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Old 04-17-2010, 09:46 AM   #1
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Join Date: Apr 2010
Posts: 1

Hi all,
I am a Matco Tools Distributor in San Diego (Kearny Mesa 92111). I use a Freightliner Mt 45 Box Truck for this business. I started this business recently, in September.

I have been successful and COMPLETELY functional using a Coleman brand 800 watt low cost MODIFIED sine inverter to power my laptop computer, thermal and laser jet printers,my flat screen monitor and some florescent drop lights that are product to be sold. I light those drop lights so customers shopping on the truck can see how they function. This inexpensive inverter is mounted on the thick-stout 4" wood protection wall that separates the driver from things like the tool boxes and other inventory. This inverter is mounted on the wall side just behind the driver seat just above the house battery charging units. Its a bit of a pain to reach behind the seat to turn it on and off each time.
Wanting my computer and printers to have cleaner power so they could last longer, last month I bought a 2500 watt continuous power with a 5000 watt Hi-surge power PURE SINE wave inverter made by Power Express(model PE-2500PSW).

Yesterday I drilled an access hole through the lower corner of the 4" thick protection wall at the truck's wall body and the floor so I could run connection wires from where the connection heat sink is(same side of the wall as the driver seat) to the other side of the wall where the desk that contains the items that need electricity are. I used 4awg wire to connect the new inverter to the heat sink strip. This strip is where the large 1awt battery cable connects. This 1awt cable comes from two new 12 volt floating type deep cycle house batteries that are positioned in the showroom area about 10-14 feet away from that heat strip(Yes that means there is about 14' of 1 awg heavy battery cable from the batteries to the heat sink strip). Also connected to that heat sink strip are the battery chargers and the inexpensive Coleman inverter. All of this is on the side of the wall nearest the driver's seat. The other side of the wall where the standing work station type desk is had no electronic charging stuff in that area until I positioned the new inverter on the floor there. I drilled that hole and ran those cables so the new inverter could be on the other side of the wall to the old inexpensive inverter and be close to the apparatus' that needed its power. I also decided to put the inverter on the opposite side of the wall to the other one because I didnt want to see unsightly wires sticking around behind the drivers seat. I also wanted to gain accessibility to the inverters on or off switch abilities--the new inverter has a remote switch to do that. Additionally, customers walking into the truck see the drivers seat and what is behind it first when entering the truck to go into the show room area of this truck. I like the idea of a nice first impression. The wires that were there were not that clean looking.

Now the issue. The new expensive inverter powers up all the things the old inexpensive one did. However there is obvious interference from this new expensive pure sine wave inverter where there was none from the cheap one. I CAN NOT use the credit credit card swiper that is connected via usb to my Dell Lap-Top. With the new inverter in play the card swiper/reader wont detect the credit card's. It is critical that I take credit cards this way. I also can not play the radio on any AM station due to intense static. The radio is an issue ONLY when I plug in the cord that connects the wall outlets. If I unplug that cord the radio plays fine even though the computer and everything which is connected through a separate power strip plugged directly into the new inverter is still working. Clearly the new inverter is transferring interference to this outlet connection cord that has most of its wire in the walls and this is causing the static to travel from the attached outlet cord/wall wire to the radio. It was a real pain to pull those 4awg and the two wires that make the electric outlets on the walls work through the hole I made in the protection wall. As a point the power wires and the wires that connect the outlets are in close proximity to one another. Maybe I have to move the cord for the outlets out of that access hole so they don't sit right on top of the welding type 4awg wire I have used as power cable. I dont want to pull all this wire to test and see if the wall is what is keeping the interference from reaching the credit card reader. I think the cord is transferring the static to the radio, I wonder if the thick protection wall provides a deflective barrier so the credit card swiper reader doesn't receive any interference? I am doubtful that the wall is needed to make sure no interference from the new inverter reaches either the credit card swiper/reader.

Is anyone aware if there some kind of a filter or other device any other suggestions? Any other idea's before I undo what I really would rather keep in place?
All help is gratefully accepted--

Gary Z is offline   Reply With Quote
Old 04-17-2010, 08:43 PM   #2
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Old 04-17-2010, 09:03 PM   #3
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Join Date: Feb 2006
Location: OKC, Ok.
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Ham radio guys are knowledgable when it comes to static generated by 120VAC & how to eliminate even the most minor AC interference.

Suggest goggle ham radio for more info or try Ebay for a 120VAC line filter.
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Old 04-19-2010, 07:20 PM   #4
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Gary Z,
I'm not sure I rate the guru title (thanks Geofkaye) but I will try to help.

It just so happens I have a PE-2500PSW as well. I haven't gotten to the point of hooking up my computer to the AC inside my living quarters yet, so I may or may not have a problem myself. I also rarely use the radio in the truck (cab) when the inverter is on so I hadn't noticed anything, and I hadn't tested specifically for any kind of interference.

