120V 100W/400W AC power outlet & AM radio
- Thread starter dawudih
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Are you listening to the built-in AM radio, or plugging one into the inverter?
If you are plugging one into the inverter, and if it does connect to the audio system, you should isolate that using an audio isolation transformer. Common mode chokes on the audio and/or power might work, too. If not, it's a power filtering problem. The inverter doesn't put out a clean sine wave like wall power. It approximates it with square waves (called "modified sine wave", which is OK for lightbulbs but bad for almost anything else. It takes a big filter to smooth out modified sine wave power. Last time I looked into it, I determined it wasn't really practical. If the radio has a transformer that puts out DC power, then it's a lot easier to filter DC power. You can use some capacitors and/or a common mode filter.
It could be that whatever you are plugging into the inverter is causing interference. Try an incandescent light and see if it's still a problem.
If the built-in inverter is causing interference with the built-in AM radio, then there's not much you can do except replace the inverter or the radio. It's possible that one or the other is defective, but I doubt it, and I would suggest getting a high quality standalone inverter instead. If you don't want to replace the inverter, I have a few suggestions:
Inverters operate at a high frequency internally to convert 12V power to high voltage, which they then chop up to make the modified sine output (probably similar for a pure sine inverter, too). It sounds like the problem is that the power conversion has a harmonic in the broadcast AM band, and it's getting into the audio system. That's poor design, but maybe they never tested it because AM radio is rarely used any more, and the inverter is not commonly used either.
You could try adding filtering on the DC side of the inverter. You would have to find the inverter (I think it's in the trunk, near one of the wheel wells), tap into the wiring harness, and add filter(s) appropriate for the load and frequency. The electrical system is complicated because everything is interconnected. I don't have time to design a filter for Toyota for free (they can hire me as a consultant and I will do it), but taking a guess I would try several hundred to 1000 uF of low ESR capacitors in parallel as close as possible to the inverter. You could also add some ceramic capacitors around 1-10uF each, but there might be too much inductance in the wiring from them to the inverter to be useful. You can get capacitors cheap from Digikey.com. Don't get stupid 1F capacitors that people use for audio systems. More capacitance is better, but large value capacitors do not work as well at high frequencies.
http://www.ti.com/lit/an/slta055/slta055.pdf
You could also try a common mode choke on the DC side of the inverter. Run the +12V and ground through it. It probably won't help much, but it probably won't hurt, either.
You could run a dedicated, fused, and shielded power cable from the battery to the inverter. I would use shielded twisted pair wire. Connect the shield and the negative wire to the negative terminal of the battery. Connect the positive wire, with an inline fuse, to the positive terminal of the battery. At the inverter end, ground the shield to the body as close as possible to the inverter. Connect the positive and negative wires to the inverter, and hope that the inverter has two terminals. Make sure the inverter is not connected to the body by any mounting fasteners or ground wires. If the case of the inverter is used as ground, electrically isolate the whole thing and connect the case to the negative wire of your new cable. You need something like 8-14 gauge shielded twisted pair cable, rated for automotive temperatures. Make sure it's lower gauge (thicker) than the existing wiring. I have no idea if you can buy a cable like that anywhere. It might not fix the problem, anyway.
If you are plugging one into the inverter, and if it does connect to the audio system, you should isolate that using an audio isolation transformer. Common mode chokes on the audio and/or power might work, too. If not, it's a power filtering problem. The inverter doesn't put out a clean sine wave like wall power. It approximates it with square waves (called "modified sine wave", which is OK for lightbulbs but bad for almost anything else. It takes a big filter to smooth out modified sine wave power. Last time I looked into it, I determined it wasn't really practical. If the radio has a transformer that puts out DC power, then it's a lot easier to filter DC power. You can use some capacitors and/or a common mode filter.
It could be that whatever you are plugging into the inverter is causing interference. Try an incandescent light and see if it's still a problem.
If the built-in inverter is causing interference with the built-in AM radio, then there's not much you can do except replace the inverter or the radio. It's possible that one or the other is defective, but I doubt it, and I would suggest getting a high quality standalone inverter instead. If you don't want to replace the inverter, I have a few suggestions:
Inverters operate at a high frequency internally to convert 12V power to high voltage, which they then chop up to make the modified sine output (probably similar for a pure sine inverter, too). It sounds like the problem is that the power conversion has a harmonic in the broadcast AM band, and it's getting into the audio system. That's poor design, but maybe they never tested it because AM radio is rarely used any more, and the inverter is not commonly used either.
