Need a switch for 8 gauge wire

[fuzzybabybunny]

So I made a thread a while back about wiring a 400W inverter and running my laptop and subwoofer off of it. It's hooked directly to the car battery but it's mounted in the trunk connected with 12 gauge wire.

Long term report:

I think the voltage drop due to the thin wire is severely affected the reliability of the inverter. Even when driving the inverter will turn on and off and the subwoofer will turn off frequently. The low voltage alarm of the inverter is always on, and when I'm parked it sometimes has trouble just staying on powering just the laptop.

So I want to replace the wire with 8 gauge, but I need a switch in the cabin so I can turn the inverter that's in the trunk on and off.

How do I get a switch that can handle being hooked to an 8 gauge wire?

 

[PottedMeat]

You should consider using a automotive relay + switch.

The switch is connected to the coil of the relay and +12V. The other end of the coil on the relay is grounded. The contacts on the relay are connected to the inverter. When you turn on the switch the coil is energized and connects the high current contacts together, activating the inverter.

At 400W, ~30A I would go with a 40A relay like this:
http://www.radioshack.com/product/in...ductId=3020762

Then you can use a cheap little toggle switch.

And I would switch to 6 gauge wire. At 400W that inverter will suck down ~33A.

 

[RGUN]

I would play it safe and get 4 gauge, its not THAT much more expensive, and run a fuse inline. I've had great success buying from these guys

Cable
http://www.knukonceptz.com/productMaster.cfm?category=Kolossus Fleks Kable

Fuse Holder
http://www.knukonceptz.com/productDetail.cfm?prodID=FH-44

And as stated above a relay would be a safe way to switch it.

 

[Gillbot]

use a relay

 

[The J]

This page gives good info regarding the maximum current to run through a wire: http://www.bcae1.com/fuses.htm

 

[l0cke]

 

[fuzzybabybunny]

Do I basically solder the wire to the relay? 8 or 6 GA is pretty thick... that's a lot of solder, right?

And can 8GA wire use easy crimp connectors?

 

[l0cke]

Do I basically solder the wire to the relay? 8 or 6 GA is pretty thick... that's a lot of solder, right?

And can 8GA wire use easy crimp connectors?

You should get a relay socket, like this:

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=330-075

 

[fuzzybabybunny]

You should get a relay socket, like this:

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=330-075

I'm confused.... that part uses 14AWG wire though. I thought the whole point of this was to upgrade all parts to at least 8AWG wire...

 

[Rubycon]

Your switch will make/break 12V DC power to the relay coil which draws tiny power. This is how most of your car works. Imagine how big the ignition switch would be if it had to control power to the starter motor on its own!

Relays can be socketed or have screw terminals. Larger relays/contactors can accept large conductors directly or you can use crimp style lugs/rings. Make sure the positive lead has a fuse close to the battery as well. Long unfused runs are highly discouraged as they will cause fires if the wire shorts to ground. Chaffing along firewall openings is the most common cause of faults due to inexperienced installers that do not adequately protect wires passing through the firewall.

 

[fuzzybabybunny]

So is this how I'm supposed to wire it?

 

[imagoon]

So is this how I'm supposed to wire it?

You switch power (+) not ground. Relay the 12v side. Also if you motivated, you can pull relay power off of something like the radio circuit so the inverter shuts down when the key if off.

 

[ecom]

I told you to use a relay when you first started this...

Anyhow, your diagram looks fine. YOu can switch either the hot or ground side and it will turn the inverter on and off just fine.

The toggle switch can be connected to a different power source such as the cigarette lighter if it makes it more convenient. What you are switching is a coil inside the relay which causes the switch to throw and power on the inverter. Bosch type automotive relays are usually around 75 ohms so that's less than 200mA that you need to go through the switch.

 

[Howard]

So is this how I'm supposed to wire it?

I need to get me a three-terminal fuse...

 

[fuzzybabybunny]

I'm having trouble finding relays that are 125A and 12V for a 4AWG wire. Radio Shack only goes up to 40A. I'd like to get one that Rubycon suggested with the ability to accept these wires directly or with crimp style lugs/rings.

As for the relay power, I'd still like to have it pull power directly off of the battery because there are many cases where I want the inverter to be on when the car is off. But this runs the risk of depleting the battery if I'm not careful and stranding me unless I can get a jump start.

 

[Rubycon]

I need to get me a three-terminal fuse...

They have those - they are called flashlamps!

 

[Howard]

I'm having trouble finding relays that are 125A and 12V for a 4AWG wire. Radio Shack only goes up to 40A. I'd like to get one that Rubycon suggested with the ability to accept these wires directly or with crimp style lugs/rings.

As for the relay power, I'd still like to have it pull power directly off of the battery because there are many cases where I want the inverter to be on when the car is off. But this runs the risk of depleting the battery if I'm not careful and stranding me unless I can get a jump start.

