Wire sizing for inverter in small camper

chrisski

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Is there a decent chart or calculator tool online for low voltage dc high amp cables in conduit?

What do you think of this calculator:
 

corn18

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Is there a decent chart or calculator tool online for low voltage dc high amp cables in conduit? I’m not aware of one myself. Then again I’ve not yet experienced that application.
The Blue Sky calculator has derating options that you can select.

Screen Shot 2021-09-28 at 08.49.42.png
 

LVLAaron

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If that’s actually 20A of 120VAC load, your 1000 inverter is only good for 8A at 120V. Also 20A at 120V is 200A at 12V not factoring for losses.

Nah, 20 amps @ 12v. Fridge pulls 6@12v max. Laptop charger pulls maybe a couple amps @ 12v. Ceiling fan is 12v and is an amp or two. Lights are 2 amps.
 

12VoltInstalls

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What do you think of this calculator:
Interesting. No math or lookups required.
I did notice this2CF28A16-1A50-437E-BF37-C07BDEC83158.png
which basically stated AC values assumed although I selected DC. That doesn’t make a difference, but it also does in some ways.
 

boondox

Chief Engineer, RedNeckTech Industries
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This is good advice. Don't wire a 1000W inverter like it's a 500W inverter.


5% is a lot for an inverter. Some devices won't like getting such low voltage. For something critical like an inverter I would try to get less than 3%.
Well, the 5% is with a 20% extra load overhead that I added, using 100 amps (1200 watts) instead of 83 amps (1000 watts). But yes, I do agree that shooting for under 3% is best practice.
 

boondox

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That’s not really extra. There’s losses.
True. 1000 watts out the inverter is 1200 watts input or so and then there are other losses. So the 2ga is on the edge but certainly safe although it might cause a low voltage inverter shut off at max load.
 

McCarthy

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Well, this is why a calculator can be handy. Assume the 15 feet posited by the OP. He said 1000 watts maximum but I would add 20% to cover any loads aside from the inverter and some surge. The OP doesn't state it but we will guess that it is a 12V system. So that means we are going to provide for 100 amps of load. Using a 6 AWG wire that comes out to a 12.27% loss. Way too much. Even 4 gauge comes in at 7.7% loss, too much for me. Two runs of 4 gauge comes out to 3.85% loss, acceptable.

Even if we go for exactly 1000 watts with no overhead that comes to 83 amps. With a single run of 4 awg that is 6.53% loss. 6 gauge would be 10.3%.


What part of "Maybe a fan or a laptop charger. Anything bigger I'd run the generator." don't you understand?

The fans I run in my camper pull max 15 watt, my laptop draws 65 watts.

6 AWG is plenty, even if he spikes into something pulling 600 watt for a little while.
 

corn18

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The idea is to wire for the hardware. It’s a 1kW inverter. Wire it to be used as intended so it’s not a surprise (or possible hazard) when someone tries to use the full potential of the inverter.
In his original post, he said he is doubling up 4ga wire. That is more than enough to handle a 1000W inverter.
 

rmaddy

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In his original post, he said he is doubling up 4ga wire. That is more than enough to handle a 1000W inverter.
That’s fine. I was replying to the post suggesting 6AWG was enough to handle lower loads.
 

McCarthy

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The idea is to wire for the hardware. It’s a 1kW inverter. Wire it to be used as intended so it’s not a surprise (or possible hazard) when someone tries to use the full potential of the inverter.

That renders his question and intent useless. I go by what people say and want, not by eventualities that may arise when somebody else hooks up more than he planned. As soon as we start treating everybody like a kid we are doomed to begin with. In reality we need to go back to personal responsibility and away from more regulations, code and laws.

If you want to stick to the book and code, most of the builds I have seen won't pass.
 

LVLAaron

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Gang, lets all be friendly.

The only reason I mentioned the smaller loads was because I don't intend to run any 100% duty cycle 1000 watt space heaters - I didn't know if wiring needed to be sized bigger for continuous loads over a long distance like this.
 

boondox

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That renders his question and intent useless. I go by what people say and want, not by eventualities that may arise when somebody else hooks up more than he planned. As soon as we start treating everybody like a kid we are doomed to begin with. In reality we need to go back to personal responsibility and away from more regulations, code and laws.

If you want to stick to the book and code, most of the builds I have seen won't pass.

It isn't about book and code. It is about a competent, functional install. If installing 1Kw inverter is is simple common sense to wire it for 1 kW. I'd call that taking personal responsibility for the equipment you install. And when giving advice for someone who may or may not know the details I feel a personal responsibility to make sure that they at least understand what risks or limitations there may be. I guess you feel that following Ohm's law is an infringement on your personal liberty. Do what you like but remember that the laws of physics enforcement department never sleeps. And Murphy is usually on the job too.
 

McCarthy

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Gang, lets all be friendly.

The only reason I mentioned the smaller loads was because I don't intend to run any 100% duty cycle 1000 watt space heaters - I didn't know if wiring needed to be sized bigger for continuous loads over a long distance like this.

Do you own an amp clamp meter and something like a portable induction cooktop or anything with variable draw up to 1200 watt? I'd like to know how much your build-in inverter draws at max before going into protection mode. Most build-in inverters are cheap junk and often convert less than they claim. I bet it goes into protection mode before sustaining 83 amps at 12 v.

And if that's the case, ONE 4 AWG wire will be enough - as I stated in my first post, with only 3% loss and at 15 feet, even by the linked calculator.
 

boondox

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Do you own an amp clamp meter and something like a portable induction cooktop or anything with variable draw up to 1200 watt? I'd like to know how much your build-in inverter draws at max before going into protection mode. Most build-in inverters are cheap junk and often convert less than they claim. I bet it goes into protection mode before sustaining 83 amps at 12 v.

And if that's the case, ONE 4 AWG wire will be enough - as I stated in my first post, with only 3% loss and at 15 feet, even by the linked calculator.

One run of 4 AWG with a 15 foot run and 83 amp load comes in at 6.45%. If actually pulling 1kW, assuming 80% inverter efficiency at full load that comes to 100 amps and 7.77% drop. I agree that cheap inverters rarely live up to their claims and feeding it low voltage only decreases what it will be able to actually do.
 

LVLAaron

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Do you own an amp clamp meter and something like a portable induction cooktop or anything with variable draw up to 1200 watt? I'd like to know how much your build-in inverter draws at max before going into protection mode. Most build-in inverters are cheap junk and often convert less than they claim. I bet it goes into protection mode before sustaining 83 amps at 12 v.

And if that's the case, ONE 4 AWG wire will be enough - as I stated in my first post, with only 3% loss and at 15 feet, even by the linked calculator.

I do have a clamp meter. Nothing to produce the load though. Closest thing I have is a 500 watt space heater.
 

boondox

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You might pick up a heat gun. Handy for shrink tubing and other things and make a good dummy load.
 
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