I'm thinking of installing a medium size inverter so I can use my laptop while running on 12V DC. This Power Bright unit is an example of what I'm considering.There's a space under one of the dinette seats, right near the power center, which would be great for this. The 12V fuse bank has two unused circuits, so I figure I'll use one! So about installing this: (1) one wire runs from the fuse bank to the positive (usually red) connector on the inverter. Yes?(2) If the inverter has a chassis ground connector, this could go to the frame of the converter, right next door, which has a chassis ground connector. Yes?(3) But what about the "ground" connector on the inverter? Usually black. When I look at, for example, the 12VDC connector which is intended for the TV set up front, there are two wires: one orange and one white. The orange wire goes back to the fuse block. And the white goes back to a ground bus right behind the fuse block. This bus, in turn, is grounded to the chassis. This bus is REALLY hard to get at; I'd have to do some serious dismantling of stuff. I see why the ground wire has to be run to the TV cabinet, which isn't near any chassis ground points. BUT -- and this is the real question here -- in my situation, can't I just connect the inverter's ground wire to the same point as the chassis ground? Aren't these two electrically equivalent? Or am I missing something big?Thanks!Rich

You must connect the inverters - and + to your 12v source. You can certainly use the frame as that connection.The chassis ground terminal on the inverter should also be connected to the frame even though the inverter will function without it. It's a safety feature. It will connect the ground pin of the 120v AC outlet on the inverter to the chassis ground.By the way, how big is a medium size inverter to you? I doubt the extra fuse in your block is rated for more than about 20 or 30 amps. That translates to about a 200 to 300 watt inverter. Any larger than that and you will need to connect it directly to your battery with large cables and large fuses.

Have you considered getting a 12v power brick for your laptop. If I knew the make and model, I could look it up. Much more efficient, more useful, and can be used in more places.

Rich:I'm not quite sure of what your idea of a "medium size inverter" is?.....400 watts?...800 watts?400 watts would most likely do the job for you but you really should get the inverter and then install it as per the manufacturers instructions, so start there.Once you get there then that would be a good time to ask your questions.

Hi,You don't need 600 watts. 300 would be plenty and likely even 150 would do the job.I'd suggest Go Power, Samlex or Morningstar for the pure sine wave inverter.Install the inverter as close to the battery bank as is humanly possible. While one could use the power distribution center, it is not a good idea.Remember 300 watts represents at least a 30 amp load to the battery bank. My power distribution has only 15 amp fuses in it.

Thanks, all.To respond to some of the issues raised.So the conversion from watts of inverter output to load on the battery in amps is roughly 10:1? A 150-watt inverter would draw roughly 15 amps? My battery "bank" is one 12V battery, located under the steps in the front of the coach. The place I'd like to use the laptop (or charge my phone or iPad for that matter) is about 10-12 feet aft of that position, in the dinette. The power center is right there, hence my idea to locate the inverter there. Don, what is that not a good idea? I'm not challenging you, just trying to learn. The laptop is an Apple MacBook with an early magsafe power connection. It's a 13-inch, aluminum, late 2008 machine. KD4UPL, I appreciate the nuts and bolts answer to my question. If I understand you, I can attach both the (-) and the chassis ground connections from the inverter to the chassis ground on the converter and be safe and functional. The unused slots in the fuse bank have no fuses, but almost everything else is a 15-amp fuse, to I'm suspecting that's about max.

Electrical ground question(s) | Good Sam Community

KD4UPL
Explorer
May 15, 2014
You must connect the inverters - and + to your 12v source. You can certainly use the frame as that connection.
The chassis ground terminal on the inverter should also be connected to the frame even though the inverter will function without it. It's a safety feature. It will connect the ground pin of the 120v AC outlet on the inverter to the chassis ground.
By the way, how big is a medium size inverter to you? I doubt the extra fuse in your block is rated for more than about 20 or 30 amps. That translates to about a 200 to 300 watt inverter. Any larger than that and you will need to connect it directly to your battery with large cables and large fuses.
ChooChooMan74
Explorer
May 15, 2014
Have you considered getting a 12v power brick for your laptop. If I knew the make and model, I could look it up. Much more efficient, more useful, and can be used in more places.
BoonHauler
Explorer
May 15, 2014
Rich:

I'm not quite sure of what your idea of a "medium size inverter" is?.....400 watts?...800 watts?