I just checked, and with my inverter on I get a barely audible buzz on a strong AM radio station (KGO). I tuned the radio to an empty AM channel and got strong buzz that I could hear easily from outside the truck. My inverter is located in an underbed box on the right side ahead of the rear wheels. When I turned the inverter off the buzz went away. My AC circuits are wired in through the 3 prong plugs in the front of the inverter. When I pulled one of my three plugs the buzz mostly went away. The other two plugs contributed to the buzz only slightly. I went inside the living quarters and tuned on/off the only AC light in there at the moment and it had no effect on the buzz.

All of this leads me to believe that my problem (to the extent that I even have a problem) is due to radiated emissions coming from the AC wiring in the living quarters acting like an antenna and spraying RF(Radio Frequency) noise that is being picked up by the AM radio antenna in the cab.

I have no direct electrical connection between the 12V that supplies the radio in the cab and the 12V that drives the inverter. That suggests that the problem is not feeding through the 12V power supply into the radio. That is also supported by the fact that the problem goes away when the AC wiring is disconnected from the inverter (but the DC wiring remains and the inverter is still turned on).

Your problem sounds similar, but much worse, and may not be the same problem at all.

Fortunately they make ferite cores that can be clamped on to an AC power cord. Here is one such example from a quick web search.

I am not recommending these, but they are cheap so you have little to loose by trying one. The ferrite material absorbs the relatively high frequency energy that is messing up the radio, but has no effect on the 60hz AC line frequency. It will turn that tiny amount of energy into a tiny amount of heat that you will never notice. It should be clamped on the power cord as near the inverter as practical, and you should install one on every AC cable coming from the inverter. By "cable" I mean the black, white, and green wires in a common jacket, or at least that is how I will have to do it in my application. If you have separate wires you can put a separate ferrite on each. Since they just snap on you can try them in different configurations easily and see what works best. You can even try putting more than one core on the same wire to see if you get further improvement.

You can also put a ferrite core on the DC wires to the inverter. You would need larger cores to accommodate the heavier wires though. It is also probably not necessary as your description of your problem is similar to mine in that it goes away when you unplug the house wiring.

I will go get some ferrite cores myself and let everyone know if it has any impact in my situation.

I donít think the proximity of the DC Power wires and the AC wires is a problem. They could transfer a little RF energy back and forth but I donít think that would contribute much to the issue, especially if you kill the RF with a ferrite before they get together.

Beyond all that, you may have an entirely different problem. You said some things in your post that concern me. I am not sure if I fully understood the topography of your layout, but it sounds like your batteries are over 14 ft. of #1 AWG wire from your inverter. The instructions that come with the inverter recommend keeping that wire short, and using #0 or #00 AWG wire for runs over 6 feet. I would also hope you are not relying on the chassis for ground return currents. You could easily have over 250A flowing through your frame, and steel is not really that great of a conductor.

Beyond the sheer resistance of the DC current path there is the inductance. Your inverter draws very short bursts of very high current from the batteries. To put this in very non-technical terms, you could have the electrical equivalent of water hammer due to the long wire from the batteries to the inverter. Aside from whatever RF (Radio Frequency Energy) it might radiate, it could also slam the transistors in the inverter and cause them to fail prematurely.
Your previous square wave (not sign wave) inverter drew much longer slugs of current at a much lower frequency and was therefore less likely to cause radiated emissions problems. There are other potential problems as you know though.

By the way, I donít know what a ďheat sink stripĒ is, but I suspect you are talking about a bus bar, which is just a bunch of studs or screws on a common conductor which makes it easy to connect a bunch of wires together.

Good luck!
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Old 04-19-2010, 08:08 PM   #5
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....YEAH!...I'M WITH HIM!....geofkaye and the Rivercity Girlz agreeing with RAN D. ST. CLAIR....{WHAT EVER HE SAID}
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Old 04-20-2010, 06:54 PM   #6
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I picked up some clamp on ferrite cores from my local electronics junk store today and tried them on the AC wires from my inverter. Unfurtunately, they did nothing to aleviate the buzz on my AM radio. Fortunately that buzz is only significant on an unused AM channel, meaning it really isn't a problem for me.

It remains to be seen what impact if any it will have on my TV or Wi-Fi. AM radio is on a really low frequency (535Khz to 1605Khz). That's only about 30 times faster than the highest audio frequency you can hear, so for radio waves it is really slow (frequency, not speed).

I suspect the ferrite cores are better at filtering higher frequencies so they may still do me some good for my Wi-Fi frequencies (2.4Ghz). Then again, I may not have needed any filtering in that band in the first place.

Broadcast TV is in the range of 54 Mhz to 890 Mhz which is about 100 times higher than AM radio. The ferrite cores may do me some good up there, but I still don't know if I even need them.

Gary Z., I am not sure if any of this is going to help you. I did promise to let everyone know what the ferrite cores did (nothing), so now I have done that. There are lots of more sophisticated AC line filters, but they cost more money. I don't feel like I am qualified to make any further recommendations, especially if they are going to cost you money and not necessarily solve your problem. At this point I imagine you are regretting your decision to buy the "pure sign wave" inverter. I guess you will just have to try various different things to see what works. Sorry, that's not very helpfull..

Good Luck

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