Inverter Interference

[Salacia]

I hope that the group has some tips for me here.

I have a freedom 20 inverter. It works great, but produces quite a bit of audio interference on any devices that are directly plugged into a 110v outlet in the boat. I've tested it with my ipod, my computer, and other devices. When they are connected to 110v and the inverter is on there is a significant buzz. If the inverter is on and the devices are run on battery there is no interference. As well, if they are plugged in but the inverter is off there is no buzz.

It's obviously a signal coming in over the 110v cord and being produced by the inverter. Any tips on how to filter it out are much appreciated.

Thanks again to the group!

[Alan Wheeler]

Not an easy task. The problem will be the inverter. Most likely, it is a "modified sine wave" output. Now I am not going to get all nerdy and to accurate here. What I am about to cover will suffice for the most of us.
Modified Sine wave means the inverter firstly produces a square wave. This wave is "shaped" in steps so as to resemble a Sinewave. Two aspects create the interference. Firstly, It is the edge of each step that produces an harmonic distortion, thus the noise you hear on Radios and TV etc. The other is created by the same edge, but it causes a "ringing" effect in transformers and thus a buzz in most power supplies. Some switch mode supplies as in Laptops etc, will not even run on some inverters.
So how do you overcome the problem, well simply put, the only filter praticaly large enough is in fact the battery bank. But the lower they discharge, the more the noise will increase on equipment.
The only otherway is to use a "Pure Sine wave" inverter for criticle equipment like the computer. Pure Sine wave units are expensive and not usually large in output, so the modified unit is probably still required for things that require power but noise is not an issue. i.e. cooking equipment etc.

[Alan Wheeler]

Oh I forgot one important point. Some of that interference can be radiated and picked up by the Radio and TV via their antennea. The only way to reduce this interference is to dress all power and antennea leads as far away from each other as possible and keep the recievers away from the inverter as far as possible.

[Rick]

The first thing to look for is just how the inverter is wired to the battery bank and how the battery bank itself is configured. There are many ways that an audio buzz can occur with an inverter. If the problem is with the way that the inverter is wired up then even a sine wave inverter will still be problematic.

With the Freedom 20 the the cables to the battery should be no longer than 6 feet AND the positive and negative cables should be twisted together. If you have long cables, like some installations have in order to go to a conveniently placed disconnect switch and fuse, then the ripple of the inverter will be excessive and the ac waveform will even be affected. The individual batteries comprising a bank should each have the same intrinsic overall positive and negative cable length reaching the inverter's attatchment point.

If the batteries are not high quality having very low internal resistance as well as high capacitance (not the same as A-h capacity) then you can help the situation by installing a 27,000 uF 25 Volt low ESR capacitor across the ends of the inverter cable using 10 inches of #10 AWG wire to each terminal of the cap.

Now after you've read all of this and evaluate your installation give us more feedback and we'll continue on.

[rleslie]

Rick & Alan

1)"The only way to reduce this interference is to dress all power and antennea leads as far away from each other as possible and keep the recievers away from the inverter as far as possible."

Does this also apply to True Sine Inverters? Please tell me that it doesn't; I just mounted my Xantrex True Sine directly under my SSB receiver!!!

2)"With the Freedom 20 the the cables to the battery should be no longer than 6 feet AND the positive and negative cables should be twisted together."

First...why do they need to be twisted?
Secondly....my inverter is directly under my 600AH battery bank (about 30" of 2/0), do they still need to be twisted?

You guys are an absolute wealth of knowledge!!!! THANKS!!


Roger

[Rick]

Roger,
All switch-mode power supplies make radio-frequency noise regardless of whether the output of the supply is a sine wave, a square wave or dc or whether the input is dc a sine wave or whatever. Power inverters used in boats and recreational vehicles are subsets of the general class of switch-mode power supplies. The quantifiable amount of RFI generated varies with design, implementation, and installation.

The designs which minimize the generation and propogation of noise cost more than virtually any product which you will see available (at least now and the near future) and affordable for use in the marine market, especially the high power units which are bi-directional in that they operate either as a charger or as an inverter. Just as a comparison, we "enjoy" being able to purchase an inverter/charger for less than a dollar per watt (in the USA) yet if you purchase a "relatively simple" dc/dc converter which complies with international standards for conducted and emitted RFI (radio frequency interference) you might pay 50 dollars per Watt.

Conducted RFI is interference which is generated through the conductors (either input or output) and anything connected to such wires must have internal rejection of such interference to escape its effects. Most marine and RV installations suffering audio system and radio system interference suffer from conducted RFI first and emitted RFI second. Because there are many boats with installations suffering essentially no problems with their audio, radio, tv, and computer systems (having your specific model of inverter/charger) the first "thing" to look for is just how your unit is wired in that might effect conducted interference.

