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Old 03-07-2011, 10:04 AM   #1
hockeyshot20k
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Post Power inverter,12V power socket, What is going on?

I'll try and keep this simple and sweet. I got a 95 Saturn SL2. The cigarette lighter stopped working after some time. Dont know why. So I installed a 12v power socket directly to my battery using the exact same gauge wire that was used to hook up the power inverter to the battery with the jumper cable that came with the inverter so I know I have the correct gauge wire. I installed a 7amp inline fuse towards the end of the positive wire that is hooked up to the battery, right before I connected the 12v sockets positive wire. The reason I put an inline fuse was to protect my inverter. The inverter is used to charge my laptop while im driving to different states. My laptop has GPS software and transmitter/receiver to tell me where I need to go. I found it to be a whole lot more accurate then google maps, and a lot easier to see on my laptop then phone and it was cheaper at the time to go this route then it was to buy a portable GPS. Plus I have my itunes playlist for my music. Moving on now, once I got the inverter up and running, I used it to charge my cell phone and see if any issues may arise. Everything worked like a charm. Now I am heading on 450mile trip. Car was running, power inverter was plugged into the 12v socket and I had my laptop hooked up to the inverter. I turned on the inverter and next thing I know, the 7amp inline fuse blew. So I replaced it with another 7amp fuse. Same thing. So I tried a 10amp fuse and I think I blew the fuse inline fuse on the inverter. Cant remember if it was the fuse on the inverter or the inline fuse by the socket. Its been about a month now since I had this incident and I changed fuses so many times, I cant keep it straight with what I did or what order I did things in when it came to replacing the fuses. Im not sure if my laptop is pulling to much power because of its 17" screen and dual hard drive and a higher end graphics card at the time the computer was made. Not sure if that helps any. As of right now, Ive left the inverter alone due to time constraints. Here is a list of make/model numbers for my laptop, the charger for my laptop and the inverter. When it comes to watts, amps, volts etc, I have no idea which numbers are important or which numbers I should be looking at; inverter, laptop or charger for the laptop. I also have a the links to the specs of each item.

POWER INVERTER: 410W made by Schumacher model # XL41DU
http://www.batterychargers.com/Produ...ProductName=94 026993

LAPTOP: Gateway P172XFX:
http://reviews.cnet.com/laptops/gate...4507-3121_7-32 933935.html

LAPTOP CHARGER: Gateway P-172X
http://www.level8technology.com/gate...adapter-gatewa y-p-172x-laptop-ac-adapter-8310

Thanks everyone. I tried to be specific as possible and short as I could to help figure out what the problem may be. Thanks again
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Old 03-07-2011, 11:08 AM   #2
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Re: Power inverter,12V power socket, What is going on?

Why not just get a car cord for your laptop?

Currently you are using 12v-DC car battery- converting to 110 a/c with an unnecessary inverter, then you are converting back to DC for your laptop with the power converter on its cord.

Go on-line and buy a car cord for your laptop. They are all over Ebay for $20- just use car cord gateway and pick one out.
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Old 03-07-2011, 03:04 PM   #3
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Re: Power inverter,12V power socket, What is going on?

You need togo from 12volts DC to around 20volts DC for a laptop.
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Old 03-07-2011, 03:13 PM   #4
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Re: Power inverter,12V power socket, What is going on?

The owner's manual for that inverter doesn't list what the maximum current draw could be, so the appropriate fuse rating is a bit difficult to select for your application. I expect that you are running the power wires a lot further now than what the inverter came with. With the longer leads, and under load, the wire size can become critical. You may be trying to power the inverter with insufficient voltage/current and it's working a bit harder to compensate. Also, are you plugging the laptop cord in to the inverter, then connecting the inverter to the lighter socket, or do you give the inverter time to stabilize before connecting the supply for the laptop?

The best option may well be to get the car cord DC-to-DC converter as brcidd suggests. If you are convinced that you need to make the setup with the inverter work, you may need to go with heavier gauge wire, make sure it's fused appropriately, and make sure you let the inverter stabilize before connecting the laptop.

