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Could someone check my (modified) DIY milk crate diagram?

bosun120

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Nov 19, 2021
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I'm looking to build my first milk crate system build, however with a different inverter and a few added components (battery meter, switch).

I would like to "upgrade" my inverter to handle up to 1000W Continuous, as I'd like the capability to operate a small electric kettle, which AFAIK the smallest ones still use up to 700-800W.

@chrisski in another thread recommended using 1/0 gage wiring for the connections between the battery and inverter.

I was wondering if this forum could check my diagram and parts list (below) to make sure everything looks compatible & there isn't something missing:

Solar Gen Schematic.png

Parts List (with links):
  1. LiFePO4 Battery
  2. Inverter (Pure Sine 1000W)
  3. Battery Meter
  4. Battery On/Off Switch
  5. ANL Fuse Holder & ANL Fuse (200A)
  6. Inline Fuse (40A)
  7. Fuse Block
  8. AC-DC Power Supply
  9. Power Cord
  10. Charge Controller
Dash Lines = 1/0 Gage Wiring
Solid Lines = 10 Gage Wiring

Thank you.
 
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A 1000W inverter on a 12V system can pull up to about 100A from the battery at full power (1000W / 12V / 85% efficiency = 100A).

For 100A you should use at least 4AWG wire though 2AWG would be better. The 150A fuse would be fine with either wire. 1/0AWG of course will work since it can be used up to about 175A.

But you also have DC loads so that will pull even more current from the battery. Since you are planning 10AWG to the fuse block, one must assume you don't plan to have more than 30A of DC loads at any one time.

Combining the 100A max load from the inverter and 30A of DC loads your battery wires need to handle about 130A. Now you are looking at at least 1AWG and your main battery fuse should be 175A.

You can use 1/0AWG with a 150A fuse as planned but if you max out the inverter and your DC loads at the same time then it's possible the fuse could blow needlessly.

One thing missing in your diagram is a fuse between the battery and the fuse block. Since the 10AWG should not be used for more than 30A I would add a 40A fuse.

You should also connect the fuse block between the main battery fuse and the disconnect switch or between the disconnect switch and the inverter. It depends on whether you want the fuse block to be controlled by the disconnect switch or not.

Your proposed ANL fuse is terribly cheap. Don't skimp on circuit protection. Buy a quality fuse and holder from a respected fuse maker such as Bussman or Littlefuse.
 
The battery meter is incorrectly placed. I suppose you don't want to measure only the energy used by the inverter, but all the energy going in and out of the battery. And if so - it should be on the ground path of all grounds.
 
A 1000W inverter on a 12V system can pull up to about 100A from the battery at full power (1000W / 12V / 85% efficiency = 100A).

For 100A you should use at least 4AWG wire though 2AWG would be better. The 150A fuse would be fine with either wire. 1/0AWG of course will work since it can be used up to about 175A.

But you also have DC loads so that will pull even more current from the battery. Since you are planning 10AWG to the fuse block, one must assume you don't plan to have more than 30A of DC loads at any one time.

Combining the 100A max load from the inverter and 30A of DC loads your battery wires need to handle about 130A. Now you are looking at at least 1AWG and your main battery fuse should be 175A.

You can use 1/0AWG with a 150A fuse as planned but if you max out the inverter and your DC loads at the same time then it's possible the fuse could blow needlessly.
@rmaddy Thank you. So are you saying that the wiring in my diagram is OK, ie. still use 1/0 gauge for wiring between battery & inverter, and use 10 gauge for the rest?

One thing missing in your diagram is a fuse between the battery and the fuse block. Since the 10AWG should not be used for more than 30A I would add a 40A fuse.
Would something like this inline fuse work? Is this used to prevent any potential damage from the battery to the rest of the components (power supply, SCC)?

You should also connect the fuse block between the main battery fuse and the disconnect switch or between the disconnect switch and the inverter. It depends on whether you want the fuse block to be controlled by the disconnect switch or not.
I would like the switch to turn on/off the LiFePO4 battery to turn off parasitic draw. Someone suggested in another thread to put the switch right after the battery positive terminal, with an inline fuse before.

Your proposed ANL fuse is terribly cheap. Don't skimp on circuit protection. Buy a quality fuse and holder from a respected fuse maker such as Bussman or Littlefuse.