400 watts would most likely do the job for you but you really should get the inverter and then install it as per the manufacturers instructions, so start there.

Once you get there then that would be a good time to ask your questions.
pianotuna
Nomad III
May 15, 2014
Hi,

You don't need 600 watts. 300 would be plenty and likely even 150 would do the job.

I'd suggest Go Power, Samlex or Morningstar for the pure sine wave inverter.

Install the inverter as close to the battery bank as is humanly possible. While one could use the power distribution center, it is not a good idea.

Remember 300 watts represents at least a 30 amp load to the battery bank. My power distribution has only 15 amp fuses in it.
rich85704
Explorer
May 15, 2014
Thanks, all.

To respond to some of the issues raised.

So the conversion from watts of inverter output to load on the battery in amps is roughly 10:1? A 150-watt inverter would draw roughly 15 amps?

My battery "bank" is one 12V battery, located under the steps in the front of the coach. The place I'd like to use the laptop (or charge my phone or iPad for that matter) is about 10-12 feet aft of that position, in the dinette. The power center is right there, hence my idea to locate the inverter there. Don, what is that not a good idea? I'm not challenging you, just trying to learn.

The laptop is an Apple MacBook with an early magsafe power connection. It's a 13-inch, aluminum, late 2008 machine.

KD4UPL, I appreciate the nuts and bolts answer to my question. If I understand you, I can attach both the (-) and the chassis ground connections from the inverter to the chassis ground on the converter and be safe and functional. The unused slots in the fuse bank have no fuses, but almost everything else is a 15-amp fuse, to I'm suspecting that's about max.
pianotuna
Nomad III
May 15, 2014
Hi,

It is not a good idea because the power center was designed with 15 amps of output (or less) per circuit. A 300 watt inverter can draw 30 amps.

Yes, the conversion, after inverter losses, works out at about 10 to 1.

Your apple laptop absolutely requires a pure sine wave inverter. That is, unless you enjoy fried apples and ham.
beemerphile1
Explorer
May 15, 2014
rich85704 wrote:
Thanks, all.

To respond to some of the issues raised.

So the conversion from watts of inverter output to load on the battery in amps is roughly 10:1? A 150-watt inverter would draw roughly 15 amps? ....

No, the watts stays the same whether it is 12vdc or 120vac. The amperage is what changes.

150 watt divided by 120vac = 1.25 amp
150 watt divided by 12vdc = 12.5 amp

You also need to add 10% or 20% for the inefficiency of the inverter.

For my 400 watt continuous 800 watt peak inverter I used a 75 amp fuse and 4 gauge wire straight to the battery.
rich85704
Explorer
May 15, 2014
Don, thanks! I'm thinking a MUCH smaller inverter, 150W max, for the laptop and charging the phone and iPad. Seems like that brings the load down to 15 amps max on that circuit, and should be safe. But here's the rub: the lower-power inverters I can find so far are not pure sine wave. Lots of units which are advertised to plug into a cigarette lighter in your car, and for the purpose of laptop use. Does the fried apples analogy hold for a device which runs off a power brick like my lap top?

R
pianotuna
Nomad III
May 15, 2014
Hi Rich,

Apples are a special case. Do not attempt to use a MSW inverter to power them.

PSW inverters cost more. My own personal choice would be the Morningstar unit.
wa8yxm
Explorer III
May 15, 2014
For small inverters your question is good (100 watt and down, possibly a bit bigger)

For 1KW inverters and up such as the one you linked to forget your plan won't work

Run heavy cable, at the very minimum starter cable (4ga) directly to the battery through a proper size "T" fuse, Get two of those cables, one red, one black, Hook the red one to the red terminal, black one to the black terminal, lay them side by side and wrap with tape or use a Split loom (That ribbed plastic tubing that goes over wires) to keep them side by side, The red wire runs to the "T" fuse then a shorter jumper to the battery positive, the black direct to the battery negative. If you must add a DC switch (Do not trust the one on the inverter it can go anywhere in the red line.

The wiring to your fuse panel can not handle that kind of load.

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