Have you monitored input voltage and output power from the built-in display just prior to the fuse blowing? Often cigarette lighter ports are only rated for 15 amps or less. The manual for your inverter suggests that you should only be connecting 120 Watt or smaller inverters to the lighter sockets. I'm guessing the issues with this setup could be resolved with heavier guage wiring, higher current capacity connections, and the proper fusing.

-Rod
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Old 03-07-2011, 06:10 PM   #5
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Re: Power inverter,12V power socket, What is going on?

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Originally Posted by danielsatur View Post
You need togo from 12volts DC to around 20volts DC for a laptop.
Great!!
The car cord will do it-- that is why they make them...I use one all the time, with no issues.

Just seems silly to change DC to AC and then back to DC again- There will be "losses" in each conversion, primarily in heat generated.
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Old 03-08-2011, 01:00 AM   #6
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Re: Power inverter,12V power socket, What is going on?

The laptop charger puts out about 6.3A at 19v or 120 watts. Going upstream from that, you have the DC converter in the cord which consumes energy as heat. Going upstream from that, you have the AC inverter which consumes energy as heat, not to mention runs a fan to keep it cool. Upstream from that you have the connection at the accessory plug which consumes energy as heat. Further upstream you have 6' of wire which consumes energy as well.

To get 6.3 amps at the laptop, you need a heckofalot more amps drawn at the battery terminal. Maybe 15 or more.

Look at it this way... you have a 410W inverter which is over 30 amps potential at 13v. Use 10 ga wire, use a 30A fuse. If you still have problems, there is a short; most likely in the inverter itself.

Many inverters are horrifically inefficient... like 30-40% for the cheap ones, 50-70% for the good ones. Worst case scenario, to get 120W at the charger, you might need 400+ watts being drawn from the battery to get it.
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Old 03-08-2011, 03:49 PM   #7
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Re: Power inverter,12V power socket, What is going on?

There good for a 100watt light bulb, small vacuum, detail buffer, or another cigar lighter.
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Old 03-08-2011, 05:25 PM   #8
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Re: Power inverter,12V power socket, What is going on?

please do not confuse watts DC with watts AC. The easiest way to figure out exactly what you are drawing (current) is to use an ammeter inline with power cord coming off the battery. You can temporarily wire the ammeter in as the fuse to see what the draw is. Wire size is probably ok (would actually have to see what the current draw, length and wire gauge is) but most of the voltage drop in these cases is due to poor wiring connections.
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Old 03-13-2011, 12:58 PM   #9
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Re: Power inverter,12V power socket, What is going on?

Can I remove the inline fuse since the inverter has a built in fuse? I checked my car out yesterday, and I had a 25amp fuse for the inline fuse, and that sent to many amps to the inverter which caused the built in fuse for the inverter to blow. I believe the fuse at the tip of the inverter plug was a 10A fuse. I believe there is two fuses in the inverter. One at the tip of the plug that plugs into the power socket, and another one that is inside the inverter itself. So I should be protected with anything that I plug into the inverter. I used #10 AWG for the positive and negative wires that run from the battery to the power socket which is the exact same gauge wire that the jumper cables that came with the inverter. The #10 AWG is about 1.5-2ft max longer then the the jumper cable; not a big difference as I thought it would be. I cant get the power cord for the laptop in time for my trip this week, and i havent seen any stores near me who sell the power cord. Thats why I wanted to see if I could remove the inline fuse temporary since the inverter has a built in inline fuse. Thanks
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Old 03-13-2011, 01:36 PM   #10
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Re: Power inverter,12V power socket, What is going on?

Sure you can remove the in-line fuse-- but now all the wire from the battery to the inverter socket IS NOT protected, so if you run the cable through the firewall, or the door- or the wire gets chaffed- then you are in for some smoke. Removing the in-line fuse will not stop the one in the head of the inverter from blowing.

Here's a thought, since you want to invert to 110V a/c- then attach inverter directly to the battery and run an extension cord into the car cabin- At least you won't have the overheat or the long DC wire concern.

