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QUICK QUESTION: Is it BAD to switch the ground on/off instead of the +ve?

W

WarDemon666

Platinum Member
I accidently soldered my power wire directly to my inverter, im now asking myself if I can use the ground to switch it on and off instead?

I know it will work, but is it dangerous?

Also, i forgot to fuse the +ve also, but I know that my inverter has 2 fuses @ 25 in it.. will that be good enough to run a few things? inverter is 40A/ 400watts max...

Thanks a lot!
 
I can't forsee a problem.

I'm a EE, but it's also 12:30 and I've been up since 5:30, so you may want a second opinion. But, so long as that's your only ground point, you should be fine. Now, if you some how short it to ground (IE, system gets shorted to the case to ground) it might be a problem.
 
Uh, what application?

A 12 VDC to 120 VAC inverter, mounted in a vehicle?

How's it mounted?

Without you answering, I'd say no.

In a car, the entire body, frame, and anything attached that's made of metal is electrically live with -12 VDC, so the inverter could ground itself through the mounting screws, making it impossible to power down.

EDIT: The inverter is fused at 50 amps to protect itself, not your car's wiring. You should also fuse the power wire as close to the +12 VDC source as possible. (For a 50 amp draw, you should probably use 8 ga. wire or thicker, with an inline fuse or a seperate fuse block as close as possible to the battery--look for amplifier wiring kits for a ready-made solution.) If you don't, you're asking for trouble if the insulation is breached and a short circuit is created. Car batteries can supply an incredible amount of amperage, enough to turn the +12 VDC wire into a big, long, white-hot heating element, resulting in lots of smoke and possibly a fire.
 
Originally posted by: Thegonagle
Uh, what application?

A 12 VDC to 120 VAC inverter, mounted in a vehicle?

How's it mounted?

Without you answering, I'd say no.

In a car, the entire body, frame, and anything attached that's made of metal is electrically live with 12 VDC, so the inverter could ground itself through the mounting screws, making it impossible to power down.
Click to expand...

Agreed. I think the answer is, in theory, not a problem, in practice, yeah, probably a poor idea.
 
Originally posted by: Thegonagle
Uh, what application?

A 12 VDC to 120 VAC inverter, mounted in a vehicle?

How's it mounted?

Without you answering, I'd say no.

In a car, the entire body, frame, and anything attached that's made of metal is electrically live with 12 VDC, so the inverter could ground itself through the mounting screws, making it impossible to power down.
Click to expand...


Its going to be mounted under the passenger seat, with carpet pretty much everywhere, im wondering if I should secure it on a piece of wood or soemthing?

Thanks again 🙂

Theres nothing else I should worry about?

How about the no fuse issue, is it REALLY an issue? 🙂

Oh! and Im going to be using a relay to power it, but the relay wire harness has some really small wires compared to the ones on the inverter, should i solder the 8awg(from the inverter) directly onto the relay or should i just use the relay harness wires?

I bought some 30A relays cause I thought my inverter was 30A but it turns out its 40, should I use different relays? The inverter is rated at 400 watts but ill never use more than 150 so I dont think it should be a problem, right?
 
Originally posted by: Thegonagle
read my edit above--I am concerned about the lack of a fuse for the power wire.
Click to expand...


Thanks for your most useful post.

Do you think it may be dangerous to drive around for a week before I have time to go buy an inline fuse?

I guess im going to have to RE wire everything AGAIN 🙁

I was in such a rush to get everything finished that I took the easy way out. Now I have to do this all over again 🙁
 
Originally posted by: WarDemon666
Originally posted by: Thegonagle
read my edit above--I am concerned about the lack of a fuse for the power wire.
Click to expand...


Thanks for your most useful post.

Do you think it may be dangerous to drive around for a week before I have time to go buy an inline fuse?

I guess im going to have to RE wire everything AGAIN 🙁

I was in such a rush to get everything finished that I took the easy way out. Now I have to do this all over again 🙁
Click to expand...
An inline fuse should only be a few dollars, and be realitivly simple to install.

What are you running from the inverter? If it's nowhere near it's rated maximum, you'll be fine for a while.

As for your relays..

