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Wire size and fuse size for inverter conflicting information?

sonny93

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Dec 17, 2020
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Hi there, I have a 500W inverter I am planning to power with 280aH array of 4 cells and a 100A BMS.
Doing the basic calculation as follows 500W inverter max load/12V battery = 41 Amps. I need a wire thick enough to carry 41A

Based on Will's advice in his book, I based my max load on the inverter and ordered 10AWG wire to connect the BMS and battery to the inverter:
"500 watt inverter requires 10 gauge"
and further for the fuse, I purchased a 50A:
"500 watt inverter should have a 50 amp fuse"

here is wills chart
1616022310121.png
What am I missing here? I am so confused by this conflicting information, and a bit frustrated at the potentially failed purchase..
Going off of this, my wire will burn out before my fuse?


This one has its max current at 30A
1616022548643.png
1616023307871.png
 
Different resources make different recommendations due to different assumptions.


Indicates a 1.7% voltage drop at 50A/2ft/12V. Very acceptable.

A wire's rating is based on its insulation. 10awg can carry crazy current, but you don't want to melt the insulation or cause it to catch fire. Insulation temperature rating limits the wire's ampacity.

The same blue sea systems site that provides the middle chart recommends 10awg on this calculator for the same parameters:


and indicates 10awg is good to 60A with 105°C insulation.
 
If this is a cheap "truck stop" inverter I would estimate its 80% efficient.
500 ac watts / 0.8 efficiency / 12 volts = ~52 amps
~52 amps / 0.8 fuse headroom = 65 amps

And you don't want your wire getting to 105C which is 221F.
I suggest #6 awg wire rated for 105C which will keep the wire temperature reasonable.
Just my unsolicited $0.02CAD.
 
+1. Wire insulation also affect the Ampacity rating of the wire, Vdrops is another story.
 

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You could also double up on the 10 awg wire.
If you do, fuse each wire separately.
 
Different resources make different recommendations due to different assumptions.


Indicates a 1.7% voltage drop at 50A/2ft/12V. Very acceptable.

A wire's rating is based on its insulation. 10awg can carry crazy current, but you don't want to melt the insulation or cause it to catch fire. Insulation temperature rating limits the wire's ampacity.

The same blue sea systems site that provides the middle chart recommends 10awg on this calculator for the same parameters:


and indicates 10awg is good to 60A with 105°C insulation.
Thats great news

The other question I had was related to the fuse I purchased from eBay.

  • The listing indicated the wire attached to the 50A would be 10AWG, so I was going to solder insulate it to the copper wire
  • I received a 50A fuse with 7-8AWG wire
I am wondering if it is going to be okay for me to solder different sized wires together?
 
50A fuse is inadequate. Need 1.25X current. Quality crimp or solder should be fine.
 
500W/12V = 41.67A, so 41.67A * 1.25 = 52A fuse so 50A fuse is close enough.
BTW, to actually getting 500W on the AC output of the Inverter, the DC curent will be higher than 41.67A due to conversion lost.
No worries, as snoobler indicates:
" and indicates 10awg is good to 60A with 105°C insulation."
 
I apologize. I didn't do the math. 500/12 = 41A. It's fine.
Geez I’m sorta new here but you seem to have the ideas down so when I read ‘no’ I was wondering how/where I went awry solving for A.

Then I saw the follow up...
 
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