I put an inverter 1500W underhood on a Yukon this way- and run an extension cord under the frame rail back to the back seat. My B-I-L runs his oxygen machine off of it while he drives. Works great.
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Old 03-13-2011, 01:55 PM   #11
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Re: Power inverter,12V power socket, What is going on?

Quote:
Originally Posted by brcidd View Post

Here's a thought, since you want to invert to 110V a/c- then attach inverter directly to the battery and run an extension cord into the car cabin- At least you won't have the overheat or the long DC wire concern.

I put an inverter 1500W underhood on a Yukon this way- and run an extension cord under the frame rail back to the back seat. My B-I-L runs his oxygen machine off of it while he drives. Works great.
Isnt this what I am doing all ready? The inverter is hooked straight to the battery by using the #10 AWG and run into the front passenger seat. I got dc power due to the inverter on the laptop cable so dont I still have the DC issue?. To me that sounds like I already have it set up ur way unless I am skipping something in my understanding
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Old 03-13-2011, 07:17 PM   #12
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Re: Power inverter,12V power socket, What is going on?

He's suggesting you install the inverter under the hood, then run 110V AC wire from the underhood inverter to the cabin for your laptop. That minimized the length of the wire between the battery and the inverter. However, I doubt your inverter is intended for external use so the moisture/water possibility and heat may mean the inverter won't live long, plus there's probably not much extra space under the hood to safely mount the inverter.

What rating is the fuse that's in the inverter? Assuming the inverter is working properly, the inverter will only draw as much current as it needs, using a 25 amp fuse on the power line will not "send too many amps" to the plug. But the inverter probably needs more than 10 amps of current on power on, and the socket/plug that you are using for the inverter may only be rated for 10 amps. If that's the case, you don't want to just go with a larger fuse in the plug/tip. You might consider a slow blow fuse rather than a fast acting which is probably what's in it.

If the inverter only requires 7.5A or something, you could just use a 7.5A fuse in place of the 25 amp fuse, that way the 7.5A fuse will blow before the 10 amp, but I would find it quite hard to believe that the inverter is rated for that low of a current. If you remove the 25 amp fuse that just means that the 10 amp fuse in the plug/tip will still blow but you will no longer have protection between the socket and the battery - that's a bad thing.

I like PaulD's suggestion above of actually measuring how much current the circuit will draw. Try connecting the inverter straight to the battery with a series current meter or a clamp on DC current probe. Set the meter to "MAX" and fire up the inverter. Then plug in the laptop cord and power up the laptop. While the OS is booting is probably the most demand the laptop will put on the circuit during normal operation. What is the maximum current draw the meter saw? Now add a few amps to account for line loss and such and pick the appropriate fuse for the line. I think you're going to need to get rid of the cigarette lighter connection as that's probably your weak link in the circuit currently.

-Rod
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Old 03-15-2011, 07:51 AM   #13
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Re: Power inverter,12V power socket, What is going on?

Quote:
Originally Posted by hockeyshot20k View Post
Isnt this what I am doing all ready? The inverter is hooked straight to the battery by using the #10 AWG and run into the front passenger seat. I got dc power due to the inverter on the laptop cable so dont I still have the DC issue?. To me that sounds like I already have it set up ur way unless I am skipping something in my understanding
The inverter takes low volts/high amps and converts it to high volts/low amps. Transmitting power at low amperage is easy. Transmitting 12v and 20A 6 feet to the passenger compartment requires big heavy cable. Putting the inverter near the battery means you only need a couple feet of heavy cable and then a cheap $5 extension cord to the passenger compartment.
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Old 03-18-2011, 11:52 PM   #14
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Re: Power inverter,12V power socket, What is going on?

just wow, 14 Ga wire should be plenty to run 20A of wire accross 8-10 ft - that will NOT be a heavy gauge cable. An inverter takes DC and converts it AC, typically 12VDC ot 110VAC. The fuse on the wire from the battery to the inverter is NOT to protect the inverter, it is to protect the car's electrical system. If you mount the inverter in the engine bay, make sure it is designed for that (read heat resistant and waterproof). In many cars, you may not have much room for it in the engine bay. You might also consider mounting a 110V plug somewhere in/on the dash or center console area for convenience.
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