Are they rated at 30A at 12VDC? 30A at 12V is a lot different than 30A at say, 120VAC. 🙂

I'd go solid state on the relay. I suppose that makes it harder to use a simple capacitor and resistor to get a time delay effect, since a solid state relay will operate on ~3V.

You can, indeed, buy relays that have time delay built in.

But wait - Are you sure the power switch carries the whole load of the inverter? That seems rather unlikely...

Unless I'm missing something. I thought you were going to use the relay to turn it on.. What is the point in using a relay between the battery and the inverter?
 
Originally posted by: Eli
Originally posted by: WarDemon666
Originally posted by: Thegonagle
read my edit above--I am concerned about the lack of a fuse for the power wire.
Click to expand...


Thanks for your most useful post.

Do you think it may be dangerous to drive around for a week before I have time to go buy an inline fuse?

I guess im going to have to RE wire everything AGAIN 🙁

I was in such a rush to get everything finished that I took the easy way out. Now I have to do this all over again 🙁
Click to expand...
An inline fuse should only be a few dollars, and be realitivly simple to install.

What are you running from the inverter? If it's nowhere near it's rated maximum, you'll be fine for a while.

As for your relays..

Are they rated at 30A at 12VDC? 30A at 12V is a lot different than 30A at say, 120VAC. 🙂

I'd go solid state on the relay. I suppose that makes it harder to use a simple capacitor and resistor to get a time delay effect, since a solid state relay will operate on ~3V.

You can, indeed, buy relays that have time delay built in.

But wait - Are you sure the power switch carries the whole load of the inverter? That seems rather unlikely...

Unless I'm missing something. I thought you were going to use the relay to turn it on.. What is the point in using a relay between the battery and the inverter?
Click to expand...


Hehe. It doesnt turn on automatically, i used a seperate relay to press the power button once it has power, but its going to be for a carputer so i need another relay to turn on the power when i have the ignition on etc...

I guess im going to go get some more relays if ever they break, but i dont tihnk ill ever take more than 30A.....
my relays are 40/30A so it should be good (40 is for open, 30 for closed right?)
 
The main reason that no one puts the switch on the common side is that you can never isolate power from the load.

In other words, as long as the power lead is connected, the inverter will see voltage, whether the switch is on or off. If you want to (safely) work on the inverter wiring, you really need to disconnect the battery lead every time.

It won't affect the operation of the system, but you'll increase your chance of getting a shock or ruining your equipment.
 
Originally posted by: WarDemon666
Originally posted by: Eli
Originally posted by: WarDemon666
Originally posted by: Thegonagle
read my edit above--I am concerned about the lack of a fuse for the power wire.
Click to expand...


Thanks for your most useful post.

Do you think it may be dangerous to drive around for a week before I have time to go buy an inline fuse?

I guess im going to have to RE wire everything AGAIN 🙁

I was in such a rush to get everything finished that I took the easy way out. Now I have to do this all over again 🙁
Click to expand...
An inline fuse should only be a few dollars, and be realitivly simple to install.

What are you running from the inverter? If it's nowhere near it's rated maximum, you'll be fine for a while.

As for your relays..

Are they rated at 30A at 12VDC? 30A at 12V is a lot different than 30A at say, 120VAC. 🙂

I'd go solid state on the relay. I suppose that makes it harder to use a simple capacitor and resistor to get a time delay effect, since a solid state relay will operate on ~3V.

You can, indeed, buy relays that have time delay built in.

But wait - Are you sure the power switch carries the whole load of the inverter? That seems rather unlikely...

Unless I'm missing something. I thought you were going to use the relay to turn it on.. What is the point in using a relay between the battery and the inverter?
Click to expand...


Hehe. It doesnt turn on automatically, i used a seperate relay to press the power button once it has power, but its going to be for a carputer so i need another relay to turn on the power when i have the ignition on etc...

I guess im going to go get some more relays if ever they break, but i dont tihnk ill ever take more than 30A.....
my relays are 40/30A so it should be good (40 is for open, 30 for closed right?)
Click to expand...
Ah, that makes sense.

Yeah, that's probably NO/NC ratings.
 
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