from batteries to bus bar and then the 2awg for the bus bar to the inverter. 4AWG from batteries would give you better fudge factor, but you'll have to step up between the bars and the IO.

Granted if you are buying a spool there's no reason you can't just rock the 2AWG all the way around. :)
 
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Zil

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All these calculations are for quality marine grade cable. To select the proper size cable for the vdc side of the circuit. There are voltage drop tables. We measure the length of the cable. We note the voltage and amperes expected for the device. I size a 300W x 24Vdc inverter at 125 amps plus 25% factor for 156 Adc So 160 amperes. Blue Sea circuit wizard lists 1AWG with the inverter <5 feet away from battery. 10 feet of cable. Then we select the fuse with ampacity table. Blue Sea table indicates 1awg cable safe to 245 amperes. @50 amp fuse too large, so I and Blue Sea recommend a 200 to 225 ampere ANL, Class T, or Terminal fuse. It is always better to up-size dc cables.
 

kenryan

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I would use a breaker, rather than a fuse. The reason is that the breaker can also be used as your disconnect switch. The purpose of the breaker is to protect the wire, so normal loads are irrelevant. You need to look up the ampacity rating of your particular 2AWG wire. If it is rated for 90C then the ampacity is 130 amps. So the maximum breaker rating would be 130 amps.

Because you might not easily find a 130 amp breaker, it would be good to know the minimum breaker size as well. Now is when you can look at normal loads. 3000 watts divided by 24 volts equals 125 amps. So you don't have a lot of leeway on breaker size -- 125-130 amps.

There is no reason you cannot go larger with your wire. In fact, you might want to do that in order to minimize voltage drop. If instead you used 1/0 rated for 90C your ampacity would increase to 170 amps, and you could then use a breaker rated at 170 amps or less, and you would have less voltage drop.

That is the reasoning behind choosing breaker size, and those are some examples of your options. If it were me, I would probably go with 1/0 because I do not like to cut corners on fat wires. But there is absolutely nothing wrong with using 2 AWG as long as your breaker is properly sized.

Link to ampacity chart

Link to voltage drop chart
 

skoobus

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Thanks for the replies everyone!

Being as my battery bank will be within 3-5 feet from the inverter I don't think voltage drop will be an issue so I'll still go 2 AWG (assuming I read that VD diagram you posted correctly -all the diagrams for this stuff look like postmodern art! lol)

I'm getting spartan brand wire I've heard its quality stuff (hopefully) It says on amazon rated for 105 celcius so thats what you meant by "90c rated" right? I am getting a (small) spool btw, want to keep things uniform and as simple as I can

Good thinking on the circuit breaker, I've been using wil prowse's website and he says to use a fuse between the inverter and batteries but a circuit breaker would double as a disconnect and do the same thing. Looks like 150a is what I will go with -blue sea

Now that I'm realizing I need bus bars.. I can oversize them like wires just to be safe right?
 

kenryan

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Remember, a wire is only as good as its terminal crimp. I take all my fat wires to a local professional who has a nice pneumatic crimper. To me, it is money well spent. A bad crimp on a fat wire carrying lots of amps can get ugly.
 

skoobus

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for bonus points: I just need a bus bar for the negative side, right? same size as the circuit breaker -150 amps?

sorry, I'm learning!
 

skoobus

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Remember, a wire is only as good as its terminal crimp. I take all my fat wires to a local professional who has a nice pneumatic crimper. To me, it is money well spent. A bad crimp on a fat wire carrying lots of amps can get ugly.
I'm planning on getting the hammer crimp, says it can handle 2 awg.. anyone have bad experience with those?
 

kenryan

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I'm planning on getting the hammer crimp, says it can handle 2 awg.. anyone have bad experience with those?
I have one in my toolchest. I used it twice. Did not like the results, and don't plan on ever using it again unless it was some sort of emergency. If you are going to do it yourself I would recommend either a hydraulic crimper or one that you put in a vice and squeeze. The objective of crimping is to end up with a gas tight seal -- squeezing things so tightly that even air cannot get in.
 

skoobus

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I have one in my toolchest. I used it twice. Did not like the results, and don't plan on ever using it again unless it was some sort of emergency. If you are going to do it yourself I would recommend either a hydraulic crimper or one that you put in a vice and squeeze. The objective of crimping is to end up with a gas tight seal -- squeezing things so tightly that even air cannot get in.
A lot of people on the reviews of the hammer crimp said to just put it in a vise instead of hammering, is that what you mean?
 

kenryan

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No, there are other crimpers available that are made to be put in a vice, although I am having trouble finding one now, and I am not certain how large of cable they can handle. Search this forum for "crimper."
 

