Dc -ac Inverters

[WB6UHQ]

Anyone got any tips on curing the RFI from the cheap DC - AC inverters? You can hear one 50 feet away on HF. Grrrrrrr. These things are great for keeping a laptop charged while in a portable or RV situation.

73. Dennis
WB6UHQ

[WA9SVD]

Anyone got any tips on curing the RFI from the cheap DC - AC inverters? You can hear one 50 feet away on HF. Grrrrrrr. These things are great for keeping a laptop charged while in a portable or RV situation.

73. Dennis
WB6UHQ

Unfortunately, there's a REASON they are cheap, and you have discovered that sad fact. They have little or no filtering. Then again, by their very design, they are QRM generators par excellance
You might do better with a home-brew design for a (most likely) step-up converter to change your battery voltage into the voltage normally provided by the AC adaptor. That way, you could provide as much filtering as needed.

[KC9ECI]

How much voltage does your laptop take to charge? Small solar panel?

[KB3PXR]

How much voltage does your laptop take to charge? Small solar panel?

I doubt that, some laptops today come standard with a 85 to 90 watt power supply. :eek: Granted these are high end models, but my mom's came with a 60 watt supply. :eek: The last time I played with my inverter with anything radio around I had no problems with broadcast band and mine is a cheap one.

[KC0BUF]

Take it apart and look for places you can apply standard rfi prevention. You can check the Handbook or sundry other places to find out what they are.

By the way, give it some time off the grid before taking it apart. Save yourself a nasty shock.

[WA9SVD]

Take it apart and look for places you can apply standard rfi prevention. You can check the Handbook or sundry other places to find out what they are.

By the way, give it some time off the grid before taking it apart. Save yourself a nasty shock.

That's all well and good IN THEORY. But most of the cheap inverters are (mis)designed to fit into the smallest possible space, and adding proper filtering elements (chokes, ferrites, capacitors) just won't fit into the original packaging.

[kb1ils]

It's been probably about ten years since I looked into this, but as I recall, the cheaper ones use a modified sine wave, and the higher-end ones use a pure sine wave. If you can get a pure sine wave model, it should be much quieter. At least in theory...and to the best of my memory...

EDIT/ADDENDUM:

A quick search brings me to a site that reinforces what I recalled, emphasis mine:

"Do I need Modified Sine Wave, or Pure Sine Wave?

Advantages of Pure Sine Wave inverters over modified sine wave inverters:

a) Output voltage wave form is pure sine wave with very low harmonic distortion and clean power like utility-supplied electricity.

b) Inductive loads like microwave ovens and motors run faster, quieter and cooler.

c) Reduces audible and electrical noise in fans, fluorescent lights, audio amplifiers, TV, Game consoles, Fax, and answering machines.

d) Prevents crashes in computers, weird print out, and glitches and noise in monitors.

e) Reliably powers the following devices that will normally not work with modified sine wave inverters:

Laser printers, photocopiers, magneto-optical hard drives
Certain laptop computers (you should check with your manufacturer)
Some fluorescent lights with electronic ballasts
Power tools employing "solid state" power or variable speed control
Some battery chargers for cordless tools
Some new furnaces and pellet stoves with microprocessor control
Digital clocks with radios
Sewing machines with speed/microprocessor control
X-10 home automation system
Medical equipment such as oxygen concentrators "

[WA9SVD]

It's been probably about ten years since I looked into this, but as I recall, the cheaper ones use a modified sine wave, and the higher-end ones use a pure sine wave. If you can get a pure sine wave model, it should be much quieter. At least in theory...and to the best of my memory...

EDIT/ADDENDUM:

A quick search brings me to a site that reinforces what I recalled, emphasis mine:

"Do I need Modified Sine Wave, or Pure Sine Wave?

Advantages of Pure Sine Wave inverters over modified sine wave inverters:

a) Output voltage wave form is pure sine wave with very low harmonic distortion and clean power like utility-supplied electricity.

b) Inductive loads like microwave ovens and motors run faster, quieter and cooler.

c) Reduces audible and electrical noise in fans, fluorescent lights, audio amplifiers, TV, Game consoles, Fax, and answering machines.

d) Prevents crashes in computers, weird print out, and glitches and noise in monitors.

e) Reliably powers the following devices that will normally not work with modified sine wave inverters:

Laser printers, photocopiers, magneto-optical hard drives
Certain laptop computers (you should check with your manufacturer)
Some fluorescent lights with electronic ballasts
Power tools employing "solid state" power or variable speed control
Some battery chargers for cordless tools
Some new furnaces and pellet stoves with microprocessor control
Digital clocks with radios
Sewing machines with speed/microprocessor control
X-10 home automation system
Medical equipment such as oxygen concentrators "


A "pure sine-wave" inverter would be the obvious choice, but not cheap. The "modified" sine-wave is sort of wishful thinking. It's really a two or three step wave of combined square waves, and rich, very rich, in harmonics, and very difficult to filter adequately.

[ky5u]

Use Solar Panels and charge at night to get a full charge.

[WB2WIK]

Use Solar Panels and charge at night to get a full charge.

::If you don't get sufficient power that way, visit the sun directly; however, to prevent fatal burning, only go at night.

[WA2ZDY]

Use Solar Panels and charge at night to get a full charge.

MMy wife and I each have one of those newfangled Citizen "Eco-Drive" solar powered wristwatches. They're nice enough and all but I told her it's a good thing we sleep and don't care what time it is at night!

Steve, isn't that sun safety stuff covered in the book called "Fun In Da Sun" by Icarus?

