Laptop Inverters vs. HAM Radio

Mar 2, 2004
Northern Colorado

I'm trying to avoid the permanent solution of hooking up a massive inverter straight to my battery. I'm not only doing this cause of the power drain, but also to avoid the interference it created with my HAM radio.

My laptop is the sole thing I'd hook into this. My laptop specs are as follows...

Compaq Presario R3000z w/ AMD 64 2.0GHz
1 gig RAM
80gig 5400rpm Hard Drive
128 Meg Dedicated Video Card
15.4 Widescreen Bright
Internal Wireless Card
GPS Puck running via USB
Cell Phone modem via USB

Trying to figure out what I would need in terms of a cig-lighter inverter. Here are a few I've found on eBay.

95w Inverter
100w Inverter
175w Inverter

I know most of those are listed at peak ratings and the actualy continuous wattage is lower. I currently have a Vector 70w Continuous and wonder if that'll be enough. I got it for $13 and change brand new, so I figured I could use it to charge cameras if need be, but if it'll support my laptop continuously, then I'd rather not get another one.

Any suggestions or comments?

EDIT: To comment on John's post below, I do have a 750 watt inverter available to me, however, I am trying to avoid having to use it. My main issue is the interference with the ham radio seeing as I have to wire both directly to the battery terminal.

I'm not sure what the drain on the battery/alternator is with the inverter running with only my lappy hooked up, but its not something I am overly concerned with.

You ommited the power consumption specs for your laptop, which can vary widely. Many laptops consume 60W or less (some much less), however I've also seen a few with higher consumption specs.

A lot of 75W inverters mention that they are suitable for laptops, but with the above information in mind you can see this is only marginally so, and not for all laptops either. My opinion is to exceed the power consumption by a comfortable margin, and also provide a bit of extra capacity in case you need that cell phone charged as well as your other goodies. Of your choices I would pick the 175W, but I would also urge you to go for a 300-400W model instead. These can be run from the cigarette lighter (not for full load) and run nice and cool under light loads.


Take the power required by the laptop (volt x amps; that is, if the
laptop power pack is rated 15 volts at 6 amps, that's 90 watts). Then
double it to get a conservative inverter requirement, e.g. 180 watts in
this example. Neither the inverter nor the laptop power pack is 100%
efficient, the 90 watts is the power pack's OUTPUT power, it's input
power requirement will be significantly higher (the typical efficiency
is 60% to 80%, but will vary).

However, personally, I'd get a 300 watt inverter, which is about the
limit of what you can draw from a car cigarette lighter. You may want
to use it for other things, but you can't get much more than about 300
watts (if that) without direct connection to the car battery.

I think I have a 300-450(can't remember which) that I run off a cigarette outlet. In my escort, it runs no problem. However after a while in my wife's car (a Honda Civic), it starts beeping at me - then I just unplug it for a while and then plug it in again.
I've got a 400 watt inverter and it is awesome. I power some of the weather equipment, as well as the laptop and WxWorx. 400 would be perfect; however, you may want to hardwire it. I've noticed problems occasionally when I transmit on high power on the radio, it sometimes killed the inverters power. Not sure if others had that problem as well...
Hey Tony,

A month or so a go I picked up a 75w plug-in type inverter to take along on a trip in my wife’s car. My 800w is hard wired in my truck. Anyway, the only thing I tried to run on it was my laptop and it would not power it up at all. It just kept cycling on/off. I returned it to Best Buys when we got home because the packaging claimed it was for a laptop. So long story made short, I would probably go for the 175w. But keep an eye on it because you can overheat the cheep-o wiring that feeds the in dash plug in.

Good luck
Perhaps I should rename the topic seeing as I'm probably going to see a lot of higher inverters wired straight to the battery. Seeing as that's probably my most viable option, how can I prevent the interference on my HAM radio.

My old problem in the Tracer; both my HAM and inverter were wired directly to the battery. When the inverter was on, the HAM would have static issues when not in use (squelch wouldn't shut it off). Not sure what if any issues transmitting, but the constant noise made it a pain to monitor the channels seeing as all I got was noise between transmissions.