You could try adding filtering on the DC side of the inverter. You would have to find the inverter (I think it's in the trunk, near one of the wheel wells), tap into the wiring harness, and add filter(s) appropriate for the load and frequency. The electrical system is complicated because everything is interconnected. I don't have time to design a filter for Toyota for free (they can hire me as a consultant and I will do it), but taking a guess I would try several hundred to 1000 uF of low ESR capacitors in parallel as close as possible to the inverter. You could also add some ceramic capacitors around 1-10uF each, but there might be too much inductance in the wiring from them to the inverter to be useful. You can get capacitors cheap from Digikey.com. Don't get stupid 1F capacitors that people use for audio systems. More capacitance is better, but large value capacitors do not work as well at high frequencies.
http://www.ti.com/lit/an/slta055/slta055.pdf
You could also try a common mode choke on the DC side of the inverter. Run the +12V and ground through it. It probably won't help much, but it probably won't hurt, either.
You could run a dedicated, fused, and shielded power cable from the battery to the inverter. I would use shielded twisted pair wire. Connect the shield and the negative wire to the negative terminal of the battery. Connect the positive wire, with an inline fuse, to the positive terminal of the battery. At the inverter end, ground the shield to the body as close as possible to the inverter. Connect the positive and negative wires to the inverter, and hope that the inverter has two terminals. Make sure the inverter is not connected to the body by any mounting fasteners or ground wires. If the case of the inverter is used as ground, electrically isolate the whole thing and connect the case to the negative wire of your new cable. You need something like 8-14 gauge shielded twisted pair cable, rated for automotive temperatures. Make sure it's lower gauge (thicker) than the existing wiring. I have no idea if you can buy a cable like that anywhere. It might not fix the problem, anyway.
dawudih
New member
The built in inverter is causing noise with the built in AM radio when my kids tablets are plugged in during road trips; sorry I didn't clarify.
I like your second option, just using a home run directly from the battery; probably a neg. run only??? Also to ensure the inverter chasis isn't the actuall ground, if it is, isolate it. I think you're right, poor design since AM isn't popular any more. I'll also try a different load on the receptical before doing all this & let you know.
I don't know if replacing the ground wire alone will solve your problems, and it might make things worse. If there's no way to take care of the interference at the inverter, you need to give the interference a low impedance path back to the battery, and for AC (noise) that means a small loop area between the power and return. The power and ground must be kept close together (ideally twisted together, and better yet, shielded), otherwise you inadvertently make an antenna. At AM frequencies this is the most likely way the radio is picking up interference. The power goes from the battery, to the switch, to the inverter. The return current wants to closely follow the path of the power, but if you constrain it on a wire or on the body away from the power wire, the loop area will act as an antenna. Using the body as ground constrains the return current less than using an isolated wire, but it's not ideal since it doesn't follow the power wire the whole way.
The only way running a ground wire would improve the problem is if you run it right next to the power wire (like zip tied to it) along the entire circuit from the battery, near the switch, to the inverter.
The inadvertent antenna could be a problem on the 120V side, too, though both wires probably follow the same path from the inverter to the outlet.
Maybe try a different charger for the tablets, or get one that runs on 12V. Inverters don't like small reactive loads like chargers, so it might cause the inverter to operate less efficiently.
I have a 4th gen, but if I get a chance I'll see if I can replicate the problem. I think it only puts out 100W, so it might be a slightly different design than the 5th gen.
The only way running a ground wire would improve the problem is if you run it right next to the power wire (like zip tied to it) along the entire circuit from the battery, near the switch, to the inverter.
The inadvertent antenna could be a problem on the 120V side, too, though both wires probably follow the same path from the inverter to the outlet.
Maybe try a different charger for the tablets, or get one that runs on 12V. Inverters don't like small reactive loads like chargers, so it might cause the inverter to operate less efficiently.
I have a 4th gen, but if I get a chance I'll see if I can replicate the problem. I think it only puts out 100W, so it might be a slightly different design than the 5th gen.
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