Emitted interference is the most difficult to solve and the "easiest" method is merely to provide as much geometric separation between the source and the reciever which means separating the wires and units as far as possible to take advantage of the phenomenon that the susceptibility decreases as the reciprical of the distance squared. The easiest method of preventing the generation of interference lies with the design and physical packaging....not something that you can likely change. Shielding of either the source or receptor is always bandied about within the marine community yet the truth is it is a waste of time because of the difficulty in being able to do a proper job (which very few people are capable of doing either in theory or in practice) especially when considering the level of power that has to be dealt with in the case of inverter/chargers. Really effective shielding uses continuous enclosure of the source with material that shields both the electric and magnetic fields....that means using ferrous materials and magnetic materials...who has that capability? (that means that aluminum foil and copper braids, etc. just will not satisfy the total requirement).

Twisting together the input power positive and negative cables introduces coupling between the two that takes advantage of self-canceling fields (called differential mode cancellation) caused by the "gulping" of power that the inverter takes from the battery in the inverter mode or the battery takes from the charger in the charger mode. Adding capacitance between the two cables filters the voltage fluctuations as well (if needed).

By making sure that the inverter/charger power cables do not share cable runs with your susceptible loads eliminates "ground and power loops" (power loops are the mirror-image of ground loops) you will minimize the voltage fluctions induced into your suseptible receivers caused by the inverter/charger. That is why I advise single continuous leads from the inverter/charger all the way to the battery terminals. Loads should be only attachted to the battery terminals on TOP of the power (inverter/charger or other heavy drain potential sources of interference like refer compressors). No other loads or sources should share wiring with the inverter/charger all the way to the battery terminals. The ONLY exception is a short cable from a battery monitor shunt to the battery negative. All wires must be attached to the load side of the shunt in order to allow the monitor to "see" all sources and loads to/from the battery.

How are you doing so far?
Rick

[rleslie]

Rick wrote: "How are you doing so far?"

So this is what being seasick feels like!!!!


I follow the general flow, if not the details. To make a long story short.....I need to move my SSB from just above the inverter.

"making sure that the inverter/charger power cables do not share cable runs with your susceptible loads" They are dedicated wires straight from the batts to the inverter. Twisting them makes sense.

I'll re-read this a few times and I'm certain that the details will sink in.

Thanks!!!

Roger

[Alan Wheeler]

"so this is what seasickness feels like"
Yep, it's caused by Headspin.
That was an excellent post Rick. I couldn't have wroded that better, infact, I wouldn't have come close.

[Extemporaneous]

Just thought I'd bring this to the front and ask if anything has changed with current technology and possibly filters available today.
Extemp.

Originally Posted by Rick

Roger,
All switch-mode power supplies make radio-frequency noise regardless of whether the output of the supply is a sine wave, a square wave or dc or whether the input is dc a sine wave or whatever. Power inverters used in boats and recreational vehicles are subsets of the general class of switch-mode power supplies. The quantifiable amount of RFI generated varies with design, implementation, and installation.

The designs which minimize the generation and propogation of noise cost more than virtually any product which you will see available (at least now and the near future) and affordable for use in the marine market, especially the high power units which are bi-directional in that they operate either as a charger or as an inverter. Just as a comparison, we "enjoy" being able to purchase an inverter/charger for less than a dollar per watt (in the USA) yet if you purchase a "relatively simple" dc/dc converter which complies with international standards for conducted and emitted RFI (radio frequency interference) you might pay 50 dollars per Watt.

Conducted RFI is interference which is generated through the conductors (either input or output) and anything connected to such wires must have internal rejection of such interference to escape its effects. Most marine and RV installations suffering audio system and radio system interference suffer from conducted RFI first and emitted RFI second. Because there are many boats with installations suffering essentially no problems with their audio, radio, tv, and computer systems (having your specific model of inverter/charger) the first "thing" to look for is just how your unit is wired in that might effect conducted interference.

Emitted interference is the most difficult to solve and the "easiest" method is merely to provide as much geometric separation between the source and the reciever which means separating the wires and units as far as possible to take advantage of the phenomenon that the susceptibility decreases as the reciprical of the distance squared. The easiest method of preventing the generation of interference lies with the design and physical packaging....not something that you can likely change. Shielding of either the source or receptor is always bandied about within the marine community yet the truth is it is a waste of time because of the difficulty in being able to do a proper job (which very few people are capable of doing either in theory or in practice) especially when considering the level of power that has to be dealt with in the case of inverter/chargers. Really effective shielding uses continuous enclosure of the source with material that shields both the electric and magnetic fields....that means using ferrous materials and magnetic materials...who has that capability? (that means that aluminum foil and copper braids, etc. just will not satisfy the total requirement).

Twisting together the input power positive and negative cables introduces coupling between the two that takes advantage of self-canceling fields (called differential mode cancellation) caused by the "gulping" of power that the inverter takes from the battery in the inverter mode or the battery takes from the charger in the charger mode. Adding capacitance between the two cables filters the voltage fluctuations as well (if needed).

