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Old 23-01-2008, 11:46   #1
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Noisy Freedom Inverter / Charger

I think I have tried everything there is. But am open to any ideas now. The Freedom 25 Chgr/Invtr is placing a terrible hum/buzz on my DC wiring which is then disrupting my instruments and my VHF. In fact, many that are tryign to hear me transmit simply can not understand me over the noise.
I have used 50mm2 cable to the battery banks. The distance of cable is only 4ft, so 8ft total in cable. The cables are also twisted around each other to help cancel out magnetic induction. A terminals have been crimped and the terminals cleaned before being tightly bolted down. So there should be as little resistance as humanly possible to achieve between chgr/intr and Battery bank. The bank is four 6V 300Ahr batteries in series parrellel to get 12V. In theory, the capacitance of the bank should act as enough filter, but it seems to have little affect.
My next train of thought is to try and design some form of an inductance type filter for the downstream DC supply circuti to all instruments. But I am not sure that is really going to work.
I know a few here have the Freedom series of units, has anyone had this issue or resolved it.
Open to all and any thoughts, no matter how strange.
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Old 23-01-2008, 14:24   #2
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Hi Alan

We have a Freedom 10 charger/inverter. We get no noise in invert mode so that has not been a problem for us. However in charger mode we get a hum on the DC so is only a problem in the marina. Our radios, etc all have their DC sourced from a bus in the main DC panel so not individually cabled back to the batteries.

This hum (which sounds like 50Hz or second harmonic of) only affects the VHF (Icom IC-M502) and SSB (Icom IC-M802) radios and nothing else and on those the hum feeds through into the transmitted signal as well as being audible on receive. It probably affects the AM/FM radio but is not noticed because of the strong signal strengths in the marina overcome it. Is easy to determine that it is on the DC and is the charger as is still on the radios when disconnect the antennas and the hum increases in strength with the charge rate.

We did have some hum on our TV when in 12v mode (it is a 230/12v one) but that was from an earth loop so a different matter. We have no problem with our instruments (all Autohelm/Raymarine) or anything else.

For the VHF I found that one of the noise filters sold for automobile audio systems killed it dead. They are a 3 wire passive combination of big inductor and capacitor and cheap. Trikky Dikky used to sell them but no longer now as far as I know. While a 5A one of those would probably be ok rating wise I found that the voltage drop across the one I tried was high (forgotten what) so I installed a 30A one and that was fine and carry a spare in case of failure.

For the SSB if I use it in the marina, which is not often because of so much other noise in the area, I just turn the charger off. I did try making a filter but because of the low frequency of the hum, the high current and the need to minimise voltage drop the inductor was just going to be too big. As it is not a problem when off shore power with no charging I have not really worried about it any more. The VHF I did because it was easy and cheap.

I suspect that one of the same filters would sort the problem with the instruments too, if their problem is also due to the hum. I carry a 5A one just in case of need for something I might install that gets affected. Whether it will sort any noise problem you may have in invert mode I don't know but suspect so.

I am on the boat at the moment so is a bit slow surfing but when I get home tonight I'll have a hunt on the internet and see if I can give you some links to the types of filters I mean.

John
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Old 23-01-2008, 15:30   #3
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Alan - have you tried a brute force filter on the Inverter/Charger?

Probably a Pi network with the biggest reasonable inductor you can find and a couple of "big honkin capacitors". I've capacitors over 1 farad at an auto sound system place - they need them for the big bass amps some folks put in their vehicles.

I've found that batteries react too slow to have any useful capacitance to quiet noise.

The other alternative is to replace your inverter charger with a Magnum Energy unit. That's what we did and got rid of all the inverter/charger noise.

Good luck on your project!

Bill
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Old 23-01-2008, 16:19   #4
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Alan - have had a chase around on the boat and find that I have an extra 5A filter which you are welcome to try. I wouldn't recommend it for permanent installation for the VHF due to voltage drop but should work on Tx for a test and will work on Rx to see if it knocks the noise.

I assume that it will be plenty big enough for the instruments current draw though.

These filters are simple passive brute force ones as RaptorDance suggests but in my experience they are cheaper to buy than to build oneself. Have a look at Jaycar's site items AA3072 and AA3076 as examples of the automotive market ones - I don't know how good theirs are though (the ones I have are in solid rectangular boxes and were quite a bit cheaper).

If interested just PM or email a mailing address and I'll post it tommorrow.
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Old 23-01-2008, 20:24   #5
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Wheels, is this hum being created when the inverter is producing 12vdc from the mains power? Only?

While filtering certainly might work, I think it might pay to find out where the hum is coming from, i.e. loose plates or windings in a transformer, a cold solder joint, a faulty cap in the unit...

