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Old 04-28-2019, 11:29 AM   #1
Mini-Skoolie
 
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400W/200AH System Overview: Wire Sizing?

Pictured below are all my components (plus 2x 100aH deep-cycle lithium ion batteries in parallel) for a 12V, 200aH system with 400W of solar panels. So far I do not have a shore power charger.

My loads are: AC: a chest freezer with a temperature controller, small fans for cooling, a projector, electric keyboard, and the occasional Instantpot pressure cooker
DC: a 12V ventilation fan2 laptops, 2 phones, 10x LED lights.
For these appliances, do I need a breaker box for my AC system? Or is it fine straight from the inverter (it has overload protection)?

I followed this guide and have no experience with electrical otherwise, besides research into other people's systems.

Pure Sine Inverter: 2000W, 12V input
Batteries: 2x 100 Ah lithium ion
MPPT Solar Charge Controller: 40A
Fuse Block:
On the packaging for the fuse block, it recommends a max. 125A fuse from the battery positive. However, I have the Inverter, MPPT Controller, and Fuse Block attached to the 250A ANL Fuse Holder
Does this act as the fuse for the DC Fuse Block? If so, is this too high? Should I put another smaller fuse between the holder and the Fuse block. So far, I have just been following the above-mentioned guide.

My biggest trouble is figuring out wire size. I've looked at the sizing charts, but I'm afraid of overheating wires.

My inverter came with 2x 7AWG 60A wires for positive battery --> inverter, and 2x for the negative. Do I double up these wires? Or are they meant to go from battery-->Fuse-->Inverter?

I have a 50A circuit breaker between the 40A MPPT, but do not know what size wire to use between.
For the DC Fuse Block, it recommends 4-6 AWG from the positive post, is this the standard I should between the MPPT, fuses, and inverter?

Finally, I have a 100A Bus bar for the negatives, would all the negative wires be the same size as the positive ones?

I am also figuring out where to ground the inverter and what size wire for that

Any feedback/ideas/help is appreciated!! I hope I'm not overheating anything, and maybe this could give other people ideas
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Old 04-29-2019, 05:21 AM   #2
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My advice is to do some measuring - collect some data. How much power does the freezer consume, the Instapot, etc...?? A Kill-A-Watt meter is very valuable for this.

Without knowing the actual loads that must be supported by the system, we are just guessing. With that in mind...

If 2000 watts is the maximum your inverter will output (not a 2000W with 4000W 'surge' type unit) it may pull up to about 190 amps (@12VDC) - that is with the 15% conversion loss. If the length of the cable from battery to inverter is 5' or so, a cable size of in the 0 to 2/0 range is appropriate.

In my opinion, it is always best to install a proper circuit panel for the AC system. If you were running only one or two components/accessories from the inverter, I might feel differently.

Regardless of AC or DC, remember that the circuit breaker/fuse is there to protect the wire. So, fuse at the power source and match the capability of the wire. A 250 amp fuse protecting a 12 GA wire (for example) can be a dangerous thing.

Wire sizing is a matter of knowing the load to carried (amps and voltage) and the distance. Lots of charts and online calculators available to help with that. I suspect the challenge you are having is from not knowing the first bit.

Quote:
Originally Posted by FabulousFox View Post
My inverter came with 2x 7AWG 60A wires for positive battery --> inverter, and 2x for the negative. Do I double up these wires? Or are they meant to go from battery-->Fuse-->Inverter?
Those are included by the marketing department as means to make people think they are getting 'more'. In reality, they should be thrown away if you are going to use the inverter up to its advertised capabilities (2000W output). 60 amps @ 12VDC = 720 watts.

Quote:
Originally Posted by FabulousFox View Post
Finally, I have a 100A Bus bar for the negatives, would all the negative wires be the same size as the positive ones?
Yes. It is all one "circuit."

Quote:
Originally Posted by FabulousFox View Post
I am also figuring out where to ground the inverter and what size wire for that
Are you asking about chassis ground (or "earth ground" or sometimes "RV ground")?? If so, you should connect the inverter chassis to your vehicle chassis. In most cases, this is accomplished with a #8 bare copper wire "grounding wire."

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Originally Posted by FabulousFox View Post
I hope I'm not overheating anything, and maybe this could give other people ideas
Overheating is never good, obviously. However; it isn't the real problem. The real problem is fire. Electricity is a very powerful thing and it can really mess up a person, trip, adventure, life.... Please be careful and thorough.
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Old 04-29-2019, 09:11 AM   #3
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I agree with JD.

Measure and add up all of your loads and then spec a battery bank and inverter. Finally, size your panels to properly support your batteries.

A tiny bit of math in my head has me guessing that the system that you have spec'd above will not support your loads as described above.
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Old 04-29-2019, 12:08 PM   #4
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Quote:
Originally Posted by JDOnTheGo View Post
My advice is to do some measuring - collect some data. How much power does the freezer consume, the Instapot, etc...?? A Kill-A-Watt meter is very valuable for this.

Without knowing the actual loads that must be supported by the system, we are just guessing. With that in mind...