By making sure that the inverter/charger power cables do not share cable runs with your susceptible loads eliminates "ground and power loops" (power loops are the mirror-image of ground loops) you will minimize the voltage fluctions induced into your suseptible receivers caused by the inverter/charger. That is why I advise single continuous leads from the inverter/charger all the way to the battery terminals. Loads should be only attachted to the battery terminals on TOP of the power (inverter/charger or other heavy drain potential sources of interference like refer compressors). No other loads or sources should share wiring with the inverter/charger all the way to the battery terminals. The ONLY exception is a short cable from a battery monitor shunt to the battery negative. All wires must be attached to the load side of the shunt in order to allow the monitor to "see" all sources and loads to/from the battery.

How are you doing so far?
Rick

[David M]

I have a 3000 watt Statpower (Xantrex is the parent company now) true sine wave inverter-charger. It makes absolutely no electrical noise, either RF or through the DC or AC wires. Being a research vessel, I already have and have brought aboard quite a bit of fancy electronics that are sensitive to line noise and anything other than a true sine wave. I even saw the wave form on an oscilloscope once. It really is a pure sine wave form. I simply don't have problems related to my inverter. The only type of noise I hear is the cooling fan running occasionally.

I was just looking around on the internet and found a few Statpower Prosine 1000 true sine wave inverters for under $700. Perhaps some other true sine wave inverters do make noise, not these apparently.

You can always return it if it does make nosie.

[btrayfors]

David,

There are others with very low RFI emissions. Victron, for one.

The ProSine inverters are wonderful technology, but heavens knows what Xantrex will do with it now that they own it. I know a marine electrical shop which refuses to install Xantrex anything due to their extremely poor tech assistance and support after sale.

Also, Rick, there are some DC-DC converters with very low RFI emissions and which aren't too pricey. Depends on what you're talking about. I reviewed one a couple of years back: the W4RRY booster for power to ham radios. Great little device, and low cost (about $100 now, I believe).

What the above discussion fails to say is that there are several brands/designs of inverters which are just downright RFI noisy, even if installed correctly. Some of the old Heart inverter/chargers are in this category. Many, many other electrical devices found aboard boats are downright dirty as far as RFI is concerned, including inverters, digital voltmeters, and things with computers in them. Some, of course, are much better than others.

Bill

[Extemporaneous]

Originally Posted by btrayfors

What the above discussion fails to say is that there are several brands/designs of inverters which are just downright RFI noisy, even if installed correctly. Some of the old Heart inverter/chargers are in this category. Many, many other electrical devices found aboard boats are downright dirty as far as RFI is concerned, including inverters, digital voltmeters, and things with computers in them. Some, of course, are much better than others.
Bill

Anyone know how RFI Dirty the Magnum Energy MS Series Inverter / Chargers are?
Particularly the MS2012-U.

Thanks,
Extemp.

[btrayfors]

Magnum Energy products are serious designs by ex-Xantrex engineers. Their build quality is reportedly quite high. This model is approved for emergency vehicle use, and has a number of certs.

I haven't seen any details on the RFI suppression, but I'd write or call them and ask. I'm sure they'll be happy to answer.

Bill

CONTACTS:

Customer Service Email: support@magnumenergy.com

Order Entry Email: sales@magnumenergy.com

Sales and Marketing Email: marketing@magnumenergy.com

Warranty Administrator Email: warranty@magnumenergy.com

Webmaster Email: webmaster@magnumenergy.com

Click for current Employment Opportunities

Magnum Energy's Address:
2211 W. Casino Road
Everett, WA 98204
Phone: 425-353-8833
Fax: 425-353-8390

[Extemporaneous]

Originally Posted by btrayfors

Magnum Energy products are serious designs by ex-Xantrex engineers. Their build quality is reportedly quite high. This model is approved for emergency vehicle use, and has a number of certs.

I haven't seen any details on the RFI suppression, but I'd write or call them and ask. I'm sure they'll be happy to answer.

Bill

CONTACTS:

Customer Service Email: support@magnumenergy.com

Order Entry Email: sales@magnumenergy.com

Sales and Marketing Email: marketing@magnumenergy.com

Warranty Administrator Email: warranty@magnumenergy.com

Webmaster Email: webmaster@magnumenergy.com

Click for current Employment Opportunities

Magnum Energy's Address:
2211 W. Casino Road
Everett, WA 98204
Phone: 425-353-8833
Fax: 425-353-8390

Thanks,
Extemp.

[Paul Elliott]

Originally Posted by rleslie

To make a long story short.....I need to move my SSB from just above the inverter.

First, see if you have an interference problem. You should try different loads; the inverter may behave quite differently driving a lightbulb than driving a drill or a computer power supply.

Also, the noise from the inverter can be radiated (in which case, distance to the antenna is more critical), or it can be conducted. In either case, ferrite chokes may help.

Do some tests first. You may not have to move anything.