75 Amp 750w inverter - 100 Amp fuse OK?

[JCruse]

Is a 100 amp fuse an acceptable choice for wiring up a 750w inverter? I think the rating is either 72 or 75 amps. Thanks.

 

[NLXTACY]

A 75A fuse doesn't burn at exactly 75A. It could allow small spikes. Now you are putting in a 100A which could allow even higher current to pass. Not only could you overload the inverter which is only rated to 75A (assuming that's what the manufacturer recommends). Not only that what about the wiring? If you undersize the wiring now you are heating up the wires. I'd rethink this.

 

[JCruse]

I was just coming back to add that I'm wiring it with 4 gauge cable. Both sides back to the battery, and the small extra ground terminal to a nearby bolt in the body.

So I should use a smaller fuse? I always thought you leave a little room for small, short transient spikes before the fuse cuts power. No?


Also, is it better to mount the unit up front and run the AC to the back with an extension? Or run the DC all the way back? I've read both.

 

[NLXTACY]

I was just coming back to add that I'm wiring it with 4 gauge cable. Both sides back to the battery, and the small extra ground terminal to a nearby bolt in the body.

Perfect in theory but I don't know what the manufacturer recommends. 4awg is probably ok for the run BUT what are the chances that you will be pulling other accessories from those same cables? If you think you might, you need to reconsider the size. Not saying 4awg is right or wrong, just that you should consider your overall goals.

So I should use a smaller fuse? I always thought you leave a little room for small, short transient spikes before the fuse cuts power. No?

No, you always use what the manufacturer recommends. If its 75A then that's what you should be using.

Also, is it better to mount the unit up front and run the AC to the back with an extension? Or run the DC all the way back? I've read both.

Consider first the location of the fuse. You want the main fuse as close to the battery as possible. Reason is you do not want a large spike traveling down the entire run of cable if you don't need it to.

Generally speaking you always want to use the 12v option over the 110v option because 12v is just more efficient then 110v. If it were me, I'd mount the inverter in the back with a large gauge run of pos and neg OR better yet, run 2 smaller gauge runs each of pos and neg. So if you are running 4awg, use (2) 8awg instead. Just a thought.

 

[LAMBCRUSHER]

750 watts/12 volts=62 amps....how are you getting 75 amps? Is that the manufacturers rec? if that is the spec for overcurrent protection, then that is the size of time delay fuse you should run. #4 wire is good to 90 amps depending on the insulation class of the wire you're using. in the A/C electrical world, we wouldn't do parallel runs till you get to #6 wire size, altho in theory, a pair of conductors at the EXACT same length per run will effectively double the ampacity of that size of conductor(2 X # 8= about 100 amps capacity) both wires per pole of a parallel fed circuit must be of equal length or the shorter one will try to carry the full load until it fails. HTH

 

[Tapage]

So if you are running 4awg, use (2) 8awg instead. Just a thought.

why it's that .. I have a couple of long runs in my Cruisers always with one cable .. with proper rating.

 

[JCruse]

I just read the installation instructions - I had to get a magnifying glass to see the writing it was so small. It was the specs that listed 72 amps, that's where I got that number from. (I've read that Thor inverters put out 15% more power than their rating so maybe that's why it's not 62) But the instructions say to use a 50 amp fuse so that's what I ordered.

Is there actually room under the door jambs for 4 AWG cables? I didn't look like it to me last time I had them off. Any tips for this installation?

both wires per pole of a parallel fed circuit must be of equal length or the shorter one will try to carry the full load until it fails. HTH

That's interesting.

Generally speaking you always want to use the 12v option over the 110v option because 12v is just more efficient then 110v. If it were me, I'd mount the inverter in the back with a large gauge run of pos and neg OR better yet, run 2 smaller gauge runs each of pos and neg. So if you are running 4awg, use (2) 8awg instead. Just a thought.