100 Proof

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I'm planning on getting the hammer crimp, says it can handle 2 awg.. anyone have bad experience with those?
I've used both a hammer crimper and a hydraulic crimper with good results. If you use the hammer crimper, use a 2 - 3 pound sledge hammer, not a carpenters hammer. Swing for effect. Crimping is not the time to stick out your pinky finger and be dainty. :geek:

If your high amp loads are for less than a few minutes, a GOOD QUALITY circuit breaker will work fine. I've found though that high loads that last for longer times will generate a bunch of of internal heat in the breaker and eventually trip even a good quality a breaker at well below it's rating. That is why fuses are recommended for inverters.
 
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kenryan

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@100 Proof is right. Read the manual for your inverter. Often a "Class T" fuse will be specified. I think I may have been mistaken about the vise crimper. I have used one for hose fittings but I cannot find any such animal for electrical cables. Like I said, I take my fat wires to a local professional and consider it to be money very well spent.
 

Zil

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What ever you use. Please put a catastrophic fuse at the positive battery terminal. It is recommended to use a Class T fuse on LiFePo battery. An ANL fuse or a MRBF fuse on lead chemistry. Then it will not matter if the circuit breaker welds its contacts together. 2awg will work with 3000W @ 24V. Use 200 amp fuse at positive battery terminal end of that 2awg cable..
 
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skoobus

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Thanks again everyone, I'll go with a 200amp class t fuse as suggested.

I've heard good things about putting the hammer crimp in the vise so I'm gonna give that a try and see how it goes, if that goes south I'll look and see if I can find any pros in the area and go that route
 

OM617YOTA

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I used a hammer crimper in a hydraulic press. No complaints thus far, but I've only used it a few times.
 

Just John

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Hi all, I've got my main components picked out and now I'm getting all the smaller doodads and cabling.

I've got 6 of the ECI power 12v 100ah batteries going in to a 24v battery bank, as far as I can tell 2 AWG wire is recommended by my inverter (Growatt 24v 3000 watt AIO) but the manual is pretty hard to understand, all the info I can find is pretty conflicting.

1. Will 2 AWG work well in this case for both the batteries and to the inverter AIO?
2. How exactly do I size a disconnect switch for my bank?
3. How do I size the fuse?

Thanks in advance

3000 x 1.2 = 3600W (assume 80% efficiency inverter)
3600 ÷ 24 = 150 amps


Plug 150 amps at 24v into the calculator. 4 awg will work for 10 feet. 2 awg is better.
Fuse should be sized to protect the wire, not how much you think you will draw.
200 amp fuse and 2 awg wire will work fine depending on how long the run is. It is exactly what I use.

Use a breaker as an on/off disconnect, but don't cheap out. A quality breaker made in the USA is at most $10 more than a cheap Chinese breaker, and will actually work as designed.

I used the 200 amp version here:

Edit to add that running a 24v at 3000W Victron Muliplus with this, and a 200 amp class T fuse. Works fine. I use a hydraulic crimper, quality cable, Ancor tinned lugs and heatshrink.
 
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Zil

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I use my Ftz crimper for cables 6awg through 4/0awg. Its a ratchet crimper it works best with Ftz lugs.
 

12VoltInstalls

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I'm planning on getting the hammer crimp, says it can handle 2 awg.. anyone have bad experience with those?
Electrically they can work fine.

I don’t have a hydraulic or ratchet crimper. My ‘big’ crimper is a die/swage unit like small bolt cutters, 20”? handles that fits 8ga-1ga. I think it was under $50usa but the “nice” crimpers for 2/0, 1/0 are hundreds of dollars. Maybe somebody has info on one for less?

The hammer crimper won’t ‘gas tight’ a terminal. It does 1/0 and 2/0 ok, 3/0 barely fits or doesn’t fit, essentially. I only needed 3/0 once and I’m pretty sure I I used square bar in a shop press onto the bottom channel of my press brake.
Center it up nicely, tap to start the crush and it will hold the wire loosely. Examine it- if all good and straight/symmetric drive it with an angry 3# hammer swing. Occasionally an additional whack is needed if for some reason there’s wide airspace. Heat shrink- done. It seems when you make a good crimp that you might have to grab a smaller hammer and help the terminal out of the crimper sometimes.

A swage die crimper is better. I should make a new mandrel for my hammer crimper that is B-type crimp. They all come with one that makes a V. It works, not ideal imho.
 
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