Was the unit working "hum free" until recently, so that something failing could be to blame? Or has this inverter always hummed?
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Old 23-01-2008, 21:02   #6
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Firstly, thanks Midland. But I have all the stuff to build one here, so I may do that.
HS, the ivtr/chgr has only been recently installed. Although I did purchase it second hand. The Hum is on both ivt and chg. You can hear the Hum suddenly get louder when the freezer cycles on for instance. On Ricks advise, I took a look inside for faulty joints, but found nothing. It all looked really good. However, while I had it apart, I replaced the Main positive DC cable. I might just pull the cover again and double check that the connection is tight, seeing as it is the only thing I haven't checked. I don't think that will be it though.
I do think it is a problem with filtering. Rick, if you are reading this, do these things have filters that I need to check??
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Old 23-01-2008, 22:10   #7
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Same problem here (Freedom 30). I haven't attempted to chase it down yet, and it doesn't happen on both my VHF radios, so I've sort of suspected a grounding issue at the nav station (where there is hum) and didn't really blame the charger. Someday I'll chase this, but it's down the list
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Old 23-01-2008, 22:29   #8
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Yeah if it is not happening on both radios, then chances are you have a problem at the nav station or the wiring to it.

For my problem, maybe there is an internal issue with the charger. Maybe that is why it was for sale.
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Old 23-01-2008, 22:48   #9
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Have fun Alan. I know I and the guy who did the boats systems when built did . I also understand the problem is par for the course with this family of inverter/chargers when combined with susceptable equipment. It may have been fixed in later models so interesting to know yours is not new - ours is now over 11 years old. We are also an isolated ground DC boat so the opportunity for ground loops is pretty much zero (but see below).

If you find any alternative solution to simple 3 element low pass filters in the DC supply to susceptable equipment without going to an expensive active solution or a large sized passive solution for the whole DC load of the boat would love to hear of it.

If you are adventurous, as I said we have an isolated ground DC system, but the capacitance between the DC cabling and the steel hull being the AC earth (in your case maybe the armature) is quite high (I've forgotten what it was but was a surprise to me). I have wondered if this contributes to the hum, the capacitance being high enough to provide a loop from negative to AC earth at the hum frequency (never checked it but sounds like 50 Hz or second harmonic from memory).
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Old 23-01-2008, 22:56   #10
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Might be of help to know that we do also get "semiconductor crackle" on radios when in invert mode(from memory) and charge mode (definitely), and using an antenna inside the boat. But that is radiated and not on the DC - but being steel all our radio antennas have to be outside boat so are effectively shielded from it.

It must escape on the cables from the inverter to be radiated though as the inverter itself seems well shielded.
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Old 24-01-2008, 07:15   #11
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My 10 buzzed, i found a buzz in both dc and a/c. My coffee grinder buzzed whenever it was plugged in. Don't know why, it went away when I put the pure sine wave model in. Guess i am not much help, other then the fact that it seems to be more or less "normal"
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Old 24-01-2008, 08:57   #12
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Wheels, is this buzz audible to the ear--not just something the electronics pick up? I have an old TrippLite inverter/charger that does that. Bad laminates in the transformer, they are chattering from the AC on the mains power and there's nothing to be done about it.
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Old 24-01-2008, 12:16   #13
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Both actually. You can hear the charger buzz as well as the same noise on the radio etc. But a noisey lamination won't be the cause of the noise being seen on the DC line. Noise on the DC line will however, cause the transformer to buzz. Although the modified waveform is better quality than my original cheap "made in China" inverter.
Oh well, I'll keep playing.
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Old 24-01-2008, 14:18   #14
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Suggest you persevere Alan as they are ok inverters for quasi-sinusoidal ones and for their design age (and Xantrex still supply them). They also seem to have a good reputation for reliability. In the end the noise problem can be solved for a few dollars.

I don't know if you have looked already but Xantrex have an extensive library of technical papers on their web site. I have not looked recently but when I last looked there was nothing about the noise issue there, but they may have added something since.

We have found ours has run everything we have tried on it and we have tried most things (including notebooks, handheld radio, camera and PDA chargers, AC powered radio transmitter, variable speed drills, etc). Only common thing not tried is a microwave cooker.

We have only ever had one issue which was not the inverter itself. The isolating switch on the DC supply side (a good K&N one) got a bit noisy when making which threw the inverter's microprocessor into a tiz so's it just sat flashing lights at one instead of starting up.
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Old 24-01-2008, 20:19   #15
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There is only one thing that won't work, my electric shaver. It wouldn't work on the last inverter either.
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