That's funny. The person who posted to run the AC back instead of DC cited the fact that AC travels better as in it's use in power lines. It seemed to make sense just based on that fact alone.







.

 

[NLXTACY]

Is there actually room under the door jambs for 4 AWG cables? I didn't look like it to me last time I had them off. Any tips for this installation?

You can run it alongside the other wire run. There is a plastic "cover" that runs over the stock wiring. Just lay the new cable alongside of it.

That's funny. The person who posted to run the AC back instead of DC cited the fact that AC travels better as in it's use in power lines. It seemed to make sense just based on that fact alone.

Power lines use alternating current. There are tons of articles about but if you REALLY want an interesting read: http://en.wikipedia.org/wiki/War_of_Currents

Basically: "Edison originally advocated purely D.C. power with every home having a bank of batteries, that they would take to a central location to have recharged, to run their lights and so on. Westinghouse advocated A.C. which could be generated in a central location and then sent by wire to individual homes. Edison maintained that running the high voltage into homes would be too dangerous. Westinghouse argued that requiring people to transport wet-cell batteries (like automobile batteries) to have them recharged was dangerous and difficult. Once Westinghouse was able to transform A.C. from high to low voltage so that the high voltage did not have to go into the home, he won.
(Although if electric cars catch on, Edison's method will become popular also."

So the relevance to what you are doing is, in regards to AC, is zero.

 

[george_tlc]

This thread is funny - in a non-technical way

Some of you folk are ignoring or not aware that there is power loss involved going from one voltage to another, be it a DC : AC , DC : DC , AC : DC or AC : AC.

Don't convert voltage or AC/DC unless you have no option. 750W output will be more like 820W input assuming ~90% inverter efficiency.

E.g., if your fridge can run on 12V, do NOT convert 12V DC to 110AC to run the fridge via the AC input. You will lose power in the conversions due to efficiency losses.

AC has a simple advantage in power transmission lines that it is relatively easy to step up to 300k VAC or more so that resistive losses over long haul (city to city, across states, across the country) are less. It has NO advantage for your use in a vehicle.

The only reason to have an inverter in a vehicle is to run things that can ONLY run from 110AC. Anything else that can run on 12V, run it direct.

Personally, I'd use a circuit breaker rather than a fuse for an inverter. You may overload the inverter momentarily starting up a large load and you don't want to be replacing fuses all the time....

And yes, if you want to run say 30' from the battery to the AC load, then having the inverter 12V input closer to the battery is more efficient in terms of voltage drop on the 12V side (due to much higher input current) and run the long/extension as 110VAC. Of course, make sure that 110VAC cable is SAFE from chaffing etc...

cheers,
george.

 

[greentruck]

SNIP
Consider first the location of the fuse. You want the main fuse as close to the battery as possible. Reason is you do not want a large spike traveling down the entire run of cable if you don't need it to.

Generally speaking you always want to use the 12v option over the 110v option because 12v is just more efficient then 110v.
SNIP

A couple of more notes...

The main reason you want a fuse as close to source/battery is to protect against the circuit being compromised by a bad connection, cut and ground to body, etc. Yes, protection of the load is important, but you also have to consider a lot of other stuff that could go bad, in an accident, etc.

As for AC in the truck. It's not a long way to run cables for DC. It's best to use DC to the inverter and have the inverter close to the load. If you run with an energized inverter up front and AC power on long runs in the truck, then there's the chance something will get lose and potentially shock someone. It's best in mobile/temporary applications to have that AC cord where you can see all of it and protect it. Something as simple as slamming the door on a cord in a wet camp could have serious consequences.

Just being cautious about mobile circuit design. YMMV

 

[LAMBCRUSHER]

edison did not want you to have batteries in your home- he owned ALL the copper mines, and wanted to sell you-us the needed amount of copper to carry current from one of his army of power gen plants to your house- on his copper, that you bought. a/c requires much less mass of conductor to carry the same amount of current(work) and that's why he spent so much money electrocuting livestock with Telsas/ and Westinghouses A/C delivery......

