How best to wire a DC power inverter in truck?

[Cliffh]

I'm looking to install a 700w DC inverter in the cab of my pickup; it'll come in handy around the yard and while traveling.

The directions state that the inverter should be disconnected when starting the vehicle, when it's not in use and if a battery charger is used. 

I'd prefer to mount a switch of some kind in the cab so I don't have to open the hood & disconnect the wires. 

One method under consideration is to use an old Ford starter solenoid and a toggle or rocker switch in the cab.  But I'm open to other possibilities.

[zxcvbob]

I have one (400W) mounted under the dashboard of my truck and plugged into one of the cigar lighters.  It's been there about 7 or 8 years and plugged in all the time.  I use it frequently for an electric razor and sometimes for a 110V trouble light.

Yours has a power switch, doesn't it?

[Nick1911]

Starter solenoids overheat rapidly if left energized.

A full 700 watts is 58 amps at 12v.  Be sure to size wire for this draw, and use a fuse at the battery.

I would hard wire it in, and leave the switch on the unit off unless needed.

[zahc]

400W would draw 33 amps. Most cigarette lighter plugs are on a 15 or 20 amp fuse so I'm guessing you don't really draw 400W from it.

700W is going to draw around 60 amps.

I would pull from the positive battery terminal or fuse box with an inline 50A fuse, through a switch, into the inverter. You can get pretty gnarly switches. If you can't get a big enough switch or don't want to mount a giant mad-scientist knife switch on your dash, you can use something like this

http://www.ebay.com/itm/BOSCH-TYCO-RELAY-75-AMP-12V-HEAVY-DUTY-HIGH-CURRENT-/290499370197

[zxcvbob]

400W would draw 33 amps. Most cigarette lighter plugs are on a 15 or 20 amp fuse so I'm guessing you don't really draw 400W from it.

700W is going to draw around 60 amps.

I would pull from the positive battery terminal or fuse box with an inline 50A fuse, through a switch, into the inverter. You can get pretty gnarly switches. If you can't get a big enough switch or don't want to mount a giant mad-scientist knife switch on your dash, you can use something like this

http://www.ebay.com/itm/BOSCH-TYCO-RELAY-75-AMP-12V-HEAVY-DUTY-HIGH-CURRENT-/290499370197

I very seldom run more than 100W.  Have gone up to about 200W or so.  The point was this has been hooked up hot all the time for quite a few years.  I'm not sure if the lighter circuit is switched off by the key when the starter is engaged...  It is hot when the key is off.

I would just hook a 700W up direct to the battery or starter with a probably 8 gauge wire and a 50A or 60A fusable link (or inline fuse) and leave it hot all the time.  Turn it off when not in use.  

[Jim147]

If you want to hard wire it but only turn it on when needed I would find a place to mount one of these.

http://www.jegs.com/i/JEGS-Performance-Products/555/10305/10002/-1

jim

[Cliffh]

The inverter came with a set of 8 gauge cables.  They're too short to make it from the battery to the cab but that's not a problem, already figured to have to make a new set of cables.  I think I've already got a source for the cable, it looks as if our motorhome had an inverter DIY installed at some time in the past - at least the wiring's still there.

The recommended installation is to attach both cables directly to the battery.  I assume the ground cable could be grounded to the engine/frame, but my plan was to go ahead and attach both to the battery.  Wouldn't take much more cable and running them both to the same destination would be a bit easier than running them in different directions.

.... If you can't get a big enough switch or don't want to mount a giant mad-scientist knife switch on your dash, you can use something like this

http://www.ebay.com/itm/BOSCH-TYCO-RELAY-75-AMP-12V-HEAVY-DUTY-HIGH-CURRENT-/290499370197

Yeah, I was hoping to avoid having a huge knife switch mounted on the dash.  Not only would it take away from the beauty of the 23 year old interior, I'd hate to see what the dog looks like with her hair shooting out in all directions.

