Author Topic: Question on hard wiring a power inverter in my car  (Read 9907 times)

Offline Nate

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Question on hard wiring a power inverter in my car
« on: July 17, 2012, 12:34:03 PM »
I have used power inverters for years right from the cigarette outlet.  Now I am interested in wiring one directly to my battery to power things like a bread maker, TV ect.  Ideally I would like the inverter inside the car so I can easily plug things in.  This would involve running a cable from the battery through the firewall, and into the passenger compartment.  This seems like a real PITA.

Would it be easier and SAFE to connect the inverter to the battery and simply run a short grounded extension cord from the inverter, though a gap on the side of the hood, through the passenger door  and into the passenger compartment?  Would the extension cord be pinched too much from the passenger door and hood?

Also, is a fuse needed between the battery and inverter?  If so what are the guidelines for amps on the fuse?  I have a 450watt inverter now.  I am looking to wire in this one temporarily and upgrade to an 800 later.  Thanks!
NATE

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Offline cmxterra

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Re: Question on hard wiring a power inverter in my car
« Reply #1 on: July 17, 2012, 01:47:26 PM »
Problem with that is that most inverters are not weather proof or resistant. You run the risk of starting a fire.

The link below will let you calculate the size fuse you would need
http://www.supercircuits.com/resources/tools/Volts-Watts-Amps-Converter

« Last Edit: July 17, 2012, 01:52:48 PM by cmxterra »
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Offline idelphic

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Re: Question on hard wiring a power inverter in my car
« Reply #2 on: July 17, 2012, 02:01:48 PM »
Running power from the batter to the passenger compartment isn't as difficult as one might think.  There are generally a number of rubber grommets in the firewall for wires and such.  Automakers will use the same firewall between models - it just depends on what options are installed. 

Generally you can find a unused grommet that you can pass a cable through.  We used to use a coat hanger to tape wire to to feed it into the cab.

Alternately, you can take your vehicle to any Car radio installer and ask them to run the cable for you.  This is what I did on my Xterra years ago and they did so without issue.  I asked for a 30AMP 'Mega' fuse at the battery, and #8 wire ran with some extra lee way.

With your plan to run a 800watt inverter in the future, I would run BOTH the positive and negative to the battery.  FUSE BOTH SIDES, and have another pair of fuses inside the car.  the 30AMP inline 'MEGA' fuse holder is about $6 each.. but a fuse is cheaper to replace then the whole car...

If I think about it, I'll post a photo of my truck install which runs a 50watt Amateur radio.
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Offline rustyknife

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Re: Question on hard wiring a power inverter in my car
« Reply #3 on: July 17, 2012, 02:09:01 PM »
As previously said you need to protect the inverter from the weather issues. Also, normally when I installed these in my trucks they were inside and I ran some heavy cables to the battery bank. 800W is not near enough to run the items you mentioned. Increase that to 1500W a least and you will only be able to run one thing at a time. The last one I installed was 2000W peak/1500W continuous. There should be a set of instructions in the box when you buy it. Best wishes.
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Offline Curtis

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Re: Question on hard wiring a power inverter in my car
« Reply #4 on: July 17, 2012, 02:36:16 PM »
I'm a truck driver and have mounted many inverters inside the sleeper over the years, up to 2500 watts.  And you'll need more than 800watts for the appliances you listed as rustyknife said. The bigger (in wattage) the inverter and the farther from the battery you get the heavier the cable you will need.  DON'T SKIMP ON THAT.  The reason the cables that come with inverters with the clips on the end are so light gauged is because they are so short.  For instance if you are going with 800 watts and less than say... 6 feet, the easiest/cheapest solution will be heavy jumper cable.  Again don't skimp on this.  If you have the wrong combination of too long of a run length with too light a gauge and drawing a lot of wattage/amps from the battery, you will have a fire.  Below is a link I found right quick that will give you an idea about both cables and fuses.  The table is at the bottom of that page.  I ran extrememly heavy cable and did not use a fuse once and got away with it just fine... not recommended.
http://www.newenglandsolar.com/catalog_pages/inverter_cables.htm

I would not run an inverter under the hood for regular use.  It will not last as cmxterra said.  When using it there I would even leave the hood up or put the inverter outside the engine compartment.  Inverters need to move a lot of heat with their fans and the temp under a hood wouldn't help that at all.  And of course, they are not even water resistant.  There may be some inverters made for mounting outside (like RV models etc...) but they aren't what we are talking about here.