Why do you need a 125A relay? Those are NOT going to be cheap.

 

[Rubycon]

Why do you need a 125A relay? Those are NOT going to be cheap.

He could use a double pole contactor however most coils need 24VAC but that's at low power so a simple switching upconverter can provide that. They make a nice clunk when pulled in. Mercury displacement relays are much quieter however they may be positional dependent and thus sensitive to motion.

 

[fuzzybabybunny]

Goddamn I am so confused now. People are telling me 6AWG, then 4AWG, and with 4AWG I should have a 125A fuse so I figure I need a 125A relay as well but these are impossible to find.

What exactly do I need???

Since I can't find a 125A 12V relay I'm just going to get a 75A 12V relay, which means I might as well downgrade to 6AWG wire because there's no point in getting 4AWG wire that can do 125A if the relay can only do 75A. But it seems 6AWG is an odd size that's hard to get so it's either 4AWG or 8AWG so I might as well just go 4AWG.

http://cgi.ebay.com/ebaymotors/ws/e...rms=algo%3DLVI&its=I&otn=2&category=33573

It says it uses standard wire rings but from the picture the screws for the wire rings look REALLY small if I'm going to be using fat 4AWG wire. WTF?

Get maybe 20ft of this red 4AWG wire:

http://www.knukonceptz.com/productDetail.cfm?prodID=KFX4R

And 5ft of this black 4AWG wire:

http://www.knukonceptz.com/productDetail.cfm?prodID=KFX4BK

And this in-line 120A fuse:

http://www.knukonceptz.com/productDetail.cfm?prodID=FH-44

Now where do I go to get ring connectors that will fit that damn 75A relay that will also crimp onto 4AWG wire???

 

[Rubycon]

First of all (looking at the OP) are you SURE a 400W inverter is enough? You mention subwoofer. Is this a HT or PC subwoofer? What are the specifications? If your inverter cannot satisfy the load in the first place using a heavier gauge wire is NOT going to make it magically work!

Did you take a voltage reading of the inverter input when it was under load before? As long as it's receiving adequate voltage (11.5V or better) it should be OK. (check manufacturer specification for voltage operating range)

Secondly a 400W inverter even with horrible 50% efficiency (most decent ones are easily 90% efficient!) will draw around 60A. 75A relay/fusing will suffice. Your inverter is most likely using far less than this figure; probably around 40A at full load.

The easiest way to get larger wire to fit is break out the soldering iron and solder a piece of larger gauge wire to the size that fits your relay terminal. Remember to ALWAYS fuse correctly for the smallest gauge wire in the circuit. If your fuse rating is too high and a short occurs far away the wire may become dangerously hot before the fuse opens. If it does not your car may burn up!

 

[fuzzybabybunny]

Yes, I'm sure the 400W is enough. I actually ran this same exact system for years, but that was with much shorter wire that did not result in the same voltage drop as I'm experiencing now. The subwoofer is a PC subwoofer capable of 200W RMS, but I hardly ever crank it that loud in my small hatchback.

I did not take a voltage reading, but I suspect that it is the case. I guess I'll go ahead and order the parts mentioned in the previous post and just solder wire to the relay.

 

[PottedMeat]

Now where do I go to get ring connectors that will fit that damn 75A relay that will also crimp onto 4AWG wire???

These are way overpriced but you can probably find an alternative somewhere else:
Ring Terminal Connector for 4ga wire
IDEAL 2-Pack Terminal Wire Connectors
Item #: 114970 | Model #: 770323

Lowes/Home Depot also has spade connectors for the coil terminals like these ( I don't know if they're 0.25" though ):
IDEAL 12-Pack Terminal Wire Connectors
Item #: 135862 | Model #: 770311

 

[Rubycon]

Another way to get a terminal on 4AWG is to cut a piece of 3/8" ID soft copper tubing about an inch long. Flatten half of this in a vice. Drill a 1/4" hole in the center of the flattened section. Clean up the open side (internally) and heat with a propane torch enough to get rosin core solder to flow around on the inside. Do the same - tin your wire end. Holding the tubing (with pliers unless your fingers are artificial! ) and heat the tubing with a larger flame until the tinned inside is flowing and slide over the tinned wire end. Add solder around the edge of the copper (keeping the flame close to the flat side with the hole) until it flows around and makes a nice joint. Remove the heat and be sure to keep the joint perfectly still until it cools sufficiently for the solder to solidify. You will have a much stronger terminal than crimping!

 

[Howard]

Probably one less resistant to vibration and fatigue, though. Soldered joints don't hold up to pulling well. Now, you could make a ghetto crimp out of the open half though.

 

[Rubycon]

Probably one less resistant to vibration and fatigue, though. Soldered joints don't hold up to pulling well. Now, you could make a ghetto crimp out of the open half though.

It's 4AWG it will be fine it's not used for pulling cows you know!