If you want to hard wire it but only turn it on when needed I would find a place to mount one of these.

http://www.jegs.com/i/JEGS-Performance-Products/555/10305/10002/-1

jim

I've got to stop drooling over all those engine parts in the JEGS catalog and start looking at some of the other parts they offer!   

Now to decide which would be the better approach, brute force or more fancy???  The JEGS switch would require less wiring and at least three less components....  But then again, I could use a lighted rocker switch with the Bosch unit....

The manual didn't mention using a fuse, but it does make sense.  Possibly something like this fusible link:  http://www.ebay.com/itm/Buss-Fusible-Link-FLB-50-Fuse-Car-Auto-50-Amp-32V-/280584091657

[dogmush]

You're on the right track. Cables to bat, fuse of appropriate size, etc.

I'd switch it through a relay of if it were mine. Small switch on the dash, relay up under thehood or dash.

Here's an 80A 12VDC relay:
http://www.amazon.com/Automotive-Socket-Transparent-5-Wire-Relays/dp/B0086SX7VM

You can probably get one out of napa as well.

[bedlamite]

You're on the right track. Cables to bat, fuse of appropriate size, etc.

I'd switch it through a relay of if it were mine. Small switch on the dash, relay up under thehood or dash.

Here's an 80A 12VDC relay:
http://www.amazon.com/Automotive-Socket-Transparent-5-Wire-Relays/dp/B0086SX7VM

You can probably get one out of napa as well.

An 80A relay with 24ga wire?   That's trouble that hasn't happened yet.

Use the one zahc linked to, with 8ga wire.

[dogmush]

Well use the right wire, obviously. That was just the first relay of appropriate size google found.

The prewired socket is probably a chinese plot to burn down all our filthy, capatolist trucks.

I missed that zahc had even linked one, but Bosch is my go to for this kind of thing. If it were me, Id still hit an automotive supply house and get it locally.

Either way, use a relay, not amsolenoid or big ass switch.

[cassandra and sara's daddy]

I can't swear it's the best but the way I rigged my 3000 watt was 2 wire running back to the cabineton my utility box. It's fused right of the battery.then a shorter piece of 2 wire from the inverter to a ground on the frame of the truck. I didn't trust the ground on the utility body. I run a DeWalt 12 inch miter saw off it. It can also handle starting my 8 horsepower snowblower

[Triphammer]

If the illustration is accurate for the BOSCH the terminals are only rated @30amps. The relay probaly has an inrush rating of 75. The plug in relay from amazon has male quick connects. Wouldn't trust it for more than 20 amps regular use. Probably dropped a decimal & it's an 8 amp relay.
 I like the one from Jegs. I've used them on boats before. They're available from harbor freight in a recessed style.

http://www.harborfreight.com/catalogsearch/result?q=battery+swicth

 If you really want to use a remote switch, I'd parralel a couple 30 amp relays or find a multi (2 or 3) pole relay & parrallel that. Only one coil to worry about.
 Just looked. These are not starter relays but look the same.

http://www.mcmaster.com/?m=true#general-purpose-relays/=ll9721

[Jim147]

I guess I could play with a 24v coil, single pole condenser contactor to see if 12vdc would work the coil.

jim

[dogmush]

If the illustration is accurate for the BOSCH the terminals are only rated @30amps. The relay probaly has an inrush rating of 75. The plug in relay from amazon has male quick connects. Wouldn't trust it for more than 20 amps regular use. Probably dropped a decimal & it's an 8 amp relay.
 I like the one from Jegs. I've used them on boats before. They're available from harbor freight in a recessed style.

http://www.harborfreight.com/catalogsearch/result?q=battery+swicth

 If you really want to use a remote switch, I'd parralel a couple 30 amp relays or find a multi (2 or 3) pole relay & parrallel that. Only one coil to worry about.
 Just looked. These are not starter relays but look the same.

http://www.mcmaster.com/?m=true#general-purpose-relays/=ll9721

He specified no big switches. And McMaster Carr involves some custom wiring.  I just picked the first relay I saw as an example, not a suggestion of that particular one.  But there's no need to reinvent the wheel here.  64 impalas don't jump into the air on 24g wire.  High current automotive electrical stuff exists.