One last detail.  Not all cable is the same.  You want copper for sure.  More strands of smaller wire in the cable is better and more flexible yet a little less durable.  It will carry more juice than fewer strands of heavier wire without heating up too much.  And last but not least, use good connectors/cable ends.  You're only as good as your weakest link.  Would be a shame to spend 200 bucks on inverter and cable then burn your 20thousand dollar car to the ground because you didn't spend 10 bucks on good cable ends.  Hope that helps some.
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Offline Nate

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Re: Question on hard wiring a power inverter in my car
« Reply #5 on: July 17, 2012, 04:20:51 PM »
I never thought of the weather aspect of the inverter under the hood.  I assumed it was pretty dry under there.  We all know what happens when we ASSume.  Thanks for the tips on wire.  I was looking at getting 6 or 4 gauge wire just to be safe.  Thanks for the calculator.  To use it correctly do I put 12 under volts since that is the volts of the car system and under watts I put the wattage of the inverter?  The resulting amps would be the size of fuse I would want correct?

 Right now I drive a 97 passat tdi, but most likely I will be doing this with a 05 windstar I will be buying from my dad as soon as he finds a new van with all the "essentials" mom wants. 
NATE

"This is the Law of the Yukon, that only the Strong shall thrive;
That surely the Weak shall perish, and only the Fit survive."  Robert Service

Offline welshman

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Re: Question on hard wiring a power inverter in my car
« Reply #6 on: July 17, 2012, 09:56:12 PM »
800watt inverter will require at least 70 amp fuse      divide 800w by 12 volts will give you 66 amps
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Offline Curtis

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Re: Question on hard wiring a power inverter in my car
« Reply #7 on: July 17, 2012, 10:15:59 PM »
As to the 4 or 6 gauge cable to be safe.  There are several standards for wire/cable gauge/size standards.  By one I would say it's to big and by another I'd say it's too small off the top of my head.  For instance there is a big difference between 4 and 4/0 in AWG gauges.  4AWG is .204 inch raw wire diameter and 4/0AWG is .454 inch.  That's a quarter inch difference.  AWG is the standard but they can't just make it easy. The first link is a table that shows all the gauges.  The second link will give you better information to make your choice considering gauge/length/wattage/amperage.  Just pay attention to whether you talking about X gauge or X/0 gauge.

http://www.bulkwire.com/wiregauge.asp  Gauge chart for sizes.

http://www.solarhome.ru/en/basics/batteries/sizing_cables.htm   Another chart with a fairly simple formula following.
"But whether the Constitution really be one thing, or another, this much is certain—that it has either authorized such a government as we have had, or has been powerless to prevent it.  In either case, it is unfit to exist." ~Lysander Spooner
from:  'No Treason:  The Constitution of No Authority'

Offline Curtis

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Re: Question on hard wiring a power inverter in my car
« Reply #8 on: July 17, 2012, 10:33:12 PM »
I looked closer at that second link and... okay it's not that simple when I don't know what you have and what you are going to do with it, exactly.  I would go with no less than 4AWG cable if less than 6-8 feet, but you should really do the math with your inverter and the biggest appliance you're going to run off it.

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from:  'No Treason:  The Constitution of No Authority'

Offline bartsdad

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Re: Question on hard wiring a power inverter in my car
« Reply #9 on: July 18, 2012, 01:21:25 AM »
Here's another thought on wiring. You can get kits to wire in an amplifier for a car stereo. Most of them include wire and fuse holders and the necessary connectors. Most also include on the package a chart to determine wire size based on run and current draw.

I'm thinking something like this.  I'm not endorsing this, just using as an example.
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Offline statesofmind

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Re: Question on hard wiring a power inverter in my car
« Reply #10 on: July 18, 2012, 06:16:39 AM »
As far as inverter size, l have always read that you want to run an inverter as close to the amount of watts needed for the item you plan to use.  Not sure what the bread maker draws, but 450 is fine for most newer TVs, especially if they are LED sets. I'm currently running a DVD player and LED TV off a 400w inverter and it never even really heats up.