That's the ultimate issue I am trying to address. I currently own a VECTOR VEC 043 750-Watt Power Inverter (VECTOR VEC043) which I got new on Amazon for under $50. Going the battery route, I'll replace the clips with connectors so it'll go to the battery.

Are you sure all ground connections were clean and solid in your old setup? Poor grounds can create noise issues... Did you run the neg. from the inverter to the battery, or did you ground it to the car body (assuming the body is metal)? Poor welds, etc, can mean >0ohm resistance from your grounding point to the battery, which can create issues.
Tony I neglected to mention another option: use a DC-DC converter. You can buy quality units that plug directly into the cigarette lighter and supply the DC voltage required by the laptop. I used one regularly up until last year (made by APC) and had no interference issues with any of my Ham equipment with it.

Are you sure all ground connections were clean and solid in your old setup? Poor grounds can create noise issues... Did you run the neg. from the inverter to the battery, or did you ground it to the car body (assuming the body is metal)? Poor welds, etc, can mean >0ohm resistance from your grounding point to the battery, which can create issues.

Jeff, the ground was hooked to the battery if I recall correctly. Couldn't I get something from Radio Shack to help eliminate some noise issues?

I also intend to get a switch so I can mount the inverter someplace out of the way and someplace along the wiring, make a switch where I can turn the inverter off-an-on from up front as opposed to on the inverter itself.

I forgot how much fun it is to outfit a new vehicle! :lol:
Tony, do you know if the interference is coming over the air or through the wires? I wonder if it is possible to find a way to isolate the radio from the rest of the circuits (power it with rechargeable batteries)?

I have noticed that my laptop seems to cause more interference than the inverter itself. When my laptop is on, both the AM and FM radio lose their ability to pick up anything but the strongest signals. Doesn't happen with the inverter is on and just charging batteries.

It might be the inverter is actually causing the interference due to the increased load from the laptop, but I do know that my radio is affected only when the laptop is running. The computer is up front right next to the radio so this might also have some effect.
Tony, any Pix of the new vehicle? :D

Some work-in-progress on my blog and before pics on my website.

Dan, I know I did have stronger interference with the laptop running, but if I had the inverter on, it would also cause interference (not as bad). For instance, if I tripped the mic, it would take sometime before the noise would come back. If the laptop was running, it would follow immediately.
I have a 75 watt inverter that I run for just my laptop, my laptop is said to only need 70 watts to have full power, etc. I haven't had any problem with mine as of yet, the only problem that I run into is that my inverter can get to be pretty warm sometimes when I'm running it. I think look at the specs of what your laptop says it needs and then see if you can just go a little higher than it and you should be just fine. I don't see you having problems with the radio, I know I haven't had anything like that over the past year.

I'm sure others have more experience though and can help ya out more, thats just my lil' input on it.
:( I have never had this problem, I run 2 400w and a 800w inverter in my van. Operate 3 laptops,printer,sat recv. on one 400w. Run 1 lt and camera equipment on the other 400. The 800w is used to run tv's and the like. Have 2 yesue ham units,scanners,cb radio and never had this problem on any of them. I would check the radio by seeing if a diff. radio does the same thing. You can get noise reducers at radio shack or a local shop. Oh, and 2 light bars. I use coleman Inverters.
I've had the exact problem you are describing. I have a Kenwood 707A and a 400 watt power inverter. The radio and inverter are wired directly to the battery, + and - using different wires. My solution was to purchase a noise filter from HRO for my 707A. It plugs in-line to the radio power cables. I haven't had any noise issues after installing the noise filter. My inverter and radio are about 4' apart.

I linked the wiring diagram for my Xterra below. The only difference is the noise filter is connected to the radio not the inverter as pictured. Also linked to my page that has some more images of the install.


As few years back, I had an inverter and ham radio wired to the same feed. Whenever I transmitted on the ham radio (at med or high power), it would take out the inverter that ran my desktop computer. The way I solved this was very simple.

I ran two positive feeds from the battery to my equipment. One is solely for the ICOM dual band ham radio and the other powers two 750 AND 500 watt inverters (they run the flat panel monitor, desktop PC, etc). Since then, problem solved. I don't have any filters or extra batteries either. I use a beefed up car battery and David Drummond's idea of using a WalMart battery b/c of the warranty and ease of exchange is very very smart.

I sincerely hope this helps.