If 2000 watts is the maximum your inverter will output (not a 2000W with 4000W 'surge' type unit) it may pull up to about 190 amps (@12VDC) - that is with the 15% conversion loss. If the length of the cable from battery to inverter is 5' or so, a cable size of in the 0 to 2/0 range is appropriate.

In my opinion, it is always best to install a proper circuit panel for the AC system. If you were running only one or two components/accessories from the inverter, I might feel differently.

Regardless of AC or DC, remember that the circuit breaker/fuse is there to protect the wire. So, fuse at the power source and match the capability of the wire. A 250 amp fuse protecting a 12 GA wire (for example) can be a dangerous thing.

Wire sizing is a matter of knowing the load to carried (amps and voltage) and the distance. Lots of charts and online calculators available to help with that. I suspect the challenge you are having is from not knowing the first bit.
I'll get a Watt meter to test, for now I estimated the Watt/hour for my appliances. I keep making mistakes in my understanding of the calculations, so I'll try it here:

For my 110 VAC appliances
*Freezer: 200 Watts/hour divided by 110VAC is 1.82 Amps/hour. Assuming it is run for 24 hours, the amount of Amp Hours per day is 43.68Ah. However, this is just the draw from the inverter? From the battery to the inverter, it is 200W/12.5 VDC= 16Ah? Making 384 Ah/day.
Assuming that is correct (I'm still not sure haha), I could do that for all my AC appliances:
*Instapot: 1000W/110 VAC= 9.1 A. Multiply by 1/2 hour a day= 4.55 Ah/day from the Inverter. From my battery it would be 1000/12.5 VDC= 80A(.5 hours)= 40Ah/day
*Labtop Chargers (2): 60W/110VAC= 0.55 Ah (x2 labtops)=1.1 Ah (x6 hours)= 6.55 Ah/day from the inverter. 60W/12.5 VDC= 4.8 A(x2 labtops)= 9.6 (x6 hours) = 57.6 Ah/day from the battery
With just these things, I have 54.78 Ah/day from my Inverter to AC appliances and 481.6 Ah/day from my batteries to the inverter. With that logic I could use this calculator to have a 7 AWG wire and a 55A fuse from my inverter to AC outlets/circuit panel?

But, I'm not sure about from the battery to the inverter.

For the Solar Charge MPPT to the batteries, I have 400W of panels @12.5 VDC, giving me 32 A? The MPPT is listed as 40 A on the product itself. So I should use a 6 AWG wire and a 50 A fuse?
Is any of this right? Just when I think I'm getting a grip on electrical haha Thank you so much, every electrician so far has not gotten back to me.
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Old 04-29-2019, 12:15 PM   #5
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If you are running a 12v system and are going to consume 481 a/h daily you are going to a LOT more than 400 watts of solar.
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Old 04-29-2019, 01:18 PM   #6
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In 'rough' form, that is correct. The value of the Kill-A-Watt is that it measures the actual power consumed over a period of time (Ah). Many devices advertise 1000 watts but don't actually use 1000 watts the whole time they are operating. A freezer (for example) may have a compressor duty cycle of 50%. The Instapot may consume 1000 watts for a minute or two when first turned on but my taper to very little power once it is hot (maybe - I don't know that - thus the reason to actually measure it).

The item missing from your calculations (battery to inverter) is the conversion loss. That's difficult to calculate but many inverters are in the 85-90% efficient range. So, 1000 watts in does not equal 1000 watts out (making your numbers look even worse).

[QUOTE=FabulousFox;322542]...7 AWG wire and a 55A fuse from my inverter to AC outlets/circuit panel?

Ok, I'm probably getting confused here. Apologies... I thought you were asking about using those #7 cables for the 12VDC side of the inverter. You must size your system for peak load. If your are consuming 200 watts (freezer), 1000 watts (Instapot), and 120 watts (other, which I bet is low) all at the same time, you'll need something around 122 amps @ 12VDC (including a 15% conversion loss) from the batteries. 122 amps zipping down that #7 wire is going to do something interesting - probably involving smoke.

If planning to use #7 for AC power side only (inverter to breaker/distribution panel) you are golden. Depending on the length of that run, 12-2 may be overkill (and 14-2 sufficient). If not familiar with those numbers, 12-2 means a three wire "cable" with #12 wires. Three wire is required for AC (hot, neutral, and grounding wire).

Quote:
Originally Posted by FabulousFox View Post
For the Solar Charge MPPT to the batteries, I have 400W of panels @12.5 VDC, giving me 32 A?
Sort of. If charging, the voltage will be around 13.5 VDC or higher. Lithium charges at different voltages than lead-acid so be aware of that (maybe, depends on your batteries - do what the manufacturer recommends). Under ideal conditions, you can probably expect something around 30 amps (13.5VDC).

Quote:
Originally Posted by FabulousFox View Post
The MPPT is listed as 40 A on the product itself. So I should use a 6 AWG wire and a 50 A fuse?
How long is the run?? Assuming less than about 16', #6 should be fine.
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