« Last Edit: July 18, 2012, 06:22:54 AM by statesofmind »
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Offline CovertPrepper67

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Re: Question on hard wiring a power inverter in my car
« Reply #11 on: July 18, 2012, 08:31:46 AM »
One thing to take into account is that as electronics age the power rating they can handle decreases. If you want to reliably run an 800W widget, you should look at sizing an inverter that puts out 1000-1250W. Having an inverter that gives you a little room allows for any start-up surges that might be required and gives you plenty of workable power as the device ages.

Another reason you do not want to size an inverter, or any electronics to run all out whenever they are in use is the product tolerances might not allow for it. If the parts that go into the device are produced with poor quality control then each part that goes into the device will have a different limit.

A rule of thumb I always use when doing first estimations at power supply size is (Wattage I need to supply(Load)/80%) = Wattage of source(Inverter)

A good 1000W inverter that I use is this one.
http://www.blackanddecker.com/power-tools/VEC049DCB.aspx

Anyway just $0.02 from an Electrical Eng.

Offline statesofmind

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Re: Question on hard wiring a power inverter in my car
« Reply #12 on: July 18, 2012, 09:16:20 AM »
Great Point Covert!  That's what I was getting at.  Some people say to get the biggest inverter you can afford, whether or not you need it.  But it is not efficient to be running a 2300 watt inverter for a simple little tv or a light or 2.  Get something that can handle the load, with a little room to spare.
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Offline CovertPrepper67

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Re: Question on hard wiring a power inverter in my car
« Reply #13 on: July 19, 2012, 10:51:55 AM »
Thanks Statesofmind, I got to think about this and I realized O forgot to add in an important little note. I also have a 150W inverter that plugs into a cigarette light that I use more often, almost daily, and that powers my laptop or other small stuff.

I recommend having a smaller inverter, <400W for everyday situations, and a larger >1000W for big items and emergency house power.

The little one is a great place to start, then as you get experience with it, you should be better able to gauge the size for a larger inverter.

Offline digdug18

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Re: Question on hard wiring a power inverter in my car
« Reply #14 on: August 28, 2012, 04:59:12 PM »
I have used power inverters for years right from the cigarette outlet.  Now I am interested in wiring one directly to my battery to power things like a bread maker, TV ect.  Ideally I would like the inverter inside the car so I can easily plug things in.  This would involve running a cable from the battery through the firewall, and into the passenger compartment.  This seems like a real PITA.

Would it be easier and SAFE to connect the inverter to the battery and simply run a short grounded extension cord from the inverter, though a gap on the side of the hood, through the passenger door  and into the passenger compartment?  Would the extension cord be pinched too much from the passenger door and hood?

Also, is a fuse needed between the battery and inverter?  If so what are the guidelines for amps on the fuse?  I have a 450watt inverter now.  I am looking to wire in this one temporarily and upgrade to an 800 later.  Thanks!


What kind of car are you installing this in? Because you might need to upgrade your battery, alternator, or adding an extra battery and isolator. It depends on your engine and alternator size, but also if your planning on running these items when the car is off.


Offline Nate

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Re: Question on hard wiring a power inverter in my car
« Reply #15 on: August 30, 2012, 06:59:34 AM »
@digdug
Eventually this set up is for an 05 ford minivan.  I will be inheriting this one from dad once he finds a new van mom likes.  The bread maker idea is mainly for when we are driving somewhere.  It seems efficient to me to make food while traveling.  I no longer need the tv as I played around with my digital tv converter box and my portable dvd player.  I can run the dvd player right from the 12v outlet, connect the converter box to the dvd player, run the converter box from an inverter from another 12v outlet, connect an antenna and I have TV.  Watching tv is not planned for driving.  I can of course watch DVD's while driving, but that is not safe!  ;) 
NATE

"This is the Law of the Yukon, that only the Strong shall thrive;
That surely the Weak shall perish, and only the Fit survive."  Robert Service