Cliffh
Here, use this one:
Battary isolater for car stereo

28 bones shipped, over rated for the draw you need so you can upgrade, designed to run on 12VDC from a car, big enough terminals to do what you need.

[Frank Castle]

Any car stereo shops, should have cables and fuses.



 

[zxcvbob]

got a link to the inverter you're using?

[AZRedhawk44]

400W would draw 33 amps. Most cigarette lighter plugs are on a 15 or 20 amp fuse so I'm guessing you don't really draw 400W from it.

700W is going to draw around 60 amps.

'Splayn math, plz.


P = E * I

P is power in watts
E is volts
I is current in amps

or, I = P/E.  However you want it.

A 700 watt AC inverter providing 700 watts @ 120vAC is only presenting a little less than 6 amps of current.

6 amps is 6 amps is 6 amps.  Current is current.

Presenting 6 amps on a 12v DC system will draw 6 amps * 12 volts = 84 watts DC.  Watts are worthless.  Amps are power.  Convert amps, not watts.

Assuming a 100% efficient conversion from DC to AC, you still just need 6 amps.  Typical losses are 10-15% for little inverters, so you need 6.5 or 7 amps.  No?

[zxcvbob]

400W / 115V = about 3.5 amps
400W / 13V =  about 30 or 31 amps

It has to draw roughly 10 times as much current (assumes high efficiency but not 100%) from the battery as what you are supplying at the output.

[Gewehr98]

Bob explained it before I could.  Many, many more amperes drawn on the DC side of the inverter, because of the lower voltage.

[Nick1911]

And, your wire size is pretty much only concerned with amps.

The wire adds resistance to the circuit.  How much heat the wire will incur depends on the voltage drop across the wire, multiplied times the current running through it.

At 58 amps draw, the inverter is only presenting a .20 ohm load to the 12v battery.  10 feet of, say 12ga will add 0.032 ohms.  The voltage drop on the wire is thus 1.92 volts, which at 58 amps is 111 watts of power that the wire must dissipate.

10 feet of 8ga will add 0.012 ohms.  The voltage drop on the wire is thus 0.72 volts, which at 58 amps is 41 watts of power that the wire  must dissipate.  Much more reasonable and less likely to melt the insulation and start a fire.

[geronimotwo]

  Currentpower is current power.

fixed it for ya!

i'm also betting on their being some internal losses, so it would likely draw more than 60 amps IF running a 700 watt appliance.  check the manual for the input power/current.

also, get the fuse as close to the battery/junction box as possible

[Cliffh]

got a link to the inverter you're using?

Sorry, no.  It's an old Harbor Freight unit I picked up years ago against the day I'd need it.  That day is near.

Didn't think about car stereo shops having cable and fuses.  Too bad there isn't one within ~40 miles of here...  There are a few chain auto stores.

I asked SWMBO whether she'd pretty a "pretty" installation (small switch in cab with relay under hood) or go with the "brute force" route (like the JEGS switch).  Surprised the hell out of me when she said to go with the JEGS switch, maybe with the faceplate but that's not necessary.

So, I'll come off the positive side of the battery with a 50a fusible link and 8ga wire to the switch on the dash, then 8ga to the inverter, with 8ga from the battery negative terminal directly to the inverter.

Having the inverter in the cab will allow use of the 120v while on the road, and I can run an extension cord out the window when running tools in the yard, etc.

Y'all have helped with the "one new thing a day" for a couple days now.  Thanks!

[zxcvbob]

Is this 700W continuous?  Or 700W peak?

[Cliffh]

Is this 700W continuous?  Or 700W peak?

I'll have to answer tomorrow.  I don't recall and don't have access to the manual right now.

[zxcvbob]

I'll have to answer tomorrow.  I don't recall and don't have access to the manual right now.

The reason I ask is HF is pretty "optimistic" with their peak performance specs.  Hook the inverter up to the battery with the included alligator cables and make sure it will run your intended load before you start spending money on disconnects and cutting holes in the dash.