[K1CJS]

If you want to power your computer, there are alternate power supplies available that do not rely on any inverter type circuitry at all, they're made specifically to work from 12 vdc. One of those is your best bet, but they are rather pricey. ($100.00)

[WA9SVD]

If you want to power your computer, there are alternate power supplies available that do not rely on any inverter type circuitry at all, they're made specifically to work from 12 vdc. One of those is your best bet, but they are rather pricey. ($100.00)

If they run off 12 Volts, and the laptop requires more than 12 Volts, then the units HAVE to have SOME sort of inverter. Not necessarily one that converts 12 Volts to line voltage, but ANY "boost" type power supply will have an inverter circuit (or some such switching circuit) which is then rectified and either converted to the higher voltage needed directly, or added to the original 12 Volt source. And as such, they will be a source of potential RF interference.

[K1CJS]

If they run off 12 Volts, and the laptop requires more than 12 Volts, then the units HAVE to have SOME sort of inverter. Not necessarily one that converts 12 Volts to line voltage, but ANY "boost" type power supply will have an inverter circuit (or some such switching circuit) which is then rectified and either converted to the higher voltage needed directly, or added to the original 12 Volt source. And as such, they will be a source of potential RF interference.

I stand corrected--you are right. I was considering the 12 volt to 120 volt inverters that are popular now. The 12 volt to 18 volt supplies still use a type of inverter circuitry, but hopefully are not as noisy as they are better made--and more costly than the 18.00 Wally World specials.

[K4GUN]

I just bought a 600 watt pure sine wave inverter off ebay. I haven't used it yet so I don't have a review, but for $200, it seemed like a pretty good deal. Here is a link to the ebay store: http://stores.ebay.com/Energy-Igloo

[WA9SVD]

I stand corrected--you are right. I was considering the 12 volt to 120 volt inverters that are popular now. The 12 volt to 18 volt supplies still use a type of inverter circuitry, but hopefully are not as noisy as they are better made--and more costly than the 18.00 Wally World specials.

I don't have the original QST article at my fingertips, but a couple of years ago there was a project for a "boost" circuit that would provide a fairly constant 13.8 Volts DC at up to about 20 Amps from a "12 Volt" storage battery until that battery dropped below 11 Volts; it "added" it's voltage to the existing battery supply.
It should be possible to use a similar circuit with appropriate changes to get the 16-20 Volts required by most recent laptops. (And since the current output wouldn't have to be close to 20 Amperes, it should be easier to filter the circuit to keep it RF quiet.)
Fortunate for me, the laptop I use for portable operations, including Packet, has a 9.6 Volt battery, and 12-14 Volts is the voltage rating for the original AC supply/charger. Works perfectly directly off the car battery or Marine deep cycle.

[K8ERV]

This may not apply, but my Dell Vostro has 3 wires from the ac supply, one is some kind of sense wire, seems to check for the "correct" supply (Dell of course). Just feeding the 18volts does NOT work, it is not accepted. Bummer.

TOM K8ERV Montrose Colo

[WA9SVD]

This may not apply, but my Dell Vostro has 3 wires from the ac supply, one is some kind of sense wire, seems to check for the "correct" supply (Dell of course). Just feeding the 18volts does NOT work, it is not accepted. Bummer.

TOM K8ERV Montrose Colo

Is that a relatively new laptop, or an older model? I know some older Epson laptops took a 4-wire hook-up from the "charger" to the computer; you would have to figure out what the extra wires were used for to convert a single DC voltage to what's necessary. PITA.

[K8ERV]

Recieved 6 Aug 07. Hoped to use my 12-18v lap adaptor for my camper, but no go. Thanks Dell.

TOM K8ERV Montrose Colo

[N5USR]

Huh. I knew the older C-series Dell Latitudes had a 3-wire plug, but thought the new ones were just a slightly-nonstandard coaxial 2-wire plug. Took a look just now, after reading your post, and sure enough - it has a center pin, and a ring around that pin has a contact on BOTH the inside and outside - still three wire! Sneaky...

[K1CJS]

Yes, I know. The Four year old Dell laptop that I have also has the three pin plug, and an 18 volt battery. I have bought an aftermarket supply ($120.00--ouch!) that does work with it, and is supplied with either 120 volt AC or 12 volt DC, but it still has to have that three pin plug. The third wire is a sort of sampling wire that is connected across one cell of the laptop battery, I guess to check on charge level or feedback level or some such thing. Unless the proper signal voltage is applied to that wire, the charger/power supply will just not work.

[n0vl]

I have two sine-wave inverters, one 300w, one 1500w. Tried to use them to power lighting at field day last year and both caused horrible noise on the HF rigs even with nothing connected to the outputs. The circuitry most likely consists of a high-frequency switching circuit that chops the output to form the sine-wave and apparently that noise is being coupled back into the DC power leads which act as the antenna. Both of these units were in nice metal cases, grounding the case did not help.

[WA9SVD]

I have two sine-wave inverters, one 300w, one 1500w. Tried to use them to power lighting at field day last year and both caused horrible noise on the HF rigs even with nothing connected to the outputs. The circuitry most likely consists of a high-frequency switching circuit that chops the output to form the sine-wave and apparently that noise is being coupled back into the DC power leads which act as the antenna. Both of these units were in nice metal cases, grounding the case did not help.

Did you try capacitors (about 1000 Volt, .005 uF) across the AC output, and ferrites everywhere? Have you looked at the waveform with an oscilloscope to see if it's truly a "sine" wave or even close? Sometimes the "sine-wave' calim is, shall we say, exaggerated by the marketing department.

[ab9lz]

MMy wife and I each have one of those newfangled Citizen "Eco-Drive" solar powered wristwatches.


I have an "eco drive" wristwatch too, it's a 30 year old Rolex.

73 m/4