Would it be OK to use the same ANL Fuse Holder, but replace with this Blue Sea ANL Fuse (200A)?

I have updated the diagram and parts list to reflect this.
 
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The battery meter is incorrectly placed. I suppose you don't want to measure only the energy used by the inverter, but all the energy going in and out of the battery. And if so - it should be on the ground path of all grounds.

@brum I would like the meter to measure the current battery capacity/percent.

Should I put it between the battery negative terminal & the fuse block busbar ground (see updated OP diagram)?
 
So are you saying that the wiring in my diagram is OK, ie. still use 1/0 gauge for wiring between battery & inverter, and use 10 gauge for the rest?
Essentially, yes. But 1/0 is bigger than needed as I explained.

Would something like inline fuse work? Is this used to prevent any potential damage from the battery to the rest of the components (power supply, SCC)?
That kind of inline fuse is fine for the wire between the battery and fuse block. Fuses are there to protect the wiring, nothing else.

I would like the switch to turn on/off the LiFePO4 battery to turn off parasitic draw. Someone suggested in another thread to put the switch right after the battery positive terminal, with an inline fuse before.
Then you want the wire from the fuse block to be after the switch, just like the wire to the inverter. This way when you turn off the switch, there is no power to inverter nor any power to the fuse block.

Battery positive -> main fuse -> switch -> inverter and fuse block
Battery negative -> battery monitor -> inverter and fuse block

Would it be OK to use the same ANL Fuse Holder, but replace with this Blue Sea ANL Fuse (200A)?
I wouldn't use that cheap holder with a good fuse. Get a good holder and a good fuse. And 200A is too large for your needs. Though if you use 1/0AWG it is safe to use a 200A fuse.
 
Can't find your diagram, broken link?
ANL are a poor choice for even smaller LiFePo batteries. But getting them from Blue Sea means you get quality fuses. They do have an interrupt capacity of 6000 amps. The holder is as important as the fuse.
 
@brum I would like the meter to measure the current battery capacity/percent.

Should I put it between the battery negative terminal & the fuse block busbar ground (see updated OP diagram)?

The battery minus terminal should go only to the power meter shunt. All other grounds should be connected to the other part of the shunt.

I see you've moved it, but it is still incorrect. Nothing except the shunt should be connected to the battery minus terminal.
 
The battery minus terminal should go only to the power meter shunt. All other grounds should be connected to the other part of the shunt.

I see you've moved it, but it is still incorrect. Nothing except the shunt should be connected to the battery minus terminal.
In addition to this, both the inverter and the fuse block positive wires need to be after the switch.
 
I'd still prefer a Class-T fuse for a lithium battery, although with a 50Ah battery probably not top grade origin you're probably fine with the ANL - but that's only probably. Also, your big fuse should protect the whole battery, not just the big load. Any short on the battery is nasty.
 
The fuse breaking capacity is not based on the battery capacity, but more on its internal resistance. 50Ah and 300Ah batteries can both have identical internal resistance and if so - the breaking current should be the same. No matter what the capacity is. In fact, the EVE LF105 and EV304 both are rated at 0.5mOhm internal resistance. Just checked the LF50 and it is marked as 0.7mOhm internal resistance.

Quick math shows the following - 0.5mOhm internal cell resistance at 3.5V is ~7kA current if the battery is shorted. Put 100% above for safety reasons and you need 15kA breaking capacity. I found a cheap solution for my case, but I'm pulling at most 15-20A from the battery. There are 10x38 fuses rated at 120kA breaking capacity. Eaton has such and they are quite cheap. Cheap and common car audio fuse holders are designed for them. The drawback is that their 10x38 fuse series goes up to 32A only.

In the setup above the advisable approach is to consider the short circuit current of the battery and get a fuse that can break it.
 
Since you're pulling so many amps, why not move to 24 or 48v? It'd lower your amperage cabling needs and would generate less heat on the fuses and wires.
 
Since you're pulling so many amps, why not move to 24 or 48v? It'd lower your amperage cabling needs and would generate less heat on the fuses and wires.
A 1000W inverter on a 12V system is only 100A. Nothing wrong with that. There would only be excessive heat if you used undersized wiring or had poor connections.
 
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