 

[LAMBCRUSHER]

use the longer run of DC in the vehicle. 12 volts is very stable and not as stubborn to find a ground as the a/c will be.....

 

[Bogo]

a/c requires much less mass of conductor to carry the same amount of current(work) and that's why he spent so much money electrocuting livestock with Telsas/ and Westinghouses A/C delivery......

No, it's the same for both AC and DC. The electrons are agnostic and don't care if they are being used in DC current or AC current. They will do the same amount of work both ways. It is just very easy to step up and down AC voltages with a simple transformer. It takes a much more complex circuit to step up or down DC voltages. Therefore AC won out.

 

[JCruse]

I think AC won out mostly because J P Morgan owned the technology. Wealth has it's privileges...

But either way WOW thanks guys for a really enlightening, informative thread! I can read up on this stuff for hours, and I will be checking out the link. Again thanks.

I'm going to be using the 50A fuse for now, since that's what I have, and maybe later on when I know more about what gear I'll be running I'll make a final decision on a circuit breaker.

And yes, the inverter is going in the back.

 

[e9999]

One, if not the main, reason why AC won over is that it's very easy and inexpensive to increase the voltage with a dirt-simple coil transformer. And transmitting power long distance is much better (read less loss at a given power) at high voltage.
Interestingly, high voltage DC transmission lines are making a strong comeback now that power inverters are getting better and cheaper.

I'm guessing also that AC may be more likely to give you parasitic signals (hums etc) in your audio system etc if there may be a shielding issue than DC would.

But what is this about 2 lines in parallel and one takes the full load...? Are those magical lines?

 

[tclark]

Two 8 gauge wires do not equal one 4 gauge, doesn't work that way. Why would you want to run two smaller wires instead of one larger one? Maybe I'm missing something but I see reason for that to be better?

 

[JCruse]

Welp, everything has arrived, I got the 4 gauge cable (20ft), Thor 750W inverter, 4x 4 Gauge connectors, a 50amp ANL fuse, Scosche E2 ANL fuse holder, digital battery gauge, and I also got a Blue Sea 12v DC socket and twist lock plug along with an inline waterproof fuse holder to provide 12v to the back of the 80 as well. Now all I need is somebody to put it all in! LOL

I got some 12 AWG wire and connectors for the 12v plug that will tap into the heavy line going to the inverter. I'm just not quite sure the best way to do that. I'm actually not 100% sure about the whole thing to tell the truth. Normally when I start a project I can "see" the whole thing in my head before I start, but with this, my first interior/electrical mod to the cruiser, I just cant 'see' the finished layout. And lets not forget that I was the guy putting a 100A fuse in front of a 750 watt inverter...

 

[tclark]

Just run the main power(4 ga) to the back of the rig (with a large main fuse near the battery) to another fuse panel or distribution block(ideally a fuse panel) and split off from there. Simple, reliable, easy to add on and easy to troubleshoot. Another block or distribution point for a equal sized ground wire to a solid ground on the frame takes care of the negative side. Use zip ties or something similar to support wires along the way and leave plenty of slack for working on the system. One of the most important things really is the connections---a good solid crimp with a good pair of crimpers(not the cheap stamped crap you see everywhere) and heat shrink(ideally adhesive lined) will make for a solid trouble free connection. Some guys say solder is better, others say it stiffens the wire and causes it to break. Either way, that's the most critical part of what you're about to do.

 

[JCruse]

Oh I was going to run the main cables direct to the inverter posts (with an under hood ANL fuse) and then tap two 12awg wires directly off the posts to the DC socket, with another fuse in-line of course. No good?


Oh what gauge wire from the fuse box or splitter to the unit?

 

[Tapage]

in the electronic section was a small debate about soldering vs crimping .. what I got from that debate was better crimped.